Tig weld turns green after a time

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Hello all first post here. Just had a problem at work where we tig welded some stainless steel wire baskets a couple of months back and have just heard that the welds in the baskets have turned a shade of green and seem slightly porous and are been returned as they are used in the medical field for cleaning they need to be perfect. First thoughts is that it is a gas problem as no filler rod is used, what is more likley, not enough gas during weld or gas not staying on long enough after weld to protect. Bit of a mystery as same welders have made same product same method for years and this is first time we have this problem, and also different welders made this order but all baskets affected. It seems like a gas problem but is there any other possibility that could cause this.
Reply:Any chance there's traces of copper in the weld?
Reply:No copper it was 2 stainless steel wires welded together no filler rod just the two wires melted together one wire was 5 mm thick other was 7mm.
Reply:I cant think why an issue with the gas would turn stainless green, especially a few months after the fact.  By slightly porous, are these pores open to the surface or did the wire break and they are looking at the cross section?If open to the surface, I cant imagine this wasn't noticed during welding.  It sounds more like base material contamination than a gas issue to me.Have we all gone mad?
Reply:First thought...Chromium Oxides can be green or black in color.  You really need to take some magnified photos of the affected welds and get a close look at what's going on.  Post the photos if you can.  Here's a bunch of questions I'd ask in order to troubleshoot the problem.  (in no particular order)What type of stainless wire?  Changed supplier recently?  Do you have material certs for the baskets that are failing?  Do the lots of stainless steel used in these baskets differ in chemistry from previous lots?How does the customer use the baskets?  Are these baskets immersed in water?  Or some other fluid?  Are they used in an autoclave to sterlize instruments?  What's the environment they see in use?  If immersed in a liquid, did the supplier change the liquid used?  Could they have switched to something that is corrosive?Do you have any old baskets sitting on the shelf that haven't been used by the customer?  Do they show the same green corrosion and pitting?Do you have a welding procedure that's followed?  Have you changed the amp setting used during welding?  Or any other part of the welding process?Pitting doesn't appear over time due to the shielding gas.  Porosity from poor gas coverage during welding is usually immediately visible.  Pitting corrosion can develop over time, and knowing the little bit you've related so far, this seems like a possibility.  But we need more information to help you get to the root of the problem...Stainless steel welds can be sensitized to corrosion; depending on the type of stainless and the time spent between 600 and 1000°C during welding...Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:I'd add a couple of questions to that list:Has anyone ground, sanded, buffed, polished, etc... any brass, copper, or other metals in your shop recently that would have left dust floating around?Did you clean the wires to be welded prior to welding?  If so, what cleaner did you use...did you use acetone?  Were all of the affected baskets cleaned using cleaner from the same container?  It's possible someone contaminated the acetone with copper or some other compound while using it on another job.--Wintermute"No man's knowledge here can go beyond his experience." - John Lockewww.improvised-engineering.comManufacturer Agnostic:Blood----------Sweat---------Tears----|------------------|----------------|----Lincoln Red, Miller Blue, Esab Yellow
Reply:I agree with  A_DAB_will_do ; you need to know the cleaning procedure and chemicals involved. Are the wires affected everywhere, or only at the welds? What type of stainless, and did it occur before with the same type, or has anything recently been changed, either in the materials or procedure. Might have nothing to do with the welds; the gas is the last thing I'd worry about. Might be the heat treating it gets during the weld, though.Maybe their solutions have gotten contaminated with HCl, or some organo-chloride, like CHCl3.Tell them they should really be using Titanium; "it's the latest High-Tech fad!"
Reply:Thanks for all the replies, will try and get pictures on Monday when i return to work, to answer a few of your questions, its only the welds that are being affected not any of the rest of the wire, nothing is sanded or buffed and no foreign materials ie dust floating about. Will also find out monday if base material has changed or supplier as the more i read your answers the more suspicious of the wire i get. Our first thought was that not enough gas was used or the torch was being lifted away from the weld immeditley while the steel was still red and not allowing enough time for the gas to protect the weld until it cooled. Will also try find out what chemicals the customers are using to clean and have they recently changed anything on their side. Again thanks for all the replies and suggestions.
Reply:Leftover pickling acid on the welds maybe?