9 replies to this topic

[kasri]

Dear All,

Please guide me how to calculate the pipeline settle out pressure from the results arrived from steady state simulation which has each node pressure profile details. also please clarify how to consider the elevation effects in the settleout pressure, for ex. settleout pressure at Pipeline start point(may be at lower elevation) and at end point ( may be at higher elevation) or vice versa.

Thanks,

kasri

Edited by kasri, 06 December 2015 - 09:58 PM.

[S.AHMAD]

Dear Kasri

 

Could you please explain the meaning of settle out pressure? My suggestion is for you to go back to basic. Enhance your understanding of Bernoulli equation.  When kinetic energy does no available the the pressure is only related to elevation.

 

That is the only comments that I have at this moment unless you let us knowmore  what is you problem and why you need to know about settle out pressure.

[kasri]

Dear Ahmad,

thanks for response. The settle out pressure mentioned here is for export gas pipeline from offshore platform to onshore .the intention of this calculation is to find the pressure(settle out ) in the pipeline when the production stops /shutdown.

Thanks

[S.AHMAD]

Based on the information given, the settle out pressure depends the modus operandy. Let say that the offfshore supply pressure is P₁ and the onshore pressure is P₂. If we are closing the offshore valve first when shutdown then the settle out presurre shall be P2. However if onshore pressure is closed first thern the settle out pressure shall be P!.Under situation that the pipeline is vented to flare the pressure shall be atmospheric. If both valve at offshore and onshore are closed then the settle out pressure shall be govern by gas law PV=nRT.

[S.AHMAD]

correction: The settle out pressure shall follow gas law PV=nRT.

[kasri]

dear Ahmad,

Thanks for the response. I had attached simple sketch to have clear understanding and proposed some calc. method as per earlier understanding.

in that calc., methodology used to estimate P4 pressure is correct or Psettle itself include all elevation effects.

If the proposed method is not correct please advice what changes required to find P4.

thanks

Attached Files

•  Model Calc.xlsx   12.69KB   76 downloads

Edited by kasri, 08 December 2015 - 12:09 AM.

[kasri]

Dear Ahmad,

Any corrections required in the calc. Please advice.

Thanks

[S.AHMAD]

Salam dear Kasri

 

When we shut-off the system ie all valves are closed the the initial pressure is the same that ia P1=P2=P3 P4,  This is because when we closed all valves it means there no flow and hence there is no pressure loss. hat means if the pressure upstream is closed first then the initial settle out pressure shall be P₄. However if the onshore valve is closed first the the initial settle out pressure shall be P₁. Subsequent pressure shall change according to temperature. If the initial pressure is T1 and the current temperature then the as per gas law the relationship (P₂/P₁)=(T₂/T₁) can be applied to determine the pressure since nR/V = constant.

 

Hope the above siple explanation is sufficient.

 

Best rgards

 

S. Ahmad

[kasri]

Dear Ahmad,

Thanks for your valuable response.

Please inform when all the valves closed , considering there is no immediate change in temp. the arrived pressure will be the PnVn/Vn. But the pressure calculated above may be true for shorter distance pipeline without elevation changes.

For ex. If  P1 is at lower elevation and P4 is at very higher elevation , the settle out pressure at P1 and P4 will be different due to higher elevation difference, even at all valves closed condition isn't? if such a case how to find pressure at P1 and P4 from the calculated pressure( Psettle =PnVn/Vn).

Please share your views.

[S.AHMAD]

Dear Kasri

 

You are right that elevation may contributes but for gases system because of very low density the effect on HP gases system is negligible you can ignore it.

You can calculate the pressure using P=density x g x differential elevation.

 

Since you know the elevation why not you do some calculation and compare with system pressure.... if the elevation is sky high probably you need to consider sky high means it is too high for example if you are designing for the gas pipeline to the moon yes you may need to include in your calculation otherwise don't waste your time... any way good idea to calculate the effect of elevation probably it was a mistake for me to ignore it in the past. For liquid yes the effect may be significant factor.

 

Hope the above short response is useful..

 

S. Ahmad