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In the petroleum, chemical, electric power and other industrial fields, heat exchangers are widely used as a common pressure vessel. The most commonly used is the shell-and-tube heat exchanger, which consists of a casing, a heat transfer tube bundle, a tube sheet, and a baffle. (Baffle) and tube box and other components.

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

With the development of the national economy, the advantages of buried pipelines are increasingly recognized by the public. At the same time, the problems caused by the leakage of buried pipelines are increasingly concerned by the public. Therefore, the preservation of buried pipelines has become an important issue. . 1. Buried pipeline and laying environment Here we say that buried pipelines are specifically metal pipes, and considering the prevalence of use in water supply and drainage projects, we have chosen two metal pipes for discussion, one is ductile iron pipe and the other is carbon steel pipe. In most cases, buried pipelines are laid in the topsoil. The average person would think that the soil is a granular solid, but in fact, when we conducted related research, we thought that the soil is a three-phase system of solid, liquid and gas, and the latter two played a crucial role. Among them, solid materials include soil minerals, organic matter and microorganisms, and liquids and gases exist in the pores of soil particles. The soil can be pided into sandy soil, clay soil and loam. Among them, the sandy soil has many sediments, coarse particles, fast water seepage, poor water retention performance, good aeration performance, and slime. The nature of the soil is exactly the opposite of sandy soil, and the nature of the loam is middle. Pipes are buried in soils of different natures, and the degree of corrosion is different. In fact, in many cases, a pipe needs to be in contact with soil of different nature, and the different physicochemical properties of the pipe surface are likely to lead to increased corrosion of the pipe. Therefore, in this case, anticorrosion construction should be better. jobs. 2. Types of corrosion of buried pipelines and introduction Metal corrosion is pided into chemical corrosion (specifically non-electrochemical corrosion) and electrochemical corrosion. Among them, the latter accounted for the vast majority. Electrochemical reactions are a branch of a chemical reaction that must have the presence of a metal as an electrode, an electrolyte as a reaction environment, and a conductive loop. Most of the corrosion of buried pipelines is caused by electrochemical reactions. There are many types of buried pipeline corrosion, including galvanic corrosion, concentration battery corrosion, pitting, pitting and so on. Here, we focus on three common forms of corrosion, galvanic corrosion, concentration cell corrosion, and microbial corrosion. 2.1 galvanic corrosion Primary batteries are the most basic form of electrochemical reactions and are often used in situations where electrochemical reactions are introduced. The picture below is a schematic diagram of a primary battery. In the figure, copper and zinc are respectively used as the two poles of the battery, the two poles are immersed in the same electrolyte solution, and the wires are connected to the two poles. When the two poles are connected by wires, due to the different properties of the two metals, zinc is more active than copper, and a potential difference is generated. The zinc as the positive electrode of the primary battery loses electrons, and the copper of the negative electrode acquires electrons. As a result, the corrosion of the zinc electrode is intensified, and the corrosion of the copper electrode is slowed down or even stagnated. The greater the potential difference between the two metals separated in the potential sequence, the stronger the corrosion, so the two metals in the potential sequence that are far apart should not be connected together. In fact, the primary battery is more like a double-edged sword. This principle is often used in engineering to slow the corrosion of steel pipes. In actual operation, there are several points to note. One is to replace a pipe. When a pipe is replaced due to corrosion damage, if it is not noticed, the new pipe segment will often fail quickly. Because the new pipe section is an anode, it tends to be short, while the old pipe section is a cathode, which is often long. A small section of new pipe needs to supply several times its own old pipe section, and its corrosion rate will be much greater than the corrosion rate of its own buried ground. There is also a weld of the pipe. The metal body of the steel pipe and the metal composition of the weld are different. The potential difference between the two can reach 0.275V. Therefore, the adjacent portion of the weld with low potential after being buried in the ground is easily corroded. . Therefore, in the above circumstances, we should do a good job in anti-corrosion work. 2.2 Concentration battery corrosion Concentration batteries are quite common in the corrosion of buried pipelines, which are pided into metal ion concentration difference batteries and oxygen concentration difference batteries. Concentration batteries are also essentially caused by the difference in metal potential between the two poles. The metal ion concentration battery is because the concentration of metal ions in the electrolyte where the two poles are different, and the oxygen concentration battery, as the name suggests, is because of the electrolyte solution where the two poles are located. Caused by different oxygen concentrations. Among them, oxygen concentration batteries are most common in buried pipeline corrosion. This has a lot to do with different soil properties. The concentration of oxygen in different parts of the pipeline is different. The natural potential (non-equilibrium potential) of the pipeline in the oxygen-depleted part is low, which is the anode of the corrosion original battery. The anode dissolution rate is obviously higher than the anode dissolution rate of the remaining surface, so it suffers from corrosion. The pipeline passes through the soil junction of different natures. The clay section is depleted of oxygen and is prone to corrosion, especially at the junction of the two soils or the location of the buried pipeline near the excavation end. In actual operation, the buried pipelines are often in different tamping layers, the pores of the soil are different, and the oxygen holding capacity naturally differs, which provides conditions for the formation of oxygen concentration batteries. 2.3 Microbial corrosion Microbial corrosion is essentially bacterial corrosion, which is also an electrochemical corrosion in nature, except that the medium changes the physical and chemical properties of the interface of the material it contacts due to the propagation and metabolism of the corrosive microorganisms. There are many types of bacteria involved in bacterial corrosion, and the most harmful one is sulfate-reducing bacteria (SRB). Sulfate-reducing bacteria are bacteria that use organic matter as a nutrient to reduce sulfate to sulfide under anaerobic conditions. SRB is an anaerobic bacterium that needs to grow under anaerobic conditions and actually multiplies rapidly in a local anaerobic environment. Von Wogozen Kuhr et al. proposed a classical depolarization theory in 1974. It is believed that pitting corrosion of buried cast iron pipes is due to the activity of SBR to deoxidize the metal surface by hydrogenase. The overall reaction formula is as follows: 4Fe + SO42- + 4H2O ==3Fe(OH)2 + FeS + 2OH- 3. Anti-corrosion of buried pipelines In view of the corrosion principle and process described above, the anticorrosion means of the buried pipeline in the project is mainly pided into three aspects, external application, lining and cathodic protection. Among them, the external application mainly includes asphalt, galvanized, PE tape, etc., the inner lining mainly includes resin, cement mortar, plastic, etc., and the cathodic protection is also pided into two kinds of DC power supply and no DC power supply. Next, we introduce the anti-corrosion measures for ductile iron pipes and carbon steel pipes. 3.1 ductile iron pipe In terms of material properties, the anti-corrosion performance of ductile iron pipes is better than that of carbon steel pipes. Therefore, it has been widely used in the field of buried pipeline transportation. At present, the ductile iron pipe adopts the cement lining as the internal anti-corrosion form, the zinc layer plus the asphalt as the external anti-corrosion form, and has been completed in the production process, and the anti-corrosion treatment is not required after the construction and installation. This has become a common practice for spheroidal graphite cast iron pipe manufacturers at home and abroad, and is suitable for most soil types. It has been proved by practice that the anti-corrosion effect is also very obvious. Among them, it is important to point out the importance of the zinc layer as a means of external preservation. First, electrochemical protection The potential of iron is -0.440 mV, and the potential of zinc is -0.763 mV, which is lower than the potential of iron, and the potential of oxygen is 1.4 mV. Thus, the potential difference between the zinc and oxygen is large, and the primary battery is more easily formed, thereby protecting the cast iron pipe wall. Second, form a stable protective layer Once the asphalt coating on the surface of the zinc layer is destroyed, the zinc layer is in contact with the soil, and the metal zinc combines with carbonates in the soil to form insoluble zinc carbonate, which is tightly bonded to the tube wall. Forms a dense, continuous, insoluble, non-leakable coating to prevent corrosion. Third, the self-healing of the damage Local damage may occur during pipeline transportation or installation. Zinc is rapidly converted to zinc ions by the action of the primary battery. Zinc ions migrate through the pores of the asphalt layer to seal the pores and cover the damage, forming a stable and insoluble protective zinc layer. In addition, the zinc layer and the asphalt have excellent adhesion, which is essential in corrosion protection. 3.2 carbon steel pipeline The corrosion resistance of carbon steel pipes is poor, but because of its high pressure resistance and good processability, it has also been widely used in buried pipelines.Therefore, its anti-corrosion practice has become the focus of the project. At present, the technologies used for external corrosion protection of buried steel pipes mainly include petroleum asphalt anti-corrosion layer, coal coke-stained porcelain anti-corrosion layer, polyethylene adhesive tape anti-corrosion layer, sintered epoxy powder anti-corrosion layer, and two-layer structure polyethylene anti-corrosion layer. Three-layer structure polyolefin anti-corrosion layer technology. Here, we mainly introduce the polyethylene adhesive tape anti-corrosion layer technology. The polyethylene adhesive tape anticorrosive system consists of a primer, an inner anticorrosive tape and an outer protective tape. The anti-corrosion layer is pided into different grades. According to different pipe diameters, environment, anti-corrosion requirements and construction conditions, different anti-corrosion layer structure and thickness are selected. Polyethylene adhesive tape anti-corrosion layer has excellent water resistance and oxidation resistance, low moisture absorption rate, good insulation, anti-cathode peeling, impact resistance, wide temperature range, stable performance in the temperature range of 30~80 °C. The anti-corrosion quality of polyethylene adhesive tape mainly depends on the adhesion of the adhesive film interface. The non-solvent adhesive is used to bond the polyethylene-based film and the solvent-free adhesive under heat under a certain pressure to make the polyethylene adhesive tape strong and stable, and the quality of the anti-corrosion layer is obtained. Guarantee. The main disadvantage of the polyethylene adhesive tape anti-corrosion layer is that it has poor resistance to soil stress, especially at high temperatures, resulting in cathode shielding due to poor adhesion and compactness. 3.3 Cathodic protection Cathodic protection is an anti-corrosion method for protecting the outer wall of a buried pipeline according to the principle of the original battery. According to the principle of the original battery, only the anode of the two electrodes is corroded. Therefore, the cathodic protection is to make the metal pipe become a cathode by artificial means to prevent corrosion. There are two types of cathodic protection, one is cathodic protection without external current. The specific method is to use a metal material (active) that is more reductive than steel, such as magnesium, zinc, etc. as an anode, and bury it in the ground, connect the anode to the pipeline with a wire at a certain distance, and naturally form a large one in the soil. The result of the circuit is that the anode metal is corroded and the steel or cast iron pipes are protected. This method is often used in situations where soil resistivity is low, power is not available, and pipe coating is good. There is also a cathodic protection method that applies DC power. The specific method is: burying scrap iron or the like in the vicinity of the metal pipe, as an anode, connecting with the anode of the direct current, and the cathode of the power source is connected to the pipeline. The current flows from the DC power source through the cable to the artificial scrap iron anode, and then flows into the protected pipeline through the soil, and flows from the pipeline back to the cathode of the power supply through the cable, so that the protected pipeline becomes a cathode, thereby preventing soil corrosion of the pipeline.This method is more suitable when the soil resistivity is high or the metal pipe is exposed. In fact, cathodic protection is often used in conjunction with the outer coating of the pipe to achieve better corrosion protection. Source: China Steel Pipelines Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

At present, China’s metal hose industry is facing a situation of internal and external pressure. The industry’s turning point is approaching. Its extensive growth mode has already encountered severe challenges. The shortage of resource elements, increased environmental pressure, low-cost competition, and quantitative expansion have been developed. More and more difficult to sustain. At present, independent innovation has become the consensus of all walks of life. With the intensification of market competition, independent innovation will become the inevitable way for enterprises to reduce costs and obtain profits. Tongfeng Metal Hose believes that innovation is the key to transformation and upgrading, especially in manufacturing, and it is better to master cutting-edge core technologies and improve competitiveness. 1. Technological innovation At present, most of the metal hose products exported from China are products with relatively low technical content. These products are highly substitutable. If they do not improve the technical content and reduce the cost, they will soon be replaced by some countries with lower production costs. Replace. Technological innovation is also an application innovation, and companies must think about how to turn a technology into a product on the market. Nowadays, as people’s understanding of upgrading the level of China’s metal hose industry is deepening, more and more people in the industry realize that if the idea of “market-for-technology” continues, the industrial development space will eventually be eroded. China’s metal hose industry has developed to a certain level. The key issue at present is to tackle the problem, form the core competitiveness of the industry, get rid of the dependence on key technologies, boldly break through the key technologies of raw material defects and the core technology of cold forming, and increase the independent research and development. Strength. 2. Marketing innovation In the face of fierce competition in the metal hose market, compared with multinational companies, local metal hose companies tend to be inferior in management, technology and brand, and are more inclined to adopt cost leadership, which is a low-cost growth strategy. . However, in the long run, the cost advantage should not be over-reliant. Avoiding the price war, changing the low-end line to the mid-to-high-end line, and focusing on the industry chain is also one of the strategies. For marketing success, metal hose companies can increase the bargaining power of raw material prices and reduce the price of metal hose materials. Reducing the price of metal hose materials, it is difficult to achieve the efforts of only one company. In terms of bargaining power, metal hose enterprises must rely on industry associations to negotiate. In addition to price considerations, seeking the market is also a part of marketing innovation that can not be ignored. China has a broad market, and the near-water tower is one of the advantages of domestic metal hose marketing. In recent years, the Chinese government’s policy of stimulating domestic demand has been very intensive, and many domestic companies have benefited from it. Today’s metal hose enterprises should strengthen market competition research, determine their own market positioning according to their own advantages, launch metal hose products that meet the market needs, reasonably priced, and obtain reasonable profits. This is the survival competition of metal hose enterprises. The road is not only conducive to the metal hose enterprise’s own brand building and sustainable healthy development, but also helps the whole machine, vehicle manufacturers and metal hose OEMs to establish partnerships and promote common development. 3. Brand innovation After years of improvement and innovation, China’s metal hose industry has reached a more mature stage in technology, resulting in an increasingly obvious homogenization of technology and quality of products, and the brand has become a major consideration in procurement. In the brand building and brand advantage, the domestic Tongfeng metal hose enterprises are ahead of the domestic industry. But compared with multinational companies, the market value generated by brands is still unmatched. In the metal hose industry, the vast majority do not have a special brand management department, brand construction lacks strategy, pays attention to short-term interests, and lacks long-term planning. The main reason for this situation is that many companies confuse brand appeals and product appeals, focusing only on product appeals and not paying attention to corporate brand appeals. In the metal hose market, the main driving force of domestic sales is the advantages in terms of products, services and brands. Brand is the intangible asset of a company, and it is the embodiment of the differentiation of production products of different enterprises. In addition to quality awareness and integrity, brand building must have clear high goals. Enterprises should develop a development strategy for corporate brands based on the height of the company. Source: China Duplex Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The weld seam has a high residual weld height Stress corrosion cracks are easily formed at the weld toe The stress concentration of the butt joint is mainly caused by the weld height, and the weld of the butt joint has the greatest stress at the weld toe. The magnitude of the stress concentration factor depends on the weld height h, the angle θ at the weld toe, and the radius r of the corner. When the weld height h increases, the θ angle increases and the r value decreases, which increases the stress concentration factor. The greater the residual height of the weld, the more severe the stress concentration and the lower the strength of the welded joint. After the welding, the remaining height is reduced, as long as it is not lower than the base metal, the stress concentration is reduced, and sometimes the strength of the welded joint can be increased. The outer weld seam is high, which is not conducive to corrosion protection. If the epoxy resin glass cloth is used for anti-corrosion during operation, the outer weld seam is high, which will make it difficult to press the weld toe. At the same time, the higher the weld, the thicker the anti-corrosion layer should be. The thickness of the anti-corrosion layer is calculated based on the apex of the outer weld, which increases the anti-corrosion cost. Spiral submerged arc welding is often prone to “fish ridge-back” outer welds, which makes it more difficult to guarantee the quality of corrosion protection. Therefore, it is also important to adjust the spatial position and welding specifications of the welding head to reduce or eliminate the outer seam of the “fish-back”. The outer weld seam is high, which affects the shape of the pipe after water pressure expansion When the straight seam submerged arc welded pipe is expanded by water pressure, the steel pipe is wrapped by the left and right outer parts of the inner cavity and the steel pipe with the same diameter expansion diameter. Therefore, the residual height of the weld is too large, and the shear stress of the weld is large when the diameter is expanded, and the phenomenon of “small straight edge” is likely to occur on both sides of the weld. However, experience has shown that when the residual height of the outer weld is controlled at about 2 mm, there will be no “small straight edge” phenomenon when the water pressure is expanded, and the shape of the pipe will not be affected. This is because the residual height of the outer weld is small and the shear stress on the welded joint is also small. As long as the shear stress is within the elastic deformation range, the rebound will occur after unloading and the tube will return to its original state. The inner weld seam is high, increasing the energy loss of the conveying medium If the inner surface of the submerged arc welded pipe for transportation is not treated with anti-corrosion treatment, the residual weld height of the inner surface of the submerged arc welded pipe is large, and the frictional resistance to the transport medium is also large, thereby increasing the energy consumption of the transfer line. Control measures for weld height Steel pipes with large wall thickness should be opened For steel pipes with a wall thickness greater than 14.3 mm, X-shaped bevels shall be opened and pre-welded. If the pre-welding conditions are not mature, the roots should be cleaned by gouging after internal welding, or the roots should be automatically ground by grinding, or the roots should be milled. The outer welds are processed into U-shaped grooves before welding and then welded. . Adjust the welding line energy Check the welding line energy is appropriate, generally check with the acid etching of the welded joint. One is to check the degree of overlap between the inner and outer welds, and the other is to check the width of the weld bead. The specification for the amount of overlap is generally greater than 1.5 mm, but the author believes that the amount of overlap between the inner and outer welds is suitably 1.3 to 3.0 mm. If it exceeds 3.0 mm, the line energy is large. The line energy is large, not only the penetration depth is large, but also the weld seam height is also large. If the groove or the U-shaped groove is not opened, the weld seam height is even larger. This is because the greater the welding line energy, the more the welding wire melted per unit time. For high-strength steel, the line energy of welding should be strictly controlled. When welding high-strength steel sheets, in order to reduce the line energy of each layer, multi-pass welding (two or more passes) is generally used, and the shape factor of the weld is to be within 1.3 to 2.0 mm. Finer front wire should be used for multi-wire welding When multi-wire welding is adopted, if the matching of the original outer welding three wire diameter is 4mm+3.2mm+3.2mm (DC-AC-AC), the front wire is preferably changed to Ф3.2mm. Because the same current is used, the use of Ф3.2mm wire is greater than the Ф4mm wire. That is to say, the front wire adopts a welding wire of Ф3.2mm, and even if some line energy is reduced, the same penetration effect when using Ф4mm can be achieved, which is because the filament has a higher current density than the thick wire. Experience has shown that under the same conditions, the front wire of Ф3.2mm is about 20% larger than the front wire of Ф4 mm. This is more effective when the outer weld is not opened or the groove is not cut. However, when welding a steel pipe with a wall thickness greater than 14.3 mm and requiring a front wire current of about 1000 A, a front wire of Ф4 mm should be used, otherwise the stable combustion of the arc may be affected. Spiral welding must adjust the position of the inner and outer welding heads The spiral submerged arc welded pipe shall be adjusted to the position of the inner welding head during internal welding to minimize or eliminate the “saddle shape” inner weld; during the outer welding, the spatial position of the welding head shall also be adjusted to minimize or eliminate the “shoulder shape”. “The outer weld seam, which is mainly achieved by the adjustment of the off-center value of the external weld joint. For the spiral welded pipes of different calibers, the off-center values of the outer welded joints are different. Precautions For the butt weld of the submerged arc welded pipe, the first is to make the weld be smooth and the corner radius of the weld is large, otherwise the stress will be generated at the weld toe of the weld stress concentration part. Corrosion cracks. It is more suitable to control the residual height of the submerged arc weld below 2.5 mm. When spiral submerged arc welded pipe is used for internal welding, the spatial position of the inner and outer welds should be carefully adjusted to minimize the inner weld and avoid the “saddle shape”, and the outer weld does not have “fishback shape”. It is recommended that the “saddle shape” of the inner weld be to be specified when formulating the standard for conveying spiral welded pipe. Source: China Welded Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Forging is one of the two major components of forging (forging and stamping) by using a forging machine to apply pressure to a metal blank to plastically deform it to obtain a forging with certain mechanical properties, a certain shape and size. Forging can eliminate defects such as as-cast looseness caused by metal in the smelting process, optimize the microstructure, and at the same time, the mechanical properties of the forgings are generally superior to those of the same materials due to the preservation of the complete metal flow lines. For important parts of the relevant machinery with high load and severe working conditions, forgings are often used except for the available rolled sheets, profiles or welded parts. Deformation temperature The initial recrystallization temperature of steel is about 727 ° C, but 800 ° C is generally used as the piding line. Above 800 ° C is hot forging; between 300 and 800 ° C is called warm forging or semi-hot forging, forging at room temperature. It is called cold forging. Forgings used in most industries are hot forging, warm forging and cold forging are mainly used for forging of parts such as automobiles and general machinery. Warm forging and cold forging can effectively save materials. 2. Forging category As mentioned above, according to the forging temperature, it can be pided into hot forging, warm forging and cold forging. According to the forming mechanism, forging can be pided into free forging, die forging, rolling ring, and special forging. 1) Free forging Refers to a method of processing a forging that uses a simple universal tool or an external force directly applied to the blank between the upper and lower anvil of the forging equipment to deform the blank to obtain the desired geometry and internal quality. Forgings produced by the free forging method are called free forgings. Free forging is mainly for the production of forgings with small quantities, and forgings are processed by forging equipment such as forging hammers and hydraulic machines to obtain qualified forgings. The basic processes of free forging include upsetting, drawing, punching, cutting, bending, twisting, misalignment and forging. Free forging is a hot forging method. 2) Die forging Die forging is pided into open die forging and closed die forging. The metal blank is pressed and deformed in a forging die having a certain shape to obtain a forged piece, and the die forging is generally used for producing a part having a small weight and a large batch size. Die forging can be pided into hot forging, warm forging and cold forging. Warm forging and cold forging are the future development directions of die forging, and also represent the level of forging technology. According to the material, die forging can also be pided into black metal die forging, non-ferrous metal die forging and powder product forming. As the name implies, the materials are ferrous metals such as carbon steel, non-ferrous metals such as copper and aluminum, and powder metallurgy materials. Extrusion should be attributed to die forging and can be pided into heavy metal extrusion and light metal extrusion. Closed die forging and closed upset forging are two advanced processes for die forging. Since there is no flash, the material utilization rate is high. Finishing of complex forgings is possible with one or several processes. Since there is no flash, the area of force applied to the forging is reduced and the required load is also reduced. However, care should be taken not to completely limit the blank. To this end, the volume of the blank is strictly controlled, the relative position of the forging die is controlled, and the forging is measured to reduce the wear of the forging die. 3) Rolling ring Rolling ring refers to the production of ring-shaped parts of different diameters by special equipment grinding machine, and also used to produce wheel-shaped parts such as automobile wheels and train wheels. 4) Special forging Special forging includes roll forging, cross wedge rolling, radial forging, liquid die forging, etc. These methods are more suitable for the production of parts with special shapes. For example, roll forging can be used as an effective preforming process to significantly reduce subsequent forming pressures; cross wedge rolling can produce steel balls, drive shafts, etc.; radial forging can produce large forgings such as barrels and step shafts. 5) Forging die According to the movement mode of the forging die, forging can be pided into pendulum, pendulum swivel, roll forging, cross wedge rolling, boring ring and cross rolling. Swing, swivel and shackle can also be used for precision forging. In order to improve the utilization of materials, roll forging and cross rolling can be used as a front-end process for slender materials. The same rotary forging as free forging is also partially formed, which has the advantage that it can be formed in the case of a smaller forging force than the forging size. This type of forging, including free forging, expands from the vicinity of the mold surface to the free surface during processing. Therefore, it is difficult to ensure accuracy. Therefore, the movement direction of the forging die and the swaging process can be controlled by computer. The forging force obtains products with complex shapes and high precision, such as forgings such as steam turbine blades with large variety and large size. The die motion and degree of freedom of the forging equipment are inconsistent. According to the characteristics of the bottom dead center deformation, the forging equipment can be pided into the following four forms: Limiting the form of forging force: hydraulic press that directly drives the slider. Quasi-stroke limit mode: hydraulic press that drives the crank-link mechanism. Stroke Limiting Mode: Mechanical presses that drive the slider with cranks, connecting rods and wedge mechanisms. Energy limiting method: a screw and friction press using a screw mechanism. In order to achieve high accuracy, care should be taken to prevent overload at the bottom dead center, control speed and mold position. Because these will have an impact on forging tolerances, shape accuracy and forging die life. In addition, in order to maintain accuracy, you should also pay attention to adjust the slider rail clearance, ensure the stiffness, adjust the bottom dead center and use the auxiliary transmission and other measures. There are also slider vertical and horizontal movements (for forging of the elongated parts, lubrication cooling and high-speed production of parts forging), the use of compensation devices can increase the movement in other directions. Different methods are used, the required forging force, process, material utilization, production, dimensional tolerance and lubrication cooling method are different. These factors are also factors that affect the level of automation. 3. Forging materials Forging materials are mainly carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium and the like and alloys thereof. The raw state of the material is bar, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation is called the forging ratio. Correct selection of forging ratio, reasonable heating temperature and holding time, reasonable initial forging temperature and final forging temperature, reasonable deformation amount and deformation speed have a great relationship to improve product quality and reduce cost. Generally, small and medium-sized forgings use round or square bars as blanks. The grain structure and mechanical properties of the bar are uniform and good, the shape and size are accurate, and the surface quality is good, which is convenient for mass production. As long as the heating temperature and deformation conditions are properly controlled, high-quality forgings can be forged without requiring large forging deformation. Ingots are only used for large forgings. The ingot is an as-cast structure with large columnar crystals and a loose center. Therefore, it is necessary to break the columnar crystal into fine crystal grains by large plastic deformation, and loosely compact, in order to obtain excellent metal structure and mechanical properties. The powder metallurgy preform which is pressed and sintered can be made into a powder forging by hot forging without flashing. Forging powder is close to the density of general die forgings, has good mechanical properties, and has high precision, which can reduce subsequent cutting. The powder forgings have a uniform internal structure and are not segregated and can be used to manufacture workpieces such as small gears. However, the price of powder is much higher than the price of ordinary bars, and its application in production is limited. By applying static pressure to the liquid metal poured in the mold to solidify, crystallize, flow, plastically deform and form under pressure, a die forging of desired shape and properties can be obtained. Liquid metal die forging is a forming method between die casting and die forging, and is particularly suitable for complex thin-walled parts which are difficult to form by general die forging. Forging materials in addition to the usual materials, such as various components of carbon steel and alloy steel, followed by aluminum, magnesium, copper, titanium and other alloys, iron-based superalloys, nickel-based superalloys, cobalt-based superalloys The deformed alloys are also finished by forging or rolling, except that the alloys are relatively narrow in plasticity, so the forging difficulty is relatively large, and the heating temperature, opening and forging temperature and final forging temperature of different materials have strict requirements. 4. The process Different forging methods have different processes, wherein the hot forging process has the longest process, and the general sequence is: forging blanking; forging billet heating; roll forging stock; die forging; trimming; punching; Intermediate inspection, inspection of the dimensions and surface defects of forgings; forging heat treatment, to eliminate forging stress, improve metal cutting performance; cleaning, mainly to remove surface oxide scale; correction; inspection, general forgings to pass the appearance and hardness inspection, important forgings It is subject to chemical composition analysis, mechanical properties, residual stress and other tests and non-destructive testing. 5. Forging features Compared with castings, metals can improve their microstructure and mechanical properties after forging. After the hot-working deformation of the cast structure by the forging method, the original coarse dendrites and columnar grains become the equiaxed recrystallized structure with fine grains and uniform size due to the deformation and recrystallization of the metal, so that the original segregation in the steel ingot, The compaction and welding of loose, stomata and slag inclusions make the structure more compact and improve the plasticity and mechanical properties of the metal. The mechanical properties of castings are lower than those of forgings of the same material. In addition, the forging process can ensure the continuity of the metal fiber structure, so that the fiber structure of the forging is consistent with the shape of the forging, and the metal streamline is complete, which can ensure the good mechanical properties and long service life of the part by precision die forging and cold extrusion. Forgings produced by processes such as warm extrusion are incomparable to castings. A forging is an object to which a metal is pressed to shape a desired shape or a suitable compressive force by plastic deformation. This power is typically achieved by using a hammer or pressure. The forging process creates a refined grain structure and improves the physical properties of the metal. In the practical use of components, a correct design enables the particles to flow in the direction of the main pressure. The casting is a metal molded object obtained by various casting methods, that is, the smelted liquid metal is poured into a pre-prepared mold by pouring, injecting, inhaling or other casting method, and after cooling, after falling sand, cleaning and then Processing, etc., the resulting article with a certain shape, size and performance. Source: China Welded Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The finished products of seamless precision steel pipe will have the problem of uneven eccentric thickness. But how is it produced? Many people have not figured out. Today we will talk about cold drawn steel pipe, cold-rolled steel pipe, hot-rolled steel pipe, etc. The eccentricity of seamless seam steel pipe is generated. Why is the concentricity of seamless steel pipe not so ideal? The existence form and severity of uneven wall thickness of perforated capillary tube directly affect the existence and severity of uneven wall thickness of steel pipe after rolling. When rolling the pipe on the automatic pipe rolling machine, the top rod is bent away, the head position is deviated from the center of the hole type, resulting in uneven wall thickness, and the maximum wall thickness and minimum wall thickness position in the cross section of the pipe and the pipe head are almost fixed. The same is true; the unevenness of the wall thickness from the tube end to the tube head is gradually increased. Therefore, reducing the residual curvature of the ram and reducing the axial force of the ram when rolling the tube is significant for reducing the unevenness of the wall thickness. effect. The larger the wall reduction, the more serious the wall thickness of the waste pipe is. When the wall reduction is small, the automatic pipe rolling machine has the effect of reducing the wall thickness unevenness of the perforated pipe. 4 hole type adjustment is not correct, when the roll gap is not parallel, the wall thickness of the waste pipe will be intensified. Our seamless steel tube plant performed a Fourier transform on the measured wall thickness data of Φ400mm automatic tube rolling mill, perforation, secondary perforation (extension), automatic rolling and uniform rolling process, and obtained uneven wall thickness. The quantitative analysis and the reasons for its formation, and based on this, proposed ways to improve the uneven wall thickness of steel pipes: After the secondary perforation (extension), the distribution of the uneven wall thickness on the waste pipe is retained to the finished pipe, so improving the secondary perforation (extension) is the key link to improve the wall thickness accuracy of the finished pipe. The main measure is to improve The tool is designed to increase the concentricity of the ram and the head with the rolling line during the rotation. Improving the uneven thickness of the capillary tube after perforation is an important part. The main measures are to improve the heating uniformity of the tube blank, improve the precision of the centering hole, lengthen the length of the entire belt and the length of the reverse cone, and improve the ejector and the head. Concentricity with the rolling line during the rotation. Although there is a serious symmetry wall thickness unevenness during rolling, it does not have a certain effect on reducing the spiral wall thickness. Therefore, two tubes should be rolled during the rolling process, and the waste pipe should be turned over 90° between the passes. The leveling process can basically eliminate the symmetry wall thickness unevenness, but the effect of eliminating the spiral wall thickness unevenness is very small. Therefore, the capacity of the leveling machine should be improved. Fourier transform is an effective means to study the uneven wall thickness during the cross-rolling process. This method can also be used to study the uneven wall thickness of other steel tube production units. Head shape design, the ideal head rolling cone should be parallel with the roll exit cone. If the head is designed according to the traditional Matviev formula, the rolling cone of the head is not parallel with the exit cone of the roll, the metal is Such a gradually enlarged deformation in the gap will inevitably result in insufficient tube wall rolling and uneven wall thickness of the capillary tube, and the wall thickness unevenness of the capillary tube is more serious with the increase of the feeding angle; Due to the insufficient rigidity of the ram, bending occurs during the perforation process, so that the head cannot maintain the centering position, so that the wall thickness of the piercing capillary is uneven; Uneven wear or damage to the head. (2) Guide plate. The distance between the guide plates is too large. During the perforation process, the centering of the perforations is maintained by the restriction of the guide plates. The distance between the guide plates is large, and the heads are greatly changed in the upper and lower positions, which makes the head unstable, resulting in uneven wall thickness of the capillary tubes. The uneven wear of the upper and lower guide plates also aggravates the uneven thickness. (3) Rolls. Roll centerline deflection: During the production process, the screws on both sides of the puncher are not installed correctly, or the axial deflection occurs between the two rollers due to the thread and bearing wear. The feed angles of the two rolls are inconsistent. Distortion of the deformation zone results in uneven wall thickness. Large feed angles cause the head to be more parallel with the rolling cone of the roll. Improper roll speed will also affect the wall thickness accuracy. (4) Centering and heating of the tube blank. Centering hole eccentricity and uneven heating (yin and yang) will cause uneven wall thickness. (5) Stiffness, structure and adjustment of the punch. The rigidity of the punching machine is not enough, and the locking mechanism on it is not reliable; the centering device of the ejector is inaccurately adjusted, the operation is unreliable and the distance from the fuselage is far; the adjustment of the rolling center line is generally lower than the center line of the rolling mill. The purpose is to improve the stability of the rolled piece. If the adjustment is too large, the relative relationship between the tools in the deformation zone will change asymmetrically after the rolling line moves down, which will also affect the uneven wall thickness of the capillary. Summarize: In summary, the uneven thickness of the eccentricity of the seamless steel pipe is not completely avoided, and can only be strictly controlled step by step. If you have any thoughts on our analysis, please leave a message for us to discuss. Source: China Seamless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Duplex stainless steel has been continuously developed and improved over the years, and some fields have replaced austenitic stainless steel. In recent years, the use of super duplex stainless steel has also created favorable conditions for expanding the use of duplex stainless steel and developing new steel grades. Duplex stainless steel not only has the commonality of ordinary stainless steel, but also has its own characteristics. The performance requirements and limitations of using duplex stainless steel are detailed below. First of all, to control the gold ratio, the most suitable ratio is that the ferrite phase and the austenite phase each account for about 50%, and the maximum number of one phase cannot be greater than 65%, so as to ensure the best overall performance. If the two ratios are out of tune, it is very easy to form a single-phase ferrite in the welded HAZ, which may be sensitive to stress corrosion cracking in the medium. Secondly, it is necessary to master the metallographic transformation of duplex stainless steel and familiarize with the TTT and CCT transition curves of each steel grade, which is very important for correctly guiding the process of heat treatment and thermoforming of duplex stainless steel. Third, the continuous use temperature range of duplex stainless steel is -50 ° C to 250 ° C, the lower limit is subject to the brittle transition temperature of stainless steel, the upper limit is limited by the brittleness of 475 ° C, and the upper limit temperature should not exceed 300 ° C. Fourth, the duplex stainless steel should be directly cooled quickly after solution treatment. Slow cooling will lead to the precipitation of brittle phase, which will reduce the toughness and local corrosion resistance of stainless steel. Fifth, the lower limit temperature of hot working and thermoforming of high chromium molybdenum duplex stainless steel shall not be less than 950 °C, super duplex stainless steel shall not be less than 980 °C, and low chromium molybdenum duplex stainless steel shall not be less than 900 °C to prevent precipitation due to brittle phase. Surface cracks are caused during processing. Sixth, it is not possible to use 650-800 ° C commonly used in austenitic stainless steel to eliminate stress treatment, usually using solution annealing treatment. For the double-phase stainless steel after surfacing the surface of low-alloy steel, it is necessary to consider the toughness and corrosion resistance due to the precipitation of the brittle phase, especially the local corrosion resistance, when performing the overall treatment at 600-650 °C. Reduce the problem and minimize the heating time in this temperature range. Seventh, the point is to master the welding rules of duplex stainless steel. The equipment of duplex stainless steel can be safely used and has a great relationship with the welding process. Some equipment failures are usually related to welding. The key is the control of line energy and interlayer temperature. It is also important to choose the right solder material. Finally, when using duplex stainless steel in different corrosive environments, it is necessary to understand that the corrosion resistance of stainless steel is relative, and there are certain applicable conditions, which are affected by temperature, pressure, medium concentration and the like. Therefore, pay special attention to the selection of materials. Source: China Duplex Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The quality problems caused by heat treatment of steel pipes are mainly reflected in several aspects (performance, organization, defects, size, surface, etc.). 1 Performance and organizational issues Performance and organization issues, depending on the composition and original state of the material, as well as the rationality of the heat treatment process and the level of process control, are the core of heat treatment quality control. If the heat treatment process is not well developed or implemented, the properties of the pipe (such as yielding, tensile strength, elongation) will exceed the requirements stipulated by the standard; for the organization, there will be tissues that are not allowed by standards such as weiss body and band. 2 Size problem It mainly shows the curvature in the longitudinal direction (axial direction) and the ellipticity and outer diameter of the cross-sectional direction (radial). 2.1 Causes of bending of steel pipes 2.1.1 Uneven heating of steel pipes produces bending The heating of the steel pipe is uneven, the temperature is different along the axial direction of the pipe, the microstructure transformation time is different during quenching, and the volume change time of the steel pipe is different, resulting in bending. 2.1.2 Steel pipe quenching produces bending Quenching is the preferred heat treatment method for high strength casing and high steel grade line pipe production. The microstructure changes very rapidly during quenching, and the structural transformation of the steel pipe causes a change in volume. Since the cooling rate of each part of the steel pipe is inconsistent, the speed of the tissue transformation is inconsistent, and bending also occurs. 2.1.3 Pipe blank causes bending If the chemical composition of the steel pipe is segregated, even if the cooling conditions are completely the same, bending will occur during cooling. 2.1.4 Uneven cooling causes bending After the heat treatment of the alloy steel pipe, the steel pipe is usually cooled naturally while rotating. At this time, the axial and circumferential cooling rates of the steel pipe are not uniform, and bending occurs. If the bending of the steel pipe does not meet the requirements, it will affect the subsequent processing (such as transportation, straightening, etc.) and even affect its performance. 2.1.5 Bending on the sizing machine Alloy steel pipes, especially those with narrow outer diameter tolerances (such as line pipes and casings), generally require sizing after tempering. If the centerline of the sizing rack is inconsistent, the steel pipe will bend. 2.2 The main reason for the ellipticity and outer diameter of steel pipes When quenching, the structural transformation of the steel pipe is inconsistent, the steel pipe will produce ellipticity; due to the ellipticity, most steel pipes need to be sized after quenching and tempering. If the sizing control process is not good, the outer diameter will appear super difference. 3 Defects and surface problems 3.1 Quenching crack of steel pipe The quenching heating temperature of the steel pipe is too high, or the heating time is too long, or the heating temperature is severely uneven, which may cause quenching cracks. If the chemical composition of the steel pipe is segregated, the steel pipe may be mixed and easily cause quenching cracks. 3.2 Overheating or overheating of steel pipes If the quenching heating temperature of the steel pipe is too high or the heating time is too long, it may cause overheating or overheating. In severe cases, the steel pipe may collapse. 3.3 Surface decarburization or severe oxidation of steel pipes When the steel pipe is heated, the surface is seriously decarburized or severely oxidized due to improper control of heating temperature and heating time or adjustment of air-fuel ratio. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Online normalization is a heat treatment process developed in recent years, namely deformation and normalization. It is a steel pipe after rolling the continuous rolling pipe, cooled to a recrystallization temperature on a cold bed, and then reheated the furnace. After heating the steel pipe to a temperature of Ac3 or above in the furnace, it is kept for a period of time to make the metallographic phase of the steel. The structure is transformed into austenite, and then discharged, and the austenite structure is transformed into pearlite by the sizing machine or the reduction machine after air reduction or air cooling, fog cooling, etc., thereby realizing the performance of the steel pipe, which is modern control. Rolling scheme. Online normalization performance requirements: While achieving the strength requirements, it achieves excellent matching of toughness and strength, has good weldability, and has excellent low temperature toughness. The purpose of online normalization: (1) making the structure of the steel uniform and grain refining; (2) Improve the mechanical properties of some steel grades; (3) Improve the metallographic structure and properties of low carbon steel and low alloy steel to create conditions for the diffusion of alloying elements. The ferrite plus pearlite structure is exhibited under a metallographic microscope. If it is a microalloyed steel, a precipitated phase and a second phase particle can be observed under a transmission electron microscope. On-line normalization is to insert a normalizing process in the middle of the rolling process, and use part of the rolling residual heat to shorten the normalizing heating time. Microalloyed on-line normalized steel replaces off-line normalizing or modulating steel, reducing costs associated with heat treatment, finishing, energy, decarburization, and iron loss (oxidation). In short, online normalization not only simplifies the process but also saves energy. Compared with quenched and tempered steel, on-line normalized steel has better cutting performance because the ferrite pearlite structure has better cutting performance than the tempered sorbite structure. Online process description: The rolled steel is cooled to below Ar1, and all of the austenite is transformed into a ferrite pearlite structure, that is, reheated, and all transformed into austenite, and air-cooled to obtain a relatively fine ferrite pearlite structure. According to the size of the workpiece, determine the cooling time before entering the reheating furnace, ensure that the temperature is below the Ar1 temperature, determine the time of the workpiece in the reheating furnace, ensure that the alloy dissolves, the microstructure is transformed into austenite, and homogenized. Set the reheater temperature. In order to dissolve all the gold elements into the austenite and homogenize the austenite, the workpiece in the furnace should be kept in the specified heating temperature range for a suitable period of time, the length of the workpiece and the effective thickness of the workpiece, the steel grade, and the loading. The furnace method, the amount of furnace charge, the temperature of the furnace, the performance of the furnace and the degree of sealing are related. Different cooling methods mean different cooling speeds of the workpiece, such as stack cooling, side-by-side cooling, workpiece spacing, cold, single cooling, and cooling rate from small to large. Generally, the grain size decreases, the percentage of pearlite increases, and pearlescence The spacing of the body sheets is reduced, resulting in an increase in strength and impact toughness. The holding time of the workpiece in the reheating furnace is an indispensable control parameter. The holding time is insufficient, the strength is not up to the requirement, the holding time is too long, energy is wasted, the production efficiency is lowered, and the surface of the workpiece may be decarburized. Before the online normalizing steel enters the reheating furnace, it undergoes a staged rolling process, and each part of the workpiece must complete the transformation of the austenite to the entire microstructure of the ferrite pearlite, so the part where the workpiece is cooled relatively slowly is also Must be cold below Ar1. The control of the temperature of the reheating furnace is critical to the performance of the steel. The reheating furnace heats the workpiece, not only to ensure the necessary tissue transformation and diffusion, but also to dissolve all the alloying elements in the austenite. The temperature is low, the strength is insufficient, the temperature is high, the toughness is lowered, and the temperature is too high and the strength is also lowered. Microalloying elements are added to steel for two purposes, namely grain refinement and precipitation strengthening. Both effects are caused by the precipitation of microalloyed carbides, nitrides or carbonitrides. Online normalization causes bending: In the (reheating furnace) cold bed bending, the steel tube itself is inconsistent in structural transformation, which is the cause of bending. Some steels not only obtain ferrite pearlite at a certain cooling rate, but also produce a part of bainite structure, bainite. The tissue stress is large, and the steel pipe is partially cooled first, and the portion where the bainite is first generated may be bent. Bending occurs after entering the reheating furnace. This is because the inlet of the steel tube in the reheating furnace is difficult to maintain the temperature of other parts. When the temperature of the tube is too low, the higher furnace temperature in the furnace will increase the thermal stress of the tube sharply. When the furnace condition is not ideal, the tube is not ideal. The different parts will have a large difference in thermal stress due to the inconsistent temperature inside the furnace. This causes the tube to bend. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

There are thousands of varieties of steel pipes used in various industries. Each steel tube has a different trade name for its different properties, chemical composition or alloy type and content. Although the fracture toughness value greatly facilitates the choice of each steel, these parameters are difficult to apply to all steel pipes. The main reasons are as follows: First, because a certain amount of one or more alloying elements need to be added during the smelting of steel, different microstructures can be obtained by simple heat treatment after the material is formed, thereby changing the original properties of the steel; Second, because the defects generated during steel making and casting, especially concentrated defects (such as pores, inclusions, etc.) are extremely sensitive during rolling, and between different heats of the same chemical composition steel, even in the same steel billet Different parts change differently, which affects the quality of the steel pipe. Because the toughness of steel pipes depends mainly on the microstructure and the dispersion of defects (strictly preventing concentrated defects), rather than chemical composition. Therefore, the toughness changes greatly after heat treatment. To further explore the properties of steel pipes and the causes of their fractures, it is also necessary to understand the relationship between physical metallurgy and microstructure and toughness of steel pipes. 1. Ferrite-pearlite steel fracture Ferritic-pearlite steel accounts for the vast majority of total steel production. They are typically iron-carbons containing between 0.05% and 0.20% carbon and alloys of other small alloying elements added to improve yield strength and toughness. The microstructure of the ferrite-pearlite consists of BBC iron (ferrite), 0.01% C, soluble alloy and Fe3C. In carbon steels with very low carbon content, cementite particles (carbides) remain in the ferrite grain boundaries and grains. However, when the carbon content is higher than 0.02%, most of Fe3C forms a sheet-like structure with some ferrite, which is called pearlite, and tends to be a “grain” and a ball node (grain boundary precipitate). Dispersed in the ferrite matrix. In the microstructure of low carbon steel with a carbon content of 0.10% to 0.20%, the pearlite content accounts for 10% to 25%. Although the pearlite particles are very hard, they are very widely dispersed on the ferrite matrix and are easily deformed around the ferrite. Generally, the grain size of ferrite decreases as the pearlite content increases. Because the formation and transformation of pearlite balls can hinder the growth of ferrite grains. Therefore, the pearlite will indirectly increase the tensile yield stress δy by raising d-1/2 (d is the average grain diameter). From the point of view of fracture analysis, there are two types of steel in the range of carbon content in low carbon steel, and its performance is of concern. First, the carbon content is below 0.03%, carbon exists in the form of pearlite ball joints, and has little effect on the toughness of steel. Second, when the carbon content is high, the toughness and Xiabi are directly affected by the spheroidal form. curve. 2. The impact of the process It has been found that the impact performance of water-hardened steel is better than that of annealed or normalized steel because the rapid cooling prevents the formation of cementite at the grain boundary and promotes the grain size of the ferrite. Many steel pipes are sold under hot rolling conditions, and rolling conditions have a great influence on impact properties. Lower finish rolling temperatures reduce the impact transition temperature, increase the cooling rate and promote the grain thinning of the ferrite, thereby increasing the toughness of the steel tube. The thick plate is slower than the thin plate because of the cooling rate, and the ferrite grain is thicker than the thin plate. Therefore, the thick plate is more brittle than the thin plate under the same heat treatment conditions. Therefore, normalizing treatment is often used after hot rolling to improve the performance of the steel sheet. Hot rolling can also produce anisotropic steel and various mixed structures, pearlite strips, and oriented ductile steel with the same grain boundary and rolling direction. The pearlite band and the elongated inclusions are coarsely dispersed into scales, which have a great influence on the notch toughness at the low temperature range of the Charpy transition temperature range. 3. Effect of ferrite-soluble alloying elements Most alloying elements are added to low carbon steel in order to produce solid solution hardened steel at certain ambient temperatures, increasing the lattice frictional stress δi. However, it is currently not possible to predict lower yield stresses using only formulas unless the grain size is known. Although the determinants of yield stress are normalizing temperature and cooling rate, this method of research is still important because the range of toughness can be reduced by predicting a single alloying element by increasing δi. The regression analysis of the non-plastic transition (NDT) temperature and the Charpy transition temperature of ferritic steel has not been reported so far, but these are also limited to the qualitative discussion of the effect of adding a single alloying element on toughness. The following is a brief introduction to the effects of several alloying elements on the properties of steel. 1) Manganese. The vast majority of manganese is about 0.5%. The addition of a deoxidizer or a sulfur-fixing agent prevents thermal cracking of the steel. The following effects are also found in low carbon steel. ◆ Carbon-containing 0.05% steel, after air cooling or furnace cooling, has a tendency to reduce the formation of cementite film at grain boundaries. ◆ The ferrite grain size can be slightly reduced. ◆ Produces a large number of fine pearlite particles. The first two actions indicate that the NDT temperature decreases as the amount of manganese increases, and the latter two effects cause the peak of the Charpy curve to be sharper. When steel has a high carbon content, manganese can significantly reduce the transition temperature by about 50%. The reason may be due to the large amount of pearlite, rather than the distribution of cementite at the boundary. It must be noted that if the carbon content of the steel is higher than 0.15%, the high manganese content plays a decisive role in the impact properties of normalized steel. Because of the high hardenability of steel, austenite transforms into brittle upper bainite rather than ferrite or pearlite. 2) Nickel. The effect of adding steel to manganese is to improve the toughness of the iron-carbon alloy. The size of the action depends on the carbon content and heat treatment. In steels with a low carbon content (about 0.02%), the addition of 2% can prevent the formation of cemented cementite in the hot-rolled state and normalized steel, while substantially reducing the initial transition temperature TS and increasing the Charpy impact. Curve peak. Further increase in nickel content and improvement in impact toughness are reduced. If the carbon content is low until no carbide occurs after normalizing, the effect of nickel on the transition temperature will become very limited. The addition of nickel to normal-fired steel containing about 0.10% carbon has the greatest benefit of refining the grains and reducing the free nitrogen content, but the mechanism is still unclear. It may be due to the fact that nickel acts as a stabilizer for austenite, thereby lowering the temperature at which austenite decomposes. 3) Phosphorus. In a pure iron-phosphorus alloy, phosphorus segregation due to ferrite grain boundaries reduces the tensile strength Rm and causes intergranular embrittlement. In addition, since phosphorus is also a stabilizer for ferrite. Therefore, adding steel will greatly increase the δi value and the ferrite grain size. The combination of these effects will make phosphorus an extremely harmful embrittlement agent, undergoing transgranular fracture. 4) Silicon. Silicon is added to the steel for deoxidation and is beneficial for improving impact properties. If both manganese and aluminum are present in the steel, most of the silicon is dissolved in the ferrite, and δi is increased by solid solution hardening. The combined effect of this effect and the addition of silicon to enhance the impact properties is that silicon is added in weight percent in a stable grain size iron-carbon alloy, raising the 50% transition temperature by about 44 °C. In addition, silicon is similar to phosphorus and is a stabilizer for ferrite, which promotes ferrite grain growth. Addition of silicon to normalized steel by weight percent will increase the average energy conversion temperature by about 60 °C. 5) Aluminum. There are two reasons for the addition of alloys and deoxidizers to the steel: first, the formation of AlN with nitrogen in the solution to remove free nitrogen; second, the formation of AlN refines the ferrite grains. The result of both of these effects is that for every 0.1% increase in aluminum, the transition temperature is lowered by about 40 °C. However, when the amount of aluminum added exceeds the need, the effect of “cure” free nitrogen will be weakened. 6) Oxygen. Oxygen in the steel causes segregation at the grain boundaries resulting in intergranular fracture of the iron alloy. The oxygen content of the steel is as high as 0.01%, and the fracture occurs along a continuous channel created by the grain boundaries of the embrittled grains. Even if the oxygen content in the steel is very low, the crack will nucleate at the grain boundary and then diffuse through the crystal. The solution to the problem of oxygen embrittlement is to add deoxidizers carbon, manganese, silicon, aluminum and zirconium to combine with oxygen to form oxide particles, and to remove oxygen from the grain boundaries. Oxide particles are also advantageous materials for retarding ferrite growth and increasing d-/2. 4. The effect of carbon content in the range of 0.3% to 0.8% The carbon content of the hypoeutectoid steel is between 0.3% and 0.8%, and the pro-eutectoid ferrite is a continuous phase and is first formed at the austenite grain boundary. Pearlite is formed in austenite grains and accounts for 35% to 100% of the microstructure. In addition, a variety of aggregated structures are formed in each austenite grain to make the pearlite polycrystalline. Since the pearlite strength is higher than that of the pro-eutectoid ferrite, the flow of the ferrite is limited, so that the yield strength and the strain hardening rate of the steel increase as the carbon content of the pearlite increases. The limiting effect increases with the number of hardened blocks, and the pearlite is enhanced by the refinement of the pre-eutectoid grain size. When there is a large amount of pearlite in the steel, micro-cleavage cracks are formed at low temperatures and/or high strain rates during the deformation process. Although there are some internal aggregated tissue sections, the fracture channels initially travel along the cleavage plane. Therefore, there are some preferred orientations within the ferrite grains between the ferrite sheets and adjacent aggregated structures. 5. Bainitic steel fracture Adding 0.05% molybdenum and boron to a low carbon steel with a carbon content of 0.10% optimizes the austenite-ferrite transformation, which usually occurs at 700 to 850 °C, without affecting the austenite at 450 ° C and 675 ° C thereafter. Kinetic conditions for bulk-bainite transformation. Bainite formed between about 525 and 675 ° C is generally referred to as “upper bainite”; and formed between 450 and 525 ° C is called “lower bainite”. Both tissues consist of acicular ferrite and dispersed carbides. When the transition temperature is lowered from 675 ° C to 450 ° C, the tensile strength of untempered bainite will increase from 585 MPa to 1170 MPa. Because the transition temperature is determined by the alloying element content and indirectly affects the yield and tensile strength. The high strength obtained by these steels is the result of two actions: 1) When the transition temperature is lowered, the bainitic ferrite sheet size is continuously refined. 2) Fine carbides are continuously dispersed in the lower shell. The fracture characteristics of these steels depend to a large extent on tensile strength and transition temperature. There are two roles to note: First, a certain level of tensile strength, the Charpy impact performance of bainite under tempering is far superior to the untempered upper bainite. The reason is that in the upper bainite, the cleavage facet in the spheroidal light cuts a number of bainite grains, and the main size determining the fracture is the austenite grain size. In the lower bainite, the cleavage plane in the acicular ferrite is not aligned, so the main feature that determines whether the quasi-cleavage fracture surface is broken is the acicular ferrite grain size. Because the acicular ferrite grain size here is only 1/2 of the austenite grain size in the upper bainite. Therefore, at the same strength level, the lower bainite transformation temperature is much lower than that of the upper bainite. In addition to the above reasons, the carbide distribution. In the upper bainite, the carbide is located along the grain boundary and increases the brittleness by lowering the tensile strength Rm. In the tempered lower bainite, the carbides are distributed very uniformly in the ferrite, while at the same time increasing the tensile strength and promoting the spheroidized pearlite refinement by limiting the cleavage cracks. Second, it is important to note the change in transition temperature and tensile strength in untempered alloys. In the upper bainite, a decrease in the transition temperature causes the acicular ferrite to refine the size while increasing the elongational strength Rp0.2. In the lower bainite, in order to obtain a tensile strength of 830 MPa or more, it can also be achieved by a method of lowering the transformation temperature and increasing the strength. However, since the fracture stress of the upper bainite depends on the austenite grain size, and the carbide particle size at this time is already large, the effect of improving the tensile strength by tempering is small. 6. Martensitic steel fracture The addition of carbon or other elements to the steel delays the transformation of austenite into ferrite and pearlite or bainite. At the same time, if the cooling rate is fast enough after austenitizing, the austenite will become martensite by the shearing process. Without atomic diffusion. An ideal martensite fracture should have the following characteristics. ◆ Because the transition temperature is very low (200 ° C or lower), tetrahedral ferrite or acicular martensite is very fine. ◆ Because the transformation occurs by shearing, the carbon atoms in the austenite are too late to diffuse out of the crystal, so that the carbon atoms in the ferrite are saturated and the martensite grains are elongated to cause lattice expansion. ◆ The martensite transformation takes place over a certain temperature range because the initially formed martensite sheet increases the resistance of the subsequent austenite to martensite. Therefore, the transformed structure is a mixed structure of martensite and retained austenite. In order to ensure the stability of the steel, tempering must be carried out. High carbon (0.3% or more) martensite, tempered for about 1 hour in the following range, and went through the following three stages. 1) When the temperature reaches about 100 ° C, some supersaturated carbon of martensite precipitates and forms very fine ε-carbide particles, which are dispersed in martensite to reduce the carbon content. 2) The temperature is between 100 and 300 ° C, and any retained austenite may be transformed into bainite and ε-carbide. 3) In the third stage of tempering, approximately 200 ° C depends on the carbon content and alloy composition. When the tempering temperature rises to the eutectoid temperature, the carbide precipitate becomes coarse and Rp0.2 decreases. 7. Medium strength steel fracture In addition to eliminating stress and improving impact toughness, tempering has two effects: First, transform the retained austenite. The retained austenite will transform into a tough acicular lower bainite at a low temperature of about 30 °C. At higher temperatures, such as 600 ° C, the retained austenite transforms into brittle pearlite. Therefore, the steel is first tempered at 550 to 600 ° C, and the second tempering is performed at 300 ° C to avoid the formation of brittle pearlite, which is called “secondary tempering”. Second, increase the diffuse carbide content (increased tensile strength Rm) and reduce the yield strength. If the tempering temperature is raised, both will cause an impact and the transition tempering range will decrease. Because the microstructure becomes fine, at the same strength level, the tensile plasticity will be improved. Temper brittleness is reversible. If the tempering temperature is high enough to exceed the critical range and the transition temperature is lowered, the material can be reheated and treated in the critical range before the tempering temperature can be raised. If trace elements appear, it indicates that the brittleness will be improved. The most important trace elements are bismuth, phosphorus, tin, and arsenic, plus both manganese and silicon have a brittle effect. If other alloying elements are present, molybdenum can also reduce temper brittleness, while nickel and chromium also have a certain effect. 8. High strength steel (Rp0.2>1240MPa) fracture High-strength steel can be produced by the following methods: quenching and tempering; austenite deformation before quenching and tempering; annealing and aging to produce precipitation hardened steel. In addition, the strength of the steel can be further increased by strain and re-tempering or tempering strain. 9. Stainless steel break Stainless steel is mainly composed of iron-chromium, iron-chromium-nickel alloys and other elements that improve mechanical properties and corrosion resistance. Stainless steel corrosion protection is due to the formation of a chromium oxide-impermeable layer on the metal surface that prevents further oxidation. Therefore, the stainless steel can prevent corrosion in the oxidizing atmosphere and strengthen the chromium oxide layer. However, in the reducing atmosphere, the chromium oxide layer is damaged. The corrosion resistance increases as the content of chromium and nickel increases. Nickel can improve the passivation of iron. Carbon is added to improve mechanical properties and to ensure the stability of austenitic stainless steel properties. In general, stainless steel is classified using microstructure. ◆ Martensitic stainless steel. It belongs to iron-chromium alloy and can be austenitized and post-processed to form martensite. It usually contains 12% chromium and 0.15% carbon. ◆ Ferritic stainless steel. Containing about 14% to 18% chromium and 0.12% carbon. Because chromium is a stabilizer for ferrite, the austenite phase is completely inhibited by more than 13% chromium and is therefore completely Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Common weld molding defects in stainless steel pipes include incomplete penetration, unmelted table, burn through, undercut and weld. The cause of these defects is often caused by improper groove size, improper selection of welding process specifications, or misalignment of the weld wire to the center of the weld. Incomplete penetration: The phenomenon that the joint root is not completely penetrated during welding is called incomplete penetration. Stainless steel water pipes can cause such defects in both single-sided and double-sided welding. The main reason for the formation of incomplete penetration is that the welding current is small or the welding speed is too high, or the groove size is not suitable and the welding wire is not aligned with the center of the weld. Unfused: When welding, the part of the stainless steel pipe weld metal and the base metal or between the weld bead and the weld bead is not completely fused. Unfused can be pided into sidewalls that are not fused, layers that are not fused, and roots that are not fused. The molten pool metal is discharged to the tail under the action of the arc force to form a groove. When the arc moves forward, the groove is filled with liquid metal. If the liquid metal layer at the groove wall has solidified, the liquid is filled. The heat of the metal is not sufficient to cause it to melt again, resulting in unfused. In the case of submerged arc welding, slag inflow occurs in the fusion zone. In order to prevent such defects during high-speed welding, it is necessary to increase the melting width or use double arc welding. Burn through: When the stainless steel pipe is welded, the molten metal flows out from the back of the weld, and the phenomenon of forming a perforation is called burn through. Stainless steel pipe welding current is too large, the welding speed is too small or the groove gap size is too large, etc. may form such defects. Undercut: The phenomenon that the stainless steel water pipe is formed along the base material of the weld toe to form a depression or a groove is called a undercut. The undercut may be continuous or intermittent. Stainless steel water pipes may cause such defects during high current high speed welding. This type of defect can also occur if the mishandling is done while welding the butt joint. Welded metal: The metallurgy formed by the molten metal flowing into the unmelted base metal outside the weld when the stainless steel pipe is welded is called a weld bead. There is local fusion at the weld. The weld is caused by too much filler metal, which is related to the small gap and groove size, low welding speed, small voltage or large wire extension length. Unfilled: Stainless steel water pipes are formed by continuous or intermittent grooves on the weld surface due to insufficient filler metal during welding. Collapse: Excess metal that collapses through the root of the weld is called collapse. Stainless steel water pipes, in addition to the above defects, in addition to the above defects, there are back shrinkage grooves, poor profile, super high, surface irregularities, surface pores, root pores, poor weld joints, arc scratches, splashes, etc. Weld molding defects, mostly due to improper welding processes. Therefore, the development of a suitable stainless steel pipe welding process, careful operation can fundamentally prevent the occurrence of weld molding defects. In addition, it is very important to take timely contingency measures when certain process conditions change during stainless steel pipe welding. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)