San Bruno prelim NTSB report

I confess to an almost voyeuristic fascination with pipeline incidents, of which the latest remains San Bruno.  Partly that interest is the hope that we can learn from the misfortunes of others, but it’s also partly just naked curiosity (well, that’s what makes media businesses viable isn’t it?).

The part of me that hopes to learn was interested in this preliminary report from the US National Transportation Safety Board.  It adds some specific detail but not a lot more overall understanding to what we already knew (or could plausibly speculate).  To my mind the highlights of this report are:

  1. The most immediate cause was a minor pressure upset due to a control malfunction arising from a power failure during maintenance work.  But the pneumatically operated overpressure protection valve worked as intended so the pressure rise was only modest, and still within MAOP (390 psi vs. 400 psi).
  2. The pipe in the vicinity of the failure included an amazing assemblage of short pups, many only slightly longer than the pipe diameter.  That seems to at least partly explain the course of the fracture, with its branches and abrupt changes of direction corresponding to the girth welds.

No information yet on where and why the fracture initiated, but the report contains a long list of the completed and planned investigatory work and a promise of further updates as the investigation progresses.

I would hope that there is no pipeline in Australia that has been assembled from multiple short rings of pipe, but I suppose it’s possible that some of the oldest lines contain features that would not be tolerated in modern construction.

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