API 620 - 3rd Ed. 1965. Allowable Partial vacuum
API 620 - 3rd Ed. 1965. Allowable Partial vacuum
(OP)
In the tenth edition of API 620, 2002, the following is written in Section 5.10.5.2 under "External Pressure Limitations". It states that "cylindrical sidewalls of vertical tanks designed in accordance with these rules for storing liquids..............may be safely subjected to a partial vacuum in the gas or vapour space not exceeding 1 ounce per square inch with the operating liquid level in the tank at any stage from full to empty." One (1) ounce/ sq. inch equals 0.43 kPa.
An existing storage tank we are reviewing wasbuilt to API 620 in 1968 has a design pressure of 1.0 psig (approximately 6.9kPag). I am trying to ascertain the value of the maximum partial vacuum the tank was designed to in 1968. I'm not sure if 1 ounce per square inch was used then. I believe the third edition of API 620, 1965, was used for the original design of the tank.
I am trying to obtain a copy of the old edition through our technical library but no luck so far. Is there anybody who can advise what the allowable partial vacuum was for the early edition (1965) of API 620.
Thanks
An existing storage tank we are reviewing wasbuilt to API 620 in 1968 has a design pressure of 1.0 psig (approximately 6.9kPag). I am trying to ascertain the value of the maximum partial vacuum the tank was designed to in 1968. I'm not sure if 1 ounce per square inch was used then. I believe the third edition of API 620, 1965, was used for the original design of the tank.
I am trying to obtain a copy of the old edition through our technical library but no luck so far. Is there anybody who can advise what the allowable partial vacuum was for the early edition (1965) of API 620.
Thanks





RE: API 620 - 3rd Ed. 1965. Allowable Partial vacuum
Joe Tank
RE: API 620 - 3rd Ed. 1965. Allowable Partial vacuum
RE: API 620 - 3rd Ed. 1965. Allowable Partial vacuum
In each of the two editions, Section 3.10.5 External Pressure Limitations states "......cylindrical sidewalls of vertical tanks designed in accordance with these rules for storage of liquids..............may be safely subjected to a partial vacuum in the gas or vapour space not exceeding 1 oz per sq. inch (Note 2) with the operating liquid level in the tank at any stage from full to empty."
Note 2 stated that "The vacuum relief valve or valves shall be set to open at a smaller partial vacuum so that the 1 oz/sq. in. partial vacuum will not be exceeded when the inflow of air (or gas) through the valves is at its maximum specified rate"
So the allowable partial vacuum in the vapour space has been consistently set at 1 oz/sq.inch or approx 0.43kPa.