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Posted By Stewart Maxwell
I am currently reviewing arrangements for hydro testing and I am looking for some advice on what arrangements (i.e. blast chambers, enclosures etc) and procedures other companies have in place to make this operation safe. I would be interested to know what pressures people believe are low/high risk.
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Posted By Jay Joshi There are:- HSE's priced guidance "Safety in pressure testing" 3rd edition (1998) GS4 HSE Contract Research Report 168/1998 "Pressure test safety" that can be accessed on the HSE website:- http://www.hse.gov.uk/re...rr_pdf/1998/CRR98168.pdf
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Posted By Stuart Nagle
Stewart.
You do not mention what exactly you are looking to test hydrostatically?
Perhaps you could be a little more detailed
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Posted By Oliver Shaw Hi Stewart, We have recently prepared a "safety case" for hydrostatic testing of research pressure vessel. By the nature of research, the "design pressure" is variable! GS4 was good. A collegue developed a spreadsheet to establish the "bunker wall thickness". If you want to know more, call me at info@productivity-in.co.uk. Ollie Shaw
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Posted By Jane Blunt
Dear Stewart
From what I understand, you cannot divide things into categories of safety using pressure alone. The critical factor is the stored energy, and this is related to the product of the pressure and the volume.
Jane
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Posted By Hilary Charlton
Water does not retain pressure - this is a very important point when considering hydrostatic testing. Make sure all vessels are rated to at least 1.5x design pressure. However, I am assured by my engineering friends that if a vessel were to split during hydrotest the water would simply spill out rather than explode because of this lack of retention.
Hilary
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Posted By Jay Joshi
The reason why hydrostatic testing is recommended in preference to pneumatic testing is that a gas is much more compressible compared to liquids(liquids are very minutely compressible). Due to this, compressed gases have higher energy that is released during decompression
For example, the energy released during a total failure of pressure equipment containing compressed air at pressures frequently used in pressure testing is more than 200 times the energy released by the same volume of water compressed to the same pressure.
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Posted By Jane Blunt
Jay is quite right about the compressibility of gases relative to liquids, and that this is why liquids are used for pressure testing.
As to what happens to a vessel if it fails - it may not be as quiet and harmless as you think. I know a pressure test facility where there is a patch on the roof that has been repaired. The story goes that a flange on a pressure vessel failed during hydraulic test and exited the building via the roof (many decades ago). If true, and I have no reason to suppose that it is not, this is ample reason for taking special precautions when testing.
Jane
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Posted By Paul Crump
Stewart
Could you confirm what you mean by the term hydrostatic testing? Are you refering to testing hydrostatic/hydraulic systems or are you refering to testing something else by filling it with a liquid and pressurising it?.
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Posted By Jane Blunt
I have been talking about the testing of vessels and systems, which may in service be used for gases or steam, by filling them with a fluid (usually water) and pressurising to a specified multiple (often 1.5 x) their safe operating limits, to demonstrate that they are indeed safe to work at their safe operating limits.
Jane
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Posted By Hilary Charlton
Yes, this is exactly the sort of hydrostatic testing we do here. However, standard pressure is between 20-40 Bar and all our equipment is rated for 2x design pressure as we take the equipment to 1.5x design.
We do take special precautions though when we go above this level including a perspex and wire mesh cage with a lid around the area and we cordon the area off to prevent unnecessary personnel within the testing environment. As I say, my engineering friends (of which I have many) tell me this is unnecessary but they appreciate that I prefer to go the extra yard to be sure. High pressure tests are also done under a permit to work system so really I guess it depends on what pressure we are talking about. For 20-40 bar we do it day in and day out as a standard process, for 450 bar we take special measures.
Hope this helps
Hilary
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Posted By Hilary Charlton
Dear Stewart
Just thought I would clarify the above, yes we do hydrostatic pressure testing on a pre-existing specially designed rig. Were I to purchase a new rig then I would call in the experts to set it up for me - even though we have over 30 years experience, I would want expert clarification that it was safe and a certificate to say so.
I recommend if you are going ahead with pressure testing that you seek expert advice prior to setting up your system. This is the sort of testing where you cannot be too careful and you have to allow for idiots who may assume that gas testing is OK on this rig because of the pressure limitations. We do not gas test above 1.5 bar without very special precautions.
Hilary
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