Cracking in Welds of Heavy-Wall Nickel Alloy Piping During Fabrication

The capacities of petrochemical plants have increased considerably during the last decade.  The large-scale plants commonly require significant large size and heavy-wall piping components, which are sometimes beyond the range of the manufacturers’ experiences.  The result has been an increasing frequency of serious problems during fabrication by manufacturers, as well as during fabrication at the construction site.

This paper presents investigations into a recent cracking case occurred during fabrication in girth welds of heavy-wall Alloy 800HT piping where Alloy 117 (SMAW) welding consumables were used.  Cracking during operation are outside the scope of this paper.

The studies have been primarily focused on reheat cracking (also referred to as relaxation cracking or stress relief cracking) during multi-pass welding and postweld heat treatment.  Since the cracking presented here occurred only in weld metal of Alloy 117, high-temperature tensile properties of Alloy 117 were investigated comparing with that of Alloy 617 (GTAW) and other Ni base alloys.

This paper also offers several recommendations to mitigate the risk of cracking during fabrication.