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Stainless steel In layman’s terms, stainless steel is steel that is not easy to rust. In fact, some stainless steels have both rust resistance and acid resistance (corrosion resistance). The rust resistance and corrosion resistance of stainless steel are due to the formation of a chromium-rich oxide film (passivation film) on its surface. This rust resistance and corrosion resistance are relative. Tests have shown that the corrosion resistance of steel in weak media such as the atmosphere and water and oxidizing media such as nitric acid increases with the increase of the chromium water content in the steel. When the chromium content reaches a certain percentage, the corrosion resistance of the steel occurs. Sudden change, that is, from easy to rust to not easy to rust, from not resistant to corrosion. There are many ways to classify stainless steel. According to the organization structure at room temperature, there are martensitic, austenitic, ferritic and duplex stainless steels; according to the main chemical composition, they can be basically pided into two major systems: chromium stainless steel and chromium nickel stainless steel; pided by purpose There are nitric acid-resistant stainless steel, sulfuric acid-resistant stainless steel, seawater-resistant stainless steel, etc. According to the type of corrosion resistance, it can be pided into pitting-resistant stainless steel, stress-corrosion-resistant stainless steel, intergranular corrosion-resistant stainless steel, etc.; according to functional characteristics, it can be pided into none Magnetic stainless steel, free-cutting stainless steel, low temperature stainless steel, high strength stainless steel, etc. Because stainless steel has excellent corrosion resistance, formability, compatibility, and toughness in a wide temperature range, it has been widely used in heavy industry, light industry, daily necessities industry, and architectural decoration industries. . According to ISO / TS / 5510-2003 , EN10088-1 : 1995 , ASTMA959-01 , EN10095-01 and other foreign standards, corrosion resistance is the most important feature and the Cr content is at least 10 . . 5 % or containing C largest one . 2 % of steel is stainless steel. The main technical requirement of heat-resistant steel is that they can bear higher than550 ℃The temperature of the gas and its combustion products are affected. Austenitic steel (Austenitic stainless steel) Stainless steel with austenitic structure at room temperature. When the steel contains about 18% Cr , 8% to 10% Ni , and about 0.1% C , it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni steel and the high Cr-Ni series steel developed by adding Cr and Ni content and adding Mo , Cu , Si , Nb , Ti and other elements on this basis . Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. It is impossible to strengthen it through phase transformation. It can only be strengthened by cold working. Such as adding S , Ca , Se , Te and other elements, it has good machinability. In addition to resistance to oxidizing acid medium corrosion, this type of steel can also be resistant to corrosion by sulfuric acid, phosphoric acid, formic acid, acetic acid, and urea if it contains elements such as Mo and Cu . If the carbon content in this type of steel is less than 0.03% orTi and Ni can significantly improve its resistance to intergranular corrosion. The high-silicon austenitic stainless steel with concentrated nitric acid has good corrosion resistance. As austenitic stainless steel has comprehensive and good comprehensive properties, it has been widely used in various industries. The main alloying elements of austenitic steel are Cr and Ni , which have a face-centered cubic lattice of γ and δ phases, and cannot be magnetized. The stability of austenitic steel can be improved by increasing the austenite forming elements C , Ni , Mn , N and Cu . Austenitic stainless steel has good general corrosion resistance. Any heat treatment process will not harden it. However, due to the increase of N content or cold forming, the mechanical properties of steel can be improved. Austenitic steel has good weldability, high low temperature impact toughness, and high safety to prevent brittleness. Ferritic stainless steel (Ferritic steels) The stainless steel whose structure is mainly ferrite in use. The chromium content is between 11% and 30% , and it has a body-centered cubic crystal structure. This kind of steel generally does not contain nickel, and sometimes contains a small amount of Mo , Ti , Nb and other elements. This kind of steel has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. It is mostly used to make atmospheric resistance. , Water vapor, water and oxidizing acid corroded parts. This type of steel has disadvantages such as poor plasticity, significantly reduced plasticity and corrosion resistance after welding, which limits its application. The application of out-of-furnace refining technology ( AOD or VOD ) can greatly reduce interstitial elements such as carbon and nitrogen, so this type of steel is widely used. Cr is a main alloying elements, does not C binding Cr determine the corrosion resistance of steel elements. Ferritic stainless steel having a C amount is limited to 0.08% or less , heat treatment does not significantly hardening , work hardening can significantly increase the hardness. Ferritic stainless steel is annealed at a temperature below the temperature at which austenite is formed . The annealing temperature depends on the chemical composition, usually the highest is 850 ~950°C. Austenitic ferritic duplex stainless steel (Austenitic ferritic＜duplex＞steels) It is a stainless steel with austenite and ferrite structure each accounting for about half. In the case of low C content , the Cr content is 18% to 28% , and the Ni content is 3% to 10% . Some steels also contain alloying elements such as Mo , Cu , Si , Nb , Ti , and N. This type of steel has the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance, while still maintaining iron Stainless steel475 °CBrittleness, high thermal conductivity, and superplasticity. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel. Typical duplex stainless steel contains high Cr ( 20% to 26% ), no Mo or less than 4% Mo , and low Ni content , which is about medium. It has obvious duplex structure at room temperature, typical metallographic structure It contains 40% to 60% of austenite in the ferrite matrix . They are stronger than austenitic steels. It has exceptionally good stress corrosion resistance, and the addition of N can sufficiently retain the toughness and corrosion resistance that are not annealed after welding . Martensitic stainless steel (Martensitic steels) The stainless steel whose mechanical properties can be adjusted by heat treatment is generally a kind of hardenable stainless steel. Typical grades are Cr13 type, such as 2Cr13 , 3Cr13 , 4Cr13, etc. The hardness is higher after pure fire, and different tempering temperatures have different strength and toughness combinations. It is mainly used for steam turbine blades, tableware, and surgical instruments. According to the difference in chemical composition, martensitic stainless steel can be pided into martensitic chromium steel and martensitic chromium-nickel steel. According to the different structure and strengthening mechanism, it can be pided into martensitic stainless steel, martensitic and semi-austenitic (or semi-martensitic) precipitation hardening stainless steel and maraging stainless steel. The C content of martensitic steel ranges from 0.08% to 1.00%, or even higher. Through martensite transformation after quenching, the strength can be greatly improved, and tempering is usually required. Usually delivered in the normal annealing (ferrite) or quenched + tempered state. Martensitic stainless steel has a body-centered cubic structure and can be magnetized. When containing S amount> 0.15% when cutting steel , it can be used to withstand high-speed mechanical machining , but is not conducive to corrosion. Chromium nickel molybdenum stainless steel Stainless steel with chromium, nickel and molybdenum as the main alloying elements. For example, 00Cr17Ni14Mo2 , 00Cr19Ni13Mo3 , 0Cr18Ni16Mo5, etc. are austenitic stainless steels , and 0Cr26Ni5Mo2 is austenitic-ferritic stainless steel. Cr-Ni-Mo stainless steel, the corrosion resistance to both oxidizing medium , and corrosion resistance to reducing medium; both uniform corrosion , and resistance to localized corrosion. Chromium is the basic element for stainless steel to obtain corrosion resistance. Chromium against general corrosion, pitting and crevice corrosion very favorable, favorable corrosion and stress corrosion resistance against inter-crystalline; and molybdenum against general corrosion Advantageously , very advantageously against pitting and crevice corrosion. The combination of chromium and molybdenum greatly improves the corrosion resistance of stainless steel . Nickel is the most effective element to improve the toughness of stainless steel. Precipitation hardening steels (Precipitation hardening steels) Precipitation hardening steel is also called age hardening steel. Such steel having high corrosion resistance while also having high strength level. Steel high strength of the final because at lower temperatures the heat treatment phase intermetallic compound precipitation results from martensite. Stainless steel grade group 200 Series — Cr – Ni – Manganese Austenitic Stainless Steel 300 series – chromium – nickel austenitic stainless steel Model 301- good ductility, used for forming products. It can also be hardened by mechanical processing. Good weldability. Abrasion resistance and fatigue strength are better than 304 stainless steel. Model 302—The corrosion resistance is the same as that of 304 , and the strength is better due to the relatively high carbon content. Model 303—It is easier to cut than 304 by adding a small amount of sulfur and phosphorus . Model 304– general model; that is 18/8 stainless steel. The old GB grade is 0Cr18Ni9 and the new grade is 06Cr19Ni10 . Model 309- has better temperature resistance than 304 . Model 316 Following 304 after the second of the most widely used of steel, mainly for the food industry and surgical equipment, add molybdenum to obtain a special corrosion-resistant structure. Because it has better resistance to chloride corrosion than 304, it is also used as “”Marine steel ” is used. SS316 is usually used in nuclear fuel recovery devices. 18/10 grade stainless steel is usually also suitable for this application level. Model 321— except for the addition of titanium to reduce the risk of material weld corrosion, other properties are similar to 304 . 400 Series – ferritic and martensitic stainless steel Model 408 good heat resistance, low corrosion resistance, 11% of of Cr , . 8% of of Ni . Model 409— the cheapest model (British and American), usually used as a car exhaust pipe, is a ferritic stainless steel (chrome steel). Model 410— Martensite (high-strength chromium steel), with good wear resistance and poor corrosion resistance. Model 416— Add sulfur to improve the processing performance of the material. Model 420—” cutting tool grade ” martensitic steel, similar to the earliest stainless steel such as Brinell high chromium steel. It is also used for surgical knives, which can be very bright. Model 430 —Ferritic stainless steel, for decoration, such as car accessories. Good formability, but poor temperature resistance and corrosion resistance. Model 440— High-strength cutting tool steel with slightly higher carbon content. After proper heat treatment, higher yield strength can be obtained. The hardness can reach 58HRC , which is among the hardest stainless steels. The most common application example is the ” razor blade ” . There are three commonly used models:440A, 440B ,440C,and also440F(Easy processing type). 500 series – heat – resistant chromium alloy steel. 600 series — Martensitic precipitation hardening stainless steel. Model 630—The most commonly used precipitation hardening stainless steel model, usually called 17-4 ; 17%Cr , 4%Ni . Physical, chemical and mechanical properties of stainless steel The physical properties of stainless steel are mainly expressed in the following aspects: ①. Coefficient of thermal expansion: the change in the quality of the material due to temperature changes. The expansion coefficient is the slope of the expansion-temperature curve, the instantaneous expansion coefficient is the slope at a specific temperature, and the average slope between two specified temperatures is the average thermal expansion coefficient. The expansion coefficient can be expressed by volume or length, usually expressed by length. ②. Density: The density of a substance is the mass per unit volume of the substance, and the unit is kg/m 3 or 1b/in 3. ③. Elastic modulus: When applying a force to the two ends of the edge per unit length can cause a unit change in the length of the object, the force required per unit area is called the modulus of elasticity. The unit is 1b/in 3 or N/m 3. ④. Resistivity: The electrical resistance measured between two opposite faces of a cubic material per unit length, expressed in units of Ω•m , μΩ•cm or ( obsolete) Ω/(circular mil.ft) . ⑤. Permeability: Dimensionless coefficient, indicating the degree to which a substance is easily magnetized, and is the ratio of magnetic induction intensity to magnetic field intensity. ⑥. Melting temperature range: Determine the temperature at which the alloy begins to solidify and when it is solidified. ⑦. Specific heat: The amount of heat required to change the temperature of a unit of material by 1 degree. In the British system and the CGs system, the specific heat values ​​of the two are the same, because the unit of heat ( Biu or cal) depends on the amount of heat required to raise 1 degree per unit mass of water . The value of specific heat in the International System of Units is different from the English or CGS system because the unit of energy ( J ) is defined by a different definition. The unit of specific heat is Btu(1b•0F) And J/ ( kg •k ). ⑧. Thermal conductivity: A measure of the rate at which a substance conducts heat. When a temperature gradient of 1 degree per unit length is established on a unit cross-sectional area material , then the thermal conductivity is defined as the heat conducted per unit time, and the unit of thermal conductivity is Btu/(h•ft•0F) Or w/(m •K). ⑨. Thermal diffusivity: It is a performance that determines the rate of advancement of the internal temperature of a substance. It is the ratio of thermal conductivity to the product of heat and density. The unit of thermal diffusivity is Btu/(h•ft•0F) Or w/(m•k). Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is quenching medium? The medium used for quenching and cooling the workpiece is called quenching cooling medium (or quenching medium). The ideal quenching medium should have the condition that the workpiece can be quenched into martensite without causing too much quenching stress. This requires slow cooling above the “nose” of the C curve to reduce the thermal stress generated by rapid cooling; the cooling rate at the “nose” should be greater than the critical cooling rate to ensure that the undercooled austenite does not undergo non martensitic transformation; under the “nose”, especially when Ms points the temperature, the cooling rate should be as small as possible to reduce the stress of structural transformation. The common quenchants are water, aqueous solution, mineral oil, molten salt, molten alkali, etc. Water Water is a quenching medium with strong cooling capacity. It has a wide range of sources, low price, stable composition and is not easy to deteriorate. The disadvantage is that in the “nose” region of C curve (about 500-600 ℃), water is in the steam film stage, and if it is not cooled fast enough, it will form a “soft point”; in the martensite transformation temperature region (300-100 ℃), water is in boiling stage, and cooling is too fast, which will easily cause martensite transformation speed to be too fast and produce great internal stress, resulting in deformation and even cracking of the workpiece. When the water temperature rises, there are more gases in the water or insoluble impurities (such as oil, soap, mud, etc.) in the water, the cooling capacity will be significantly reduced. Therefore, water is suitable for quenching and cooling of carbon steel workpieces with small section size and simple shape. Saline and alkaline water After the high temperature workpiece is immersed in the cooling medium by adding appropriate amount of salt and alkali in the water, the crystals of salt and alkali precipitate in the steam film stage and burst immediately. The steam film is destroyed and the oxide skin on the surface of the workpiece is also blasted. In this way, the cooling capacity of the medium in the high temperature region can be improved. Its disadvantage is that the medium is corrosive. In general, the concentration of brine is 10% and that of caustic soda solution is 10% ～ 15%. It can be used as quenching medium for carbon steel and low alloy structural steel workpiece. The service temperature should not exceed 60 ℃. After quenching, it should be cleaned and antirust treated in time. Oil Mineral oil (mineral oil) is generally used as cooling medium. Such as oil, transformer oil and diesel oil. Generally, No. 10, No. 20 and No. 30 engine oils are used. The larger the oil number, the higher the viscosity, the higher the flash point, the lower the cooling capacity and the higher the service temperature. At present, there are three kinds of new quenching oil: high speed quenching oil, bright quenching oil and vacuum quenching oil. High speed quenching oil is a kind of quenching oil whose cooling rate is increased in high temperature region. There are two basic ways to obtain high-speed quenching oil. One is to select different types of mineral oil with different viscosity and mix them with appropriate ratio to improve the cooling capacity of high-temperature zone by increasing the characteristic temperature; the other is to add additives to ordinary quenching oil to form powdery ash like plankton in the oil. The additives are barium salt, sodium salt, calcium salt, phosphate, stearate, etc. The production practice shows that the cooling rate of high-speed quenching oil in the unstable region of undercooled austenite is obviously higher than that of ordinary quenching oil, while the cooling rate of high-speed quenching oil in low-temperature martensitic transformation zone is close to that of ordinary quenching oil. In this way, high hardenability and hardenability can be obtained, and deformation is greatly reduced. It is suitable for quenching alloy steel workpieces with complex shapes. Bright quenching oil can keep the bright surface of workpiece after quenching. Bright quenching oils with different cooling rates can be obtained by adding polymer additives with different properties into mineral oil. The main component of these additives is brightener, which is used to suspend aging products insoluble in oil and prevent accumulation and precipitation on the workpiece. In addition, the additives of bright quenching oil also contain antioxidants, surfactants and refrigerants. Vacuum quenching oil is a cooling medium for vacuum heat treatment and quenching. Vacuum quenching oil must have low saturated vapor pressure, high and stable cooling capacity, good brightness and thermal stability, otherwise the effect of vacuum heat treatment will be affected. Salt bath and alkali bath quenchants are generally used in step quenching and isothermal quenching. New quenchant There are polyvinyl alcohol aqueous solution and three nitrate aqueous solution. The co cooling capacity of polyvinyl alcohol (PVA) aqueous solution with mass fraction of 0.1% – 0.3% is between water and oil. When the workpiece is quenched into the solution, a layer of vapor film and a gel film are formed on the surface of the workpiece, and two layers of film are used to cool the heating workpiece. After entering the boiling stage, the film is broken and the workpiece cooling is accelerated. When the temperature reaches low, the PVA gel film is formed again, and the workpiece cooling rate decreases. Therefore, the solution has low cooling capacity in high and low temperature regions, high cooling capacity in the middle temperature zone and good cooling characteristics. The Trinitro nitrate aqueous solution is composed of 25% sodium nitrate + 20% sodium nitrite + 20% potassium nitrate + 35% water. At high temperature (650 ～ 500 ℃), due to the precipitation of salt crystals and the formation of steam film, the cooling capacity is close to that of water. At low temperature (300-200 ℃), because of its high concentration, poor fluidity and cooling capacity close to that of oil, it can replace water oil double medium quenching. Cooling method The most widely used quenching classification in production practice is based on different cooling methods. There are mainly single liquid quenching, double liquid quenching, step quenching and isothermal quenching. Single liquid quenching It is a quenching operation method that the austenitic chemical parts are immersed in a certain kind of quenching medium and cooled to room temperature. Single liquid quenching medium includes water, brine, alkali water, oil and specially prepared quenchant. In general, carbon steel is quenched and alloy steel is quenched with oil. The operation of single liquid quenching is simple, which is conducive to the realization of mechanization and automation. Its disadvantage is that the cooling rate is limited by the cooling characteristics of the medium, which affects the quenching quality. For carbon steel, single liquid quenching is only suitable for the workpiece with simple shape. Double liquid quenching It is to immerse the austenitic chemical parts into a medium with strong cooling capacity, take out the steel parts before reaching the quenching medium temperature, and immediately immerse them in another medium with weak cooling capacity for cooling, such as water before oil, water before air, etc. Double liquid quenching can reduce the tendency of deformation and cracking. The operation is not easy to master, so it has some limitations in application. Martensite step quenching It is a quenching process in which the austenitic chemical parts are immersed in the liquid medium (salt bath or alkali bath) with the temperature slightly higher or lower than the martensitic point of the steel for a proper time. After the inner and outer layers of the steel parts reach the medium temperature, they are taken out for air cooling to obtain the martensitic structure, which is also called graded quenching. The results show that the staged quenching can effectively reduce the phase transformation stress and thermal stress, and reduce the quenching deformation and cracking tendency because the staged temperature stays at the same internal and external temperature of the workpiece. Step quenching is suitable for alloy steel and high alloy steel workpieces with high deformation requirements, and can also be used for carbon steel workpieces with small section size and complex shape. Bainite austempering It is a quenching process, sometimes called austempering, in which steel parts are austenitized and rapidly cooled to the bainite transformation temperature range (260-400 ℃) and kept isothermal to transform austenite into bainite. The general holding time is 30-60min. Compound quenching The workpiece is quenched below MS to obtain 10% – 20% martensite, and then isothermal in the lower bainite temperature region. The results show that the M + B structure can be obtained by this cooling method. The martensite formed during pre quenching can promote bainite transformation and temper martensite at isothermal temperature. Compound quenching can avoid the first kind of temper brittleness and reduce the residual austenite volume, that is, the tendency of deformation and cracking. Special parts are also compressed air quenching, spray quenching and jet quenching. Source: China Pipe Fitting Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com) (wilsonpipeline Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. wilsonpipeline products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.) If you want to have more information about the article or you want to share your opinion with us, contact us at sales@wilsonpipeline.com

In the depth of Tarim Basin in Xinjiang, natural gas is transported to all parts of the country through gas transmission pipeline after being exploited and refined. However, due to the corrosion of the pipeline, gas leakage has been repeated. A new gas pipeline made of 2205 duplex stainless steel containing molybdenum is expected to reduce gas leakage and prevent environmental disasters while protecting resources. 4500 tons is the largest single order of duplex stainless steel in China so far. What is natural gas? Natural gas refers to all natural gases existing in nature, including gas formed by various natural processes in the atmosphere, hydrosphere and lithosphere (including oilfield gas, gas field gas, mud volcanic gas, coal bed methane and biogenic gas, etc.). The definition of “natural gas” is a narrow definition from the perspective of energy, which refers to the mixture of hydrocarbon and non hydrocarbon gas naturally contained in the formation. In petroleum geology, it usually refers to oil field gas and gas field gas. It is mainly composed of hydrocarbons and contains non hydrocarbon gases. Some of the earliest uses of natural gas can be traced back to 500 BC, when the Chinese used hollow bamboo stems to send natural gas into stoves and boil seawater to make salt. Today, China is trying to reduce carbon emissions and get rid of its dependence on coal, so China’s natural gas industry continues to develop. Tarim Basin is one of the largest natural gas reserves in China, and its underground reserves are estimated to be more than 200 trillion cubic feet. Natural gas production in the vast Gobi Tarim Basin is located in the most western provinces of China, sparsely populated. In the vast Gobi and the desolate desert, the production and transportation of natural gas is a great feat. Due to the strong wind, the sand is all over the sky, there is no road, and the poor working conditions make drilling, especially the laying and construction of pipelines extremely difficult, time-consuming and expensive. Natural gas is transported from oil and gas wells to nearby refineries for processing. The balance between natural gas input and refinery capacity is essential to maximize production efficiency. As a result, construction of a new pipeline connecting the two refineries has started. Upon completion, the refinery will be able to direct the inflow of natural gas to optimize capacity utilization. Finally, the refined natural gas from Tarim Basin enters the west east gas pipeline and is transported to all parts of the country for use. The new pipeline is located in the orange area of Tarim Basin, Xinjiang, China Prevent gas leakage The environmental conditions in Tarim Basin bring many challenges to pipeline operation. The vast desert of Taklimakan has a dry climate. It is hot in summer and cold in winter. Strong wind often forms huge sandstorm, which makes working conditions extremely bad. The soil in this area is highly corrosive and contains a large amount of soluble salt, which is left after evaporation of water all year round. In addition, the carbon dioxide content in natural gas is very high, and it contains up to 10% chloride, which also increases its corrosivity. Under such conditions, only materials with high corrosion resistance can provide a permanent solution. The pipeline for transporting high corrosive crude natural gas is usually composite steel pipe, that is, carbon steel pipe is lined with 316 stainless steel thin layer. This kind of pipeline can resist the corrosion of corrosive gas and the initial cost is cheaper than the whole stainless steel pipeline. However, it is much more difficult to weld the composite steel pipe on site than in the factory controlled environment. The stainless steel weld in the inner layer will be diluted by carbon steel, which will reduce its corrosion resistance. It has been found that one of the reasons for frequent leakage of natural gas in Tarim Basin is weld corrosion of composite pipeline. The consequences of natural gas leakage are environmental damage, loss of revenue, and the worst case is explosion, so the leakage must be repaired as soon as possible. However, in this remote desert, finding and repairing the leak is a difficult, time-consuming and even dangerous task. Therefore, the natural gas company for the new pipeline to seek a more durable pipeline material, the first time to prevent the occurrence of leakage. The pipeline is located in the remote desert area in the West Molybdenum improves the performance of the pipeline The new pipeline connecting the two refineries is 3.3 km long, 325 mm in diameter and 406 mm in diameter, with wall thickness ranging from 7 to 17 mm. In order to avoid corrosion completely, engineers chose to use stainless steel as a whole instead of coating or carbon steel clad pipe. The results of literature study and test show that 2205 duplex stainless steel can resist the corrosion of natural gas. Compared with 316 stainless steel, duplex stainless steel with 3% molybdenum content has better pitting and crevice corrosion resistance. In order to test whether 2205 duplex stainless steel pipeline has enough corrosion resistance to salt desert, a three-year corrosion study was carried out. The test samples buried in sand are inspected every year and the results are satisfactory. In addition to its excellent corrosion resistance, duplex stainless steel also has other advantages: its excellent strength can make the pipe wall thinner, reduce the weight of the pipeline, so as to facilitate transportation, handling and installation, which is an important consideration under the extreme climate conditions in Tarim Basin. The thinner wall thickness also reduces the time and cost of welding and avoids the complex problems related to the composite pipe. These advantages mean longer service life and maintenance free, helping to protect the environment and employee safety. Although the initial cost is slightly higher than the clad pipe, the duplex stainless steel solution has a significant impact on reducing the overall cost of natural gas production. 2205 duplex stainless steel piping waiting to be installed on site Durable solutions Life cycle costing (LLC) is becoming more and more popular. Material selection is based not only on the initial installation cost, but also on the cumulative cost of future maintenance and operation. Over time, duplex stainless steel pipelines can recover costs by avoiding natural gas loss and eliminating maintenance and replacement costs. The “pipeline dragon” in Xinjiang not only optimizes the natural gas production in the western region, but also becomes a pioneer in realizing sustainable energy utilization. Investment in the construction of 2205 duplex stainless steel pipeline marks the shift from low cost to more sustainable and lasting solutions. Source: China Duplex Stainless Steel Gas Pipeline Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Due to its corrosion resistance, stainless steel pipe is widely used in pipelines of various oil routes, and the corrosion phenomenon of stainless steel pipe is analyzed. From the selection of pipes and piping connection form, this paper puts forward the stainless steel pipe in the machining process, key points of construction technology and the pipeline corrosion protection are discussed, in order to offer a reference for technical personnel. With the rapid development of petroleum, chemical, pharmaceutical and papermaking industries, more and more chemical substances are transported by storage tanks and pipelines made of stainless steel. There are many kinds of stainless steel pipe materials, such as 304, 304L, 316L, 317, 317L, 2507 and 2205 and ferritic stainless steel, etc. due to the good corrosion resistance and processing performance of stainless steel, it is very suitable for the production of chemical pipeline. The following on the chemical transportation of stainless steel pipe processing technology and precautions to make some discussion. Corrosion resistance and common corrosion phenomena of stainless steel pipe The corrosion resistance of stainless steel is mainly due to a layer of oxide film called passive film, which is the cathode for the base metal. When damaged, the adjacent metal (in saline water) is used as sacrificial anode. The passivation of the passivation film depends on the chemical and metallurgical composition of the base metal. For example, the content of molybdenum (MO) is of great significance to the passivation film. The common corrosion phenomena of stainless steel chemical pipeline are as follows: ① Pitting corrosion: pitting corrosion is caused by the local destruction of the passive film. It is usually caused by the presence of small external particles on the steel surface, such as welding slag and dust. It will cause holes in the metal, which can be small enough to be difficult to distinguish by the naked eye. ② Crevice corrosion: it is due to the existence of gaps in the structure, such as the root of welded joint, the lower end of gasket and screw, and the internal part of threaded joint. When all solutions are retained in these places, local corrosion will be formed quickly. ③ Stress corrosion: it occurs on materials which are often subjected to high tensile stress and are in special corrosion medium. Increasing nickel content in stainless steel can reduce the occurrence of stress corrosion cracking. ④ Intergranular corrosion: when some stainless steels are heated to 450 ° C ~ 850 ° C, the deposition of chromium carbide and the reduction of chromium in the vicinity of crystal interface (i.e. the chromium is reduced to less than 12%), the corrosivity of this area will be weakened, which is a serious corrosion of grain boundaries. ⑤ Galvanic corrosion: corrosion that occurs when stainless steel is in contact with another alloy in an electric solution, resulting in a potential difference. The above-mentioned corrosion phenomena are usually caused by improper maintenance or use. For example, there is a high chloride content in the pipeline which becomes the most corrosive stagnant solution. If the weld of the pipe is not completely cleaned, high-temperature oxides will be produced on both sides of the root of the weld. Selection of material and connection form of pipe joint The selection of stainless steel pipe, flange, positioning elbow, tee, saddle foot and gasket should consider the chemical composition and element content of the material. In addition, the connection forms of stainless steel pipe are generally pided into butt welding and flange connection. Among them, flange connection is pided into ordinary flat flange connection and high foot flange connection. Generally speaking, the appearance of butt welding is more beautiful, reducing the flange joint, reducing the possibility of leakage, but it increases the difficulty for the processing side. Treatment of pipe butt welding The welding requirements of pipe butt welding are high, and each joint should be inspected by film. In order to reduce the oxidation corrosion in the pipe during butt welding, argon is needed to be filled for protection. If the gas is filled in the actual system, the consumption of argon is very large. In addition, in the process of construction, the passivation treatment of the pipe welded on site is relatively easy to be carried out on the external surface, while the internal part of the pipe is not so easy. A series of problems, such as passivation treatment tools and containers, large amount of waste liquid treatment and flushing water discharge, need to invest a lot of manpower and material resources, and the effect is not very ideal. Features of flange connection If it can be changed to flange connection, the situation will be very different. Although the use of flanges increases production costs, it also increases the possibility of leakage. However, compared with the passivation process of integral piping system, the passivation of flange connection is simple and the quality is guaranteed. The passivation treatment of flange connection only needs to apply passivation paste on the inner and outer surface of flange welding position. The process is simple and reliable, and the whole pipe system need not be treated in the later stage, only local passivation is needed. In the flange connection, the common flat flange and the high foot flange can meet the requirements of the pipeline design specification. The advantages of the ordinary flat flange connection are that the price of the flange is much cheaper than that of the high foot flange. The disadvantages are as follows: due to the different welding forms of flange, it is easy to form chemical effusion at the joint after connection, resulting in corrosion at the pipe joint. The advantage of high foot flange connection is that there is no liquid accumulation after connection, which eliminates the shortcomings of flat flange connection. However, the price of high foot flange is higher, which increases the production cost, which is its deficiency. Key points of stainless steel pipe processing Blanking and chamfering of stainless steel pipe Special cutting and chamfering machine should be used for cutting stainless steel pipe, and plasma flame cutting should not be used as far as possible. Carbon steel material should not be used in clamping support and shelf making during blanking, and stainless steel material should be used as shelf. It is better to wrap the claw of chamfering machine with a thickness of about 1.5mm. The blade of chamfering machine should be made of high-speed tool steel. Calibration, bending and welding of stainless steel pipe The calibration of stainless steel pipe shall be carried out on the calibration platform made of special stainless steel plate in the designated stainless steel processing area. It must be emphasized that the stainless steel should avoid contact with carbon steel in the whole production process, mainly to prevent the iron element in iron powder from polluting the stainless steel and causing crystalline corrosion. If it is inevitable to contact with carbon steel in production, it must be treated by strict passivation process. Bending of stainless steel pipe Stainless steel pipe manufacturing should avoid bending process as far as possible, because of the friction between the plug core of the pipe bender and the inner wall of the pipe during the bending process, the method to eliminate the pollution is to send the polluted pipe to the factory with professional passivation treatment for processing, which is neither economical nor convenient. The commonly used method in construction is to use fixed bend to make bend. In this way, the internal part of the pipe spliced after filling with argon gas will not oxidize basically. It only needs to use passivation paste on the external surface, and the workers can carry out passivation treatment by themselves to meet the quality requirements. Welding of stainless steel pipe To discuss the welding problem of stainless steel pipe, two problems need to be solved: one is to ensure its welding strength, which is one of the key technologies for local strength of pipeline or piping system; the other is to ensure the corrosion resistance of welding area and adjacent base metal area. Generally speaking, the common welding method can refer to stainless steel welding process. However, different welding materials and welding process parameters should be selected according to different base metal. At the same time, attention should be paid to prevent the arc from hitting the external area of the weld; controlling the heat input and interlayer temperature to prevent overheating; preventing the weld and base metal from being excessively oxidized by shielding gas. Argon arc welding is used for welding flange and pipe, and groove single side welding and double side forming process are adopted. After welding, the welding seam shall be photographed and inspected by dye flaw detection. After passing the inspection, it shall be transferred to the next process for passivation treatment. Connection of pipes and valves The piping system is usually connected with butterfly valve. The butterfly valve is compact in structure, and its strength is not very high. Pay attention to the flatness and distance between the flanges during pipe calibration. Otherwise, the stress after installation is too large, coupled with the factors such as vibration during operation, it is easy to break the butterfly valve. Especially in the local repair of butterfly valve or pipe, if the pipe is too rigid and difficult to disassemble, the scope of pipeline disassembly and assembly should be expanded to avoid forced disassembly and hard installation in local area. In the process of field welding, the butt welding of pipe should be avoided, and welding flange should be used instead to connect the pipe and pipe. The advantages of this process are as follows: first, it can avoid passivation treatment inside the pipe due to butt welding; second, it can carry out reliable passivation treatment on the inside and outside surface of the pipe by using flange connection. In the construction process of stainless steel pipe, the fastening of horse foot can be carried out with ordinary spanner, but the wrench can not directly contact with the pipe hard collision, so as to avoid the scratch phenomenon. Surface treatment of stainless steel pipe Every welding seam in stainless steel pipe must be passivated. Generally, if the pipes processed in the field cannot be passivated by themselves, they shall be sent to professional manufacturers for passivation treatment. If the surface can be passivated by itself, stainless steel pickling passivation paste can be purchased for treatment. The use method of passivation paste: the passivation paste shall be evenly applied on all welding seams and grinding points with paint brush, and the surface of all processed parts shall be applied. After 24 hours, rinse with water (please operate according to the manual of passivation paste). Requirements for processing area of stainless steel pipe It is necessary to follow the principle that stainless steel pipes are free from contamination during storage and processing. Therefore, the following protective measures should be taken to minimize the possibility of the passive film being damaged due to contamination. When transporting stainless steel pipes, the covered lifting tools should be used. The iron rope and chuck can not directly contact the stainless steel surface, so the electromagnetic crane should not be used. The hanging basket must be tightly covered with a flat rubber of more than 3 mm. The fixing of the hanging basket and rubber shall be firmly bound with nylon tie used by electrician, and iron wire shall not be used for binding. During site installation, it should be taken from the special basket as far as possible, and can not be placed on the site at will. If it is necessary to place it on the site, non-metallic isolation materials shall be laid on the surface of the site. Stainless steel pipes shall be stored in a separate isolation area, and shall not be mixed with carbon steel materials; the fabricated parts of stainless steel pipes shall also have a separate process storage area, and shall be far away from sandblasting parts and other carbon steel parts. When stainless steel pipes and fabricated parts are stored on steel shelves, the shelves shall be protected with wood. The small dirt on the surface should be cleaned up in time to maintain a clean and dry environment. Discussion on surface treatment of stainless steel pipe In order to maintain the corrosion resistance of stainless steel pipe, the surface of stainless steel pipe shall be cleaned and maintained, and the surface shall be pickled. This method is very necessary to remove the residual high temperature nitride and restore the corrosion resistance of stainless steel, and the effect is good. Before pickling, all oil stains, dirt, etc. shall be cleaned with appropriate solvent or alkaline solution, and the residue shall be washed with clean water after pickling. The other is sand blasting, which is used to remove high temperature oxides and pollutants from the surface of stainless steel. However, the sand must be clean silica sand without iron and rust particles. It should be clean new sand. Once sprayed, it can not be used for the second time. According to the introduction of relevant construction units, the stainless steel pipes were treated with oxalic acid in series washing and passivation process. After a period of time, the pipes were corroded, but the practice proved that this method was not good, and some parts were even rotten. After inspection, the main reason is that passivation can not be carried out after welding inside the pipe. Therefore, instead of pickling process, high foot flange connection was used to eliminate the defect that the inner part of the pipe could not be passivated. Therefore, it is suggested to adopt passivation series washing during construction, select stainless steel pump with flow rate of 3-5m3 per hour, mix the solution with nitric acid and hydrofluoric acid, and heat it to about 40°C; for 20-30 minutes of serial washing, the solution configuration shall be tested with test block. Conclusion To strengthen the quality monitoring of the whole process of stainless steel welded pipe processing, to achieve traceability of the quality of the processed pipe, it is necessary to monitor the construction of each process, inspect and track the name of the processor and the processing content. The specific method is as follows: make two cards of software and hardware, and record the operator, inspector, quality condition and date of each process synchronously. The contents of the project include: pipe coding, marking, cutting, chamfering, grinding, bending, pipe calibration, welding, filming, in-situ pump pressure, passivation treatment (field and field), test and acceptance. As a process flow sheet, the soft card shall be kept on completion, and the hard card shall be tied on the stainless steel pipe with copper wire or nylon rope until delivery. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.steeljrv.com) (wilsonpipeline Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. wilsonpipeline products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.) If you want to have more information about the article or you want to share your opinion with us, contact us at sales@wilsonpipeline.com

The environment of offshore oil and gas platform represents some of the most severe environmental conditions for its construction materials. Offshore platforms must be able to operate safely for decades under the impact of extreme weather and big waves. The most challenging sites are the Arctic Ocean and its surrounding waters, where frequent storms further aggravate the extreme corrosivity of the environment. Under such harsh conditions, the service life of molybdenum alloy materials, especially duplex stainless steel and super duplex stainless steel, is longer than that of any other materials. A small and critical component is the super duplex stainless steel bolt. What is an offshore platform? Offshore platforms are used to extract and process the oil and gas resources on the seafloor. They are equivalent to an offshore chemical plant. The offshore platform is equipped with a complete set of self-sufficient equipment including power generation, seawater desalination, living facilities, etc., and the volume of all equipment should be compressed as much as possible, occupying the smallest space. In order to reduce the size of supporting and anchoring devices, the weight of the platform should be minimized. In addition to oil and gas production and processing equipment, several miles of pipelines are needed on the platform to transport oil and gas. The pipeline is connected by flange, which needs a lot of bolts. In the past, the bolts of hot-dip galvanized steel were used. Material selection of oil platform Statoil, the Norwegian oil company, is developing the Johan Sverdrup field on the Norwegian continental shelf. It is one of the largest oil fields discovered in this area in recent years. By 2022, the second phase project will be fully completed, and the oilfield will become the largest oil production base in the North Sea. The expected life of the oilfield is 50 years. The longer life expectancy and the requirement of light and compact platform set a high standard for the selection of platform components, equipment and pipelines. Johan sverdroub oil platform starts production in 2019 © Statoil The company’s experience in other oil fields in the North Sea shows that the corrosion of traditional bolts is very serious and the service life of hot-dip galvanized steel fasteners is limited. The service life of galvanized protective coating is generally 8-10 years. Beyond this time, the steel fastener itself will be corroded. Therefore, the total life of these fasteners in marine environment is only 15 years. Only intact fasteners can ensure the safe and reliable operation of large and complex pipeline system of offshore platform, and ensure the safety of marine environment. The importance of fasteners is beyond doubt. In the harsh marine environment, the corrosion of hot-dip galvanized bolts on the platform is serious © Statoil Due to the extreme importance of fasteners and the extension of the effective life of old offshore platforms with technological progress and the improvement of oil production level, thousands of fasteners have to be replaced when they reach their service life. The replacement task is very heavy, the investment is huge and affects the normal operation of the platform. In order to avoid similar problems in the future, Statoil replaced all the hot-dip galvanized bolts on the old platform with super duplex stainless steel bolts. The design life of the Johan Sverdrup project is 50 years and duplex stainless steel was designated from the beginning. The economical duplex stainless steel is used for various structural components such as cable tray, pipe support device and other secondary components in non high temperature environment. Its advantages are long life, less maintenance and light weight. Lightweight is the key to control the construction cost of the platform. The heavier the upper platform is, the higher the requirements for the lifting capacity of the crane ship are, so the construction cost of the platform is greatly increased. On the contrary, by reducing the upper weight, the lower supporting structure can be smaller and lighter, and the construction cost will also be reduced. Jacket installation of Johan Sverdrup platform © Jan Arne Wold/Statoil Standard 2205 duplex stainless steel is used for condensing pipe and oil and gas pipe, and super duplex alloy is used for caisson, sea water pipeline and umbilical pipe. This project uses a variety of duplex stainless steel pipes with diameters ranging from 50 mm to 500 mm. The diameter of super duplex steel fastener for flange joint is 12-36mm. Super duplex steel bolts and nuts of different specifications © Bumax Super duplex stainless steel Super dual phase alloy has high strength and good corrosion resistance to various forms of corrosion. The excellent corrosion resistance of super duplex stainless steel is due to its 3.5% molybdenum. Therefore, super duplex stainless steel is suitable for processing liquid and acid chemicals with high chloride content in seawater environment. They are increasingly used in oil and gas, seawater desalination, power generation, marine engineering and other corrosive environments. The yield strength of duplex stainless steel and super duplex stainless steel is twice as much as that of solution annealed austenitic stainless steel 304 or 316, which is higher than that of 304 and 316 commonly used on offshore platforms after work hardening treatment. And they have good ductility and toughness at – 80 ℃, so they are important materials for Arctic Ocean or Arctic polar application. Beyond oil field to the future In addition to oil and gas fields, super duplex stainless steel fasteners have recently been used in energy projects such as offshore wind power generation. The greater Gabbard wind farm in the North Sea, 23 km from the coast of England, has 140 offshore wind turbines using UNS s32760 super duplex stainless steel fasteners. The Hummer gateway wind farm, also located in the North Sea, uses more than 50000 super duplex stainless steel bolts to secure turbine components. The problems encountered in the operation of offshore wind farms are the same as those of offshore oil fields: corrosive marine environment requires high strength alloy to reduce weight, maximize efficiency and prevent environmental disasters. Super duplex steel bolts are also used in offshore wind turbines © West Special Fasteners Marine technology is constantly developing to meet the world’s energy needs in a more efficient, safer and more environmentally friendly way. At the same time, various types of duplex stainless steel have become more and more important factors in design decision. Duplex stainless steel has excellent corrosion resistance, high strength, good ductility and toughness. Therefore, they have a long service life and require little maintenance. They can realize lightweight and cost-effective design. From the perspective of investment return, they can not only recover higher initial investment, but also obtain excess return. The duplex stainless steel contains molybdenum. Molybdenum element endows the material with unique properties, which makes these high-end stainless steel materials widely favored. Source: China DSS Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The high temperature valve has good quenching property and can be deeply quenched instead of the surface quenching of anti saw lock on the market. In general information, the valve with working temperature T > 450 ℃ is called high temperature valve. However, there is no unified standard for the classification of high temperature grade of high temperature valves. High temperature working conditions mainly include sub high temperature, high temperature grade I, high temperature grade II, high temperature grade III, high temperature grade IV and high temperature grade V, which are respectively introduced below. Sub high temperature Sub high temperature refers to the valve working temperature in the 325 ~ 425 ℃ region. If the medium is water and steam, WCB, WCC, A105, wc6 and wc9 are mainly used. If the medium is sulfur-containing oil, C5, CF8, CF3, CF8M and cf3m are mainly used. At this time, the valves made of CF8, CF8M, CF3 and cf3m are not used to resist the corrosion of acid solution, but are used in sour oil products and oil and gas pipelines. In this condition, the upper limit of the maximum operating temperature of CF8, CF8M, CF3 and cf3m is 450 ℃. High temperature grade I When the working temperature of the valve is 425 ~ 550 ℃, it is high temperature class I (referred to as PI). The main material of PI valve is CF8 in astma351 standard, which is “high temperature grade I medium carbon chromium nickel rare earth titanium high quality heat resistant steel”. Because PI grade is a specific name, the concept of high temperature stainless steel (P) is included here. Therefore, if the working medium is water or steam, high temperature steel wc6 (t ≤ 540 ℃) or wc9 (t ≤ 570 ℃) can also be used, while high temperature steel C5 (zg1cr5mo) can also be used for sour oil, but they can not be called PI grade here. High temperature grade II The working temperature of the valve is 550 ~ 650 ℃, which is designated as high temperature class II (referred to as P Ⅱ). Grade II high temperature valve is mainly used in heavy oil catalytic cracking unit of refinery. It includes high temperature lining wear-resistant gate valve used in three swirl nozzle and other parts. The main material of P Ⅱ valve is CF8 in astma351 standard, which is “high temperature grade II medium carbon chromium nickel rare earth titanium tantalum strengthened heat resistant steel”. High temperature grade III The working temperature of the valve is 650 ～ 730 ℃, which is designated as high temperature class III (referred to as P Ⅲ). The P Ⅲ high temperature valve is mainly used in heavy oil catalytic cracking unit of refinery. The main material of P Ⅲ high temperature valve is CF8M in astma351 standard, which is “high temperature grade III medium carbon chromium nickel molybdenum rare earth titanium tantalum strengthened heat resistant steel”. High temperature grade IV The operating temperature of the valve is 730 ~ 816 ℃, which is designated as high temperature grade IV (referred to as P Ⅳ). The upper limit of operating temperature for class P IV valves is set at 816 ℃ because the maximum temperature provided in the standard asmeb16134 pressure temperature class selected for valve design is 816 ℃ (1500 V). In addition, when the working temperature exceeds 816 ℃, the steel is close to entering the forging temperature region. At this time, the metal is in the plastic deformation range, and the metal has good plasticity, and it is difficult to bear high working pressure and impact force without deformation. The main material of P IV valve is CF8M in astma351 standard, which is “high temperature grade IV medium carbon chromium nickel molybdenum rare earth titanium tantalum strengthened heat resistant steel”. F310 (C content ≥ 01050%) and f310h in CK-20 and astma182 standards. High temperature grade V If the working temperature of the valve is higher than 816 ℃, it is referred to as p-v. the P-V high-temperature valve (used as cut-off valve instead of regulating butterfly valve) must adopt special design means, such as lining insulation lining or water or air cooling, etc., to ensure the normal operation of the valve. Therefore, there is no stipulation on the upper limit of the operating temperature of the p V class high temperature valve. This is because the control of the working temperature of the valve is not only based on the material, but also solved by special design means, and the basic principle of the design means is the same. According to the working medium, working pressure and special design method, the reasonable material which can meet the valve can be selected. In P V class high temperature valve, the insert plate or butterfly plate of flue gate valve or butterfly valve is usually made of hk-30 and HK-40 superalloys in astma297 standard. They can resist corrosion in oxidation resistance and reducing gas below 1150 ℃, but can not bear impact and high pressure load. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Classification and grades of nickel-based alloys (seven types): Industrial pure nickel (P41): 99.5% nickel. Such as Ni200, Ni201. Ni-Cu alloy (P42): such as: Monel 400 (Ni66Cu32) and so on. Ni-Cr alloy (P43): such as: 0Cr30Ni70, corronel230 (Cr35Ni65), inconel671 (Cr50Ni50). Ni-Cr-Fe alloy (P43): such as: inconel600 (Cr76Ni15Fe8), inconel625 (Cr61Ni21Mo9Fe3). Ni-Mo alloy (P44): such as: hastelloy A (Ni60Mo19Fe20), hastelloy B (0Ni65Cr28Fe5V), hastelloy B-2 (00Ni70Mo28). Ni-Cr-Mo alloy (P44): such as: hastelloy C (Ni60Cr16Mo16W4),  hastelloy C-276 (000Ni60Cr16Mo16W4), hastelloy C-4 (000Ni60Cr16Mo16Ti). Ni-Fe-Cr alloy (P45): such as: incoloy 800 (Ni32Fe46Cr21), incoloy 825 (Ni42Fe30Cr21). Welding characteristics of nickel-based alloys: The welding of nickel-based alloys has similar problems to the welding of austenitic stainless steels: (1) Welding hot cracks. (2) Porosity: Compared with low carbon steel and low alloy steel, porosity tends to be greater, especially for dirty grooves and welding wires. (3) Corrosion resistance: Most nickel-based corrosion-resistant alloys have little effect on corrosion resistance after welding. However, for some alloys of Ni-Cr, Ni-Mo, and Ni-Cr-Mo series, chromium depletion occurs near the heat-affected zone, resulting in intergranular corrosion and stress corrosion performance in some media. (4) Process characteristics: poor fluidity of liquid weld metal; shallow weld metal penetration. Key points of the welding process: (1) Correct selection of welding materials. (2) Joint type: a joint type with a large bevel angle and a small pure edge. (3) Cleaning near the groove and welding wire: the characteristics are important to prevent thermal cracks and pores. (4) Preheating before welding: generally, preheating before welding is not required, and the temperature between layers should be controlled below 100 ℃. But when the temperature of the base material is lower than 15℃, it should be heated to 15-20℃ to avoid moisture condensation. (5) Welding process: Limit the heat input, adopt a small amount of wire and keep the arc voltage stable, and adopt the operation method of short arc without swing or small swing. For the small diameter pipeline welding process, forced cooling measures should be taken to reduce the high temperature residence time of the weld and increase the cooling rate of the weld. Timely cleaning of slag and spatter on the surface of the weld after welding to prevent S and other impurities in the slag from embrittlement or deterioration of the weld. (6) Post-weld heat treatment: Generally, post-weld heat treatment is not recommended. But sometimes heat treatment is required to ensure that no intergranular corrosion or stress corrosion occurs during use. Classification and model of welding rod: GB/T13814-92 “Nickel and Nickel Alloy Electrodes” standard is equivalent to American ANSI/AWS A5.11-89 “Nickel and Nickel Alloy Covered Electrodes”: Industrial pure nickel electrode: ENi-0, ENi-1; Ni-Cu series electrode: ENiCu-7; Ni-Cr-Fe series electrodes: ENiCrFe-0 to ENiCrFe-4; Ni-Mo series electrodes: ENiMo-1, ENiMo-3, ENiMo-7; Ni-Cr-Mo series electrodes: ENiCrMo-0 to ENiCrMo-9; Coating type: titanium calcium type (03), alkaline (15, 16). Classification and model of welding wire: According to GB/T15620-1995 “Nickel and Nickel Alloy Welding Wire”: Industrial pure nickel welding wire: Ni-Cu series welding wire: ERNiCu-7; Ni-Cr series welding wire: ERNiCr-3; Ni-Cr-Fe series welding wire: ERNiCrFe-5, ERNiCrFe-6; Ni-Fe-Cr series welding wire: ERNiFeCr-1, ERNiFeCr-2; Ni-Mo series welding wire: ERNiMo-1, ERNiMo-2, ERNiMo-3, ERNiMo-7; Ni-Cr-Mo series welding wire: ERNiCrMo-1 to ERNiCrMo-4, ERNiCrMo-7 to ERNiCrMo-9. Selection principle of nickel-based alloy welding materials: (1) Selection of welding materials when welding the same nickel material: The same welding materials as the base metal alloy series should be selected; If there is no requirement for corrosion resistance, welding materials different from the base metal alloy system can also be used, but the joints should be guaranteed to have the performance required by the design. For example: Monel 400: welding rod ENiCu-7; welding wire ERNiCu-7; Inconel600: welding rod ENiCrFe-1; welding wire ERNiCrFe-5; Incoloy 800H: welding rod ENiCrFe-2; welding wire ERNiCr-3; Hastelloy C-276: welding rod ENiCrMo-4; welding wire ERNiCrMo-4. (2) The following factors should be considered for the welding of dissimilar nickel materials and between nickel materials and austenitic stainless steel: The strength of the weld (including high temperature durability) and the corrosion resistance meet the design; Use welding materials with a coefficient of linear expansion similar to that of the base metal. Consider the sensitivity of welding materials to welding cracks and pores. For example: Austenitic stainless steel and Monel 400 welding: welding rod ENiCu-7; welding wire ERNiCu-7. Monel 400 and Inconel600 welding: welding rod ENiCrFe-3; welding wire ERNiCr-3. Incoloy 800H and Hastelloy C-276 welding: welding rod ENiMo-3; welding wire ERNiMo-3. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is Q235? Q235 steel is a kind of carbon structural steel. It is equivalent to A3 and C3 steel in the old standard gb700-79, and the Russian toct brand is used. Q in the steel grade represents the yield strength. In general, the steel is directly used without heat treatment. Q235 ordinary carbon structural steel is also called A3 steel. Ordinary carbon structural steel plate is a kind of steel material. Q represents the yield limit of this material, and the following 235 refers to the yield value of this material, which is about 235mpa. The yield value decreases with the increase of the thickness of the material. Due to the moderate carbon content, good comprehensive properties, good combination of strength, plasticity and welding properties, it is widely used. The yield strength decreases with the increase of the thickness of the material (the yield strength is 235mpa when the plate thickness / diameter is ≤ 16mm; 225MPa is the yield strength when the thickness is 16mm < plate thickness / diameter ≤ 40mm; 215mpa is the yield strength when 40mm < plate thickness / diameter ≤ 60mm; 205mpa is the yield strength when 60mm < plate thickness / diameter ≤ 100mm; 195mpa when the plate thickness / diameter is ≤ 150mm; 195mpa when the thickness / diameter is less than 150mm; and ≤ 200mm when the thickness / diameter is less than 150mm The yield strength is 185mpa). Due to its low carbon content, good comprehensive properties, good combination of strength, plasticity and welding properties, it is widely used. It is composed of Q + number + quality grade symbol + deoxidation method symbol. Its steel grade is prefixed with “Q” to represent the yield point of the steel, and the subsequent number represents the yield point value in MPa. For example, Q235 represents the carbon structural steel with yield stress (σ s) of 235 MPa. If necessary, the symbol indicating the quality grade and deoxidation method can be marked after the steel grade. The quality grade symbols are a, B, C and D. Symbol of deoxidation method: F stands for rimmed steel; B represents semi killed steel; Z is killed steel; TZ stands for special killed steel. Killed steel can not be marked, that is, Z and TZ can not be marked. For example, q235-af stands for class a rimmed steel. Carbon steel for special purposes, such as bridge steel, marine steel, etc., basically adopts the expression of carbon structural steel, but the letter indicating the purpose is added at the end of steel grade. According to GB / T 700-2006 standard, carbon structural steel Q235 is pided into four grades according to metallurgical quality: A, B, C and D. Q235: Grade A, B, C and D (GB / T 700-2006) Q235A contains C ≤ 0.22% Mn ≤ 1.4% Si ≤ 0.35% s ≤ 0.050, P ≤ 0.045 Q235B grade contains C ≤ 0.20% Mn ≤ 1.4% Si ≤ 0.35% s ≤ 0.045 P ≤ 0.045 (with the consent of the demander, the carbon content may not be greater than 0.22%) Q235C contains C ≤ 0.17% Mn ≤ 1.4% Si ≤ 0.35% s ≤ 0.040, P ≤ 0.040 Q235D contains C ≤ 0.17% Mn ≤ 1.4% Si ≤ 0.35% s ≤ 0.035, P ≤ 0.035 There are many examples of cold working dies made by low carbon martensite hardening process in China. The thickness of Mo CR bowing layer is more than 100 μ m, the surface Mo Cr content can reach 20%, Cr content can reach 10%, the carbon content of supersaturated carburizing surface is more than 2.0%, the surface composition is close to molybdenum high speed steel, and the surface hardness is up to 1300hv after quenching and tempering, More than general metallurgical high speed steel. The wear test shows that the friction coefficient increases with the increase of contact stress, and the average relative wear resistance is 2.2 times of GCr15 carburized and quenched steel. The main uses of Q235 are as follows: ① It is widely used in construction and engineering structure, or mechanical parts with low performance requirements. C. Grade D steel can also be used as some professional steel. ② It can be used for all kinds of mold handle and other unimportant mold parts. ③ Q235 steel is used as punch material. After quenching, it can be directly used without tempering. The hardness is 36 ~ 40HRC, which solves the problem of punch cracking in use. Standard of Q235 Brand Q235 （ GB/T 700-2006 Carbon structural steel) Grade A B C D Deoxidation method F 、 Z F 、 Z Z TZ Chemistry component C ≤ 0.22 ≤ 0.20 ≤ 0.07 ≤ 0.07 Si ≤ 0.35 ≤0.35 ≤0.35 ≤ 0.35 Mn ≤ 1.40 ≤ 1.40 ≤ 1.40 ≤ 1.40 P ≤ 0.045 ≤ 0.045 ≤ 0.045 ≤ 0.045 S ≤ 0.050 ≤ 0.050 ≤ 0.050 ≤ 0.050 yield strength thick degree or straight path ≤ 16 ≥ 235MPa ＞ 16~40 ≥ 225MPa ＞ 40~60 ≥ 215MPa ＞ 60~100 ≥ 215MPa ＞ 100~150 ≥ 195MPa ＞ 150~200 ≥ 185MPa tensile strength 370~500MPa Posthumous elongation rate thick degree or straight path ≤ 40 ≥ 26% ＞ 40~60 ≥ 25% ＞ 60~100 ≥ 24% ＞ 100~150 ≥ 22% ＞ 150~200 ≥ 21% to attack test Temperature (℃) — +20 0 -20 Impact energy J — ≥ 27 Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is stainless steel strip? Stainless steel strip can be regarded as the extension product of ultra-thin stainless steel plate. It is a kind of long and narrow stainless steel plate which is usually manufactured to meet the needs of various industrial mechanical products. Stainless steel strip is also called stainless steel strip. The maximum width of stainless steel strip can not exceed 1220 mm, but the length is not limited. According to the processing method, the stainless steel strip can be pided into cold-rolled stainless steel strip and hot-rolled stainless steel strip. Stainless steel strip has excellent strength, precision, surface finish and other properties, which is widely used in aerospace, petrochemical, automobile, textile, electronics, household appliances, computer and precision machining and other pillar industries. Classification of stainless steel strip Stainless steel sheet supplied in coils can also be called strip steel. Divided into hot rolling, cold rolling, ordinary stainless steel strip, high quality stainless steel strip and precision stainless steel strip. There are many kinds of stainless steel belts, including 201 stainless steel belt, 202 stainless steel belt, 304 stainless steel belt, 301 stainless steel belt, 302 stainless steel belt, 303 stainless steel belt, 316 stainless steel belt, J4 stainless steel belt, 309S stainless steel belt, 316L stainless steel belt, 317L stainless steel belt, 310S stainless steel belt, 430 stainless steel iron belt, etc. The thickness is 0.02mm-4mm, and the width is 3.5mm-1550mm. Stainless steel with domestic (imported) stainless steel strip: stainless steel coil strip, stainless steel spring band, stainless steel stamping band, stainless steel precision belt, stainless steel mirror belt, stainless steel cold rolling strip, stainless steel hot rolling strip, stainless steel etching strip, stainless steel stretching belt, stainless steel polishing belt, stainless steel soft belt, stainless steel hard belt, stainless steel medium hard belt, stainless steel high temperature resistant belt, etc. Cold rolled stainless steel strip Stainless steel strip or coil is used as raw material and rolled by cold rolling mill at room temperature. The conventional thickness is 0.1 mm ~ 3 mm, while the width is 100 mm ~ 2 000 mm. Cold rolled stainless steel strip has the advantages of smooth surface, smooth surface, high dimensional accuracy and good mechanical properties. Most products are rolled and can be processed into coated steel plate. The production process sequence of cold-rolled stainless steel strip or coil is acid pickling, normal temperature rolling, process lubrication, annealing, leveling, fine cutting and packaging. Stainless steel hot rolled strip Hot rolled stainless steel strip is made by hot rolling mill with thickness of 1.80mm-6.00mm and width of 50mm-1200mm. Hot rolled stainless steel has the advantages of low hardness, easy processing and good ductility. Its production processes are acid pickling, high temperature rolling, process lubrication, annealing, leveling, fine cutting and packaging. Difference between cold and hot rolled stainless steel strip There are three main differences between cold-rolled stainless steel strip and hot-rolled stainless steel strip Firstly, the strength and yield strength of cold-rolled stainless steel strip are better, and the ductility and toughness of hot-rolled stainless steel strip are good. Secondly, the thickness of cold-rolled stainless steel strip is ultra-thin, while the thickness of hot-rolled stainless steel strip is larger. In addition, the surface quality, appearance and dimensional accuracy of cold-rolled stainless steel strip are better than those of hot-rolled stainless steel strip. Properties of stainless steel strip Like other materials, the physical properties of stainless steel strip mainly include the following three aspects: melting point, specific heat capacity, thermal conductivity and linear expansion coefficient, electromagnetic properties such as resistivity, conductivity and permeability, and mechanical properties such as young’s modulus of elasticity and rigidity coefficient. These properties are generally considered to be inherent characteristics of stainless steel materials, but they are also affected by such factors as temperature, processing degree and magnetic field strength. In general, the thermal conductivity and electrical resistance of stainless steel are lower than that of pure iron. Correlation between physical properties and temperature (1) Specific heat capacity With the change of temperature, the specific heat capacity will change, but in the process of temperature change, once the phase transformation or precipitation occurs in the metal structure, the specific heat capacity will change significantly. (2) Thermal conductivity Below 600 ℃, the thermal conductivity of all kinds of stainless steel is in the range of 10 ~ 30W / (m · ℃), and the thermal conductivity increases with the increase of temperature. At 100 ℃, the order of thermal conductivity of stainless steel is 1Cr17, 00Cr12, 2Cr25N, 0cr18ni11ti, 0Cr18Ni9, 0cr17ni12m ο 2 and 2cr25ni20. At 500 ℃, the order of thermal conductivity is 1 CR 13, 1 CR 17, 2 CR 25 n, 0 CR 17 Ni 12 m o 9 2, 0 CR 18 Ni 9 Ti and 2 CR 25 Ni 20. Compared with ordinary carbon steel, the thermal conductivity of austenitic stainless steel is about 1 / 4 of that at 100 ℃. (3) Coefficient of linear expansion In the range of 100-900 ℃, the linear expansion coefficients of the main stainless steel grades are basically in the range of 10 ˉ 6 ˉ 6 ˉ 1 ˉ 130 * 10 ˉ 6 ˉ 1, and it increases with the increase of temperature. For precipitation hardening stainless steel, the linear expansion coefficient is determined by aging treatment temperature. (4) Resistivity At 0 ~ 900 ℃, the specific resistance of the main grades of stainless steel is 70 * 10 ˉ 6 ~ 130 * 10 ˉ 6 Ω· m, and it increases with the increase of temperature. When it is used as heating material, the material with low resistivity should be selected. (5) Permeability Austenitic stainless steel is also known as non-magnetic material because of its low permeability. Steel with stable austenite structure, such as 0 CR 20 Ni 10, 0 CR 25 Ni 20, etc., will not be magnetic even if it is processed with large deformation more than 80%. In addition, austenite stainless steels with high carbon, high nitrogen and high manganese, such as 1cr17mn6nisn, 1Cr18Mn8Ni5N and high manganese austenitic stainless steels, will undergo phase transformation under large reduction, so it remains non-magnetic. At high temperatures above the Curie point, even strong magnetic materials lose their magnetism. However, some austenitic stainless steels, such as 1cr17ni7 and 0Cr18Ni9, have metastable austenite structure, so martensitic transformation will occur during large reduction or low temperature processing, which will have magnetic properties and increase permeability. (6) Elastic modulus At room temperature, the longitudinal elastic modulus of ferritic stainless steel is 200kn / mm2, and that of austenitic stainless steel is 193kn / mm2, which is slightly lower than that of carbon structural steel. With the increase of temperature, the longitudinal elastic modulus decreases, the Poisson’s ratio increases, and the transverse elastic modulus (rigidity) decreases significantly. The longitudinal elastic modulus will affect the work hardening and microstructure aggregation. (7) Density The density of ferritic stainless steel with high chromium content is small, while that of austenitic stainless steel with high nickel and manganese content is high, and the density becomes smaller due to the increase of spacing between the elements at high temperature. Physical properties at low temperature (1) Thermal conductivity The thermal conductivity of all kinds of stainless steel is slightly different at very low temperature, but generally speaking, it is about 1 / 50 of that at room temperature. At low temperature, the thermal conductivity increases with the increase of magnetic flux (flux density). (2) Specific heat capacity At very low temperatures, the specific heat capacities of various stainless steels are different. The specific heat capacity is greatly affected by temperature. The specific heat capacity at 4K can be reduced to less than 1 / 100 of the specific heat capacity at room temperature. (3) Thermal expansion For austenitic stainless steel, there is a little difference in shrinkage rate (relative to 273k) below 80K. The content of nickel has a certain effect on the shrinkage. (4) Resistivity At very low temperature, the difference of resistivity between different grades increases. The alloy elements have great influence on the resistivity. (5) Magnetism At low temperature, the effect of mass susceptibility on load magnetic field of austenitic stainless steel is different with different materials. The contents of different alloying elements are also different. There is no difference in permeability between different grades. (6) Elastic modulus At low temperature, the Poisson’s ratio of austenitic stainless steel with magnetic transformation has an extreme value. Source: China Stainless Steel Strip Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Galvanized: Zinc is relatively stable in dry air and is not easy to change color. In water and humid atmosphere, it reacts with oxygen or carbon dioxide to form oxide or alkaline zinc carbonate film, which can prevent zinc continuous plating oxidation and play a protective role. Zinc is easily corroded in acid, alkali and sulfide. Zinc coating is usually passivated. After passivation in chromic acid or chromate solution, the corrosion resistance is greatly enhanced because the passivation film formed is not easy to interact with humid air. For spring parts, thin-walled parts (wall thickness < 0.5m) and steel parts requiring high mechanical strength, dehydrogenation must be carried out. Copper and copper alloy parts can not be dehydrogenated. Zinc plating has the advantages of low cost, convenient processing and good effect. The standard potential of zinc is relatively negative, so the zinc coating is anodic to many metals. Application: zinc plating is widely used in atmospheric condition and other good environment, but it is not suitable for friction parts Cadmium plating: For parts in contact with marine atmosphere or sea water and in hot water above 70 ℃, cadmium coating is relatively stable with strong corrosion resistance and good lubrication. It dissolves slowly in dilute hydrochloric acid, but it is very easy to dissolve in nitric acid, insoluble in alkali, and its oxide is also insoluble in water. Cadmium coating is softer than zinc coating, hydrogen brittleness of coating is smaller, adhesion is stronger, and under certain electrolysis conditions, cadmium coating is more beautiful than zinc coating. But the gases produced by the melting of cadmium are toxic, and so are soluble cadmium salts. Under general conditions, cadmium is a cathodic coating on steel and an anode coating in marine and high temperature atmosphere. Application: it is mainly used to protect parts from the atmospheric corrosion of sea water or similar salt solution and saturated seawater vapor. Many parts of aviation, navigation and electronic industry, spring and thread parts are plated with cadmium. It can be polished, phosphated and used as paint primer, but it can’t be used as tableware. Chromium plating: Chromium is very stable in humid atmosphere, alkali, nitric acid, sulfide, carbonate solution and organic acid, and is easily soluble in hydrochloric acid and hot concentrated sulfuric acid. Under the action of direct current, if chromium layer is used as anode, it is easy to dissolve in caustic soda solution. The chromium coating has strong adhesion, high hardness, 800 ~ 1000V, good wear resistance, strong light reflection, and high heat resistance. It does not change color below 480 ℃ and begins to oxidize above 500 ℃. The hardness decreases significantly at 700 ℃. Its disadvantages are hard, brittle and easy to fall off, especially when subjected to alternating impact load. It is porous. Chromium is easy to passivate in air and form passivation film, which changes the potential of chromium. Therefore, chromium on iron becomes a cathodic coating. Application: it is not ideal to directly plating chromium on the surface of iron and steel parts as anti-corrosion coating. Generally, the purpose of rust prevention and decoration can be achieved by multi-layer electroplating (i.e., copper plating → nickel → chromium). At present, it is widely used to improve the wear resistance of parts, repair size, light reflection and decorative lights. Plate with nickel: Nickel has good chemical stability in the atmosphere and alkali liquor, and is not easy to change color. It is oxidized only when the temperature is above 600 ℃. It dissolves slowly in sulfuric acid and hydrochloric acid, but soluble in dilute nitric acid. It is easy to passivate in concentrated nitric acid, so it has good corrosion resistance. The nickel coating has high hardness, easy polishing, high light reflection and beautiful appearance. In order to overcome this shortcoming, multi-layer metal coating can be used, and nickel is the intermediate layer. Nickel is a cathodic coating on iron and an anode coating on copper. Application: usually in order to prevent corrosion and increase aesthetic use, it is generally used to protect decorative coatings. Nickel plating on copper products is ideal, but because nickel is more expensive, copper tin alloy is often used instead of nickel plating. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Reasonable selection, proper storage and correct use of manufacturing materials are the prerequisite and basis for ensuring the quality of pressure vessels. This article makes some meaningful discussions on the material quality management issues in pressure vessel manufacturing, hoping to serve as a reference and reference for colleagues in the industry. As a special pressure-bearing equipment, pressure vessel has been widely used in petrochemical, energy, scientific research and military industries. Its quality is directly related to the production safety of these industrial fields, so it must be given full attention. In order to ensure the manufacturing quality of pressure vessels, the first requirement is to manage and control the quality of vessel materials. If the pressure vessel manufacturing materials used have quality defects, no matter how the subsequent optimization and improvement of the process process, the final product quality is difficult to guarantee. Therefore, reasonable selection, proper storage and correct use of manufacturing materials are the prerequisite and basis for ensuring the quality of pressure vessel products. Based on this standpoint, this article makes some meaningful discussions on the material quality management issues in pressure vessel manufacturing, hoping to serve as a reference for colleagues in the industry. The pressure vessel parts are as follows: 1. Tube sheets 2. Baffles 3. Flanges 4. Heat Exchanger Bundle Tubes, etc Overview of pressure vessel manufacturing As a special pressure-bearing equipment, the pressure vessel’s manufacturing quality is very important for the safety application in the industrial field. At present, in order to ensure the production quality of pressure vessels, my country has issued corresponding standards and specifications, which must be designed and manufactured in strict accordance with the requirements of the national standard. In practical applications, the types of pressure vessels are different, and their functioning principles and application fields are also different. This requires that in the process of manufacturing them, the manufacturing quality must be ensured to meet the actual application requirements. In addition, as a special type of equipment, pressure vessels are more difficult to manufacture than general vessel products. The entire manufacturing process has very high quality and safety requirements, requiring close coordination and cooperation from multiple disciplines. In reality, there are many factors that affect the quality of pressure vessel manufacturing, and any error in any of them will affect the quality of the final product. Material selection is the first step of manufacturing, and strict quality control is also necessary. Considering that there are many types of materials available in practice, and the final material quality still depends on the control of storage and other links, it is of great significance to strengthen the control of factors related to material quality in the manufacturing process and must be given sufficient attention. Matters needing attention in material substitution In the manufacturing process, if a thick plate is used instead of a thin plate, the structure of the joint may be changed. For example, when the thickness increases more, the welding structure may change. When the overall thickness is replaced by thinness, even if the local stress at the joint between the head and the cylinder is not increased, it will affect the quality of the container product to a certain extent, and it will also cause the welding, flaw detection and heat treatment processes used in the original design to be changed. Land no longer applies. In addition, the substitution of materials for pressure vessels may also lead to changes in the weight of the container products, which in turn will affect the supporting support and foundation of the products. In short, in the manufacture of pressure vessels, in principle, it is not allowed to substitute materials randomly, because different materials will have different performances. Even if one performance has reached a higher level, it may be replaced by another. In terms of low-to-high, and these will make the process measures and schemes used in the entire production process must be modified accordingly, but this change often results in poor solderability and doubled manufacturing process difficulty. So we must be cautious about material substitution. Material quality management measures in pressure vessel manufacturing Material procurement measures For machinery manufacturing, the procurement of raw materials is a key basic link to control the quality of the final product, and the manufacturing of pressure vessels is naturally no exception. Taking into account the chaotic order of the current material supply market, even for materials of the same specification, quality differences caused by different manufacturers abound. Therefore, pressure vessel manufacturers must strengthen management of the procurement of raw materials. First of all, we must conduct credit checks on the production and suppliers of materials, and select those with good credit and long-term cooperative relations. Secondly, after each material purchase is completed, the company should evaluate the supplier’s supply speed, service quality and product quality, and record the evaluation results in the material supplier’s files for future material supplier selection Provide evidence. Finally, pressure vessel manufacturers should establish a sound and complete material procurement quality control system, strengthen supervision of whether the purchased materials comply with relevant national and industry standards, and strengthen inspections of the material quality certificates and other certification materials provided by suppliers. The responsibility for inspection is assigned to the inpidual, and strive to ensure that the selected materials meet the design performance index requirements. Measures in the acceptance link The quality management department shall strengthen the quality acceptance of the delivered materials, and the inspectors and engineers may conduct quality inspections on whether the materials meet the relevant standard requirements. Before the materials are put into storage, they must go through scientific acceptance and supervise whether the acceptance process meets the relevant process specifications. Make sure that the procedures are complete when materials are put into storage. Acceptance records of materials must be filled in accurately. All the above processes must form a clear process specification. Once there is an acceptance problem, the responsibility traceability mechanism can be activated immediately to find out the problems in the acceptance process and improve it. Material storage measures The purchased materials shall be classified and stored when they are put into the warehouse. They shall be kept scientifically according to the specifications, composition and physical and chemical properties of the materials, and shall be marked accordingly. The material storage warehouse should meet relevant requirements such as ventilation and drying, and different sensors should be set up in the storage area according to different materials to monitor whether the storage environment meets the storage requirements of the materials in real time to ensure that the materials will not appear in storage Degeneration and other issues. Finally, in the process of distributing materials, we must strictly abide by the “application-review” system, standardize the application and distribution process of materials, and ensure the scientific and reasonable use of materials. Material recycling measures Before using the material, the size and specification of the material should be checked according to relevant regulations and drawings. Only after the inspection is qualified can it be used for pressure vessel manufacturing. Mark the materials that have been received and still have surplus after manufacturing. After the materials pass the inspection and confirmation, the return procedures can be processed. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is carburizing? Carburizing is a kind of surface heat treatment technology, which points to the heat treatment method of quenching after carburizing atoms on the surface of steel parts. Through the infiltration of carbon, the wear resistance, durability, toughness and other properties of steel components can be significantly improved. The steel used to make carburized parts is called carburized steel. The main heat treatment process of carburized steel is generally quenching and low temperature tempering after carburizing. After treatment, the core of the part is a low-carbon martensite structure with sufficient strength and toughness, and the surface layer is hard and wear-resistant tempered martensite and a certain amount of fine carbide structure. Some structural parts work under strong impact and wear conditions, such as gearbox gears on automobiles and tractors, cams and piston pins on internal combustion engines. According to the working conditions, these parts are required to have high surface hardness and wear resistance, while the core is required to have higher strength and appropriate toughness, that is, the performance of the workpiece “hard surface and tough inside” is required. In order to take into account the above dual properties, low-carbon steel can be achieved by carburizing quenching and low-temperature tempering. At this time, the core of the part is a low-carbon steel quenched structure to ensure high toughness and sufficient strength, and the surface layer (at a certain depth ) Has high carbon content (0.85%～1.05%), high hardness (HRC>60) after quenching, and good wear resistance can be obtained. Composition characteristics of carburized steel The carbon content of carburized steel is generally very low (between 0.15% and 0.25%) and belongs to low-carbon steel. This carbon content ensures that the core of carburized parts has good toughness and plasticity. In order to increase the strength of the core of the steel, a certain amount of alloying elements, such as Cr, Ni, Mn, Mo, W, Ti, B, etc. can be added to the steel. Among them, the main role of Cr, Mn, Ni and other alloying elements is to increase the hardenability of steel, so that the surface layer and core structure can be strengthened after quenching and low temperature tempering. In addition, a small amount of carbide forming elements such as Mo, W, and Ti can form stable alloy carbides, which can refine grains and prevent steel parts from overheating during carburization. A small amount of B (0.001%～0.004%) can strongly increase the hardenability of alloy carburized steel. Classification of carburizing steel According to different hardenability or strength grades, alloy carburized steels are pided into three categories. 1) Low hardenability alloy carburized steel That is, low-strength carburized steel (tensile strength≤800MPa), such as 15Cr, 20Cr, 15Mn2, 20Mn2, etc. This type of steel has low hardenability, the core strength is low after carburizing, quenching and low temperature tempering, and the strength and toughness are poorly matched. It is mainly used to manufacture wear-resistant parts with low stress and low strength requirements, such as camshafts, piston pins, sliders, pinions, etc. of diesel engines. The core grains are easy to grow when this kind of steel is carburized, especially manganese steel. If the performance requirements are high, this type of steel often adopts the secondary quenching method after carburizing, that is, normalizing treatment is performed after carburizing to eliminate the overheated structure formed during carburizing, and then reheating and quenching. 2) Medium hardenability alloy carburized steel That is, medium-strength carburized steel (tensile strength=800～1200MPa), such as 20CrMnTi, 12CrNi3A, 20CrMnMo, 20MnVB, etc. This type of steel contains about 4% of the total alloying elements. Because the two elements of Cr and Mn are added to the steel, it can more effectively improve the hardenability and mechanical properties (tensile strength=1000～1200MPa). Generally used to manufacture heavy-duty medium and small wear-resistant parts and medium-load gears with larger modulus. Such as gearboxes and rear axle gears of automobiles and tractors, gear shafts, cross pin heads, spline bushings, valve seats, cam discs, etc. Because this kind of steel contains Ti, V, Mo, the tendency of austenite grains to grow during carburizing is small, so it can be quenched directly from the carburizing temperature to about 870°C, and after low temperature tempering, the parts have Good mechanical properties. 3) High hardenability alloy carburized steel That is, high-strength carburized steel (tensile strength> 1200MPa), such as 12Cr2Ni4, 18Cr2Ni4WA and so on. This type of steel contains a total of alloying elements ≤7.5%. Because it contains more Cr and Ni elements, it can greatly improve the hardenability of the steel. In particular, the addition of more Ni can improve the strength while making the steel good Of resilience. This type of steel can be used as important large parts that bear heavy loads and strong wear, such as the active traction gear of diesel locomotives, diesel engine crankshafts, connecting rods and precision bolts on cylinder heads. Due to the higher alloying elements, the C curve shifts to the right, so the martensite structure can be obtained even when cooled in air; in addition, the martensite transformation temperature also drops sharply, so that the carburized surface layer will remain after quenching A large amount of retained austenite. In order to reduce the amount of retained austenite after quenching, high temperature tempering can be used before quenching to spheroidize the carbides or cold treatment after quenching. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)