Comprehensive reliability analysis of blistered ‘LPG wash water vessel’ in FCC unit – Part I: Failure analysis

LPG wash water vessel of INDMAX process unit – an improvised patented FCC technology of Indian Oil Research and Development centre experienced severe hydrogen blistering damage calling for replacement of the wash vessel. Considering the lead time of supply of new vessel, it was decided to carry out Engineering Critical Assessment (ECA) using IOC’s in-house developed software, before taking the vessel in service. The vessel was re-put into service at de-rated operating conditions for a period of more than 6 months and there after the vessel was replaced. It was desired to carry out a detailed investigation on failed vessel post replacement, to find out the root cause analysis and reconfirmation of the ECA methodology adopted for reliability assessment employed during the study. This paper enumerates the findings of the failure analysis carried out on the vessel post replacement. Part-II of the paper describes the detailed ECA analysis carried out during service as well post replacement of the vessel.

► Blistering failure of a petroleum industry pressure vessel due to the presence of mid-wall lamination.
► Operational short coming resulted in the ingress of H2S that further resulted in sour environment development.
► Though post weld heat treatment of vessel was recommended to prevent SSCC, No care was taken for lamination checking.
► Plates for sour service to undergo ultrasonic check for defects and Hardness control to be a part of WPQ.
► Operational procedure to be improved to avoid H2S slippage for sour service if not considered in the design.