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.