Ed Craig on MIG Welding Stainless Steel
WHAT IS STAINLESS STEEL?
Austenitic, Martensenitic and Ferritic Stainless Steels Austenitic Stainless Steels are the ones we are most familiar with. These chrome nickel steels, in contrast to lower cost stainless have more alloys and are “non magnetic” (Exception, types 310 – 330) Austenitic Facts: Austenitic grades typically contain a minimum of 18% chrome – 8% nickeland are often called 18/8 steels. Austeniticsteels: Grades 20-202-205-301-302-303-304-305-308-309-310-314-316-317-321-329-330-347-389-177PH- 17 4PH-PH15-7Mo-AM 350-AM 355 A 286.
Common Designations:
304 (S30400) – 304L(S30403) 316(S31600) 316L (S31603) – 347 (S34700). Grades 301-302-304-305-308 usually welded with E308. 18/8grades used for machine parts exterior buildings and industrial parts.18/8not to exceed 800F 426C service temperature.Manganesegrades of stainless “200″series similar to 18/8 grades. Manganese in this series is used for “extrastrength” Welding the manganese grades usually requires the use of the E308Lfiller.| Martensiticand Ferritic Grades arecommon stainless grades that we don’t want to weld and if we do, we weld withgreat caution. MartensiticChrome steels. Weldability, limited. Preheatingtypical 250°C to 450°C. Postweld treatment: Slow cooling to 120°C(martensitic transformation) and annealing at 750°C or hardening (generally1000°C / oil), tempering (generally 750°C). Watch for formation of chromiumcarbide between 500°C and 650°C…Note:When welding these grades the weld procedure concerns and focus will be on HEATtreat requirements.
STAINLESS STEEL INTERNATIONAL WIRE SPECS.
| Stainless Filler Metal Information: | ||||
|---|---|---|---|---|
| Stainless Filler | International Specs | Chemistry | Manufactures designations | Applications |
| Electrode E308 | Germany SG X5 Cr Ni 19.9 ISO 23.12 UNS W30940 | C 0.08 Mn 1 – 2.5 Si 0.25-0.6 Ni 9-11 Cr 19.5-22 | Thyssen-Therm J Kobe-MGS Lincoln L18.8 Pacweld -PW176SS Sanvik 19.9 | E308is typically used when the corrosive conditions are not severe |
| Electrode E308L (low carbon) | GermanySG X2 Cr Ni 19.9 ISO 119.9L UNS W30843 | C0.03 Mn 1 – 2.5 Si 0.25-0.6 Ni 9-11 Cr 19.5-22 | ESAB-OK 16.10 Thyssen -JE Sandvik 19.9L | Note(L). The lower carbon is used to avert the formation of carbide precipitation |
| Electrode 308LSi | nbsp; | nbsp; | ESAB-OK 16.12 Thyssen – JESi Sandvik 19.9LSi Filarc – PZ6061/6561 TREFIL2PPSG | NoteSi or Hi Si. The high silicon can increase arc stability and the weld wetting,which is important for some the low amp, sluggish, short circuit welds |
| Electrode 309 | GermanySG X12 Cr Ni 22.12 ISO 23.12 UNS W30940 | C0.012 Mn 1 – 2.5 Si 0.25-0.6 Ni 12-14 Cr 23-25 | ESAB-OK 16.53 Sandvik- 24.13 Thyssen -Therm 25.14 | Usedfor welding 309 and austenitic to ferritic (carbon) steels |
| Electrode 309L | nbsp; | C 0.03 Mn 1 – 2.5 SI 0.25-0.6 Ni 12-14 Cr 23-25 | nbsp; | Usedfor weld overlay applications or butter passes. |
| Electrode 310H | nbsp; | C0.10 -0.12 Cr 26 Ni 22 | nbsp; | (H)Has minimum carbon content lower carbon can cause micro cracking causing tensilereductions |
| Electrode 310 | Germany SG X12 CrNi 25.20 ISO 25.20 UNS W31040 | C 0.08-0.15 Mn 1 – 2.5 Si 0.25-0.6 Ni 20-22.5 Cr 25-28 | nbsp; | Toweld 310 and 304 clad and stainless overlay |
| For low or high temp, corrosive or any critical applications always confirm electrodechoice with wire manufacturer. Using ELC ensure weld gas has less than 3%CO2. A low co2 mix is less oxidizing than a low oxygen mix.For low carbon baseuse low carbon filler identified by EXXXL | ||||
| Electrode 312 | Germany SG 9250XRC UNS W31240 ISO 29.9 | C 0.15 Mn 1 – 2.5 Si 0.25-0.6 Ni 8-10 Cr 28-32 | nbsp; | HigherFerrite. More “crack resistance” than E309. |
| Electrode 316 | Germany SG9250ZRC UNS W31640 ISO 19.12.2 | C0.08 Mn 1 – 2.5 Si 0.25-0.6 Ni 11-14 Cr 18-20 Mo 2-3 | ESAB-16.35 Thyssen – Therm G. Sandvik 19.12.2 | for316 steels and good for “high temp” corrosion resistance |
| Electrode 316L | GermanySG X2 CrNiMo 19.12 ISO 19.12.2L UNS W31643 | C0.03 Mn 1 – 2.5 Si 0.25-0.6 Ni 11-14 Cr 18-20 Mo 2-3 | nbsp; | |
| Electrode 317L | 317 Germany SG CrNiMo 1813 ISO 19.13.4 UNS W31740 317L UNS 31743 | C0.03 Mn 1 – 2.5 Si 0.3-0.65 Ni 13-15 Cr 18.5-20.5 Mo 3-4 | nbsp; | Hasmoly to increase the tensile strength. Has excellent corrosion resistance andhigh temp properties Note contains considerable ferrite which can lower toughnessproperties. |
| Electrode 318 | Germany SG X5 CrNiMoNb 1912 | nbsp; | nbsp; | |
| Electrode 320 | nbsp; | nbsp; | usedfor welding Carpenter 20 plus 20Cb-3 stainless | |
| Electrode 321 | UNS W32140 | C 0.07 Mn 1.43 Si 0.58 Ni 10.52 Cr 18.58 | nbsp; | nbsp; |
| For weld data and information on Carbide Precipitation scroll down to welddata | ||||
| Electrode 347 | GermanySG X5 CrNiHb 1999 UNS W34740 ISO 19.9No | C 0.069 Mn 1.59 Si 0.49 Ni 9.96 Cr 20.82 | ESAB 16.11 Thyssen Therm H. Sandvik – 19.9Nb | usedfor 321 – 347 better corrosion resistance than 308E347-321wire is stabilized with small amounts of Ti or Cb to prevent carbide precipitation |
| Electrode 349 | UNS 34940 | nbsp; | nbsp; | nbsp; |
| Electrode 410 | Germany SG 5 350 UNS W41040 ISO 13-EZ13-189 | nbsp; | nbsp; | nbsp; |
| Electrode 430 | Germany SGS 250 Zr ISO 17 – EZ17 UNS W43040 | nbsp; | nbsp; | nbsp; |
SMUT AFTER PICKLING ON STAINLESS:
Stainless smut is a common problem that resultsafter pickling. Smut is an undesired discoloration that deposits on stainlesssteel surfaces after pickling, it appears as a dark sticky film. Its difficultto pinpoint why the smut has formed. There are a large number of possible causesand factors. The most frequent of these are:
- Contaminated surfaces(dirt and or glue residues from plastic film).
- Uneven pickling.
- Inadequate rinsing.
- Poor water quality.
- Substandardcirculation/stirring in the pickling bath.
- Old, contaminated picklingbath.
- Poor steel quality.
- Nitrate-free pickling solutions.
SMUT
Research has shown that smut is more likely to occur when metal dissolution by the pickling acid increases Fe2+ levels tothe point where the redox potential of the pickling solution falls below a certainvalue (Fe + 2Fe3+=gt; 3Fe2+). Under these conditions, a passive chromium layeris not formed. This leaves the steel surface vulnerable. Loose oxide particlesand other elements in the pickling acid may then easily attach themselves to thesurface. Low alloy-stainless steels are more sensitive to smut formationthan are their high-alloy counterparts. This may be due to the high pickling rates that, particularly with high acid levels, are characteristic of low-alloy steelgrades. Reducing smut with FinishOne™ Besides excellent NOx reduction and passivating power, FinishOne™ has also demonstrated that it is a real “smutkiller”. Sprayed onto a still wet steel surface, it promotes Fe2+ to Fe3+oxidation and thus prevents smut formation (Fe2+ + FinishOne =gt; Fe3+ + H2O).Smut caused by silicone residues on the surface Smut and NOx reduction using FinishOne™.Smut caused by a film of oil on the surface When Fe3+ is the dominant ion, theresultant passivation protects steel surfaces from both corrosion and adhesion.A final rinse with FinishOne™ ensures a passivated surface that is free fromwater stains. Ifthey do not receive proper post-weld treatment, stainless steels soon lose theirstainless property. Thus, correct pickling, passivation, et cetera are all vital.This is especially true in the pulp and paper industry, where highly aggressivemedia are used at high temperatures. Avesta Finishing Chemicalshas the products, expertise and support to meet the stainless steel finishingrequirements of the pulp and paper industry worldwide.
POORWORK HABITS, POOR HANDLING AND POOR MAINTENANCE CAN MAKE STAINLESS FABRICATIONSUSCEPTIBLE TO RUST.
If you work in a weld shop that welds stainless, you may have seen rust form on those stainless parts. To get corrosion to form on stainless does not take much. Liftthe stainless parts with a fork lift, strap the parts with a steel band, clean the parts with a steel brush or steel wool or grind steel parts near the stainless parts and a few days later that familiar rust will appear. There is a good reason that weld and fab shop are asked when making stainless parts to to isolate stainless from carbon steel components. When you look at that shiny stainless part remember it’s protected by a self healing, very thin oxide film and as long as that film is intact and there is oxygen present,the stainless remains rust resistant. Even when the stainless surface is damagedand not contaminated, the stainless film will recover. However when the stainlessis attacked by carbon steel contamination, the film is unable to recover and under the film their is active metal waiting to corrode. That welder grinding carbon steel parts creates micro steel particles that fly through the air and can attach themselves to a stainless part. Left in an open environment, the carbon steel grinding particles eventually dissolve and the iron oxides that result will contaminate the surface of the part. The iron oxide contamination prevents or reduces the oxygen from reacting with the stainless part in the contaminated area making not allowing the oxide film to occur. This results in an active stainless which is sensitive to the formation of rust. Abrasivemovement of any carbon steel against a stainless part, such as from steel rollson conveyors, fork lifts or crane steel handling clamps will also contaminatethe stainless. A common method of none abrasive carbon steel contact can comefrom manual or robot welding stainless in a carbon steel fixture. If the carbonsteel fixture components are are in close proximity to the stainless welds, thiscan lead to carbon pickup in the stainless that will in a short period resultin the formation of corrosion. Apartfrom the common stainless contamination that results during material forming /handling, a very common cause of corrosion resultsfrom the use of grinding wheels contaminated with steel particles or steel wirebrushes. When lifting parts with a fork lift, use none steel components that separatethe steel forks from the stainless. When you strap those stainless parts, placewood between the bands and the stainless. With stainless weld operations usingcarbon steel fixtures, ensure no carbon steel part is within 25 mm of the welds.If fixture parts are within close proximity of the welds replace the carbon steelscomponents with stainless, copper or aluminum.Rustaround Stainless Welds Question:Ed. Recently our company fabricated 316L gage pipe. The finished weld productshave been out doors at the site for approximately 2 weeks and now about 15% ofthe welds are showing rust at the weld seams. Our procedure for weld cleanup wasto use a stainless wire brush followed with a citric acid passivation. We really are at a loss as to why this happened. Answer from Brad Hass. This very interesting for me, we had a similar problem on 304L structures for a blast freezer. It turned out to be from the use of a 302ss poweredbrushing operation. We had a company come in, to apply pickling gel to the damaged areas. It works! The reason I don’t believe you had a carbon steel brush in use,is citric acid treatments will remove that, and will not remove contaminationfrom 302 and 304 powered brushing. Nitric/Hydroflouric and brush electropolishing is the only thing we have found to remove this. I have confirmed all the above with salt spray testing 24 hr 5% solution. One other thing the larger the bristle diameter the worse the contamination. I recommend in the future 316L brushes for your clean up, this works. Brad..Replyf rom Ed.In weld shops welding inconsistency is normal and therefore cleaning practices should also be looked at.. If the shop manager came in on the second shift, would he find Fred the welder cleaning the stainless welds with carbon steel brushes or wheels, or with contaminated stainless brushes or wheels.When I look at the pipe seam and circumferential welds, it’s notable that the corrosion is localized , (caused by one individual) and only a small percentage of the welds were contaminated. Therefore it’s logical to assume that an inappropriate cleaning method was used during fabrication and welding.I believe that possibly in some areas the correct stainless brushes or wire wheels were utilized and at other times the welders picked up carbon steel brushes or used cleaning wheels or abrasives that were contaminated from their use on steel components Thestainless flange cleaned with B570 and coated with a nanolyer available fromInnomet.Anyrust formation on stainless should be removed and the fab shop has many ways toapproach this task..It’s logical in the fab shop to pick up steel wool or a grinderand take that to the contaminated area, however the wheels or wool can cause surfacedamage which combined with the existing contamination can again lead to latercorrosion spread over a wider area. Rust can be removed from the stainless surfacewithout damaging the surface with the use of pickling liquids or inorganic chemicals.The negative aspect of pickling or inorganic chemical is the impact on the environmentand the hazards to the people who apply the chemicals. With this in mind theirare in 2008 some unique products available that eliminate iron oxides and providedeep cleaning of contaminated stainless parts . Of course the most cost effectivepractice for the e fab shop, is don’t allow the stainless parts to be contaminated.Checkout a company call Innomet and look at their unique chemical approach to stainlesscleaning and rust removal. Innomet visit. http://inno-soft.nl/en/index.html.
WELDING
Welding High Strength, High Carbon Steels with Austenitic Stainless or Nickel Filler Metals. Austenitic stainless steels are prone to hot crackingand so attention is required to cleaning before weldingand welding using low to medium weld parameters. Concern for formation of chromiumcarbide at grain interface especially if the carbon content is higher then 0.04%.No preheat is usually required. Filler metal:% C = max. 0.04%Inwelding carbon steels to stainless, the austenitic / nickel filler metals offerunique features that can reduce weld crack potential in both the welds and weldheat affected zone (HAZ). Carbon to stainless welds require that the stainlessweld metal have sufficient ferrite to resist cracking. When welding carbon steelto stainless and a 309L wire is used, the resultingferrite is approximately 14-16FN. If thesteel is a high carbon steel, a 309L, first weld pass on the carbon to stainlesswill likely end up with “insufficient ferrite”. The carbon from thehigh carbon steel when mixed with the stainless weld will suppress the ferriteformation. Instead of the 309L for this application, a 312 electrode may be recommended. The 312 filler metal, (70 to 90 FN in the weld metal) produces muchhigher ferrite levels than the 309L. This is the prime reason the 312 is recommendedfor applications sensitive to weld cracks. Filler metals such as 307 – 308 Moand 310 can resist cracking with the aid of alloys and without the aid of ferrite.
HOW AUSTENITIC AND NICKEL WELD ELECTRODES CAN HELP HIGH STRENGTH CARBON STEELS.
High carbon, high strength steels welded to each are subject to hydrogenassisted cracking. 1 High hardness. 2 A source of hydrogen. 3 High stresses. These are the three fundamental requirements for hydrogen assistedcracking. Withthe high carbon steels, high hardness is typical in the HAZ unless very high,(often not practical) preheat and interpass temperatures are utilized for thewelds. The stresses that can influence HAZ cracking typically resultfrom weld residual stresses caused by weld shrinkage, these stresses can be furtherexaggerated by weld joint restrictions as found in certain fixtures.As we are all aware, hydrogen in the weld can be derived from many sources. An alternative to a high carbon, high strength filler metals, in which thecarbon dilution from the base metal will result in a hard weld, subjecting theweld to transverse cracking, is to use an austenitic or a specific nickel basedfiller metal (ENiCrFe-2). The austenitic or nickel filler metals greatlyreduces the weld transverse cracking potential. Also these filler metals greatlyreduce, slow down or trap the weld hydrogen that can diffuse from the weld intothe HAZ, this greatly reduces HAZ hydrogen cracking potential. Thediffusion of hydrogen though austenitic and nickel filler metal welds and steelcan be approximately 80 – 110 times slower than through carbon steels and welds.The use of the austenitic and nickel filler metals can greatly reduce crackinghowever these filler metals can still absorb hydrogenso these electrodes should be treated with the same respect and rules that applyto any low hydrogen filler metals. Note:MIG welding. Use Ed’s unique Stainless, Duplex MIG Gas Mix to reduce any typesof weld cracking. With any stainless flux cored wires use the argon CO2 mixesrecommended for carbon steel flux cored wires. When to use a 308L, 309L or 316L filler metal.308L and 308LSi is predominately used on austenitic stainless steels, such astypes 301, 302, 304, 305 and cast alloys CF-8 and CF-3. For hightemperature applications such as in the power industry, higher carbon 308H electrodeswill provide superior creep resistance than does 308L . Use 309L and309LSi when joining 309 or mild steels / low alloy steels to stainless steels.Use 309 when joining dissimilar stainless steels such as 409 to itself or to 304Lstainless. CG-12 is the cast equivalent of 309. Some 308L applications may be substituted with 309L filler metal, but 316L or316 applications generally require molybdenum. Note, 309L contains no molybdenum. 316L and 316LSi should be used with 316L and 316 base metals. CF-8Mand CF-3M are the cast equivalents of 316 and 316L, respectively.Type 347 stainless steel filler metal is used for 347 and 321 base materials becauseit matches these stabilized grades. CF-8C is the cast equivalent of 347. Type347 filler metal is also suitable most 308L filler metal applications.Excellentstainless gas shielded flux cored wires are available from Alloy Rods andKobleco.Around the Globe Sanvik and Avesta set the standardfor MIG Stainless wires.
ELIMINATESTAINLESS WELD POROSITY:
Weld porosity, a cavity discontinuity that forms from a gas reaction. The porositycan be trapped in the weld or at the weld surface. The porosity is typically roundin shape but can also be elongated. In contrast to argon oxygen mixes, Ed’s Stainless.Duplex gas mix was developed for less oxide reaction, less porosity potential.
ROBOTS AND MIG POROSITY.
When you find the robot weld porosityis always at the same location and the weld porosity is not at the weld startsor ends, examine the robot movement and see if the robot arm is causing a restrictionof the gas flow line. Also it’s common with robot cells to see a severe gas flowrestiction due to the narrow orrifice found in gas line connections. In a robotcell its critical to measure gas flow as it exits the gun. If the porosity isat the weld start or stop increase the gas pre flow and post flow times. “Arial, Helvetica, sans-serif2″> “Arial, Helvetica, sans-serif2″> Weldporosity, a cavity or discontinuity that forms in the weld from a gas reactionin molten metal. Theweld porosity can be trapped in the weld or evident at the weld surface. Weldporosity is typically round in shape, but can also be elongated. Weld porosity is caused by the absorption of oxygen, nitrogen and hydrogeninto the molten weld pool. The gases are then released on solidification and maybecome trapped in the weld metal.Nitrogenand oxygen absorption in the weld pool usually originates from inadequate or contaminatedgas shielding, leaks in the MIG gas line, excess gas flow rates, draughts andplate contamination.Hydrogencan originate from a number of sources including moisture from the electrodes,moistureon the parts, contaminates on the workpiece surface. (Usedry pre-heat gt; 100F , oxy fuel gt; 250 F)CLUSTERWELD POROSITY. A localized group of pores with random distribution.Causes. Arc blow, insufficient, inconsistent or excessive weld gas flow, materialor weld wire contamination, (low) weld parameters or poor technique.
PIPING,WORM HOLE, WAGGON TRACKS POROSITY.
Sometimes called “waggon tracks”.Typically found in the center of the weld, parallel to weld axis. Classic porositywhen moisture is evident in gas shielded flux cored wires, (the cheaper the productthe more prone to waggon tracks). Increasingthe flux cored wire stick out and increasing the wire feed rate helps by addingenergy to the wire. Baking flux cored wires and storing the wires in a dry environmentalso reduces potential. Slow weld speeds, make welds larger, avoid weaves. Allrecommendations are intended to increase the weld arc energy and decrease theweld cooling rate. Worm holes are elongated gas pores producing a herringbone appearance on a radiograph. Worm hole porosity is common in gas shieldedflux cored welds when the electrodes have too much moisture in the wire flux. WELD ROOT POROSITY. Weld root porosityfrequently occurs when MIG welding using “argon oxygen” (oxidizing)mixes on parts gt;6 mm. With these gas mixes the resulting root is typicallynarrow, finger shaped. The root finger area solidifies rapidly trapping porosity.To reduce the stainless root weld porosity, change to an argon 2 – 4 CO2 gas mix.Increase the weld parameters, slow the weld speed and avoid weld weaves.
ALIGNEDWELD POROSITY.
Linear porosity, an array of small round pores typicallyfound in a line. Often caused from the base metal lubricants or metal surfacecontaminate. Add weld energy (increase wire feed), increase push angle allowingthe arc to break up surface oxides ahead of weld.
SCATTEREDWELD POROSITY.
Weldporosity scattered randomly throughout the weld or welds. If the MIG weld surfaceis gray and looks oxidized, the porosity is typically a result of insufficientgas flow. If the weld surface looks clean with scattered porosity the porosityis usually caused by the base metal part or electrode contamination, or perhapsthe weld data used causes the weld to freeze too rapidly.
LARGEPORE WELD POROSITY.
If weld surface is clean and does not look oxidized,the large pore MIG / FCAW porosity could be a result of excessive gas flow. Gasturbulence is caused with gas flow greater than 40 cuft/hr. Optimum MIG and fluxcored gas flow for carbon steels is 25 to 35 cuft/hr, the gas flow should be measuredas it exits the gun nozzle. If the weld surface is dirty (oxidized) the causeof larger pore porosity is ofen a result of insufficient gas flow, less than 20cuft /hr.
Jan2004. Sandvik Announces New Ultrahigh- Strength Stainless Steel “NANOFLEX”:
Sandvik Materials Technology recently developed a newstainless steel called Sandvik Nanoflex that featuresultra high strength and good formability, corrosion resistance, and surface finish.According to the company, the steel is well suited for mechanical applicationsrequiring lightweight, rigid designs such as medical equipment and for replacementof hard-chromed, low-alloy steels in the automotive industry. Examplesof the strength properties of Sandvik Nanoflex are 1700 MPa tensile strength,1500 MPa yield strength, 8% elongation, 45-58 HRC hardness, and a Charpy V impactstrength of a minimum of 27 J at -20°C. Exact strength values depend on theproduct form and the manufacturing route. Despite its high hardness,the company claims it is easy to perform cold forming operations such as bending,cutting, turning, and grinding. After reaching the desired shape, a simple low-temperatureheat treatment gives the material its high strength without distorting the workpiece. This materialalso displays good welding properties. It is available in tube, strip, wire, andbar forms.
| Stainless Filler Metal Selection | |
|---|---|
| StainlessType | FILLERMETAL SELECTION AWS A5-9. Use first choice. Confirm choice with wire manufacturer |
| AUSTENITICCHROME NICKEL NONE MAGNETICStainless201 to austenitic 200-300 series use201used for low temp cryo applications to -320F | 308 for 330 use 312 |
| Stainless202 to austenitic 200-300 series use | 308for 330 use 312 |
| Stainless201-202-301 303 to mild steel use | 312 |
| Stainless210 – 202 -301 to mild steel. Stainless type 201 requires special considerationrequired to avoid hot cracking as ferrite extremely low | 312can reduce cracking as it provides much higher ferrite than 309. |
| Stainless301 to austenitic 200-300 seriesuse | 308for 330 use 312 |
| Stainless302 to austenitic 200-300 seriesuse | 308for 330 use 312 |
| Stainless302 – 302b 304 to mild steel use | 310 |
| Stainless 302- 302B -304 to mild steel use | 310 |
| Stainless303 to austenitic 200-300 seriesuse | 308for 330 use 312 |
| Stainless303 to 310-314-330- use | 312 |
| Stainless303 to mild steel use | 312 |
| Stainless304 to austenitic 200-300 seriesuse | 308for 330 use 312 |
| Stainless305 308 to mild steel use | 312 |
| Stainless 305to austenitic 200-300 series use | 308for 330 use 312 |
| Stainless305 – 308 to mild steel use | 312 |
| Stainless308 to austenitic 200-300 seriesuse | 308for 330 use 312 |
| Stainless309 to 309 – 310 – 314 -316 –317 use | 309 |
| Stainless 309to 330 use | 312 |
| Stainless 309to 347 use | 308- 347 |
| Stainless310 to 310-3140 | 310 |
| Stainless 310to 316 use | 316 |
| Stainless310 to 317 use | 317 |
| Stainless 310to 321 use | 308 |
| Stainless 310to 330 use | 312 |
| Stainless 310to 347 use | 308 |
| Stainles 310to mild steel use | 310 |
| Stainless314 to 314 use | 310 |
| Stainless 314to 316 use | 316 |
| Stainless314 to 317 use | 317 |
| Stainless 314to 321 | 308 |
| Stainless314 to 330 use | 312 |
| Stainless314 to 347 use | 308 |
| Stainless314 to mild steel use | 310 |
| Stainless316 to 316 – 317 use | 316 |
| Stainless316 to 321 – 347 use | 308 |
| Stainless316 to 330 | 312- 309 |
| Stainless316L to mild steel use | 309 |
| Stainless316LN a nitrogen addition to a low carbon stainless Incesase both corrosion resistanceand strength as compared to 316L | 316Lor 317L 317L typical for corrosion 316L for toughness (cryogenic typeapplications |
| Stainless317 to 317 | 317 |
| Stainless317 to 321 | 308 |
| Stainless317 to 330 use | 312 |
| Stainless317 to 347 use | 308L |
| Stainless317 – 321 – 348 403 – 405 410 414 416 to mild steel use | 309 |
| Stainless321 to 321 – 347 | 347 |
| Stainless321 to 330 use | 312- 309 |
| Stainless330 to 330 use | 330 |
| Stainless330to 347 use | 312- 309 |
| Stainless348 | 347 |
| Stainless384 | 309 |
| StainlessAM 350 | AM350 |
| Stainless410 Condition A ASTM 276 12% Chrome, chrominum / martensitic steel | toitself or carbon 309L |
| Stainless501 502 430 431 442 448 to mildsteel use | 310 |
| PH15-7Mouse | WPH15-7Mo |
| 17-4PHuse | 17-4PH |
| A286 | A286 |
| Sanicro28 27 Cr – 31 Ni -Mo 3.5 -Cu 1 Tensile 73 ksi Yield 31 ksi | Sanvik27.31.4.LCu ER028L |
| DuplexFerritic Austenitic SAF 2304 UNS 32304 DIN X2CrNiN 24-4 23 Cr – 4 Ni – N 0.1 Tensile 87 ksi – Yield 58 ksi | 308MoL |
| DuplexFerritic Austenitic SAF 2205 UNS S31803 22 Cr – 5.5 Ni -Mo 3 – N Tensile 990 ksi – Yield 65 ksiWeldNote: For MIG use argon with 2% CO2. When welding 2205 or 2304 to dissimilar butterfirst with ER309MoL then weld with 308MoL No concern for interpass temp, highamps can be use | 2209 |
| Duplex3RE60 18.5 Cr – 4.9 Ni – 2.7 Mo | weldsame as 2205 |
| 254SMO alloy | ElectrodeAvesta p12 Sanvik Sanicro 60 ENiCrMo3 |
| Stainlessto carbon | 309or 312 which has higher ferrite reduces cracking |
| MARTENSITICSTEELS 403 – 410 – 414 416- 420-422 -431- 440 Preheat and interpass temp 500F 260C Post heat 1350F 732Cgt; Control cool 50F / hr to 1100Fgt; Control cool to 1100F 600C then air cool. Treat the 500 series the same as the Martensitic series | |
| Stainless403 to 400 series use | 410ASTM 276 |
| Stainless403 to 501 use | 502 |
| Stainless403 to 505 use | 505 |
| Stainless405 to 505 use | 505 |
| Stainless405 to 501 use | 502 |
| Stainless405 to 430 use | 430- 309 |
| Stainless405 to 400 series use | 410 |
| Stainless410 to carbon steel | 309L |
| Stainless410 – 414 WELD same as 405 | |
| Stainless416 – 440 butter with 312 or 309 first | |
| Stainless416 to 505 -502-501 -446 – 440 -430 -420 use | 309 |
| Stainless416 to 431-420-416 use | 410 |
| Stainless420 to 505 | 505 |
| Stainless420 to 501-502 use | 502 |
| Stainless420 to 446 use | 430 |
| Stainless420 to 440 -420 use | 420 |
| Stainless420 to 431 -430 use | 410 |
| Stainless430 to 505 use | 505 |
| Stainless430 to 446 – 440 – 431 – 430 use | 430 |
| Stainless430F to 400 series use | 309 |
| Stainless431 to 505 use | 505 |
| Stainless431 to 501 -502 use | 502 |
| Stainless431 to 446-440 use | 309 |
| Stainless440 weld same as 431 | |
| Stainless446 to 505 use | 505 |
| Stainless446 to 501 – 502 use | 502 |
| Stainless446 to 446 use | 309 |
| Stainless505 to 505 use | 505 |
| Stainless501 to 505 – 502 – 501 use | 502 |
| Stainless502 to 505 – 502 use | 502 |
| Ferriticsteels 405 – 409 – 429 – 430 -434 – 436 – 442 -444 – 446 | |
| 444to 444 or to other metal use | 316Lor 309MoL |
| Ferriticmagnetic avoid prolong heat in the range of 750F -1700F (400-925C | |
| Feriticpreheat at 350F 176C To improve ductility | |
| Ferriticsteels most frequent electrodes | 309- 310 – 312 |
| Ferriticsteel if post heat required use Austenitic filler | |
Intergranularcorrosion, also calledintercrystalline corrosion
Intergranularcorrosion, also calledintercrystalline corrosion, occurs on or adjacent to the grain boundaries of ametal. It is caused by microsegregation of impurities and alloying elements onthe grain boundaries.The driving force of intergranular corrosion is the differencebetween the electrode potentials of the grain boundary and the grain itself, whichform a galvanic cell in presence of an electrolyte. Intergranularcorrosion of stainless steels:Themicrostructure of metals consist of a granular composition. The grains formedare small crystals. The crystal surfaces join the surfaces of other grains toform grain boundaries. Grain boundaries separate the grains. With stainless, intergranularcorrosion, (intercrystalline corrosion), occurs on or adjacent to the grain boundariesof a metal. Somecauses of intergranular corrosion are welding, stress annealing, improper heattreating or overheating in service. Inspectors have difficulty in detecting theearly stages of intergranular corrosion. This form of corrosion results in a lossof strength in metal parts where the grains have fallen out.Intergranularcorrosion is caused by microsegregation of impurities and alloying elements onthe grain boundaries. The driving force of intergranular corrosion is the differencebetween the electrode potentials of the grain boundary and the grain itself, whichform a galvanic cell in presence of an electrolyte. If the phases segregatedat the grain boundaries have lower value of electrode potential they will oxidize(anodic reaction) and the grain metal having higher value of electrode potentialwill provide cathodic reaction (reduction). Dissolution of anodic grain boundariesstarts from the surface and advances along the grains interfaces. The processresults in deterioration of the bonding between the grains and drop of mechanicalproperties. If the precipitates at the grain boundaries have higher electrodepotential the grains will dissolve (anodic reaction). In this case the grain boundarieswill not be attacked.
Asummary of Stainless Welds and Sensitization.
Metallurgistcould write a book on this subject. I will try to keep it short and I hope itseasy to understand. With a stainless welds on specific alloys, sensitization occurs in the weld’sheat affected zone (HAZ) whenthis zone is between approx. 900 and 1600F. Sensitization occurs whenthe carbon content is sufficient to produce precipitation of chromium rich carbidesalong the HAZ grain boundaries.The formation the chromium carbides results in a chrome depleted area around thegrain boundaries. This location will be in the weld’s HAZ at the furthest pointfrom the weld. If the weld’s HAZ depleted chromium carbide area issubject to a corrosive medium the grains can rapidly corrode and cause separationfrom the weld.A 304L metal will contain a maximum of 0.03% carbon. In contrast a 304 base metalcan contain twice the carbon level of the 304L. Welding and subjectinga 304 base to 900F to 1600F will cause sensitization in HAZ. Solutionto Stainless Sensitization.
- Use a low carbon ( L grade) stainless. The typical 0.03 max carbon content is not sufficient for carbide precipitation.
- Consider a stabilized stainless steel such as 347 or 321. These steels are stabilized against chrome depletion with alloy elements that have a greter affinity to form carbides.
- Type 347 which is similar to 304 has niobium (columbium) for carbide formation. Let the niobium do its job and the chrome has no carbides to attach to, thus we prevent carbide precipitation.
- Type 321 is also similar to 304. Type321 contains titanium and the titanium does the same job as the niobium. Keep in mind both the 321 and 347 are typically much more costly than the 304L.
What about those common multi-pass “316 or 308 welds”?
Of course the multi-pass welds are subject to the 900F to 1600F, however the weld metal in contrast to the stainless base metal will contain a small amountof ferrite in the austenitic structure. Chrome diffuses in ferrite approx.100 times faster than it will in the austenite. The ferrite has more chrome thanthe austenitic matrix. The ferrite area will be rich in chrome so this area can supply an area subject to sensitization. nbsp; Avesta: A typical Pulp and Paper Mill Layout Typical Pulp and Paper Mill Weld Consumables from Avesta AVESTA 308L/MVR Avesta 308L is excellent for the welding of evaporators, storage tanks, etc. made from 304L (EN 1.4307, Outokumpu 4307), a general purpose steel. AVESTA316L/SKR For welding 316L (EN 1.4404/1.4436,Outokumpu 4404/4436), a well-proven austenitic grade that is used extensivelyin the pulp and paper industry. AVESTAP12 Avesta P12was specially designed for welding fully austenitic 6 Mo steels, e.g. Out ok umpu254 SMO (EN 1.4547). Owing to their good resistance to corrosion (stress, pittingand crevice), these steels are used in, amongst other things, filter washers and wash presses in modern ECF bleaching plants.AVESTAP54 Avesta P54 is an iron-based filler metalthat was specially developed for welding fully austenitic 6 and 7 Mo steels(e.g. Outokumpu 254 SMO) in applications where conventional nickel-based alloysare vulnerable to transpassive corrosion. D stage filters in the ClO2 bleachingof pulp are just one example. AVESTAP5 A molybdenum-alloyedfiler of the 309MoL type, commonly used in the pulp and paper industry fordissimilar welding.Stainlessand Nitrogen Purge Gas Question. Edas you are aware Nitrogen is a lot cheaper than argon when utilized as a purgegas for stainless. My question, When MIG welding stainless tanks edge or cornerwelds, tube or pipe open root welds, can nitrogen react with the stainless andhave a negative impact? Answer: Nitrogen has adiatomic, “two atoms” per molecule. Nitrogen in the diatomic form isusually insoluble in molten stainless. However if the nitrogen gets into the weld arc, the plasma arc energy can seperate the diatomic molecules and create monatomic molecules. The monatomic molecules are soluble in the weld. The nitrogen,monatomic (seperated molecules) become an alloying element and can reduce theferrite in a stainless weld. A reduction in ferrite in some alloys can cause theweld to be more austenitic and sensitive to hot cracking. If nitrogen enters aweld or the welding arc, it can have a negative and sometimes a positive influence.Thats the reason one of my gas mixes for duplex has the addition of nitrogen,and the other gas mix does not. There are stainless alloys which donot need ferrite like 320 / 310. With these alloys nitrogen has no negative impacton these alloys. Also if the stainless alloys have high ferrite levels they typicallycan afford to loose a little of the ferrite to the nitrogen. With closed root, austenitic stainless welds, as found in tanks, corner, edge welds,or thin gage, partial penetration tube welds, nitrogen is the logical, economical,purge gas choice for all austenitic, duplex, martensitic and precipitation hardening stainless steel applications. The only concern would be a few specific, ferritic alloys in which nitrogen could cause severe weld mechanical issues. With an open root “MIG stainless weld” the nitrogen purge gas has little opportunity to get into the weld arc as the gas flow rate / pressure of the weldinggas should be higher than that of the purging gas . However nitrogen could stillbe picked up by the weld. . With duplex stainless there should be no concerns for open root nitrogen issues. The majority of the common, open root stainless alloys will not be adversely affected by nitrogen purge gas. However in the world of product liability, here is the welding bottom line. If your weld job is large enough to produce a substantialcost reduction from using nitrogen gas, then it’s logical to “pre qualify the nitrogen purge welds” and have the weld chemistry, ferrite and mechanical stested. Failed Stainless Pipe Weld Tests.Question:Ed we weld austenitic stainless and carbon steel pipes. For cost reduction, in our stainless weld tests we only utilize “carbon steel pipes” and 309L SMAW or flux cored, electrodes. We frequently have root cracking issues, or during the bend test the weld sample breaks. What is strange is that we visually examine all the roots and we wont let them be mechanically tested unless the welds look OK. Why the inconsistency? why do some tests welds pass and other good looking welds fail?Ed’sAnswer: The bottom line the 309L electrode is designedto weld “carbon steel to stainless” this electrode was not designedto weld carbon steel to carbon steel thats why we have carbon steel electrodes. Use the 309L electrode on two carbon steel pipes and weld dilution becomesa concern in the weld root area. If the weld parameters and edge prep is suchthat the resulting weld dilution is minimal, the resulting 309L weld should beaustenite with a little ferrite. It’s the austenite / ferrite combination thatprovides weld ductility.Ifwhile welding the carbon steel pipe root, the welder uses higher current, slowerweld speeds or a wider weld weave, the 309L weld can end up with more weld dilutionwith the carbon steels, reducing the weld ferrite level and making the weld moreaustenitic. A reduction or loss of ferrite can make the weld subject to “hotcenterline cracking” (hot cracking, the weld cracks during the weld or soonafter).A hot weld crack surface in a bend test can be identified by a blue or gray color.Even if the root pass does not crack the high austenite composition can turn tomartensite when cooling. The brittle martensite can readily fracture during thebend test. (a silver color or bright fracture surface). Thebottom line if you look at the costs involved in the stainless to carbon steelpipe weld test, it makes little sense to use two carbon steel pipes. Ensure foryour weld test that one of the test pipes is at least stainless.FAILED 308L FLUX CORED WELDS SUBJECT TO HIGH TEMP:
Gasshielded stainless flux cored wires have an Achilles Heel: Aspointed out by Kotecki in the QA section, March Weld Journal, it would appearthat there is a problem with the use of specific stainless flux cored wires onpressure vessel applications subject to high temperatures or post heat treatment.In the stainless application reviewed, the weld shop applied a stress relief of1475F for 12 hours to a 304L pressure vessel welded with gas shielded 308L fluxcored wires. After the heat treatment many cracks were found in the 308L fluxcored welds. These welds had no cracks before the post heat treat. Itwould appear the flux cored wire manufactures add specific alloys and compoundsfor easy slag removal. One compound contains bismuth. Note fromEd: The bottom line for the 308L gas shielded flux cored weld cracking issuesor part / weld premature creep failures at elevated temperatures is the stainlessgas shielded flux cored wires utilized contain a compound containing “bismuth”This compound assists in easy slag removal. It’s been reported that with levelsof bismuth at 200 ppm. (200 ppm is a typical bismuth level) weld cracks have occurredat a reheat temp of 1050F. Whatshould you do if your stainless pressure vessel is to be used in a high temp applicationor the vessel requires post heat treat.POST HEAT TREAT: To avoid major issues on an application subject to high temppost heat treat, its logical that a weld qualification procedure should encompassthe required post heat treatment. This way you can check the welds in the realworld welded condition. CONTROL THE BISMUTH LEVELS: For high tempapplications gas shielded stainless flux cored wires are available with bismuthlevels ; 20 ppm. These products are supposed not to exhibit reheat cracks orpremature creep failure. Talk to your weld wire supplier about your concerns forthe high temp. REPUTABLE WIRE MANUFACTURERS: Don’t purchase weldconsumables that fell of the back of a truck on their way from China. Deal withreputable flux cored wire companies like Sanvik, Avesta and ESAB. PROCESS ALTERNATIVES. Consider SAW or MIG. Its important to note, thatthe majority of stainless are put into service at tempertures below ; 500Fand these applications have not been subject to the issues discussed. Howeverthere are also 300 series that undergo annealing and stress relief or are subjectto high temp gt; 900F applications in the power industry. Microfissuresand 310 stainless.
Question. Ed when welding 310 stainless we a longitudinal bend test evaluation of weld sampleswe often end up with small linear shaped porosity which so far has gone unexplained.We weld a lot of stainless in this shop and so we are aware of cleanliness requirementsand the use of good weld consumables , however the 310 pores are something wecan’t seem to shake. Most of the pores are less than 2 mm in length, and so theyare acceptable however our designer has expressed concern that we may notbe using the best weld consumables. Any ideas Regards Paul.Answer:First 310 stainless and a few other grades are completely austenitic containingno ferrite. It’s common with 310 – 330 multi-pass welds to find microfissures(not porosity) forming at the interface between the welds. It’s also commonto find these microfissures with longitudinal face or root bend tests. The microfissuresdon’t occur with austenitic grades like 308L that contain ferrite. Reports fromthe WRC state that the small microfissures typically will not influence fatique,creep and corrosion properties, and as the 310 is very tough the microfissurestypically don’t propogate, however they can initiate pitting corrosion or reducethe critical pitting temperture. You can reduce the amount of microfissuresby using filler metals with extra low sulfur and phosphororus, use stringer passes,maximum size similar to 6 mm fillet and ensure you use a max interpass temp of250F.
StainlessWeld Data.
When MIG Welding stainless you can use the optimum MIG wire feed data recommended atthis site for carbon steels. The only change that will be required is weld voltage.As stainless will use a low reactive gas mix, less weld volts will typically berequired. In contrast to MIG on carbon steels, when MIG stainless welds are made,typically 2 – 3 lower volts are required. Keep stainless clean, only usestainless wire brushes.Stainlesssteel has a very thin and stable oxide film rich in chrome. This film reformsrapidly by reaction with the atmosphere if upset or damaged. If stainless steelis not adequately protected from the atmosphere during welding or is subject tovery heavy grinding operations, a very thick oxide layer will form. The thickoxide layer will be noted by it’s blue tint. This oxide will have a chrome-depletedlayer under it and this layer can impair corrosion resistance. Withstainless weld applications, both the oxide film and depleted layer must be removed,either mechanically (grinding with a fine grit is recommended, wire brushing andshot blasting will have less effect), or chemically (acid pickle with a mixtureof nitric and hydrofluoric acid). Once cleaned, the surface can be chemicallypassivated to enhance corrosion resistance, (passivation reduces the anodic reactioninvolved in the corrosion process). Carbon steel tools such as drilss,wire brushes or steel grinding wheels can contaminate the stainless surface. Alsosparks from grinding carbon steel can embed fragments into the surface of thestainless steel. The carbon contamination or grinding fragments can rust if moistened. STAINLESSamp; CARBON PICKUP. Withfixtures avoid carbon steels in close proximity to stainless welds, as carbonpick up possible, the weld area will rust. There are many ways to introduce carbonto stainless welds. For stainless vert up welds on parts 3 to 6 mm, considerpulsed, For stainless all position welds on parts gt; 6 mm, first logicalchoice will be always be stainless gas shielded flux cored wires. Minimizethe drive roll tension applied to stainless flux cored wires. For stainlessflux cored weld data, use the carbon steel flux cored wire data found in my fluxcored book. For stainless flux cored use an argon mix with 15 – 25 CO2.
STAINLESS amp; CARBIDE PRECIPITATION (chrome depletion):
Useweld data to avoid Carbide Precipitation. (CP)Ifany part of stainless-steel is heated in the range 900-1400°F (482-760°C)for any reasonable time there is a risk that the chrome will form chrome carbidesCr23C6 with any carbon present in the steel along the austenite grains. Thi resultsin depletion of chromium from the austenitic grains resulting in decreasing thecorrosion protective passive film. This effect is called sensitization. It isalso called weld decay since it usually happens during welding process when thezone around the weld is heated. Forstainless corrosive environments control of CP is critical. CP typicallyoccurs within 3 mm of either side of a weld HAZ A chrome depletedarea may not resist the corrosive environment. To combat CP use (L) low carbonbase and filler metals. Ensure the C02 gas composition has less than 5 % CO2.
STAINLESS AND STABILIZED ELECTRODES:
You can combat CP with stabilized fillers which provide alloys that grab the carbonbefore it can affect the chrome. Alloys like E347 which work at reducing chromedepletion. Stabilized fillers are typically used in high strength hightemp service. However if base metal is not an L grade CP will occur.Rapid cooling of stainless through the 800 – 1600F range reduces Carbide Precipitation.TIGwelding and the influence of “sulfur” in austenitic stainless applications. When the parts to be welded have normal sulfur content(greater than 0.005%) an interesting event can occur. With increasing weld temperaturethe surface tension of the weld pool also increases. The result is the hottestpart of the fluid weld surface is attracted to the middle of the weld pool causingdeep narrow weld penetration. With lower sulfur in the weld, the weldsurface tension is less. The resulting weld is wider with less fusion. When twoparts welded together have different levels of sulfur tension the weld may pulltowards the lower tension, lower sulfur part, resulting in inconsistent weld fusionor penetration favoring one side of the weld joint. This occurrence is especiallynotable when automated TIG welding Dissimilar parts such as cast parts to sheetor pipe. The following weld solutions may assist the sulfur issues. 1 Pulse the application. 2 Use a weave. 3 Weld twice. 4 Useheat sink back up bars in close proximity to weld.
Weld Cracks:
308 WELDS CRACK DURING POST HEAT TREAT. Question: We just finished welding a 304L pressure vessel. The procedure called for 308welds which were made with the gas shielded flux cored process. A stress reliefof 1475F for 10 hours was required. We know the welds were sound before the heattreatment, however immediately after the post heat treat we found cracks in theflux cored welds. This stainless expert (KotececkiMarch 2008 Weld Journal) providesa good summary of this unique cracking problem. It seems that with gas shieldedflux cored wires you will find a small amount of bismuth-bearing compounds. Thesecompounds assist in weld slag removal. Bismuth and similar elements at specificlevels can causes cracks if the parts are put into service and the temps are above900F and possibly lower temperatures at long time periods. The bottom line, ifyour stainless vessel is going to have post heat treatment or be placed in servicewith high temperatures ensure your flux cored wire contains ; 20ppm bismuth.Ask the electrode manufacturer does their wires contain any elements that cancause reheat cracks or premature creep failure.
MIG OR TIG WELDING THAT STAINLESS ROOT…
To ensure good corrosion resistance of thestainless weld root, the root must be protected from the atmosphere by an inertgas shield during welding and subsequent cooling. The gas shield should be containedaround the root of the weld by a suitable dam, which must permit a continuousgas flow through the area. Welding should not commence until sufficienttime has elapsed to allow the volume of purging gas flowing through the dam toequal at least the 6 times the volume contained in the dam. Once purgingis complete, the purge flow rate should be reduced so that it only exerts a smallpositive pressure, sufficient to exclude air. If good corrosion resistance ofthe root is required, the oxygen level in the dam should not exceed 0.1% (1000ppm); for extreme corrosion resistance this should be reduced to 0.015% (150 ppm).Backing gasses used for purging are typically argon or helium; nitrogen is oftenused as an economic alternative where corrosion resistance is not critical, nitrogen+ 10% helium is a good mix. A wide variety of proprietary pastes and backingmaterials are available than can be use to protect the stainless root insteadof a gas shield. In some applications where corrosion and oxide coking of theweld root is not important, such as large stainless steel ducting, no gas backingis used.
General Stainless (P-8) 300 Series Pipe Weld Procedure Data. Max interpass Temp 350F
| Process | Filler Diameter | Metal | Polarity | Amps | Wire Feed | Volts |
|---|---|---|---|---|---|---|
| GTAW 3/32 Tungst | 1/16- 1.6mm | 300 series Stainless | DC Straight | 95-145 | N/A | 14 |
| SMAW EXXX-15-16 | 1/8 3.2mm | 300 series Stainless | DC Reverse | 95-145 | N/A | 20-24 |
| SMAW EXXX-15-16 | 5/32 4mm | 300 series Stainless | DC Reverse | 125-175 | N/A | 21-25 |
| FCAW EXXX-T1 argon with 25 CO2 | 045 | 300series Stainless | DC Reverse | 130-180 (140) | 230/280 | 22-25 |
Corrosion Potential.
Materials used in oil and gas extraction are affected to several different types of corrosion, often caused by seawater and spray. The types of corrosion, which can occur on stainless steels in marine environment, are pitting and crevice corrosion, and for standard austenitic grades also stress corrosion cracking (SCC), if the material temperature is above 60°C (140°F). These are all localised attacks – general corrosion need not be consideredfor stainless steels in seawater. High temperatures, high chloride contents and low pH values increase the risk of localised attacks in any chloride-containing environment. Of these, temperature is usually the most influential factor. However, there is a fourth important consideration: the electro-chemical corrosionpotential of the environment. In seawater, this potential is affected by biologicalactivities on the steel surface. Since seawater is, in a sense, a living corrosive environment, it is sometimes difficult to define exactly what the service conditions will be. At normal seawater temperatures, a biofilm will form on the steel surface and result in a corrosion potential of +300 to +500 mV/SCE. Attemperatures above ~40°C (100°F) the biological activity will cease and the corrosion potential will drop. The use of continuous chlorination, to stop marine growth, may increase the corrosion potential to values as high as +600to +800 mV/SCE. This, however, can be avoided through the use of intermittent rather than continuous chlorination. Benefitsover Cu and CuNi-based alloysStainlesssteels are very resistant to erosion corrosion compared with Cu and CuNi-basedalloys, which are very sensitive to this form of attack. Water in harbours, around off shore platforms, and near chemical plant sites is often contaminated e.g. withammonia (NH 3 ) and sulphides (S 2- ). These compounds, even in very small quantities,cause localised attacks on copper-base alloys, while stainless steels are notaffected at the impurity levels involved. Sourcorrosion: Wet and sour service: The corrosivity of an oil andgas well is increased by the presence of chlorides in water solutions, carbondioxide, and hydrogen sulphide.Theenvironment is considered sweet as long as no hydrogen sulphide is present. Carbondioxide alone can however cause high corrosion rates on carbon steel, since itis acidifying the solution. This is further accelerated if chlorides are present.Sourenvironments are defined when the partial pressure of hydrogen sulphide is above0.05 psi. At higher partial pressures, the corrosion rate on carbon steel is substantiallyincreased by means of making the water phase more acidic and by forming iron sulphidescale. Sulphide Stress Cracking (SSC) is common in high strength steels containingmartensite. It can also occur in ferritic steels.Stainlesssteels are different. Sandvik Sanicro 28, Sanicro 29, SAF 2205 and SAF 2507 gradesare completely resistant to corrosion in wells rich in carbon dioxide with a highamount of chlorides in the water phase. If hydrogen sulphide is present, thereis still no general corrosion, but the risk of localised corrosion increases,especially with regard to SSC. TheNACE TM-0177 test. Experiments have been carried out at room temperature inaccordance with the NACE TM-0177 test (5% sodium chloride, 0.5% acetic acid, saturatedwith hydrogen sulphide).Thethreshold stress for cold-worked Sandvik SAF 2205/22Cr is about 90% of the yieldstrength, which is very good when compared to results for high strength, ferriticstainless steels.SandvikSanicro 28, in the cold-worked condition, results in no failures up to very highstress levels. The high alloy duplex stainless steel Sandvik SAF 2507 is alsoresistant to cracking in the solution-annealed condition.Ingeneral terms, this test shows that Sandvik Sanicro 28 has a higher resistanceto sulphide stress cracking compared to SAF 2205/22Cr, which is much more resistantthan 13Cr. Sandvik Sanicro 29 has an ever higher resistance to localised corrosionand sulphide stress cracking than Sandvik Sanicro 28.Itshould be remembered that the chemistry of the “NACE solution” is notrepresentative of the conditions in most sour oil and gas wells. This is especiallytrue for acidity, where the pH value is lower in the NACE test. Results from theNACE TM-0177 test, therefore, should not be used for determining the suitabilityof different grades, but more as a ranking test. Other tests, more representativeof actual service conditions, must be used to determine the suitability of differentgrades. Practical experience of specific grades is, of course, extremely useful. Visit Sanvik’s web site for more excellent data on stainless and duplexproducts, however if you want the best stainless MIG process control data visit 
