Abstract :

After 13years of operation, U-bend pipe joint connecting heat exchangers at a methanol plant was failed in a catastrophic manner. Hydrogen attack associated with decarburization was identified as the failure mechanism. Damage or structure degradation was started at the inner surface of a circumferential weld connecting the U-bend pipe joint to the heat exchanger shell' nozzle then, propagated toward outer surface where a catastrophic brittle fracture was occurred. The cause of this failure is related to an improper selection of the material for the subject working conditions. In order to minimize the possibility of such failure in the future and then, increase the lifetime of the concerned equipment, the used ASTM A105 steel was replaced with a higher grade type; ASTM A335 P11 (1Cr-0.5Mo) steel. Periodic inspection was scheduled for the concerned equipment to evaluate its condition in order to be able to make the right decision for its replacement to avoid emergency shutdown. This includes mainly magnetic particle test, ultrasonic test, microstructure examination using replica technique as well as hardness measurements.