Buried pipeline pre-upheaval stress check

[ali1000]

Dear Specialist;
I'm facing a problem of upheaval buckling of a gas buried pipeline.

In fact when doing upheaval study report , company ask to include a stress verification taking into consideration Bending moment resulting from the imperfections (0,1 to 0,5) , in order to check the most stringent acceptance criteria for the imperfection (UHB susceptibility or the actual stress).

As my understand, company ask to add pre-upheaval flexure study. But I did not found any approach or theory covering those calculations.

does any one have idea about this point?

Thanks in advance

 

[LittleInch]

Upheaval buckling is a well known issue, but has only fairly basic calculations.

~first off what sort of temperature difference are you getting?
Soil depth?
Soil type?
Number of thermal cycles before the buckling appears
Any photos??

Do a simple search on this site

https://www.eng-tips.com/search.cfm...eaval&t=&h=&searchSite=1&searchArea=1&d=1&s=1

and check out some of the other posts then get back to us if you don't get it.

Tends to be hot lines (> 60C) in sandy soils where the backfill allows ratcheting and / or poor soil cover.

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

 

[ali1000]

Dear LittleInch,
thank you for your reply

temperature difference = 70 °C
Soil depth : 1.5 m
soil type : compacted

my concern is how to estimate bending stress ,at imperfection zone, just before buckling ( pre-upheaval ).

sicenrely

 

[LittleInch]

Temperature difference of 70C you're in trouble.

This is a complicated area which is difficult to explain on an internet forum and really needs some specialist stress analysis input here.

Even at 1.5 m (cover?) you are going to get problems with expansion and upheaval buckling.

These "imperfections" - 0.1 etc - is this metres?

You really need to run this through a stress analysis program such as ceasar, but you will run into difficulties at that sort of temperature difference.

Address the temperature issue first before the pipe.



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

 

[ali1000]

1.5 m is a cover depth ,

imperfections are in meter of course.

does exist any ampirical method to do this verification? . Because in caesar stress analysis is not commom to consider pipeline imperfection .

 

[LittleInch]

Have you followed any of the posts in the search?

Try the one with the Palmer up lift calculation. Pretty basic but seems to work.

Was designed for off shore but commonly used on shore.

0.5m imperfection the pipe will come out of the ground, almost certainly.

Ceasar does handle this but you need to simulate an overbend situation.

but trust me 70 degrees C of expansion is difficult to contain in a buried pipe without some sophisticated analysis and design thought.

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

 

[1503-44]

Personally I don't think that 0.5m imperfection is a reasonable number for onshore construction. That would be very sloppy construction work. I would limit that to 0.2 - .25m maximum. Offshore is a different ball game entirely. Close tollerence is often impossible to obtain. Onshore there isn't much of an excuse for allowing 0.5m.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"