Pipeline Overbend Stress Calculation

[Tauhooyee]

How to calculate pipeline overbend stress on the onshore pipeline during operation?
I have the problem just like after completed HDD work and tie-in with overbend to keep the pipeline profile according to requirement.
Can anyone to help to solve this stress calculation check?

 

[alchemon]

What type of stress are you concerned with? And more generally, what type of pipeline is this - size, WT, material, operating conditions, etc.? The more general question defines how the pipeline is regulated, and therefore in many cases defines what you can and can’t do. For reference if this is an onshore natural gas pipeline, it is probably regulated by CFR 192. That code defines the “maximum allowable stresses” (indirectly).

From a pure calculation standpoint - the hoop stress (which is what most people are concerned with) will be the standard equation using the thinned wall of the piping due to the cold bend. An important parameter to define then is the bend radius.

 

[Tauhooyee]

Dear Alchemon
very appreciate for your answer.
Our pipeline design base on ASME B31.4,
I would like to know the stress check at tie-in point with HDD both end during operation.
Just like a hanging point after back fill and operation at the overbend point, I am not sure combined stress should be check by what formula.

 

[LittleInch]

Needs a drawing.

Can't work out what your issue is at the moment

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

 

[alchemon]

I believe he is talking about the required overbend at the top of the HDD, which would coincide with either the entry or exit drill angle. It is really no different than any overbend - other than the angle may exceed 15 degrees depending on HDD design. I am not really a liquids guy - but what he is really asking is how to determine combined stress (hoop/longitudinal/thermal/etc) in an overbend with B31.4 fluid.

OP - we will need to know how to plan to make the bend: cold bending, induction, fitting (trimmed or not), etc.

 

[LittleInch]

Section 402 in B 31.4 applies, especially section 402.7

If the overbend is a formed bend ( either cold or hot) it has no residual stresses unlike an eleastic bend.

Which do you refer?

This is why we need a drawing and some details of this overbend

But this i just "static" stresses. you really need a stress analysis program if you've got large temperature changes

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

 

[Tauhooyee]

Dear All
Very Appreciate for all responded.
I am already uploaded the sample of the drawing.
My opinion is the pipe in HDD section look like is in the bentonite fluid and it has the buoyancy force acting to the pipe.
The tie-in point with bend (almost cold bend) is on the ground as i mention before is look like hanging.
So, What would the stress shall be check in case of design temp. 10-50 degree C.

 

[LittleInch]

In operation the bentonite solidifies.

This is a cold bend of 7 degrees.

It will be buried and supported so there is no real stress here.

It is no different than any other vertical bend.

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

 

[alchemon]

You didn’t really ask this to begin with, but your plans are drawn such that the bore entry/exit will be a combination bend (at the specified bend radius). Not really impossible to drill, but is much, much more difficult. Just FYI, I generally try to avoid combination bends in HDD, and instead draw as a true sag bend until the bottom tangent, and then extend by roughly one drill rod length, and then begin a side bend. But you may not have room to do that here.