Abstract
Metallographic studies and mechanical tests, including isostress rupture tests, were conducted on 1Cr-1/2Mo steel samples removed from a 37 year old catalytic reforming reactor vessel. The vessel operates in a hydrogen environment at 900°F (482°C) maximum. The base metal and to a lesser extent the heat affected zone (HAZ) exhibited some isolated grain boundary voids. Fissures or microcracks were not observed. No significant changes were found in the tensile strength and ductility but a small reduction in yield strength was noted. Both base metal and the weld metal had low toughness. However, HAZ exhibited good impact properties. Deembrittlement heat treatment resulted in only moderate improvement in the impact properties.
The actual fracture time for the reactor material in the isostress rupture tests and the fracture time for unused 1Cr-1/2Mo steel calculated from the curve published in ASTM DS 50 differed only by 20%. Extrapolation of the isostress rupture test data indicated that the remaining life of the reactor vessel is in excess of 20 years if the current operating temperature of 900°F (482°C) is maintained. To further ensure operation safety a periodic nondestructive examination of critical areas is recommended.
