B31.3, Category M, Sensitive Test 1

[bulkhandling]

I'm in mining consulting business where there are not many Category M fluids. We use B31.3 for piping design.

Per ASME B31.3, para. M345 Testing, a sensitive leak test shall be included in the required leak test.

My understanding is : a normal hydrostatic test is required (1.5x design pressure) and a air and bubble test is also requried (para. 345.8, 1.25x design pressure or 15psi+ design pressure, whichever is less).

I specified the requirements in the line list for the previous projects but myself did never supervised the tests on site. When I talked about those tests lately with the commissioning engineers, none of them remembered they did the bubble test and telling me that was overkill. We all agreed that the Category M was specified correctly for those fluids.

How do you think?

 

[bulkhandling]

My question is do you think if my understanding is right or not. What is your experience what facing a Category M test?

 

[JohnBreen]

Hello,

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[AndyChE]

Sorry to dredge up an old thread, but I think the question still remains:

For a piping system that has been classified as Category M fluid service, is both a hydro test (or pneumatic test) AND a sensitive leak test required?

I read all the threads listed and didn't see this addressed. ASME B31.3 interpretation 20-48 says that both a sensitive leak test and a hydrostatic/pneumatic test are required, but this doesn't make sense to me especially if you are doing the sensitive leak test first and then following it up with pneumatic test.

Is this double test the committee's intention or am I and bulkhandling reading this incorrectly? (Apologies as this probably belongs in the ASME Issues forum.)

 

[vpl]

AndyChE

Wouldn't the sensitive leak test be done at a lower pressure? So, the hydrostatic test is done to make sure that the tank will not suffer a gross failure if it is overpressurized and the leak test is done to make sure there aren't any small leaks of the Class M fluid.

And if there is an official ASME Interpretation, then that is the official ASME answer.

Patricia Lougheed

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[AndyChE]

Thanks for your thoughts. Provided that the test temperature is below the design temperature and you don't overstress the pipe the test pressure is at least:

150% of the design pressure for hydrostatic leak test
110% of the design pressure for pneumatic leak test
25% of the design pressure for a sensitive leak test (or 15 psi whichever is lower)

The hydro and sensitive state specifically "at least", but the pneumatic states "shall be". But I would assume that you could test at a pressure higher than that.

So if you ran a pneumatic test at 110% of the design pressure I would think that would cover both. Here is the link to the interpretation (it is 20-48 and it is on page 49 of the PDF):

http://cstools.asme.org/csconnect/pdf/CommitteeFiles/19338.pdf

 

[vpl]

AndyChE

The subject of doing pneumatic versus hydrostatic has been addressed several times on Eng-Tips. You might want to look at them. There are concerns about personnel safety associated with them.

Personally, I'd do the gross failure first and the sensitive leak test second; especially if you are using a fairly expensive gas for the sensitive leak test. Also, if you decide to do only one test, don't be surprised if your local jurisdiction tells you to do the second one anyways.


Patricia Lougheed

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[pipexp]

Correct me if my under standing is wrong. What I understand is that 150% of the design pressure for hydrostatic leak test is done to check that the system will not fail in the event of over pressurisation. In piping system there are specification break in the the piping i.e. that is like #600 class piping syatem may be connected with #150 drain system. During hydro test at 150%, the two system must be separated by blinds in between the two system. After hydro-test the blinds in the system will be removed and whole piping system should be tested with 25% of the design pressure for a sensitive leak test (or 15 psi whichever is lower). This is the justification of hydro-test and senstive leaktest.

 

[fxcostac]

As i see them both are necessary, as you deal with an M classified is important to guaranty both soundness and stress resistance that may appear to be the same but not always are the same.

 

[SJones]

I'm with pipexp. Perform the leak test on the finally assembled system after hydrotesting. Not only are test pack sections separated but items such as valves and instruments are left out of the test sections to protect them. The valves and instruments then have to be installed - what if they leak?

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/