Optimized Welding of Stainless Steel Tubings for Corrosion Free Exposure to HBr Gas

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Abstract
Hydrogen bromide gas phase corrosion of welded 316L electropolished stainless steel tubings to be used for the distribution of ultra clean gases has been investigated by using two techniques: one is leaching of the corroded tubings and subsequent chemical analysis of the dissolved metallic elements, the other one is bromine penetration depth at the stainless steel surface by Auger spectroscopy. These test procedures were applied to optimize the back shielding gas used for orbital welding of such tubings. A correlation is found between the oxygen concentration in the back shielding gas and the gas phase corrosion. Purified argon as back shielding gas insures best corrosion resistance due to the minimum thickness of superficial iron oxide, and maximal chromium concentration underlying the top iron/manganese oxide layer. Tubings made of stainless steel containing very small concentration of manganese exhibit lower level of corrosion. A corrosion enhancement mechanism by manganese is proposed.