Cold worked SS corrosion resistance.

[javierb14]

if a 304L, 321, or 347 ss pipe is mandrel bent/cold worked, then is it more susceptible to corrosion and the associated cracking at elevated temperatures?

the part in question is a 321 tight radius mandrel bent tube used on an automobile exhaust. its a turbocharger exhaust were high temperatures are quite high. the tube cracked/failed at the bend before it failed at the weld.

TIA javier
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[Metalguy]

Cold-worked metal is anodic to annealed, so yes, cold-working does reduce corrosion resistance-but it probably varies depending on the environment.

Did your pipe fail via corrosion or a fatigue crack (or corr. fatigue)?

 

[kenvlach]

Yes, cold working leaves residual stress in the metal which leads to defects in the oxide film. see the reference given in
Corrosion of threaded stainless steel screws on Aluminium plates
thread338-47695

The temperature necessary for annealing 321 SS is 1750-1950 F (954-1066 C) according to the Carpenter Technology SS book, which I expect is much higher than the turbo exhaust temperature.

There is also the chance that impurities (steel, lube) left on the SS from the bending reduced the protectiveness of the surface oxide.