OPTIMIZED WELDING OF STAINLESS-STEEL TUBINGS FOR CORROSION FREE EXPOSURE TO HBR GAS

Hydrogen bromide gas phase corrosion of welded 316L electropolished st ainless steel tubings to be used for the distribution of ultra clean g ases has been investigated by using two techniques: one is leaching of the corroded tubings and subsequent chemical analysis of the dissolve d 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 weldi ng of such tubings. A correlation is found between the oxygen concentr ation in the back shielding gas and the gas phase corrosion. Purified argon as back shielding gas insures best corrosion resistance due to t he minimum thickness of superficial iron oxide, and maximal chromium c oncentration underlying the top iron/Manganese oxide layer. Tubings ma de of stainless steel containing very small concentration of manganese exhibit lower level of corrosion. A corrosion enhancement mechanism b y manganese is proposed.