16 replies to this topic

[fedi.abdeljawed]

Currently we experienced an pressure increase in pipe initially filled with butane at  an operating pressure ~ 7 barg. After each export of Butane we have a valve at the tie-in point with our local costumers to be closed. Thus due to solar radiation these trapped volumes start increasing to reach ~ 70 barg where a manual venting is required as design didnot consider thermal expansion for this pipe segment. 

 

The question here if butane can reach these values or there is an issue with its purity as it exceeds critical properties .  

  

[latexman]

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Yes, liquid butane can reach tremendous pressures when trapped and heated.  This is normal behavior.  A TRV should have been provided.  To releave the pressure a very small quantity of butane will need to be released, or you can "pop" a TRV around the valve on the supply end back to the tank, or at the customers end, if they have a tank.  The quantity is so small there's no need to worry about it's value.  Follow your jurisdictions environmental rules/laws, if any.

[breizh]

Hi,

Consider this link to estimate the coefficient of expansion of butane .

Edit:  new link

https://www.csb.gov/...tions.pdf?16444

 

Good luck

Breizh

[fedi.abdeljawed]

is it possible to use a balance line connected to a buried pipeline where according to our records no pressure buildup is occuring and use only when shutdown mode as we export in batch mode . because we cannot install TRV is this area  

[latexman]

Well, we have no details, like P&IDs, so it's impossible to answer that specific question.  It depends on a lot of things.

[fedi.abdeljawed]

We have a pipeline with the pig receiver , then a metering skid,  HIPPS and a PCV to control PPL pressure around 16 barg . downstream PCV pressure ~ 7barg during export . total pipe length ~ 16m 4inch size. 

During Shutdown and hot days ~ 50 deg C all this path records a pressure increase 70 barg. Actually we use temporary venting with tubing  manually with available drain connections . 

the idea is to re-route this to upstream pig receiver where we have a connection available and use only during shut down thus these volumes will have expansion into PPL . i have done some TRV calculation by HYSYS the volumes shown are very small ~ 12 kg/h but i didnot understand how this small expansion can result such huge pressure values . for other products such propane with same area we did not record similar thermal expansion. 

can you support on this ?    

[latexman]

With the actual operating pressure and temperature in the butane and propane pipes, look at a phase diagram for each. Propane is probably in or near the two phase region, and butane is probably in the liquid region only. Vapor propane is compressible. Liquid butane is essentially incompressible. Pipe and fittings are extremely rigid. The liquid butane expands and the pipe will not. Pressure increases tremendously.

What information points to a purity problem?

[breizh]

HI,

To second the comments made by Latexman, consider this link to compare the properties of Butane and Propane according to their range of pressure and temperature. Butane is most likely Liquid.

https://webbook.nist...hemistry/fluid/

 

note : You may need to get a copy of API 521 6th edition to support your calculation.

Good Luck

Breizh

[PaoloPemi]

as noted by Latexman and breizh, n-Butane and Propane have different properties at those conditions,
a quick estimate : for a trapped liquid,  starting from 10 Bar.a and 30 C and final temperature about 50 C, assuming a volumetric expansion of container (steel piping) ~0.2 % and neglecting pressure expansion of container (which would require a iterative solution), the estimated final pressure with Propane would be below 11 Bar.a while > 90 Bar.a for n-Butane... including the contribute of pressure expansion of container you obtain lower values,
the model for fluid properties is GERG 2008 (in Prode Properties), you should obtain similar values with your Hysys...

[breizh]

Hi,

To add to my previous replies.

After calculation, using the reference attached and your data, I got 135 bars for Butane. 

Breizh

[fedi.abdeljawed]

So what are the possible solutions in case no TRV can be installed in this piping section . Can we use a balance line with PPL where pressure increase is not occuring ?

[breizh]

Hi,

Can you elaborate the reason why you cannot install a TRV and route the discharge to the right place?

At the end of the day, it will be your decision, you should write a MOC (modification of change) and submit to your management for approval.

 

Breizh 

[latexman]

Can we use a balance line with PPL where pressure increase is not occuring ?

What is PPL?

[fedi.abdeljawed]

PPL = Pipeline

[latexman]

Can we use a balance line with PPL where pressure increase is not occuring ?

 

Can you explain why "a balance line with PPL where pressure increase is not occuring" might be okay, but a TRV with discharge to the "PPL where pressure increase is not occuring" is not okay?

[fedi.abdeljawed]

A pipeline, approximately 15 km long, between export pumps and tie-in to storage area ,

 

As the discharge of the TRV’s to the atmosphere was not possible, and not having another independent line, 

As the end of the pipeline, in the port, is normally closed, the pressure increase in the segment closed 

Solutions:
Use of balanced bellow PRV’s.  back to pipeline 

or Use a balance line to equalize pressure between pipeline and piping segment ?

[latexman]

Being unfamiliar with a balance line, and how it works, is it manually opened to piping segment during high pressure? P&ID or sketch?

On the surface, the solution sounds promising. I prefer the balanced bellows PRVs as TRV, since I am not familiar with balance line operation.