Golden Weld for natural gas pipelines 1

[thony999]

Happy New Year all!
We recently replaced a section of a 12'' duplex stainless steel natural gas pipeline, which required us replacing a 2m spool and welding two joints.

Because of the length of the line (12km) and the volume of water that will be required, we have decided to treat the 2 welds as golden weld and carry out radiography and ultrasonic tests rather than hydrotesting.

Is there any standard that prevents us from doing this? Is there a mention of situations where we can do this in any of the ISO/API/ASME standards?

Feedback will be appreciated

 

[weldstan]

As a repair, this would be permitted under B31.3 and API 570 with approval of the Owner's Inspector.

 

[weldstan]

Provided the replacement section is pressure tested prior to installation, the tie in welds may be exempt from pressure testing if they are radiography or UT inspected.

 

[LittleInch]

B31.8 section 851.5.1 specifically allows for this type of repair, but as noted above, the replacement section needs to be hydrotested prior to insertion into the line and then 100% NDT.

ISO 13623 just requires 100% Rt or UT for tie in welds not pressure tested.

IMHO, you should use at least two different NDT tests and as many as you can which are relevant, e.g. Dye pen and 100% visual inspection during welding.

My motto: Learn something new every day

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

 

[weldstan]

I neglected to state per B31.8 in my second reply. Thanks LittleInch.

 

[racookpe1978]

Now, the difficulty for such a short "new pipe" is welding the two test flanges onto the "new pipe", then cutting them off after the hydro test to install the inserted pipe. The inserted pipe welds should not be on the same spot as the cut-off test welds => Make the test section slightly longer than the cut-out section; weld on the test flanges and test fittings, hydro test the pipe, cut off the test flanges and test fittings, prep the ends (cheaper in place than in the field - IF you know actual final lengths and gaps, ship the pipe - +++ Make sure the final length of pipe can be shipped in one piece!!! , install the pipe, fit up and weld the pipe, do the NDE, bury the pipe.

 

[thony999]

Thanks for your contributions

 

[Inspectengr]

Additionally, do include Dye Penetrant testing of the old pipe BEVEL AREAS before welding new pipe. It will a quality check and additionally, may prevent many defects in the pipe weld.

This is from experience based.
Hope it helps.
Thanks