NGC Completes Pipeline Rupture Investigation
12 April 2002
Natural Gas Corporation Holdings Limited (NGC) said today it had completed its investigation into the rupture of its high pressure gas pipeline at Himatangi, near Foxton, in February. NGC was pleased that the investigation found its systems worked swiftly to address the rupture and return gas supplies to normal.
The rupture prevented continuous gas supply to the lower North Island, but residential and essential service customers continued to be supplied from linepack (residual gas remaining in the pipeline). The ability to maintain deliveries to these customers during the emergency was possible due to the co-operative efforts and support of gas retailers and their larger customers to reduce gas offtake. Full supplies were restored within 24 hours of the rupture occurring.
The internal investigation confirmed that the bulldozer which struck the pipeline was operating on the pipeline easement without NGC’s knowledge or authorisation, and within sight of signs warning of the presence of the pipeline. The bulldozer was being operated by an employee of a contractor carrying out work on a cowshed for the landowner.
NGC has a programme of individual landowner advice and education to ensure awareness of its transmission pipeline system and the need to have any work on the easement checked and permitted.
From observations during routine aerial surveillance of the pipeline route, NGC was aware of drilling work being carried out on the farm by a different contractor, but, as this was off-easement, it did not require a permit from NGC. However, NGC took the precaution of following up the aerial observation with a site visit to the drilling contractor and found they were well informed about the presence of the pipeline.
NGC later became aware of the cowshed construction work, but this was more than 50 metres away from the easement and also did not require notification to, or authorisation by, NGC. NGC received no indication that work would be carried out over the easement.
NGC has closely examined its systems and procedures for emergency response, and the wider matters of pipeline safety and awareness, easement surveillance and work permitting. These were found to be robust and the report concluded that NGC could not have taken any further practical steps to reduce the likelihood of this incident.
NGC has assessed the cost of the rupture, including repair work and lost gas, at approximately $120,000, and is considering what further action it may take. No decision on any further action has been reached.