Corrosion around S/S welds

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I am trying to weld 3" stainless food grade pipe for use as a brine line.  The problem is the when I've previously done this the weld fails due to corrosion.  It is used as a calcium chloride brine solution and the welds are tigged with 316 filler rods.What can I do to resolve this? I need to run about 200' of pipe constructed from 16' pieces....plenty welds.
Reply:Is it failing in the HAZ, or over the weld?Are you using 316, or 316L filler.Is the pipe 316, or 304 (which is typical for food grade)?
Reply:Not sure of the exact failure point, it developes after about 1 year.  From the looks of it its in the weld.  The pipe is 316 and filler rod is 316L.  I guess my question is what is the best method for welding what I need?  I don;t want to have to repair welds after a year.
Reply:I've had problems with corrosion before on stainless.  Make sure your using new discs,s.s.buffing wheels and even use brand new gloves. As for the filler try using emory cloth and acetone to clean the filler wire before you use them as filler
Reply:I hope your purging the inside of the tube?  If not, this is your first problem.You also might be overheating the material and causing something called carbide precipitation.  There is plenty of information on it already floating around here so Im not going to go into details on what it is and how it is caused, but that it most likely the other cause of your problems.Have we all gone mad?
Reply:316L is supposed to reduce carbide precipitation.  Is the brine hot?Can you passivate the welds?
Reply:It runs at -20F at the coldest setting.  They are long runs of pipe an can attempt to passivate them but I will have to attempt to make something.  Is there anything else besides trying to passivate the welds?
Reply:Yes I do purge the lines with argon.
Reply:Then I would say your welding technique is to blame, your getting the material too hot.Get a picture of a weld after its done, and one after its failed.  Then it should be easy to tell.Have we all gone mad?
Reply:If the pipe isn't a 316L grade also, you're not going to solve this easily.  Pipe and welding filler metal need to be 'L' grade material in order to minimize sensitization(carbide precipitation) due to welding.  You can also try using 347 filler metal, as this is stabilized with Ti and/or Nb.  You'll need to qualify the procedure using this filler metal and get approval from the customer, since it's not the typical 316L filler used.  The 347 filler will certainly cost more too.  But the Ti and Nb(CB) alloying additions will help resist any chromium carbide precipitation.  If your base metal is 316, and not 316L, then the 347 grade filler metal might tip the balance.As others have mentioned, your prep must be excellent.  Stainless brushes, solvent to remove any grease or oil(sources of carbon), and back purge with pure Ar. Originally Posted by aztechNot sure of the exact failure point, it developes after about 1 year.  From the looks of it its in the weld.  The pipe is 316 and filler rod is 316L.  I guess my question is what is the best method for welding what I need?  I don;t want to have to repair welds after a year.
Reply:To much heat, not enough purge, bad pipe, bad fittings, carbon contamination from wire wheels, brushes, etc....... Could be a ton of things, rule them out one at a time.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Originally Posted by aztechIt runs at -20F at the coldest setting.  They are long runs of pipe an can attempt to passivate them but I will have to attempt to make something.  Is there anything else besides trying to passivate the welds?