(135c) Furnace Reverse Steam Flow

This paper details the events that resulted in a failure of the steam piping between the steam drum and the convection section of a pyrolysis furnace during re-start of the furnace. The furnace had been shutdown due to an electrical outage, and was being restarted to decoke the furnace tubes. As the furnace was heating up to the decoking temperatures, the steam drum vent and the superheat vent were opened to vent steam. The superheater vent was slowly closed to increase the steam drum pressure as the heater temperatures increased, and the superheater vent was eventually closed to around 5%, fluctuating between 0-5% during the remainder of the startup. As the steam drum pressure continued to build to the point that it could be exported to the header, the piping between the steam drum and the firebox failed at an elbow, causing damage to the superheat coils, insulation on other piping. The superheated steam flow meter indicated a flow, but the investigation team determined the meter was incorrect and that there was either no flow or back flow going into the steam drum. The intent of this paper is to increase awareness on the hazards associated with reverse flow where the piping and equipment is not rated for the conditions associated with reverse flow, and not focus on the sequence of events related to this failure. Focusing solely on the incident overshadows the necessity to prevent reverse flow under any circumstance, known or not known to have occurred.