Multiple Cracks of Piping Weld Joints in Treated LPG System in Merox Unit

Abstract MEROX Unit receives LPG feed contaminated with mercaptan which are organic sulphur compounds (R-SH). The purpose of the MEROX unit is to extract mercaptan from the LPG feed by caustic treatment. This caustic treatment typically converts mercaptan into di-sulfide and produces the treated LPG with a low amount of sulfur in the form of RSH, COS & H2S compounds and negligible presence of caustic components. The carbon steel welds in these treated LPG systems for these units were found with multiple cracks near the welds zone after being continuously in service for 10 years. The first leak was identified at the two weld joints made of 8” near the control valve and thereby we have extended the scope to assess the integrity of the system and to prevent any further failure as well to avoid any impacts on this unit. These cracks were observed to be initiated from the weld root and propagating towards the OD of the pipe which are generally straight in nature with irregular branches. The reason for failure was unknown until we conducted a failure analysis and uncommon in treated LPG systems due to the lower presence of corrodent components. Considering above mentioned factor detailed failure analysis was conducted to establish the root cause for this cracking mechanism and also deep dive investigation was carried out with the help of a multi-disciplinary team to prevent similar failures within the facility for different units as well as for all other operating facilities. This paper will outline the significant efforts undertaken throughout the failure analysis in order to conclude the direct root cause, contributing factors, mitigation, preventive measures, and other control techniques. This paper will provide significant information to the industry to avoid similar failures soon either existing or new construction facility.