I respect all opinions and experience shared on this thread, and welcome debate on sound technical grounds. I will of course agree that there is a whole lot of difference at least in potential energy involved between a larger as compared to a quite small pipelines in pneumatic tests. When it comes to the particular/general subject of designing systems and choosing means of field tests, however, I think it is helpful to have different views expressed in threads that can be read by future (some admittedly impressionable, and not limited to the OP) readers who might not have detailed knowledge of the subjects but before they themselves dive into same. Unexpected failures in even quite small pipelines could conceivably initiate much larger problems in perhaps non-obvious ways (e.g. chain or domino-type reactions with other pipelines, structures or equipment etc.) Particularly in crowded industrial environments e.g., perhaps near "Final Destination" type scenatios are not out of the question. There is thus perhaps a fine line between “fear mongering” or “over-reaction” as opposed to promoting a healthy respect for all hazards of pneumatic as opposed to at least generally more preferable (by a great many organizations and standards) air removal and hydrostatic testing.
I will also agree that are likely some individuals or organizations who in some circumstances have or believe they have sufficient knowledge and control of/over all manner of risk factors in the life cycle of piping systems, that can even be quite lengthy and complicated by the time even new (not only existing) pipelines are tested, to make recommendations for properly run pneumatic testing. Some of these may even be capable of arguably reasonable/defensible e.g. FMEA-like hazard-risk analyses in this regard (see
In the modern age when unfortunately much material and even skill/engineering is "outsourced", and even vandalism, sabotage and terrorism have become some increasingly visible considerations, the picture has become no less complicated. I agree however with Duwe6 that there could very well be many others who are enticed to pneumatic testing out of expediency or “value engineering”, though maybe with much less of a “clue” as to what including all manner of measures/proper procedures and risks are involved. Perhaps as Shakespeare once verbalized, “therein lies the rub”.
As to the earlier statements however that “San Bruno was a fuel-air explosion on a pretty grand scale. Not explosive decompression”, as a pipe geek and that it was in the news I followed the investigation of the San Bruno incident as closely as I could (including speed-reading the voluminous and quite detailed NTSB report that eventually came out at
As I didn’t remember seeing any statements that read exactly like that stated in this thread by others in that formal investigation, I went back and again looked over the detailed report a little closer. While it is quite obvious that there was a whole lot of “ignition” and fire etc. that did a whole lot of damage to folks and property, nowhere did I read a specific statement by the experts in charge of examining this particular incident that claimed it was the ignition of the “fuel” that opened this gaping pipe rupture, self-excavated the crater, or even hurled the big pipe piece(s). I also saw that it was found the rupture occurred at the pressure it did due to a faulty weld, and then furthermore that the report also prominently criticized the "grandfathering" of this particular line so that it apaprently was not required to be field high pressure hydrostatically tested like some other lines (saying that the required level of stress from same would have brought this defect to light, presumably without all the fatailities and property damage etc.) I have also heard there have even been some fairly spectacular craters reported opened up in pneumatic testing and/or somehow in a few cases some very spectacular ones also without ignition even in gas transmission pipelines (these get little press particularly when they happen in remote areas). Contrary to what was stated in anothers post, pneumatic testing can involve huge fluid expansion energy (several hundred or even thousands of times that of water, depending on pressure?) - e.g. about 5 MJ/m^3 of contained volume at ~500 psi pressure. While not necessarily to be "feared", I believe it deserves a great deal of respect, for I believe just that volume is said to be the blast energy equivalent of nearly 2-1/2 pounds/> one kilogram of explosive trinitrotoluene (TNT)! That being said, there is of course no question that at least suitably confined gas mixed with air (e.g. in some sort of suitable volume enclosures etc.) can really do some additional concussive damage when it ignites, and I am aware that at least one third-party critic after the fact has claimed and presented at least some technical arguments that fuel-air explosions have not been given their fair due by at least some of these formal investigative panels in San Bruno and elsewhere (see
In one other case I noticed this gentleman brought out as evidence that that particular pipeline was backfilled with (otherwise hard to dispose of?) sections of scrapped pvc pipeline that could have collected somewhat confined gas-air mix pockets large enough to be problematic. While I’m not going to claim specific relevance to the OP, I just want the record to be as clear as best I understood to these formal findings.
As to modern fault-finding “investigations” by panels or for that matter juries etc. when a catastrophe occurs, I guess I also agree someone is likely in the modern world and with modern experts/tools to find things they can argue have been done wrong (and now often multiple things that have been done wrong by multiple folks!) While that can be attributed as “incompetence” or worse of professionals or others that might stick, some of us who have been around the real world for some time and agree that these have been done wrong also acknowledge these incidents as further proof that even despite good intentions human beings and many procedures etc. are not perfect (we don’t think at least most folks really want to hurt others). It is some interesting that I saw some records in legal proceedings not long ago that appeared to find that the greatest fault in pneumatic test gone awry with fatality was assigned to the dead/maimed man (while I guess he could indeed have been most at fault, I think this was likely of little consolation to him or his family, though I guess this may however have been in effect a rather painless satisfaction of even the harshest Code of Hammurabi though protecting others who may have been associated with the incident and were left unhurt/unpenalized and with all their limbs etc.). [In disclosure these particular cases I remember reading were indeed with type(s) of plastic pipe instead of steel.]
Finally, I agree also hydrotests need to be done as safely as possible, and particularly when large pipelines and very high pressures/thrusts etc. are involved (water is not really totally “incompressible”, particularly when there is a whole lot of water in large diameter pipelines, or after all where there happens to be a lot of air either known or unknown trapped within a test reach). It should thus be common sense to not stand behind exposed unblocked hydrostatic test closures or other thrust foci of any piping when you can stand somewhere else, though it may be helpful to tell/remind some folks who may not realize risks!
While I don't dictate nor write "policy" for any company, as to the stove and burned cat scenario, the contrapositive is of course when the so-learned cat does not jump up back onto the stove, he/she will assuredly not get burned whether or not it is hot or cold (if after two or three weeks being locked in the house, with all the mice gone and that is where the only food is, I guess they might however have second thoughts. Everyone have a good weekend. ]
