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Steel heating to 1050 ~ 1100 ℃, then rapid cooling in water, to get a single-phase austenitic organization, this process is called solution treatment. Solution treatment temperature should choose according to the carbon content of stainless steel, usually take limit at high carbon content, carbon content lower limit, but the temperature is unfavorable and exorbitant, both also shoulds not be too low. Temperature is too high, will appear a large number of ferrite, and make the steel coarse grains, such bad, not only make the fabrication procedure and reduce steel uniform corrosion resistance. From the point of view of intergranular corrosion, the higher the heating temperature, the greater the degree of supersaturation of austenite, after precipitation of chromium carbide reheat temperature range, chromium carbide precipitation process is more intense, to increase the susceptibility to intergranular corrosion of steel. If the temperature is too low, the composition of the steel and the sufficient dissolving of carbide are not sufficient to achieve the effect of solidification. Solution treatment should prevent surface carburizing, when heating for carburizing steel increases, the susceptibility to intergranular corrosion of the valve, the valve body, valve seat, a kind of direct contact with the working medium of the so-called internal parts, the performance requirements of general corrosion and intercrystalline corrosion resistance requirements is much taller than other stainless steel valve parts, therefore, internal parts of the surface of the solution treatment especially need to pay attention to carburizing. When heated, usually in neutral or slightly oxidizing atmosphere. Processing or machining allowance for after heat treatment is no longer a small parts, before heating furnace should be paid attention to cleanliness, and remove the oil on the surface of the parts, to prevent the dirt decompose when heated, make parts surface carburizing. After the solidification process, the strength of the steel increases with the increase of carbon content. However, the strength of this kind of steel is not high in general, compared with the treatment of sensitization and stabilization. Therefore, the curing process is also the maximum softening treatment. Solution treatment to dissolve carbide at high temperature in a steel is heated, and for the next fast cooling and fixed in austenite, so the corrosion resistance of steel with the highest of solution treatment, for not including 18-8 of titanium or niobium steel, solution treatment is one of the important means to prevent intergranular corrosion. Solution treatment of heat preservation time shoulds not be too long, it have close relationship with the diameter and thickness of the parts, the material of 25 mm in diameter, according to can according to commonly 2 ~ 3 minutes/mm to calculate time of heat preservation. Commonly used solution treatment, the cooling system of water-cooling, but for the cover sleeve, sleeve seat and jacketed valves outer jacket and thin wall parts and air cooling can be applied. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Hydrogen corrosion may occur in ammonia synthesis, hydrogen desulphurization and oil refining. Carbon steel is not suitable for high pressure hydrogen device for above 232 ℃. The hydrogen diffusion into the steel, and in the grain boundary or pearlite zone and reaction of iron carbide and produce methane, the methane (gas) can’t spread to the outside steel all together, and white spots and cracks in metal or one of them. In order to prevent to produce methane, cementite must replacement into stable carbide, chromium, vanadium, titanium, or must be added into the steel drill. Data points out, improve the chromium content allows the use of higher temperature and hydrogen partial pressure formed in the steel chrome carbide, and it encounters of hydrogen is stable. In the use of harsh conditions (temperature higher than 593 ℃), the chromium content is more than 12% chromium steel and austenitic stainless steel in all known applications are corrosion resistance. Most metals and alloys do not react to nitrogen at high temperatures, but atomic nitrogen can react with a lot of steel. It also permeates the steel and forms a brittle nitride surface layer. Iron, aluminum, titanium, chromium and other alloy elements may participate in these reactions. The main source of atomic nitrogen is the decomposition of ammonia. Ammonia converter, the system of ammonia plant production of heater and in 371 ℃ ~ 593 ℃, a nitriding furnace under atmospheric pressure ~ 10.5 Kg/was have ammonia decomposition of the operation. In these atmospheres, chromium in low-chrome steel appears. It may be affected by the corrosion of nitrogen atoms to produce chromium nitride, and release of the carbon and hydrogen to generate methane, as above, then possible to generate white spots and cracks, or one of them. But chrome content more than 12%, the carbides in the steel than chromium nitride is more stable, so the response will not appear in front of, so now the stainless steel used in the high temperature of hot ammonia environment. The status of stainless steel in ammonia is determined by temperature, pressure, gas concentration and chromium nickel content. Field experiment results showed that the ferrite and martensite stainless steel corrosion rate (alteration metal depth or carburized depth) is higher than austenitic stainless steel, the nickel content, the higher the better corrosion resistance. As the content increases the corrosion speed increases. The austenitic stainless steel is highly corrosive in the high temperature halide vapors and is more corrosive than chlorine. For high Ni – C r stainless steel, used in dry gas temperature limit, fluorine is 249 ℃, chlorine is 316 ℃. Source: China Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Physical properties of stainless steel Comparison of physical property data of stainless steel and carbon steel, carbon steel, the density is slightly higher than that of ferritic and martensitic stainless steel, and slightly lower than the austenitic stainless steel; resistivity by carbon steel, Ferritic, martensitic and austenitic stainless steel sort increment; linear expansion coefficient of size sorting is similar, austenitic stainless steel and carbon steel minimum; carbon steel, Ferritic and martensitic stainless steel magnetic, austenitic stainless steel is not magnetic, but the cold hardening generated into martensite transformation will produce magnetic heat treatment, available method to eliminate this martensite and restore its non-magnetic. Austenitic stainless steel compared with carbon steel, has the following characteristics: 1) the high rate of electric negative is about 5 times of that of carbon steel. 2) the coefficient of linear expansion is 40% larger than that of carbon steel, and the coefficient of linear expansion increases correspondingly as the temperature increases. 3) low thermal conductivity, about 1/3 of carbon steel. Mechanical properties of stainless steel Austenitic stainless steels are similar to most other metal materials, and their tensile strength, yield strength and hardness increase with decreasing temperature, while plasticity decreases with decreasing temperature. Its tensile strength increases at a temperature range of 15~80 degrees C, which is even. More importantly, as the temperature decreases, the impact toughness decreases slowly, and there is no brittle transition temperature. Therefore, stainless steel can maintain sufficient plasticity and toughness at low temperatures. Heat resistance of stainless steel Heat resistance refers to the high temperature, both antioxidant or gas medium corrosion resistance, namely thermal stability, while in high temperature double enough strength, namely heat intensity. Source: China Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The first mode of production: the tube billet (plate, strip) is formed directly into the pipe, and its main process is the forming, welding and sizing of plate tape. Features: low production process, simple engineering process, short production cycle, low precision of product. The second mode of production: the tube billet welding (plate, belt) direct forming into a certain size of steel pipe, and then after cold drawn or cold rolled into a finished product steel tube, known as the DOM welded steel pipe. Its main process is forming, welding, sizing, cold rolling or cold drawing (with a mandrel or no mandrel), or continuous cold drawing (that is, the welding, cold pulling joint production line). Features: the production procedure, the technological process and production cycle is long, covers an area of big, dimension precision products, both inside and outside surface is bright and clean, good mechanical properties and microstructure of state. The third kind of mode of production: the tube billet welding (plate, belt) direct forming into a certain size of steel pipe, into the continuous cold sinking into a finished product reducing mill for steel. Its main process is forming, welding, continuous cooling reduction. Features: the production process is compact, the process flow is concise, the production efficiency is high, the specification scope changes fast, the production small diameter and thin wall electric welding steel pipe. Source: China Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

(1) preface: It is well known that stainless steel has its unique strength and high abrasion resistance and its excellent anti-rust properties. It is widely used in chemical industry, food machinery, electromechanical industry, household electrical appliance industry. At present, a lot of entering the home decoration industry, giving people the feeling of luxuriant nobility. The application of stainless steel will be more and more widely available, but the application of stainless steel will largely determine its surface treatment technology. Let me talk about the surface treatment of stainless steel for discussion. (2) introduction of stainless steel varieties: Stainless steel usually contains high quality metallic elements such as chromium (CR), nickel (NI), molybdenum (MO) and titanium (TI). Common stainless steel is chromium stainless steel, which contains CR > = 12%. Nickel chromium stainless steel contains CR > = 18%, including NI > = 12%. From the stainless steel metallographic structure: the austenitic stainless steel, for example: 1CR 18 NI9TI, cr18ni11nb. Martensitic stainless steel, such as CR17, CR28, etc. It is commonly referred to as non-magnetic stainless steel and magnetic stainless steel. (3) surface treatment of stainless steel: At present, the surface of stainless steel surface is treated with white treatment. (2) the surface mirror is polished. (3) surface shading treatment. In the process of processing, the stainless steel is processed by the coil plate, the edge, the welding, or the handling by the agent. The hard, black, black oxide skin is mostly NICR2O4 and NIF two, the EO4 component, which was previously used in a strong corrosion method with hydrofluoric acid and nitric acid. But this method is costly, polluting the environment and harmful to the human body. The corrosion was larger and gradually eliminated. There are two methods for the treatment of this type of oxidation: (1) the use of the blasting method. (2) adopt the chemical method. It is used to wash the cleaning liquid with an inorganic additive with non-contaminated pickling paste and normal temperature. Thus, the purpose of whitening the stainless steel. It basically looks like a look. This method is suitable for large and complex products. Stainless steel surface gloss treatment: According to the complexity of the stainless steel products and user requirements is different respectively by mechanical polishing, chemical polishing and electrochemistry polishing method to achieve mirror Shi Guangze. Here are three ways to make a choice: Table 1 Project method advantage Disadvantages Applicable Products Remarks Mechanical polishing Good leveling, bright Labor intensity, serious pollution, complex pieces difficult to process, shiny decline, high investment and cost Simple parts, medium and small products, complex parts can not be processed The whole product gloss is not consistent, shiny to keep time is not long Chemical polishing Less investment, complex pieces can throw, high efficiency, fast Lack of brightness, polishing fluid to humidification, gas spill, the need for appropriate equipment Complex products, low brightness requirements of the product can be used Small batch processing is more cost-effective Electrochemical polishing Up to the mirror glossy, long-term maintenance, process stability, less pollution, low cost, good pollution prevention One-time investment large, complex parts to be installed equipment, auxiliary electrodes, mass production to cool Dirt products, requiring a long time to keep the mirror light, bright products Stable process, easy to operate, can be widely used Stainless steel is not only used in the color of stainless steel, it also increases the color of the product, and increases the durability and wearability of the products. The stainless steel coloring method has the following: (1) ionic deposition oxide or oxide. (2) high temperature oxidation. (3) chemical oxidation. Electrochemical oxidation. (4) the gas phase cracking method. A brief description of various methods is summarized as follows: (1) ion deposition oxide or oxide method, is put stainless steel workpiece in the vacuum evaporation plating in vacuum coating machine, such as: titanium plating hand watch case and band. It is usually golden. This method is suitable for mass production. Because investment is big, cost is high, small batch product is not economical. (2) the high temperature oxidation method is in particular molten salt, the workpiece stays in certain scope of process, the workpiece to form a certain thickness of oxide film, and present a different color. (3) chemical method is in particular solution, the color of the membrane, are formed by chemical oxidation generally have used “by law”, but need to be able to guarantee a batch of product colour and lustre is consistent, must be controlled by reference by telex. (4) electrochemical method, which is used in a particular solution, by electrochemical oxidation. (5) gas phase cracking, which is more complicated, is less applied in industry. (4) description: This paper briefly introduces the method of surface treatment of stainless steel, which is specific to the requirements of the products and which method to choose. Depending on the product, the material and the surface requirements are different. Choose to implement the feasible work plan. Since the formula for the process is trade secret, it is not easy to write here, please understand. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Additives have the effect of inhibiting corrosion and increasing light. It can form a complicated adsorption layer on the surface of stainless steel, activate the microconvex point on the surface of the parts, and blunt the microconcave point to make the polishing effective. Refers to this kind of additive of polishing fluid viscosity regulator, corrosion inhibitor, etch, activator and antifoaming agent, because they exist, chemical polishing can smoothly, surface polishing effect. The additives include inorganic salt, organic salt, organic compound, surfactant, etc. (1) inorganic salt. They are mainly sulphate, phosphate, nitrate, acetate, molybdate, chloride, fluoride, etc. (2) organic compounds are mainly glycerin (glycerin), if ding, organic amine, gelatin, dextrin, sodium dodecyl sulfate and thiourea, polyol, cellulose ether and polyethylene glycol, chlorine alkyl which the organism, halogen compounds, sulfosalicylic acid, azo dyes, etc. (3) the light agents that have a strong effect are benzoic acid, salicylic acid, sulfonic acid, benzene diphenol, and fluoroseason ammonium salt. The type and concentration of additives are determined by the quality of polishing, and the average dosage is 0.1% ~ 1.0%, which is the composition and temperature of the polishing liquid. The sulfur vein is easily decomposed in high temperature, so it should not be used at high temperature. Some additives, such as collagen, dyes, salicylic acid, hydroquinone, etc., should be pre-arranged in saturated solution and in the polish. As a inhibitor, it is suitable for the use of 1 ~ 5g/L, which is used as a inhibitor of butyl dimethylamine (dimethylbenzene) and ulothene (CH2) 6N4. As a light agent, chlorine alkyl, halogen, and sulfonic acid are used for 3-5g/L. The mixture of cellulose ether and polyethylene glycol is 20 ~ 40g/L. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The 904L stainless steel number is 00cr20ni25m02.5cu, which is a highly alloyed super-austenitic stainless steel with low carbon content. In dilute sulphuric acid, there is a good corrosion resistance, and the addition of copper makes it very resistant to acid, designed for harsh conditions. So this kind of stainless steel is used mainly for the manufacture of corrosion resistant pressure vessels. The elements of 904L are mainly composed of elements such as Cr and Ni, which are difficult to process, and the machining is poor, and the main reasons are as follows. 1) 904L stainless steel is more powerful than other kinds of stainless steel. Because 904 l although not high hardness (70 ~ 90 HRB), but has good plasticity and elongation of 40% or higher, a reduction of 50% or more, the tensile strength at б b p 490 mpa, yield strength at 0.2 or greater б 216 mpa, and large plastic deformation in the process of cutting, the cutting force increases. 2) the thermal conductivity is low. Thermal conductivity of 904 l stainless steel (20 ℃) is 12.9 W/(m K), low thermal conductivity, only a quarter of the 45 steel (45 steel thermal conductivity is 47.5 W/(m K)). Thermal conductivity is one of the main factors influencing the cutting heat conduction, the lower the thermal conductivity of the material processed, heat was taken away by the chip and workpiece is less, while the accumulation of heat on the cutting tool, the tool wear easily. 3) it is easy to be a cross product. Due to the 904 l stainless steel toughness is big, so in the process of cutting and cutting tool materials, strong affinity, when cutting tool rake face and chip of the underlying strong friction in metal, under the action of high temperature and high pressure will produce adhesion phenomenon, generate the devolop tumor, is not easy to obtain high surface roughness requirements of machining surface. 4) shavings are not easy to bend and break. 904L stainless steel has a high elongation rate, so it is not easy to bend and break in the cutting process. If appropriate measures are not taken, it will affect the normal process of the cutting process and can easily scratch the surface and even cause the cutter to collapse and damage. Due to the above characteristics of 904 l stainless steel, with conventional cutting tools and the traditional method of cutting, even select a very small cutting parameter, cutting tool is still easy to wear and tear, low machining efficiency, and it is difficult to achieve pattern required by the surface roughness of workpiece and machining accuracy. Source: China 904L Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The 304 stainless steel pipe is the most widely used for stainless steel, the equipment for food, general chemical equipment, and the atomic energy industry. 304 stainless steel pipe is a kind of common stainless steel pipe, it is widely used to make for a good comprehensive performance, corrosion resistance and formability of equipment and parts. The 304 stainless steel pipe is the most widely used stainless steel, heat resistant steel. Used in food production equipment, chemical equipment, nuclear power, etc. 304 stainless steel pipe chemical composition specification C Si Mn P S Cr Ni (nickel) Mo SUS304 less than or less than 0.08 is less than or equal to 1.00 or less than 0.03, or less than 0.05, or 0.03, 18.00-20.00, 8.25 ~ 10.50 Stainless steel is a versatile stainless steel material that is stronger than stainless steel in the 200 series. It is also good for high temperature, which can be up to 1000-1200 degrees. 304 stainless steel has excellent corrosion resistance and good corrosion resistance. The 304 stainless steel material concentration is less than 65 percent of the boiling temperature, which is highly resistant to corrosion. Alkaline solution and most organic acids and inorganic acids also have good corrosion resistance. In air or chemical corrosion resistant to corrosion medium of a kind of high alloy steel, stainless steel is a beautiful surface and corrosion resistant performance is good, need not after surface treatment, such as color of plating and the surface of the stainless steel inherent performance, used in a variety of steel a, often called stainless steel. It represents the performance of 13 chrome steel, 18-8 chrome nickel steel. From the perspective of metallography analysis, because the stainless steel containing chromium and make the surface form very thin chromium film, the film is isolated from intrusion in the steel corrosion of oxygen. Stainless steel pipe weight formula: [outer diameter – wall thickness] * 0.02491 = kg/meter (weight per meter) Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The quality of the surface of the stainless steel tube is mainly determined by the pickling process after the heat treatment. However, if the surface heat treatment is formed on the surface of the heat treatment, the surface roughness and uniformity can not be improved by acid pickling. So should pay full attention to heat treatment before heating or heat treatment surface cleaning. … The quality of the surface of the stainless steel tube is mainly determined by the pickling process after the heat treatment. However, if the surface heat treatment is formed on the surface of the heat treatment, the surface roughness and uniformity can not be improved by acid pickling. So should pay full attention to heat treatment before heating or heat treatment surface cleaning. If the thickness of the surface of the stainless steel tube plate is not uniform, the thickness of the surface of the base metal below the thick and thin place is also different, and the surface oxide of the surface oxide is dissolved and oxidized by the oxidized skin The degree of different, so the steel surface is not uniform. Therefore, when the heat treatment is heated, it is necessary to uniformly form the scale. To meet this requirement, attention should be paid to the following conditions. (1) If the surface of the workpiece is attached with oil, the thickness of the scale of the oil adhering site and the thickness and composition of the other parts are different and carburizing. The carburized part of the base metal will be severely attacked by acid. Heavy oil burner when the initial combustion of oil droplets, if attached to the workpiece, the impact is also great. The operation of the fingerprints attached to the workpiece will also be affected. Therefore, the bath for the major members do not touch the stainless steel pipe directly, do not make the workpiece stained with new oil. Must wear clean gloves. If the surface of the workpiece if the cold processing of lubricating oil, etc., must be in the trichlorethylene degreasing agent, caustic soda solution in the full degreasing and then rinse with warm water, and then heat treatment. (2) If the surface of the workpiece there are debris, to be other organic or gray attached to the workpiece, the heating of course, will have an impact on the scale. (3) Oxygen or oil flames Direct contact with the surface of the stainless steel pipe and the place where there is no difference in the scale of the scale. Therefore, it is necessary to make the treatment member not directly in contact with the flame port during heating. (4) If the local part of the treatment part before the heat treatment of residual scale, after heating the remaining parts of the scale and the site of no scale, there will be the thickness of the scale and composition of the difference, causing pickling after the surface is not Evenly, so not only pay attention to the final heat treatment, but also pay full attention to the middle heat treatment and pickling. (5) the effect of different surface finish If the surface finish is different, even if the same heating, the surface roughness and fine oxide scale is not the same. For example, where the local defects are cleaned and where they are not cleaned, the conditions of the formation of the scale are different, so that the surface of the workpiece is not uniform after pickling. (6) the difference between the furnace atmosphere Furnace atmosphere in the local differences, the formation of a scale will change, which is caused by acidity after the reasons for uneven. Therefore, in the heating, the furnace parts of the atmosphere must be the same. To this end, we must also consider the cycle of the atmosphere. In addition, it is necessary to evaporate the moisture, and the parts of the direct contact with the water vapor are different from those of the other parts, and the formation of the scale is, of course, It is different. Therefore, objects that are in direct contact with the heated workpiece must be fully dried to use. However, after drying, such as placed at room temperature, in the case of high humidity, the water will still condense on the surface of the workpiece. So, it is best to dry before use. Source: China Steel Tube Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

304 stainless steel pipe with its good heat resistance, and is widely used in the production of corrosion-resistant and forming the equipment and mechanical parts. At present, 304 stainless steel pipe has been widely used in food, chemical, atomic and other industrial equipment and decoration areas. GB 304 Chemical composition: grades 0Cr18Ni9, C≤0.08, Si≤1.00, Mn≤2.00, P≤0.035, S≤0.030, Ni: 8.00-11.00, Cr: 17.00-19.00 TP304 Chemical composition: C≤0.08, Si≤1.00, Mn≤2.00, P≤0.045, S≤0.030, Ni: 8.00-11.00, Cr: 18.00-20.00 304L Chemical composition: Grade 00Cr18Ni10, C≤0.03, Si≤1.00, Mn≤2.00, P≤0.035, S≤0.030, Ni: 8.00-11.00, Cr: 18.00-20.00, 304, TP304, 304L Simple distinction: ① 304 and TP304: 304 is the national standard, grade 0Cr18Ni9, TP is the abbreviation of Tube / Pipe, is the American standard representation, it is mainly used for piping with stainless steel; GB 304 and TP304, carbon content and Phosphorus content is different, the main difference is the difference between Cr chromium content, which TP304 chromium content is higher, reaching more than 18, so its corrosion resistance and price than the national standard 304 slightly higher. ② 304 and 304L comparison: 304L and 304 is the main difference between the different carbon content, of which 304 carbon content is less than or equal to 0.08, and 304L carbon content is less than or equal to 0.03; Secondly, 304 is a versatile stainless steel, It is widely used in the manufacture of equipment and components that require good overall performance (corrosion resistance and formability), and 304L is a variant of 304 stainless steel with a low carbon content for applications where welding is required. The lower carbon content minimizes the amount of carbides that are precipitated in the heat affected zone near the weld, and the precipitation of the carbide can cause the intergranular corrosion of the stainless steel in some environments. Domestic and foreign 304 grade table: Grade China Japan American British Germany 304 0Cr18Ni9 SUS304 TP304 304S15 X5Cr-Ni18 Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Allegheny Ludlum’s 317LXN™ is molybdenum-bearing austenitic stainless steel with greatly increased resistance to chemical attack as compared to the conventional chromium-nickel austenitic stainless steels such as Type 304. AL 317LXN™ alloy also offers higher creep, stress-to-rupture, and tensile strength at elevated temperatures than conventional stainless steels. The alloy has low carbon to provide resistance to sensitization during welding and other thermal processes. The combination of increased levels of molybdenum and nitrogen enhance resistance to pitting and crevice corrosion especially in process steams containing acids, chlorides and sulfur compounds at elevated temperatures. Nitrogen also serves to increase the strength of this alloy. This alloy is intended for severe service conditions such as flue gas desulfurization (FGD) systems.Information provided by Allegheny Ludlum Corporation. Table 1 ASTM A240 Chemical composition (wt%) Component Elements Properties Metric English Comments Carbon, C <= 0.030 % <= 0.030 % Chromium, Cr 17 – 20 % 17 – 20 % Iron, Fe 60 % 60 % as balance Manganese, Mn <= 2.0 % <= 2.0 % Molybdenum, Mo 4.0 – 5.0 % 4.0 – 5.0 % Nickel, Ni 13.5 – 17.5 % 13.5 – 17.5 % Nitrogen, N 0.10 – 0.20 % 0.10 – 0.20 % Phosphorous, P <= 0.040 % <= 0.040 % Silicon, Si <= 0.75 % <= 0.75 % Sulfur, S <= 0.030 % <= 0.030 % Corrosion resistance: 317LXN, 317LX and 317L stainless steel in the medium corrosive media in the more ordinary 304 stainless steel has a higher corrosion resistance, usually, 18-8 stainless steel does not produce corrosion of the environment, the stainless steel is not Mo Will produce corrosion, but strong oxidizing acids, such as nitric acid. In the sulfuric acid solution, 317LXN, 317LX and 317L are more resistant to corrosion than 304 stainless steel, and as the Mo content increases, the corrosion resistance increases. These three stainless steels can withstand corrosion at 49 ° C and 5% sulfuric acid. When the temperature is below 38 ° C, these three stainless steels also exhibit excellent corrosion resistance in higher concentrations of sulfuric acid. However, field tests are recommended to better assess the effect of specific operating conditions on corrosion behavior of the alloy. In the process environment containing sulphide-containing furnace gas condensate, these three stainless steels are more resistant to corrosion than the 316 stainless steel. In this environment, the concentration of acid will significantly affect the corrosion rate of corrosion and corrosion of the alloy, which should be carefully tested by field test corrosion of various alloys. Table 2 shows the uniform corrosion rates for 317LXN, 317LX and 317L strip samples in ASTM standard test solutions, and the values for 316L, AL-6XN and AL-276 alloys are also listed in the table for comparison. Test solution Corrosion rate MPy（mm/y） 316L 3317L 317LXTM 317LXNTM AL-6XN? AL276TM 20% Acetic acid 0.12 (<0.01) 0.48 (0.01) 0.24 (<0.01) 0.12 (<0.01) 0.12 (0.01) 0.48 (0.01) 45% Formic acid 23.41 (0.60) 18.37 (0.47) 11.40 (0.29) 11.76 (0.30) 4.56 (0.12) 2.76 (0.07) 10% Oxalic acid 48.03 (1.23) 44.90 (1.14) 46.68 (1.19) 35.76 (0.91) 10.92 (0.28) 11.24 (0.28) 20% Phosphoric acid 0.60 (0.02) 0.72 (0.02) 0.72 (0.02) 0.24 (<0.01) 0.24 (<0.01) 0.36 (0.01) 10% Sulfuric acid 635.7 (16.15) 298.28 (7.58) 255.00 (6.48) 157.80 (4.01) 84.36 (2.14) 13.93 (0.35) 10% Sulfite 71.57 (1.82) 55.76 (1.42) 25.08 (0.64) 15.60 (0.40) 24.00 (0.61) 2.64 (0.07) 50% Sodium hydroxide 77.69 (1.92) 32.78 (0.83) 69.18 (1.76) 85.68 (2.18) 15.96 (0.41) 17.77 (0.45) ASTM A262 B（FeSO2·H2SO4） 26.04 (0.66) 20.76 (0.53) 23.52 (0.60) 17.28 (0.44) 21.36 (0.54) 264.5 (6.72) ASTM A262 C (65%HNO3) 22.31 (0.56) 19.68 (0.50) 48.24 (1.23) 16.32 (0.42) 29.04 (0.74) 908.0 (23.06) ASTM A262E (Cu·CuSO4·H2SO4) pass pass pass pass pass pass The carbon content of these three alloys is less than 0.03%, low carbon content effectively improve their resistance to intergranular corrosion during welding or forging. 317LXN, 317LX and 317L stainless steel contain higher Cr, with better resistance to intergranular corrosion. However, it should be noted that prolonged exposure to the temperature range of 417-816 ℃, due to the precipitation of δ phase, will greatly reduce the corrosion resistance of these alloys, while the material may also become brittle. The higher N content of 317LXN delays the precipitation of δ and carbide precipitates. Table 3 pitting index of various alloys Alloy PRE 316 317L 317LXTM 317LXNTM AL-904LTM AL-6XN AL TEMP 625 AL276TM 25 30 34 38 36 48 52 69 As shown in Table 3, the high Mo high N significantly improved the pitting index (PRE) of the alloy, that is, the corrosion resistance of the alloy, the PRE value was based on the corrosion test results. The corrosion test found that CI-point corrosion performance, N is 30 times the effectiveness of Cr, is 9 times the Mo. The critical crevice corrosion temperature of stainless steels and nickel-based alloys measured according to the modified ASTM G48 B test method is significant (see Table 4). It can be seen from Table 4, with the austenitic stainless steel Mo and N content increased, the alloy critical crevice corrosion temperature also greatly improved. Table 4 the critical crevice corrosion temperature of various alloys Alloy ℃ 316 825TM 317L 317LXTM 317LXNTM AL-904LTM AL-6XN AL TEMP? 625 AL276TM －3 －3 2 18 24 20 43 45 55 317LXN, 317LX, 317L stainless steel in the acidic solution containing CI- or other halogen ions in the 316,304 type stainless steel has better resistance to corrosion and crevice corrosion, so the three kinds of stainless steel is often used for flue gas Desulfurization system (FGD). Table 5 shows the crevice corrosion test data for the various alloys in the simulated FGD solution. Table 5 Corrosion data of various alloys in simulated FGD test solutions Alloy Weightlessness（g/cm2） 24℃ （75°F） 50℃ （122°F） 70℃ （158°F） 317L 317LXTM 317LXNTM AL-6XN AL TEMP 625 AL276TM 0.0007 0.0000 0.0000 0.0000 0.0000 0.0000 0.0377 0.0319 0.0129 0.0000 0.0000 0.0001 0.0500 0.0462 0.0462 0.0266 0.0149 0.0004 According to ASTM G 48 B operating procedures, the test time: 72 hours Solution Ingredients: 7 vol% H2SO4, 3 vol% HCI, 1 wt% CuCI2, 1 wt% FeCI3 Antioxidant: In the atmospheric environment, Cr-Ni-Mo stainless steel has excellent oxidation resistance and low descending speed when the temperature is lower than 871 ~ 899 ℃. Manufacturing: 317LXN, 317LX, 317L stainless steel physical properties and mechanical properties similar to the conventional 316 and 304 stainless steel, which can be used in the same way as ordinary stainless steel manufacturing. Forging: the three kinds of stainless steel recommended forging temperature is 1150 ~ 1205 ℃, the final forging temperature of 927 ~ 955 ℃. Heat treatment: 317LXN, 317LX, 317L stainless steel can be in the temperature range of 1080 ~ 1175 ℃ heat treatment, and then according to the thickness of water or air cooling. The plates should be heat treated at 1150 ° C and 1170 ° C and then allowed to cool the material from red and white at an annealing temperature to black in 3 minutes. Hardness: These three kinds of stainless steel can not improve the hardness by heat treatment. Welding: welding with high alloy welding material to maintain the corrosion resistance after welding. When welding 317L stainless steel, the welding material should contain at least 6% Mo; welding 317LX and 317LXN stainless steel, the welding material should contain at least 8% Mo, such as the use of 625 alloy as a welding material. In the actual welding operation, if you can not use high matching welding materials, and can not be post-weld heat treatment and pickling, you need to carefully consider whether the self-welding weldment to meet the requirements of the process conditions. 317LXN, 317LX, 317L Self-welded welders are heat treated and pickled to obtain the best corrosion resistance. ASTM A-380 “Recommended procedure for descaling and cleaning of steel surfaces” can provide more information on pickling information. Table 6 ASTM A-240 provides the minimum mechanical properties Performance 317L 317LXTM 317LXNTM Tensile Strength MPa 515 515 550 Yield Strength （0.2%）MPa 205 205 240 Elongation (5%) 40 40 40 Hardness (Max) 217BHN / / UNS NO. S31703 S31725 S31726 Table 7 317LXN, 317LX, 317L stainless steel physical properties Density 8.0 g/cm3 Elastic Modulus 200 GPa Melting point 1320—1400 ℃ Thermal conductivity 20~100℃ 14.6 Walts/m °K Thermal expansion coefficient 100℃ 500℃ 1000℃ 16.5 18.2 19.5 10-5/℃ 10-5/℃ 10-5/℃ Specific heat 0.46 J/G °K Conductivity 0.79 μ-ohm-m Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. The atmospheric corrosion The corrosion resistance of the stainless steel pipe fitting is basically the amount of chloride in the atmosphere. Therefore, it is extremely important to be near the ocean or other chloride sources to corrode stainless steel pipe fitting parts. A certain amount of rain is important only when the chloride concentration of the steel surface ACTS. The rural environment of 1Cr13, 1Cr17 and austenitic stainless steel pipe fittings can be used for various purposes, and there will be no significant change in appearance. As a result, the stainless steel pipe fittings exposed in rural areas can be selected based on price, market availability, mechanical performance, manufacturing performance and appearance. Industry environment in the absence of chlorine pollution environment, 1 cr17 and austenite size stainless steel pipe fittings can work for a long time, basically no rust, could form dirt film on the surface, but when the film after clear, bright still maintained the original appearance. In an industrial environment of chloride, corrosion of stainless steel pipe fittings will be caused. Marine environment 1 cr13 and 1 cr17 stainless steel pipe fittings in the short term will form a thin film rust, but will not result in obvious changes in the size, shape stainless steel pipe fittings such as 1 cr17ni7 austenite, cr18ni9 1 and 0 cr18ni9, when exposed in ocean environment, may be some rust. Rust is usually shallow and can be easily cleared. The 0Cr17Ni12M02 contains molybdenum stainless steel pipe fittings which are basically corrosion-resistant in the Marine environment. In addition to atmospheric conditions, there are two other factors that affect the corrosion resistance of stainless steel pipe fittings. It is the surface state and the manufacturing process. The machining level affects the corrosion resistance of the stainless steel pipe fitting in the environment of chloride. Matte surfaces are very sensitive to corrosion. The normal surface of industrial processing is less sensitive to corrosion. Surface precision is also affected by the removal of dirt and rust. It is easy to remove dirt and rust from the surface of highly refined processing, but it is difficult to remove from the surface. For matte surfaces, if you want to maintain the original surface, you need to clean up a lot. 2. The fresh water Fresh water can be defined as water from rivers, lakes, ponds or Wells, regardless of acidity, salt or salt. The corrosion of fresh water is affected by the pH, oxygen content and scale of the water. Scale (hard) water. The corrosion is mainly determined by the amount and type of scaling of the metal surface. The formation of this scale is the presence of minerals and temperature. Non-fouling (soft) water is generally more corrosive than hard water. It can be reduced by increasing pH or by reducing oxygen content. 1Cr13 stainless steel pipe fitting is significantly more resistant to fresh water than carbon steel, and has excellent characteristics in fresh water. This type of steel is widely used for such purposes as the need for high strength and corrosion-resistant docks and DAMS. However, it should be considered in some cases. 1Cr13 May be sensitive to moderate erosion in fresh water, but point erosion can be avoided by cathodic protection methods. The 1Cr17 and austenitic stainless steel pipe fittings are almost completely resistant to freshwater corrosion at room temperature (ambient temperature). 3, Acidic water Acidic water is a contaminated natural water that is leached from ore and coal, which is much more corrosive than natural fresh water. , because the water contained in the sulfide leaching of ore and coal, acidic water usually contains a large number of free sulfuric acid, in addition, the water contains a large number of ferric sulfate, has very big effect to corrosion of carbon steel. Carbon steel, which is affected by acidic water, is usually quickly corroded. The results of experiments using the various materials used by acidic river water indicate that the austenitic stainless steel pipe fitting has high corrosion resistance in this environment. Austenite size stainless steel pipe fittings in fresh water and acid water has excellent corrosion resistance, especially its corrosion film on the heat conduction block is small, so widely used stainless steel pipe fittings pipe in the heat exchange purposes. 4, Salt water The corrosive characteristics of salt-water are often seen in the form of pitting. In the case of stainless steel pipe fittings, it is largely due to the partial destruction of the passive film with the corrosive effect of salt water. The other reason for the corrosion of these steel is that they are attached to the stainless steel pipe fittings and other seawater organic materials can form the strong differential batteries. Once formed, these cells are very active and cause a lot of corrosion and pitting. In the case of high salt water, such as pump impeller, the corrosion of austenitic stainless steel pipe fitting is usually very small. In the case of the condenser with stainless steel pipe fitting, the water flow rate is greater than 1.5m/s, so that the seawater organic and other solids are the least concentrated in the pipe. The structure of stainless steel pipe fittings for the treatment of saline water is best designed to reduce the gap and use thick wall parts. 5. Soil Metals embedded in the soil, depending on the weather and other factors, are at any time in a complex state of flux. In practice, the austenitic stainless steel pipe fittings have excellent properties for most soil corrosion, while 1Cr13 and 1Cr17 have some erosion in many soils. The 0Cr17Ni12Mo0 stainless steel pipe fitting is completely resistant to corrosion in all soil experiments. 6. Nitric acid The stainless steel pipe fitting and austenitic stainless steel pipe fittings and austenitic stainless steel pipe fittings have excellent corrosion resistance. 1Cr17 stainless steel pipe fitting is widely used in the processing equipment of nitric acid plant. However, since 0Cr18Ni9 usually has good forming performance and welding performance, it has replaced 1Cr17 stainless steel pipe fitting in large quantities in the above use. The corrosion resistance of other austenitic stainless steel pipe fittings is similar to that of 0Cr18Ni9. The stainless steel pipe fitting is usually slightly more corrosive than 0Cr18Ni9, and the higher temperature and concentration have a greater detrimental effect on it. If improper heat treatment of steel, hot nitric acid will make austenitic stainless steel and iron grain size fitting produce intercrystalline corrosion, therefore, can use the appropriate heat treatment to prevent this type of corrosion, or use this type of corrosion resistant stainless steel pipe fittings. 7. Sulfuric acid Standard stainless steel pipe fitting plates are rarely used in acid solutions because they can be used in a narrow range. At room temperature, the type 0Cr17Ni12Mo2 stainless steel pipe fitting (the standard number for the most sulfuric acid corrosion) is less than 15% in sulfuric acid concentration. Or more than 85% resistant to corrosion. However, at higher concentrations, carbon steel is commonly used. The martensitic and iron body shape stainless steel pipe fittings are generally resistant to sulfuric acid solutions. As in the case of nitric acid, if the stainless steel pipe fitting is not properly treated, sulphuric acid can cause corrosion. For welding structures that do not undergo heat treatment after welding, use the low carbon number 00Cr19Ni10 or 00Cr17Ni14M02, or the stabilized number 0Cr18Ni11Ti or 0Cr18Ni11Nb stainless steel pipe fittings. 8. Phosphate Austenitic stainless steel pipe fittings have good corrosion resistance to phosphate and are widely used in the production and processing equipment of phosphoric acid. At temperatures up to 107 ℃ under the condition of various concentrations, its effective corrosion resistance. Under the condition of the highest temperature about 95 ℃, with 0 cr17ni12m02 stainless steel pipe fittings of equipment is a good way to deal with (phosphoric acid) “more than 100% H3p04). It should be noted that fluoride or chloride salts are sometimes found in phosphoric acid produced by wet process. The presence of these halogens in acids may have detrimental effects on corrosion resistance of stainless steel pipe fittings. The corrosion resistance of the martensitic and iron stainless steel pipe fitting parts is significantly worse than the austenitic stainless steel pipe fitting, so it is not commonly used in this acid. 9. Hydrochloric acid Even at room temperature, the solution of hydrochloric acid at various concentrations quickly corrodes the stainless steel pipe fittings. stainless steel pipe fitting is not possible in this acid. 10. Other inorganic acids Austenite size stainless steel pipe fittings in almost all kinds of concentration and temperature are generally has good resistance to boric acid, carbonic acid, chlorate and the performance of the chromic acid corrosion, 100% except the chlorate. The corrosion resistance of 1Cr13 and 1Cr17 stainless steel pipe fittings to chromic acid is significantly inferior to austenitic stainless steel pipe fitting, but it has the performance of relatively good boric acid and carbonic acid corrosion. 11, acetic acid, Austenite size stainless steel pipe fittings general has excellent resistance to acid corrosion performance, grain size and martensite and iron the purpose of the stainless steel pipe fittings for most acetic acid corrosion resistance is not appropriate. Austenite size stainless steel pipe fittings at room temperature can resist the corrosion of various concentrations of acetic acid, at higher temperature, 0 cr17ni12mo2 and 0 cr19ni13m03 than other austenite size acetic acid corrosion resistance of stainless steel pipe fittings have been better. 12, formic acid At room temperature, any austenitic stainless steel pipe fittings can be treated completely with formic acid. However, when it is hot, it can quickly corrode stainless steel pipe fittings that do not contain molybdenum, and therefore require the use of 0Cr17Ni12M02 and 0Cr19Ni13M03. At various temperatures, the acid will soon corrode the martensite and the stainless steel pipe fitting. 13, oxalic acid In general, stainless steel pipe fitting has good resistance to oxalic acid corrosion at least 50% at room temperature and maximum concentration. At higher temperatures, however, the oxalate solution, as at room temperature and concentration at 100%, will corrode all stainless steel pipe fittings. 14, lactic acid 0 cr18ni9 stainless steel pipe fittings in the highest temperature of about 38, < / SPAN > when ℃ can be used for lactic acid storage devices. At higher temperatures, non-molybdenum austenitic stainless steel pipe fitting is a bit denuded, so the priority is 0Cr17Ni12M02 and 0Cr19Ni13M03. Martensitic stainless steel pipe fittings are generally less resistant to lactic acid corrosion. 15, alkali stainless steel pipe fittings usually have a good performance against weak alkaline corrosion, such as ammonium hydroxide. For strong base, such as sodium hydroxide and potassium hydroxide, the highest temperature is about 105 ℃, the concentration of about 50%, the highest austenite size stainless steel pipe fittings with good corrosion resistance, high temperature and the concentration of corrosion rate may become significant. When the temperature is above the normal pressure boiling point (and the lower temperature, near 50%), the stainless steel pipe fitting of the austenitic body will appear in the stress corrosion crack. 16,, Salt acid Besides the halide solution under certain conditions, stainless steel pipe fittings in general has excellent resistance to corrosion performance, hydrochloric acid solution for acid salt, corrosion resistance of stainless steel pipe fitting in a certain extent inevitably affected by salt water solution formed by the influence of the special acid. The stainless steel pipe fitting parts (0Cr17Ni12Mo2 and 0Cr19Ni13Mo3) are usually better than other stainless steel pipe fittings in the case of a higher temperature acidic solution. In stainless steel pipe fittings used in halide solution, especially in chloride solution, should take into account the average corrosion rate is low, but the pitting corrosion and stress corrosion crack (or) under certain conditions can also be produced. Although there are many in chloride using stainless steel pipe fittings obtain excellent effect (such as food processing equipment and under the condition of relatively low temperature flowing seawater) but must consider the different purposes. The occurrence of spot or stress corrosion cracks depends on many factors, such as environment and equipment design and operation. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)