Buried Steel Pipeline

[ECD40]

We will be installing a 14" diameter steel pipeline with a yield strength of 42,000 psi to carry a fluid of 1.2 SG for a about 5 miles, all below the surface. How do we link the field welding procedure and inspection of the field welds to the allowable design strength of the pipe. The static pressure will be about 200 psi and the fluid will be travelling at about 7 feet/sec.
What decrease in allowable design stress is recommended for the field welding? What are the relevant pressure pipeline codes?
This must be a common problem for the oil and gas transmission people.
Thanks,
ECD40

 

[LittleInch]

Well ASME B 31.4 is probably a good start though other design codes may be more relevant to your location but you don't say where you're located.

However I don't understand your question. Welding doesn't result in any loss of strength. What are your concerns?

I would also say that designing and constricting a pressurised pipeline is a potentially hazardous undertaking and needs to be designed and constructed by people that know what they're doing. Your question does not fill me with confidence I'm afraid. There could be significant legal & lethal issues in doing it wrong.

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[ECD40]

Hello LittleInch,
Maybe I should have said my concern is the level of inspection that is performed to demonstrate that the welding does not become the weakest part of the pipeline for design purposes. I believe that it's called 'Joint Efficiency'. Full radiography should earn a higher rating than partial radiography or ultrasound. So I'm looking for the Joint Efficiency for different levels of inspection of the same weld performed to the required welding code.
Is there some table in some piping code that links these variables.
Thanks,
ECD40

 

[SJones]

Select a pipeline design code, then select an appropriate, concomitant pipeline construction code. Between them, they will detail the minimum requirements for nondestructive testing which may, or may not, be linked to pipeline criticality. B31.4 gives NDT frequency linked to pipeline location or weld type. It will be down to the pipeline owner to satisfy the regulatory authorities that appropriate inspection has been performed. This may involve specifying supplementary NDT if necessary. It's not so much "joint efficiency" as it is 'structural reliability' and value - how much does it cost to get a warm feeling?


Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[LittleInch]

There are joint factors in the pipeline codes which apply for different types of pipe, but the vast majority are 1.0

I have never heard or seen of any such table where the level of inspection has an impact on the finished pipeline.
You develop a welding specification and then test it and then apply it.
the level of inspection you give can range from typically a minimum of 10% to 100% or variable depending on test results and location as S jones states ( section 434.8.5 in B 31.4)

You then need to hydrostatically test the pipeline to ( in B 31.4) 1.25 x design pressure at the highest point. This provides a reasonably good verification that the welding and construction is acceptable.

I had to go look up joint efficiency, but it appears to be a Pressure vessel / storage tank thing which doesn't apply to pipelines. All weld metal and weld tests I've ever seen the weld metal is stronger than the parent metal. On destructive testing the break should never be in the weld metal but always the parent metal.



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Also: If you get a response it's polite to respond to it.

 

[weldstan]

You seem to be confusing design efficiency of welded pipe (material) versus seamless pipe under B31.3 and welds under ASME VIII. They are not applicable per B31.4 as stated by SJones and LittleInch.

 

[ECD40]

To LittleInch, Steve Jones and weldstan - thanks for your valuable input. The project is actually a mining project with a pipeline on surface to transport the mined product to the processing plant. We'll be sure to engage a competent pipeline contractor.
I appreciate your participation.
Over and out.
ECD40

 

[Metalero]

Hi ECD40.

You need qualified welding procedures and qualified welders. For that you must build coupons with the same pipe and welding for destructive tests such as tension and guided bending to verify and confirm that the mechanical properties of the joint are equal or major to the pipe. In addition you also shall verify the soundness by nondestructive inspection. You could support yourself on ASME BPVC Secc IX or API STD 1104.

MAV

 

[ECD40]

Hello MarriolaV,
Thanks for your input. I'll follow up on the references that you provided.
ECD40

 

[weldstan]

You could use B31.3 for your design and construction.

 

[LittleInch]

You could use B31.3 for your design and construction.

Noooooooooooo. B31.3 is a fine code but is designed for above ground PIPING. B 31.4 is an equally fine code designed for below ground PIPELINES. The OP has a 5 mile long below ground pipeline.

They might both use steel round pipes, but please use the right tools for the job. I would assume the competent pipeline designer and contractor ECD40 will use will know this.



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