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Gerhard Schiroky & Gary Henrich, Swagelok Company, Solon, Ohio, USA

ABSTRACT

A study was performed to determine the corrosion behavior of welded tube samples of ultralow-manganese and low-manganese 316L alloys in corrosive gaseous environments. First, a weld-fume analysis was performed to determine which elements evaporate to a significant extent during orbital welding with 316L test samples containing different amounts of manganese. Second, welded tube sections were exposed to corrosive gases and the surfaces were characterized by scanning electron microscopy (SEM) both in the short term (24 h) and in the long term (28 days). It has been claimed that during welding, the manganese evaporates from the weld pool and redeposits in the heat-affected zone, primarily downstream of the weld pool, causing corrosion to occur. However, this study showed that all sample alloys demonstrated very similar corrosion behavior, and they released predominantly iron in approximately the same amount. Thus, it is believed that the evaporation and redeposition of iron, not manganese, negatively impacts the corrosion resistance of welded low-manganese and ultralowmanganese stainless steel alloys in chlorine-containing, moist, gaseous atmospheres. The conclusions suggest that ultralow-manganese alloys do not perform any better than less costly low-manganese alloys when components are welded and subjected to corrosive (28 days) atmospheres. Therefore, lowmanganese alloys should be selected by the cost-conscious users of fluid-system components for the demanding applications of semiconductor processing.