Fire from pressure gauge screw connection in a chemical plant

A hydrogen leak occurred from a screw connection of a pressure gauge installed on the hydrogenation pre-feeder line alcohol production plant. Due probably to static electricity, the hydrogen ignited.

The cause of the leak was a dent on the pressure gauge's seat, where erroneously an aluminium gasket was installed together with a copper gasket. Since the regular inspection in October 2014, the aluminium metal had to be replaced by a copper one, but instead of the replacement, a copper gasket had been applied on top of the aluminium one.

The INITIATING CAUSE was a damaged metal gasket unable to stand the internal hydrogen pressure.
The ROOT CAUSE was a mistake occurred during the last maintenance, possibly in combination with unclear instructions. The operator may not have realised that the aluminium gasket was still sitting in the joint seat, when he mounted the new copper gasket. On top of that, the aluminium gasket was damaged, probably due to the difficult operation of extracting it after use.

scew connection, gasket

DESCRIPTION of the CHEMICL PROCESS
The facility where the leak occurred was a 1,6-hexanediol manufacturing production unit. 1,6-hexanediol is an organic compound with the formula (CH2CH2CH2OH)2. It is industrially made by the hydrogenation of adipic acid or its esters [Wikipedia, https://en.wikipedia.org/wiki/1,6-Hexanediol]

GASKET MATERIAL HISTORY
When the 1,6-hexanediol manufacturing facility first began operations, copper gaskets were used for metal joints, but they were later replaced by aluminium gaskets. The reason for the change was unclear. The aluminium gaskets stuck onto the receiving seat, making them difficult to remove. Therefore, in October 2014 they were changed to copper gaskets, which have a proven track record.

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(1) The use of aluminium gaskets was prohibited.
(2) A procedure manual for the pressure gauge replacement was issued and all operators were trained in the procedure.
(3) A special tool was developed, to be used in case of difficult removal of the gasket, to avoid damaging the seat.
(4) A skill certification system was implemented for gasket replacement work.
(5) A checklist was developed requiring to record the removal of the gasket, the integrity of the seating surface and its installation.