Root causes of fire in a solvent pipe at a petrochemical plant

J.L. OTEGUI; P.G. FAZZINI; A. IBARRA PINO

Sitges, Spain

Conferencia; ICEFA 3; 2008

The purpose of the present study is the analysis of the root causes of a leak followed by a small fire in a 2” solvent pipe, during blanket heating to 300 C to dissolve polymer clogs, in a Petrochemical Plant. Fractographic and metallographic analyses showed that the failure is characterized by intergranular through the thickness propagation of longitudinal cracks initiated at the outer pipe surface. This cracking mode is called r‑type cavitation. The leaking solvent self ignited, and polymer deposits inside the pipe carbonized, this means that maximum pipe temperature during blanket heating was around 550 C. At this temperature yield strength of the pipe material got below nominal hoop stress. Other microstructural indications of extended exposure to very high temperatures are decarburization near the outer wall surface, carburization near the inner wall surface, and destruction of the lamellar pearlite throughout the pipe wall thickness. Possible previous creep damage due to repeated heating of the affected section was ruled out, since no previous heating was carried out on this pipe.   The failure occurred due to an excessively high temperature, much above the specified 300 C maximum, which is the result of the failure of the temperature control system in one of the heating blanket sets. This event is considered the main event that caused the localized fire, however, other conditions and exceeded barriers are discussed, related with faults in the procedures and safety measures, including insufficient support of the ongoing investigation by some of the people involved in the incident. It is now considered that a main fire could have been produced, due to the reduced effectiveness of prevention and mitigation measures. As a result, changes in the de-clogging and safety procedures were introduced