A hydrogen leak occurred at a chemical plant around 1 am on a pipeline inside a steam cracking unit located between the C2 and C3 hydrogenation installations. The gaseous mix transported through this 2″ pipe (at 30 bar, 40°C) was composed of 95% hydrogen, 4% methane and 1% nitrogen. The pipe ran in a rack within the cold sector, at a height of 6 m. The personnel shut down the steam cracker before repairing the pipeline; they isolated the sector and the C2 and C3 cuts were sent to the flare system. The leak was successfully sealed at noon, and the steam cracker remained down for a full 24 hours.

Runoff due to water vapour condensation was observed on a cold pipe located above the perforated piping assembly. This drop-by-drop action had weakened the pipeline, causing corrosion and thinning of the upper surface. The perforation had resulted from a pressure shock introduced during the process. The Classified Facilities inspection authorities noted that the pipeline had not been protected against corrosion by a coat of paint. This pipe section, despite being monitored by an accredited inspection body focusing on individual problem areas, had been repainted in 1990 and then verified in both 2000 and 2007. During the 2007 inspection, it had been commented that the particular section was inaccessible due to the expansion layer formed by corrosion/erosion and therefore could not be controlled. The 2007 investigations did not allow for measuring the magnitude of corrosion, and no specific guideline was issued for the restoration of this section (painting work at the very least). The inspectors also noticed runoff on the pipe racks through this zone, along with a major degradation of pipe paint, which in some cases had totally disappeared.