Definittion of Volatile Liquid in API 2000

[AgsMyDude]

7th Edition of API 2000 para 3.3.2.2.1.b states that liquids with vapor pressures over 0.73 psi are defined as being volatile and therefore have out-breathing increased beyond that of nonvolatile liquids. Due to the ambiguity of "psi" and relatively low pressure specified, I am looking to confirm that they are using absolute units here (i.e. psia). Seems like it would be unusual to use gauge pressure when discussing vapor pressures but even water at 95F would be considered volatile by this definition (if they indeed mean 0.73 psia).

Thanks in advance

 

[IFRs]

I think it has to be absolute vapor pressure since if it were gage pressure the liquid would be boiling.

 

[JStephen]

The vapor pressure is the partial pressure of the product/vapor in the tank. It does not imply any particular pressurized condition existing in the tank.
For "air", you can derive partial pressures for water vapor, nitrogen, oxygen, etc., and those should add up to 14.7 psi
For water vapor, vapor pressure would be around 0.4 psi.
It is not uncommon to have a product with 6 or 8 psi vapor pressure, but in a tank designed and operated at atmospheric pressure.

 

[AgsMyDude]

Thanks for the responses. IFRs point is well made. I am still curious on how that threshold was selected (95F water is volatile??) if anyone has insight there.

 

[MJCronin]

API 2000 should be made more specific ....

MJCronin
Sr. Process Engineer

 

[IFRs]

Not sure if this is relevant but API 2000 is similar to the US EPA (see 40CFR60 subpart kb) when defining the TVP threshold for VOC emission controls. And yes - API 2000 should be fixed IMHO.