Pneumatic test o hydrostatic one for a Tie-In??

[mgtpip]

Hi,

We are going to provide Tie-In (cold cut) presure test for a gas treating plant. We find a doubt concerning the hydrotest to apply over this Tie-In because pipes downstream we find are very long headers and it would take us too much time to test them. Would be possible and safe to apply a pneumatic test due to ASME 31.1 and ASME 31.4?. Would be possible just to do the hydrotest over the Tie-In (only including the blind, spectacle, gate vale and split tee) without doing the hole (without extraction the coupon) and then consider the complete line downstream chequed?

Thanks

 

[0707]

After performing 100% Rx to the field welds I would say yes.

 

[zdas04]

There is a concept called the "golden weld" which allows a pre-tested fabrication to be welded into place without a leak test or a strength test. This concept has been de-emphasized some in recent years, but it is still part of the mainstream thinking. The way it works is to have the fabrication either hydro or pneumatic tested and then when you install it you do an appropriate amount of NDT on the tie in welds. This always includes 100% x-ray, but it can also include dye penetrate and/or magnetic flux tests.

The key is to document your welding procedure, the welder's certification test papers, the NDT required, and all test results in your permanant project files.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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[vpl]

You might also want to check out the discussion in thread794-176703 on the same subject.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[vzeos]

mgtpip,
It depends on the code that covers your installation. Here’s what the federal code says about natural gas pipelines. It seems to fit your situation (I think the same applies to oil pipelines). As far as I know, the strength test only applies to pipe; not welds. Welds are required to be NDT.

[tt]Title 49: PART 192.505 Strength test requirements for steel pipeline to operate at a hoop stress of 30 percent or more of SMYS.
……
……
(e) For fabricated units and short sections of pipe, for which a post installation test is impractical, a preinstallation strength test must be conducted by maintaining the pressure at or above the test pressure for at least 4 hours. [/tt]

http://ecfr.gpoaccess.gov/cgi/t/tex...3.1.1.1.3;idno=49;cc=ecfr#49:3.1.1.1.3.10.9.3

 

[GrimesFrank]

In our jurisdiction, with agreement with the authority, a tie-in weld (final weld to tie in new piping to existing system) may have only an operational pressure test performed so long as a volumetric NDE was performed. The new assembly would've been hydrotested before the tie-in.

In my opinion, pneumatic testing is a "last resort alternative" to hydrotesting not an either/or, flip a coin choice.

Talk to your jurisdiction authority.

Frank "Grimey" Grimes

Rule 25. of Swanson's "Unwritten Rules of Management"

Have fun at what you do. It will reflect in your work. No one likes a grump except another grump.

 

[pennpiper]

This was the last part of your question.

" Would be possible just to do the hydrotest over the Tie-In (only including the blind, spectacle, gate vale and split tee) without doing the hole (without extraction the coupon) and then consider the complete line downstream chequed?"

Make sure you also follow "zdas04's" cmments about welds and welder qualifications.

And then, I say yes you can do this.

 

[BigInch]

I agree with Zdas and,

For pipeline work under B31.4 or B31.8 and/or CFR 49, parts 192 (Gas) or 195 (liquids), Hydrotest any fabricated assembly before tying-in. Lower and tie in the fabricated assembly, then X-Ray the tie-in welds.

Pneumatic testing cannot be done to as high a pressure as would be permitted when using water, thus the resulting allowed maximum operating pressure of the completed and tied-in assembly might be very much under the maximum allowed operating pressure of the whole pipeline. Not a good situation.

The alternative is to lower in, tie in then plug the upstream and downstream pipeline segments (with a hot tap plug or a freeze plug or similar device), then test the fabricated asssembly including the parts of the pipeline between the plugs. Way too much trouble, unless there is absolutely no other alternative.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Most common practice (and allowed by US codes) is pretested pipe, tested welders, qualified procedures, weld in pretested section, 100% xray, keep documentation, purge, put in service. I've done this on lines upto ANSI 1500, B31.3, B31.8.