Pipe testing - Air vs water testing 4

[lfg2007]

I am being told that air testing is the same as water testing for pipie pressure testing. I do not believe that the air pressure required would be the same as water. Also theree is probably a saftey issue for high pressure test. Test would be 150 psi water max.

Any thoughts

 

[zdas04]

Damnit, do a search before asking a question. This topic has been beaten up, but you do add one bit of foolishness that I haven't seen before--that you would require higher pressure for air than for water. I'm not sure where tha came from, but pressure is pressure. If you pressurize a pipe to 150 psig with air or with water, the induced stresses will be the same.

You will find in a search that there are people within eng-tips.com who feel that a pneumatic test (although sanctioned by ASME) is irresponsible. You'll also find people who think that a pneumatic test is quite responsible as long as the test is engineered.

Do a search and if you still have questions, start a new thread, if I were you I would red flag you post and ask that the thread be removed to prevent future embarassment.

David

 

[cvg]

see the search below:

search for pipe pressure testing

 

[LSThill]

Please read ASME PCC2

L S THILL

 

[lfg2007]

I know that when pressure testing piping with air versus water the test psi is not the same. Several of your colleagues indicate that an air test would required about 4x less psi.

 

[vpl]

I know that when pressure testing piping with air versus water the test psi is not the same.

If you already knew the answer, then why did you post the question?

Several of your colleagues indicate that an air test would required about 4x less psi.

I'm not sure how you know zdas04's colleagues...if you mean other posters on this forum, that doesn't mean a thing. Someone might have stated that in a thread, and been firmly shot down.

I will tell you that, as a regulator, there is no way that I would accept an air test at 37.5 psig as being equal to a water test at 150 psig. What's your basis? ... "I read it on the Internet" won't hack it.

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.

 

[lfg2007]

OK

Boy did I mess with the wrong crowd.

I will try to be clear as a non professional in this area it is not always easy. Probably not a website for newbies or to waste money on support.

Everyone is talking about pressure testing the properties of piping for failure or matereial characteristics.

I need to know about pressure testing piping for leaks when installed. Typical (NOT NUCLEAR) spec call for 1-1/2 times working pressure for leak testing. In the past I have been told that 150psi of water is not the same as 150 psi of air. For stress analysis pressure is pressure but for leakage I am told differently. Many have said that air is more compressible than water and will release stored energy quicker in case of failure at joints and valves.

Regardless - The search which i tried did not help and I am not sure why asking for help is treated with such dissdain.

Boy I am disapointed.

 

[monkeydog]

A search in Eng-Tips for "leak test" resulted in the following:
Advanced Search
You are in the site-wide keyword search. If you'd like to search a particular forum, navigate to that forum and click on the "Search" button in the gray navigation bar.
Hundreds of records matched your query of leak test.

Don't be upset because you did not ask the question properly. A pressure test is normally interpreted as a proof pressure test.

 

[cvg]

the following post (see below) which was found by my previous search seems to reinforce the fact that a lower pressure air test is generally not considered good enough for acceptance testing, may be difficult to tell how much leakage is occuring and that air testing in general could be more dangerous. However, there may be some benefit in the method since it is quite easy and may be useful in finding leaks and fixing them prior to the final acceptance test. Air testing also doesn't require pumping or disposal of test water which could be quite time consuming and costly for a large pipeline.

note that their may be differing opinions on this subject since testing may be done on 1) typical underground, potable water systems (perhaps bell and spigot joint), 2) above ground plant piping (welded, flanged etc.) and even in 3) nuclear powerplants with much different requirements for allowable pressures and leakage and risks involved for each scenario. Since we do not know any details about the subject project, there of course can be gross speculation involved.

http://www.eng-tips.com/viewthread.cfm?qid=133832&page=8

 

[BigInch]

lfg,

Still you need to read the code, if you want to be considered competent in what you're attempting to do. And if you did that, you probably wouldn't need to be asking the question at all.

Leak tests can be done with air, ONLY if 5 very specific conditions are meet and which do not result in creating hazards. Its not just a whim to decide to use air. It is an excessive hazard that can only be used when hydros is not possible. Its not totally the easiest solution either, as piping welds must be 100% radiographed/UTed and structural welds examined via liquid penetrant, if an air test is done.

If the code is B31.3, see pp 345.1 to 345.9

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[Apakrat]

lfg2007 (Mechanical) on 14 Jan 09 14:46 wrote:

Many have said that air is more compressible than water and will release stored energy quicker in case of failure at joints and valves.

A rule of thumb thought from an old pipeline hydrostatic test eng. for Transwestern Pipeline Co.

Air viscosity may be about 175 times less than H₂O but it takes about 800 time more volume of air to reach a pressure than it does H₂O.


At 74th year working on IR-One PhD from UHK - - -

 

[cvg]

lfg - the fact that you posted on the piping and fluid mechanics forum generally limits your audience to industrial plant piping and oil / gas pipelines. However, if you mean to test a potable water system, you will not be using B31.3. You also may not be welding joints, radiographing them or using dye penetrant testing. You would probably be using AWWA standards. These standards do not recommend air testing at all. Hydrostatic testing is to 1.25 time the highest working pressure. Test is for two hours and you may not exceed the allowable amount of "makeup water" required to hold the test pressure. In other words, some leakage is allowed up to the limit. All observed leaks are to be repaired.

The only time I have ever seen air testing done is very low pressure air testing for sanitary sewers and manholes. Air pressure is only raised to a few psi. This is usually a substitute method for a hydrostatic leak test.

 

[Apakrat]

Many times, a better alternative to using air pressure for leak testing piping is to use a vacuum test. This will find small leaks that air pressure will not indicate until held under pressure for lengthy time periods.

If the vacuum will not hold, then the expense is justified by replacing with low pressure from some form of gaseous substance which can be detected with a sniffer.

DO NOT FORGET: Gaseous/air pressure structural or leak testing is affected by changing ambient temperature radically greater than by actions on fluids.

At 74th year working on IR-One PhD from UHK - - -

 

[Unotec]

Apakrat, you're absolutely correct.
lfg, you did post a question regarding pressure test piping without mentioning leaks.
I'd follow Apakrat's advise and warning.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[lfg2007]

All

Thanks for the information and sometimes redirection.

 

[e123344]

note that you most certainly do not want to perform a vacuum test unless 1) your pipe is designed for full vacuum, 2) that you have flanges, gaskets etc that are designed and specified for vacuum. Note that pipes are essentially much 'weaker' in vacuum than pressure, so essentially taking the vacuum test approach would more than likely add to your pipe wall thickness and hence the cost - the degree percentage wise of increased cost i am not certain of but will depend on the positive design pressure and diameter of your pipe.

suggest you pay heed to responses generally where handles have stars.

 

[shmar]

hi, it mainly depend on what lines you are testing. if this is a fuel line you would not want to test it with water!!!
you can reach the same pressure with water and air, water will give you more visual leak testing for long lines.

 

[Ballbearing1]

zdas04,
I am unsure why you jumped on lfg2007 and yet have been strangely quiet while we have had numerous incorrect postings on this subject.
The posters on this forum come from all over the world so the ASME and API codes are widely used but as far as I am aware not the AWWA standards.

zdas04
"...'but pressure is pressure. If you pressurize a pipe to 150 psig with air or water, the induced stresses will be the same."
Incorrect - the stored energy of 150 psig of air is much more dangerous than 150 psig of water, that is why the same piping is tested to 1.5 x design pressure for hydrotest and 1.1 x design pressure (B31.3)and 1.2 x design pressure (B31.1) for pneumatic testing.

lfg2007,
Your 4 x less psi may have been misintepreted by yourself, pneumatic can be 40% less than hydrotest.

Biginch,
"It is an excessive hazard that can only be used when hydros is not possible."
Incorrect - B31.3 states it can be done if a hydrostatic leak test is impracticable - not impossible.

"..must be 100% radiographed / Uted and structural welds examined via liquid penetrant, if an air test is done."
Please advise where in the code this requirement is stated ?

cvg
"If you mean to test a potable water system, you will not be using B31.3."
I am a Welding Inspector on the US$5 billion Goro Nickel Project in New Caledonia. I am a New Zealander working for a Canadian / Brazilian company in a French territory. We have miles and miles of potable and process water systems that are all fabricated and welded to B31.3.

shmar
"If this is a fuel line you would not want to test it with water."
Fuel lines are hydrotested (with water) daily all over the world.
The only lines we do not hydrotest on site are sulphuric acid lines. (I am not a chemist but I think it is due to exothermic reaction)

lfg2007,
Dependant on your code and whether the pipe is buried you may not even have to hydrotest.
If the test was 150 psig then you would presume the design pressure was 100 psig ( 1.5 x) which would make it Cat D in B31.3 and an ISLT only is required.

My apologies if I have managed to offend everyone,
Regards,
BB

 

[BigInch]

Ballbearing,

zdas04,
I am unsure why you jumped on lfg2007 and yet have been strangely quiet while we have had numerous incorrect postings on this subject.
The posters on this forum come from all over the world so the ASME and API codes are widely used but as far as I am aware not the AWWA standards.

Comments by all are voluntary. Nobody gets paid to do this, hence some, if not many, posts go uncommented by the "regulars". Some days there are simply more important things to do. Some days you just don't feel like working for free, going to lunch, or going to bed. And some days, you just get tired of saying the same thing over and over. Sometimes you get to them before we do. Sometimes, its just pointless. Obviously the OP knows more about the problem than us talking heads do, so if he's building a water line to B31.3 and somebody tells him he isn't, the OP is free to ignore that comment and procede with building and testing to B31.3. I don't see a necessity to correct those kinds of comments (all the time). If some poster wants to waste everyones time by second guessing all the covenents and answering every permutation and exclusion to every permutation of every unasked question ... please leave me out of it. And sometimes the post has just moved off the first page. If that happens, I've usually lost interest by then and won't ever return to make corrections. Making corrections is tedious the first time, never mind in perpetuum.

Fortunately this morning I have a few minutes. You quoted out of context of the original post, so I will have to respond accordingly.

zdas04
"...'but pressure is pressure. If you pressurize a pipe to 150 psig with air or water, the induced stresses will be the same."
Incorrect - the stored energy of 150 psig of air is much more dangerous than 150 psig of water, that is why the same piping is tested to 1.5 x design pressure for hydrotest and 1.1 x design pressure (B31.3)and 1.2 x design pressure (B31.1) for pneumatic testing.


Energy density may be higher, but as zdas says, stresses are equal.


lfg2007,
Your 4 x less psi may have been misintepreted by yourself, pneumatic can be 40% less than hydrotest.
I'm not sure... and I don't feel like doint the math and responding. Sorry

Biginch,
"It is an excessive hazard that can only be used when hydros is not possible."
Incorrect - B31.3 states it can be done if a hydrostatic leak test is impracticable - not impossible.

I said "not possible", not "not impossible", The code uses "impractical" as you state, however, if you do attempt to avoid making air tests as I believe you MUST, and as you should in order to minimize risk of all kinds, impractical does in effect equal impossible, so I have no problem with the symantics that I used.
[/color]

"..must be 100% radiographed / Uted and structural welds examined via liquid penetrant, if an air test is done."
Please advise where in the code this requirement is stated ?

Please see Section 945.1, 2 & 3.


cvg
"If you mean to test a potable water system, you will not be using B31.3."
A talking head giving advice on some unjustified assumption that the OP can freely accept or ignore based on his more detailed knoweledge. Not a constructive comment in the first place, as its based on technically unjustified assumptions (even though the mathematical probability might be high) and, if I comment on that, it just makes me guilty of the same thing.


I am a Welding Inspector on the US$5 billion Goro Nickel Project in New Caledonia. I am a New Zealander working for a Canadian / Brazilian company in a French territory. We have miles and miles of potable and process water systems that are all fabricated and welded to B31.3.
You could just as easily have designed those water lines to no code, as cvg contends, and, as I have seen from South America to India, other or no codes for water lines are about a ZILLION times more common than B31., so simply on a probability basis cvg is correct

shmar
"If this is a fuel line you would not want to test it with water."
Fuel lines are hydrotested (with water) daily all over the world.
The only lines we do not hydrotest on site are sulphuric acid lines. (I am not a chemist but I think it is due to exothermic reaction)

[Being that you are in pipelines, I suspect you are quilty (as I often am) of thinking that the OP is talking about pipelines where water testing would be the norm, but the OP said "pipes". Perhaps Shmar thinks this pipe might be a fuel line on a A380 that needs to be tested in place. If so, who am I to argue? I know less about that than Shmar.
Why should zdas comment on that? I don't want to.[/color]

lfg2007,
Dependant on your code and whether the pipe is buried you may not even have to hydrotest.
If the test was 150 psig then you would presume the design pressure was 100 psig ( 1.5 x) which would make it Cat D in B31.3 and an ISLT only is required.

But you assume, without justification, that the OP is testing to B31.3

My suggestion is that EVERYBODY, READ the OP and concentrate on making a constructive comment to that rather than making outrageous assumptions, mentioning some obvious exclusion as a contradiction to another's post and arguing in perpetuum about the last poster's text. At least if nothing else of true engineering interest arose.

Deal?


PS No offence noted... or taken.


**********************
"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]

I think I'll just stay out of this. I've had similar discussions with welding inspectors my whole life (my step father was one). The breadth of knowledge in that field is generally impressive, but the depth is occasionally lacking and trying to augment it has often proved frustrating to me. I don't do frustration for free if I can help it.

David