DIB-1 ball valve pressure relief device

[TransMech]

Dear Senior,
I have a question regarding to DIB-1 ball valve external pressure relief device, due to thermal pressure expansion we have to install external pressure relief device for DPE ball valve in liquid service.

The code of ASME B 31.3 section 322.6 which defines that the pressure relief device shall be in accordance with BPV code, that being said, the check valve which usually to be installed on external pressure relief device is not permitted, the check valve is not certified pressure relief device by code.
but I read the code of ASME B31.1 section 107.8.3, which says ASME code stamp and capacity certification are not required on nonboiler external piping.
Does anyone has this kind of recommendation or directive on this?
Very appreciate in advance!

Regards

 

[LittleInch]

The section you refer to in 31.3 is essentially about pressure relief of piping systems, but the devices need to be in accordance with BPV. This does not mean that the Pressure relieving device needs to inspected and approved by an ASME inspector, just that it is designed and built to that code.

I don't know what you mean by " the check valve which usually to be installed on external pressure relief device". I can't recall seeing a check valve in a relief system. Please expand on what you mean by this - a sketch or diagram would help....

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[valvit]

I presume you are building a valve to API 6D, since you are referring to DIB-1. For now, B31.3 makes no reference to API 6D as an approved valve standard, but ASME committee are including it for B31.3-2015 revision, so thats good news. Also note the title of 24th Edition of 6D now includes "Piping Systems" to align with B31.3-2015.

B31.3, B31.1, B31.8 are all piping codes. The pressure relief design must protect the entire piping system and all associated fittings, and is the responsibility of the piping engineer, not the valve manufacturer. This means that the check valve (pressure relief device) you are installing on the ball valve, is outside the scope of the requirements of B31.3. Meaning, your device is not intended to protect the entire piping system, just your ball valve while. Depending on whether or not the valve ball has a pressure communication hole or not, the ball valve pressure relief system may only need to protect the valve while in the closed position. Valves with a pressure communication hole, are protected by the piping pressure relief system, when the valve is in the fully open position, valves without a pressure communication hole are not.

With current environmental regulations, and end-user specifications, it is rare that the valve pressure relief device is permitted to relieve to atmosphere. I strongly advise you ensure your client is aware of how your valve relieves pressure, and in what operating condition the relief is possible (i.e. valve open, valve closed, temperature change, fluid expansion due to temperature change) so they consider this in their overall design. If DPE x DPE is required, then a method of piping off the fluid ejected during a pressure relief event may be required. An easier solution may be to offer a Self-Relieving seat on one side, and DPE on the other (see DIB-2 in API 6D). This will likely make the valve uni-directional with a client-specified upstream/downstream preferred direction.

I hope this helps.

@LittleInch - Many ball valve manufacturers will use a simple poppet-style check valve, installed in the valve body to protect the body cavity from over-pressure due to thermal expansion of the fluid. A ball valve with Double Piston Effect (DPE) seats on both sides can trap fluid in the body cavity. If that fluid is liquid, and undergoes a change in temperature, the body cavity can see a pressure increase. If that pressure is above 1.33X the valve pressure rating, API 6D says you must have a device to relieve that pressure.

Valvit

 

[LittleInch]

valit,

I understand very well why you need a relief valve in a double DPE valve, but what do you mean by "poppet style check valve". is this a spring relief valve by another name?



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Also: If you get a response it's polite to respond to it.

 

[valvit]

LittleInch,

Yes, it is a spring relief valve. Commonly 1/2" NPT or ISO 228 parallel thread.

Valvit

 

[TransMech]

Thanks valvit and littleInch, very appreciated for your guys input. This is awesome.
The ball valves we use for oil service,which don't have pressure communication hole, because we request to verify the upper seal through body drain, pressure must be relieved back to upstream, directly connect with pipe, the concerns and issues are thermal expansion issue whatever the DIB-1 valve is close and open, which also defines by API 6D.
Those parallel thread check valve is key component for this pressure relief device, I am wondering whether it is allowed to be used for pressure relieving, or to use pressure relief valve.

Regards.

 

[LittleInch]

I think I'm getting confused by what you mean by this check valve. Can you please post a link or example so I can understand it or draw a sketch. To me a check valve requires very little or differential pressure top open it, but seals on reverse flow. You seem to use this term to mean a spring relief valve?? Or do you mean some sort of extra valve??

Do you mean that you connect the ball cavity back to the upstream side of the valve vie a check valve and piping??

That to me is not permitted as it would mean any passing of the downstream seat could very easily bypass the seat. Also the sealing of your upstream seat is dependant on one 1/2" check valve of dubious sealing properties.

For most double DPE or DIB valves the body bleed / relief needs to be piped to the drain system. A real pain, but that's how it is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.