Abstract: PetroChina Dushanzi Petrochemical Company is progressing from a four-year overhaul cycle to a five-year overhaul cycle. The butadiene extraction unit is a polymerization-prone section (with the propyne distillation tower 20-C-401 being a critical risk point in the system due to moisture presence in the medium). As the late operational phase approaches, the accumulation of butadiene polymers within the tower system progressively clogs the trays, resulting in production fluctuations and even forcing the unit to shut down. Dushanzi Petrochemical Company successfully addressed the bottleneck of propyne distillation tower clogging during the pre-overhaul phase by implementing water flushing, as confirmed through consultations with industry and design experts. This approach has balanced material flows between upstream and downstream units and achieved the expected outcome.

Key words: dual prevention mechanism, construction contractor, HSE, risk checklist, risk control measures, hidden hazard investigation and management