Using an accumulator for thermal relief.

[dmstron]

We have liquid manifold systems that are periodically isolated. To protect from thermal expansion the systems are relieved thru a relief valve to a sump or across an isolating valve to downstream.
I am curious whether anyone has used a hydraulic accumulator for this purpose.

 

[btrueblood]

It can be done. Whether or not it would be wise, is another decision to be made. Among the what-if cases, leakage of the accumulator charge (for a gas-type accumulator) is the one that would worry me; you would have no expansion volume left (piston/bladder up against the wall) to absorb the thermal transient, and no way to know this without inspection/maintenance (which leaves room for error). That said, it might be helpful as a backup system to what you are doing already.

 

[dcasto]

A 1/4" to 1/2" check valve across an isolation valve is what I always recommend.

 

[BigInch]

Which way do you point the check?

http://virtualpipeline.spaces.msn.com

 

[dcasto]

out of the blocked in segment. We also assume that there is no way you can have thermal overpressure on a buried line of if there is 3 feet of buried line per foot of exposed line.

 

[BigInch]

I really never seen this. A check would kinda' defeat the purpose of having an isolation valve, no? Do you mean a relief valve across an iso valve? I think I've seen that once or twice. What about 2 or 3 adjacent blocked in segments all exposed to thermal overpressures in a sta/plant? Isn't it better just to use a small relief valve to an HC drain or something? That's the std way as I know it. Its positive protection in all cases.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

you put the check valves around tthe block valves until you reach a point where you can't go anywhere other than to a system to handle it. The check valve has a spring that dosen't allow it to open until the line exposed to thermal heat is say, 50 or 100 psig higher than the line it is opend to.

Look, no LDARS, no wasted materials, no VOC's, no mandated inspections every 6 months, no fuss no muss.

look at how cameron valves use this principle.

http://www.c-a-m.com/cam/search/showdocw.cfm?DOCUMENT_ID=8110

componet 2c...

 

[BigInch]

I think that's when a check valve becomes a relief valve, in which case I can buy in to it.

http://virtualpipeline.spaces.msn.com

 

[sailoday28]

Can't check valves leak?
Regards

 

[BigInch]

Check valves (supposedly) only leak in one direction.


And change that 27 Oct 07 4:37 post from, "can buy into it" into "can't buy into it". Reconsidering, IMO it defeats the intent of the codes. That is a relief valve in everything, but name.

http://virtualpipeline.spaces.msn.com

 

[hydromech]

With a clean system, an accumulator would give satisfactory and safe service.

There would be no reason for the nitrogen to leak out. Depending on the working pressure, a diaphragm, bladder or piston accumulator could be used.

A bigger acc' would give bigger gaps between service intervals.

By law the accumulator has to be protected from over pressure situations, so if the precharge was lost and the acc' filled up, you would still see a similar level of protection as the relief valve took care of the extra pressure.

Cost is an issue though, as accumulator cost much more than isolation valves.

If cost was not a problem, I would go for the acc'.

Adrian

 

[dcasto]

BigInch, all of our regulators have bought into it. In DOT liquid lines PSV's must be inspect twice per year. At one facility we had 100 3/4" thermal reliefs. We switched to check valves and no problems.

In purity benzene or butadiene service, PSV's are a no no, think about it.

 

[BigInch]

I can see why you want them. Why is it that checks don't need to be inspected when they function as a relief valve? The regulators will go for it, because it is not addressed in the codes, so its an apparent loophole.

Benzene is pretty much the same as gasoline, for which we run relief valves to a closed HC drain both in the surface and the underground facilities.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

You still need to have your check valves inspected, but on a 2 year rotation or longer. The whole thermal relief scenerio is a real one, but in reality, most valves will leak the drop it takes to relieve the pressure. So I look at it as double jeopardy, the valve has to not leak and the check valve has to fail to get into an overpressure situation.

On our pipelines, we don't have a closed drain system and at the delivery points the customers won't let us tie into their's. Now what. Can you buy into them now?

 

[BigInch]

In the refineries we couldn't tie into the owner's HC drains, or any other system. We built our very own. The only thing we could use was their security system, since we were inside the big fence anyway.

http://virtualpipeline.spaces.msn.com

 

[budt]

What is the system pressure when operating?

What do you want to limit pressure to when isolated?

What is the typial and/or maximum volume from expansion?

How many positions need this protection?

What is min/max operating temperature of the atmosphere
the accumulator must operate in?


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING