Standard Document for Instrument Relief Valves

From your description I can't say I have experience with your particular situation but it may be helpful to know a little more detail.

What is the intent of your relief device, is it intended for safety reasons or just pressure control?

If it is intended for safety reasons, then what is it that you are trying to protect, what is the source of overpressure and to what codes may it have been constructed? The construction codes followed may define the allowances for overpressure protection such as in ASME Sec VIII.

Since you indicated instrument relief valve, are you are trying to protect instrumentation? If so, I'm not sure what codes may apply.

Now if what you are trying to protect conforms to the B31.3 Process Piping or the ASME Sec VIII Pressure Vessel codes, then it would seem reasonable to expect that an ASME certified relief valve is used. I don't know about Nupro, but Circle Seal does offer an ASME certified relief valve.

scooter911, The B-31.3 code applies to "Chemical Plant and Petroleum Rifinery Piping" I do belive IA drops out under this particular code and is picked up under B-31.1 "Power Piping". Check with Swagelok & Circle seal, for the standards that they use for quality control and testing. They undoubtedly will be picked up under one of the ANSI/ASME codes. It may well be your Safety Engineer has picked up std/spec. for spring material that is utilised within actual various process conditions.

Standards and specificatons are great, until they're misunderstood and missapplied.

Hope this helps.
saxon

My in house document states:
A pressure relief device shall be set within the following tolerances:
Set Pressure Tolerance:
a. Two psi for valves up to and including 70 psi.
b. Three percent for valves to be set above 70 psi.
Spring Adjustment tolerance:
a. Plus or minus 10% for valves rated at set pressures of 250 psi or below.
b. Plus or minus 5 percent for valves rated for a set pressure above 250 psi.
My problem is I have a lot of relief valves in this old NASA facility that are upwards of 40 years old and there tested every two years. Most I don't know the original set pressures, their intended ranges and the company has gone out of business.
My other main problem is that I get a Nupro or Circle seal valve with a 50-150 range from the manufacturer, I can't apply a sping tolerance to this.
I've tried to interpret these rules to our inexperienced quality folks but they read word for word what is on the paper. In order to change the paper, I need something other than B31.3 and Section VIII. Most relief valves are under 3/4 inch and have large ranges and interchangable springs to allow for any range in the MAWP of the valve. This doesn't fit the B31.3 or Sec. VIII info I have and am looking for a document that might bring some light to this.

I hope this explains it

Thanks

Scooter,
Great question! The safety guy is correct in saying the relief valves for piping systems designed in accordance with ASME B31.3 have to meet certain ASME BPV requirements.

THESE REQUIREMENTS ARE LISTED IN ASME B31.3, PARA. 322.6.3
(Please read that paragraph.)

It says the RV must comply with ASME BPV Code Section VIII, Div 1, UG-125 ... etc ... BUT!!! EXCLUDING UG-135(e) and UG-136(c) (Note: I'm reading from a 1990 edition, so check the latest edition.)

ASME BPV Code, Para. UG-136(c) requires the valve to be ASME coded, but this paragraph is specifically excluded by the piping code as I've noted above. Read UG-136(c) for the full explanation of what is NOT required for piping code reliefs.

So instrumentation RV's need not be Code stamped! That's the big difference between the piping code and pressure vessel code when it comes to RV's.

One other note, see also reliefs from Generant and Fluid Mechanics, two very good suppliers IMO. (Generant used to mfg Circle Seal valves, and still does under their own name with much better price and service.)

Sorry Scooter, looks like our posts overlapped. I hadn't read your second post before posting my reply, so it looks like I mistook what you were getting at. Nevermind...

Scooter:

The requirements for set pressure tolerances and spring resets are ASME Sec. VIII. The 10% below 250 psi is old, the limit is 5% now, but it also allows for use within the manufacturer's spring range or more provided the manufacturer approves the extended range. However, ASME Sec. VIII is intended for diameters over 6". The applications you refer to are for instrumentation. Since instrument tubing is small, this may be the reason the valves you refer to are not ASME Code stamped.

J. Alton Cox