SERVICE INDUCED DAMAGE ASSESSMENT OF REFORMER FEED HEATER TUBES IN CONTINUOUS CATALYST REFORMING UNIT (CCRU)

摘要

Substantial loss in tube wall thickness from the inside was observed in the firstheaterwhich is also called the charge heater. The tubes were 5 Cr 0.5 Mo and the thinning was primarily in the outlet end. Subsequently, six months later, pinhole leakage occurred in the same heater causing shutdown of the unit. Heater tube samples were collected from all three heaters and confirmed carburization of tubes after studies. The carburization mechanism has been experienced for the first time in Continuous Catalytic Reformer Unit (CCRU) of a petroleum refinery in India.Investigation carried out showed failure due to carburization, the extent of which was found to be negligible at the inlet end and progressively increasing to full wall carburization towards the outlet end. This was observed in all the three heaters but the maximum effect was in charge heater. The cause of heavy carburization mainly at the outlet end has been attributed to increased throughput, higher tube temperature, and cracking of Tri-chloro Ethylene (TCE) and hydrocarbon. The active carbon formed as a result of cracking diffuses readily in steel at high temperature causing carburization of the tubes and subsequent failure. Low sulfur in the feed also contributed to this carburization.