Maui Pipeline Failure Reports

Almost exactly 12 months ago on 24 October 2011 there was a failure of the DN 750 Maui Pipeline which runs 307 km from from the Taranaki region to the Auckland region of New Zealand.  The pipe leaked as a result of pipe deformation from a slow landslip.  Because the Maui pipeline is a crucial energy source for the northern part of the North Island there have been extensive investigations.   The NZ Government has just released a long series of documents about the failure and its implications, available here.

There are hundreds of pages of supporting documents and so far I have skimmed just a couple.  From this I will make only a couple of observations:

The main review report is not a technical document but dwells on the effects of the interruption to gas supply for the five days it took to repair the pipeline and resume operation.  The economic cost of the outage was estimated at NZ$200 million, or NZ$40 million per day.  There were widespread implications for the dairy industry (with flow-on environmental effects arising from farmers’ need to dispose of milk that could not be processed) and also impacts on health and disability services due to loss of ancillary functions such as heating, hot water and laundry.

I have written before about the community impacts of supply disruption, and this is another salient illustration.

The other interesting observation is the nature of the failure.  I have not yet read the technical reports but this photo seems to tell a fairly clear story:

Deformed pipe with crack highlighted

Ignore the small black arrows but look closely at the black oval.  You can just see a crack where the buckle induced by the landslip has initiated a fracture along the seam weld.  (The diamond-shaped piece of black tape marks the top of the pipe.)  An interesting failure mode.  There are many more photos in the collection of technical investigations here (125 pages and 7.6 MB).  It will be interesting reading.

 

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3 Responses to Maui Pipeline Failure Reports

  1. Anonymous says:

    When I saw the images my initial reaction was that the HAZ was defective in some way. However this seems not to be the case according to the tests. If I have read the technical report correctly, the pipe showed no defects on any kind. It complies with all of the API 5LX (22nd ed.1975) to which it was manufactured and would comply with the current version of API 5L in all respects (except for an optional longitudinal test which is not reinvent to this failure). If the pipe itself has any “blame” it appears limited to the weld toe forming a stress concentration but only once the yield strength had been exceeded.
    As such, it seems that this is not a failure of the pipe as such but rather a failure in the planning of the pipeline route (through an unstable land slip area).
    Peter,
    1) is the above a fair interpretation of the report in your opinion?
    2) what do you think this means for pipeline routing in Australia in the future?
    3) what does this mean for pipelines in existing land slip areas? For example, I note that some areas (such as south central Victoria) contain high pressure, large diameter pipelines in land slip prone areas. These pipelines represent major supply infrastructure to capital cities…

  2. petertuft says:

    You’re way ahead of me in actually reading the reports, so I can’t comment further on their content. As for the implications for Australian pipelines in landslip areas I don’t think anything has changed.

    I’m aware of at least three vulnerable pipelines in three states. For one of those, in which I was involved in the design, there was no alternative route available so we sought the geotechnical advice and instituted a regular monitoring program (which I hope the operator is continuing – way beyond my control now). For that site the geologist was satisfied that rapid movement was highly unlikely so monitoring of any residual creep would allow for rectification if ground movements became excessive. I think that is also the case for the other sites I’m aware of.

    Often in Australia landslip occurs when forests are cleared for farming, which of course happened generations ago so steep sites that show signs of past land movement are likely to have settled down by now (no guarantees of course). The problem usually tends to be one of creep under conditions of abnormal rainfall rather than sudden slump of an entire hillside.

    Not having read the NZ reports in full I’m not sure what monitoring had been done for the Maui pipeline. However it seems that they have now identified a number of other sites and I presume that they will be watching them very closely indeed in the future.

  3. this information is very use full for me,
    whether the pipe bulge always occur due to changes in soil structure (landslide)?

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