Pneumatic Testing Pipeline 1

[AQUE]

Hi

I am involved in pneumatic testing some long distance buried HDPE pipelines. Currently we use 270MJ for the stored energy limit per section and calculate exclusion zone. Due to the test pressure and pipe diameter DN710, the number of test sections and golden welds are too much. Hydro testing for the line is not an option due to water availability.

There is an idea to use hose to connect test sections. The theory is the small hose will limit the rate of energy that can be transferred from one section of the test section to the other in the event of a rupture. This means, we link several test sections. Each section has a stored energy of 270MJ but the exclusion zone is based the 270MJ of a single section only.

I am a little worried what if two or more sections rapture at the same time. I know the possibility is very low but as I specify the exclusion zones for the test, I would be on the safe side.

Any thoughts?

 

[LittleInch]

Just a couple of points. I would like to know for interest where you got 270MJ from - why not 300 or 250? What is your calcualted exclusion zone? What is your test pressure? How are you isolating the sections? How long are the sections? Where is the pipeline - desert / unoccupied or the middle of a town?

All these things impact on the advice we might be able to provide.

Given that I can only assume that you still need to isolate each section, I assume that your only real saving here is time for the test as you can test several sections at one go with pressure up time taking longer as you need to use the hose to fill the next section?

Unless the pipes are parralel, I can't see what the issue is with exclusion zones as they would need to be applied anyway and should not be additive. Pipies in parrallel should not be tested i this way unless you have several metres between them.

Unless catastrophic rupture happened at excatly the same time, once one section went then the pressure in the others would start to fall.

Testing PE, as I'm sure you're aware, is not the same as steel and you would also need to consider how any extended pressure up time affected the results due to the tendecny of PE to creep under sustained pressure

My motto: Learn something new every day

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

 

[AQUE]

The 270 is derived from ASME PCC2 for calculating exclusion zone. When energy exceeds 271, the formular changes. One engineer says the formular becomes less reliabe to determine safe exclusion zone. Though never reference materials are provided to support this point.

The test pressure is only 800kPag. The whole pipeline is 30km longe. The pipeline is in a very remote area but next to a busy site road but can be closed.

Each section is not isolated. A very small diameter hose is used to connect each section so that they can be tested at the same time. The idea is to save time to test them at one go. However they want use to exclusion zone for 270MJ instead of the total.

The original plan is to test them one by one and the each section is maximised to 270MJ.

I am worried if two or more sections repture at the same time.

 

[AQUE]

Sorry forgot to add thank you.

 

[LittleInch]

Thanks for the info - I'll look it up. I think you should be able to justify each section being it's own test energy due to the very low connectivity between each section, but you need to write this down and submit it for review and approval. It would help if at the test pressure you could isolate all the sections, but this measn putting someone into the exclusion zone.

As i said though, if two sections did rupture, then is the consequence different from if they had happened independantly? Ypu would need to apply all the excluson zones at the same time, but I don't see why these should be any bigger than they would be otherwise.

Sure , it's a bit of a fix to get around an understandable and worthy energy limit, but unless you can see why one rupture would create another, or rather show that one rupture wouldn't create another one, then I can't see why this shouldn't be possible to justify, but justify it you must.

My motto: Learn something new every day

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

 

[zdas04]

That stored energy calc is utter dreck. It assumes that the energy of the entire pipeline would participate in an explosive decompression. Nonsense. If I'm being generous, the energy is the stored energy between atmospheric pressure an test pressure with a volume of 20 m of pipe in each direction. Beyond that, the gas flows into a failure at sonic velocity AFTER THE EXPLOSION IS OVER. For stored energy you should use 40 m of your 710 DN line. You will get a number much smaller than including the whole line, and one more representative than using the whole line.

You didn't say your SDR number so it is impossible to calculate an inside diameter or stored energy.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[LittleInch]

zdas04, That's all fair enough and I fully agree it's one way of looking at it, but probably isn't written into any code or procedures so a little difficult to reference unless you run some transient analysis.

You could also consider a calc based on the PRCI report "line rupture and spacing of parallel lines", which provides a calculation to determine the size of the crater caused by a rupture based on different soil type, line size, pressure etc.

Make your exclusion zone say double or triple the crater size and then at least you've got something to use in your justification report. At least air won't catch fire....

My motto: Learn something new every day

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

 

[zdas04]

Yeah, ASME PCC2 is based on a NASA report that has been widely quoted. When the author was asked how the gas that was "far" from the failure could participate in an explosive decompression event he basically said "next question". That report never should have gotten the prominence that it has gotten because it was bad science and wishful thinking. Now industry has to justify deviating from standards that reference it. My analysis of the data indicates that you should have a standing wave within tens of meters of the end of the failure that limits the energy available to participate in the explosion to a relatively small volume. Still considerable energy, but in the range of "sticks of dynamite" not "kilo-tons of dynamite". It is nothing to be caviler about, but it also isn't Hiroshima.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[SNORGY]

As much as I don't necessarily agree with how far on the other end of the spectrum you stand on the issue of pneumatic testing, it is clear in every post on the subject that you have put a lot of tangible thought into it in support of your stance. Your post has t deserve a star because it forces - and is evident of - constructive thought.

 

[BigInch]

I believe zdas is totally correct.

I also just think that one should take a look at the number of accidents that happen and the damage and injuries that result. As much as I believe in hydrotesting pipelines, IMO 100% full radiography or impementing and combining other additional integrity measures, might be a better option than air testing. One thing for certain, 10 miles of pressure energy is not going to contribute to the potential energy behind a rupture.

Independent events are seldomly independent.

 

[AQUE]

Hi

Thank you all for your inputs.

I agree with you all about the total energy of the air will n ot contribute to the shock wave. However to get my ass covered, I have to use it to set up the minimum exclusion zone.

I feel more confident now to running multiple 270MJ section connected by small hoses. I think what I should pay more attention to are the flying missiles when a rupture occurs.

 

[BigInch]

At least an exclusion zone usually doesn't cost much to set up in the areas where it is allowed to be used.

Independent events are seldomly independent.