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.
Key words: Alloy 800HT, Alloy 617, reheat cracking, ductility dip, PWHT, heavy-wall