In a refinery, process gas (80% hydrogen, 14% methane, 1.8% hydrogen sulphide, C2, C3 and C4 gases at 50 bar and 300°C) leaked from the elbow of a desulphurisation unit pipeline. The inflammable cloud released into the air exploded and triggered a fire. The refinery was shutdown, and a major part of the facilities destroyed. Traffic in the adjoining roads and in the town of ESCAUT was interrupted for 1 hour.

The facility built in 1974 was completely overhauled in 1989 during which corrosion in the elbow was detected. The elbow was consequently replaced. The other elbows of the same pipe however were free of corrosion. Between 1989 and 1992, the thickness of the pipeline and the state of the elbows were regularly checked for any anomalies. The enquiry following the accident revealed the source of the leak to be a spontaneous crack at the 90° elbow on the 8” pipeline.

The facility was rebuilt by reducing the use of the 90°C elbow and the gas transfer speed by increasing the diameter of the pipelines.