Hydrotest or Pneumatic test? 1

[alfchoi]

We have a problem in pipe pressure testing,
We are able to conduct the pipeline pressure test using air instead of water to the same requirements as expressed in desired standard in certain condition. But my question is, would we need to modify the line parts or consider any thing for this change or would we have any constrain on line length in new test procedure?

 

[BigInch]

Its doubtful that you can nor should you do an air test to the "same requirements".

Without more details, no comment on the rest.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[vpl]

alfchoi

You might want to read this thread: thread378-238325

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[MJCronin]

Wheeeee...!!!

GOOGLE "pneumatic test" and disaster or accident or explosion......What fun..!!

http://www.absa.ca/newsletter/v07-2002/v7-iss2.pdf

http://www.eng-tips.com/viewthread.cfm?qid=176703

http://books.google.com/books?id=jm...X&oi=book_result&resnum=10&ct=result#PPA54,M1

Annnd........ best of all.......that famous flying tank in Brazil !!!

( Case #8)

http://www.psig.sg/Don/Case Studies 2006.pdf

Comments ??

-MJC

 

[BigInch]

They call it "testing" for a reason.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

You might also want to Google this site. I found thread794-176703 (mentioned above), and thread378-112658 thread378-235027 there are more, but they start getting repetitious after a while.

Bottom line of all of them is that there are a BUNCH of people who feel that doing a static strength test with a gas is irresponsible and fairly evil. There are some people who feel that pneumatic tests can be done safely and are allowed by the code.

My argument is always that the Engineer designing the test is obligated to actually design the test and determine where stresses will be maximum and what that max value will be. Also what is the minimum ambient temperature that is acceptable to start/perform/complete the test. If you do your sums, there are many times that a pneumatic test can be done much more safely than a hydrostatic test (think Rocky Mountains, pressure at the top of a hill vs. pressure at the bottom).

David

 

[rconner]

A couple years before the U.S. Continental Congress met I understand a Scottish poet penned the lines,

“The best laid schemes o’ mice an’ men / Gang aft a-gley.” [often translated to the effect, "The best-laid plans of mice and men/often go awry," (in Robert Burns 1785 poem, "To A Mouse, on Turning Her Up in Her Nest, With The Plough")]

While proponents of the pneumatic testing practice (and maybe even some when there might be other alternatives conceivable to skilled engineers, at least if considered far enough upfront) might argue the “often” wording, it appears that now 224 years later this is perhaps no less true. I believe what can go “awry” or wrong is in reality limited only by the frailies and imagination of Man, and what designs and products etc. he hath wrought.

One thing is for sure, WHEN things go wrong for any reason in at least high pressure pneumatic testing of large diameter tanks and piping, there can be hell to pay!

 

[dcasto]

i always use pnuematic tests on my cryogenic equipment. Under b31.3, there is no strenght test of the piping, you never get anwhere near mechanical limits.

My collegues that use hydro, it takes 3 times as long to start up, it costs more, and when something goes wrong, it takes days to fix.

 

[BigInch]

Well then stand back. The objective of B31.3 is not to do a strength test, its to find leaks and other defects, which can occur well below design pressures.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rconner]

Might want to stand waaaaaaay back. In addition to latest Shanghai incident, I happened to notice some time ago also yet another rather recent incident in Australia described at the site

http://www.worksafe.vic.gov.au/wps/...fails+under++air+pressure+test+-+Kills+worker

with the heading, “Pipeline fails under air pressure test - Kills worker” where they apparently for whatever arguable reasons were pneumatically testing a much smaller 300 mm pvc water (perhaps ironically?) line with only 100 psi air pressure. One worker was reportedly killed and another injured in the ensuing blast, in which debris was reportedly “strewn over an area of up to 100 metres, including into residential properties.”
You just about have to think that someone involved in each of these unfortunate incidents (and many more I have heard of involving pneumatic testing in many years) THOUGHT what they were doing would work (in addition to the obvious of being cheaper and expedient, and requiring maybe thinner or less reinforced pipes/supports). Unfortunately, it appears “stuff” (of all sorts) nevertheless “happens” in some pneumatic testing that may not have exhibited that level of violence had appropriate filling and hydrostatic testing been conducted.
My condolences to the victims and their families etc. Have a good weekend.

 

[dcasto]

35 years and none in my industry....

 

[vesselfab]

i used to build aluminum silos & blenders that could not hold the weight of water in big diameters such as 180-240".

we tested with 1/4 psig just for leaks.

still had a top cone roof pop off once

pnuematic tests with large volumes, even at moderate pressures, scare the bejeezers out of me

 

[StressGuy]

Out of curiosity, what industry would that be, dscasto?

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[Bribyk]

The other day, we had a large-ish engine exhaust manifold that was being pressure-/bubble-tested at 40 psi with air when one of the gaskets let go (incorrectly installed). The hammer-effect wrecked and emptied the water tank rather quickly. Gotta respect compressed gasses...

 

[rconner]

Have noticed yet another one at

https://portal.navfac.navy.mil/port...k/tab81582/plastic pipe test failure 6-00.doc

(this one apparently with just some air trapped at 100 psi -- if such "shrapnel" gets embedded in a body, I read somewhere else it might not be readily located/detected at least with a conventional x-ray).