Integrity Assessment of Pressure Vessels and Pipelines Under Fire Accident Environment

In recent years, fire accidents take place frequently in Chinese oil refining plants. More and more attentions have been paid to the safety assessments of pressure vessels and pipelines exposed to high temperature of the fire scene. In this paper, combining with several integrity assessment cases of pressure vessels and pipelines after fire accidents in China, the effects of thermal exposure temperature, duration time and cooling rate on the microstructure, mechanical properties, corrosion resistance and fatigue fracture behavior were studied by simulation test research and field inspection. Based on analysis and study of API 579 standard, a method of integrity assessment is proposed under the condition that the information on fire accident is not clear, the thermal exposure zone cannot be classified and the field sampling is limited. This assessment method is based on the similarity of hardness and metallographic structure of the material during the fire accident, by which the like material was treated by thermal simulation tests to obtain the similar damage material with similar hardness and metallographic structure to one obtained in the field examination, and the similar damage material is used to obtain various properties of the materials, and then the integrity assessment of the equipment experiencing the fire accident can be completed. The thermal simulation process to obtain similar damage materials is in fact the reproduction process of thermal exposure temperature, duration time, and cooling rate of the metal in the fire accident. This integrity assessment method is faster and simpler compared to API 579 standard and is suitable for the equipment subject to severe fire accident and in high-class thermal exposure zone.