Maui pipeline on the edge

02:15, Feb 08 2014
Maui gas pipeline
The last leak in the Maui gas pipeline two years ago cost the national economy an estimated $200 million.

Two years ago the Maui pipeline developed a leak. It wasn't a big leak - but the 138 hours it took to repair it and get gas supply restored again cost the national economy an estimated $200 million.

That's how important the pipeline is.

The energy industry uses units of energy that are difficult to explain. One such measurement is a terajoule, which is a trillion units called joules - and one TJ of gas is enough to meet all the needs of an average home for eight years.

And each day the Maui pipeline transports 325 terajoules of gas north from Taranaki.

The line, which is the largest capacity high pressure gas pipeline in New Zealand, starts its journey at the Maui onshore gas production station at Oaonui and snakes its way to the Huntly Power Station 307km away.

Before it leaves Taranaki it picks up gas from a total of 10 gas fields. It might be called the Maui pipeline because when it was opened it transported gas exclusively from that once-giant offshore field, but these days thanks to an open access agreement it also transports product from other gasfields on and off the shore, and pumps it north.


Tens of thousands of consumers use the gas from this pipeline. Every factory and hospital, and thousands of businesses and households throughout the entire northern North Island depend on a constant and reliable supply.

If the supply fails, it can cause economic and social disaster. It happened in October 2011 when the pipeline developed the leak at Pukearuhe - for example, the dairy industry had to dump 48 million litres of milk.

Now, it is in increasing danger of failing again.

In the wake of that 2011 leak a Government investigation showed that the pipeline was at risk of being ruptured by landslides or erosion at a total of 59 different locations, and as a result the pipeline's owner Maui Development Ltd was ordered to develop an improved management plan for the whole line.

That plan is now complete, and for the first time it has been publicly disclosed under new rules contained within the Commerce Act. Officially known as the Asset Management Plan and Forecast Information, it details the condition of the pipeline and how it is going to be managed between now and 2024.

The plan points out that even though the pipeline is now more than 30 years old, it will need to continue to operate for at least another 30 years. But while investigations show the condition of the pipeline itself is good for its age, erosion is increasingly threatening the land through which it passes. This is making sections of the pipeline increasingly vulnerable to land movements which can be triggered by a range of forces including heavy rain, earthquakes and sea erosion.

That's what happened with the Pukearuhe incident in 2011. Subsequent studies showed that it was built within the vicinity of a slow-moving landslide, the middle of which had moved 1.75 metres over the next three decades - leaving 25 metres of the Maui pipeline within its edge. The pipeline leak was caused when that landslide movement buckled the pipeline, causing a crack to develop.

Those studies also concluded that not only will the landslide movement continue, but also the speed of the landslide is increasing.

And the repaired section of pipeline remains within the landslide. A lot of work has been undertaken there to prevent another failure in the short to medium term, but the experts are warning there needs to be a longer-term solution if that section of line is to remain secure for the next 30 years.

But that's the least of the worries for the pipeline's owners, because there are now other parts of the Maui route that are getting a lot worse.

The worst of them is a 1.8km section of pipeline that runs close to the edge of White Cliffs just south of Tongaporutu. Clifftop erosion of more than a metre every three years has now put the line within 16 metres of the edge. This has forced MDL to rapidly develop a plan to bypass the affected area - it intends doing it by importing a special rig that will horizontally drill a hole under the cliffs to below sea level. The pipeline will be re-routed along this hole and connected to the existing line north and south of the eroding area.

There are several other areas where the erosion is getting worse. One particularly bad section is just south of Piopio where hillside slumping has actually exposed and bent the pipeline, which had been buried up to 2m underground. Vehicle access is now being created through farmland so contractors can get heavy machinery to the site for repair work.

All this is to cost massive amounts of money - the documentation shows MDL is to spend at

least $166 million over the next 10 years on inspections, maintenance and repair work. And that's assuming nothing else goes wrong with the Maui pipeline during that time.

Information contained in the Asset Management Plan shows that an average of more than $3 million is to be spent each year on a beefed-up maintenance and inspection programme - aerial inspections using helicopters and fixed-wing plane now take place over the entire pipeline route every three months, more troublesome areas are inspected every month, and the line is checked after every storm, flood or earthquake.

In addition, $3m to $4m will be spent annually on refurbishment and renewal maintenance, and close to $5.5 million is to be spent this year and no less than $1.5 million each year thereafter on maintaining and upgrading capital works such as the Pukearuhe repair project and various compressor stations along the pipeline's route.

But by far the biggest projected cost will be asset replacement and renewal. The report shows that close to $40 million is to be spent from next year on the White Cliffs realignment project, with other large amounts to be spent on equipment renewals at the compressor stations.

MDL spokesman John Pitman says while there's no imminent threat of the Maui pipeline failing, the most recent studies have made it obvious the work needs to be done now to protect it.


The Maui Pipeline 

The Maui pipeline is a 307km high-pressure gas pipeline that runs from Oaonui to the Huntly Power Station. It went into operation in 1977, and has capacity to deliver 120 petajoules of gas a year.

The pipeline is owned by Maui Development on behalf of the joint venture that owns the Maui gasfield. The technical operator is Vector Gas.

Vector also owns several high-pressure gas pipelines that are directly connected to the Maui pipeline and which are used to supply major industrial plants, dairy factories and power stations throughout the upper North Island. The gas also goes into several low-pressure lines that distribute it to Auckland, Hamilton, Whangarei, Tauranga, Rotorua, Taupo, Gisborne and many other smaller towns. There, the gas is supplied to thousands of homes, businesses and essential services such as hospitals.

The Maui pipeline was originally built to supply gas from the Maui field to points nominated by the Crown. However since 2005 it has been operated as an Open Access pipeline and now carries gas from different Taranaki gas fields. There are currently 12 different parties who ship their gas through the line.

If the Maui line failed, the Vector line would not be capable of carrying anywhere near the gas required for normal operations throughout the upper North Island.

30 More Years? 

The Maui pipeline is the backbone of New Zealand's gas transmission system.

Current natural gas sources look sufficient to maintain flows through the line to industrial and domestic markets for at least another 20 years. If local gas supplies did fall and LNG (liquefied natural gas) had to be imported, the Maui line would most likely be used to transmit this imported gas.

Therefore, given the latest gas supply forecast, the minimum desired asset life for the Maui line is a further 30 years.

Past 30 years there is less certainty about gas supply but it is prudent to assume demand for the Maui line will continue for as long as it is economical to maintain it.