Gas pipeline pup

[juliusochuko]

Hi All,

We are constructing a 24''Gas pipeline,at the intersection point from the other contractor,the pipeline was terminated with 90deg,sweep elbow,the ditch of the incoming pipeline has an offset of over 200meters,is it possible/code requirement to add and pup in other to aligned the Gas pipeline,and is there any code that permit such practice.

waiting on the anticipated response.

Thanks
Julius

 

[LittleInch]

I'm not sure what your question is or can understand why you have a 200 metre gap.

A drawing would help, but what's the issue here?

If you meant 200mm, then no there is no code on pup sizes. Search this site and you'll find many opinions, but few, if any, code wording. Usual guide is make adjacent welds as far apart as you can and anything less than 100mm tends to run you into trouble, but no, AFAIK, there is no minimum pup size - it all comes down to practicality.

so yes the codes permit this, but no there is no guidance on size.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

I don't allow pups shorter than 2 X pipe nominal diameter. This isn't a code issue, it is a fit up and x-ray issue. It is really hard to get a shorter pup to fit up (it will tend to expand as you heat it and you end up spending too much time fighting with it), and x-ray interpretation gets really hard if the welds are too close together. If LittleInch's assumption about it being 200 mm instead of 200 m is correct, I'd cut out some pipe to get a workable pump (it will be a lot less expensive in the long run). If he's wrong and you meant to say 200 m, then you will have something like 20 full joints in this "pup" and no problem.

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

 

[DekDee]

zdas04,
With all due respect, as a former pipeline radiographer I find your comments a bit strange.
Films are only 4"(100 mm) wide so if you have two girth welds on the same film I think the proximity of the HAZ of the two welds would be much more important than the distance between the two welds for RT review.
Even if you had two girth welds on the same film why would there be problems with interpretation ?
Regards,
DD

 

[zdas04]

DekDee,
I am not a pipeline radiographer (and I don't play one on TV). I had a short pup in a pipeline once (6 inch in a 20" line to adjust for the length of a non-standard valve) and the radiographer told me that it caused him problems with interpretation. If he said why, I either didn't understand or promptly forgot his reason. I just filed away a minimum pup length and got on with my life. I wish I had paid more attention. If you have different information, thanks for sharing.

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

 

[DekDee]

zdas04,
No idea what he is talking about - seems a very weird response.
The only problem you have with interpretation is when two girth welds are captured on the same film. (generally found more in refinery situations)
It is the interpreters responsibility to report everything noted on the film.
One weld may be a new weld (and is perfectly acceptable) and the other weld may have defects (and may be rejectable) but it is an existing weld and has been in service for 20 years.
Client wants to know why you (the radiographer) has shot something that was not requested and is now going to cost him big money while the plant is shut down to repair ?
Hope that clarifies,
Cheers,
DD

 

[racookpe1978]

It depends really on wall thickness, but "best practice" and "standard practice" and "thumb rules" sometimes conflict.

Assume "best practice" assumes a Heat Affected Zone 25 mm (1 inch) wide - from the weld edge.
"Poor practice" could assume a HAZ of 12 mm (1/2 inch) wide.

Ignore the butt weld 1/8 inch gap for a moment, and assume the pup piece length will be L.
For thumb rule convenience, assume the butt weld pipe prep is 30 degrees per side = 1/2 TWall.

So, "best practice" to avoid crossing the HAZ would be: You find the end of the HAZ from weld 1, then require the pup piece be long enough that the start of the HAZ from weld 2 does not touch that HAZ edge.

L_minimum = (1/2 Twall + HAZ_1) + (HAZ_2 + 1/2 Twall).
L_minimum = Twall + 2x HAZ.