Pneumatic testing

[albaweld]

We are some months away from doing pneumatic testing, and doing as much sourcing as possible. We are up against a bit of a wall though. This may sound as if we are not professional but we need to source a TNT formula for our volume etc, we have contacted the safety authorities and codes..B31:3. But are not having much success. Can anyone guide us on the proper path? We understand the severity of this and will not proceed until everything is in place and we have proper approvals.

 

[zdas04]

There was an equation from NASA kicking around a few years ago, but it was really crap. Their basic assumption was that the stored energy of all the gas in the entire system (regardless of configuration) would explosively decompress in the sub 500 mS time frame. Now think about a 20 mile long 30-inch diameter pipeline tested to 1000 psig. By their formula the energy in the explosion would be on the order of a large hydrogen bomb. What nonsense. Maybe the gas in a joint or two would explosively decompress, but the rest of the line would just be fluid-flow towards the leak. I've never seen an equation that tried to predict what portion of the gas explodes and what part just flows. The NASA equation and the write up around it are real boogeyman stuff.

On my web page (address in the signature box below) I have a document on the "Samples" page that discusses many of the issues around static testing and the choice between hydrostatic and pneumatic tests. I've had really good feedback on it and I think it is the best committee-prepared document I've ever participated in.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[albaweld]

Thanks for that...very informative.

 

[SNORGY]

See also this earlier thread...

thread378-258605

I think I'll visit zdas04's website as well. No doubt some good information there.



Regards,

SNORGY.

 

[jte]

I'm not sure of the basis, but ASME PCC-2 provides a TNT equivalent formula in Article 5.1 Appendix II and a biological damage calc (i.e. your lungs will burst if you are within x ft) in Appendix III. Structural and shrapnel damage is not addressed in the current 2008 (or 2010/2011) edition, but might make it into the 2012/13 version.

http://catalog.asme.org/Codes/PrintBook/PCC2_2008_Repair_Pressure.cfm

jt

 

[zdas04]

SNORGY,
Thanks for providing the link. I must be getting meaner since last time I called the "point source" assumption "poppycock" this time I called it "crap". Either way, I don't buy it.

David

 

[SNORGY]

No worries.

Besides, the revised term is easier to spell.

I know that the Regulatory Authorities in my region "bought" my energy per unit mass rationalization towards the computation of how far the pieces could fly if something blew up. If nothing else, it was creative.

Then again, I have been known to estimate check valve closure times in water hammer transient analyses by drinking beer out of a flip-top beer stein in the bathtub and then holding it under water to see how long it takes the lid to close.

Again, in that instance, the authors of the software commended my creative thinking.

Most of the stuff I do nowadays is towards developing suggested guidelines that other folks can at least "move forward" with if they can't spend the time or don't have the time to fully understand or apply the theory. I think as engineers we could all crunth the numbers if we had to.

I agree with you, though. In a long length of pipe that breaks "here", the hole usually stays approximately "here", but there's still a whole bunch of energy "over there" that has to "get here" before it's released. In other words, you are right: it's not one big "KABOOM" event.

Regards,

SNORGY.

 

[BigInch]

It probably needs to be related to the energy that is being directed towrards progressively ripping the pipe. There are some procedures I've seen for estimating that in relation to the placement of crack arrestors on dense phase CO2 pipelines. I might be able to find them, if anyone's interested. Let me know.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

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

 

[wicltd11]

Can someone tell me what this represents. E= P x V [In (P/Pa)]
and
TNT = E*5.269*10-7 (lbs)

Is this formula over kill when it comes to pneumatic testing?? Thanks

 

[jte]

I agree with the general sentiment of it being difficult to expend all of the stored energy in a few milliseconds. Tagging along with SNORGY, I think the value of the equation / exercise is not to precisely define the size of the event, but to put an upper limit on it. I think few would argue that the event could be of greater magnitude. Thus, for a relatively intractable problem, we have at least bounded the answer: If a failure occurs, the result will be somewhere between "nothing" and "x lbs of TNT". That info alone might be enough to allow folks to move on and make a decision.

wicltd11 - The formula you quote is similar, though slightly different to that given in PCC-2 (see link above). I believe in your "E" equation you meant to have ["natural log" P/Pa] instead of [In P/Pa].

jt