A 200 kg leak of liquid propylene occurred at around 1 am on a copolymerisation reactor being restarted in a primary plastic materials plant. The resulting cloud that formed was detected by the unit’s network of gas detectors. The workshop’s interlocks isolated the section of the unit concerned, stopped the leak and initiated the shutdown of the unit. Operators wearing personal breathing apparatus isolated the circuits. The event lasted just a few minutes. The unit’s N2 circuit would then be purged as a precaution.

Within the scope of maintenance on the installations since October 28th, the reactor had been placed under a nitrogen atmosphere with a 60 cm hose connecting it to the site’s N2 network. Before restarting the unit, a round was conducted the day before to disconnect all hoses from the “N2 injection points”. One of the 3/4″ hoses had been forgotten during the checks and cracked when the installations were restarted, causing the leak. The procedure used to remove the N2 lines did not include a check-list, but simply a drawing indicating the N2 injection points within the unit. During a cursory visual check, the “taut” hose concerned may have been confused with a fixed line. Its short length may have prevented it from forming a loop, contrary to the other hoses that were not forgotten. The crew that installed the hoses was not the same as the one that removed them.

Also following the previous rupture of a branch connection on 500 kg propylene tank leak on 10/28/2006 (ARIA 32611) and an intervention by the Classified Installations Inspectorate on November 15th, the operator proposed several corrective technical and organisational measures: insertion of a “check-list” in the procedure outlining the removal of hoses prior to the restart of the unit to avoid any forgotten elements, replacement of the existing hoses with hoses capable of resisting the reactor pressure, use of longer hoses for better visual recognition of the permanent piping…