Storage tanks, as explicitly stated, are covered by the API 2000 Standard. Process pressure vessels are subject to the recommendations found in API 520 (parts 1 & 2) as well as to API 521. Presumably, from the relief device manufacturer’s comments regarding API 2000, it must be a Storage Tank – API 650 or API 620? That would explain why API 520 does not apply. You don’t define what type of vessel you sized a relief device for under the Fire Case. I’m going to attempt to “shed some light” on the differences between:ġ) API Standard 2000 – “Venting Atmospheric and Low Pressure Storage Tanks Ģ) API Recommended Practice 520 – “Sizing, Selection and Installation of Pressure Relieving Devices in Refineries”. I accept that I may not be using the latest version of either of the standards so may require an upgrade, but can anyone shed any light on the apparent above discrepancies? RE: API 520 v API 2000 vent sizing for fire relief cases Needless to say, I accepted the manufacturer's sizing, however I do find the differences to be curious. One other area of contention is that the conversion factor from kg/hr to scfh is curious to say the least (I supplied a kg/hr figure to the manufacturer based on Q/λ and the manufacturer converted from there - this did not tie in with API 2000's direct calculation for SCFH). It appears that they are not - API 2000 has different equations based on the heat input from a fire (It appears to be more comprehensive). However, this got me looking at the difference between the two standards - surely they cover the same ground (excluding pressure), so shouldn't they be seamless between 14.99 psig and 15 psig? As it turns out, he was right, since the set pressure was below 15 psig. The relief device manufacturer came back to me and advised that the relief device I had specified was sized wrongly according to API 2000. I recently sized a relief device for the fire case for an existing vessel using API520. I first posted this in the API forum, but didn't get any response there, so am posting it here to see if anyone who frequents this forum can cast any more light on it.

Api 2000 venting calculation software