I have previously made passing mention of historical Australian pipeline incident rates as an aid to estimating which frequency category to select from the risk matrix when doing a risk evaluation. It seems worth briefly updating that in the light of recent further analysis of the Australian pipeline incident database.
In a nutshell, the overall average loss-of-containment rate for Australian pipelines is around 0.03 per 1000 km.yr. That includes failures from all causes, based on data from the last 5 years.
More usefully, the failure rates (ie. loss-of-containment frequency) due to external interference are:
- 0.022 Overall average
- 0.016 Rural areas
- 0.07 Urban areas
(Values in incidents per 1000 km.yr, but based on all failures in the database; analysis for the last 5 years would be meaningless because there have been no external interference failures since 2005.)
These numbers need to be used with great caution. They are so approximate that I hesitated to use even two digits (but one wasn’t quite enough for the first two values). They are averages that apply to pipelines with wildly varying levels of protection, and of course wildly varying environments even within the broad urban and rural classifications. If your pipeline has robust physical and procedural protection measures it will probably have a much lower failure likelihood than the average, and conversely for a pipeline that has minimal protection. I don’t know with certainty but I suspect that the level of physical and procedural protection could affect the failure rate by orders of magnitude (eg. the failure rate of a pipeline sufficient thick that it cannot be penetrated by any plausible threat will be vastly lower than the average).
Despite these cautions, thoughtful use of numbers like these can help avoid over-optimistic or over-conservative risk evaluations. Having tried purely judgement-based frequency estimates for a particular threat followed by a sanity check using numbers such as those given here, I have been surprised at the difference, even when the initial judgement was made by very experienced pipeline people.