BillHustonBlog: The main cause of gas pipeline explosions is....?

Just found this article where Williams' Chris Stockton is quoted:

http://patch.com/new-jersey/southbrunswick/pipeline-spokesman-says-sound-comparable-refrigerator

:: Gas pipeline explosions are not unheard of, but adding a compressor station does not increase the risk of an explosion, he added. "The main cause for gas explosions is people digging and accidentally striking the line,"

So there are two statements here I would like to fact check.

1) Adding compression does not add additional risk of pipeline failure,

2) External strikes are the primary cause of failure.

Does anyone have any data to confirm or refute these statements?

#1 is counterintuitive, and I have data which seems to refute both.

In my project to calibrate the federal PIR formula, I have collected data on several of the largest or most recent pipeline failures:

1: Edison NJ 3/23/1994 *S
2: Carlsbad NM 8/19/2000 *SC
3: Appomattox VA 9/14/2008 *SC
4: Cleburne TX 6/7/2010 *E
5: San Bruno, CA 9/9/2010 *S
6: Sissonville WV 12/11/2012 *SC
7: Salem PA 4/29/2016 *SC
8: Unityville PA 6/9/2016 *SC

Note: I did not make any effort to cherry-pick these to prove any point. I only selected these because they were major or recent failures, and where I could learn the diameter, MAOP, and learn the impact radius from published reports.

Legend:

-------------

*S: Spontaneous Failure (not external strike)

*C: Within 4 miles downstream of a compressor

*E: External Strike

So from this somewhat small sample, I find that:

* 7/8 (87.5%) were spontaneous failures (related to corrosion, operator error, equipment failure, materials defect, etc)

* 1/8 (12.5%) were from an external strike

* 5/8 (62.5%) were within 4 miles downstream from a compressor where pressure is generally nearest MAOP.

This seems to me fairly convincing evidence Stockton is wrong on both counts.

I would appreciate any evidence or commentary which sheds more light on this.

Thanks,