Abstract: For production and storage plants involving key regulated hazardous chemicals, key regulated hazardous chemical processes and major sources of danger for hazardous chemicals, a hazard and operability analysis (HAZOP) should be conducted every three years. In order to improve the effectiveness of HAZOP analysis of in-service plants, achieve the goal of regular HAZOP analysis of in-service plants, identify possible safety and operational risks in the operation of in-service plants timely and accurately, and avoid repeating the content of HAZOP analysis of newly built plants, this paper analyzed the purpose of HAZOP analysis of newly built plants and in-service plants. By comparing and contrasting the purpose of implementation, participating units, focus and analysis, and the implementation of recommended measures, this paper explained the differences in HAZOP analysis for new plants and in-service plants, and proposed the direction and focus of HAZOP analysis for in-service plants. This provided a reference for effective HAZOP analysis of in-service plants. 

Key words: HAZOP, new plants, in-service plants