Appropriate leak test method?

[KLee777]

I'm looking for some guidelines/rules of thumb as to what kind of leak test to specify for different piping applications. Of course, sometimes these are readily apparent due to the line's intended service and design pressures, but, for simple maintenance repairs, is there any way to determine what type of test (hydro, pneumatic, service) is more appropriate? I'm aware of the dangers of pneumatic testing - this is only used here if absolutely necessary, and always under strict requirements. I'm a little more confused about when it's OK to just service test something.

I am aware of the hydrotest requirements in B31.3, but some applications (like cutting out and replacing a leaky 3/4" drain valve in potable water service, something minor/innocuous/low pressure) just don't call for a full hydro...it's OK to just service test it. But that situation seems obvious.

Here's the problem: I'm a design engineer new to the field and I'm just looking for some simple ways to determine appropriate test methods for small maintenance repairs to piping. When is it OK to just service test something?

Sorry I'm not more clear, but I'm not really sure if guidelines like these exist or if it just comes with experience in the field.

Thanks.

 

[BigInch]

The system is only as good as its weakest weld. Makes no difference if that's on a 3/4" D or 48" D. Also makes no difference, if its water, oil, gas, or x. If its operated under B31.3, you must abide by all its provisions.

You do a tightness test before a full hydro.




"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************

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

 

[moltenmetal]

Not quite true. Under B31.3, the owner can elect to service test Category D (nonhazardous) service piping in lieu of a full hydrotest, whereas hydro or pneumatic testing is mandatory for normal fluid service and the other fluid services. So it can matter what's in the line, if the owner elects to treat it that way. If the owner does not elect to in-service test such lines, then this piping does revert to the hydro/pneumatic test provisions under B31.3.

As to what tests to specify for each type of service: the code gives no guidance on this issue. The code stipulates the minimum testing requirements based on the fluid service category and various other circumstances. Owners can choose to go beyond these code-minimum tests whenever they feel it is both safe and warranted (and as long as they are willing to pay the cost and schedule implications of this extra testing). What they are NOT permitted to do is to claim that these extra tests are "code required".

Some examples of extra testing some people use are a pneumatic leakage test (after the hydrotest) for gas services, or a sensitive leakage test (using helium) for hydrogen services. Which extra tests are specified varies by industry, owner/company and experience.

 

[KLee777]

Thank you, moltenmetal. I wasn't sure if I wasn't just missing it in the code, but apparently not. Good to know. It'll just take some time for me to learn what to do in the cases where the code doesn't provide guidance. Fortunately there are many experienced people here at the site willing to help me on this issue.

Thanks again.

 

[GrimesFrank]

KLee,
This takes a discussion with your IA.
When you refer to "small maintenance repairs to piping" are you saying replacing components or weld repairs?

In my jurisdiction we apply our 'golden weld' agreement we have with the authority when welding a sub-assembly into an existing system. Hydro the assembly then inspect (MT) & apply max operational pressure after you have tied in the assembly.

You need to talk to your welding group and your inpsection authority.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel

 

[KLee777]

GrimesFrank,

Both. Any type of repair in the field will eventually come across my desk, whether it be a weld repair, pipe spool replacement, replacement of leaking valves, etc. I work directly with the inspectors here so they are the ones giving me a little guidance as the how the test is actually carried out, but they look to me for test type, test pressure, and medium. I specify required NDE, too.

This is only a small part of my overall job, but the one I'm most unfamiliar with. Like I mentioned in my post, I come from the consulting world and feel like I'm on another planet out in the field - but it's only my 2nd week so I have to learn to give myself a break. (-:

Thanks.

 

[BigInch]

Sorry, I wasn't aware of the non-hazardous product service clause. Otherwise, I adhere to GrimesFrank's method, golden weld or rehydro the section.

"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************

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

 

[GrimesFrank]

KLee,
What you need to do is to standardize the response with an 'official' agreement with the IA. That way your field workers don't have a question about it.
In general you want to assure yourself that you have weld integrity, the easiest way to do that is independent testing methodology.
When you say inspectors, do you mean your company's QA inspectors or are you saying your state's/province's authorized inspection agency? The IA should not be looking to you, he should be stating what he would allow and you trying to push the line with technical justification.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel

 

[KLee777]

GrimesFrank,

I meant our company's QA inspectors. They come to the engineer for test requirements. They're very experienced so they usually know how we do things on-site, but the decision is still mine in the end. That's what I meant when I said they are providing me with a little guidance.

When you mention the IA, exactly who are you referring to? We may have contact with this individual but I may not fully understand his role as yet. It's hard to keep up with everyone out here. It will take me a while to understand the organizational structure.

Oh, it might help to know that I'm working in an oil refinery. Not sure I mentioned that before.

 

[MJCronin]

My two cents...

For new construction projects, large engineering companies frequently issue internal guidelines that address these issues on a "system by system basis".

This is usually summarized in a document issued by the engineering company called "Piping Pressure Test Specification". Based on the engineering company's familiarity with the AI's requirements, it meets the AI's needs.

A "pressure test code" referencing a specific test for a specific pipe is usually part of the piping line list

When you work for the owners of a refinery or process plant, you frequently find that this kind of important document has been discarded long ago by the plant's MBA owners....

My opinion only...

-MJC

 

[GrimesFrank]

KLee,
Your state safety inspection authority, or I guess in the US your insurance carrier's inspection authority. The gov't body regulating your pressure vessels and systems.

Your company's internal inspectors only do what they are told...the gov't's inspectors 'interpret' what the regulations and statutes want, to insure you are operating a 'safe' plant/refinery.

Here in Ontario Canada we have the TSSA. I know in the US you have the National Board of Boiler Inspectors.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel