The investigation has found that the direct cause of the leak was corrosion under the insulation in a 4″ pipe for heavy naphtha from the distillation tower. The lack of inspection and repair meant that the corrosion had continued long enough for a hole to form in the pipe.
Piping and equipment in a refinery can be exposed to external and internal corrosion. To monitor and repair such damage, they are inspected at specified intervals.
The pipe where the leak occurred had been removed from the maintenance program by mistake in 2008. This error was discovered in 2013, but instead of being restored to the program, the pipe continued to be let out of the equipment strategy. This pipe was accordingly last inspected for corrosion under its insulation in 2004.