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

The root causes of a leak followed by a small fire in a 2 in. solvent pipe in a Petrochemical Plant are discussed. The fire occurred during blanket heating to 300 °C to dissolve polymer clogs. 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, polymer deposits inside the pipe carbonized, microstructure changed. All these indicate that pipe temperature during blanket heating reached 550 °C, much above the specified 300 °C maximum. At this temperature yield strength of the pipe material got below nominal hoop stress due to normal internal pressure. The failure of the temperature control system in one of the heating blanket sets was the main event that caused the fire. However, other conditions and exceeded barriers are discussed, related with safety procedures and insufficient support of the ongoing investigation by the contractor involved in the incident. As a result, changes in the declogging and safety procedures were introduced.