PSV inlet piping 1

[udz]

Hello,
We had relief sizing done on a vessel, and it was determined that the inlet piping exceeded the 3% pressure drop rule. One option on the table was to increase the pipe diameter, but in order to use the existing relief valve, it would require reducing the pipe from 4" to 3" prior to the inlet of the valve. Are there any pipe design codes that would prevent us from doing this?

Appreciate your responses

 

[JoeWong88]

udz,

Increase inlet line size to meet 3% pressure drop rule (per API Std 521) and further reduce it to meet PSV inlet flange is common practice. Any specific reasons you choose not do so but to find other codes to make design sort of "comply" ?

The 3% Rule is a good engineering practice and not strict and compulsory rule. If your system does not permit you to increase inlet line size, you may select a high blowdown PSV and the inlet line loss can exceed 3% as long as you maintain margin requested in API.

Hope this help.
JoeWong

 

[udz]

JoeWong88,
Thanks for the information. The current piping is somewhat constricted, making repiping difficult. Increasing the line size and reducing at the inlet of the PSV appears to be the most viable alternative.
Thanks!

 

[roker]

hello,

if you have a spare 3" nozzle you can use it for direct mounting the PSV, or use an existing 4" vapor line connected to the vessel and install the PSV on this line.

regards,
roker

 

[JoeWong88]

udz,

roker's proposal "direct mounting the PSV" may be a good idea to reduce inlet pressure loss...by doing this, you have to check if the PSV is lower than the sub/main header and possibility of liquid accumulation at the PSV discharge.

Liquid accumulation at PSV discharge leads to corrosion, severe vibration due to slugging flow and hamming in the event of PSV relieve.

JoeWong