HI Emmanuel
As you are perfectly aware we are using underground pipelines for ease of routing and keeping the temeprature rather unchanged therefore tensile and compressive stresses due to changes of temperature and pressure is a little strange.
For any reason if one is to use hot fluid through the underground pipes he can do any thing to reduce stresses!!!!!!!!!! because the assumption is that the pipe does not move otherwise it is not called underground pipelines.
For solving the problems based on my experience one should use sleeves or reducing the temperature of fluid before entering it through the pipe.
regards
Mohsen
Emmanuel Tompeter <tompeteremman@yahoo.com> wrote:
Dear Balakrishnan,
Thanks for so much for bringing an interested topic like this for discussion.
Before i contribute please explain more in details follow.
1.Transition point between the fully restrained and the partially restrained portion.
2. Which portion of the pipeline is said to be Partially Restrained portion & Fully restrained portion? ie Above ground portion and Underground. and why ?
3. you mention two major stress that act on a buried pipeline. what about longitudinal tensile stress result from combine effect of temperature and presure change?
4.longitudinal compressive stress result from combine effect of temperature and presure change?
I'll be grateful if you through more light on the above issue so that, we can discuss.
Thanks,
Tompeter,Emmanuel
> Dear Pipeline Engineers,
>
> For a buried pipeline which is Continuously in
> Fully restrained condition, the only stresses (in
> addition to hoop stress) acting on the Pipeline
> under Soil / Sand are:
>
> 1) Thermal Stresses due to Difference between
> Operating & Instalaltion Temperatures.
> 2) Poisson effect (gamma X Hoop stress)
>
> But this portion of Pipeline cannot move because
> of the soil / pipe interaction and the resulting
> resistive forces. Before going into my problem,
> please note the Design parameters which are given
> below:
>
> Service: High Pressure Gas
> Pipeline Size: 14"
> Design Pressure: 130 Bar g
> Design Temperature: 110 deg C
> (Operating Temperature: 90 to 95 Deg C ONLY)
>
> Materail of Construction: Duplex Stainless Steel.
>
> Now let us check the Virtual Anchor Length (L):
>
> We have an Above ground portion and Underground
> portion of Pipeline.There is a transition point
> between the fully restrained and the partially
> restrained portion. For the given Desin parameters
> and Soil properties we can calculate the Virtual
> Anchor Point which is the transition point between
> Partially Restrained portion & Fully restrained
> portion.
>
> Now, coming back to my Design issues:
>
> I am planning to bury the entire 30 Kilometer
> Pipeline with 20 to 30 meter above ground
> installations at either end for Launcher / Receiver
> facilities. Previously (in simillar case) we used to
> give intentional offsets / expansion loops on the
> buried route. This is to ensure that the maximum
> straight length (say L meters ) is always less than
> twice the Virtual Anchor Length (2L) and hence
> throughout the Pipeline length, it is behaving as
> Partially restrained pipe. This approach will ensure
> that the pipe is free to move in both directions
> with respect to the mid point of 2 x L.
>
> But, our client is questioning this approach.
> According to him there is no need of Stress analysis
> of the fully restrained portion of Pipeline. He is
> assuming that fully restrained pipe has ZERO
> mobility, even due to temperature difference. Also
> he is asking me to route the pipe straight
> throughout, unless there is no geographical
> requirement of offesting.
>
> Our stand is that theoreticall this concept of
> FULLY restrained portion may look fine. But we
> normally come across issues like upheaval buckling
> (vertical movement) and Snaking (Horizontal
> movement) of pipe inside buried area. That means
> Pipe has always a tendency to move within the
> trench. So we conclude that there is a need of
> frequent offests for a high temperature metallic
> buried Pipeline.
>
> I would like to get some feedbacak on this
> requirement of Offests on buried routing of metallic
> pipelines (desin Temp 110 deg C) from your
> experiences & industrial practices.
>
> Regards,
>
> Balakrishnan
>
>
>
>
>
>
> "We make our world significant
>
> by the courage of our questions
>
> and the depth of our answers"
>
> -- Carl Sagan
>
>
>
> ---------------------------------
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> here.
>
> [Non-text portions of this message have been
> removed]
>
>
[Non-text portions of this message have been removed] Received on Sun Nov 11 02:16:00 2007
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