Hi- I'm sizing conservation vents and emergency vents for several older API 650 tanks and need some advice. The mechanical drawings for the tanks say the MAWP is "atmospheric", but there is a noted test pressure of 2-3 psig.
These tanks are NOT API 650 appendix F tanks, so the MAWP is limited to the basic calc of roof weight / cross sectional area of the tank (or approximately 1.5 inWC every time). However, the tanks have been operated for a number of years with a nitrogen blanket at 3 inWC and the current valves are set anywhere from 28 - 45 inWC for pressure relief. So, I don't think the real MAWP is 1.5 inWC.
Is there a guideline anywhere that allows the test pressure to be used as the MAWP in the calculation for the valve size?
Thanks!
These tanks are NOT API 650 appendix F tanks, so the MAWP is limited to the basic calc of roof weight / cross sectional area of the tank (or approximately 1.5 inWC every time). However, the tanks have been operated for a number of years with a nitrogen blanket at 3 inWC and the current valves are set anywhere from 28 - 45 inWC for pressure relief. So, I don't think the real MAWP is 1.5 inWC.
Is there a guideline anywhere that allows the test pressure to be used as the MAWP in the calculation for the valve size?
Thanks!