leak from a hydrogen pipe at a refinery

An unignited gas release occurred on a hydrogen pipe. The pipe was part of a rack carrying several other pipes and was mainly used to supply hydrogen to the naphtha hydrodesulphurisation unit.
No hydrogen was flowing on the day of the release, nevertheless the pipe was at the nominal operating pressure of 2.25 MPa. Local corrosion at the external surface of the pipe and progressed, undetected, till perforation of the wall (approximately  1 mm in diameter).

The affected pipe was isolated by closing the upstream and downstream valves and depressurised. The hydrogen was sent to the flare and replaced by nitrogen.

The INITIATING CAUSE was undetected local corrosion, started at the pipe’s outer surface and progressing through the 6 mm think wall this full perforation.

An anti corrosion coating had been applied years before to the pipe, but the surface preparation before painting had been insufficient, leaving rust trapped under the coating. The trapped rust could be seen by the to the naked eye only as a little coating bulge. The corrosion progressed from the outer surface inward, eventually causing the perforation.
External corrosion inspection was performed, but there were no tool and assessment criterion for inspections beneath the coating.
The ROOT CAUSE could be attributed to an inadequate corrosion protection procedure. Since the plant was located near the sea, possibly characterised by specific corrosion phenomena, an additional root cause factor could be a lack of consideration on material degradation during the design phase.

The plant emergncy service deployed two large capacity chemical high reach water spraying trucks, one large capacity chemical truck, and 154 personnel.
The following is the detaield sequence of events.
13:40 The control room contacted the Environment Safety Group.
13:40 The Environment Safety Group called the public safety number (fire department).
13:50 Emergency response headquarters established.
13:52 The affected pipe was blocked by closing the upstream and downstream valves; flaring of the pipe contained gas began.
13:55 On site headquarters set up.
13:56 Public fire crews entered the site.
14:43 Depressurisation completed by venting gas to the flare.
14:55 Nitrogen purge of the pipe started.
15:15 Gas detection around the leak point confirmed no combustible gas (hydrogen containing) remained; public fire crews verified leak stoppage (zero reading on gas detectors).
16:35 Temporary repair of the defective section (band clamp repair as instructed by fire crews) completed.
16:38 Public fire crews left the site.

The KHK report lessons learnt from this event were:
1. Surface preparation is paramount when applying protective coating; it must be performed thoroughly, taking environmental factors into account, and the resulting coating thickness must be verified.
2. External corrosion must be treated as a potential source of through wall damage; coating bulges or cracks should be regarded as inspection targets. Residual rust can lead to crevice corrosion that progresses to perforation.
3. Protective coating service life is limited (approximately 10 years from the time of fresh coating or recoating). Appropriate service life limits and regular recoating are essential.

1. The external corrosion inspection guidelines were revised: The procedure for visual inspections included checking for coating bulges as well as obvious corrosion. When coating bulge or cracking is observed, a secondary inspection by the department responsible for equipment management will be required.
2. The present incident has been added to the guideline and communicated to all staff.
3. Coastal line pipelines have been re-inspected in accordance with the revised guidelines.
4. To strengthen inspection capability, of mobile camera will be used more broadly as inspection tool. Their number has been increased.