Cracking was observed on three austenitic 1½” dia SA 182 F304L integrally reinforced forged nozzles to head attachment welds from a fourth stage suction separator vessel. What was peculiar was that three other nozzles of the same size were also welded to the 22 mm thk. head, but suffered no cracking whatsoever. Investigations revealed that the three cracked nozzles were integrally reinforced forgings, while the ones which remained intact were not. Metallurgical and hardness tests revealed the forgings were sensitized, contained strain induced alpha prime α’ martensite and were harder than the intact wrought nozzles. The fractured surface was brittle and SEM revealed intergranular cleavage with a faceted ‘rock-candy’ appearance. The vessel operated at 80 bars at 50°C in 98% CO2, however 1% H2 entrainment in the CO2 stream was known to occur daily.
Question: Was this failure due to HIC, SCC or a combination?