ASME Stamped Vessels Have No Relief Devices 2

[ScottPearson]

I have several solvent storage tanks stamped at U-Stamped at 40 psig/150 F with a Conservation Vent/Vacuum vent installed on the tank. A secondary emergency manway vent is also on the tank. Typical pressures do not exceed atmospheric/ambient conditions, however I need to consider a Fire Scenario and Pump Overpressure. Vapor Pressure of the solvents at normal Temps do not exceed the MAWP. There is also not Nitrogen or purge gas connected to the tanks. The reported capacities appear to be ok for these even at the low set pressures (4 oz vent -6 oz hatch) The problem I see is that these devices are not stamped with capacities or set pressure.

Do I need an additional Relief Valve/Rupture Disc etc to satisfy the code? Are the conservation vent and hatch all that are necessary or is an ASME certified relief device at a stamped capacity required? i.e. do all ASME Stamped vessels need Stamped/Certified Relief Devices on them even when they are typically run at conditions much less than what the MAWP is on the vessel? And, can these be set at pressure below 15 psig?

 

[jte]

Scott-

Per VIII-1 UG-125 you need a pressure relief device which complies with UG-125 through UG-137. Markings on valves are addressed in UG-129 and include, among other things, set pressure and rate. So it sounds as though you do need to add another valve.

You may set the set pressure however low you want - the Code only sets upper limits on opening pressure and pressure in the vessel while relieving.

One workaround for you may be to keep your existing setup for everyday protection and add a valve which complies with the Code at the 40 psig MAWP for your extreme scenarios. 'Course for your Code calc's you cannot take credit for the other non-Code devices. Might be able to use a smaller valve that way.

jt

 

[EGT01]

Vessel design is not my expertise but I wonder if this is one of those situations where the required "design pressure" was less than 15 psig but you procured a Section VIII code stamped vessel anyway. Then because of the minimum fabrication requirements you ended up with a vessel with MAWP of 40 psig.

I don't know if that is ScottPearson's situation and I hope this doesn't deviate too much from his post but it makes me wonder about the obligations of procuring a Section VIII code stamped vessel when you never needed it to be in the first place. Does that mean you have to maintain the vessel per code (code relief, code repairs, inspections, whatever else) even if your designated design pressure is less than 15 psig or, in other words, your intended service is never greater than 15 psig? I suppose it would make sense to do it that way but would you have to?

Anyway, even if the existing relief devices were sized following API 2000 for low pressure storage, I think that it requires the relief devices to be marked with set pressure and relief capacity (see section 4.6.2 Marking of Venting Devices).

 

[ScottPearson]

That's exactly the situation. I'm not sure why they installed ASME Vessels for what is 99.99% of the time Atmospheric (or close to Atmos) service. And you bring up some excellent questions EGT01. The vessels currently do not have spare nozzles on which I could easily add a Relief Valve or Rupture Disc. Are the code repairs, inspections etc required?

I've read UG-125 through 134 several times and have found no exceptions to not having a Stamped Relief Valve/Rupture Disc even when there is a Conservation Vent/Non-code rupture manway in place and in essence are used as safety devices.

I would guess I need to only replace the hatch with a code stamped Rupture Disc of some kind.

 

[jte]

Scott-

You can always place the PSV on the attached piping (usually piping off the top of the vessel) per UG-135. In accordance with UG-135(d)(1) you may have block valves in between the vessel and PSV provided you CSO (car seal open) them or otherwise "positively control" them so they do not get closed while the vessel is in service. Chances are that a fairly small valve set at say 38 psi on a bleeder would do the trick.

Depending on your jurisdiction, you may be able to remove the "U" stamp therby allowing your existing setup to do its job. But "99.99% of the time" isn't enough. You'd have to convince me that your existing venting would keep the pressure below 15 psig 100% of the time.

Let the flames begin!

jt

 

[ScottPearson]

Are conservation vents and hatches from companies such as Varec or Protectoseal ASME Rated? I'm not too worried about the stamp, the calcs show the sizes on the existing devices can handle the flow. Its more the marking and capacities that I'm concerned about. So, its really a question as to whether I need new Stamped relief or can I leave the existing (non-stamped) vent and hatch in place.

 

[codeeng]

If you put an existing ASME vessel into a tank service (<15 psi) I don't see why you need to comply with ASME re pressure relief. Sizing your hatch for max pump-in/out rates and emergency (fire) relief rates per API is all that is required. My opinion only.

 

[jte]

I think that to put/keep the U stamped vessel in service it needs to have a PSV regardless of the operating pressure. The PSV must be an ASME stamped device.

I see two exceptions: First, with the written concurrence of the jurisdiction and consultation with the plant's insurance company, remove the U stamp. At that point the nameplate must also be replaced/modified to indicate a MAWP less than 15 psig. The second option is to use Code Case 2211 retroactively to avoid the need for a relief device altogether. See thread292-102991

jt

 

[codeeng]

I guess you need to do what you have to do regarding registration, but the last thing I would do is install an ASME PSV. After all, what are you protecting, a nameplate?

 

[EGT01]

Conservation type vents will indicate tested/certified per API 2000. Relief devices for pressure vessels will indicate certified by the National Board and carry the UV stamp for valves and UD stamp for rupture discs. Without knowing specifics, I would suspect there is some difference in the testing since there is some difference in the construction of each type relief device and the class vessels for which they are intended.

I do see that UG-130 has a footnote that says
"Vacuum relief devices are not covered by Code Symbol Stamp requirements."
I'm not sure how that may figure into the discussion but that got me thinking, are there ASME code vacuum valves? Then I found this thread that has some interesting information that ASME has no provisions for certifying valves below 15 psig though there is reference to a "NV" stamped valve.
thread292-35470

This also seems supported by the vendor data on a Kunkle model 215V & 337 vacuum and pressure relief valves.

http://www.kunklevalve.com/catalog/KUKMC-0383-US.pdf

So it would seem that if you want relief protection below 15 psig, you are not going to get a ASME code relief valve. In that case, relief devices certified to API 2000 would seem to be as good a choice as any.

I'm still a little unsure about this as an argument but if nothing else, I'm getting the impression that to avoid any potential conflicts with code requirements, it is not necessarily a good idea to have a vessel ASME stamped for low pressure applications (<15 psi) just because the code would allow it.

 

[ScottPearson]

That's the crux of the question. Do all ASME Stamped Pressure Vessels need ASME Rated Relief Devices? In low pressure (<15 psi) applications, are non-stamped Vents and Relief Hatches (with adequete capacity) OK to use?

 

[TGS4]

As jte said, this is a matter that is best discussed with your juristiction, and your insurance company. Ultimately, it's their decision.

 

[ScottPearson]

I spoke with the state Boiler and Pressure Vessel inspection dept and they said that all ASME stamped devices need an ASME Stamped Capacity Relief device. The existing Conservation Vents and Pressure Hatch do not satisfy this requirement

So, I think we're going to talk about removing/rerating the tank instead of putting in more PSM/Inspection work and also thereby removing the U-Stamp requirements for upkeep.

Thanks for all of the input

 

[jte]

Scott-

So as I suspected, the jurisdiction requires the Code requirement for a Code stamped PSV to be maintained.

Did you speak with the jurisdiction about removing the U stamp or is that an internal discussion? I'm curious 'cus I'm building a case to remove the U stamp from some currently stamped vessels which could easily have been bought without the stamp as piping components. In the past, my jurisdiction has not permitted this approach...

jt

 

[EGT01]

Thanks for letting us know what you found out. If you don't think it inappropriate, could you tell us which state/jurisdiction that you talked with?

 

[ScottPearson]

The tanks are in Missouri and they mentioned the same thing, recertifying the tanks to under 15 psi. We've started that process already so we'll see where that goes.

The inspector asked if there were inspection tags on the tanks and I had not seen them. He than told me there are literally thousands of pressure vessels in the state that they don't know about and they have not inspected.

 

[chicopee]

You have a situation that may require only a rupture disc. Pressure rating would probably be based on a vapor pressure for a particular temperature such as 140 F. relieving capacity would probably have to take into consideration the added factor of an external fire. Basically I woulf be using the same logic required for propane storage tanks when considering pressure rating and relieving capacity .

 

[GenB]

open vessels do not need PR divices Code or non Code,
if you pressurize the vessel then you will need the protection and the min will be the MAWP of the vessel or the mAWP of the attachng piping if the piping do not have the required Valves,
in your case i would install 15 psi valves because they are cheaper, more reliable, easy to maintain,
(see conbraco ind. web site,),
the max operating pressure o the valves can be 12 psi,
If opening for valve not on the vessel, you can install it on the inlet piping attached to the vessel right after the shutoff valve (no valve shall be between the vesel and the relief valve) 'hope this helps,
ER

 

[ScottPearson]

As I stated earlier, the code states that an ASME certified relief device is necessary, this could be a rupture disc, relief valve etc. As long as it is stamped with the proper capacity

This issue is still up in the air and a decision of either recertification or adding relief has not been made as of yet. I would lean toward recertifying, if only to get out of the inspection and upkeep of ASME vessels.

 

[GenB]

Your jurisdiction probably will not bother you (yearly insp reqd) if you are at 15 psi safety,

but if you pressurize the system you need some kind of relief or as you said.- you are waiting to hurt (kill) someone if the vessel overpressures- pumping or other.
it is sad to learn of you waiting to act on this.
ER