7 replies to this topic

[axmedis77-student]

I am working on a PRV installed on a suprheater vessel ,the actual valve overpressure was 10% as per the initial sizing, however the client have decided to review the set pressure and specify an accumulation of 106% based on AS1228.  Would that be problem if the overpressure is higher than the acuumulation. And how would that diffrence affect the performance of the PSV

 

With Regards.

[fallah]

Hi,

 

Below link might help you regarding the query:

 

http://www.cheresour...tion-allowance/

[axmedis77-student]

Hi Fallah,

 

Thanks you for you quick response, I did read the link you have sent me .

My only concern is  that the valve was initially sized on a 10% overpressure and the client’s review of the set pressure with a required  accumulation of 106%  (71.5 bar) will not be achieved, as the  valve overpressure will be higher (73.5 bar) than the accumulation pressure in this case.

 

I am not sure if we will need to carry out sizing calculation to get a new valve.

 

Regards

[fallah]

Hi,

 

Please let's know the values of the PSV set pressure and vessel's MAWP.  The calculation on the accumulation and relieving pressure values which you submitted as above will result in below values for the set pressure and MAWP:

 

MAWP=67.45 barg

Set Pressure=66.8 barg

 

Then, to respect the code limitation you should set the opening pressure of the PSV at 65 barg (instead 66.8 barg) will result in the relieving pressure of 71.5 barg at 10% overpressure. I think this set pressure reduction is possible because the reduction value (1.8 bar) is within +/-5% of the PSV set pressure, but will lead to a little bit reduction in PSV capacity due to reduction in its relieving pressure.

[axmedis77-student]

Thanks again Mr. Fallah,

 

I confirm your values, the MAWP is 67.5 bar and the set pressure is 66.5 as the 10% overpressure is meant to be 71.15 bar and not 73.5 bar my apologies, also the valve is protecting a superheated steam vessel. I am still trying to figure out the effect of having this valve online with its 10% overpressure and 106% accumulations based on the client's review. My understanding is that the valve will start relieving until it reaches the accumulation pressure and then once the pressure is relieved it will start closing down, so it will not reach that level of overpressure , please correct  me if I am wrong.

 

I have contacted the valve supplier and asked them about the overpressure percentage of the valve, I am not sure if it could be lowered.

 

Kind regards

 

ahmed

[fallah]

Ahmed,

 

With 66.5 barg set pressure and 10% overpressure the relieving pressure would be 73.15 barg as i commented in below in red color:

 

 

 

I confirm your values, the MAWP is 67.5 bar and the set pressure is 66.5 as the 10% overpressure is meant to be 71.15 (73.15) bar and not 73.5 bar my apologies, also the valve is protecting a superheated steam vessel. I am still trying to figure out the effect of having this valve online with its 10% overpressure and 106% accumulations based on the client's review. My understanding is that the valve will start relieving until it reaches the accumulation pressure and then once the pressure is relieved it will start closing down, so it will not reach that level of overpressure , please correct  me if I am wrong.

 

I have contacted the valve supplier and asked them about the overpressure percentage of the valve, I am not sure if it could be lowered.

 

 Then, because the relieving pressure would be higher than the accumulation pressure, to meet the code requirement you should lower the PSV set pressure as i mentioned in my previous post. Overpressure percentage to be remained at 10% and just the set pressure decreasing will lead to a decrease in relieving pressure till to be equal to accumulation pressure.

[axmedis77-student]

Thanks MR. Fallah for your feedback and the correction ...(73.15) bar ,  I will have to propose this option to the Client as it was their decision to increase the set pressure.

 

Kind Regards

Ahmed

[fallah]

Ahmed.

 

To decrease not increase...!

 

 

Thanks MR. Fallah for your feedback and the correction ...(73.15) bar ,  I will have to propose this option to the Client as it was their decision to increase the set pressure.