I continue to be surprised at some of the pipeline incidents reported in the US. This recent article talks about two occasions on which pipelines were over-pressured to nearly 160% and nearly 190% of MAOP. Fortunately there were no further consequences such as loss of containment. One of the pipeline sections was 21 miles long (34 km), and with that volume of linepack the overpressure was clearly not a momentary failing. But the article is in the general media, not a technical report, so there is a lot unsaid. Reading between the lines one can infer that in each case there was a lack of redundancy in the pressure control system so that a simple failure had a serious outcome.
It would be interesting to know whether HAZOP studies had been done for these pipelines. While no HAZOP is perfect (nor any other risk identification technique) one would expect that a properly completed HAZOP should have a high likelihood of identifying and fixing single failures that can lead to such extreme overpressure.
Pipelines and their facilities are very simple in comparison to process plants, but not so simple that a HAZOP review is a trivial exercise. Those in which I have participated have always made quite a number of recommendations for improvement in both the safety and operability of the installation. I’ve also had the experience of being in a HAZOP for a routine new installation using an older “standard” design that was found to have some significant shortcomings, to the surprise of those who had been using it for a long time.
In my experience HAZOP studies were not done for Australian pipelines until the early 1990s. If that’s generally true then there are possibly a lot of older installations out there that have never been through the process. HAZOP is now mandatory for new pipeline designs under AS 2885.1-2007 – see Clause 2.4.2(a). However the standard is not retrospective so it doesn’t mandate HAZOPs for existing pipelines. Nevertheless if there is no record of a HAZOP for your pipeline then that’s something you should think about quite seriously.