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Hot rolling is rolling in stainless steel above the recrystallization temperature of the casting process, the organization will destroy the ingot, steel grain refinement, but also eliminate the defect microstructure of stainless steel, to make the organization more dense, improve mechanical properties. Such improvements generally reflected along the rolling direction, will make the stainless steel to a certain extent is not isotropic, formed in high temperature and pressure will be welded pouring when bubbles, cracks and loose. Production process of hot rolled stainless steel tube The production process of hot rolled seamless steel tube mainly includes the preparation of billet before rolling, tube billet heating, piercing, rolling, sizing and cooling, finishing and other basic processes. There are three deformation processes for producing seamless hot rolled seamless tubes: piercing, rolling and sizing. Here is to introduce the purpose and requirements of these processes. Hot rolling stainless steel tube production perforation The solid stainless steel tube is made into a hollow capillary, which is shaped, and the section of the rolled piece is round and circular. This equipment is a piercing mill. The perforation process requirements, we must first ensure that the capillary wall and out of uniform thickness, small ellipticity, geometric size and high precision; followed by the inner and outer surface of stainless steel shell should be smooth, can not have the defects of scarring, folding, crack; the third is to have perforation speed and rolling cycle corresponding to the entire process. Set the pace of production, increase the capillary finishing temperature can meet the requirements of pipe rolling machine. Hot rolling stainless steel tube production rolling tube The thick wall of the tube into a thin wall of the pipe; that is, fixed wall, is based on the subsequent process of reducing diameter and empirical formula to determine the wall thickness of the process pipe, this machine is rolling machine. The requirements of the rolling pipe processing technology are: first, when the thick wall tube is turned into thin wall pipe, it is necessary to ensure the wall thickness uniformity of the waste pipe is higher; secondly, the quality of the inner and outer surface of the pipe is better. Production and reduction of hot rolled stainless steel tube The big round of stainless steel tube is small round, that is fixed diameter, the corresponding equipment called fixed (minus) diameter machine. For reducing sizing process requirements are: first of all to the total reduction rate and smaller diameter of a single stand diameter reduction rate conditions to achieve sizing, then can realize the use of a standard tube production of various specifications of the finished pipe, the surface quality of steel pipe also can be further improved. Source: China Stainless Steel Tube Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

By eliminating the work hardening of the stainless steel tube, satisfactory metallographic structure can be obtained, and the process equipment is bright annealing furnace, which is mainly used for heat treatment of the finished stainless steel products under the protective atmosphere. When the stainless steel pipe performance requirements are different, the requirements of the microstructure after bright annealing are different, so the process of bright heat treatment will also be different. The typical heat treatment process of 300 series austenitic stainless steel tube is solution treatment. In the heating process of the carbide into austenitic stainless steel is heated to 1050 to 1150 DEG C, the thermal insulation for a short time, can put all the carbides dissolved in austenite, and then rapidly cooled to 350 DEG C, can obtain the supersaturated solid solution of unidirectional austenite body is uniform. The key point of this heat treatment process is to rapidly cool down, that is, the cooling rate should be 55 /s, and then the temperature zone (550~850 C) will be rapidly removed after the solid solution of carbide. In addition, the stainless steel tube insulation time should be as short as possible, otherwise it will make coarse grain, affecting the surface finish. The heating temperature of 400 series ferritic stainless steel is relatively low (about 900 degrees), and to a large extent slow cooling is used to obtain annealed softening structure. The annealing method used for martensitic stainless steel can also be treated by sectional quenching and re tempering. From the above introduction, we can know that the 300 series and 400 series are different in the heat treatment processing technology, and in order to get the qualified metallographic structure, it is necessary to adjust the cooling section equipment of the bright annealing furnace. Therefore, the advanced light annealing furnace usually adopts the strong convection cooling in its cooling section, and sets three cooling sections, which can adjust the air volume independently. The strip width is pided into three sections along the width direction of the strip, and the cooling speed of the strip width direction is adjusted by the air flow persion, and the plate shape is controlled. There is an important problem in the heat treatment of cold rolled strip for stainless steel tube, that is to say, the whole strip is uniform in width and length. Muffle type bright annealing furnace with large size muffle tube from the muffle tube evenly heating air flow organization external spiral around over the strip, uniform heating. In order to ensure the uniform organization of the strip along the length, the linear speed of the stainless steel strip in the reheating furnace must be kept unchanged. Therefore, the adjustable roller tension adjustment device is equipped before and after the advanced vertical bright heat treatment furnace. It should not only make the steel import and export speed to meet the speed requirements of heat treatment, should not affect the amount of empty or full sets of sets of sets, but also according to the situation of the establishment and precision plate strip small tension adjusting strip, stainless steel plate to meet the requirements of. Source: China Stainless Steel Tube Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Now in the marine environment has a large number of stainless steel pipe materials and products, in order to adapt to all kinds of corrosion damage of the marine environment, we have developed a special type of stainless steel pipe, here to introduce in the marine environment commonly used type of stainless steel pipe products. 303 stainless steel pipe is a kind of containing sulfur and selenium cutting stainless steel pipe, mainly used to meet the cutting and roughness comparison high demand scenarios. As one of the most widely used stainless steel pipe 304 stainless steel pipe, corrosion resistance, heat resistance, low temperature strength and mechanical properties, punching, bending and other thermal processing performance is very good, and does not produce heat treatment hardening. As for the 316 stainless steel pipe, because of its chemical components added molybdenum elements, so its corrosion resistance, corrosion resistance and high temperature strength is very good, can be used in a relatively harsh environment, it has good performance of work hardening, no magnetism, very suitable for use in the marine environment. The other 321 stainless steel pipe is based on 304 stainless steel pipe on adding titanium to prevent the occurrence of intergranular corrosion, suitable for use in environmental temperature of 430 DEG -900 DEG is used, but the disadvantage is higher cost, and the processing performance is less than that of 304 stainless steel pipe. So as you can see, is widely used in the marine environment for more than 316 stainless steel pipe, 316 stainless steel pipe in contact with seawater but the corrosion resistance is limited, can not resist corrosion under all conditions, because is more susceptible to localized corrosion, cracks and pitting corrosion mainly. This limits the range of application of 316 in contact with seawater. 304 stainless steel pipe, especially the easy cutting 303 stainless steel pipe, is not suitable for working in seawater. The sulfide inclusion point of the 303 surface is the place where pitting occurs preferentially. The factors that determine the corrosion resistance of 316 steel in sea water include water quality, flow rate, temperature, oxygen content and cathodic protection. Water Quality The chloride content in water will be different from the influence of region and tide. Even in slightly salty water, the content of chloride is also higher than that in the water where corrosion is the threat of corrosion. Intermittent exposure in seawater, such as tidal zone, corrosion risk will be smaller, this is probably because of the steel surface by the change of water level of effective erosion. However, if the concentration of chloride in the humid and rainy environment, in the splash zone of water evaporation will increase the risk of corrosion. In addition, slow moving water contributes to biological contamination, and then leads to protection or crack corrosion. It’s better not to use 316 stainless steel pipes in stagnant seawater. Increasing the flow rate will reduce the risk of corrosion, so that 316 stainless steel pipes can be used in seawater. Water temperature Crack corrosion will increase with temperature, so it is not recommended to contact hot seawater. Nordic waters reach a maximum temperature of 316 steel at room temperature, even though other conditions are good. Stress corrosion cracking is usually not considered at 316 service temperature (in any case, higher temperature may lead to crack corrosion and pitting corrosion). Oxygen content in water (except gas) The stainless steel pipe depends on oxygen to maintain its passivation state, however, the oxygenated seawater is more aggressive than degassing. It has been found that the water with very low oxygen content, such as in the sea about 200 meters deep, has very little erosion. This reduces the pitting rate. Cathodic protection Cathodic protection is used in electricity to obtain contact with inert weak metals, including carbon steel and aluminum. Direct contact with these metals, on the basis of sacrificing other metals, helps to improve the corrosion resistance of 316 stainless steel pipes. Although the stainless steel pipe is beneficial, it should also be considered that the overall durability of the products involved in this combination may be weakened. Machining crack The crack and its closely related pitting mechanism are localized corrosion forms, which are usually the cause of damage to the 316 steel working in seawater. They can happen in the following process. Mechanical fastening system Intergranular corrosion can be detected in 316 stainless steel pipes exposed to seawater after laboratory sensitization (heat treatment). The application of low carbon 316L such as 1.4404 or 1.4432 should avoid the additional corrosion risk in the welded structure. Smooth surface welding quality and finishing are the key factors for the successful application of 316 stainless steel pipes in seawater, such as the actual chlorine content and other factors. Smooth, clean, leveling and finishing welds contribute to the corrosion resistance of steel. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Because of its excellent mechanical properties, high wear resistance and high hardness, the stainless steel pipe has been widely used in the processing of stainless steel pipes for military products. The surface treatment of stainless steel pipe is carried out after heat treatment, solid solution and aging, because the heat treatment process will produce thicker oxide skin and the particularity of the material itself, so it is difficult to do the pickling passivation process. Pickling passivation process Stainless steel pipe surface treatment process flow is relatively simple. But in actual processing, the difficulty of pickling passivation process is relatively large, generally pided into two aspects: on the one hand, stainless steel pipe can not be removed by ordinary derusting method to remove stainless steel pipe surface oxide skin. On the other hand, the passivation process of stainless steel pipe material meets the air will not corrode and damage size and surface finish, but in the process it must use pickling passivation strong oxidant to make this stainless steel pipe produces a passivating film on the surface, so as to achieve the purpose of anti corruption. Remove oxide after heat treatment: Ti, Ni, Cr stainless steel, Si, V, Mn, Mo and other elements, these elements will form a thick and dense oxide in the heat treatment process, and can be made of iron, chromium, nickel and oxygen to form a dense oxide film has a spinel structure the (FeCrO4), the chemical nature of the relatively stable. So it is not easy to remove the oxide film. Stainless steel pipe for low temperature solidification and aging The stainless steel pipe with low temperature and solid aging is thinner and usually pale purple. It is easier to handle the oxide scale of the stainless steel pipe. Stainless steel pipe by pickling and passivation of stainless steel after pickling, the surface oxide skin will generally clean and no corrosion of stainless steel pipe, stainless steel pipe surface without hanging ash, can be directly used for subsequent passivation processing. Stainless steel pipe for high temperature solid melting and aging High temperature solid aging stainless steel pipe has a thick oxide skin, usually black purple, even black. Because the stainless steel pipe surface generates thicker, dense and complex oxide skin, so stainless steel pipe pickling oxidation skin to be more complex. The removal of this kind of oxide skin should be carried out according to the steps of loosening oxide scale, pickling and removing dust. After loosening the oxide scale, the surface of the stainless steel pipe is often adhered with a layer of ash, and the oxide scale is removed after removing the dust. The operation process of removing dust is passivation process. The corrosion resistance of stainless steel pipe after pickling is poor in air. If exposed to air, the surface of stainless steel pipe will rust. In order to enhance the corrosion resistance of stainless steel pipe, a compact and corrosion resistant passivation film must be produced on the surface of the stainless steel pipe, so as to achieve the purpose of corrosion resistance. The quality of the passivation film will directly affect the service life and appearance of the stainless steel pipe, and the main factors affecting the quality of the passivation film are the composition of the material and the quality of the passivation solution. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The corrosion of stainless steel pipe mainly occurs in the whole contact with the media environment, which is characterized by uniform thinning along the section. Most of the corrosion occurs in the acid and hot alkali media environment. The overall corrosion resistance of stainless steel is often judged by corrosion rate (mm/a). Reasons for corrosion of stainless steel pipes Lead by causes of corrosion of stainless steel pipe is not the formation of passivating film, passivation film instability or passivation membrane damage and can not timely repair of the three; in practice, in many corrosion environment, the stainless steel pipe surface passivation film even intact, often dissolved in different speed until the control equipment, stainless steel; component, container thickness (or section) gradually thinning and failure. Measures to prevent corrosion of stainless steel pipes According to the type, concentration, temperature and other requirements of corrosion medium, the grade of corrosion resistance should be chosen. Then select suitable stainless steel grade according to the requirements of corrosion resistance grade. The corrosion resistance of stainless steel pipes is evaluated by the corrosion rate of the stainless steel pipe under the condition of full corrosion. In this medium, the corrosion rate of stainless steel pipes is corrosion resistant in the allowable range, but this is not corrosion. Because there are a lot of stainless steel pipe corrosion corrosion Handbook for reference, and the test data of stainless steel in a large number of practical medium for use, and there are a lot of practical engineering experience using stainless steel pipe, so as long as the correct selection and reasonable use of stainless steel, it can avoid the general corrosion of stainless steel. Generally speaking, in the practical application, because the corrosion resistance of the stainless steel pipe to advance in the medium, the corrosion rate of stainless steel pipe, master the equipment under the reasonable use of the service life. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The performance of stainless steel is obtained by its special chemical composition, and the main element is chromium. The chromium and oxygen combine to form a dense chromium oxide film that protects the stainless steel pipe fittings from corrosion. When the stainless steel pipe fitting has chrome oxide film, it is in the passive state, and the stainless steel pipe fittings can be corrosion-resistant. The stainless steel pipe fitting may be corroded when the protective film on the stainless steel pipe fittings is damaged or contaminated and the passivation film is formed naturally. In this case, most of the beneficial properties of stainless steel fitting may be destroyed during processing, such as heat treatment or welding, cutting, sawing, drilling and bending of such mechanical processing. Because such treatment will cause damage or contamination of the oxide film on the surface of the stainless steel pipe fitting, it will not achieve spontaneous and complete passivation. Therefore, local corrosion may occur, especially in relatively weak corrosion conditions, but also easy to rust. At the time of use, it may make the final product not satisfactory, or even cause the system to fail. The weld seam and the inside and outside sides close to the weld will cause the acceleration of the oxidation of the stainless steel pipe fitting. The color is related to the thickness of the oxide layer due to the visible oxidation in the color change zone. Compared with the oxide layer on the stainless steel pipe fittings before welding, the oxide layer of the color change zone is relatively thick, and the chromium element is also reduced, and the local corrosion resistance is reduced. For stainless steel pipe fittings, oxidation and discoloration can be reduced to the minimum by using an appropriate blowing method. After welding, it is better to do the post weld treatment such as pickling and grinding to remove the oxide layer and restore the corrosion resistance. In addition, mechanical treatment can also contaminate the surface of stainless steel fittings. Organic pollutants may be caused by lubricants. Inorganic contaminants, such as exotic iron particles, may be caused by tool contact. In general, all surface contamination may lead to plaque corrosion. In addition, the external iron particles may lead to galvanic corrosion. Spot corrosion and electrochemical corrosion are localized corrosion forms and need to be treated with water. Therefore, surface contamination usually reduces the corrosion resistance of stainless steel fittings. In order to deal with the surface of stainless steel pipe fittings, remove discoloration and restore corrosion resistance, there are many rear treatment processes. It is important to distinguish between chemical and mechanical methods. Chemical methods are: pickling (immersion, pickling or spray), auxiliary passivation (after pickling) and electrolytic polishing. Mechanical methods are: sandblasting cleaning, glass or ceramic particles shot peening, annihilation, scrub and polishing. Although all methods produce weld seams, no mechanical rear treatment will provide corrosion resistance for a strictly applicable purpose. The removal of oxides and other contaminants on the surface by chemical methods can also be used to wipe off the contamination of previously removed materials, polishing materials, or annihilation materials. All kinds of pollution, especially foreign iron particles, may be the source of corrosion, especially in humid environment. Therefore, the mechanical cleaning surface is best to be cleaned regularly under dry conditions. After pickling, clean water is needed to remove contaminants and pickling residues. The final flushing uses softened water to prevent calcium stains and contaminants from being embedded in the growing oxide layer, which is essential for the passivation layer. Also because of the use of chemical methods (pickling and electrolytic polishing) and improve corrosion resistance, so the metal dissolution than iron in acid solution and the electrolyte quickly, according to the surface enrichment of chromium, with more inert. Therefore, the chemical methods of pickling and electropolishing are the only post treatment methods that can restore the corrosion resistance of stainless steel fittings at the weld and other surface damage. Source: China Stainless Steel Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Now with the continuous development of the chemical industry in China, use of duplex stainless steel welded pipe is also increasing, the annual demand for Chinese duplex stainless steel tube in the rapid growth, and in the oil, urea and other industries also have a very good development. The main performance of duplex stainless steel tube is high yield strength and good stress corrosion resistance. The welding performance of the duplex stainless steel tube is good, and the sensitivity of welding cold crack and hot crack is low. In China, stainless steel welded pipe is mainly used in the field of decoration, in the field of petrochemical corrosion resistant welded pipe is relatively less. In terms of variety, specification, quantity and quality, China’s stainless steel has some differences in terms of market demand and technical level compared with advanced industrial countries. Specifically, in the number of products, the common use of ordinary stainless steel has been the basic supply and demand balance. But the high demand materials, the production capacity is not enough, especially the high requirements of industrial materials, such as high pressure stainless steel pot and so on, and a lot worse. In product specifications, small diameter stainless steel tube for general purpose is oversupply, large aperture and high requirements of stainless steel pipe, the market demand gap is large, such as large diameter stainless steel with 219mm tube above the need to rely on imports to make up for lack of. A super length (greater than 15m) long off, China rarely production, are basically rely on imports; in terms of varieties, compared with advanced countries, China’s stainless steel less varieties, not many varieties of high technical content, such as duplex steel, Hastelloy alloy, stainless steel and special technical difficulty large, high quality requirements, such as heat exchanger tubes, boiler tubes and other devices with urea fertilizer, low yield depends on imports, some with good resistance to corrosion of duplex stainless steel tube, China rarely production, basically rely on imports. In order to adapt to the increasingly widespread application of duplex stainless steel, China should strengthen the popularization of duplex stainless steel welding technology and the development of welding materials. Chemical and petrochemical processing industry The field of chemical engineering is the earlier and more important area of using duplex stainless steel. The catalyst tubes for medium and small methanol synthesis reactors are made of duplex stainless steel, large and medium sized units adopt 2205 steel tubes, more imported steel pipes are used, and small scale units are made of 18-5Mo type steel pipes made in china. The medium condition (HCI, steam) of the cooling coil pipe in the chlorination reactor of Qilu Petrochemical Industries Co’s VCM unit is very harsh. At present, the imported 2205 duplex stainless steel has been used, and the results need to be observed. The catalyst regeneration cooler of Shanghai Petrochemical Co ethylene plant uses 00C25Ni7Mo3WCuN duplex stainless steel similar to DP3 steel as sea water cooler tube, and the seawater outlet temperature is 40T. The coolers of pulverized coal gasification plant in Henan coal chemical plant are made of imported 2205 steel pipes. Petroleum and natural gas industry This is one of the main applications of duplex stainless steel in foreign countries. For the production of small size duplex stainless steel welded pipe, China has been more mature, but the production process of large size seamless pipe and welded pipe needs to be developed. In addition, how to reduce the price of duplex stainless steel products is also related to the development of China’s duplex stainless steel. Is to expand production and production of marketable marketable products is very important, can not be ignored is to adopt new technology, using spherical molybdenum oxide instead of metal molybdenum, nickel oxide instead of metal nickel, reducing the smelting cost, promote the use of duplex stainless steel casting technology, improve yield rate etc.. Fertilizer industry The main use of the chemical fertilizer industry China production enhanced duplex stainless steel 0Cr25Ni6Mo3CuN with aging, the wear corrosion resistance, high pressure cut-off valve for the main process of urea plant piping specifications in parts, the effect is good. The production of urea CO2 stripping and NH3 stripping is the high alloy austenitic stainless steel, and titanium, China has adopted high chromium stainless steel to replace 316L in Methylamine Pump on large scale urea plant (urea) steel. Since 80s, the Toyo Project Corporation to develop new technology of ACES urea in stripper, ammonium carbamate condenser and high-pressure decomposition tower three high-pressure devices using the DP-12 (25Cr-7Ni-3Mo-N Steel Containing Trace Tungsten and copper) and R-5 (00Cr25Ni6.5Mo1.5N) duplex stainless steel, the former is used to manufacture gas pipe, condenser tube, tube decomposition and pipelines the latter, housing for high voltage equipment. Source: China Duplex Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless iron is a kind of stainless steel, the material mainly has 409, 410, 430, 444, which belongs to the martensitic and ferritic stainless steel, they will be attracted to a magnet. While the stainless steel can resist unity refers to the atmosphere or chemical substances such as acid corrosion of steel. But it is not stainless steel does not rust, corrosion behavior in different medium. The common stainless steel materials can be pided into three types: martensitic stainless steel, ferritic stainless steel and austenitic stainless steel by metallographic structure. Martensitic stainless steel The common martensite stainless steel carbon content is 0.1-0.45%, chromium content is 12-14%, is chromium stainless steel, also commonly known as Cr13 stainless steel. Typical material models 1Cr13, 2Cr13, 3Cr13, 4Cr13 etc.. This type of stainless steel is usually used to make all kinds of valves, pumps and other parts that can withstand load and corrosion resistance, as well as some stainless steel tools. In order to enhance corrosion resistance, the carbon content of martensitic stainless steel is controlled in very low content range, usually not more than 0.4%. The carbon content is low, the corrosion resistance of stainless steels is higher, and the higher the carbon content, carbon content in the matrix is higher, so the strength and hardness of the steel is higher, but it will form the chromium carbide content also more, so the stainless steel corrosion resistance becomes worse. So it can be seen that the strength and hardness of 4Cr13 are better than that of 1Cr13, but its corrosion resistance is worse than that of 1Cr13. Both 1Cr13 and 2Cr13 are resistant to atmospheric and vapor corrosion, and are commonly used as corrosion resistant structural steels. In order to obtain good comprehensive performance, the tempered bainite is often obtained by quenching + high temperature tempering (600~700 C) to produce steam turbine blades and boiler tube accessories. While the 3Cr13 and 4Cr13 steel, because of high carbon content, the corrosion resistance is relatively poor, the low temperature quenching and tempering (200~300 C), are tempered martensite, with high strength and hardness (HRC 50), it is often used as tool steel, manufacturing medical equipment, cutting tools, oil pump shaft etc.. Ferritic stainless steel The carbon content of common ferritic stainless steel is less than 0.15%, the chromium content is 12~30%, also is a kind of chromium stainless steel, the typical models are 0Cr13, 1Cr17, 1Cr17Ti, 1Cr28 and so on. Because of the decrease of carbon content, chromium content has been improved. The stainless steel is heated from room temperature to high temperature (960~1100 C), and its microstructure has been a single phase ferrite structure. The corrosion resistance, ductility, weldability than martensitic stainless steel excellent. The corrosion resistance of high chromium ferritic stainless steel is stronger than that of chromium containing stainless steel, and the corrosion resistance is further improved with the increase of chromium content. Ferritic stainless steel can not be strengthened by heat treatment because it does not produce phase change during heating and cooling. If the grain coarsening during heating, only cold plastic deformation and recrystallization can be used to improve the microstructure and improve the properties. If this kind of stainless steel stays at 450~550, it will cause embrittlement of stainless steel, which is called “475 degree brittleness””. By heating to about 600 DEG C and fast cooling, can eliminate embrittlement. Austenitic stainless steel Join 8-11% in nickel containing 18% chromium stainless steel, austenitic stainless steel becomes. For example, 1Cr18Ni9 is the most typical model. Such stainless steel expands austenite region because of the addition of nickel, and thus metastable metastable austenite can be obtained at room temperature. Because it contains higher chromium and nickel, and single-phase austenite structure, so it has higher chemical stability than chromium stainless steel, corrosion resistance is better, is now the most widely used stainless steel. Type 18-8 stainless steel exhibited austenite and carbide microstructure in the annealed state, carbide, stainless steel on the corrosion resistance of the greater harm, so the general use of solid solution treatment, the stainless steel is heated to 1100 DEG C after cooling, the dissolution of carbide obtained under high temperature austenite, followed by rapid cooling, it obtain the austenite single-phase at room temperature. We usually said the stainless iron is a ferritic stainless steel and martensitic stainless steel. The distinction between the good and the antirust performance of the most widely used austenitic stainless steel. Source: China Stainless Steel Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Duplex stainless steel pipe is in the solution structure of ferrite in the microstructure and the austenite microstructure about each accounted for 50%, the less content usually have reached 30%, so the duplex stainless steel pipe with ferrite stainless steel and austenitic stainless steel pipe properties. Among them, compared with austenitic stainless steel pipe, duplex stainless steel pipe has more advantages, first of all, its yield strength is stronger than ordinary austenitic stainless steel pipe, but also has enough plastic and toughness needed for molding. The wall thickness of tanks or pressure vessels made of duplex stainless steel is reduced by 30%~50%, which greatly reduces the cost. The second is the pipe resistance to stress corrosion cracking excellent duplex stainless steel, especially in chloride environment, even the lowest levels containing alloy stainless steel pipe, resistance to stress corrosion cracking ability than the austenitic stainless steel pipe, and the stress corrosion resistance and is difficult to solve the problems often common austenitic stainless steel pipe. The third point is that in many media most commonly applied in 2205 duplex stainless steel pipe corrosion resistance must be better than ordinary 316L austenitic stainless steel, this is because the super duplex stainless steel pipe corrosion resistance is extremely high, in some medium, such as acetic acid and formic acid can replace the high alloy austenitic stainless steel pipe, and corrosion resistance alloy. The fourth point is the duplex stainless steel pipe has good resistance to local corrosion resistance, compared with the alloy content equivalent of austenitic stainless steel pipe, pipe corrosion and wear and corrosion fatigue properties of duplex stainless steel are better than austenitic stainless steel pipe. The fifth point is the duplex stainless steel pipe line expansion coefficient than the austenitic stainless steel pipe for low carbon steel and carbon steel, close to, to connect engineering significance, for example can be used in the production of stainless steel pipe composite plate or lining etc.. The final point is that the energy absorption capacity of the duplex stainless steel pipe is better than that of the austenitic stainless steel pipe under dynamic or static load conditions. In dealing with sudden accidents such as collision and explosion, the practical application value of duplex stainless steel pipe is very obvious. However, compared with austenitic stainless steel pipes, duplex stainless steel pipes are also defective. First of all, the universality and versatility of duplex stainless steel pipes are not comparable to those of austenitic stainless steel pipes, such as long term applications, which must be controlled below 250 degrees celsius. Secondly, its plastic toughness is lower than that of austenitic stainless steel pipe, and its cold, hot working process and formability are also inferior to austenitic stainless steel pipe. Duplex stainless steel pipe also has medium temperature brittleness zone, so it is necessary to strictly control the heat treatment and welding process system, so as to avoid the occurrence of harmful phase and damage the performance. The most obvious disadvantage of duplex stainless steel pipe compared with austenitic stainless steel pipe is that the former contains a large amount of ferrite structure. What are the advantages and disadvantages of duplex stainless steel pipe and ferritic stainless steel pipe?. The first advantage is that the comprehensive mechanical properties are higher than those of ferritic stainless steel pipes, especially plastic toughness. Brittleness is not as sensitive as ferritic stainless steel pipes. Secondly, in addition to the stress corrosion resistance, other local corrosion resistance is better than the ferritic stainless steel pipe. The cold working properties and cold forming properties of duplex stainless steel pipes are much better than those of ferritic stainless steel pipes. In addition, the welding performance of duplex stainless steel pipe is much better than that of ferritic stainless steel pipe, and it is not necessary to preheat before welding and no heat treatment after welding. Another point is that the duplex stainless steel pipe is wider than the ferritic stainless steel pipe. However, compared with ferritic stainless steel pipes, the disadvantage of duplex stainless steel pipes is the high content of alloying elements and the relatively high price, because the common ferritic stainless steel pipes do not contain nickel. The use of duplex stainless steel pipe performance and process performance are excellent, with excellent comprehensive performance of mechanics and corrosion resistance of the popular, is an engineering material corrosion resistance to save weight and save investment outstanding. Source: China Duplex Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

With the rapid development of the domestic energy industry, application of stainless steel tube is rapidly increasing, the corrosion in oil and gas pipeline construction process, surface treatment of stainless steel tube is one of the key factors determining the service life of the pipeline corrosion, but also an important prerequisite for the anticorrosion layer and stainless steel pipe can be firmly combined with the. By the certification authority, in addition to life depends on the kinds of coating, coating quality and construction of environmental factors such as anticorrosion layer, surface treatment of stainless steel pipe influences on life accounted for about half, so must be strictly in accordance with the specification requirements of tube surface coating on stainless steel surface treatment technology, the continuous optimization of stainless steel tube. At present, the common stainless steel pipe surface treatment methods are cleaning, derusting, pickling and so on, the following will introduce these methods. Clean The use of solvent, emulsion cleaning stainless steel surface, can remove oil, grease, dust, lubricants and other similar organic compounds, but this method cannot remove welding rust, oxide skin, stainless steel surface, so the corrosion production is only an auxiliary means. Tool derusting The general use of steel wire brush and other tools to polish the surface of stainless steel, which can remove loose or tilted oxide skin, rust, welding slag and so on. Hand tools rust can reach Sa2 level, Powertool cleaning can reach Sa3 level, if attached to the surface of stainless steel iron oxide solid tool, derusting effect is not ideal, can not meet the construction requirements of the anchor depth of corrosion. pickling There are usually two kinds of chemical and electrolytic method for pickling, stainless steel pipe anticorrosion only by chemical pickling, can remove the scale, rust, old coating, sometimes also used this method as sand blasting after treatment. Although the chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, but the anchor is shallow, and easy to pollute the environment. Spraying (throwing) derusting Spray (throw) shoot derusting by the high-power motor to drive the spray shot (impeller) blade rotating speed, the steel grit, steel shot, iron wire, minerals and other abrasive spraying on the surface of the steel pipe under the action of centrifugal force (left) radiation treatment, not only can completely remove dirt and rust, oxide, and stainless steel tubes in heavy abrasive the impact and friction force, but also can achieve the required uniform roughness. Spraying (throwing) and derusting can not only expand the physical adsorption of stainless steel pipe surface, but also enhance the mechanical adhesion between the anti-corrosion layer and the pipe surface. Therefore, spraying (throwing) is an ideal rust removal method for pipeline corrosion protection. Generally speaking, shot peening (sand) rust removal is mainly used for inner surface treatment of tubes, shot blasting (sand) rust removal is mainly used for outer surface treatment of tubes. Several problems should be paid attention to using jet (shot) derusting. Derusting grade For stainless steel pipe commonly used epoxy, ethylene, phenolic and other anti-corrosion coating construction process, usually require stainless steel pipe surface to near white level (Sa2.5). Practice has proved that the derusting grade removes almost all of the scale, rust and other dirt, anchor depth reached 40~00 mu m, fully meet the adhesion of anticorrosion layer and stainless steel tube, and the spray (throw) operation cost shoot derusting process at low and stable and reliable quality reaches nearly white (Sa2.5 technical conditions). Jet (throwing) abrasive In order to achieve the ideal cleaning effect, should be chosen according to the steel abrasive surface hardness, corrosion degree, the original requirements of the surface roughness, the type of coating, for single epoxy, two layer or three layer polyethylene coating, using mixed abrasive grit and steel more easily to the physical cleaning effect. A steel reinforced steel surface, and a surface steel grit etching effect. Mixed abrasive grit and steel in the steel (usually a hardness of 40 ~ 50 HRC, the steel hardness is 50 ~ 60 HRC can be used in all kinds of steel surface, even in the surface of steel C and D corrosion, rust removal effect is also very good. Cleaning and preheating In the spray (throw) shot before removing the pipe surface grease and fouling by cleaning method, the tube body is preheated to 40 60 C heating furnace, the steel tube surface to keep dry state. In the spray (throw) shoot, because the surface of the steel pipe does not contain grease and dirt, can enhance the cleaning effect, is conducive to the separation of steel shot and steel grit and rust and oxide skin of the steel surface is dry, make the steel surface derusting cleaner. In the production process of stainless steel tube to focus on its surface treatment process, process parameters and strictly control the scale removal, in the actual construction, the peeling strength of stainless steel pipe anticorrosion layer value is far higher than the standard requirements, ensure the quality of the anticorrosive coating, based on the same equipment, greatly improve the technological level, reduce production cost. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Because the stainless steel pipe fittings in the chloride ion more widespread and corrosive medium environment, will destroy the surface passivation membrane, and formation of corrosion pits, combined with the surface of the part of the inclusions, poor chrome area, grain boundary and dislocation, the stainless steel surface is very susceptible to corrosion, form the rusty spot, make lose luster, around stainless steel produced by corrosion. Therefore, use the environment as much as possible, reduce the content of chlorine ions, keep the space clean and dry, and reduce the dust adhesion. If you are in a coastal city, a humid space, and a lot of chlorine ions, then choose 316 or 316L materials that are resistant to corrosion, to reduce the erosion of chloride media. Crevice corrosion The conditions that lead to the corrosion of stainless steel cracks are more extensive. Most corrosive media will cause crevice corrosion in the stainless steel pipe. Such as rain, water vapor condensate chlorine ion will produce crevice corrosion, especially in the cracks are very small, oxygen, it is hard to get into local often appears crevice corrosion, such as water supply pipe flange, screw between links and links with other different materials, easy to produce crevice corrosion. Electrochemical corrosion When two types of metal with different potential potential energy are different, the contact between steel and stainless steel can produce potential difference and can be corroded easily. What are the measures and countermeasures to avoid corrosion of stainless steel pipe fittings? The first is to prevent it in the production process. In stainless steel pipe production enterprises, considering the safety and to prevent the corrosion of the pipe fittings in use factor, in the processing of stainless steel pipe fittings must take solid solution treatment, the heat treatment is very important. Second stainless steel pipe fittings in the welding and solid solution to ensure that the use of gas, because in the welding process and solid solution treatment process, using gas can greatly enhance stainless steel pipe welding seam and the corrosion resistance of the stainless steel body, thereby greatly enhancing the service life of the stainless steel tube products. Solid solution is an important measure to improve the application and anti-corrosion of stainless steel pipe fittings. The solid solution process can improve the processing cost, but also enhance the safety factor. Pipeline design prevention. In the process of pipeline design, not only to minimize crevice corrosion, but also reduce the construction site welding, really need to welding the first order processing, after gas protection and reduce the damage to the aperture passivation layer, the other is the installation environment is bad, there is water vapor, easily able to consider using the viega profi-press connection mode, to avoid the generation of cracks. The fourth installation construction process prevention. Corrosion resistance of stainless steel is not absolute, but relative, conditional requirement, under adverse factors and conditions stainless steel can also be corroded. Therefore, it is necessary to maintain a clean and dry environment during installation, so as to avoid moisture accumulation, which can prolong the service life of products. Followed by the construction and installed to prevent the residual grinding wheel for cutting the foam in the stainless steel tube, welding oxide and carbon powder production of corrosive medium, such as the layer to minimize the grinding wheel for cutting of stainless steel metal structure damage, prevent to produce a variety of corrosion. Source: China Stainless Steel Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Chromium martensitic stainless steel and ferritic stainless steel according to different conditions can cause stress corrosion cracking (mainly intergranular cracking) or hydrogen embrittlement, but this kind of stainless steel in MgCI2 or NaCI solution, resisting performance is far stronger than austenitic stainless steel, and under the condition of load stress is not strong, will not cause cracking. The austenitic stainless steel is liable to crack in high temperature environment containing chloride aqueous solution. In the cooling water, the water vapor in the CI – probably in more than 50 PPM, temperature in the case of more than 50 ℃ about likely to happen, there are in many cases, the dissolved oxygen in a few parts per million of C1 – concentration will also form the corrosion cracking. It is more likely to cause corrosion cracking near the boiling point or boiling point of the solution, and sometimes in a very short time. 304 stainless steel has cracking sensitivity in high temperature and high pressure water. The austenitic stainless steel in MgCI2 solution will be affected by stress corrosion cracking. 1 nacl concentration and dissolved oxygen on the influence of the stress corrosion cracking of stainless steel 304 (temperature at 260 ℃, load stress is 21000 psi) is one of the important influencing factors as related to stress corrosion cracking, in addition to stress) chloride concentration, temperature, degree of processing also leads to great impact. Temperature rise can cause stress corrosion cracking in stainless steel, and the influence size of stainless steel is also changed according to the type of alloy and the residues stress. In terms of degree of stainless steel processing, usually in the range of is not how big along with the deepening degree of stainless and much easier to crack, but it is important to note when processing degree of more than 10%, stainless steel materials will be difficult to crack. Pitting corrosion is in the case of stainless steel passivation membrane stability, when the solution PH value near the neutral, antioxidants and halogen ions, C1 – in particular, passivation membrane will be destroyed by part forming cell anode, because of the passivation membrane as cathode, making this area form a larger potential difference, and in a short period of time the phenomenon of erosion depth stainless steel. In order to avoid corrosion of stainless steel, there are mainly electrical and anti-corrosion, adding preservatives, surface spraying, controlling PH value, removing oxidant, etc. The surface treatment of stainless steel is also best to do some work on the residual stress of the surface, so that the stress can be compressed. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)