This paper was presented at the Bioprocess Engineering Symposium at the Winter Annual Meeting of the American Society of Mechanical Engineers in 1989 and is even more relevant today. The use of AL-6XN superaustenitic stainless steel has seen an increase in the pharmaceutical and food industries during the past few years in applications requiring superior corrosion resistance to that of 316L stainless steel.

Molybdenum segregation occurs during the welding of AL-6XN reducing its corrosion resistance unless filler overalloyed in molybdenum is added to the molten weld pool. Wire is typically used as filler, but this paper examined the feasibility of using a C-22 insert ring high in molybdenum in conjunction with orbital welding equipment designed for autogenous welding to weld AL-6XN.

Critical pitting temperatures (CPTs) determined by ASTM G-48 showed that autogenous orbital welds of AL-6XN had higher CPTs, and thus better corrosion resistance, than manual GTA welds without filler, and autogenous orbital welds done with a C-22 insert ring had higher CPTs than manual GTA welds with filler. The highest CPT, and the best corrosion resistance, was obtained on an orbital weld with a C-22 insert ring which had 5% nitrogen added to the argon shield gas.

This demonstrated that an insert ring used in conjunction with orbital welding was a satisfactory method of joining AL-6XN.


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