Hi all, I have been requested an opinion regarding the safety involved in the Pneumatic pressure test of a lubeoil storage tank. To be frank this is the first time in dealing with such an issue and would like some clarification if possible. The tank has a maximum allowable working pressure 1.74 bar and hydrostatic test pressure of 2.65 bar it is a 24,000 litre tank. The contractors want to conduct a pneumatic test taking it up to 4 bar pressure using air ! From what I have read from ASME docs is that the test pressure using a pnumatic method should only be 1.1 times the design pressure which should be 1.1 x 1.74 bar is this correct?


Could someone point me in the right direction regarding the testint of such vessels?

Change your contractors, they are obviously incompetent if they are looking to undertake a pneumatic test!

Think about the stored energy.

If the tank did suffer catastrophic failure during the test the pneumatic test could well prove deadly, a hydraulic test has much less stored energy.

There is documentation on the HSE site wrt this.

4 bar @ 24000 litres, work this back to atmospheric and look at the volume of air that will come out explosively in the event of a catastrophic failure.

Look here:
http://www.hse.gov.uk/pubns/gs4.pdf
Here:
http://www.hse.gov.uk/re...rr_pdf/1998/crr98168.pdf
Here:
http://www.hse.gov.uk/pubns/indg261.pdf
Here:
http://www.hse.gov.uk/co...sragtech/techmeasndt.htm

That should give you a start

MEden has a point about the quantity of liquid sloshing around. You do have to be careful of the orientation and the support of the vessel, or it may fail simply due to the weight of the water.

However, I would want to be a very large distance away if someone was going to pressure test this with a gas. Pneumatic testing is extra-ordinarily dangerous compared to hydraulic testing. Even the latter can be dangerous as parts of the vessel can be ejected with a lot of energy. Over the pressure test pit belonging to my previous employer the roof panels were new, because a part of a pressure vessel had left the building via that route when under test.

Generally vessels are tested when they are new, and subsequently they are inspected and perhaps some non-destructive testing done to check that they have not deteriorated. Full pressure tests subsequently are relatively infrequent.

ehsa

As others have already explained, hydraulic testing should always be used unless there are very good reasons against it. In a similar thread on this forum some time ago I mentioned involvement with pressure testing during my HSE days. This included a discussion with a company about pressure testing of hyperbaric chambers used by divers for North Sea oil industry work. With assistance from one of HSE's senior engineering inspectors it was agreed that hydraulic testing of such chambers was not reasonably practicable in view of i) how any test liquid would affect the electrical and other complex fittings within such chambers and ii) the time and effort, etc., needed to remove such equipment before hydraulic testing and subsequently refit it. However, for pneumatic testing very stringent precautions were required. These included doing it on a large and remote site with blast walls or berms and other measures to protect those controlling the testing remotely from a suitable bunker. Alas, the forum search facility seems to be inoperative at present so I can't find and provide a link to the relevant thread.

Another thought: Are there any good reasons why the lube oil tank (already in use rather than being made as a new entity) needs to be pressure tested? Is the tank subject to internal pressure when in use, perhaps as part of a bigger process, or is it simply a storage vessel (like many other tanks e.g. for heating oil in buildings) which just needs to be capable of containing the volume and weight of the oil?

Graham Bullough you are right and it is something we have just discussed the need for the lubeoil tank to be pressure tested, the vessels are under no other pressure other than the weight of the lubeoil within it.

The problem is that these tanks were not designed for this purpose and basically we would like to ascertain whether:

1.They leak
2. Will they collapse due to fail due to their poor state of repair and age 1984 manufacture.

Do you know what would be the procedure/standard sufficiently adequate certify the tanks are adequate for their use?

Re John Murray et al
Sorry guys - if I had bothered to re-read the OP I would have spotted the suggestion of nitrogen was to counter possible explosion/increased fire risk since the tank had held lube oil...!

Message to self: always read and re-read the OP before typing a response!

Phil