pneumatic test 6

[raptor2014]

hello guys,
am seeking your advise for pneumatic test pressure case in my project.
i have 1" s.s line sch.40s connecting to cold box,our client refuse to make hydro test on account of the sensitivity of the cold box so he insist to make a pneumatic test instead.
the design pressure for the line is 31 barg so when i calculated the test pressure according toASME B31.3 it will be 34.1 barg which i consider as extreemly high to apply, noting that the continuation to the line has design pressure of 3.5 barg and included within test limt(welded valve in between).

thanx in advace

 

[moltenmetal]

C'mon, guys- this is stupid. It's a freaking 1" line, steel rather than plastic, and only 500 psig! It's definitely possible to design a SAFE pneumatic test for those conditions. We do tests like that routinely, and we do them indoors, without immersion. We do set an exclusion zone, but it's nowhere near 15 metres! Above 500 psig, or when the compressed gas volume is greatly larger, tighter controls kick in.

A catastrophic failure at 500 psig of a line this small is going to occur only because of a) extremely poor material, embrittled AND nearly cracked through and somehow unnoticed during fabrication, or b) extremely incompetent workmanship. The likely mode of failure is leakage only. Actually, the largest single risk in this test that I can see is the risk associated with incompetent testing. A means to ensure that the pressure can't be suddenly increased greatly beyond the test pressure is essential.

What people here should be doing is engendering respect rather than fear for the damage that energy stored in compressed gas can cause.

 

[Duwe6]

"What people here should be doing is engendering respect rather than fear for the damage that energy stored in compressed gas can cause."

Call it 'respect' or call it 'fear', there still is a very low probability of catastrophic failure, but with REALLY BAD consequences. "8-inch beam at 100-ft in the air" Some form of mitigation has to be done, if you are a prudent test engineer. All LittleInch and I are saying is not to blythly pressurize a line pneumatically without a well-thought-out plan to mitigate the risks & consequences. A blow-out is a one-in-a-million [or even less frequent] incident, but it typically kills or maims someone. Just facts.
Airline crashes are a one-in-ten-million [or less] probability, but engineered mitigation is used, even in 3rd-world countries. Just sayin'

 

[zdas04]

Duwe6,
You really missed Moltenmetal's excellent point. Everything we do as Engineers has some amount of risk (or they would assign the tasks to less expensive talent). A competent assessment of the risks and appropriate processes and procedures to mitigate the risks to acceptable levels is what we are supposed to do.

Fear and superstition make zero sense. We were talking about a pneumatic test that was probably at 30% of SMYS and someone posts a link to the San Bruno explosion--that is fear mongering at its worst. When you look at incident investigations associated with pneumatic tests you see that every single one of them was a failure in Engineering or a failure to follow the test procedure. I have never reviewed an incident involving pneumatic tests that did not fall into one or the other of those two categories. Yeah, fill a line with -10C nitrogen and pressure it up to the warm SMYS and something is going to part. A competent procedure would say that you need to heat the nitrogen to near ambient temperature prior to injecting it. My procedures always say that and I make sure that I (or my inspector) confirms the injection temperature every few minutes. It is a critical variable that doesn't get specified. We specify exclusion zones of 5 parking lots, but we don't set a minimum injection temperature. The exclusion zone is fear and superstition, the minimum injection temperature is Engineering. We don't specify a minimum ambient temperature for tests, but we are really careful to fully specify the PPE that the testers must wear.

Attitudes like have been expressed in this thread are quickly leading companies and regulators to ban pneumatic testing. This is an absolutely horrible outcome. Take away yet another tool because people won't do their job? God I hope not, but I see it coming.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

I agree mainly with zdas04 and my aim was to describe what you need to do to make is as safe as practical. Just because there hasn't been a failure in other tests is no guarantee that it won't happen this time. Well thought out, written and supervised procedures are part of that mix.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

"We specify exclusion zones of 5 parking lots, but we don't set a minimum injection temperature."

Exactly. I think you and I are on the same side of the pneumatics. That they are damn dangerous when done by folks w/o significant training/education in this specific form of testing. IF injection temperatures are reasonable, and if all the welds passed in-process and final inspections, a pneumatic test is no more dangerous than driving on the freeway to work. Nothing in this world is risk-free.

But most times in my experience, the client wants a pneumatic test to cut corners and save time/money. The 100% welding inspection didn't happen, so the welds are 'suspect' - not 'bad', just of an unknown quality, thus suspect. And I have never seen or heard of an outstanding test setup like you described: "For nitrogen tests I've used liquid nitrogen trucks. The way you get liquid nitrogen up to pressure is by heating it. On any inert gas test, the first warning in the procedure is that you have to monitor injection temperature and that it must be within a very narrow band around current ambient temperature." Doing it that way dials the test risk waaay down; excellent engineering, Dave!

 

[moltenmetal]

What I object to is the fear mongering- the same as David.

Hazards have to be assessed in terms of both probability and magnitude of resulting harm. We're trying to mitigate the risk of a hazard (failure of this line in service with a commodity presumably more hazardous than compressed air or nitrogen), by doing an ENGINEERED TEST. Blowing the potential harm of that test out of proportion isn't helpful to anyone. Pointing out the hazards of pneumatic tests carried out on systems with a greatly higher P*V is all well and good, as long as it's then properly related to the poster's specific conditions.

I agree with David- what we risk as a result of over-reaction by well-intentioned but ignorant people is an outright ban on pneumatic testing. That would be a tragedy, and could result ultimately in unnecessary injury or loss of life.

 

[DekDee]

Guys,
Found some interesting info in the Pneumatic Field Testing Specification from a major US O&G company.

FIGURE 2: EXCLUSION ZONE
NOTES:
1. The projectile model selected, a DN 50 x 300 mm long nozzle detaching from the main pipe or
equipment item results in the following exclusion zone distances which have all been rounded up
to multiples of 10 m. These distances shall be observed for all pneumatic tests as a minimum
and increased if any concerns of safety are raised before any test.

APPENDIX I: EXCLUSION DISTANCES
1. Credible Failure Modes
1.1 The access to the system to be pneumatically tested is determined by calculating the
distance travelled by a projectile, which is considered to be the most likely type of failure.
1.2 The distance travelled by such a projectile is a function of mass, initial velocity after
detachment and its aerodynamic profile.

1.3 For piping systems the possible types of failure are:
• Brittle fracture of a pipe creating small shrapnel projectiles with small aerodynamic profile
• Butt weld failure of pipes up to DN 150 causing them to whip or “snake”. However, the
remainder of the pipe still attached restricts this effect and therefore the exclusion distance
• Although it would be catastrophic, butt weld failure of pressure vessels, exchangers or
equipment within a piping system is not considered to be a credible event during a pneumatic
test, since all this equipment will have been shop hydro tested.
• Sudden detachment of a branch welded nozzle connection or other pipe attachment. This
would result in a tumbling projectile, which could travel a large distance and could cause
significant injury or loss of life. It is not practicable nor possible to 100% radiograph branch
welds due to their geometry. Therefore, a failure here is considered to be far more likely than
butt welds which have been 100% radiographed.

1.4 Exclusion distances have therefore been calculated for the "guillotine failure" and
detachment of a small nozzle connection welded to a larger pipe or to an item of equipment.

3. References and Equations Used To Calculate Exclusion Distances
3.1 References
Baker W E et al "Explosion Hazards and Evaluation"
Elesevier Scientific Publishing Company, Amsterdam, 1983, pp 463-474
Baker W E "Blast and Blast Fragments from Bursting Pressure Vessels" ASME Journal
83-PVP-61.

It is interesting that the exclusion zone noted in this specification for 34 bar (3400 kpa) is 180 metres,
Cheers,
DD

 

[zdas04]

Company policies are written by folks. That bit of official looking prose could have been written by the people in this thread who object to the concept as too risky. You can bet that more than a few of the people who have commented in this thread have written company policy, maybe even that one.

I had a boss once that contended that company policies and standards are written based on the "cat on a hot stove principle" which says that if a cat jumps on a hot stove, he'll burn himself, and after that he will never jump on a stove again regardless of its temperature. This guy strongly contended that the company standards manuals get so full of prohibitions against one-off activities that they should be discarded and started over about once a decade. Life would be so much better if that happened. I went through a complete re-write once (we invalidated the standards and specified that industry standards as published would govern our Engineering activities). Within a couple of years we were writing add-ons to the code again. It was a nice couple of years.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[DekDee]

David,
I am sorry, I fail to understand your response.
I have mentioned numerous times on this forum that IMHO there is nothing wrong with pneumatic testing if performed in accordance with requirements/regulations and I have personally been involved in some huge tests over the last few years.

I posted this information purely as an example - two seemingly knowledgeable people (yourself and Duwe6) on this forum had given totally different examples of exclusion zones - one was 10-15 metres, the other was 100 - 200 metres.
I posted this to show what one of the largest O&G companies in the world considers a safe exclusion zone - I would rather work for a company who errs on the side of caution than a company who says 10-15 metres is acceptable !
Regards,
DD

 

[LittleInch]

I think you'll find the 10-15m was my guess, based mainly on buried pipe and the potential for crater forming. Wholly above ground testing of pipework clearly carries some level of risk, the key issues are how best to mitigate that risk and prevent injury to people and destruction of equipment. That does mean that you need to look at potential failures, the amount of NDT undertaken, the extent of any "temporary" (I hate that term) pipework or fittings and make sound reasonable judgements.

To get back to the OP, a 1" line at 30bar - we don't know how long or what fittings are on it - has some risk from an end cap or other fitting coming loose / brealing during the test and becoming a projectile. The key is identifying what those projectiles could be and either pointing them into the ground or a large wall or behind an earth bund or just retreating a long way. I would consider this prudent engineering and risk assessment, not risk avoidance. I have some sympathy with the view that standards are written in part to try and solve every problem found in isolated occurrences where the lowest common denominator is used and it removes the potential risk as the expense of common sense and responsible engineering.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

David, you and I agree completely here. The trouble with company standards is that they are often treated exactly like religious texts: written by the ancients who have long since departed and hence can't be consulted to obtain context, and treated as holy and inerrant wisdom by the modern acolytes- people who have zero motivation to challenge the received wisdom of the ancients because these standards help them avoid the necessity for these folks to develop and use, and be accountable for, their own engineering judgment. The standards are often decorated with threats of fire and brimstone to those who violate the rules, but little actual design guidance to permit the user to determine when they apply and when they don't.

Then there are the interactions between and among the standards- standards which individually make sense, but in combination become a monster. We've seen a $50 air pig used as a backup receiver to hold a small double-acting actuated valve closed during an air failure, become a custom-built monster with 2" minimum flanged nozzles with XXS nozzle necks, legs, lifting lugs, ASME U stamp, 3-part paint system etc., and the air failure pressure switch replaced with a 0.075% accuracy industrial pressure transmitter...and it wasn't one, it was something like 10 of them on one little project.

A standard which requires a 180 m exclusion zone around a pneumatic test on a 1" sch40 line at 500 psig has proven itself to be useless, in my opinion.

 

[zdas04]

DekDeee,
I did not mean to demean your post. I was just pointing out the reality of company policies. This one could have been written by Duwe6 who suggested 150-200 m exclusion zone above. He probably even believes that that exclusion zone is appropriate. If I had written it (and I've written dozens of procedures/policies/standards for various companies) it would have looked different.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[rconner]

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

http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis).

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

https://www.ntsb.gov/doclib/reports/2011/PAR1101.pdf).

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

http://ascelibrary.org/doi/abs/10.1061/(ASCE)PS.1949-1204.0000116?journalCode=jpsea2).

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. ]