American Welding Society Forum
I have a customer of mine that has to clean SS welded joints with acids to get the blue to red discoloration off of the surface. This is a TIG process with no filler metal.
Can anyone give me some ideas on how to weld and minimize the discoloration?
Minimize the discolouration by ensuring a good purge. I am not aware of a way to eliminate it, because the discolouration is caused by the oxide layer that is being "burned" due to the heat of the arc.
To ensure a good corrosion resistance, the weld and HAZ must be pickled and passivated after welding.
Hope this helps.
Go to the biggest tig cup you can find. A "trailing shield" will help.
Any questions-email me direct.
This one is a no-brainer-been there, done that!!
Use of Argon plus hydrogen shielding gas mixture also helps. The hydrogen has a "cleaning effect".
the only reason you are getting that discoloration is because oxygen is getting to the weld zone.all the discoloration ive ever had on my stainless welds was just like a form of oxide and what works for me is to squirt it with a water bottle then brush it off and that removes most,altho there may be a slight gold color.i would suggest one of a couple things, either switching to a bigger cup and or raising the gas cfh.
I would'nt recommend the water squirting technique right after the joint has been welded because of the O2 in the water or the rapid cooling which will cause some detrimental metallurgical effects to both the weld and the HAZ... Electropolishing or passivation is necessary sometimes.
The oxidation can be minimized or even eliminated by using a trailing shield and the biggest cup like Brande suggested. Passivation/pickling can safely remove any minimal amount of discoloration so long as it's accessable and in situations where it's not, then either passivation or electropolishing is used to ensure corrosion resistance like Nieke3 mentioned. In some cases like in UHP (ultra high purity) applications, the purging CFH is raised up substantially... Very expensive for the contractor but, very profitable for the supplier!!! After this electropolishing or passivation is performed and is also expensive but, worth it in the long run...
I wonder if it's an orbital welding application on bioprocessing systems since the person mentioned that the welds are autogenous? Hmmm...
SSBN727 Run Silent... Run Deep!!!
By Bill A
If the stainless is a 300 series or any other austenitic, spraying with water will have negligible effect on the weld or HAZ, unless you are concerned about possible effects of distortion from differential heating and cooling rates.
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