Duplex Stainless steel

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Hi Guys, i need help putting together a work instruction to weld Duplex stainless steel tank( preferably in Bullet format) any ideas, it would be much appreciated
Reply:Are you asking for a Welding Procedure?  If so, what code are you following for the fabrication of this tank?Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Originally Posted by gerritHi Guys, i need help putting together a work instruction to weld Duplex stainless steel tank( preferably in Bullet format) any ideas, it would be much appreciated
Reply:Thanks for the replies, procedures i have, heat input i understand, also ferrite control(needs to be between 30-60%)What i'm talking about is this what i've started:•Weld joint / preps shall be strictly as per drawing. •Weld joints and adjacent areas 50 mm either shall be wiped clean with ?? and free of any oil , grease or           any contaminants.•Ensure weld deposits are thoroughly clean of any scale, oxides or slag prior to depositing subsequent passes.•The ground, areas must be accessible for welding and not acute.•Weld joints shall be completely blocked off from any possible draft.•Prior to any welding the welder / operator shall fully understand the application of the WPS and the relevant parameters. •It is imperative that the welder / operator try out the set welding parameters on a test piece prior to welding on the job. •To achieve the desired  Ferrite content of 30 % - 60%  , the welding heat input shall be maintained between 0,5 kj/mm – 2.5 kj/mm   •Due to excessive welding concentrated on any localized area, distortion could occur therefore  the effective shrinkage force shall be balanced by welding.•The interpass temp shall not exceed the max permitted on the approved WPS( 150°C) .•Preheat  temperature shall be kept to the minimum and shall be evenly distributed and not concentrated in one specific area.•Weld out  in sequence ensuring that there is no excess welding on the capping.•++++++•++++•++
Reply:OK, I'm following your request now.  I would add the following to your list of requirements:-  I like acetone for degreasing and cleanup prior to welding.  But alcohol(ethanol) works too and is less expensive and less hazardous.  It just takes a longer time to evaporate.  Petroleum Ether works extremely well, but catches fire if you use harsh language around it, let alone welding heat and sparks.-  Only dedicated stainless steel brushes shall be used for inter-pass cleaning, joint preparation, and cap pass cleanup.  Contamination from welding mild steel or using mild steel brushes will ruin your day.-  All grinding shall be done with dedicated wheels, burrs, flap discs.  Avoid cross contamination wherever possible.  I've even heard of people using special stainless steel files; but those are crazy expensive.  It seems to me that a good high carbon steel file will be so hard that the transfer of material from the file to the stainless would be too small to worry over.  Still make certain that files aren't loaded with mild steel shavings from some other work.  That could cause a problem.-  Pre heat should be limited to 100°C and only used where condensation on the weld joint is a concern-  Back-purge is mandatory for welding Duplex SS.  Depending on the intended service, I might even suggest using an O2 monitor to ensure that the back purge is thorough and residual O2 is below the upper limit(something like 100PPM, If memory serves)-  You may want to specify how much color is acceptable on the inside of the root pass. Pictures of what's acceptable and what's not would be very handy for the welder to reference.-  Your heat input window is very broad.  For some grades of Duplex, perhaps too broad.  I suggest ensuring that your WPS has realistic upper and lower limits for amperage and travel speed, (and voltage for wire processes).  This will ensure that you get some consistency from one welder to another.  You may also need to look more closely at the pipe diameters and wall thicknesses and factor this into your WPSs.  I'm speaking very generally, but what works fine on small, thin wall tubing will not work on large, heavy wall pipe.-  Last suggestion.  Are you relying on your supplier to confirm that the Duplex has the right ferrite/austenite mix?  If so, ask to see the test results for whichever ASTM procedure they're following.  If it were feasible, I'd do the testing in-house.  There's nothing worse then welding up Duplex that is defective from the mill.  But the metallurgical testing needed to do this is not something most fabricators are setup to handle.  Buy from a reputable supplier with a long track record of supplying quality duplex SS.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:If you can get your shielding gas with a small amount of Nitrogen in it, it will help with your ferrite count. And as previously mention, make sure you receive a mill test report for your material. You would be surprised at what some suppliers are giving out these days.Last edited by LT1Adavanced; 01-16-2014 at 09:28 PM.
Reply:I occasionally weld Duplex Stainless at work.  While I didn't learn too much about the actual material and welding practices in school, I have been taught to always make sure I am adding filler material.  No fusing of any kind otherwise it is prone to a ferrite content issue. Scott
Reply:Never welded duplex, yet, but you may find this tech ref helpful,http://www.avestawelding.com/3756.epibrw"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi