Analysis on the Fire Accident of Hydrocracking Unit

A fire accident occurred in an oil refinery in north China. The on-site investigations proved that the fire was triggered by the leakage of tail oil from one hole on the pipeline. The detailed analysis of the metallurgical microstructure of related pipelines indicated that some micro-cracks existed in the pipeline. Under the action of tensile stress induced by inner pressure, one of the micro-cracks kept propagating and evolved into macro-crack; under the action of cyclic circumferential tensile stress and stress concentration in the crack tip, the macro-crack was transformed to penetrated crack, finally the crack was torn open by inner pressure, and then the leakage hole on the pipeline was formed and fire accident occurred.