Non-ASME Relief Valves

Legally, no. Just be sure the device relieves all your credible scenarios.

Good luck,
Latexman

Parimaldesai,

Granted you see the 3% and 10% rules associated with ASME equipment but these rules are also related to the type of relief device that is used.

Without knowing what you mean by a non-ASME relief device, it is impossible to offer any advice about the inlet and outlet line loss requirements for that device. You will get better response if you identify the type or make and model of the device.

Regarding spring loaded type relief devices used on ASME pressure vessels, the basic reason for the 3% inlet pressure loss rule is so that under flowing conditions, the pressure at the relief valve does not fall below the blowdown pressure and cause the valve to reseat. The 10% outlet loss rule is so that under flowing conditions, the builtup backpressure at the relief valve does not exceed the allowable overpressure for the valve and cause the valve to reseat.

In general, I can't say that I've seen anything like the 3% inlet/blowdown rule to apply to relief devices other than the spring loaded type used on pressure vessels. However, for other type relief devices it will likely be necessary to fully account for the inlet line loss when determining the capacity of your relief device.

As for the 10% outlet/builtup backpressure rule, I think the general intent applies to all relief devices that are not of the balanced or pilot operated type. In other words, your builtup backpressure must always be less than the amount of overpressure used to size the device.

With the low set pressure and MAWP that you have indicated, vapor relief will not be sonic through the relief device if venting to atmosphere and you will need to fully account for backpressure at the relief device when evaluating its capacity for either vapor or liquid relief.

As additional comment, not knowing what you mean by a non-ASME vessel, it is not clear that you would be allowed to set the relief device at the MAWP of the vessel. You may need to have the set pressure of the relief device such that it can meet the required relief rate without exceeding the vessel MAWP. In other words, you may be required to have the relief valve set pressure lower than the MAWP.

EGT01,
I'm sorry about not posting the details on the relief device.
Its a Fisher Controls Type 289H spring loaded throttling relief valve with 1" X 1½" size & is set @ 2 psig. It is protecting the Trough(Non-ASME, NO Code "U" Stamp) of a TorusDisc Cooler.
The MAWP of the Trough is 2 psig @ 270ºF.
The RV is on the Air Line to the Trough of the Torusdisc cooler.The flow of air in the cooler is to remove any water vapor that may be released during the cooling process.
The RV is installed after a Fisher Type 730B regulator (orifice ¾&quot. The 289 Series PRV's are used downstream of pressure regulators to protect the downstream system from overpressure. The Regulator reduces the Air pressure from 30 psig to 2 psig.
The relief device sizing case is the failure of the Regulator.
I checked the ASME & API codes to see if there is anything mentioned regarding the 3% & 10% Piping pressure Drops for non-ASME certified relief devices, but didn't find any specifics.
I hope the above details complete my question & are helpful for you to help me with my question.

thanking you in the meantime,
Parimal

Parimaldesai,

Based on the extra details you gave my reply is still no, the 3% and 10% rules do not apply. You do need to calculate the pressure at the inlet of the 289H based on the flow expected. If it has a pipe-away (I don't recall on the 289H), you need to back-calculate the pressure at the outlet of the 289H based on the flow expected. This will give the dP the 289H actually sees, which should give the flow from it's graph. I believe it's an iterative calculation, but very straightforward.

Good luck,
Latexman

Parimaldesai,

If you don't have a Fisher product catalog you may want to pay a visit to their website.

Better yet, contact a local supplier, I'm sure they will be glad to assist.

You may want to give additional thought about the selection of setpoints. Regulating the air supply from 30 psig to 2 psig and having the relief valve set at 2 psig will likely result in unnecessary venting through your relief valve.

Also, you should verify that it is acceptable for your trough to exceed MAWP since, with your relief device set at MAWP, it will require some overpressure (or pressure buildup as Fisher calls it) to achieve a flow. Actually, it seems somewhat odd that your operating pressure is equal to your MAWP, that leaves little room for error.

I think you are going to have to look at the entire design Parimaldesai.

As ETG01 said, you can't really set your overpressure regulator at 2 psig if you are controlling the air to this piece of equipment at 2 psig with an MAWP of 2 psig. Plus, although I don't have my Fisher catalog here, you might want to check the capacity curves of that regulator. Some of those have a significant droop associated with their operation meaning you will need a higher inlet pressure (perhaps much higher) than 2 psig to get your necessary flow through the regulator.

The 3% and 10% rules do not apply to a regulator. However, any inlet and outlet pressure loss will affect the capacity of the regulator and can increase the actual pressure in the equipment being protected before you get the required capacity. You need to look at the system hydraulics for a design like this.