(105b) Ethylene Decomposition in Meter Header - Sabine River Works Olefins Unit - Orange, Texas

An ethylene decomposition occurred on the evening of May 15, 2008 during an ethylene plant turnaround. Ethylene was being supplied to downstream consumers via the pipeline through a metering station adjacent to the ethylene plant. The metering header consists of two meter runs to allow maintenance without flow interruption. The incident occurred when placing the off-line meter run in service. The off-line meter run was inventoried with low pressure nitrogen and 1100 psi ethylene was introduced through a large gate valve. The subsequent quick pressurization resulted in an adiabatic compression of the nitrogen which initiated an ethylene decomposition in the pipe. The decomposition propagated through the header and was apparently quenched at a filter station in the meter run. The decomposition did not propagate into the supply pipeline. The decomposition was recognized by smoldering paint and hot pipe in the meter run. The initial response was to take the second meter line back out of service. A hot spot in the stagnant piping indicated a continuing non-propagating decomposition taking place. Action was taken to re-establish flow through the pipe with the hot spot to cool the pipe. The hot spot continued for approximately three hours before no additional heat was detected. The affected pipe was then isolated and inspected for damage and cleaned.

The incident investigation revealed both physical and system failures, resulting in several recommendations.