API 650 Maximum Pressure Emergency Venting 1

[uscme1997]

So I am evaluating an existing API 650 tank for emergency venting (fire case). The tank is anchored, so per 3.10.8.3.b the limit on internal pressure for emergency venting is determined via F.4.1. The tank has been constructed with an ASME F&D head, with no compression ring. The equation for pressure in F.4.1 requires inputs based upon the compression ring design and slope of the roof. So I am finding it difficult to calculate the allowable pressure (since there is no compression ring). Any help out there for this case?

 

[bimr]

If the tank is an API 650 Standard, there should be a nameplate on the tank with the design pressure.

 

[uscme1997]

The design pressure is 0 psig. But never-the-less, section 3.10.8 addresses emergency venting requirements regardless of the nameplate design pressure. It requires you to calculate, in accordance with F.4.1, the permitted pressure accumulation in the tank that serves as driving force for venting during the fire scenario.

Still need some help here. Thanks!

 

[JStephen]

API-650 doesn't address design or construction of tanks with F&D heads.
If you have the details on the head and it is actually an ASME head, you can check allowable pressure using ASME Section VIII. In that case, the allowable head pressure will almost certainly be larger than the allowable uplift.
If you have the head geometry, you could check it using API-620. However, API-620 can give some unreasonable results when the knuckle radius is small, and ASME would be preferred if applicable.
In either case, that will give you allowable pressure, but not estimated failure pressure.
If the knuckle radius is small (ie, a "non code head"), consider using Detail h of API-650 as an approximation, taking the contribution of the compression ring as zero or as the area of the knuckle itself.

Also, I assume you are referring to an older version of API-650, and the requirements for venting have changed up through the years, so you may want to check if the current version is applicable or not.