Rupture Set Pressure for API 620 tank

[wangzh2k]

HI all,

I run into a problem on rupture disc set pressure for a LIN storage tank.

The design pressure of the LIN storage tank is
P=2 psig

I assumed MAWP (Maximum Allowable Working Pressure) equal to design pressure.

MAWP=2.0 psig

Disc rupture pressure tolerance ?P= ±50 mbar (±0.725 psi)

According to our internal set pressure specification,

Minimum Burst Pressure of the rupture disc
BP(min)=1.1×MAWP=1.1×2.0=2.2 psig (operating rate = 80%)

Maximum Burst Pressure of the rupture disc
BP(max)=BPmin+2?P=2.2+2×0.725=3.65 psig

Disc Set Pressure:
BP(nominal)= BP(min)+?P=2.2+0.725=2.925 psig

However, fabricator and system engineering want to set it to 3.5 psig.

Since I am unfamiliar to API 620 tank, any suggestion and comment to that set pressure will be greatly appreciated.


Thanks in advance, John

 

[gr2vessels]

wang,
The maximum design pressure for the API 620 tanks is 15 psi, hence the setting of the rupture disc burst pressure at around 3.5 psi is irrelevant to the tank design. Can you be a bit more specific with your query, what seems to be your problem you need help with?
cheers,
gr2vessels

 

[JStephen]

15 PSI is the maximum pressure allowed under API-620, but it is not a standard design pressure for all API-620 tanks; they are typically specced for whatever pressure is required just as vessels are.

I don't have a copy of the standard at hand at the moment, but you may need to increase the design pressure or lower the operating pressure to obtain an adequate variation for vent or rupture disk operation. You might also check what requirements API-2000 has on vent overpressure, if any.

 

[JStephen]

See Sections 9.2.1 and 9.2.2, which limit overpressure for venting and fire exposure to 10% and 20% of the design pressure.

 

[MJCronin]

wang..

I am curious....

I have seen and specified rupture discks on small pressure vessels (expecially those with toxic or corrosive contents) but almost never on API 650/620 style tanks.

How big is your tank, what liquid is "LIN" (liquid nitrogen ?)and why are you using a rupture disc instead of a conservation vent ?

-MJC

 

[wangzh2k]

First of all, I would like to thank all your messages.

MJC,

The capacity of the LIN storage tank is 450,000 USWG.


Z Wang