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These stainless steel have the good heat-resisting performance, is suitable in the steam environment or 550℃ and the above temperature. 310S Stainless steel is a combination of good strength and corrosion resistance in temperature up to 2100oF (1149℃). Due to its relatively high chromium and nickel content it is superior in most environments to 304 or 309 stainless.  309S High corrosion-resistant, chromium nickel grade with carbon limited to .08 to reduce carbon precipitation during welding. Maximum Recommended Service Temperature Continuous 1100℃ /Intermittent  980℃ 304H the carbon content is controlled to a range of 0.04-0.08 to provide improved high temperature strength to parts exposed to temperatures above 800°F (427℃) 321H advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427℃ to 816°C).  347H in higher elevated temperature allowable stresses for these stabilized alloys for ASME Boiler and Pressure Vessel Code applications. The 321 and 347 alloys have maximum use temperatures of 1500°F (816°C)  310S | 309S | 304H | 321H | 347H Standard: ASTM A213,EN 10216-5  Anticorrosion environment: The temperature may reach 800 ℃  Application: Boiler,etc Grade(UNS):Austenitic Stainless Steel: 304/304L/304H(1.4301/1.4306/1.4948); 316/316L(1.4401/1.4404); 316Ti(1.4571); 321(1.4541);309S (1.4833); 310S(1.4845); 317L(1.4438); 321H(1.4878); 347H (1.4550); Duplex Stainless Steel: S32001, S32003, S31500, 2205(1.4462); S32304,(1.4362);S31803,2507 (S32750),S32760(1.4501);S32101(1.4162); Super Austenitic Stainless Steel: 904L, S30432, S31042, 6Mo (S31254, N08367)  Nickel Base Alloys: Alloy 20 (UNS N08020), Monel 200 (UNS 02200), Monel 400 (UNS N04400), Incoloy 800 (UNS N08800), Incoloy 800H (UNS N08810), Incoloy 800HT (UNS N08811), Incoloy 825 (UNS N08825),Inconel 600 (UNS N06600), 4J29, 4J36, GH3030, GH3039, C276 (UNS N10276) Martensitic Stainless Steel:410(1.4006), 410S(1.4000), 420(1.4021) Ferritic Stainless Steel:405(1.4002), 430(1.4016) Outside Diameter:6 – 830mmWall Thickness:0.50 – 60mmStandards (Norm):EN 10216-5; DIN 17456, DIN 17458, DIN 2462, DIN 17455GB/T14975; T14976; T13296; GB5310;ASTM A213, A269, A312, A511, A789, A790, A928, A999, A1016, ASTM B161, ASTM B163, ASTM B165, ASTM B167, ASTM B338, ASTM B407, ASTM B423, ASTM B444,ASTM B619, ASTM B622, ASTM B626, ASTM B668, ASTM B677, ASTM B829JIS G3459, JIS G3463, JIS G3446, JIS G3447, JIS G3448, JIS G3468GOST 9940;GOST 9941; Use of stainless steel under high temperature condition refer table Corrosion Resistant Stainless Steel Tubes Corrosion Resistance of Stainless Steel Tubes High Temperature Stainless Steel Tubes High Temperature Stainless Steel Tubes High Temperature Property Stainless Steel Tubes Heat resistant Stainless Steel Tubes Welded Stainless Steel Pipes Stainless Steel Tube Fitting U-bend Stainless Steel Tubes Steel Tube Pipe Classification Nickel Alloys Pipes and Tubes Heat Exchanger Tubes Duplex Stainless Steel Tubes  Boiler Tubes, Condenser Tubes Corrugated Seamless Stainless Steel Pipe Tubes DIN 2391 Seamless Precision Steel Tubes DIN2391 Seamless Pricision Steel Tubes Non Acid-resisting Stainless Steel Tubes Bright Annealing Stainless Steel Tubes High Temperature-Tubes and Pipes Standards Hydraulic and instrumentation tubes High Temperature Change Stainless Steel Mechnical Properties Fire resistance rating and testing of stainless steel Heat Resistant Stainless Steels and Corrosion Resistant Stainless Steels-Valve Steels,Iron Baes Super alloys Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Duplex stainless steel 2205 UNS S32305/S31803 is a 22% chromium, 3% molybdenum, 5-6% nickel, nitrogen alloyed duplex stainless steel with high general, localized, and stress corrosion resistance properties in addition to high strength and excellent impact toughness. Duplex stainless steel 2205 provides pitting and crevice corrosion resistance superior to 316L or 317L austenitic stainless steel tube in almost all corrosive media. It also has high corrosion and erosion fatigue properties as well as lower thermal expansion and higher thermal conductivity than austenitic. 2101 is a low nickel, lean duplex stainless steel possessing both superior strength and chloride stress-corrosion crackingresistance when compared to 300 series stainless steel. 2304 is a lean austenitic-ferritic duplex stainless steel with general corrosion resistance similar to 316, but with yield strength nearly double that of austenitic stainless steel. S31803 is a nitrogen, molybdenum enhanced austenitic-ferritic duplex stainless steel with general corrosion resistance similar to 904L, but with a yield strength nearly double that of austenitic stainless steel.  2507 is a super austenitic-ferritic duplex stainless steel with exceptional strength and corrosion resistance ideal for chemical process, petrochemical, and seawater applications. Duplex stainless steel 2205 has below capability: l High intensity and good impact toughness l It can bear stress corrosion well l Good ability to avoid patch and crack l Low heat expand modulus and better heat transmit l High pressure work l Weldable Mechanical property Yield strength (MPa) Tensile strength (MPa) Elongation (%) ≥500≥680≥30 Physics capability density： 7.85g/cm3Grade(UNS):Austenitic Stainless Steel: 304/304L/304H(1.4301/1.4306/1.4948); 316/316L(1.4401/1.4404); 316Ti(1.4571); 321(1.4541);309S (1.4833); 310S(1.4845); 317L(1.4438)321H(1.4878); 347H (1.4550); Duplex Stainless Steel: S32001, S32003, S31500, 2205(1.4462); S32304,(1.4362);S31803,2507 (S32750),S32760(1.4501);S32101(1.4162); Super Austenitic Stainless Steel: 904L, S30432, S31042, 6Mo (S31254, N08367)  Nickel Base Alloys: Alloy 20 (UNS N08020), Monel 200 (UNS 02200), Monel 400 (UNS N04400), Incoloy 800 (UNS N08800), Incoloy 800H (UNS N08810), Incoloy 800HT (UNS N08811), Incoloy 825 (UNS N08825),Inconel 600 (UNS N06600), 4J29, 4J36, GH3030, GH3039, C276 (UNS N10276) Martensitic Stainless Steel:410(1.4006), 410S(1.4000), 420(1.4021) Ferritic Stainless Steel:405(1.4002), 430(1.4016) Outside Diameter:6 – 830mmWall Thickness:0.50 – 60mmStandards(Norm):EN 10216-5; DIN 17456, DIN 17458, DIN 2462, DIN 17455GB/T14975; T14976; T13296; GB5310;ASTM A213, A269, A312, A511, A789, A790, A928, A999, A1016, ASTM B161, ASTM B163, ASTM B165, ASTM B167, ASTM B338, ASTM B407, ASTM B423, ASTM B444,ASTM B619, ASTM B622, ASTM B626, ASTM B668, ASTM B677, ASTM B829JIS G3459, JIS G3463, JIS G3446, JIS G3447, JIS G3448, JIS G3468GOST 9940;GOST 9941; Related References: 1. Duplex Stainless Steel Pipe 2. Duplex Stainless Steel 3. Super-Duplex Stainless Steel 4. Principle of Duplex Stainless Steel 5. How the Austenite Ferrite Balance Achieved 6. Corrosion Resistance of Duplex Stainless Steel 7. Stress Corrosion Cracking SCC of Duplex Stainless Steel 8. Barrier to Using Duplex Stainless Steel 9. Duplex Stainless Steel Grades Comparison Table 10. S32101 | S32205/S31803 | S32304 | S32750 | S32760 ASTM A789/A789M ASTM A 790/A 790M Duplex Stainless Steel Pipe Austenitic-Ferritic Stainless Steel Pipe Super-Duplex Stainless Steels and their characteristics 2507 S32750(1.4410) Duplex Steel S32205 S31803(1.4462) Duplex Steel S32304(1.4362) Duplex Steel Use of stainless steel under high temperature condition refer table Corrosion Resistant Stainless Steel Tube Corrosion Resistance of Stainless Steel Tubes High Temperature Stainless Steel Tubes High Temperature Stainless Steel Tubes High Temperature Property Stainless Steel Heat resistant Stainless Steel Tubes Welded Stainless Steel Pipe  U-bend Stainless Steel Tubes  Heat Exchanger Tubes Duplex Stainless Steel Tubes  Boiler Tubes, Condenser Tubes Corrugated Seamless Stainless Steel Pipe Tube DIN 2391 Seamless Precision Steel Tubes DIN2391 Seamless Pricision Steel Tube Tubing Tubes Non Acid-resisting Stainless Steel Tube Bright Annealing Stainless Steel Tubes High Temperature-Tubes and Pipes Standards Heat Resistant Stainless Steels and Corrosion Resistant Stainless Steels-Valve Steels,Iron Baes Super alloys Compared with the ferritic stainless steel, duplex stainless steel vulnerable Compared with the austenitic stainless steel, duplex stainless steel strengths and vulnerable Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

High Pressure boiler tubes are those tubes, which have the capacity of handling high pressure and temperature. We are having a comprehensive range of high pressure boiler tube. Our production unit is using premier quality of raw material in the production of high pressure boiler tubes.  Condenser are normally chosen for steam heating systems, particularly on water and CIP applications with variable temperature conditions or when inlet water or CIP temperature is low, causing thermal shock conditions. The design features a floating tube sheet arrangement to reduce tube stresses. Standard material for tube-side construction is stainless steel, making these units ideal for acid or alkali wash systems. Delivery Condition: Bright annealed (BA) or Pickel Annealed (PA)  Tubes End: Plain end with caps Packing: Wooden cases, bundle or plastic bags, plywood boxes  Test Certificate: EN 10204 3.1 3.2 PED 97/23/ECGrade(UNS):Austenitic Stainless Steel: 304/304L/304H(1.4301/1.4306/1.4948); 316/316L(1.4401/1.4404); 316Ti(1.4571); 321(1.4541);309S (1.4833); 310S(1.4845); 317L(1.4438)321H(1.4878); 347H (1.4550); Duplex Stainless Steel: S32001, S32003, S31500, 2205(1.4462); S32304,(1.4362);S31803,2507 (S32750),S32760(1.4501);S32101(1.4162); Super Austenitic Stainless Steel: 904L, S30432, S31042, 6Mo (S31254, N08367)  Nickel Base Alloys: Alloy 20 (UNS N08020), Monel 200 (UNS 02200), Monel 400 (UNS N04400), Incoloy 800 (UNS N08800), Incoloy 800H (UNS N08810), Incoloy 800HT (UNS N08811), Incoloy 825 (UNS N08825),Inconel 600 (UNS N06600), 4J29, 4J36, GH3030, GH3039, C276 (UNS N10276) Martensitic Stainless Steel:410(1.4006), 410S(1.4000), 420(1.4021) Ferritic Stainless Steel:405(1.4002), 430(1.4016) Outside Diameter:6 – 830mmWall Thickness:0.50 – 60mmStandards(Norm):EN 10216-5; DIN 17456, DIN 17458, DIN 2462, DIN 17455GB/T14975; T14976; T13296; GB5310;ASTM A213, A269, A312, A511, A789, A790, A928, A999, A1016, ASTM B161, ASTM B163, ASTM B165, ASTM B167, ASTM B338, ASTM B407, ASTM B423, ASTM B444,ASTM B619, ASTM B622, ASTM B626, ASTM B668, ASTM B677, ASTM B829JIS G3459, JIS G3463, JIS G3446, JIS G3447, JIS G3448, JIS G3468GOST 9940;GOST 9941; High Pressure Stainless Steel Boiler Tube, selected prime raw material,cold drawn, cleaning and smooth surface on OD/ID,Withstand high pressure,no deformation after cold bending, no crack and break after flattening and flaring etc.  Widely used in the following fields: High Pressure Boiler, Heater and condenser ,Boiler tubing , Condenser tubing Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Superaustenitic stainless steel has the same structure as the common austenitic alloys, but they have enhanced levels of elements such as chromium, nickel, molybdenum, copper, and nitrogen, which give them superior strength and corrosion resistance. Superaustenitic stainless steel alloys are characterized by their high nickel and molybdenum contents plus nitrogen. The most common of the alloys are 904L, AL-6XN, 254 SMO, 25-6MO and 1925 hMO.Superaustenitic metal designed to resistcrevice corrosion, pitting, chloride-induced corrosion, and stress corrosion cracking. It can also withstand alkaline and salt solutions, protecting against metallic contami- nation of product and preventing rapid degradation of the fluid transfer system. These superaustenitic stainless steel alloys have a face-centered cubic crystal structure similar to other austenitic stainless steel and are non-magnetic and their magnetic permeability remains low even after severe cold forming. The nitrogen addition provides the alloy with improved resistance to pitting and crevice corrosion, a greater resistance to localized corrosion in oxidizing chlorides and reducing solutions plus higher strength. Nitrogen also helps to significantly reduce the potential formation of harmful secondary phases during welding.Superaustenitic Stainless SteelAlloy (UNS Designation) End UseComposition nominal wt%SpecificationsDensity lb/in3 (g/cm3)Tensile Strength ksi. (MPa)0.2%Yield Strength ksi. (MPa)Elong- ation %HardnessN08020 Flue gas scrubbers, Sulphuric acid tanks and racks, Process piping, Heat exchangers, Manufacture of solvents/explosives/plastics/synthetic fibers/organic chemicals/pharmaceuticalsC 0.07 max, Mn 2.0 max, P 0.045 max, S 0.035 max, Si 1.0 max, Cr 19.0-21.0, Ni 32.0-38.0, Mo 2.0-3.0, Cu 3.0-4.0, Cb+Ta (8xC)min-1.0 max, Fe balanceASTM B-463 ASME SB-4630.292 (8.09)80 min (550 min)35 min (240 min)30 min95RockwellB maxS34565 Desalination, seawater piping, offshore oil production, pollution control (FGD)C 0.03 max, Mn 5.0-7.0, P 0.03 max, S 0.01 max, Si 1.0 max, Cr 23.0-25.0, Ni 16.0-18.0, Mo 4.0-5.0, N 0.4-0.6, Cb 0.1 max, Fe balanceASTM A 240 ASME SA-2400.29 (8.03)115 min (795 min)60 min (415 min)35 min100 Rockwell B max904L / N08904 High efficiency furnace vent pipe, pulp & paper processing equipment, welding electrodes and fittings.C 0.02 max, Mn 2.0 max, P 0.045 max, S 0.035 max, Si 1.0 max, Cr 19.0-23.0, Ni 23.0-28.0, Mo 4.0-5.0, N 0.1 max, Cu 1.0-2.0, Fe BalanceASTM A-240 ASME SB-6250.287 (7.95)71 min (490 min)31 min (220 min)35 min90 Rockwell B maxN08367 Desalination, seawater piping and critical components on offshore oil platformsC 0.030 max, Mn 2.0 max, P 0.040 max, S 0.030 max, Si 1.0 max, Cr 20.0-22.0, Ni 23.5-25.5, Mo 6.0-7.0, N 0.18-0.25, Cu 0.75 max, Fe Balance (PREN 50.0 min)ASTM A 240, ASTM B 688 ASME SA-240, ASME SB-6880.291 (8.06)100 min (Sheet) / 95 min (Plate) (690 min / 655 min)45 min (310 min)30 min100 Rockwell B maxN08367 Desalination, seawater piping and critical components on offshore oil platforms.C 0.030 max, Mn 2.0 max, P 0.040 max, S 0.030 max, Si 1.0 max, Cr 20.0-22.0, Ni 23.5-25.5, Mo 6.0-7.0, N 0.18-0.25, Cu 0.75 max, Fe BalanceASTM A 240, ASTM B 688 ASME SA-240, ASME SB-6880.291 (8.06)100 min (sheet) / 95 min (plate) (690 min / 655 min)45 min (310 min)30 min100 Rockwell B maxJS700? N08700 Wet scrubbers in municipal incinerators, wet-process phosphoric acid plants, chlorine dioxide pulp bleachingC 0.04 max, Mn 2.0 max, P 0.04 max, S 0.03 max, Si 1.0 max, Cr 19.0-23.0, Ni 24.0-26.0, Mo 4.3-5.0, Cu 0.5, Cb (8xC)min-0.4 max, Fe BalanceASTM A240 ASTM B5990.287 (7.95)80 min (550 min)35 min (240 min)30 min90 Rockwell B max Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Austenitic Stainless Steel Grades Comparison Table is intended to relate former BS, EN, German and Swedish grade designations to the current EN steel numbers, AISI stainless steel grades and UNS numbers. The table is based on the ‘wrought’ ie long products (stainless steel bars etc), flat products (stainless steel plates etc) steel numbers published in EN 10088 and related standards. Casting products use different composition and so have their own steel numbers in EN 10283. The related castings grades in both EN 10283 and BS 3100 are included in the table. The Chemical ‘Composition’ is intended to represent the composition only. This does not show the specified or typical compositions of commercially available stainless steel. Specified ranges for the wrought European stainless steel grades can be found in either the EN 10088-2 or EN 10088-3 tables. Most of the specified ranges for the ‘BS’ stainless steel grades can be found in the BS 1449 or BS 970 tables. The castings grades specified ranges can be found in the EN 10283 or BS 3100 tables. These are comparisons only and cannot be assumed to be direct equivalent grades. The data given is not intended to replace that shown in inpidual standards to which reference should always be made. Austenitic Stainless Steel Grades Comparison TableEN 10088NamesBSAISIUNSEnGerman DINSSEN 10283BS CastChemical Composition..........CCrNiMoOthers1.4301–304S31304S3040058EX5CrNi18-1023331.4308304C150.07x188––1.4303–305S19305S30500–X5CrNi18-12–––0.06x1811––1.4305–303S31303S3030058MX10CrNiS18-92346––0.10x188–0.35xS1.4306––304L––X2CrNi19-112352––0.030x1810––1.4307–304S11304LS30403––2352–304C120.030x188––1.4310–301S21301S30100–X12CrNi17-72331––.05/.15176––1.4311–304S61304LNS30453–X2CrNiN18-1023711.4309–0.030x189–0.22xN1.4372––201S20100–––––0.15x174.5–6.5Mn1.4401–316S31316S3160058JX5CrNiMo17-12-223471.4408316C160.07x17112–1.4404–316S11316LS31603–X2CrNiMo17-13-223481.4409316C120.030x17112–1.4406–316S61316LNS31653–X2CrNiMoN17-12-2–––0.030x171120.22xN1.4432–316S13316L–––2353––0.030x17112.5–1.4435–316S13316L––XCrNiMo18-14-32353––0.030x17132.5–1.4436–316S33316–58JX5CrNiMo17-13-32343––0.0517112.5–1.4438–317S12317LS31703––2367––0.030x18133–1.4439–––––X2CrNiMoN17-13-5–1.4446–0.030x171340.22xN1.4541–321S31321S3210058BX6CrNiTi18-102337––0.08x189–0.5Ti1.4550–347S31347S3470058FX6CrNiNb18-1023381.4552347C170.08x189–0.5Nb1.4563Sanicro28 /Alloy28––N08028–X1NiCrMoCu31-27-42584––0.02x26303.01.0Cu1.4567–394S17304CuS30430–––––0.04x189–4xCu1.4571–320S31316TiS31635–X6CrNoMoTi17-12-223501.4581–0.08x171120.5Ti1.4539904L904S13904LN08904–X1CrNiMoCuN25-20-525621.4584–0.020x192441.5Cu1.4547254SMO/F44––S31254––23781.4593–0.020x201860.75Cu1.45291925hMo––N08925–X1NiCrMoCuN25-20-6–1.4588–0.020x192461.25Cu Note Chemical composition figures are intended to be representative of the stainless steel grades, not typical. ‘x’ indicates a maximum Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

This type of stainless steel is dominant in the market. The group includes the very common AISI 304 and AISI 316 steel, but also the higher alloyed AISI 310S and ASTM N08904. Austenitic stainless steels is characterised by their high content of austenite-formers, especially nickel. They are also alloyed with chromium, molybdenum and sometimes with copper, titanium, niobium and nitrogen. Alloying with nitrogen raises the yield strength of the steels. Austenitic stainless steel has a very wide range of applications, e.g. in the chemical industry and the food processing industry. The molybdenum-free steel also have very good high-temperature properties and are therefore used in furnaces and heat exchangers. Their good impact strength at low temperatures is often exploited in apparatus such as vessels for cryogenic liquids. Austenitic stainless steel cannot be hardened by heat treatment. They are normally supplied in the quenching-annealing state, which means that they are soft and highly formable. Cold working increases their hardness and strength. Certain steel grades are therefore supplied in the cold stretched or hard rolled condition. Austenitic stainless steel has high ductility, low yield strength and relatively high ultimate tensile strength, when compare to a typical carbon steel. A carbon steel on cooling transforms from Austenite to a mixture of ferrite and cementite. With austenitic stainless steel tube, the high chrome and nickel content suppress this transformation keeping the material fully austenite on cooling (The Nickel maintains the austenite phase on cooling and the Chrome slows the transformation down so that a fully austenitic structure can be achieved with only 8% Nickel). Heat treatment and the thermal cycle caused by welding, have little influence on mechanical properties.  However strength and hardness can be increased by cold working, which will also reduce ductility.  A full solution anneal (heating to around 1045°C followed by quenching or rapid cooling) will restore the material to its original condition, removing alloy segregation, sensitisation, sigma phase and restoring ductility after cold working.  Unfortunately the rapid cooling will re-introduce residual stresses, which could be as high as the yield point.  Distortion can also occur if the object is not properly supported during the annealing process. Austenitic steel are not susceptible to hydrogen cracking, therefore pre-heating is seldom required, except to reduce the risk of shrinkage stresses in thick sections.  Post weld heat treatment is seldom required as this material as a high resistance to brittle fracture; occasionally stress relief is carried out to reduce the risk of stress corrosion cracking, however this is likely to cause sensitisation unless a stabilised grade is used  (limited stress relief can be achieved with a low temperature of around 450°C ). The image shows the microstructure of an austenitic stainless steel. Metallographic Test – Metallography Testing Metallographic Test Report Austenitic steels have a F.C.C atomic structure which provides more planes for the flow of dislocations, combined with the low level of interstitial elements (elements that lock the dislocation chain), gives this material its good ductility. This also explains why this material has no clearly defined yield point, which is why its yield stress is always expressed as a proof stress. Austenitic steels have excellent toughness down to true absolute (-273°C), with no steep ductile to brittle transition. This material has good corrosion resistance, but quite severe corrosion can occur in certain environments. The right choice of welding consumable and welding technique can be crucial as the weld metal can corrode more than the parent material. Probably the biggest cause of failure in pressure plant made of stainless steel is stress corrosion cracking (S.C.C).  This type of corrosion forms deep cracks in the material and is caused by the presence of chlorides in the process fluid or heating water/steam (Good water treatment is essential ), at a temperature above 50°C, when the material is subjected to a tensile stress (this stress includes residual stress, which could be up to yield point in magnitude). Significant increases in Nickel and also Molybdenum will reduce the risk. Stainless steel has a very thin and stable oxide film rich in chrome. This film reforms rapidly by reaction with the atmosphere if damaged. If stainless steel tube is not adequately protected from the atmosphere during welding or is subject to very heavy grinding operations, a very thick oxide layer will form. This thick oxide layer, distinguished by its blue tint, will have a chrome depleted layer under it, which will impair corrosion resistance.  Both the oxide film and depleted layer must be removed, either mechanically (grinding with a fine grit is recommended, wire brushing and shot blasting will have less effect), or chemically (acid pickle with a mixture of nitric and hydrofluoric acid).  Once cleaned, the surface can be chemically passivated to enhance corrosion resistance, (passivation reduces the anodic reaction involved in the corrosion process). Carbon steel tools, also supports or even sparks from grinding carbon steel, can embed fragments into the surface of the stainless steel pipe.  These fragments can then rust if moistened. Therefore it is recommended that stainless steel fabrication be carried out in a separate designated area and special stainless steel tools used where possible. If any part of stainless steel is heated in the range 500 degrees to 800 degrees for any reasonable time there is a risk that the chrome will form chrome carbides (a compound formed with carbon) with any carbon present in the steel.  This reduces the chrome available to provide the passive film and leads to preferential corrosion, which can be severe. This is often referred to as sensitisation.  Therefore it is advisable when welding stainless steel to use low heat input and restrict the maximum interpass temperature to around 175°, although sensitisation of modern low carbon grades is unlikely unless heated for prolonged periods.  Small quantities of either titanium (321) or niobium (347) added to stabilise the material will inhibit the formation of chrome carbides.  To resist oxidation and creep high carbon grades such as 304H or 316H are often used.  Their improved creep resistance relates to the presence of carbides and the slightly coarser grain size associated with higher annealing  temperatures.  Because the higher carbon content inevitably leads to sensitisation, there may be a risk of corrosion during plant shut downs, for this reason stabilised grades may be preferred such as 347H. The solidification strength of austenitic stainless steel can be seriously impaired by small additions of impurities such as sulphur and phosphorous, this coupled with the materials high coefficient of expansion can cause serious solidification cracking problems.  Most 304 type alloys are designed to solidify initially as delta ferrite, which has a high solubility for sulphur, transforming to austenite upon further cooling. This creates an austenitic material containing tiny patches of residual delta ferrite, therefore not a true austenitic in the strict sense of the word.  Filler metal often contains further additions of delta ferrite to ensure crack free welds. The delta ferrite can transform to a very brittle phase called sigma, if heated above 550°C for very prolonged periods  (Could take several thousand hours, depending on chrome level.  A duplex stainless steel can form sigma phase after only a few minutes at this temperature) The very high coefficient of expansion associated with this material means that welding distortion can be quite savage.  I have seen thick ring flanges on pressure vessel twist after welding to such an extent that a fluid seal is impossible.  Thermal stress is another major problem associated with stainless steel; premature failure can occur on pressure plant heated by a jacket or coils attached to a cold veesel.  This material has poor thermal conductivity, therefore lower welding current is required (typically 25% less than carbon steel) and narrower joint preparations can be tolerated.  All common welding processes can be used successfully, however high deposition rates associated with SAW could cause solidification cracking and possibly sensitisation, unless adequate precautions are taken. To ensure good corrosion resistance of the weld root it must be protected from the atmosphere by an inert gas shield during welding and subsequent cooling.  The gas shield should be contained around the root of the weld by a suitable dam, which must permit a continuous gas flow through the area.  Welding should not commence until sufficient time has elapsed to allow the volume of purging gas flowing through the dam to equal at least the 6 times the volume contained in the dam (EN1011 Part 3 Recommends 10).   Once purging is complete the purge flow rate should be reduced so that it only exerts a small positive pressure, sufficient to exclude air.  If good corrosion resistance of the root is required the oxygen level in the dam should not exceed 0.1%(1000 ppm); for extreme corrosion resistance this should be reduced to 0.015% (150 ppm).  Backing gasses are typically argon or helium; Nitrogen Is often used as an economic alternative where corrosion resistance is not critical, Nitrogrn + 10% Helium is better.  A wide variety of proprietary pastes and backing materials are available than can be use to protect the root instead of a gas shield.  In some applications where corrosion and oxide coking of the weld root is not important, such as large stainless steel tube, no gas backing is used. Carbon content: 304L stainless steel grades Low Carbon, typically 0.03% Max 304 stainless steel grades Medium Carbon, typically 0.08% Max 304H stainless steel grades High Carbon, typically Up to 0.1% The higher the carbon content the greater the yield strength.  (Hence the stength advantage in using stabilised grades) Typical Alloy Content 304  316  316Ti 320  321  347  308  309(18-20Cr, 8-12Ni)  (16-18Cr, 10-14Ni + 2-3Mo)  (316 with Titanium Added)  (Same as 316Ti)  (17-19Cr, 9-12Ni + Titanium)  (17-19Cr, 9-13Ni + Niobium)  (19-22Cr, 9-11Ni)  (22-24Cr, 12-15Ni) 304 + Molybdenum  304 + Moly + Titanium  –  304 + Titanium  304 + Niobium  304 + Extra 2%Cr  304 + Extra 4%Cr + 4% Ni All the above stainless steel grades are basic variations of a 304. All are readily weldable and all have matching consumables, except for a 304 which is welded with a 308 or 316, 321 is welded with a 347 (Titanium is not easily transferred across the arc) and a 316Ti is normally welded with a 318. Molybdenum has the same effect on the microstructure as chrome, except that it gives better resistance to pitting corrosion.  Therefore a 316 needs less chrome than a 304. 310 (24-26Cr,19-22Ni) True Austenitic.  This material does not transform to ferrite on cooling and therefore does not contain delta ferrite.  It will not suffer sigma phase embrittlement but can be tricky to weld. 904L (20Cr,25Ni,4.5Mo) Super Austenitic Or Nickel alloy.  Superior corrosion resistance providing they are welded carefully with low heat input (less than 1 kJ/mm recommended) and fast travel speeds with no weaving.  Each run of weld should not be started until the metal temperature falls below 100°C.  It is unlikely that a uniform distribution of alloy will be achieved throughout the weld (segregation), therefore this material should either be welded with an over-alloyed consumable such as a 625 or solution annealed after welding, if maximum corrosion resistance is required. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Compared with the austenitic stainless steel, duplex stainless steel of the vulnerable is as follows: 1 The application of universal and multi-faceted as stainless steel, such as its temperature must be controlled at 250 degrees Celsius. 2 The plasticity and toughness lower than the austenitic stainless steel, cold, heat processing process and molding properties than austenitic stainless steel. 3 The existence of temperature brittle zone, the need for strict control of heat treatment and welding technology system in order to avoid the appearance of harmful phase, damage to property. Compared with the ferritic stainless steel, duplex stainless steel strengths are as follows: 1 the mechanical properties of ferritic stainless steel than good, especially the plastic toughness ferritic stainless steel is not as brittle as sensitive. 2 In addition to resistance to stress corrosion, other localized corrosion resistance is superior to ferritic stainless steel. 3 cold and cold-forming properties of process performance is much better than ferritic stainless steel. 4 welding performance is far superior to ferritic stainless steel, the former general welding without preheating, without heat treatment after welding. 5 scope of application than the width of ferritic stainless steel. Compared with the austenitic stainless steel, duplex stainless steel strengths are as follows: 1 Yield strength than conventional austenitic stainless steel more than twice as high, and has a plastic molding needs adequate toughness. Use of duplex stainless steel tank or pressure vessel wall thickness less than the usual 30-50% austenite is beneficial to reduce costs. 2 Duplex stainless steel has excellent resistance to stress corrosion cracking capacity, even with the lowest amount of duplex stainless steel alloy has a higher resistance than the austenitic stainless steel stress corrosion cracking capacity, especially in chloride ion environments. Austenitic stainless steel stress corrosion is a common problem difficult to resolve outstanding. 3 In many applications the most common medium of 2205 duplex stainless steel corrosion resistance than the average of316L stainless stee, and super duplex stainless steel with high corrosion resistance, then a number of media, such as acetic acid, formic acid, etc. can even replace the high-alloy austenitic stainless steel, and even corrosion resistant alloy. 4 Duplex stainless steel has a good resistance to localized corrosion, with the austenitic stainless steel alloy content rather than its resistance to corrosion and fatigue corrosion and wear better than the austenitic stainless steel. 5 The linear expansion coefficient of austenitic stainless steel is low, and carbon steel close fit with the carbon steelconnections, has important engineering significance, such as the production of composite boards or lining and so on. 6 in terms of dynamic load or static load conditions, the ratio of austenitic stainless steel has a higher energy absorption capacity, which structural parts to cope with sudden incidents such as collisions, explosions, etc., have obvious advantages of duplex stainless steel, are of practical value . Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Alloying elements that help stabilize the austenitic phase reduce the tendency of the austenitic stainless steel to work hardening. Nickel additions have been used traditionally to do this, but nitrogen also has a profound affect on stability of the austenitic phase. Heat treatment Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding. Heat treatment of metals and alloys Metallic materials consist of a microstructure of small crystals called “grains” or crystallites. The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling within the microstructure. Complex heat treating schedules are often devised by metallurgists to optimize an alloy’s mechanical properties. In the aerospace industry, a superalloy may undergo five or more different heat treating operations to develop the desired properties. This can lead to quality problems depending on the accuracy of the furnace’s temperature controls and timer. Deep Drawing Composition The nickel level was increased in the superseded BS1449 grade 304S16 compared to the 304S15 level (around 8.0%). This enabled the 304S16 grade with around 8.5% nickel to be used for deep drawing applications. Both these grades are covered inEN 10088-2 as 1.4301, but the higher nickel variant can be specified as a ‘deep drawing’ grade. In contrast the higher nickel variants of 316 (1.4435) were developed for improved ‘selective’ corrosion resistance, originally in pharmaceutical applications, from lower ferrite levels. The ‘standard’ 316 type (1.4401) with around 11% nickel should be suitable for deep drawing. The BS1449 grade 305S19 with its 11.0 – 13.0 % nickel range is even more stable when cold worked. One application for this grade is for temper rolled strip for springs where low magnetic permeability is required. EN 10088-2 covers this grade as 1.4303. An alternative is the Sandvik strip grade ’13RM19′ with 6% manganese and 0.25% nitrogen in addition to 7% nickel. Stretch Forming Composition Stretch forming application grades would normally have ‘standard’ nickel levels (around 8.0 / 8.2%), but if the stainless steel sheet is intended for stretch forming the manufacturer / supplier should be informed, as the final heat treatment / process line speed conditions are adjusted to optimize the mechanical properties. The grain size of cold rolled stainless steel sheet is usually fine enough (around ASTM 7-8) to avoid ‘orange peel’ surface roughening during pressing.

Unlike martensitic stainless steel, the austenitic stainless steel are not hardenable by heat treatment as no phase changes occur on heating or cooling. Softening is done by heating in the 1050/ 1120 °C range, ideally followed by rapid cooling. This is of course the complete opposite to martensitic steel, where this sort of treatment would harden the steel. Apart from inter-stage annealing during complex or severe forming operations, for many applications, final stress relievingaustenitic stainless steel products is not normally needed. Effect of residual stresses Cold worked austenitic stainless steels will contain some ‘strain induced’ martensite, which, as well as making the steel partially ‘ferro-magnetic’, can also reduce the corrosion resistance. A highly stressed cold worked structure may also have lower general corrosion resistance than a fully softened austenitic structure. The main hazard is stress corrosion cracking (SCC), which relies on tensile strength as part of the failure mechanism. Stress relieving removes such residual tensile stresses and so improves the SCC resistance. The other main reason for stress relieving is to provide dimensional or shape stability. The risk of distortion can be reduced during forming or machining operations by stress relieving. The approach to heat treatment selection A full solution anneal stress-relieving heat treatment will re-transform any martensite formed back to austenite. (This will also give the lowest magnetic permeability possible for any particular grade.) Slow cooling is advisable to avoid introducing distortion problems or residual thermal tensile stresses and so the risk of sensitisation during a slow cool may have to be accepted. The temperature ranges used in stress relieving must avoid sensitising the steel to corrosion or the formation of embrittling precipitates. As a general guideline, it is advisable that the range 480-900C is avoided. The low carbon (304L or 316L) or the stabilised (321 or 347) types should not be at risk from corrosion sensitisation during stress relieving treatments. Stress relieving treatments for austenitic stainless steel The table shows alternative treatments in order of preference. Process or Corrosion HazardStainless Steel Grade TypesStandard Carbon 304, 316Low Carbon 304L, 316LStabilised 321, 347Annealing following severe formingCA,CA,CForming interstage annealingC(A,B)A,B,CB,A,CPost welding heavy sections and/or high service loading applicationsCA,C,BA,C,BDimensional stabilityDDDSevere SCC risk in serviceNote 1A,BB,ASome risk of SCC in serviceCA,B,CB,A,C Note 1 Standard carbon steel grades are susceptible to intergranular corrosion (ICC) on slow cooling treatments. Fast cooling treatments are not advisable as residual tensile stresses could result in SCC. Note 2 Treatment B is also intended to reduce the risk of “knife-line” attack in the stabilised grades. This form of attack is due to the solution of titanium or niobium carbides at higher annealing temperatures. Heat Treatment CodesCodeTreatment CycleA1050 / 1120 °C, slow coolB900 °C, slow coolC1050 / 1120 °C, fast coolD210 / 475 °C slow cool (approx. 4 hours per 25mm of section)

Austenitic stainless steel work-hardening significantly during cold working. This can be both useful properties, enabling extensive forming during stretch forming without risk of premature fractures and a disadvantage, especially during machining, requiring special attention to cutting feeds and speeds. What is work hardening and why is it a particular problem to the austenitic stainless steel? Work hardening is the progressive build up in the resistance to further work or deformation. One result of this is that the tensileproperties (proof and tensile strength) increase with cold work. This only happens during cold working. During hot working the steel is continually being ‘self-annealed’. There are two mechanisms operating in the austenitics. ‘Normal’ work hardening occurs as ‘dislocations’ (naturally occurring line defects that enable metals to be ductile) in the atomic lattice move during plastic deformation. The stress fields around the dislocations interact as the dislocations ‘tangle’ so that more force is then required to move them. The face centred cube (fcc) atomic structure in metals such as aluminium, copper, austenitic stainless steel etc. also results in more energy being needed to keep the deformation process going, as ‘partial dislocations’ try to move through the lattice together. This not so marked in the ferritic (bcc) structure. The austenite structure or phase is also unstable during cold deformation and breaks down to the much stronger, less ductilemartensite phase. In this condition an austenitic stainless steel becomes slightly ferro-magnetic, as the martensite formed is ‘ferro-magnetic’ ie it will attract a permanent magnet. These combined effects are reversible by solution heat treatment generally by heating to 1050/1120C and cooling quickly. Measure of work hardening – ‘n’ value Work hardening begins after the steel has ‘yielded’ and begins to plastically deform. During tensile testing, a plot of stress against strain produces a curve as plastic deformation progresses. The slope of a logarithmic plot of stress against strain gives the ‘n’ value. For ferritic stainless steel types, n values are approximately 0.2, which do not vary with strain level. The austenitic stainless steel have two n value ranges, depending on the amount of strain. A ‘stable’ austenitic would have values of n around 0.4 at low strains and 0.6 at higher strains. These grades are suitable for deep drawing. In contrast less stable grades would have comparative values of 0.4 at lower strains and 0.8 at higher strains. These grades are more suitable for stretch forming. This is because as stretching procedes, the sheet thins uniformly, resisting localized thinning and premature fracture in the walls of pressings. The work hardening properties are also reflected in the difference between proof strength (yield strength) and tensile strength. The values for austenitics are wider apart than the lower work hardening ferritics. Anisotropy (directional differences forming properies) – ‘r’ value The drawability is also affected by the anisotropy of the sheet ie the differences in strain in the plane of the sheet compared to the reduction in thickness. This ‘r’ value (strain ratio) is around 1 for austentics stainless steel and between 1 and 2 for ferritics stainless steel. The higher the value the better the sheet resists thinning and so on this basis the ferritics stainless steel would be expected to draw better than the austenitics stainless steel. This strain ratio can vary in relation to the rolling direction of the sheet. When it does the material is said to have ‘planar anisotropy’ and this can be used to predict how the sheet will form ears during drawing. The austenitics stainless steel is less prone to this anisotropy than ferritics stainless steel (ie their properties are less directional in the plane of the sheet). So with their lower proof strengths and higher work hardening rates the austenitic are usually considered better for sheet drawing and forming operations than the ferritics stainless steel.

cold working and heat treatment conditions chemical composition effects Cold Working and Heat Treatment Cold working of austenitic stainless steel can partially transform austenitic to martensitic. As martensitic stainless steel is ferromagnetic, cold working austenitic stainless steel can show a degree of ‘pull’ towards a magnet. This usually occurs at sharp corners, sheared edges or machined surface but can be detected on wrought products such as rods or bars which may have been cold straightened, following the final hot rolling or annealing in the mill. The degree to which this occurs depends on the compositional effects of austenitic stabilising elements. High nickel or nitrogen bearing grades tolerate more cold working before localised increases in permeability are noticed. These increases in permeability can be reversed by full solution annealing at temperatures around 1050 / 1120C with rapid cooling. This transforms any cold-formed martensitic to austenitic, the non-magnetic phase, which is then retained on cooling. The best austenitic stainless steel types for low permeability applications are those with high austenitic stability as these have low permeability in both annealing or cold working conditions. These include the nitrogen bearing types, 304LN (1.4311) and 316LN 1.4406 or the high nickel types such as 310 1.4845.

Austenitic stainless steel are generally non-magnetic with magnetic permeabilities of around 1.0. Permeabilities above 1.0 are associated with the amount of either ferritic or martensitic phases present in the austenitic stainless steel and so depend on: chemical composition cold working and heat treatment conditions Here discusses chemical composition effects. Grade 304 (1.4301), 321 (1.4541) and 316 (1.4401) have ‘balanced’ compositions to enable them to be readily weldable. This is achieved by ensuring that in their normal annealing (softened) condition, they contain a few percent of delta ferritic. This results in permeabilities slightly over 1.0. Additions of nickel and nitrogen promote and stabilise the austenitic phase, whereas molybdenum, titanium and niobium stabilise ferrite. The lowest permeability austenitic stainless steel are therefore the nitrogen bearing 304LN (1.4311) and 316LN (1.4406) types or the high nickel 310 (1.4845) and 305 (1.4303) types. In contrast, higher permeabilities can be expected in grades such as 301 (1.4310), 321 (1.4541) and 347 (1.4550), with either lower nickel contents or additions of titanium or niobium, which are powerful ferrite stabilising elements. During the welding of these steel, structural changes occur. Some of the austenitic in the parent material can transform to delta ferritic at high temperature and on cooling this is partly retained at room temperature. Welding filler rods and wires are usually ‘over-alloyed’ to prevent dilution in the fusion zone but more importantly are balanced to have deliberately high ferritic levels of 5% or sometimes 10%, to minimise the risk of hot cracking during welding. Consequently the permeability of the metal in the weld and the surrounding heat affected zone can be significantly higher than in the original parent material. Similar effects can occur following plasma or flame cutting of austenitic stainless steel. In general, castings have compositions with a bias towards ferritic compared to wrought grades and consequently will be moremagnetic. Effect of Cold Work and Temperature on Martensitic Formation The transformation of austenite to martensitic can be triggered either by cold work or by the effect of low temperatures. The stability of an austenitic stainless steel to such transformation is measured by using the Md30 temperature. This is defined as the temperature at which 50% of the austenite originally present will be transformed to martensite when subjected to a cold true strain of 0.30. This is about 35% engineering strain. The formula to calculate this temperature was first proposed by Angel and subsequently modified to take account of the grain size. Md30 = 551 – 462(C+N) – 9.2Si – 8.1Mn – 13.7Cr – 29(Ni + Cu) – 18.5Mo – 68Nb – 1.42 (ASTM grain size – 8) It will be noted that all elements contribute to the stabilisation of austenitic to the martensite transformation. The following table gives an approximate value for some common austenitic stainless steels:Stainless Steel TypeMd30 (deg C) 1.4310 (301) +20 1.4372(201) +201.4301 304 -20 1.4307(304L) -30 1.4311(304LN) -80