[Robert357]

When the federal legislation was being discussed to regulate pipelines (after the Bellingham and El Paso deaths), there was a huge debate as to whether some of the codes were strict enough. A key point of debate was whether hydro-static testing should be periodically required. The City of Bellingham hired an "expert" who recommended hydrostatic testing of all pipelines and a settlement between the City and Olympic Pipeline required such testing for much of that pipeline.

The issue comes down to materials science. Hydrostatic testing is a way of "proofing a system." It can also make things worse by damaging a pipeing system. For example if you have modest material cracking the hydrostatic test can increase the size of some of them. Most of the piping experts I talked to (at the time) stated that repeated and frequent hydro-static testing was generally not a good idea. They urged other non-destructive testing methods.

[snopercod]

When I was in the nuclear biz, I recall that there was legitimate concern that too-frequent hydrostatic testing of the Steam Generators could wear them out even before the plant went on line. [Diablo Canyon, the "world's longest erection"]

They did some statistical magic and estimated the number of hydro-stats before the units would have to be replaced. Somehow, the maximum number always came out a few more than they would need to do.

I am thinking that NDT might not be feasable on a long pipeline. Somehow you need to get the cobalt source inside the pipeline to do X-ray testing, then reading all those films is a black art, anyway.

Eddy current testing? I had thought that was only useful on non-ferrous materials, but could be wrong.

Mag-particle inspection would probably work well, but would be really expensive. I mean, there must be a lot of weld joints in a thousand-mile pipeline.

I'm just speculating here, since I have no special knowledge other than just seeing this kind of stuff done in other environments.