11 replies to this topic

[Karthikram]

Hi

I have a clarification for psv tube ruture scenario.

Iam checking a psv sizing for the tube rupture scenario in a cooling medium network. Currently the cooling medium system is designed for 200 psig including expansion tank. Set of Psv's are provided in the supply and return line and it is designed for tube rupture scenario for one of compressure discharge cooler. Also the psv is provided in the expansion tank for fire case. Here the cooling medium system is liquid fill system.
As per client,the psv in the header to be sized coŕresponding to liquid volume flow of cooling water at psv releiving conditions equal to gas relief rate(Gas volumetric rate). This is required because the expansion tank gas space will not be enough to cover the volume dispcement from compressor cooler upto expansion tank during tube rupture.

Is there any requirement as per API?

Do we really need to size the PSV for cooling water volume flow?

Please advise

[fallah]

Karthikram,

 

Please upload the sketch of the system you described...

[Bobby Strain]

It's even worse than you think. And, it's worse than your client thinks, too. It appears that neither you or your client has sufficient experience to design a safe system. I would look for expert help; and you won't get that for free.

 

Bobby

Edited by Bobby Strain, 12 November 2015 - 11:01 AM.

[Karthikram]

Karthikram,
 
Please upload the sketch of the system you described...

Thanks for your reply.

Here the psv in the supply header has been moved down at inlet of water inj. Pump coolers as it is designed for 150 psig. Psv in the return header and psv at the inlet of water injection pump is designed for tube rupture scenario.

Do we have any problem in cooling water displacement during tube rupture.here the expansion tank can not cover the volume from cooler upto expansion tank.

Is there requiremeny as per API


Please advise

Thanks,
Karthik.

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[Karthikram]

Dear fallah

May i know your feedback for my queries.

Thanks
Karthik

[fallah]

Karthik,

 

Please provide the detail of design and operating pressures of shell/tube sides of heat exchanger...

[Karthikram]

Mr. Naser,

 

Thanks for your feedback.

 

Shell side (cooling water): Operating @ 85.3 psig & Design is 600 psig

Tube side(High pressure gas): Operating @1016 psig & Design is 1375 psig.

 

Here I have explained in detail,

 

The PSV is provided at the exchanger which is set at 600 psig & designed for tube rupture case whereas the Cooling Medium(CM) network is designed for 200 psig. Hence additional PSV’s are provided at the supply and return header and both was initially set at 200 psig.

 

However the one of cooling medium user(water injection pump cooler fittings etc) is designed for 150 psig. So we have the moved the PSV in the supply header to the suction of water injection pump cooler and changed the set point to 150 psig to prevent from tube rupture scenario and this PSV can cover the relief rate due to tube rupture. It was accepeted before.

 

The problem here is the water injection pump cooler is located at lower elevation, so the PSV at the inlet of water injection pump(CM supply line) will always pop up first and PSV located at the return header will not pop as it is located at higher elevation (elevation diff. pressure is 30 psig) and also set @ higher set pressure (200 psig). Earlier we assumed that the PSV in the return header is an additional one and it was not recommended to change set pressure and location at this stage and we left as it is bcs PSV in the supply header at the inlet of water inj. Pump can cover tube rupture scenario.

 

The expansion tank cannot cover the liquid volume displacement from the Cooler upto expansion tank, so the liquid release is expected at the PSV’s. As per client, the PSV in the supply/return header to be sized corresponding to liquid volume flow of cooling water at psv releiving conditions equal to gas relief rate(Gas volumetric rate).

 

PSV’s located at the expansion tank, supply /return header is not sized for the Liquid volumetric flow rate which is equal to gas relief rate. Is there any requirement as per API?

 

I am thinking of the following,

 

PSV at the return header will not pop-up and set pressure of this PSV to be reduced based on elevation and also to match up the set pressure of PSV at the inlet of water inj. Pump.

Liquid release is expected at the PSV in supply header as it is located at lower elevation.

Only the volume displacement from cooler upto PSV to be considered. Also locate the PSV's as close as possible to the cooler.

Add additional PSV’s if required.

 

 

also I have checked in other projects where liquid displacement is considered when the high pressure gas is on the shell side.

 

Please share your experience

 

Thanks,

Karthik.

[Karthikram]

Dearfallah

May i know your feedback on this issue.

Thanks
Karthik

[fallah]

Karthik,

 

Your complicated and developed description of the system along with the limited info you provided causes the problem couldn't be completely recognized.

 

Anyway, please let's know why the PSV on the shell side, for tube rupture case, has been set at 600 psig while due to low operating pressure of the shell side (85.3 psig) it could be set at 150 psig; i.e. the design pressure of the weakest point in the network...at this conditions there would still be a considerable difference between operating pressure of the shell side and relevant PSV set pressure (85.3 psig and 150 psig)...

[Bobby Strain]

You need to research the subject. Relief valves will not prevent significant overpressure. You have a very dangerous situation, and you continue to ask questions about relief valves. Relief valves are totally ineffective for overpressure protection in your system. You can only hope that you never have a tube rupture. But this is not good engineering practice. With a bit of research, you will understand the magnitude of the problem. Then you can ask the right questions.

 

Bobby

[Karthikram]

Dear All,

 

Thank you so much for your response. And sorry about my complicated description.

 

To be frank, I was not in this project during the detail engg. phase and I could not able to figure out the exact reasons for PSV set pressure, PSV location, design pressure of water injection cooler etc 

 

Could you please clarify some general query listed below about high pressure gas on tube side and low pressure fluid(cooling medium) is on shell side &  is liquid-fill,

 

1. Is there any requirement in API saying that PSV to be sized for liquid volume flow at PSV releiving conditions equal to gas relief rate(Gas volumetric rate) if there is an insufficient space for lquid displacement in Cooling medium piping and expansion tank. .

 

2. Can the high pressure gas from tube rupture push the massive liquid on shell side. As per my understanding Gas will push some liquid at the beginning to create a gas path for release. Then it will be mostly gas. Some amount of liquid may carry with the gas. But liquid relief is not significant. The same procedure has been followed in my previous employer.

 

3. As per API 521, "It may be necessary to locate the relieving device either directly on the exchanger or immediately adjacent on the connected piping. This is especially important if the low-pressure side of the exchanger is liquid-full. In this case, the time interval in which the shock wave is transmitted to the relieving device from the point of the tube failure increases if the device is located remotely. In addition, there is a time delay for the gas to overcome the momentum of the liquidfilled low-pressure side prior to establishing a full flow through the relief path. This can result in higher transient overpressure on the exchangers before operation of the rupture disk or relief valve".

 

Whether the abve API description is applicable irrespective of location of low pressure and high pressure fluid in the exchanger. Please confirm

 

I have seen in couple of projects where the RD is installed directly on the exchanger to prevent from tube rupture.

 

In my case, PSV 's are provided at the exchanger to cover the tube rupture scenario but it is not set at 150 psig (design pressure of weakest point). However additional PSV's are provided closer to weakest point and set at 150 psig & designed for tube rupture scenario, but it is located far away from source of tube rupture.

What will be effect of tube rupture in the above case?

(This project is already in end of contruction phase, so we are not allowed to change anything at this stage)

 

Please let me know your feedback.

 

 

Thanks,

Karthik.

[Bobby Strain]

You still don't understand the magnitude of your problem. Nothing in your questions indicate that you are doing anything to prevent possibly rupturing the low pressure system from a tube rupture. And you seem to refuse to do any research on the subject.