Hello,

    We recently just received our third set of failed results for passing a 72 hour salt spray test for our 304L base material with 308L GMAW-P weld. The parts are done on a Panasonic TAWERS Robot with recommended pulse settings. With a 308L 0.035" Radnor wire and an Airgas Tri-gas Helium/Argon/CO2 mix. In our first attempt we didnt think we would have a problem and we sent one part. After it came off the robot we used a brand new aluminum oxide sanding disk to remove spatter and then the part sat in a phosphoric acid bath for half an hour.
    The part failed within 48 hours showing red rust on the weld, HAZ, and opposite side near the weld. Taking it a bit more seriously, we did 6 more parts, these came off the robot, spatter removed with a brand new sanding disk, wire brushed with a brand new SS brush and soaked in the acid again from 15 minutes all the way up to an hour and 15 minutes. Although these results were better, there was still red rust in all of the same areas and there was no difference in the amount of rust compared to the acid bath soak times.
    We then got even more serious. We made 4 more parts. This time we tried 4 combinations of 308L, 316LSi wires with the tri-gas and another recommendation of 95%argon/5% oxygen. Coming off the robot, spatter was removed, we then used a SS wire wheel to really remove all surface contaminants. 1 hour acid soak times. We also added the best part from the previous test to the new group but only removed the previous rust using the acid bath. It did not get wire  one from the previous group that didn't receive a SS wire wheeling. There was no difference in the wires or gas mixes that would tell me that our problem was something else. We ended up submitting one of these parts for metallurgical testing. The base metal was properly confirmed to be 304L, weld was 308L. The base metal and weld were shown to be in the proper phases. The rust was shown to be free iron only on the surface and not penetrating into the base material or weld. It was obvious that our SS wire wheel had made matters worse. What I don't get is why surface iron would not have been removed from an acid bath that can completely dissolve mild steel parts in a few hours, and how that iron would be accessible by a wimpy saltwater spray and not a heated, bubbled, acid bath.
    Our best parts were the ones that were hand brushed, but they all still failed. The ss wire wheel parts were by far the worst, but the rust was not located in an even pattern on all of the brushed surfaces but blotchy. The rust is only located on and around the weld, the rest of the part is clean. All of the rust on all of the parts is blotchy, every part has clean and rusty sections on the welds. I have consulted with 4 different weld engineers within the company, Airgas, Radnor, the metallurgist who did the testing, the corrosion testing house, the base material supplier and even the third party chemical engineer who supplies the acid wash materials. Most of their ideas have been tried throughout the tests without any solid leads. Any and all ideas on this problem would be greatly appreciated.

Thank you,

I think we need a lot more information regarding the actual welding parameters and nature of the welds, single pass, multiple pass, interpass temperatures, heat input, and specifics of the corrosion. Was it limited to the weld surface, HAZ, base metal, all three, etc.

"We built three boats, all of them sunk. What happened." That's my analogy for the day. Too little information to understand exactly what happened and what the root cause might be.

Best regards - Al

Which Airgas Tri mix did you use? They make it with 3 different % of helium content. The highest being 85 or 90%- we made the mistake a bought some one time and it was disasterous. There is a much lower helium % just for GMAW-P