The objective of this study was to perform comparative weldability evaluation of weld filler metals for an Alloy 230 / P91 steel dissimilar metal weld (DMW) that will be used in once through steam generator (OTSG) on an offshore oil platform. The weldability characteristics of filler metals EPRI P87 and Haynes 230W were evaluated using the cast pin tear test (CPTT) and a stress relaxation cracking (SRC) test in combination with metallurgical characterization using light optical and scanning electron microscopy.
Solidification cracking susceptibility rankings generated with the CPTT showed that undiluted P87 filler metal had better resistance to solidification cracking than undiluted Alloy 230W. The SRC testing preformed in the Gleeble 3800™ thermo-mechanical simulator showed that none of the tested welds failed in stress relaxation cracking mode during simulated service at 600°C under constant displacement and tensile load at 90% of the high temperature yield strength. During the SRC testing, filler metal 230W exhibited some level of stress relaxation, while no evidence of stress relaxation was found in filler metal P87.