Inlet Pressure Drop for Emergency Relief Valve
Inlet Pressure Drop for Emergency Relief Valve
(OP)
Hello, I would like to know if the 3% rule still applies for pressure relief vent protecting a tank under code API 2000. I have a filter weigh bin with pressure relief vent set at 0.625 psig (MAWP of equipment is 1psig). As per vendor (i.e. GROTH), this valve opens fully at 100% overpressure (OP) (i.e. double the set pressure). However, 10% overpressure is enough to cover the required capacity. Since my fluid is vapor, if I consider 100%OP, I have to used the rated capacity of the valve at 100%OP which results to more than 3% inlet presssure drop because of the entrance loss from te filter to the pressure relief vent valve. Actually, even the 10%OP gives me more than 3% inlet pressure drop. My question is, I wonder if the 3% rule is applicable for this valve. Valve is model # 2300A Groth vendor. The blowdown for this valve is 8%. I am worried that I chattering may occur if I have more than half percent of the blowdown. At the same time, I am not sure if the 3% rule for ASME coded equipment is applicable for API2000 vessel. Thanks and I appreciate your input.





RE: Inlet Pressure Drop for Emergency Relief Valve
API 650 tanks have no overpressure allowance. If the tank is designed for 1 psig, your relief device must be set low enough so that it passes the required volume without exceeding the design pressure. API 620 tanks are allowed a 10% overpressure but I don't recall seeing any inlet line loss criteria for either tank specification.
The 3% for ASME code vessels was based on historical blowdown settings being in about the 7% range. By limiting the inlet line loss to 3% or less, you avoided chattering in the relief valve due to excessive inlet line losses (you can still get chattering with a properly sized inlet line if the relief valve is oversized for the vapor flow to be relieved).
Interesting, I don't recall blowdown % on any tank vent valves I've looked at in the past.
You know the capacity of your Groth valve and you know the vapor flow to be relieved. If that only requires 10% overpressure when the valve is set at 0.625 psig and the tank design pressure is 1 psig, your are fine. Why are you looking at the hydraulics at 100% overpressure? Are you thinking along the line of PSV's inlet and outlet piping being evaluated at the relief valve's capacity?
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
Piping pressure drop can't cause these devices to chatter, but it can result in the tank exceeding its max allowable pressure. If the device is mounted directly on the vesel nozzle, then piping pressure drop isn't significant and can be ignored. If you have piping between the vessel and the device, or any significant backpressure cause by pipeing, scrubber, etc, then that pressure drop can result in the vessel exceeding it's allowable pressure. The set pressure needs to be adjusted to account for that.
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
Good luck,
Latexman
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
Good luck,
Latexman
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
Good luck,
Latexman
RE: Inlet Pressure Drop for Emergency Relief Valve
RE: Inlet Pressure Drop for Emergency Relief Valve
Good luck,
Latexman
RE: Inlet Pressure Drop for Emergency Relief Valve