Dear Members, I need to perform a M

[Nova N]

Dear Members, I need to perform a MOC on a pressure vessel to increase the pressure relief valve setting. The new setting is below the design max design pressure of the vessel. The vessel produces CO2 during normal operation that is captured and used upstream. What parameters and equipment do I need to evaluate to assess if the change can be done safely without affecting integrity if equipment?

 

[georgeverghese]

Post us a P&I D of this vessel with associated instrumentation and controls, and the type of PSV. Also why you've got to raise the PSV setpoint; and if there is an associated increase in required relief load.

 

[Latexman]

Most pressure vessel Codes allow the PSV set pressure to be equal to MAWP or less. Unless there is a specific reason not to, sounds like it's within Code.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[LittleInch]

Any change of pressure needs to ensure that any attached component is capable and designed to accept the higher pressure.

How does the higher pressure ( what sort of difference are we talking about here?) affect the discharge flow through the relief valve / downstream temperature of the relief system and impact on the relief / vent system

Are you changing out the relief valve?
Can the valve be increased in pressure with the same spring?

In pressure vessel speak, the key is the MAWP, not the design pressure, i.e. what the vessel is stamped at.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Nova N]

Hi, thanks I appreciate the responses and will take into consideration the rating of the PSV for the change as well as look at all other attachments. Furthermore, The relief valve spring loading will need to be adjusted for the increase setting.

Also, please indicate if I am going in the right direction with the CO2 discharge pipe on top of the vessel. The pipe is an insulated pipe of 10" ID. I will need to verify that if there is a surge in pressure where normally the vent valve would open to allow CO2 release, this CO2 will now flow through the discharge pipe causing flow above normal levels. So I will need to verify the discharge piping is rated at the higher flow/pressure.

thanks

 

[georgeverghese]

With this being a high CO2 content relief, also check if the temperature downstream of the PSV will bring the gas into freezepoint territory ( for CO2 or water etc). The lowest temp you'd see downstream is when you have the minimum operating temp upstream and the minimum backpressure possible in the relief vent collection header. Obviously, also check if all the materials of construction for this PSV ( and its piping side mating flanges) is good for this new, lower relief temp.
In all cases, it is good practice for PSV vent piping to slope DOWN into the vent collection header.

 

[Nova N]

Great, thanks All

 

[e43u8]

If the new PSV setting is still below vessel design pressure, the main matter is how much increase in PSV setting you are intended to do?...because there is a limitation, say +/- 10%, to change the setting of a PSV which is to be specified by relevant vendor...

 

[Nova N]

Thanks Again, we will be talking with the vendor and checking for compliance with them.

 

[MJCronin]

Next time, post in the "Safety Relief Valve Engineering" Forum ....

MJCronin
Sr. Process Engineer