CRACKING IN WELDS OF HEAVY-WALL NICKEL ALLOY PIPING DURING FABRICATION

摘要

Alloy 800HT (UNS N08811) and Alloy 617 (UNS N06617) are widely recognized as having high susceptibility to reheat cracking (also referred to as relaxation cracking or stress relief cracking). However, in a recent cracking case in heavy-wall Alloy 800HT piping during fabrication, the cracking was found in weld metal of ENiCrCoMo-1 (UNS W86117: welding electrode for shielded metal arc welding) only, while no cracking was found in the HAZ of Alloy 800HT or the weld metal of ERNiCrCoMo-1 (UNS N06617: filler metal for gas tungsten arc welding). This paper firstly presents investigations into the recent cracking case in the circumferential weld metal of heavy-wall Alloy 800HT piping. Then, the high temperature tensile properties of Ni base welding consumables, which are generally used for Alloy 800HT welding, are described. Cracking in service is outside the scope of this paper. This paper also offers several recommendations to mitigate the risk of cracking during fabrication.