Plant Safety: Learn from the Mistakes of Others

 “THIS ARTICLE GIVE US LESSONS FROM AN ACCIDENT HAPPENED AT U.S. WITH HEAT EXCHANGERS EXPLOSION,”

-On January 27, the U.S. Chemical Safety Board (CSB) released a case study examining the causes of a heat exchanger rupture and ammonia release at the Goodyear Tire and Rubber Plant in Houston in 2008. Use these lessons learned to check your employee tracking system and to determine whether your plant has installed valves that violate the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code.

-The CSB event summary begins by noting that the accident occurred on June 11, 2008, when an overpressure in a heat exchanger led to a violent rupture of the exchanger that hurled debris, which struck and killed a Goodyear employee walking through the area. The heat exchanger contained pressurized anhydrous ammonia, a colorless, toxic chemical used as a coolant in the production of synthetic rubber; five workers were exposed to ammonia released by the rupture.

-On the day prior to the accident, maintenance work required closing several valves on the heat exchanger. CSB investigators found that workers closed a valve that isolated the exchanger from a relief valve, to replace a burst rupture disk located below the relief valve.

-The next day, at about 7:30 a.m., an operator closed another valve—this one blocking a second, automatic pressure control valve—to begin cleaning the process line with steam. The operator was unaware that the isolation valve was also closed, thus leaving no means of relieving excess pressure in the exchanger. As a result, pressure continued to increase until the heat exchanger exploded violently. 

-The report further notes that maintenance work activity was not properly communicated between maintenance and operations personnel, resulting in a subsequent shift not being notified of the isolation of the pressure relief line.

Plant Design Mistakes

-The CSB’s final report outlines several lessons learned, including the need to adhere to the existing ASME Boiler and Pressure Vessel Code.

-CSB Investigations Supervisor Robert Hall said, “We found the accident likely would not have happened had operators followed the ASME code. It’s crucial that workers continuously monitor an isolated pressure relief system throughout the course of a repair and reopen blocked valves immediately after the work is completed.”

-The CSB’s report notes that the ASME code states that “Overpressure protections shall be continually provided... whenever there is a possibility that the vessel can be over-pressurized by a pressure source.”

‘This article for, Dr. Robert Peltier , PE “

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