51314-4181-Failure of High Temperature Shift Quench Drum in Hydrogen Manufacturing Unit

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Product Number: 51314-4181-SG

ISBN: 4181 2014 CP

Author: RAVIKUKMAR BHARHTIPUDY

Publication Date: 2014

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A Cr-Mo pressure vessel operating as high temperature shift quench drum in hydrogen manufacturing unit in a Refinery developed an in-service leak after 11 years of operation. Hot reformed gases from waste heat boiler are routed to a two bed high temperature shift converter to convert CO into CO2 & Hydrogen using catalyst. Heat of reaction between the two beds is removed by quenching with process water in the vessel that had failed. These gases from high temperature shift converter are further routed through a low temperature shift converter to a solvent based sweetening unit to remove CO2.1¼ Cr ½ Mo equipment have considerable history of premature failures in industries owing to reasons such as embrittlement loss of toughness etc. which are due to issues related to steel making fabrication practices and operating conditions.The vessel in question is made of 1¼ Cr ½ Mo alloy steel (A387 Gr. 11 Class 2) of 21mm thickness with 3mm thk. SS304L internal cladding designed to 349 psig and 800F & operating at 312 psig and 720F. Following failure the vessel was decommissioned and offered for internal inspection. Visual inspection and advanced NDT revealed extensive cracking of SS internal lining / weld overlay and base metal not only in the leaky area but also in the clad metal at several locations. With substantial efforts vessel was successfully repaired and restored to operations after NDT PWHT & hydrotest.This paper describes in detail the damage mechanisms like CO2 corrosion & possible root causes leading to failure and various challenges encountered during the course of repair including the limitations and effect of Larson-Miller Parameter on inherent strength properties as a result of repeated PWHT cycles.Key Words: Cr-Mo; Hydrogen; CO2 corrosion; High Temperature Shift Quench Drum; cracking; PWHT; Larson-Miller Parameter; strength.