High Value Learning - Gas leak from perforated closed drains line to to simultaneous operations

A 2” closed drain line was subject to bristle blasting in order to allow further inspection & fabric maintenance.

Before work commenced the line was subject to an assessment by the onshore Technical Authority and it was confirmed as safe to bristle blast. However, the assessment was undermined as the corrosion scab height had been constrained by an adjacent unistrut, which also introduced a galvanic corrosion mechanism.

The line had been previously isolated from the upstream production separator, but it was not possible to apply an isolation downstream toward the flare header. The work permit however did not identify the potential risk of backflow to this section of line or consider the ‘what if’ scenario if the line was holed during the work. When the line was subsequently perforated, it was then ineffectively reported to the site management team thus preventing a timely response and assessment of the risk to take place.

As a result, a well was lined up to the flare knockout drum in order to stimulate production. The resultant gas flow into the flare header raised the back pressure resulting in a gas release from the hole created by the bristle blasting.