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Posted By GavinR
Hi,
Just looking for some advice regarding pressure testing of a product after manufacture. The part is pressure tested at a set programmed test level of approx 300psi using compressed air supply. Would any one offer any advice as control measures that need to be implemented? Perspex guards enclosing the part during proof test is currently used but would it be necessary to reduce the pressure to a lower level for the leak test to be completed which requires the guard to be removed for access and visibility during the leak test. Plugs are connected together so if there was to be a failure it would anchored to other remaining plugs. Also full face visor is worn during leak test.
Would reduction in pressure at leak test sound like a workable control measure? Also i feel that we should conduct some form of test or calculation of the guarding to prove it is suitable to contained worst cause scenario.
If anyone has any advice or comments they would be much appreciated.
Cheers.
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Posted By Guderian
How big is the vessel/pressurised element? This wil give an indication of the likely pressure energy contained within the vessel.
If at all possible, air testing is not the chosen method - if possible hydraulic testing is much safer.
If air tested, think you will probably need to think of some better form of containment than perspex screens and a face mask - is a major structural failure possible (how big will the debris parts be and the speed/energy of release).
They could well ruin your day...
More detail required for more specific guidance
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Posted By GavinR
Thanks for your reply Guderian.
The part being tested are can be from 6" up to 20" diameter heads that have been welded and heat treated prior from 3 sections to form 1 component/part.
Would the reduction in leak test be a workable suggestion for unguarded test? I'm am def recommending engineers be tasked with calculating protection provided by the current guards from blast or projectile hazards. I'm unsure if 300psi is likely to cause a failure but suppose it must be the test pressure otherwise they wouldn't be doing to that.
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Posted By Guderian
Think you need to get your slide rule and calculator out and work out the forces involved for the various sizes of vessel you are hinting at. Pressure + Force x Area etc.
Work out the areas and transpose the equation to give you the force on the container.
What is the normal/safe operating pressure?
What is the test pressure?
What is the design pressure?
What is the mode of operation? Constant pressure or will the pressure cycle between higher and lower pressures? DOes the design give a mximum number of operational pressure cycles.
Does the container have any form of bursting disc/pressure relief? What is the vessel going to be used for?
Seems like you have a lot of work to do, to establish the safe method of undertaking the tests you want to do. As I say hydraulic pressure testing is much better.
You need to really think about the risk of a major vessel failure, the reasons may not be immediatley apparent - faulty material, poor welding, inadvertant over pressurisation.
This could go wrong in a big way - don't mess with pressure vessels unless you know YOU are sure that what you are doing is correct.
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Posted By Guderian
Oops the + should be =
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Posted By Guderian
OOPs (2) P = F/A.
Its been along day
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Posted By Alan Nicholls
Hi Gavin
Not sure if it would be a viable solution with your components, but most pressure testing of vessels and air receivers is done with water under pressure.
The company I work for manufactured air receivers, we used this method to test them. if a failure occurred you only got wet, not dead.
Good luck Alan N
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Posted By Jane Blunt
There is HSE guidance on pressure testing - document GS4. This is your best starting point.
GS4 reinforces that pressure testing should be hydraulic where practicable, because the energy released is only of order 1/200th of that from an air test, if it all goes wrong.
Even hydraulic tests can go spectacularly wrong - it depends on what you are testing. If the test item fails, depending on its geometry, test pressure etc, fragments can be ejected at speed and can be capable of killing people.
Jane
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Posted By Mitch
Used to pressure test stainless steel filters housings, 7 bar, specification was for pneumatic testing, we tested these in series in mesh cages each fitted with a pressure gauge and left for a soak test.
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Posted By Jane Blunt
Yes, sometimes it is safe to test using air.
However, note that during a hydraulic test of an ammonia converter, destined for ICI in 1965, a catastrophic failure occurred - see Engineering Failure Analysis
Volume 3, Issue 3, September 1996, Pages 157-170.
The failure resulted in a piece of the vessel, weighing 2t, being ejected to a distance of 46m.
This is an extreme example, but it should tell you that before embarking on pressure testing with either air or water you need to do a quantitative assessment. You need to get an unerstanding of the stored energy, the likely modes of failure, etc.
Starting with GS4 is a good idea. You may find you need to consult an engineer.
Jane
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Posted By Mitch
Always good practise to NDT welds prior to testing no engineer can account for the 'human element'!
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Posted By Jane Blunt
Imperfections of a particular geometry and in particular orientations may sometimes evade discovery by NDT.
Nevertheless NDT will find most imperfections.
Jane
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Posted By Ron Hunter
GavinR: Leak Testing (which you mention)as opposed to proof pressure testing can be done at a few psi above atmospheric using proprietary Helium sniffer equipment (you can buy specific mixtures for this).What you do and how you do it though will greatly depend on how the unit is assembled and how critical leak integrity is.
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