Lightning

The APIA/POG incident database received a new incident report the other day – a pipeline leak caused by a lightning strike.  The confidentiality requirements mean that I’m not going to tell you where it was or which pipeline, other than that it was in an outback environment and there was a fused crater in the pipe wall about 17 mm in diameter with a 1.6 mm diameter hole at the bottom.

What I regard as striking (!) is that lightning now ranks as the third most frequent cause of pipeline damage in the database, regardless of whether you count all incidents or just those causing loss of containment.  External interference of course remains dominant with over 80% of damage incidents.  The remaining causes and number of incidents are:

  • 8 construction defects (3 leaks)
  • 7 lightning strikes (4 leaks)
  • 6 corrosion leaks
  • 5 earth movement incidents (2 leaks)

The non-leak lightning strikes were discovered through in-line inspection where strange defect indications were investigated and revealed fused craters in the pipe wall.  There may be more of these that have not yet been discovered.

Two of the lightning incidents were associated with power lines, where the lightning initially struck the wires then ran down a stay wire that passed close to the pipeline.  So there is an obvious way to avoid that.  But apart from that situation there appears to be no mitigation available for random lightning strikes on a buried pipeline.

Earthing the pipeline (via surge diverters) serves to protect personnel and equipment who may be in electrical contact with it, but does nothing to protect the pipeline itself.  In fact, providing a good earth bond might even increase the lightning risk to the pipe (someone with more knowledge of earthing than me might wish to comment).

It seems that lightning strikes are one of the few threats to a pipeline that we cannot protect against and just have to put up with.  Fortunately all the indications are that any resulting loss of containment is minor.

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12 Responses to Lightning

  1. Chris Hughes says:

    Peter, you have stated that this incident was in the outback – does that apply to the other incidents as well? I am thinking that in any suburban environment there are likely to be multiple structures which will be preferentially struck by lightning whereas in the outback the pipeline is the only conductive structure for miles in any direction. It would be interesting to know if the statistics (limited as they are) support this theory. It would certainly allow the severity of risk to be rated as Severe or lower if the only consequence was a gas leak in an unpopulated area.

  2. petertuft says:

    Certainly none of them were in suburban areas, and most were remote outback sites with not even much in the way of trees. The power line incidents were in wooded coastal areas, but in those case the presence of other tall objects is irrelevant. Your theory that where other structures exist they will probably be struct preferentially sounds plausible.

  3. Shane Becker says:

    Got any pictures of the resultant damage you could post, Peter?

  4. Matt says:

    I find this rather interesting, especially considering that lightning attachments to thin aluminium-skinned metal aircraft are commonplace and do relatively little damage. Can you confirm that this deep cratering is always found on buried sections of pipeline? Has anyone documented evidence of lightning strikes on the adjacent ground, e.g. fused sand or fulgarite formation?

  5. petertuft says:

    I believe that all cases have been on buried pipe. The information provided to the incident database is very brief and doesn’t include background information on how the damage was diagnosed as being caused by lightning. I think it is deduced mostly from the nature of the damage, clearly involving heating and very different to most corrosion defects. However the most recent incident report did note some charring of nearby vegetation which was thought not to be due to ignited gas (if it did ignite the flame went out spontaneously).

    The comment on aircraft is interesting. Is it possible that because the plane is not earthed the energy transferred by the lightning is limited to the (presumably small) charge capacity of the aircraft and hence the damage is minor? I’m guessing that a strike to ground (including pipe) can transfer vastly more energy.

  6. Matt says:

    With aircraft strikes there is both an entrance and exit lightning attachment, with the lightning current flowing through the skin of the plane. The lightning path itself is usually from cloud-to-cloud but can be from cloud to ground, i.e. a full power strike! We also have the evidence of strikes to lightning conductor terminations, steel-framed buildings, golf course flags… check out the first photo in this document. http://www.lightningsafety.com/nlsi_lhm/Radials.pdf The ground pattern is notable but the flag doesn’t appear overtly damaged. (Of course, it could be a replacement.)
    I don’t doubt the damage was caused by lightning but I’m trying to understand the mechanism. Lightning attachment points experience arc heating and ohmic heating, but for bulk metal the heat input is too brief to inflict much direct damage. A lightning current through wet wood or resistive soil is another matter and I’m visualising something like a fulgarite channel intersecting a buried pipeline. What happens at the intersection point is the question.

    • petertuft says:

      Sorry, would love to have more information to help with this but the details in the incident database are pretty brief. I’m working on getting some photos that might help a little bit.

  7. Marijan Mikulic says:

    Hi Peter, for these lightning strike incidents, is it possible to find out the distance between the power pole stay wire and the pipeline? Reason I’m asking is because this data would be useful in determining a no-go zone guide for pipelines near power poles and their stay wires. In my experience it is not uncommon for power lines and gas pipelines to share a common service corridor.

  8. petertuft says:

    For one of them the clearance was very small – 400 mm; not stated for the other. 400 mm might be OK for another buried service (water pipe, cable, etc) but seems much too close for something that has potential to apply a load to the pipeline, let alone the electrical effects that are at issue here.

    Interestingly, both of the stay-wire-to-pipeline incidents were on the same pipeline (but at widely separated locations) so there might have been some common factor in the design or operation which tolerated such small clearances; or they might just have been really unlucky. However it does not appear that the pipeline shared an easement with a power line.

  9. Pingback: Lightning damage pictures | Pipelines OZ

  10. Have just received a very interesting article – link attached – which shows that evidence has been gleaned that pipelines in or adjacent to fault lines are extremely susceptible to lightning and corrosion effects. This could be looked at for the review of AS2885.1 as it would be well worth the while to consider the pipeline route with this phenomenon in mind.
    Cheers,
    Peter O
    http://www.pipelineandgasjournal.com/lightning-new-key-pipeline-protection

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