Pressure testing a modified gas line

[jgibbs22]

Hey Everyone:

I have a 4" Natural gas line feeding a facility. I need to add a 4" earthquake proof valve to the line by cutting out a section of straight pipe and welding the valve in with slip on flanges. My question is does ASME B31.1 allow me to waive performing a pressure test on the addition of this valve to the system? Can I just PT and perform a visual weld inspection?

Thanks

 

[jgibbs22]

Sorry, I meant B31.8, not B31.1!

 

[XL83NL]

B31 codes are for new construction - you obviously have an alteration/modification

 

[jgibbs22]

Xl83NL

Thanks for the reply. What should I use as governing go-by for this alteration?

 

[zdas04]

I'd weld it to API 1104 with a qualified procedure, x-ray all welds, and have a qualified welding inspector visually inspect, document the "minor repair" and get on with my life.

There is no requirement that I can find to retest the line (so you are not "waiving it", it isn't required), especially not for two stinking welds.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[jgibbs22]

Zdas04

Thank you for the response, I will look into API 1104. Is there a method where I would not have to pressure test or X-ray, and could just do surface type examinations? Or am I out of luck there?

 

[BigInch]

B31.8 is not always the last word. You may not only be looking at B31.8. Is it a US regulated gas pipeline? If so, see the CFRs Title 49, Part 192

you must get smarter than the software you're using.

 

[zdas04]

49 CFR 192 has a section called "Testing of Repairs" (192.719) that requires you to static test the piece being inserted (can be done prior to installation) and visually inspect and NDT the tie in welds. I can't find anything that says you have to re-test the line.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[BigInch]

Right. Welding and inspection would not be sufficient. Retest the line, no; as long as the new items being inserted have been tested.

you must get smarter than the software you're using.

 

[LittleInch]

31.8 841.3.1 Testing after construction allows for no pressure test for welded tie-in components thus

The circumferential welds associated with connecting
pretested assemblies, pretested repair pipe
lengths or sections and welded tie-in connections not
pressure tested after construction shall be inspected by
radiographic or other accepted nondestructive methods
in accordance with para. 826.2.

To me there are a few curious points in this post

1) What exactly is an "earthquake proof valve"?
2) what happens if the pipe is not earthquake proof?
3) Why are you using a slip on flange which is difficult/impossible to RT and requires as much room around it as a WN flange??
4) what is "PT"?
5) to me and probably any inspector or safety official, an un tested weld needs to have as much NDT as you can find - X ray, UT / dye penetrant and visual is not uncommon for tie-in welds which is basically what this is. If you look carefully, this is also what BI and zdas04 are saying.
6) you seem to be trying to do this on the cheap and avoid testing. That's all fine until the next one you do leaks after installation, gas escapes and something blows up - maybe you! Don't mess around with gas it's not worth it. If an incident occurs and they find out you skimped on the testing to say a couple of dollars you won't be financially independent for very long....
7) Has the line been designed / checked for strength to accommodate this new probably fairly heavy valve?
8) what pressure are we talking about here?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way