(I still intend to complete the series of posts on ALARP by making suggestions about estimating likelihood, but one or two other things first.)
Almost any safety management study needs to consider the threat of pipe damage by augers, either vertical (for power poles etc) or horizontal (bores and HDDs). I’ve run numerous workshops where there has been little argument against the suggestion that while an auger might penetrate a pipe it is highly unlikely to result in rupture. This is because penetration will take place slowly (unlike an excavator or ripper impact) and once high pressure gas (or oil) emerges the rig operator will stop drilling rather than continue until the hole exceeds the critical defect length (resulting in rupture). We usually assume a maximum hole size equivalent to a 30-50 mm orifice.
Penetration by an auger seems to be a very unlikely event anyway. Unless the auger hits the pipe square on or is in extremely hard ground it will almost certainly veer off and skid around the side of the pipe, possibly causing horrible gouging but not penetrating. It also assumes that the operator would persevere (perversely?) after hitting a hard obstacle, notwithstanding the allegedly distinctive noise of auger on metal.
But then there are events like this:
That’s near Cleburne in Texas on 7 June this year. It didn’t get extensive media coverage because “only” one person was killed.
The damage was caused by a very large auger preparing to erect very large concrete poles. The man in the first picture gives a sense of the scale. (Incidentally, that first picture also shows a lovely fracture propagation and arrest.) But although the auger was large, so was the pipe. I don’t have enough details to work out the critical defect length, but it’s a fair guess that it would be a lot bigger than the pilot bit of the auger.
So I’m interested to hear other views on the potential for augers to cause serious damage to pipelines. Do you think my hand-waving arguments above are valid? But what about the Cleburne incident?
(I’d like to develop a research proposal for the Energy Pipelines CRC to look seriously at the scope for augers to damage pipelines, but even if I get that together and it’s approved it will be quite some time before results are available. Anyone interested in working with me on that?)