underground piping 2

[B.L.Smith]

Dear Sirs,

When stress analysis of underground piping at ambient temperature is necessary?
Is there any criteria for stress analysis of UG piping?

 

[BigInch]

Thermal loads are not the only loads.
Radial pressure expansion produces longitudinal contraction, or axial tension stress if pipe ends are fixed.
External pressure. Vehicle or other mechanical loads transferred through the soil to the pipe.
Bending stresses. Are you letting the pipe elastically conform to the trench, without cold bending it? Then that elastic bending stress remains in the pipe.
Do you have a seismic load?
Do you have settlement?

I hate Windows 8!!!!

 

[B.L.Smith]

settlement is not a problem for my case. But seismic load is exist.

 

[BigInch]

No internal pressure???

I hate Windows 8!!!!

 

[B.L.Smith]

Of course internal pressure is a sustain load for calculating pipe thickness. what is the effect of internal pressure in underground piping? The joints are not mechanical joint or coupling type and piping materials are steel , therefore I don't think internal pressure has major effect on UG analysis.

 

[BigInch]

When steel pipe is restrained, internal pressure creates hoop stress and an axial tension stress = 0.3 * hoop stress.

I hate Windows 8!!!!

 

[cingold]

I'd like to know the same thing Brad.

I'm still new to stress analysis but I've seen a lot of companies have criteria for when to do analysis and what to look for for in-plant piping. For example, if you're pipe is over X inches in diameter and over Y temperature, stress analysis is required.

For pipelines, there's not as much guidance that I can find.

 

[saplanti]

Shortly, if the content temperature and the ambient temperature are the same or close to each other and the material of pipeline is steel there is no need for the pipe stress analysis.

In case the pipeline material is GRP/HDPE or any other plastic material the pipeline expands under the internal pressure similar to the pipeline material under the differential temperature. So you need to understand the behaviour of the material under internal pressure and temperature.

Understanding of the soil behaviour and its support action in all direction around the pipeline is very important. Especially the behaviour of the soil at change of directions or bends is vital.

In general there are many contributor to the underground pipeline to check/consider. There are several books for underground pipe stress analysis in addition to the software to analyse to the required codes. You need to read the assigned code of pipeline before doing anything else.

 

[BigInch]

Saplanti, "Shortly, if the content temperature and the ambient temperature are the same or close to each other and the material of pipeline is steel there is no need for the pipe stress analysis."
I think that's a rather shortly-sighted view.

Try burying STEEL pipe 6" under a railroad track, or submerging it in 4000 ft of water, or spanning 100 ft. Perhaps you mean to say that there is no need to do a thermal stress analysis, which is kind of OBVIOUS.

I hate Windowz 8!!!!

 

[saplanti]

Biginch,

You are correct, I did not mean to overwrite your statements above and they are still valid. However I read BradSmith's statement in his request are related to the thermal expansion only. I also covered the other issues within the last paragraph in my previous post, so I did not want to touch the details since BradSmith did not provide any detail for his UG pipeline, he asked very general question.

I trust this clarifies everything for both you and BradSmith.

Regards.