TIG welding of 316L stainless steel pipes
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Is it necessary to use argon shielding on the back side when TIG welding 316L stainless steel pipes? What are the consequences if no argon protection is used? I checked some of the welded parts; the welds on the back side that were protected with argon gas had good formation, while those on the inside without argon protection had poor formation – they were full of slag. Could this be due to oxidation?
Yes, when TIG welding 316L stainless steel pipes, it is necessary to use argon for back shielding in order to ensure the quality of the weld on the back side of the pipe. If no argon protection is used on the back side, the weld will oxidize, turn black, have poor shape, and its corrosion resistance will decrease, and so on.
Tungsten inert gas welding allows for one-sided welding with a double-sided finished surface. However, when the mass fraction of Cr in the base material exceeds 3%, argon gas must be supplied to the back side of the weld to prevent oxidation there; oxidation causes the weld surface to turn black.
The back side is not protected, so oxidation occurs severely, and it cannot be fully melted through.
Run an experiment: color the unprotected weld, then spray a color-developing agent, and you’ll be able to identify any defects in the weld