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Threads, do mechanical daily dealings, especially hydraulic and pneumatic, a long time domestic, metric, imperial, straight cone, sealed non-sealed, inside and outside, 55 degrees and 60 degrees . In short, I am often confused. I use it once to check it from start to finish. I am here to summarize it and hope to help. My approach is to print it out and put it on the table. When you use it, you can check it at any time. After a long time, you will naturally remember it. (One) NPT is a general-purpose American standard taper pipe thread with a tooth angle of 60° The PT tooth is an inch taper thread with a tooth angle of 55°, which is most commonly used in sealing. The inch pipe thread is a fine thread, because the tooth depth of the coarse thread will seriously reduce the strength of the pipe with the outer diameter of the thread. The PF tooth is a parallel thread for the tube. G is a 55 degree non-threaded sealed pipe thread, belonging to the Wyeth thread family. Marked as G for cylindrical thread, G is the general name for the pipe thread (Guan), 55, 60 degree pision is functional ZG is commonly called tube cone, that is, the thread is made of a conical surface. The general water pipe joints are like this. The old national standard is labeled as Rc. The metric thread is expressed by the pitch of the thread. The US and British thread is expressed by the number of threads per inch. This is the biggest difference. The metric thread is a 60-degree equilateral tooth type, and the inch thread is an isosceles 55-degree tooth type. 60 degrees. Metric threads are used in metric units, and American-English threads are used in imperial units. The pipe thread is mainly used for the connection of the pipe, and the inner and outer threads are closely matched, and there are two kinds of straight pipe and tapered pipe. The nominal diameter refers to the diameter of the pipe to which it is connected. It is obvious that the diameter of the thread is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameter of the inch thread in inches. (Two) 1, inch uniform thread Widely used in inch countries, this type of thread is pided into three series: coarse tooth series UNC, fine tooth series UNF, extra fine tooth series UNFF, plus a fixed pitch series UN. Marking method: Thread diameter – number of teeth per inch series code – accuracy level Example: Coarse tooth series 3/8-16UNC-2A Fine tooth series 3/8—24UNF—2A Extra fine tooth series 3/8—32UNFF—2A Fixed pitch series 3/8-20UN-2A The first digit 3/8 indicates the outer diameter of the thread in inches. The conversion to the metric unit mm is multiplied by 25.4, ie 3/8×25.4=9.525mm; the second and third digits 16, 24, 32, 20 are The number of teeth per inch (the number of teeth in the length of 25.4mm); the character code UNC, UNF, UNFF, UN after the third digit is the serial number, and the last two digits 2A are the precision grades. Conversion of 2, 55° cylindrical pipe threads 55° cylindrical pipe thread, which is derived from the inch series, is widely used in metric and inch countries. It is used to connect liquid pipe, gas and wire fittings to pipes. However, the codes of different countries should be pressed. The foreign code in the table (control table) is converted into the code name of our country. The 55° cylindrical pipe thread code of each country is listed in the following table. Country code China G Japan G, PF UK BSP, BSPP France G Germany R (internal thread), K (external thread) Former Soviet Union G, TPУБ ISO Rp 3, 55 ° conical pipe thread conversion The 55° conical pipe thread means that the thread has a profile angle of 55° and the thread has a taper of 1:16. This series of threads is widely used in the world, its code name, different national regulations, see the table below. According to the foreign code in the table below, it is converted into our country code. Country code China ZG, R (external thread) UK BSPT, R (external thread), Rc (internal thread) France G (external thread), R (external thread) Germany R (external thread) Japan PT, R ISO R (external thread), Rc (internal thread) 4, 60 ° conical pipe thread conversion 60° conical pipe thread refers to pipe thread with a tooth angle of 60° and a taper of 1:16. This series of threads is used in China’s machine tool industry and the United States and the former Soviet Union. Its code name, China’s past regulations for K, and later for Z, is now changed to NPT. The thread code comparison table is shown in the table below. Country code China Z (old) NPT (new) United States NPT Soviet B 5, 55 ° trapezoidal thread conversion The trapezoidal thread is a metric trapezoidal thread with a tooth angle of 30°. This series of threads is relatively uniform at home and abroad, and its code name is also quite consistent. See the thread code below. Country code China T (old) Tr (new) ISO Tr Germany Tr Former Soviet Union Tr

1. Chromium stainless steel has certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance and wear resistance. Usually used in power plant, chemical, petroleum and other equipment materials. The chrome stainless steel has poor weldability, and attention should be paid to the welding process and heat treatment conditions. 2. Chromium 13 stainless steel is harder after welding and is prone to cracks. If welding of the same type of chrome stainless steel welding rod (G202, G207) is used, it is necessary to perform preheating at 300 °C or more and slow cooling at around 700 °C after welding. If the weldment cannot be post-weld heat treated, a chrome-nickel stainless steel electrode (A107, A207) should be used. 3. Chromium 17 stainless steel, in order to improve corrosion resistance and weldability, appropriately increase the amount of stability elements Ti, Nb, Mo, etc., the weldability is better than the chromium 13 stainless steel. When the same type of chrome stainless steel electrode (G302, G307) is used, preheating at 200 °C or higher and tempering at around 800 °C after welding should be performed. If the weldment cannot be heat treated, chrome-nickel stainless steel electrodes (A107, A207) should be used. 4. When chrome-nickel stainless steel is welded, it is repeatedly heated to precipitate carbides, which reduces corrosion resistance and mechanical properties. 5. Chrome-nickel stainless steel welding rod has good corrosion resistance and oxidation resistance, and is widely used in chemical, fertilizer, petroleum and medical machinery manufacturing. 6. The chromium-nickel stainless steel coating has a titanium calcium type and a low hydrogen type. Titanium-calcium type can be used for AC and DC, but the AC welding is shallower and easier to redden, so DC power is used as much as possible. 4.0 and below diameters can be used for all-position weldments, 5.0 and above for flat and fillet welds. 7. The electrode should be kept dry when it is used. The titanium calcium type should be dried at 150 °C for 1 hour. The low hydrogen type should be dried at 200-250 °C for 1 hour (do not repeat the drying repeatedly, otherwise the coating is easy to crack and peel off) to prevent the electrode Sticky oil and other dirt, so as not to cause the weld to increase the carbon content and affect the quality of the weldment. 8. In order to prevent the corrosion between the eyes due to heating, the welding current should not be too large, about 20% less than the carbon steel electrode, the arc should not be too long, the layer is fast cold, and the narrow bead is suitable. Nine problems with stainless steel welding 1. What is stainless steel and stainless acid resistant steel? Answer: The “chromium” content of the main additive element in the metal material (other elements such as nickel and molybdenum are also required) can make the steel in a passivated state and have stainless steel properties. Acid-resistant steel refers to steel that is resistant to corrosion in highly corrosive media such as acids, bases, and salts. 2. What is austenitic stainless steel? What are the commonly used grades? A: Austenitic stainless steel is the most widely used and the most perse. Such as: <1>18-8 series: 0Cr19Ni9 (304) 0Cr18Ni8(308)<2>18-12 series: 00Cr18Ni12Mo2Ti (316L)<3>25-13 series: 0Cr25Ni13(309)<4>25-20 series: 0Cr25Ni20, etc. 3. Why is it that the welding of stainless steel has a certain degree of technical difficulty? A: The main process difficulty is: <1> The stainless steel material has strong heat sensitivity, and the residence time in the temperature range of 450–850 °C is slightly longer, and the corrosion resistance of the weld and heat-affected zone is seriously degraded. <2> Thermal cracking is likely to occur. <3> Poor protection and severe high temperature oxidation. <4> The coefficient of linear expansion is large, resulting in large welding deformation. 4. Why do you need to take effective measures to weld austenitic stainless steel? A: The general process measures are: <1> According to the chemical composition of the base metal, the welding material is strictly selected. <2> Small current. , fast welding; small line energy, reducing heat input. <3> Fine-diameter welding wire, welding rod, no swing, multi-layer multi-pass welding. <4> Forced cooling in weld and heat affected zone, reducing 450-850 °C dwell time <5> argon gas protection on the back of TIG weld. <6> The weld in contact with the corrosive medium is finally welded. <7> Weld and heat affected zone passivation treatment. 5. Why do austenitic stainless steel and carbon steel and low alloy steel weld (dissimilar steel welding) use 25-13 series welding wire and welding rod? Answer: Welded joints of welded austenitic stainless steel and carbon steel and low alloy steel. The weld deposit metal must use 25-13 series welding wire (309, 309L) and welding rod (Ao 312, Austrian 307, etc.). If other stainless steel welding consumables are used, martensite structure is generated on the side of the carbon steel and low alloy steel fusion line, which will cause cold cracks. 6. Why do solid stainless steel wire use 98% Ar+2% O2 shielding gas? Answer: When the solid stainless steel wire MIG is welded, if the pure argon gas is used for protection, the surface tension of the molten pool is large, and the weld bead is poorly formed, which is in the shape of a “humpback” weld. Add 1-2% oxygen to reduce the surface tension of the molten pool, and the weld bead is flat and beautiful. 7. Why is the surface of the solid stainless steel wire MIG weld blackened? A: The solid stainless steel wire MIG welding speed is fast (30-60cm/min), the protective gas nozzle has been run to the front end molten pool area, the weld is still in red hot and high temperature state, is oxidized by air, the surface generates oxide, and the weld is made. black. The pickling method can remove the black skin and restore the original surface color of the stainless steel. 8. Why does a solid stainless steel wire use a pulsed power supply to achieve a jet transition without spatter soldering? Answer: When solid stainless steel wire MIG is welded, φ1.2 wire, when the current I≥260-280A, can achieve the jet transition; less than this value, the droplet is a short-circuit transition, the splash is large, generally can not be used. Only with the MIG power supply with pulse, the pulse current is greater than 300A, can achieve the pulse drop transition under 80-260A welding current, no splash welding. 9. Why is the cored stainless steel wire protected by CO2 gas? No need for a pulsed power supply? Answer: At present, the cored stainless steel welding wire (such as 308, 309, etc.) is used. The flux formulation in the welding wire is developed according to the chemical and metallurgical reaction of welding under the protection of CO2 gas, so it cannot be used for MAG or MIG welding; Pulsed arc welding power supply. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In recent years, the quality, performance and greening level of China’s key basic steel new materials have been significantly improved. The development of new materials industry has also provided a new opportunity for the transformation and upgrading of iron and steel enterprises. At the same time, steel enterprises must also establish a sound upstream and downstream industry. Cooperation mechanism to accelerate the industrial application of new steel materials. The future high-performance, high-tech, high-quality “three high” steel new materials will become the main direction of high-quality development of the steel industry. In order to accelerate the research and development of new steel materials in China, this newspaper specially organized a special report on this new material, with a view to promoting the iterative upgrading of new steel material manufacturing technology from the aspects of production and application. In recent years, China has accelerated the pace of development of nuclear power. The development of nuclear power will not only improve China’s energy supply structure, but also help protect national energy security and economic security. According to the National Medium- and Long-Term Development Plan for Nuclear Power, by 2020, China’s nuclear power installed capacity will reach 58 million kilowatts. However, as of June 2018, there were 39 power stations in China, with an installed capacity of about 38 million kilowatts, accounting for about 4% of the nation’s electricity supply; 18 units under construction, with an installed capacity of about 20 million kilowatts. It can be seen that the current construction progress of nuclear power is far from the planned target. In order to complete the planning target, at least 6-8 units will be built every year by 2020 to reach the nuclear power ratio of western developed countries. At the end of April 2018, AP1000’s world’s first three-door No. 1 nuclear power unit and Taishan EPR nuclear power unit were respectively approved by the National Nuclear Safety Administration. At the end of June, Sanmen No. 1 and Taishan EPR units were connected to the grid for power generation, which means China’s nuclear power. Construction will usher in a new period of development. 1 Development of nuclear power technology in the world The current development of nuclear power technology in the world can be roughly pided into four generations. The first generation technology is mainly a prototype reactor nuclear power plant developed between 1950 and 1960. The second generation technology is mainly a large commercial nuclear power plant developed and built between 1960 and 1990. The vast majority of nuclear power plants are second-generation technologies; the third-generation technologies are mainly AP1000, EPR, CAP1400 and Hualong No.1 developed since 1990-2010, of which AP1000 and EPR units were successfully connected to the grid for the first time in June 2018. Near full power will be connected to the grid for power generation. Domestic third-generation nuclear power units such as CAP1400 and Hualong No. 1 demonstration power station are also in full swing. In addition, the world is actively researching and developing fourth-generation nuclear power technologies, such as gas-cooled fast reactors, sodium-cooled fast reactors, lead-cooled fast reactors, ultra-high temperature gas-cooled reactors, supercritical water reactors and molten salt reactors; Technologies such as nuclear fusion reactors are also actively developing in the process of multinational alliances. Among these advanced nuclear power technologies, especially domestic nuclear power technology, many key equipments and key materials, such as high-performance steel pipes and forgings, need to be localized to narrow the gap between China and the world’s advanced countries in the field of nuclear power, and for large commercial nuclear power plants. Localization lays the foundation. Therefore, it is expected that stainless steel pipes for nuclear power equipment will usher in good development opportunities in the next five years. In the materials used in pressurized water reactor nuclear power plants, a large number of high-performance steel pipes, forgings, pipe fittings and other materials are required, and many types of materials are involved, such as alloy steel, stainless steel, zirconium alloy, titanium alloy, and nickel-based alloy. 2 Various types of stainless steel tubes for nuclear power The nuclear island is a general term for nuclear reactors and reactor-related systems in the containment of nuclear power plants, including nuclear steam supply systems, containment sprinkler systems, and auxiliary systems. A large number of high performance stainless steel tubes are required in the nuclear island system. 2.1 steam generator U-shaped heat transfer tube The steam generator heat transfer tube is an important component of the primary circuit pressure boundary of the nuclear power plant, and is also the main barrier to prevent the leakage of radioactive fission products. The steam generator heat transfer tube must withstand high temperature and high pressure and medium corrosion wear during service. Quality is the key to ensuring safe and reliable operation of the steam generator. According to statistics, about 30% of the pressurized water reactors are unplanned and shut down due to corrosion damage of the steam generator heat transfer tubes. At present, the steam generator heat transfer tube is mainly selected from 800 alloy and 690 alloy. Due to the high requirements on surface quality, size control, heat treatment system and organization control, steam generator heat transfer tubes have high technical barriers, and there are few domestic and foreign manufacturers. Currently, foreign countries are mainly Valluic, France, Sumitomo Metals, and The three companies of Sandvik, Sweden, are mainly Zhejiang Jiuli and Baoyin. The third-generation nuclear power technology steam generator heat transfer tube is mainly selected from 690 alloy. A million-kilowatt unit requires more than 10,000 heat transfer tubes, with a total weight of more than 200 tons. The main specifications are Ф19.05mm×1.09. Mm and so on. The main production process of steam generator heat transfer tubes includes slab smelting and forging, hot extrusion forming, cold forming, solution heat treatment and TT heat treatment, non-destructive testing and tube forming. At present, Jiuli has completed the manufacture and installation of the 690 alloy steam generator heat transfer tubes required for Hualong No.1, CAP1400 and export overseas projects, and has been well received by customers. 2.2 Other stainless steel tubes for nuclear islands The primary circuit of the primary circuit is an important barrier to prevent nuclear fission products from leaking out to the containment under normal, abnormal, accidental and experimental conditions. Main pipes are usually required to withstand high temperatures, high pressures and corrosion. Early primary pipes generally used 18-8 austenitic stainless steel, but there were problems such as insufficient strength and intergranular corrosion. Subsequent development of the casting duplex stainless steel main pipeline due to aging phenomena and other deficiencies, the current third-generation nuclear power AP1000 and other primary circuit uses the overall forging shape of 316LN austenitic stainless steel, with high strength, good plastic toughness and other characteristics, currently domestic The manufacturers have mastered the key technologies of large-scale steel ingot smelting, large-scale forging of large stainless steel materials, and overall processing of pipe sections and achieved localization. The passive safety principle is a prominent feature of the third generation nuclear power technology. The passive residual heat removal heat exchanger is the core equipment of the core cooling system and plays an important role in the safe operation of the reactor. Among them, the non-dynamic residual heat discharge heat exchanger is connected between the upper and lower heads through a C-shaped heat exchanger tube. The material of the heat exchange tube mainly includes TP304L and 690 alloy, etc. The specifications are mainly Ф19.05mm×1.24mm, Ф19.05mm ×1.65mm, etc., each million-kilowatt unit requires a C-shaped heat transfer tube of about 1t. The reactor pressure vessel is an important equipment in the main circuit coolant pressure boundary barrier. It is a nuclear safety primary equipment and cannot be replaced during the service life of the nuclear power plant. Its service life determines the service life of the entire nuclear power plant. Since the container contains high temperature, high pressure and radioactive working medium, it is required that the structure can be kept intact under various working conditions without cracking or leakage. Therefore, the sealing design and material selection of the reactor pressure vessel are safe for the equipment. Operation is crucial. At present, in the reactor pressure vessel seal design, the double-channel metal O-ring is sealed between the cylinder and the top cover, that is, the double-ring groove is opened on the upper flange sealing surface to form inner, middle and outer three islands, arranged inside, The outer two metal O-rings form a two-channel metal O-ring seal. In the third-generation nuclear power technology, the O-ring seal ring mainly adopts the 718 alloy seamless pipe, and the specifications mainly include Ф30mm×1.2mm, Ф12.7mm×1.27mm, and the like. O-ring seal ring with 718 alloy seamless tube, due to high requirements on surface quality, size control, heat treatment system, resilience performance, etc., there are high technical barriers, mainly monopolized by American companies, there is a long product supply cycle, the price Expensive and other features. Since 2014, Jiuli has successfully developed the 718 alloy seamless tube for the sealing ring, which has the characteristics of good surface quality, high dimensional accuracy and excellent resilience performance. In addition, there is only one solder joint when soldering the O-ring, which reduces the difficulty of heat treatment and inspection. At present, the product has been successfully used in domestic nuclear power plants. 2.3 Conventional island stainless steel tube Most of the nuclear power plants are built along the coast, and the loop uses a large amount of seawater as a cooling medium. Due to the inherent properties of titanium, titanium welded pipe is particularly suitable for use as a condenser tube for seawater or heavily polluted fresh water as a cooling medium due to its excellent corrosion resistance, erosion resistance, thermal conductivity and mechanical properties. In a million-kilowatt nuclear power unit condenser, the titanium tube used in each unit is about 200t. However, due to the difficulty in manufacturing titanium tubes, it is mainly difficult to weld and heat-treat. Foreign manufacturers mainly produce manufacturing enterprises such as the United States and Japan. At present, most of the titanium tubes used in nuclear power plant condensers rely on imports, and the domestic titanium welded pipe market has a large gap. Therefore, it is necessary to study the production process of high-quality thin-walled titanium welded pipe to meet the growing domestic construction demand. The current condenser tube specifications are mainly mm22mm×0.5mm, and the titanium material is mainly TA2 (Gr.2). The high-pressure feed water heater is an important feed water heating device in the regenerative system, which plays an important role in the economics of the second-circuit operation of the unit. The heat exchanger usually adopts a U-shaped heat exchange tube. TP439 ferritic stainless steel has high strength, good erosion resistance and wear resistance, low price and good resistance to chloride ion corrosion. It is often used as the main material for U-shaped heat exchanger tubes and is widely used in foreign nuclear power plants. At present, the TP439 welding U-shaped tube of a million kilowatt nuclear power unit is about 150t, and the main specifications of the required products are Ф16mm×1.5mm. 2.4 Advanced stacking stainless steel tube While vigorously building the third-generation commercial nuclear power plants, many research institutions at home and abroad are vigorously researching and constructing the test reactors and demonstration reactors of the fourth and fifth generation nuclear power technologies, mainly including bismuth-based molten salt reactors and sodium-cooled fast reactors. , lead-type fast reactor, high temperature gas cooled reactor, nuclear fusion reactor and other pile types. In the construction process of the test reactor and the demonstration reactor, various high-performance stainless steel pipes are also required, and the materials involve stainless steel and nickel-based alloys. The bismuth-based molten salt reactor is one of the six fourth-generation nuclear power alternative reactor types. It has atmospheric pressure, no water cooling, no need to make fuel components, and can realize on-line fueling and online post-processing. However, it has problems such as high service temperature and strong corrosion of molten salt. High requirements are placed on the main pipe and heat exchange pipe materials. At present, the main material selection is nickel-chromium-molybdenum alloy, such as GH3535 alloy. The manufacture of GH3535 alloy heat exchange tube has problems such as smelting difficulty, easy segregation, and hot processing. There are few domestic and foreign manufacturers. The sodium-cooled fast reactor is also one of the six fourth-generation nuclear power alternative reactor types. It is the second step of China’s nuclear energy three-step development plan and an important part of China’s nuclear energy closed cycle. Compared with pressurized water reactors, sodium-cooled fast reactors have higher temperature (above 500 °C) and higher irradiation dose. Therefore, higher requirements are placed on the structural components of the core assembly, such as stainless steel cladding tubes. In addition, sodium cooled fast reactor steam generators, heat exchangers and other pipelines also require a large number of high-performance austenitic stainless steel pipes, such as 316Ti, 316H and so on. The specifications of high-performance stainless steel pipes involved in sodium-cooled fast reactors are mainly mm6.0mm×0.4mm, Ф22 mm×1.4mm, etc. 3 Conclusions and prospects Zhejiang wilsonpipeline Pipe Industry Co., Limited has long been committed to the research and development and production of high-performance stainless steel tubes for nuclear power. Its related products have been widely used in domestic and foreign nuclear power plants, such as 690 alloy, 800 alloy steam generator U-shaped The heat transfer tube, the O-shaped seal ring 718 alloy tube, the TP439 high heat exchanger tube, the condenser titanium welded tube, the internal component tube, the nuclear grade instrument tube, etc., have been recognized by the majority of users. Nuclear energy is an important direction for future energy development. With the research and development of third- and fourth-generation advanced nuclear power technologies, nuclear islands and conventional islands require a large number of high-performance stainless steel pipes, especially with the “Belt and Road Initiative” initiative. China’s nuclear power will go global and require localized steel products and technologies. Therefore, steel companies must strengthen the research and development and application of advanced materials and advanced manufacturing processes, and develop a series of high-performance stainless steel pipes required for advanced nuclear power technology. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The strengthening of metal means increasing the strength of the metal material by means of alloying, plastic deformation, heat treatment, and the like. The actual strength of a metal is only a few tenths of the theoretical strength, or even a few thousandth. In order to improve the strength of the metal, commonly used strengthening methods include deformation strengthening, solid solution strengthening, second phase strengthening, and precipitation strengthening. 1. Deformation strengthening As the degree of deformation increases, the strength and hardness of the material increase, and the phenomenon of decreased plasticity and toughness is called deformation strengthening or work hardening. As the plastic deformation progresses, the dislocation density increases, resulting in an increase in interaction during dislocation motion, an increase in dislocation motion resistance, and an increase in deformation resistance, thereby increasing the strength of the metal. The degree of deformation increases and the dislocation density increases continuously. According to the formula Δσ=αbGρ1/2, the intensity is proportional to the one-half of the dislocation density (ρ). The larger the Bob’s vector (b) of the dislocation, the more significant the strengthening effect. . It is usually strengthened by cold deformation (extrusion, rolling, shot peening, etc.). Deformation strengthening is an effective method to strengthen metals, especially for materials that cannot be strengthened by heat treatment; it can also make the metal evenly deformed and improve the safety of parts or components during use. Deformation strengthening also causes troubles in the production and use of materials. The deformation increases the strength and plasticity, and requires recrystallization annealing to increase the production cost. 2, solid solution strengthening The essence of solid solution strengthening is to dissolve the alloying elements into the matrix phase to form a solid solution. The internal lattice distortion caused by the difference in atomic radius and the lattice change between the two causes the strength and hardness of the metal to increase, and the plasticity and toughness decrease. The mechanism of solid solution strengthening is that the solute atoms distorted the lattice of the solid solution and hindered the dislocations on the slip surface. Second, the Kodak air mass formed by the solute atoms that were segregated on the dislocation line. The pinning effect increases the resistance of the dislocation motion; the third is that the segregation of the solute atoms in the stacking fault zone hinders the movement of the extended dislocation. In the range of solid solution solubility, the larger the mass fraction of alloying elements, the greater the strengthening effect; the larger the difference between the size of solute atoms and solvent atoms, the more significant the strengthening effect; the strengthening effect of solute elements forming interstitial solid solution is greater than that of forming solid solution Element; the greater the difference in the valence electron number between the solute atom and the solvent atom, the greater the strengthening effect. The method commonly used for solid solution strengthening is alloying, that is, adding alloying elements. 3. Second phase enhancement Second phase strengthening generally refers to the various compound particles. By dispersing the second phase particles by various means, the dislocation motion inside the alloy can be hindered, thereby improving the yield strength and the tensile strength. The alloys currently used in the industry are mostly multiphase or multiphase alloys whose microstructure is such that a second phase (excess phase) is distributed on the solid solution matrix. There are three main forms of the second phase in the steel, namely, mesh, flake and granular. The mesh shape, especially the continuous network Fe3C precipitated along the grain boundary, reduces the mechanical properties of the steel, the plasticity and toughness drop sharply, and the strength also decreases. When the second phase is in the form of a sheet, the smaller the interlayer spacing, the higher the strength, and the better the ductility and toughness. When the second phase is a granular distribution, the finer the particles, the more uniform the distribution, the higher the strength of the alloy, and the greater the number of second phases, the greater the damage to plasticity; When precipitated along the grain boundary, the grain boundary strength is lowered regardless of the form, and the mechanical properties of the steel are lowered. The second phase prevents the movement of dislocations, whether flake or granular. The second phase strengthening method is usually to add alloying elements and then heat treat or plastically process the morphology and distribution of the second phase. 4, Fine grain strengthening Fine grain strengthening: As the grain size decreases, the strength and hardness of the material increase, and the phenomenon that the plasticity and toughness are improved is called fine grain strengthening. Refining the grains can simultaneously improve the strength and improve the ductility of the steel, and is a better method for strengthening the material. The finer the grain of the alloy, the greater the number of internal grains and grain boundaries. Fine grain strengthening strengthens the material by utilizing the irregularity of the arrangement of atoms on the grain boundary and the high atomic energy. According to the Hall-match relationship, the smaller the average diameter of the grains, the higher the yield strength of the material. The methods for refining crystal grains mainly include: increasing the degree of subcooling during the crystallization process, changing the quality, treating the vibration and stirring, increasing the nucleation rate and refining the grains. The cold deformed metal refines the grains by controlling the degree of deformation and the annealing temperature. The grain is refined by a normalizing and annealing heat treatment method; a strong carbide is formed into the steel to form an element or the like. When the grain size is smaller than the critical dimension dc, an inverse Hall-Pecch phenomenon occurs, that is, the intensity decreases as the grain size decreases.

Liquefied gas is mainly produced in oilfields and refining and chemical enterprises. It has the characteristics of less pollution, high calorific value, easy transportation and simple storage, so it is widely used in civil, commercial services, industrial production and other fields. Table 1 shows the global supply of liquefied petroleum gas and forecast data from 2015 to 2021. As can be seen from the table, in recent years, global LPG production has continued to increase, with annual growth rates of more than 2%. In addition, the average annual compound growth rate of LPG consumption and output in China has reached 15.69% and 9.95%, respectively. In 2016, China’s liquefied gas production was 35.539 million tons, an increase of 19.41% year-on-year. LPG has become an important part of China’s energy structure. Table 1 Global liquefied gas supply and forecast for 2015-2021 Table 3 Partial parameters of the amine solution

In layman’s terms, stainless steel is a steel that is not easily rusted. In fact, some stainless steels have both rust and acid resistance (corrosion resistance). The stainless steel’s rust and corrosion resistance is due to the formation of a chromium-rich oxide film (passivation film) on the surface that isolates the metal from the outside medium, prevents the metal from being further corroded, and has the ability to repair itself. If it is destroyed, the chromium in the steel will re-generate the passivation film with the oxygen in the medium and continue to protect. This rust and corrosion resistance are relative. The test shows that the corrosion resistance of steel in the weak medium such as atmosphere and water and the oxidizing medium such as nitric acid increases with the increase of the water content of chromium in the steel. When the chromium content reaches a certain percentage, the corrosion resistance of the steel occurs. Mutations, from rust to rust, from corrosion to corrosion. The stainless steel is also related to the environment in which it is used. In different environments, stainless steel with different chromium content is used. The level of chromium is the fundamental factor determining the performance of stainless steel. It is reported that the standards of Europe and the United States and other countries stipulate that the minimum chromium content should not be less than 10.5%, the Japanese regulations are 11%, and the country is 12%. Stainless steel classification There are five basic types of stainless steel: austenite, ferrite, martensite, duplex stainless steel, precipitation hardened stainless steel. (1) Austenitic stainless steels are not magnetic. Representative steel grades are 18% chromium and contain a certain amount of nickel to increase corrosion resistance. They are widely used steel grades. (2) Ferrite is magnetic, and its main content is chrome, with a ratio of 17%. This material has good oxidation resistance. (3) Martensitic stainless steels are also magnetic, typically having a chromium content of 13% and containing an appropriate proportion of carbon which can be hardened by quenching and tempering. (4) Duplex stainless steel has a mixed structure of ferrite and austenite. The content of chromium is between 18% and 28%, and the content of nickel is between 4.5% and 8%. They are very resistant to chloride attack. Good results. (5) Precipitated stainless steel chromium has a conventional content of 17, and a certain amount of nickel, copper and bismuth are added, which can be hardened by precipitation and aging. According to the metallographic organization can be pided into: Ferritic stainless steel (400 series), which is chrome stainless steel, mainly represented by Gr13, G17, Gr27-30; (2) austenitic stainless steel (300 series), chrome-nickel stainless steel, mainly representing 304, 316, 321, etc.; 3) Martensitic stainless steel (200 series), chrome-manganese stainless steel, high carbon content, mainly representing 1Gr13, etc. Why does stainless steel rust? Causes of rust: Chrome is a key stainless steel material that rusts, and may have the following reasons: (1) The presence of chloride ions in the use environment is widespread, such as salt/sweat/seawater/sea breeze/soil. Stainless steel in the presence of chloride ions, corrosion is very fast, even more than ordinary low carbon steel. Therefore, there is a requirement for the use environment of stainless steel, and it is necessary to wipe frequently to remove dust and keep it clean and dry. (This would give him a “useless”.) There is an example in the United States: a company uses a oak container to hold a solution containing chloride ions that has been used for nearly a hundred years and is scheduled to be replaced in the 1990s. Because the oak material is not modern enough, the container leaks due to corrosion after 16 days of replacement with stainless steel. (2) The alloying elements which have not been subjected to solution treatment are not dissolved in the matrix, resulting in a low content of the matrix structure alloy and poor corrosion resistance. (3) Natural intergranular corrosion This material containing no titanium or antimony has a tendency to intergranular corrosion. The addition of titanium and niobium, together with a stable treatment, can reduce intergranular corrosion. A high-alloy steel that resists corrosion in air or chemically corrosive media. Stainless steel has an aesthetically pleasing surface and good corrosion resistance. It does not require surface treatment such as plating to give full surface properties to stainless steel. One of the aspects of steel, commonly referred to as stainless steel. Representative properties include high-alloy steels such as 13 chrome steel and 18-8 chrome nickel steel. From the perspective of metallography, because stainless steel contains chromium and the surface forms a very thin chromium film, this film is isolated from the intrusion of oxygen in the steel to resist corrosion. In order to maintain the corrosion resistance inherent in stainless steel, steel must contain more than 12% chromium. Used in applications where soldering is required. The lower carbon content minimizes the precipitation of carbides in the heat affected zone near the weld, which may result in intergranular corrosion (weld erosion) in certain environments. It causes damage to the stainless steel surface and attaches iron powder to cause rust. In daily life, we sometimes find that the stainless steel of some flagpoles, bus shelters, light boxes and other facilities on the street have obvious rusting pickling phenomenon. Since it is stainless steel passivation, why is it rusting? There are two reasons for these situations. One is that the chromium content of the material is low and it belongs to inferior stainless steel. The second is not stainless steel at all, but the use of electroplating to deceive users. It is understood that many decorative materials are now treated with this plating process. Since the material is general steel, when the plating layer is peeled off, it will naturally rust. Stainless steel has the ability to resist atmospheric oxidation – that is, rust, and also has the ability to resist corrosion in medium containing acid, alkali, and salt – that is, corrosion resistance. However, the magnitude of its corrosion resistance varies with the chemical composition of the steel itself, the state of addition, the conditions of use, and the type of environmental medium. For example, 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, but it is moved to the coastal area, and it will soon rust in sea fog containing a lot of salt; while 316 steel pipe will perform. good. Therefore, it is not any kind of stainless steel, it can resist corrosion and rust in any environment. Stainless steel is a very thin and strong and stable chromium-rich oxide film (protective film) formed on the surface to prevent the oxygen atoms from continuing to infiltrate and continue to oxidize, thereby obtaining the ability to resist rust. Once for some reason, the film is continually destroyed, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will be continuously separated, forming loose iron oxide, and the metal surface will be continuously rusted. There are many forms of such surface film damage, and the following are common in daily life: The surface of stainless steel contains dust or other metal particles attached to other metal elements. In humid air, the condensed water between the attached material and the stainless steel connects the two into a micro battery, triggering an electrochemical reaction. The protective film is damaged, which is called electrochemical corrosion. The surface of the stainless steel adheres to the organic juice (such as melon, noodle soup, wolfberry, etc.), in the case of water and oxygen, constitutes an organic acid, and the organic acid corrodes the metal surface for a long time. The surface of the stainless steel adheres to acid, alkali and salt substances (such as alkali water and lime water splashing on the wall), causing local corrosion. In polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide, nitrogen oxide), in the case of condensed water, sulfuric acid, nitric acid, acetic acid liquid point is formed, causing chemical corrosion. All of the above can cause the corrosion of the stainless steel surface protective film to cause rust. Therefore, in order to ensure that the metal surface is permanently bright and not rusted, the following suggestions: The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove the deposits and eliminate external factors that cause modification. The coastal area should use 316 stainless steel, 316 material can resist seawater corrosion. Some chemical components of stainless steel pipes on the market cannot meet the corresponding national standards and cannot meet the requirements of 304 materials. Therefore, it will also cause rust, which requires the user to carefully select the products of reputable manufacturers. Source: China Stainless Steel Fitting Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The elements that are intentionally added during the smelting process in order to improve and improve certain properties of the steel and to achieve certain special properties are called alloying elements. Commonly used alloying elements are chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, silicon, manganese, aluminum, copper, boron and rare earth. Phosphorus, sulfur, nitrogen, etc. also function as alloys in some cases. (1) Cr Chromium can increase the hardenability of steel and have secondary hardening effect, which can improve the hardness and wear resistance of carbon steel without making the steel brittle. When the content exceeds 12%, the steel has good high-temperature oxidation resistance and oxidation resistance corrosion resistance, and also increases the heat strength of the steel. Chromium is the main alloying element of stainless steel acid-resistant steel and heat-resistant steel. Chromium can increase the strength and hardness of carbon steel in rolling state, and reduce elongation and reduction of area. When the chromium content exceeds 15%, the strength and hardness will decrease, and the elongation and the area shrinkage rate will correspondingly increase. Parts with chrome steel are easily ground to achieve high surface finish quality. The main role of chromium in the quenching and tempering structure is to improve the hardenability, so that the steel has good comprehensive mechanical properties after quenching and tempering. In the carburized steel, chromium-containing carbides can also be formed, thereby improving the surface resistance of the material. Grinding. Chromium-containing spring steel is not easily decarburized during heat treatment. Chromium can improve the wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electrothermal alloys, chromium increases the oxidation resistance, electrical resistance and strength of the alloy. (2) Ni Nickel strengthens ferrite in steel and refines pearlite. The overall effect is to increase strength and have no significant effect on plasticity. In general, for low carbon steels that are used in rolling, normalizing or annealed conditions without quenching and tempering, a certain amount of nickel can increase the strength of the steel without significantly reducing its toughness. According to statistics, each increase of 1% nickel can increase the strength by 29.4Pa. As the nickel content increases, the yield of steel increases faster than the tensile strength, so the ratio of nickel-containing steel can be higher than that of ordinary carbon steel. Nickel, while increasing the strength of steel, has less impact on the toughness, plasticity, and other process properties of steel than other alloying elements. For medium carbon steel, since the pearl reduces the pearlite transformation temperature, the pearlite is made finer; and since nickel reduces the carbon content of the eutectoid point, the pearlite has a larger number of pearlite than the carbon content of the same carbon content. The strength of the nickel-containing pearlitic ferritic steel is higher than that of the carbon steel of the same carbon content. On the other hand, if the strength of the steel is the same, the carbon content of the nickel-containing steel can be appropriately lowered, so that the toughness and plasticity of the steel can be improved. Nickel can increase the resistance of steel to fatigue and reduce the sensitivity of steel to the gap. Nickel reduces the low temperature brittle transition temperature of steel, which is of great importance for low temperature steels. 3.5% nickel-containing steel can be used at -100 °C, and nickel-containing 9% steel can work at -196 °C. Nickel does not increase the resistance of steel to creep, so it is generally not used as a strengthening element for heat-strength steel. The iron-nickel alloy with high nickel content has a linear expansion coefficient which changes significantly with the increase or decrease of nickel content. With this property, it is possible to design and produce precision alloys and bimetal materials with extremely low or constant linear expansion coefficients. In addition, nickel is added to steel not only to resist acid, but also to alkali, and has resistance to the atmosphere and salt. Nickel is one of the important elements in stainless acid-resistant steel. (3) Mo Molybdenum improves hardenability and heat strength in steel, prevents temper brittleness, increases remanence and coercivity, and resists in certain media. In quenched and tempered steel, molybdenum can deepen and harden the parts of larger sections, improve the tempering resistance or tempering stability of the steel, so that the parts can be tempered at higher temperatures, thus eliminating more effectively ( Or reduce) residual stress and improve plasticity. In addition to the above-mentioned effects, molybdenum in carburized steel can also reduce the tendency of carbides to form a continuous network on the grain boundaries in the carburized layer, reduce the retained austenite in the carburized layer, and relatively increase the surface layer. Wear resistance. In the forging die steel, molybdenum can also maintain the steel with a relatively stable hardness and increase the deformation. Resistance to cracking and abrasion. In the stainless acid-resistant steel, molybdenum can further improve the corrosion resistance to organic acids (such as formic acid, acetic acid, oxalic acid, etc.) as well as hydrogen peroxide, sulfuric acid, sulfurous acid, sulfate, acid dyes, bleaching powders and the like. In particular, the addition of molybdenum prevents the tendency of pitting corrosion caused by the presence of chloride ions. W12Cr4V4Mo high speed steel containing about 1% molybdenum has wear resistance, tempering hardness and red hardness. (4) W Tungsten is partially dissolved in iron to form a solid solution in addition to carbide formation in steel. Its effect is similar to that of molybdenum. The general effect is not as significant as molybdenum by mass fraction. The main sample of tungsten in steel is to increase tempering stability, red hardness, heat strength and increased wear resistance due to the formation of carbides. Therefore, it is mainly used for tool steel, such as high speed steel, steel for hot forging die, and the like. Tungsten forms refractory carbides in high-quality spring steel, which can alleviate the aggregation process of carbides and maintain high high-temperature strength when tempered at higher temperatures. Tungsten also reduces the heat sensitivity of steel, increases hardenability and increases hardness. 65SiMnWA spring steel has high hardness after air-cooling, and the spring steel with 50mm2 cross-section can be hardened in oil, which can be used as an important spring to withstand heavy load, heat resistance (not more than 350 °C) and impact. 30W4Cr2VA high-strength heat-resistant high-quality spring steel with large hardenability, quenching at 1050～1100°C, tensile strength after tempering at 550～650°C reaches 1470～1666MPa. It is mainly used to manufacture springs that are used at high temperatures (not more than 500 ° C). Since the addition of tungsten can significantly improve the wear resistance and machinability of steel, tungsten is the main element of alloy tool steel. (5) V Vanadium has a strong affinity with carbon, ammonia and oxygen to form a corresponding stable compound. Vanadium is mainly present in the form of carbides in steel. Its main role is to refine the structure and grain of steel and reduce the strength and toughness of steel. When dissolved in a solid solution at a high temperature, the hardenability is increased; conversely, when it exists in the form of a carbide, the hardenability is lowered. Vanadium increases the tempering stability of hardened steel and produces a secondary hardening effect. The vanadium content in steel is generally not more than 0.5% except for high speed tool steel. Vanadium can refine grains in ordinary low carbon alloy steel, improve the strength and yield ratio and low temperature characteristics after normalizing, and improve the welding performance of steel. Vanadium is often used in alloy structural steels in combination with elements such as manganese, chromium, molybdenum and tungsten because it reduces hardenability under general heat treatment conditions. In the quenched and tempered steel, vanadium mainly improves the strength and yield ratio of the steel, refines the grain and the superheat sensitivity of the crucible. In the carburized steel, because the grain can be refined, the steel can be directly quenched after carburizing without secondary quenching. Vanadium improves strength and yield ratio in spring steel and bearing steel, in particular, increases the ratio limit and elastic limit, and reduces the decarburization sensitivity during heat treatment, thereby improving the surface quality. The five-chrome vanadium-containing bearing steel has high carbonization dispersion and good performance. Vanadium refines grains in tool steel, reduces overheat sensitivity, increases tempering stability and wear resistance, and extends tool life. (6) Ti Titanium has a strong affinity with nitrogen, oxygen and carbon, and its affinity with sulfur is stronger than that of iron. Therefore, it is a good deoxidizing deaerator and an effective element for fixing nitrogen and carbon. Although titanium is a strong carbide forming element, it does not combine with other elements to form a composite compound. Titanium carbide has strong binding force, is stable, and is not easy to decompose. It can be slowly dissolved into solid solution in steel only when heated to above 1000 °C. The titanium carbide particles have an effect of preventing grain growth before they are dissolved. Since the affinity between titanium and carbon is much greater than the affinity between chromium and carbon, titanium is commonly used in stainless steel to fix carbon therein to eliminate the depletion of chromium at the grain boundaries, thereby eliminating or reducing intergranular corrosion of the steel. Titanium is also one of the strong ferrite forming elements, which strongly increases the temperature of steel A1 and A3. Titanium improves plasticity and toughness in ordinary low alloy steels. Since titanium fixes nitrogen and sulfur and forms titanium carbide, the strength of the steel is increased. After normalizing to refine the grain, precipitation of carbides can significantly improve the plasticity and impact toughness of the steel. Titanium-containing alloy structural steel has good mechanical properties and process properties. The main disadvantage is that the hardenability is slightly poor. . In high-chromium stainless steel, it is usually necessary to add about 5 times the carbon content of titanium, which not only improves the corrosion resistance of steel (mainly resistance to intergranular corrosion) and toughness; but also tends to improve the grain growth tendency of steel at high temperatures. Welding properties of steel. (7) Nb/Cb. Part of the cerium and lanthanum are dissolved in the solid solution to effect solid solution strengthening. When the austenite is dissolved, the hardenability of the steel is remarkably improved. However, in the form of carbides and oxide particles, the grains are refined and the hardenability of the steel is lowered. It can increase the tempering stability of steel and has secondary hardening effect. Trace bismuth can increase the strength of the steel without affecting the ductility or toughness of the steel. Due to the effect of refining the grains, the impact toughness of the steel can be improved and the brittle transition temperature can be lowered. When the content is more than 8 times that of carbon, almost all the carbon in the steel can be fixed, so that the steel has good hydrogen resistance. In the austenitic steel, intergranular corrosion of the steel by the oxidizing medium can be prevented. Due to the fixed carbon and precipitation hardening, the high temperature properties of the heat-strength steel, such as creep strength, can be improved. In the ordinary low-alloy steel for construction, it can improve the yield strength and impact toughness, and reduce the brittle transition temperature and beneficial weldability. In the carburizing and quenching and tempering alloy structural steel while increasing the hardenability. Improve the toughness and low temperature properties of steel. It can reduce the air hardenability of low carbon martensitic heat-resistant stainless steel, avoid hardening and temper brittleness, and improve creep strength. (8) Zr Zirconium is a strong carbide forming element, and its role in steel is similar to that of lanthanum, cerium and vanadium. The addition of a small amount of zirconium has the functions of degassing, purifying and refining grains, which is beneficial to the low temperature performance of steel and improves the punching performance. It is commonly used in the manufacture of ultra high strength steel and nickel base superalloys for gas engine and ballistic missile structures. (9) Co Cobalt is mostly used in special steels and alloys. Cobalt-containing high-speed steel has high high-temperature hardness. Ultra-high hardness and good comprehensive mechanical properties can be obtained by adding molybdenum to maraging steel. In addition, cobalt is also an important alloying element in heat-strength steels and magnetic materials. Cobalt reduces the hardenability of steel. Therefore, the addition of carbon steel alone reduces the overall mechanical properties after quenching and tempering. Cobalt strengthens ferrite and is added to carbon steel. It improves the hardness, yield point and tensile strength of steel under annealing or normalizing conditions. It has an adverse effect on elongation and reduction of area. Impact toughness also follows. The cobalt content increases and decreases. Since cobalt has antioxidant properties, it is used in heat resistant steels and heat resistant alloys. The cobalt-based alloy gas turbine shows its unique role. (10) Si silicon can be dissolved in ferrite and austenite to improve the hardness and strength of steel. Its effect is second only to phosphorus, and stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum and vanadium. However, when the silicon content exceeds 3%, the plasticity and toughness of the steel are significantly reduced. Silicon can increase the elastic limit, yield strength and yield ratio (σs/σb) of steel, as well as fatigue strength and fatigue ratio (σ-1/σb). This is because silicon or silicon manganese steel can be used as a spring steel. Silicon can reduce the density, thermal conductivity and electrical conductivity of steel. It can promote the coarsening of ferrite grains and reduce the coercive force. There is a tendency to reduce the anisotropy of the crystal, make the magnetization easy, and the magnetoresistance is reduced, which can be used to produce electrical steel, so the magnetic resistance loss of the silicon steel sheet is low. Silicon can increase the magnetic permeability of ferrite, so that the steel sheet has a higher magnetic induction strength under a weaker magnetic field. However, silicon reduces the magnetic induction strength of steel under strong magnetic fields. Silicon has a strong deoxidizing power, which reduces the magnetic aging effect of iron. When the silicon-containing steel is heated in an oxidizing atmosphere, a SiO2 film is formed on the surface, thereby improving the oxidation resistance of the steel at a high temperature. Silicon promotes the growth of columnar crystals in cast steel and reduces plasticity. If the silicon steel cools faster when heated, the internal and external temperature difference of the steel is large due to the low thermal conductivity, and thus it is broken. Silicon can reduce the weldability of steel. Because silicon is stronger than iron, it is easy to form low-melting silicate during welding, which increases the fluidity of slag and molten metal, causing splashing and affecting the quality of welding. Silicon is a good deoxidizer. When deoxidizing with aluminum, a certain amount of silicon is added as appropriate, which can significantly improve the deoxidation rate. Silicon has a certain residual in steel, which is brought into the raw material during ironmaking steelmaking. In boiling steel, silicon is limited to <0.07%. When intentionally added, a ferrosilicon alloy is added during steel making. (11) Mn Manganese is a good deoxidizer and desulfurizer. Steel generally contains a certain amount of manganese, which can eliminate or reduce the hot brittleness of steel caused by sulfur, thereby improving the hot workability of steel. a solid solution of manganese and iron, which increases the hardness and strength of ferrite and austenite in steel; at the same time it is an element of carbide formation, which replaces a part of iron atoms in cementite, and manganese reduces the critical transition temperature in steel. It plays the role of refining the pearlite and indirectly improving the strength of the pearlite steel. Manganese’s ability to stabilize austenite is second only to nickel, and it also strongly increases the hardenability of steel. Manganese having a content of not more than 2% has been used in combination with other elements to form a plurality of alloy steels. Manganese is rich in resources and perse in performance, and has been widely used, such as carbon structural steel with high manganese content and spring steel. In high-carbon high-manganese wear-resistant steel, the manganese content can reach 10% to 14%, and it has good toughness after solution treatment. When it is deformed by impact, the surface layer will be strengthened by deformation and has high resistance. Grinding. Manganese and sulfur form a higher melting point of MnS, which prevents hot brittleness due to FeS. Manganese has a tendency to increase the grain coarsening of steel and temper brittleness sensitivity. If the smelting and pouring and chilling are not properly cooled, it is easy to make the steel white spots. (12) Al aluminum is mainly used to deoxidize and refine grains. In the nitriding steel, a hard and corrosion resistant nitriding layer is formed. Aluminum can suppress the aging of low carbon steel and improve the toughness of steel at low temperatures. When the content is high, the oxidation resistance of the steel and the corrosion resistance in the oxidizing acid and the H2S gas can be improved, and the electrical and magnetic properties of the steel can be improved. Aluminum has a large solid solution strengthening effect in steel, which improves the wear resistance, fatigue strength and core mechanical properties of carburized steel. In the hard alloy, aluminum and nickel form compounds to improve the smelting strength. The aluminum-containing iron-chromium aluminum alloy has near-resistance characteristics and excellent oxidation resistance at high temperatures, and is suitable for electrosmelting alloy materials and chrome aluminum. Resistance wire. When some steels are deoxidized, if the amount of aluminum is too much, the steel will have an abnormal structure and a tendency to promote graphitization of the steel. In ferritic and pearlitic steels, when the aluminum content is high, the high temperature strength and toughness are lowered, and some difficulties are brought to the smelting and casting. (13) The prominent role of Cu copper in steel is to improve the atmospheric corrosion resistance of ordinary low alloy steel. Especially when combined with phosphorus, adding copper can also improve the strength and yield ratio of steel, but it is not harmful to the welding performance. influences. The steel (U-Cu) containing 0.20% to 0.50% of copper has a corrosion-resistant life of 2 to 5 times that of a general carbon steel rail in addition to wear resistance. When the copper content exceeds 0.75%, the aging strengthening effect can be produced after solution treatment and aging. When the content is low, its effect is similar to that of nickel, but it is weak. When the content is high, it is unfavorable for thermal deformation processing, and causes copper brittleness during hot deformation processing. 2% to 3% of copper can resist corrosion resistance and stress corrosion corrosion of sulfuric acid, phosphoric acid and hydrochloric acid in austenitic stainless steel. (14) B The main role of boron in steel is to increase the hardenability of steel, thereby saving other less expensive metals, and nickel, chromium, molybdenum and the like. For this purpose, the content is generally specified in the range of 0.001% to 0.005%. It can replace 1.6% nickel, 0.3% chromium or 0.2% molybdenum. Boron molybdenum should be noted that molybdenum can prevent or reduce temper brittleness, while boron has a slight tendency to promote temper brittleness, so it cannot be used. Boron completely replaces molybdenum. Boron is added to the medium carbon carbon steel. Since the hardenability is improved, the properties of the steel with a thickness of 20 mm or more can be greatly improved after quenching and tempering. Therefore, 40B and 40MnB steel can be used instead of 40Cr, and 20CrMnTi carburized steel can be replaced by 20Mn2TiB steel. However, since the effect of boron decreases or even disappears with the increase of carbon content in the steel, in the selection of boron-containing carburized steel, it must be considered that after the carburization of the part, the hardenability of the carburized layer will be lower than that of the core. This feature of permeability. Spring steel is generally required to be completely hardened, and usually the spring area is not large, and it is advantageous to use boron-containing steel. The effect of boron on high-silicon spring steel fluctuates greatly and is inconvenient to adopt. Boron has a strong affinity for nitrogen and oxygen. The addition of 0.007% boron to the boiling steel can eliminate the aging of steel. (15) RE Generally speaking, the rare earth element refers to a lanthanide element (15) with an atomic number from 57 to 71 in the periodic table, plus 17 elements of No. 21 and No. 39. They are close in nature and difficult to separate. Unseparated is called mixed rare earth, which is relatively cheap. Rare earth elements can improve the plasticity and impact toughness of wrought steel, especially in cast steel. It can improve the creep resistance of heat-resistant steel electrothermal alloys and high-temperature alloys. Rare earth elements can also improve the oxidation resistance and corrosion resistance of steel. The effect of oxidation resistance exceeds that of elements such as silicon, aluminum, and titanium. It can improve the fluidity of steel, reduce non-metallic inclusions, and make the steel structure dense and pure. Adding appropriate rare earth elements to common low-alloy steels has good deoxidation and desulfurization, improves impact toughness (especially low temperature toughness), and improves anisotropic properties. The rare earth element increases the oxygen resistance of the alloy in the iron-chromium-aluminum alloy, maintains the fine grain of the steel at a high temperature, and increases the high-temperature strength, thereby significantly increasing the life of the electrothermal alloy. (16) N Nitrogen is partially used in iron and has solid solution strengthening and hardenability improvement, but it is not significant. Since the nitride precipitates on the grain boundary, the high temperature strength of the grain boundary can be increased, and the creep strength of the steel is increased. It combines with other elements in steel and has precipitation hardening. The corrosion resistance of the steel is not significant, but after the surface of the steel is nitrided, it not only increases its hardness and wear resistance, but also significantly improves the corrosion resistance. Residual nitrogen in low carbon steel results in ageing brittleness. (17)S Increasing the sulfur and manganese content can improve the machinability of steel. In free-cutting steel, sulfur is added as a beneficial element. Sulfur is severely segregated in steel. Deteriorating the quality of steel, reducing the plasticity of steel at high temperatures, is a harmful element, which exists in the form of FeS with a lower melting point. The melting point of FeS alone is only 1190 ° C, and the eutectic temperature of forming a eutectic with iron in steel is lower, only 988 ° C. When the steel solidifies, the iron sulfide is concentrated at the primary grain boundary. When the steel is rolled at 1,100 to 1,200 ° C, the FeS on the grain boundary will melt, which greatly weakens the bonding force between the grains, resulting in hot brittleness of the steel, so the sulfur should be strictly controlled. Generally controlled at 0.020% to 0.050%. In order to prevent brittleness due to sulfur, sufficient manganese should be added to form a higher melting point of MnS. If the flow rate in the steel is too high, pores and looseness will form in the weld metal due to the generation of SO2 during welding. (18) P Phosphorus has strong solid solution strengthening and cold work hardening in steel. As an alloying element added to the low-alloy structural steel, it can improve its strength and the atmospheric corrosion resistance of steel, but reduce its cold stamping performance. Phosphorus combined with sulfur and manganese can increase the cutting performance of steel, increase the surface quality of the machined parts, and be used for free-cutting steel, so the phosphorus content of the free-cutting steel is also relatively high. Phosphorus is used for ferrite. Although it can improve the strength and hardness of steel, the biggest harm is that segregation is serious, temper brittleness is increased, and the plasticity and toughness of steel are significantly increased, which makes the steel easy to be brittle during cold working. Brittle phenomenon. Phosphorus also has an adverse effect on weldability. Phosphorus is a harmful element and should be strictly controlled. The general content is not more than 0.03% to 0.04%. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Valve corrosion protection The corrosion of metals is mainly caused by chemical corrosion and electrochemical corrosion. The corrosion of non-metallic materials is generally caused by direct chemical and physical damage. 1. Chemical corrosion The surrounding medium directly reacts with the metal to cause damage under the condition that no current is generated, such as corrosion of the metal by the high-temperature drying gas and the non-electrolytic solution. 2. Electrochemical corrosion The metal is in contact with the electrolyte, causing the flow of electrons, which destroys itself in electrochemical action, which is the main form of corrosion. Common acid-base salt solution corrosion, atmospheric corrosion, soil corrosion, seawater corrosion, microbial corrosion, stainless steel pitting corrosion and crevice corrosion are all electrochemical corrosion. Electrochemical corrosion occurs not only between two substances that can act as a chemical, but also because of the difference in concentration of the solution, the difference in the concentration of surrounding oxygen, the slight difference in the structure of the substance, etc., the difference in potential is generated, and the power of corrosion is obtained. The metal with low potential and in the positive position is lost. Valve corrosion rate Corrosion speed can be pided into six: Full corrosion resistance corrosion rate less than 0.001 mm / year Extreme corrosion resistance corrosion rate 0.001 to 0.01 mm / year Corrosion resistance corrosion rate 0.01 to 0.1 mm / year Corrosion resistance corrosion rate 0.1 to 1.0 mm / year Poor corrosion resistance Corrosion rate 1.0 to 10 mm / year Non-corrosion corrosion rate greater than 10 mm / year Nine major anti-corrosion measures 1. Select corrosion resistant materials according to corrosive media In the actual production, the corrosion of the medium is very complicated. Even in the case of the valve material used in a medium, the concentration, temperature and pressure of the medium are different, and the medium is not corroded to the material. For every 10 °C increase in the temperature of the medium, the corrosion rate increases by about 1 to 3 times. Valve parts anti-corrosion precautions 1. Stem corrosion and protection Main causes of stem corrosion: Corrosion damage of the valve body is mainly caused by corrosive media, and the problem of valve stem corrosion is mainly filler. Not only does the corrosive medium corrode the stem, but steam and water can also cause spots on the stem to contact the packing. Especially for valves stored in warehouses, stem corrosion can occur. This is the electrochemical corrosion of the filler to the valve stem. The most widely used filler is the asbestos-based packing. The asbestos material contains a certain amount of chloride ions, in addition to potassium, sodium and magnesium ions, which are all corrosive factors. Valve stem anti-corrosion precautions: Do not add filler during valve storage. Without filling, it loses the electrochemical corrosion of the valve stem and can be stored for a long time without being corroded. The stem is surface treated. Such as chrome plating, nickel plating, nitriding, boronizing, zinc and so on. Reduce asbestos impurities. Washing with distilled water can reduce the chlorine content in asbestos and reduce its corrosivity. Add a corrosion inhibitor to the asbestos packing. This corrosion inhibitor suppresses the corrosiveness of chloride ions. Such as sodium nitrite. Add sacrificial metal to asbestos. This is a metal that is lower than the stem potential as a victim. This corrosion of chloride ions first occurs on the sacrificial metal, thereby protecting the valve stem. It can be used as a sacrificial metal such as zinc powder. Protected with Teflon. Polytetrafluoroethylene has excellent chemical stability and dielectric properties, and current cannot pass. If the asbestos packing is impregnated with polytetrafluoroethylene, the corrosion will be reduced. The asbestos packing can also be wrapped with a Teflon tape and then loaded into a stuffing box. Improve processing smoothness and also reduce electrochemical corrosion. 2. Closed parts corrosion and protection The main reason for the corrosion of the closure: The closure is often flushed with fluid, allowing corrosion to accelerate. Some discs, although using better materials, are still more corrosive than the valve body. The upper and lower closing members are usually threadedly connected with the valve stem and the valve seat, and the joint is deficient in oxygen than the general portion, which easily constitutes an oxygen concentration battery, causing corrosion damage. Some sealing parts are pressed into the sealing surface. Due to the lack of tightness and slight gap, oxygen concentration battery corrosion may occur. Close parts anti-corrosion notes: Use corrosion resistant materials as much as possible. The closing piece has a small weight, but plays a key role in the valve, as long as it is resistant to corrosion, even with a little expensive material. Improve the closure structure so that it is less subject to fluid erosion. Improve the connection structure to avoid the generation of oxygen concentration batteries. In valves below 200 ° C, the joint between the closing part and the sealing surface, using a Teflon raw material tape as a filler, can reduce the corrosion of these parts. While considering corrosion resistance, attention should also be paid to the erosion resistance of the closure material. Use a material that is resistant to erosion as a closure. Corrosion resistant valve selection points In the case of corrosive media conditions, anti-corrosion is the most critical place for chemical equipment. If the metal material of the chemical valve cannot be correctly selected, it is slightly inadvertent, and the equipment is damaged, which may cause accidents or even disaster. How to choose the corrosion-resistant valve for some common chemical media?

1. Application of stainless steel in petroleum and petrochemical According to the chemical composition, stainless steel can be pided into Cr stainless steel, Cr-Ni stainless steel and Cr-Ni-Mo stainless steel. According to the application field, it can be pided into medical stainless steel, atmospheric corrosion resistant stainless steel, anti-oxidation stainless steel, and Cl-resistant stainless steel. However, the most commonly used classifications are classified according to the organization of steel. They are generally classified into ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, duplex stainless steel and precipitation hardened stainless steel. In petroleum and petrochemical applications, austenitic stainless steel, ferritic stainless steel and duplex stainless steel account for a large proportion. Ferritic stainless steel generally has a Cr content of between 13% and 30%, and a C content of generally less than 0.25%. After annealing or aging, carbides are precipitated at the ferrite grain boundaries to achieve corrosion resistance. In general, ferritic stainless steels have lower corrosion resistance than austenitic stainless steels and duplex steels, but higher than martensitic stainless steels. However, due to its low production cost compared to other stainless steels, it is widely used in chemical and petrochemical applications for areas where corrosion resistant media and strength are not critical. For example, it is widely used in the environment of sulfur-containing petroleum, hydrogen sulfide, room temperature nitric acid, carbonic acid, hydrogen ammonia mother liquor, high-temperature ammonia water produced by urea, urea mother liquor, and vinyl acetate and acrylonitrile produced by vitamin nylon. Martensitic stainless steel generally has a Cr content of between 13% and 17%, a high C content of between 0.1% and 0.7%, and a high strength, hardness and wear resistance, but low corrosion resistance. It is mainly used in petroleum and petrochemical applications in environments where corrosive media is not strong, such as components requiring higher toughness and impact loads, such as turbine blades, bolts and other related components. Austenitic stainless steel Cr content is between 17%-20%, Ni content is between 8%-16%, C content is generally less than 0.12%, mainly by adding Ni element to expand the austenite transformation zone, thus at room temperature The austenite structure is obtained. Austenitic stainless steel is superior to other stainless steels in corrosion resistance, plasticity, toughness, processing properties, weldability, and low temperature performance. Therefore, it is the most widely used in various fields, and its usage accounts for about all stainless steel. About 70% of the amount. In the petroleum and petrochemical field, austenitic stainless steels have great advantages in highly corrosive media and low-temperature media, such as internal components with high corrosion resistance, especially in intergranular corrosion resistant environments, such as heat exchangers/pipe fittings. Low-temperature liquefied natural gas (LNG) conveying pipeline, urea, sulfur ammonia and other production containers, flue gas dedusting and desulfurization devices. Duplex stainless steel is developed on the basis of single-phase stainless steel, and its Ni content is generally about half of the austenitic stainless steel Ni content, which reduces the alloy cost. Austenitic stainless steel has excellent corrosion resistance and high comprehensive performance. It solves the disadvantages of weak corrosion resistance of ferrite and martensitic stainless steel and insufficient strength and wear resistance of austenitic stainless steel. In the petroleum and petrochemical field, it is mainly used in marine oil platforms resistant to seawater corrosion, acidic components and equipment, especially in pitting resistant components. Precipitation-strengthened stainless steel mainly obtains high-strength properties through the precipitation strengthening mechanism. At the same time, it sacrifices its own corrosion resistance. Therefore, it is rarely used in corrosive media, and is generally used in petrochemical machinery mining and other industries. 2. Stainless steel pipe in petroleum and petrochemical applications The petroleum and petrochemical industry is the pillar industry of the national economy, and it plays a pivotal role in the national economy. In the past 20 years, stainless steel pipes have been greatly improved in terms of production technology, whether they are seamless pipes or welded pipes. The stainless steel pipes produced by some domestic manufacturers have reached the level that can completely replace imported products, and the localization of steel pipes has been realized. In petroleum and petrochemical, stainless steel pipes are mainly used in pipeline transportation systems, including high pressure furnace tubes, piping, petroleum cracking tubes, fluid conveying tubes, and heat exchange tubes. Stainless steel is required to perform well in wet and acid service conditions. 2.1 Application of Stainless Steel Seamless Pipe for Large Diameter Thick Wall High Pressure Hydrogen In order to adapt to the processing of low-quality crude oil and meet the requirements of environmental protection, domestic refining and chemical enterprises continue to optimize the processing structure of refinery units and adjust the product structure. Among them, high-pressure hydrogenation units such as hydrocracking and hydrotreating have developed rapidly in recent years, and the processing capacity of the equipment It is also constantly improving. The main features of the hydrogen pipeline are large diameter and thick wall. For the selection of high-pressure hydrogen materials, due to its high temperature and high pressure conditions, TP321/H, TP347/H, etc. are generally used as materials for high-pressure hydrogen pipes at home and abroad. The above two stainless steel materials are stabilized by the addition of Ti and Nb. The element has high high temperature corrosion resistance and high temperature mechanical properties. At present, domestic large-diameter thick-walled hydrogen pipelines are mainly manufactured by hot perforation + cold rolling / cold drawing. The processing process is shown in Figure 1. The pipe made by hot perforation + cold rolling / cold drawing has the characteristics of good surface, high dimensional accuracy and uniform wall structure compared with steel pipes manufactured by other methods. For the high-pressure hydrogen-producing steel pipe, due to the particularity of the working medium, the requirements for the raw material of the steel pipe are high. Therefore, the requirements of the design institute for the high-pressure hydrogen pipeline are: S≤0.015%, P≤0.030%, non-metallic inclusion A Class B, C, and D are not higher than 1.5. Ultrasonic inspection is required for the finished pipe, and the artificial contrast defect is not more than 5% of the nominal wall thickness of the pipe. 2.2 Application of stainless steel welded steel pipe for low temperature LNG Due to the development of society, people’s awareness of environmental protection has increased, and clean energy has received more and more attention. LNG is a clean and efficient energy source that plays an important role in national production and life. Therefore, LNG receiving stations and LNG carriers have sprung up. LNG is to cool gaseous natural gas to -162 ° C under normal pressure to cause it to condense into a liquid. Therefore, the piping for LNG transportation must have high low temperature performance. For low-temperature LNG pipes, most of them are made of ultra-pure, low-carbon, low-sulfur, low-phosphorus stainless steel at home and abroad. In recent years, double-grade stainless steel has been very popular among LNG users, especially TP304/304L, TP316/316L and other applications. Shuangzheng Steel not only has L-grade corrosion resistance and low temperature performance, but also has high mechanical properties. At present, the mainstream low-temperature LNG welded stainless steel pipes at home and abroad are generally processed by automatic unit welding forming process, UOE forming process and JCO forming process. The main processes are shown in Figure 2 and Figure 3, respectively. The automatic welding unit is a fast, efficient and automatic method of producing welded pipes in the case of not thick wall. At present, most of the plates are formed by the rollers, and then welded, heat treated, etc., and some welding units are also It integrates advanced technology such as on-line ultrasonic welding, on-line welding ultrasonic, and automatic seam tracking technology to provide high-efficiency manufacturing operations for LNG long-distance pipeline manufacturing and reduce the manufacturer’s production period. UOE forming technology is currently the most widely used, most mature and most recognized quality low-temperature LNG welded pipe production process in the world, and its main process technology has been finalized. The JCO molding process is a new molding process in recent years. This molding technology is an organic combination of stepping pre-bending and tube CNC bending. For the LNG stainless steel welded pipe, since the use environment is in a low temperature environment of -162 ° C, it is necessary to have a high low temperature impact property for the LNG pipe. At present, most design institutes, research institutes, and manufacturers require that the low-temperature impact performance of LNG pipes is not less than 80J, and the lateral expansion amount is not less than 0.38mm according to ASME B 31.3. For stainless steel welded pipes, the weld is used as the weak link of the pipe. The quality of the weld directly affects the safety of the pipeline and even the pipeline. The welding coefficient is one of the important factors to evaluate the quality of the weld. For the low temperature LNG welded pipe, the welding coefficient is Ej=1.0, and the welded joint must be a full welded joint. After the welded joint is completed, all welds must be 100% ray-tested. The weld must be free of defects such as incomplete penetration, no weld inclusions, no undercuts, and no cracks to ensure the stability of the welded joint at low temperatures. 3. Outlook Oil pipelines are the bulk of stainless steel pipes. Stainless steel pipes play an important role in equipment manufacturing, oil recovery, oil refining and transportation in the petroleum industry. In recent years, the country has increased the development of petroleum resources. At the same time, as the world’s largest net oil importing country, with the increasing demand for petroleum, the petroleum-related industries will further develop and the demand for stainless steel pipes will continue. increase. In 2017, China’s steel industry has shown signs of recovery. Domestic leading stainless steel pipe companies have increased their cooperation with PetroChina and Sinopec to increase their market share. At the same time, domestic steel pipe enterprises have also carried out activities with foreign oil companies to push China’s stainless steel pipe manufacturing to the world platform. Source: China Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. Pipeline fluid has the advantages of low cost and safety, and is the most widely used fluid transport method. However, since most of the pipelines are buried underground, they will be corroded by the transport medium, soil, groundwater and stray currents. Corrosion will lead to thinning of the pipe wall and even leakage of the perforations, eventually causing the pipeline to fail, which not only causes huge economic losses and resources. Waste, at the same time, leakage can also cause environmental pollution. According to statistics, the world loses about 10% to 20% of metal every year due to corrosion, resulting in economic losses of more than 1.8 trillion US dollars. According to the survey conducted by the Chinese Academy of Engineering, the economic losses caused by corrosion in China in 2008 amounted to 1.2 trillion to 2 trillion yuan. At present, domestic and foreign scholars’ research on pipeline corrosion mainly focuses on the development of anticorrosive coatings, the development of corrosion inhibitors, the detection of corrosion, and the establishment of corrosion prediction models. Detailed analysis of the corrosion mechanism of the water pipeline, oil pipeline, gas pipeline, contrast protection method and corrosion monitoring method can provide reference for the related research of corrosion protection to reduce the damage caused by corrosion. This paper reviews the research status of corrosion and protection of water pipelines, corrosion and protection of oil pipelines, and corrosion and protection of gas pipelines, and puts forward some suggestions and prospects. 2 Pipeline corrosion and protection     2.1 Corrosion and protection of water pipelines     Corrosion of water pipelines is caused by corrosion components in water bodies. According to different water quality, water pipelines are generally pided into urban water supply pipelines and sewage pipelines.     2.1.1 Corrosion and protection of urban water supply pipelines     The water itself is an electrolyte, and electrodes are formed at portions where the properties of the inner surface of the pipe are different, thereby forming electrochemical corrosion. Electrochemical corrosion is the main mechanism of corrosion in urban water supply pipelines. Whether the surface of the pipe wall is clean and free of impurities has a great influence on the occurrence and development rate of corrosion. Dissolved oxygen, CO2, sulphate, chloride, and residual disinfectant during the water supply process also have an effect on the corrosion of the pipeline. Cl- in tap water will destroy the passivation film, and as a catalyst for corrosion, induce Fe2+ hydrolysis, and then corrode the pipeline. The experimental results show that the Cl-corrosion concentration range is 0.2~0.6mg/L. Microorganisms are also one of the factors affecting the corrosion of water supply pipelines. Autotrophic aerobic iron bacteria (IRB) and heterogeneous anaerobic sulfate-reducing bacteria (SRB) are the most important corrosive species. Some scholars have studied the effect of water flow velocity on corrosion. The velocity of water flow is proportional to the velocity of oxygen to the metal surface. At the same time, the water flow washes the corrosion products on the metal surface, accelerates the corrosion rate of the metal, and accelerates the corrosion of the pipeline. Of course, the pH of the water is also one of the factors that affect the corrosion of the pipeline.     The anti-corrosion methods of urban water supply pipes mainly include three types: scraping method, inner lining technology and cathodic protection method. The scraping method is a mature anti-corrosion technology for water supply pipelines, including artillery shell method, high-pressure jet method, mechanical scraping method, elastic pipe punching method, pneumatic pulse method and water hammer method. In the experimental study of high-pressure jet method, it is found that the jet angle is between 35° and 45°, the aperture is between 1.4 and 1.6mm, and the jet number between 8 and 10 will produce greater impact force and thrust. The elastic impactor method has a rust-removing effect that is not ideal because it has no lining technology. The inner lining technology is one of the commonly used anti-corrosion technologies for water supply pipes, such as cement mortar lining, epoxy lining, and lining hose method. Yang Jun used a polymer epoxy resin polymer, polyamide-alicyclic amine hardener, titanium dioxide, mixed solvent, talc powder to synthesize a special anticorrosive coating for water pipelines at a ratio of 5:1:1:1:1. This kind of coating has strong adhesion to concrete steel structure and good permeability. The cathodic protection method is also a commonly used anticorrosion method, a cathodic protection method for metal thermal spraying and impressed current, and a cathodic protection method for sacrificial anode. In addition, the use of corrosion-resistant pipes will also play a role in corrosion of pipelines. According to the phenomenon that Cr, Cu and Ca can protect the metal oxide of surface rust layer under the condition of stagnant water flow, it is proposed that the above metal elements can be added in the production of pipeline to improve the corrosion resistance of low carbon steel. At present, the methods for detecting corrosion of water pipelines include sound leakage detection method, related leak detection method, regional leak detection method and buried water pipeline leakage detection method. In the method of leak detection of buried water pipeline, the detection accuracy of water leakage point can be as high as 95%, and the positioning error of water leakage point is not more than ±1m. Some scholars have proposed using electromagnetic wave sensors and wavelet transform to detect water pipes. Safuzadeh et al. [13] developed an internal optical inspection system for pipes, including laser diodes, optical ring pattern generators and CCD cameras. The system uses reflections and physical sensors to identify defects and anomalies in the extracted images. Zhang Yefang designed a tap water pipeline leak detector. The MCU module is connected with the sensor module, power module, data input module, display module and alarm module respectively. The sensor module is set in the water pipe, and the sensor module converts the leakage signal into a pulse signal and sends it to the MCU. The module is finally sent to the display module and the alarm module. The leak detector solves the problem that the tap water pipe system in daily life is broken due to the long-term disrepair of the pipe, and the like.     2.1.2 sewage pipeline     The composition of the medium transported by the sewage pipeline is complicated, and the acid and alkali substances in the sewage will cause corrosion to the pipeline; as the residence time of the sewage in the pipeline increases, the dissolved oxygen and nitrate in the sewage are completely consumed, and the anaerobic environment inside the pipeline Will promote the formation of hydrogen sulfide gas, H2S will cause corrosion to the pipeline; S in the sewage will be converted into H2SO4 after a series of biochemical reactions, and then react with the cement-based materials in the pipeline to corrode the pipeline. In addition, for pipelines conveying certain special media, such as oil-producing water pipelines, in the gas field mining process, methanol is injected into the gas production pipeline at the wellhead to suppress the formation of natural gas hydrates, and finally form the gas-containing sewage in the gas field. Alcohol-containing sewage will accelerate pipeline corrosion. The pH, dissolved oxygen, dissolved salts, CO2, H2S, bacteria, and pressure and temperature changes in oily wastewater are all factors that corrode the pipeline. CO2, H2S dissolves in water to form acid, causing corrosion to steel. In addition, since O2 is a depolarizing agent, O2 dissolved in water can aggravate the corrosion of CO2 and H2S on the metal pipe wall. Some microbial bacteria (such as iron bacteria) can obtain the energy of metabolism by changing the valence state of iron ions in a neutral medium. The high-valent iron produced by the reaction has strong oxidizing properties, and can oxidize sulfide to sulfuric acid. Corrosion of pipes.     The anti-corrosion of sewage pipelines can also be coated with internal lining technology. However, due to the complicated water quality of sewage, high-performance anti-corrosion inner coating lining, such as titanium nano-polymer coating, is required. When the coating content is 6%, the ternary coating is ternary. The composite liquid has the best anti-corrosion effect and superior chemical corrosion resistance; the coating can fill the structural micropores, improve the bonding strength between the substrate and the coating, and has good distribution uniformity in the coating film without aggregation. Some scholars have proposed to inject air into urban sewage pipes to suppress H2S corrosion, but this technology requires higher costs, so the protection against H2S corrosion needs to explore a cheaper method. The protection methods for dissolved corrosive gases in oily sewage are pided into chemical methods and process methods. Chemical methods include corrosion inhibition and water quality modification. In the produced water of the oil field, CO2 and HCO3- can form a weak acid buffer system, and react with Mg2+, Ca2+, Fe2+ to form a precipitate to cause scaling. The water quality modification method is to break the buffer system and adjust with ions containing OH-. The agent adjusts the proportion of ions in the water to change the water to control corrosion, inhibit scaling, and purify the water. Process protection methods for oily sewage include electrolysis, degassing membranes, supergravity and stripping processes. Among them, the stripping process is widely used in engineering practice due to its large processing capacity, low operating cost and simple operation. Degassing membrane technology has yet to be confirmed due to many restrictions in the application of water treatment, and the technology is still in the laboratory research stage.     At present, the methods for sewage pipeline detection include pipeline closed-circuit television detection system, pipeline endoscopic sonar detection, pipeline inspection robot technology, pipeline scanning and evaluation technology, use of portable detection system-periscope, focus motor leakage locator and scanning electron microscope, Use multiple sensors. Among them, the closed-circuit television detection system is a commonly used technology at home and abroad. The technology has the advantages of clear image, safe operation and easy management. In addition, some scholars have studied the use of ultrasonic method to detect the drainage pipe. This technology uses the principle that ultrasonic waves propagate in water and the obstacles will reflect to achieve the purpose of detecting the drainage pipe. However, the signal of the ultrasonic echo is not particularly stable during the detection, which is likely to cause false detection and missed detection. Therefore, the ultrasonic detection is still the focus of future research.     2.2 Corrosion and protection of oil pipelines     Petroleum contains a large amount of organic and inorganic substances such as alkanes, cycloalkanes and aromatic hydrocarbons. Therefore, the corrosion mechanism and protection method of oil pipelines are complicated with respect to water pipelines.     The oil is doped with gases such as CO2, H2S, and SO2. These gases are soluble in water to form carbonic acid, and sulfuric acid causes acid corrosion. The sediment in the oil can wash the passivation film of the pipeline wall during the transportation process, causing wear and corrosion. The synergistic action of microorganisms such as dissolved oxygen and sulfate-reducing bacteria in the oil, as well as changes in temperature, pressure, and flow rate, can also cause serious corrosion to the pipeline. Obuekwe et al. describe a phenomenon of “infinite stacking of sulfides”. Through this phenomenon, the author believes that the various aerobic and anaerobic bacteria in the crude oil will act synergistically on the sulfides, which will lead to the formation of sulfides, causing corrosion of the pipeline.     At present, the protection methods for corrosion in oil pipelines include chemical addition, internal lining protection and cathodic protection. Mo-hanmed et al. synthesized a Bacillus B21 antagonist that reduces the growth of sulfate-reducing bacteria, reduces the production of sulfides, and consumes sulfate, thereby reducing corrosion of the pipeline. For different media and conditions of use, the selection of a suitable metal material is also an effective way to reduce pipe corrosion. Some scholars have studied a corrosion-resistant treatment technology for the inner and outer surfaces of long steel tubes. This technology combines chemical heat treatment and electric heating to form a layer of high corrosion resistance chemical infiltration on the inner and outer surfaces of thin steel tubes of any length. The depth can reach 0.25~0.80mm. In 3% NaCl aqueous solution, the corrosion resistance can be increased by 5 times, which is equivalent to 1Cr18Ni9Ti stainless steel. The depth of the surface hardened layer in the steel pipe can reach 0.15~0.40mm, the hardness can reach HV1200 or above, wear resistance. Increase by 2 times. Some scholars have also suggested that the state of the metal surface is also an important factor affecting corrosion. The rough surface is rougher than the polished metal surface.     The detection methods of oil and gas pipeline leakage include ultrasonic method, magnetic flux leakage method, eddy current method, etc., but the point-by-point scanning is required for detection, which is high in cost and low in efficiency, so it cannot be effectively applied in the detection of long-distance pipelines. Some scholars have proposed an acoustic emission technology, which overcomes the shortcomings of conventional detection methods, high sensitivity, easy operation, low detection cost, and is suitable for long-distance pipeline detection. There is also the use of a fiber optic sensor to fix the measuring instrument and the object to be measured. When the pipe wall becomes thin or cracks, the internal pressure change of the pipe will cause a change in the surface structure of the pipe, thereby achieving the measurement purpose, and the accuracy of the 15m sensor can be achieved. 1 micro strain. There is also a pipe wall transient electromagnetic (TEM) test that determines the degree of corrosion by detecting the wall thickness of the pipe. Some scholars have developed a microwave detection method, which determines the corrosion of the pipeline by detecting the moisture under the insulation layer of the pipeline. There is also a report on the detection of oil pipelines by metal magnetic memory methods. This technology is fast, efficient and non-excavation, and is suitable for the detection of long-distance pipelines.     2.3 Corrosion and protection of gas pipelines     The main component of natural gas is CH4, and also contains a small amount of C2H6, C4H10, CO2, CO, H2S, etc. In addition, water vapor is accompanied in the process of natural gas transportation. The temperature and pressure of the flowing medium can be reduced to liquefy the water vapor, and CO, H2S forms an acid to corrode the pipe. Electrochemical corrosion is also an important factor in the corrosion of gas pipelines. Pitting can occur in steel and liquid phase environments, and sulfide stress corrosion can also occur in natural gas media containing wet H2S. The gas flow rate, temperature, and pressure also have an effect on the corrosion rate of the pipe.     At present, the technologies used for anticorrosion of gas pipelines include coating technology, electrochemical protection technology and corrosion inhibitor anticorrosion technology. Coating techniques include anti-corrosion coatings, composite coatings, three-layer polyethylene/polypropylene coatings, epoxy powder coatings, and liquid polyurethane coatings. Among them, the three-layer polyethylene has a better effect in preventing corrosion. Since the liquid phase corrosion inhibitor is not in contact with the top of the pipeline, corrosion of the top pipeline of the moisture pipeline has been a problem. Some scholars have proposed to inject a corrosion inhibitor into the foam matrix, and the corrosion inhibitor slowly covers the injection port to form a gas phase flow through the pipeline. In this way, the corrosion inhibitor is evenly covered on the top of the moisture pipeline to achieve the purpose of inhibiting corrosion. At present, the detection methods for external corrosion of gas pipelines include tube-ground potential measurement method and in-tube current measurement method, and internal corrosion detection has leakage flux method and ultrasonic detection method. Some scholars have proposed the detection ball method, the semi-infiltration detection tube method, and the acoustic emission technology method. Wang et al. used pipeline network simulation and mature gas data acquisition and monitoring system (SCADA) to detect corrosion of gas pipelines in gas pipeline detection. For the detection of gas pipelines, Safizadeh et al. adopted a pulsed eddy current technique, which has a good effect on gas pipeline detection. In addition, Li Lianming et al. invented a natural gas pipeline online corrosion monitoring device consisting of production pipelines, valves, split pipelines and coupon devices. The device can conduct on-line corrosion monitoring of natural gas pipelines under various pressures and temperature conditions, and the results are accurate, providing data for pipeline pigging; in the process of detection, the hanging pieces can be lifted without affecting production, and the hanging pieces can be repeated. use. This technology reduces the amount of monitoring construction and saves money, and can be widely used in the field of gas field production.     3 Summary and outlook     (1) The mechanism of H2S generation in urban drainage pipelines has not been explained by relevant theories; the ultrasonic echo signals are not particularly stable when using ultrasonic methods to detect sewage pipelines. (2) Degassing membrane technology has many restrictions in the application of water treatment technology, and its economics remains to be confirmed. (3) In the process of protecting the pipeline by the elastic impactor method, there is no effective lining technology and its rust removal effect needs to be strengthened. Source: China Steel Pipeline Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In recent years, China’s oil and gas transportation methods mainly rely on oil and gas pipeline transportation to transport oil and gas through long-distance pipelines. This method is widely used in China, but this transportation method also contains a safety hazard because Pipes made of steel under the corrosion of oil and gas medium are prone to corrosion. In addition, due to some pressure, temperature and humidity from outside, the corrosion phenomenon is more serious. If oil and gas leaks during transportation, it will cause Severe fires, so it can be seen that it is crucial to strengthen the anti-corrosion and protection measures in oil and gas pipeline transportation. 2 Oil and gas pipeline anti-corrosion measures 2.1 Safety issues of oil and gas pipelines The safety of oil and gas pipelines is of paramount importance. In recent years, many soil pipelines are often affected by water, oxygen, minerals and some microorganisms, which will lead to the aging of pipelines. . In addition to this, there will be some illegal people who want to steal some interests through illegal punching, which leads to more and more cracking and stripping of the pipeline, which intensifies the corrosion of the pipeline. 2.2 Oil and gas pipeline corrosion control problems 2.2.1 Quality control during pipeline construction In the initial stage of pipeline construction, it is very important to strengthen the quality control of pipeline construction. In the pipeline exploration, not only the quality of the soil needs to be detected, but also the direction of the pipeline line, which will be related to the later stage. Corrosion of the pipeline, it is necessary to pay attention to the construction process during construction, because the order of each process will be related to the overall quality of the pipeline, in addition to the construction of the pipeline should be resolutely put an end to Steel pipes for quality problems are put into use. 2.2.2 Pipe section corrosion and control In the corrosion and control of pipelines, in order to better protect the quality of pipelines, people often pay attention to the problem of solder joints at joints. Because the pipelines are underground for a long time, if they can not be treated properly, Long-term will lead to groundwater infiltration, and when groundwater enters the toroidal pipeline, there will be some leakage problems. Since the pipe segments need to be welded at the time of joining, they are often affected by some welding points, thermal stress, etc., so it is very important to strengthen management and attention in this respect. 2.2.3 Research on waste pipe Strengthening the research on waste pipe can help to improve the anti-corrosion efficiency of waste pipe. Under normal circumstances, pipes that have been in the underground environment for a long time often cause leakage due to corrosion. In response to this problem, the author suggests that it can be strengthened. Research on waste pipes to find out the cause of corrosion. Personnel in the relevant departments can provide corrosion information on the corrosion of the pipeline by detecting the corrosion of the inner and outer walls of the pipeline, and then conduct a comprehensive study and investigation on the causes of corrosion. 2.2.4 Regular inspection and verification Regular anti-corrosion testing and verification of oil and gas pipelines is very important. In order to better ensure the normal transportation of pipelines, strict control of corrosion detection and verification should be carried out. In fact, there are many ways to prevent corrosion. People can enhance the corrosion protection of oil and gas pipelines by cathodic protection, adding coatings or injecting some chemicals. 2.3 Main measures for anti-corrosion of oil and gas pipelines 2.3.1 Anti-corrosion of the inner and outer walls of the pipeline Because oil and gas pipelines are underground for a long time, they are often corroded by some media. In the 1950s, people often chose to use asphalt and coal tar pitch as anti-corrosion materials, and in the later period, people gradually began to choose adhesive tape. Or use a thermoplastic coating to achieve the purpose of anti-corrosion of the pipeline. According to relevant statistics, after the anti-corrosion measures are added, the speed of the pipeline can be effectively reduced, and the corrosion of the pipeline can be delayed. 2.3.2 Inner coating During the transportation process of the pipeline, if the inner coating is used for corrosion protection, the corrosion protection of the oil and gas pipeline can be effectively realized, because the corrosion protection of the inner coating can not only effectively isolate some corrosive media, but also can play on the inner wall of the pipeline. It promotes the smoothing effect and reduces some friction on the inner wall of the pipe, which can also reduce the cost. According to the survey results, the anti-corrosion technology of the thermal spray glass used in the inner coating can play a three-fold high temperature, which plays a significant role in promoting the corrosion protection of oil and gas pipelines. 2.3.3 Overcoat The application of anti-corrosion coatings is also extensive. This technology is often used in soil environments. It should be noted that if there are some rocks or high-water potentials involved in oil and gas pipelines, they must be used with caution. Another type of outer coating is the PE coating. This technology is suitable for use in harsh environments where mechanical strength is critical. In the anti-corrosion of the outer coating, it is necessary to screen the selection of the outer coating according to the geological environment. In addition to this, there is a double-layer epoxy powder coating in the outer coating. This outer coating is suitable for a wide range. 2.3.4 Cathodic protection Cathodic protection mainly uses chemical methods to protect the materials in the pipeline from being oxidized. Cathodic protection mainly uses generators or power plants to supply current, so that the materials of some pipelines become less active and thus protect the pipeline. In addition, in order to achieve better protection of the pipeline effect, it should also keep the pipeline at a stable potential, and at the same time, it should be noted that the pipeline should be as close as possible to other unrelated buildings. insulation. This can play a very important role in the corrosion protection of oil and gas pipelines. 2.3.5 Drainage protection The drainage protection is mainly based on whether the pipeline has positive or negative alternating current, and the pipeline material is treated by corresponding drainage. The use of drainage protection needs to pay attention to the positive and negative alternating current in oil and gas pipeline transmission. The tributary drainage is selected. When positive and negative alternating current occurs, the polarity drainage should be selected. When the situation is complicated, it is also necessary to adjust the mandatory drainage. Only by controlling the gains and losses of electrons in the current can the protection of the pipeline be better. 2.3.6 Electrochemical protection Electrochemical protection is very common in today’s oil and gas pipelines. It is very common to use this method for electrochemical corrosion. In domestic long-distance oil and gas pipelines, the use of electrochemical protection can not only effectively sacrifice The cathodic protection method supplemented by the anode can also connect the protection pipe to the negative pole of the power supply to achieve the current protection. 3 Anti-corrosion development trend of oil and gas pipelines In China’s oil and gas pipeline transportation development, more and more people have already taken anti-corrosion measures in oil and gas pipelines as an important task. With the continuous development of society and science and technology, China has developed many high-tech Materials, the good application of these materials to the anti-corrosion of oil and gas pipeline transmission, can lay a more solid foundation for China’s economic development and oil and gas enterprise progress. 4 Conclusion In summary, the author briefly discusses some anti-corrosion and protection in the process of oil and gas pipeline transportation. Through analysis, it can be found that it is very important to strengthen the protection of oil and gas pipelines. The pipelines that protect oil and gas can not only reduce Chinese resources. The waste can also contribute to China’s economic development. Doing a good job in protecting oil and gas pipelines is also laying the foundation for a sustainable development strategy. Source: China Steel Pipeline Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Steel pipes are a very important building material, whether it is transporting fluids and powdered solids, exchanging heat, making mechanical parts and containers, manufacturing building structures, pillars and mechanical supports, or seeing home furniture. Steel pipes of various materials. What are the types of steel pipes? What is the size of the steel pipe? Let’s take a look at the knowledge of enrollment in steel pipes. 1 Introduction of steel pipe Steel pipe is a very important building material in life, and it is favored for its unique product characteristics and aesthetics. Steel pipe is an economical steel. The steel grades and specifications of the products are extremely perse, and the performance requirements are various. Steel pipes can be used as conveying fluids and powdered solids, exchanging thermal energy, manufacturing mechanical parts and containers. The use of steel pipes to manufacture building structure grids, pillars and mechanical supports can reduce weight, save 20-40% of metal, and realize mechanized construction. The use of steel pipes to manufacture highway bridges not only saves steel and simplifies construction, but also greatly reduces the area of the protective coating and saves investment and maintenance costs. 2 Types and uses of steel pipes According to production method It can be pided into seamless steel pipe and seamed steel pipe, and the seamed steel pipe is simply referred to as straight seam steel pipe. Seamless steel pipes can be used in liquid pressure pipes and gas pipes in various industries. Welded pipes can be used for water pipes, gas pipes, heating pipes, electrical pipes, etc. According to the purpose of steel pipe Pipes for pipelines. Such as: water, gas pipe, steam pipe seamless pipe, oil pipeline, oil and gas trunk line pipe. Agricultural irrigation faucets with pipes and sprinkler pipes. Tubes for thermal equipment. Such as general boiler boiling water pipe, superheated steam pipe, locomotive boiler superheat pipe, large pipe, small pipe, arch brick pipe and high temperature and high pressure boiler pipe. Pipes for machinery industry. Such as aviation structural tubes (round tubes, elliptical tubes, flat elliptical tubes), automotive semi-axle tubes, axle tubes, automobile tractor structural tubes, oil cooler tubes for tractors, square and rectangular tubes for agricultural machinery, tubes for transformers, and bearings Tube and so on. Pipes for oil geological drilling. Such as: oil drilling pipe, oil drill pipe (square drill pipe and hexagonal drill pipe), drill pipe, petroleum oil pipe, oil casing and various pipe joints, geological drilling pipe (core pipe, casing, active drill pipe, drilled , by hoop and pin joints, etc.). Tubes for the chemical industry. Such as: petroleum cracking tubes, chemical equipment heat exchangers and pipelines, stainless acid-resistant tubes, high-pressure tubes for fertilizers, and pipes for transporting chemical media. Other departments use the tube. Such as: container tube (high pressure gas cylinder tube and general container tube), instrumentation instrument tube, watch case tube, injection needle and its medical device tube. According to the material of the steel pipe Steel pipes can be pided into: carbon pipes and alloy pipes, stainless steel pipes, etc. according to the pipe material (ie steel type). Carbon pipes can be pided into ordinary carbon steel pipes and high-quality carbon structural pipes. Alloy tubes can be further pided into: low alloy tubes, alloy structure tubes, high alloy tubes, high strength tubes. Bearing tubes, heat-resistant and acid-resistant stainless steel tubes, precision alloys (such as Kovar) tubes, and high-temperature alloy tubes. 3 Specifications of steel pipes Divide 1 inch into 8 equal parts, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8 inches. This is equivalent to the usual one-to-one to seven-point pipe. The smaller size is expressed in 1/16, 1/32, 1/64, and the unit is still inches. If the denominator and the molecule can be pided (eg, the molecules are 2, 4, 8, 16, 32), they should be approximated. The inch is indicated by two cymbals in the upper right corner, such as 1/2″. For example, the water pipe of DN25 (25mm, the same below) is the British 1″ water pipe, and it is also the 8-point water pipe before liberation. The DN15 water pipe is an inch 1/2″ water pipe, and it is also a 4-point water pipe before liberation. For example, the DN20 water pipe is an inch 3/4″ water pipe, and it is also a 6-point water pipe before liberation. First, size: DN15 (4 points), DN20 (6 points), DN25 (1 inch tube), DN32 (1 inch 2 tubes), DN40 (1 inch half tube), DN50 (2 inch tube), DN65 (2 inch) Half pipe), DN80 (3 inch pipe), DN100 (4 inch pipe), DN125 (5 inch pipe), DN150 (6 inch pipe), DN200 (8 inch pipe), DN250 (10 inch pipe), etc. 4 Purchase steel pipe The color is selected to be uniform and uniform, the inner and outer walls are smooth and flat, and there are no bubbles, depressions or impurities, which affect the surface performance defects. It depends on whether the label on the product is complete. The name or trademark of the manufacturer, the date of manufacture, the name of the product, the size of the specification, the implementation of the standard number, etc. on the steel pipe, the product name, the nominal outer diameter, the pipe series S, etc. The handwriting should be clear and the check mark should match the actual. Should buy the same brand of pipe and pipe fittings, because the raw materials of different brands may not be the same, the pipe fittings will have adverse factors, long-term use will cause leakage at the weld. Good steel pipe quality is not high, not broken, so can not judge whether the quality of steel pipe can be broken. Since the impact resistance of the steel pipe is better than that of the real steel pipe, the steel pipe is more likely to be smashed, and the steel pipe is often broken. 5 Maintenance of steel pipes 1. Clean water The clean water is washed with clean water to clean the inner wall of the steel pipe, but the impurities such as calcium and magnesium ionic scales and biological slime adhering to the inner wall of the steel pipe cannot be completely removed, and the effect is not obvious. 2. Syrup cleaning The syrup cleaning is to add chemical reagents to the water, but the chemical composition is corrosive to the steel pipe, and also shortens the life of the steel pipe, which is a practice of simmering and fishing, and is not desirable. 3. Physical cleaning Nowadays, the working principle of this kind of cleaning is basically based on compressed air. The launcher uses a launcher to fire a special projectile larger than the inner diameter of the pipeline to move it along the inner wall of the pipeline at a high speed and fully rub it. Clean the inner wall of the pipe. This method has obvious cleaning effect and basically no harm to the pipeline. It is the most thorough cleaning method to date. Source: China Steel Pipeline Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)