Erosion corrosion of SS316L trays in FCC's Sour Water Stripper

FCC Sour Water Treatment Unit (with Side Reflux type) having design capacity of 22.7m³/hr.  of KNPC- MAA Refinery, Kuwait  was commissioned in 1987. Ever since the increase in throughput of sour water in 1998, the Stripper experienced repeated failure of top trays made of SS316L in year 2004 (after in service for 17 years) and subsequently in 2008 & 2009. This paper deals with the failure investigation and root cause analysis of repeated failure of top three trays of Sour water stripper(V-95-101). Optical Microscopy & Scanning Electron Microscopy (SEM) studies of failed sample were carried out. Root cause analysis have indicated that erosion - corrosion due to Ammonium bi-sulfide (NH₄HS)  in the presence of hostile environment of chloride & cyanide with increase in throughput are the contributing factors for the failure.
Remedial measures such as minor modification to the cold reflux piping, up gradation of metallurgy and increase in thickness of affected trays are also discussed in the paper.
Key words: FCC Sour water stripper, Erosion - corrosion, Ammonium bi-sulfide,  Root cause analysis, SS316L trays, KNPC – MAA Refinery