3 replies to this topic

[A mukherjee]

Hello friends,
I have two queries which are not connected at all.

1.Why API 526 does not accomodate safety valves of inlet nozzle size of 3/4".(it starts from 1")

2.In cryogenic plants,a positive pressure is maintained in the cold box by continuosly purging it.Now a breather valve(set pressure 5 mbar(g)) is present at the top of cold box,which will vent excess purge gas.Can any one guide me about sizing of this breather valve?

Thnxx in advance,
Arpan

[fallah]

Hello friends,
I have two queries which are not connected at all.

1.Why API 526 does not accomodate safety valves of inlet nozzle size of 3/4".(it starts from 1")
Because API 526 covers Flanged Steel PSV and below 1" nozzle size the valve connection would be as NPT.
2.In cryogenic plants,a positive pressure is maintained in the cold box by continuosly purging it.Now a breather valve(set pressure 5 mbar(g)) is present at the top of cold box,which will vent excess purge gas.Can any one guide me about sizing of this breather valve?

Thnxx in advance,
Arpan

[A mukherjee]

Thanxx fallah for your reply.
Any reply for question(2)?

[Lowflo]

Question 1: API 526 was originally written for the refinery industry to standardize the mechanical design, dimensions, and orifices (D-T) for PSVs. The range of body sizes was selected based on the sizes typically used in refineries. PSVs with inlet sizes less then 1" are seldom used on process vessels. There are many non-API526 PSVs that are code certified. They are available in large and small sizes, threaded and flanged connections.

Question 2: Size the breather based on the scenario that results in the largest orifice. In this application the supply pressure of your purge gas is obviously higher than the MAWP, so that is one source of overpressure. Check to see if there are others.