PG&E documents said that Line 132 was of seamless construction.  As it turns out, it was not.  It was of weaker, welded construction.  As I wrote here, welded seam pipes have long been known to be dangerous.  To run them safely, the utility company should pressure-test them with water to make sure that they will not give way.  PG&E didn’t do that.

A utility must determine the “Maximum Allowable Operating Pressure,” or MAOP, that a pipeline can be safely subjected to.  To set a safe MAOP, the utility must know how the pipe is constructed.  The weaker the pipe, the lower the MAOP.  Because PG&E doesn’t seem to know how its pipes are constructed — for example, whether they are of seamless or welded construction — the NTSB is concerned that PG&E may have set maximum pressures too high and that its pipelines are thus unsafe.

It is critical to know all the characteristics of a pipeline in order to establish a valid MAOP below which the pipeline can be safely operated.  The NTSB is concerned that [PG&E’s] inaccurate records may lead to incorrect MAOPs.

To prevent another San Bruno explosion, the NTSB is urgently recommending that, unless PG&E has actually water-tested a particular line, that it come up with “traceable, verifiable, and complete records” that describe the type of pipeline buried beneath the streets of populated neighborhoods.  The NTSB wants PG&E to use those records to confirm that the MAOP assigned to the pipeline is appropriate.

If PG&E can’t find reliable records for a particular pipeline, then the NTSB suggests that PG&E water-test the line to ensure that the assigned MAOP is safe.

Water tests are a last resort because customers’ gas will need to be turned off during the tests. But we already know that PG&E’s records can’t be trusted. If you ask me, there really is no other way.


NTSB Urgent Safety Recommendation