Thermal Relief Sizing 1

[BoarderBill]

I have a large volume chilled water system used to cool indoor jacketed vessels. The jacket outlet piping, I believe, needs to include a thermal relief valve and I need to know what should the sizing basis be. The piping system is 1-1/2". Does this relief device need to be ASME rated?

 

[ggordil]

BoarderBill,

Is there any way that the cooling water can be "blocked in" while exposed to continuous heat input? If so you need a relief valve.

As far as sizing goes, there is an equation in API for thermal expansion. Also, there is a more accurate method in Perry's.

If your system is ASME code stamped then you need to have an ASME rated relief device.

 

[MortenA]

Would you normally size a thermal relief valve (unless we are talking the fire relif case)?

I mean - from thermal expansion there will only come very little and the sammelst size RV should be sufficient.

Best regards

Morten

 

[BoarderBill]

So maybe sizing is not required and a 3/4 x 1 is sufficient and that seems logical; I just wnated to prove it to myself.

 

[tankdude1]

bill,

we usually size Trv's but only if the locked in volume is above a certain criteria (we use site standards, the criteria is determined by the product and types of isolations ect.)

the rule of thumb that i follow is that if the locked in volume is is less than 3.2m3 relief is usually not required unless the product is anything like benzene ect. if the volume is greater than 3.2m3 for volatiles or greater than 10m3 for non volatiles then relief is probably required. anything over 10m3 will need a trv. (these volumes come from our site standards but should be fairly similar wherever)

if your locked in volume is in these regions let us know and ill help you size the trv.

if we need to size the trv, we'll need to know the solar heat gain (taken from your lattitude on the earth. i think we found this from perrys or similar.) your locked in lenght of pipework and diameters if it changes. and other info but it will be a start.

Cheers,
Tank.

 

[JoeWong88]

Do i need a PSV on piping ?

Generally PSV not required for piping... however...API STD 521 2007 Addendum May 2008, section 5.14.1 (c) stated that hydraulic expansion due to solar heating on "long pipelines" shall be assessed and checked if a pressure relief valve (PSV) is required. What is "long pipelines" ? Difficult...

This section allows that a PSV may not required for thermal relief if proper administrative procedures and addition of signs stipulating the proper venting and draining procedures when shut-down and block-in are implemented. These action are acceptable and considered do not compromise the safety of personnel or equipment.

System under consideration for thermal relief consists of piping only (does not contain pressure vessels or heat exchangers), a pressure-relief device might not be required to protect piping from thermal expansion if :

1. the piping is always contains a pocket of non-condensing vapour, such that it can never become liquid-full (even it is heated and compressed); OR
2. the piping is in continuous use (i.e., not batch or semi-continuous use) and drained after being blocked-in using well supervised procedures or permits; OR
3. the fluid temperature is greater than the maximum temperature expected from solar heating (the pipe temperature direct under solar heating can reached approximately 60 °C to 70 °C, it can be as high as 85 °C for certain area i.e. Middle east) and there are no other heat sources such as heat tracing; OR
4. the estimated pressure rise from thermal expansion is within the design limits of the equipment or piping.

Do i normally calculate ?
Normally no... however... I have been asked by authority why i don't calculate. To some people, the authority seem pretty naive... To me he is doing the right thing.

If you or your company have done sufficient research and can be submitted to authority as supporting document, then don't waste your time to calculate it. Otherwise, you better get ready when authority ask for it...

JoeWong
Chemical & Process Technology

 

[zerosum]

Are the temps of the 'indoor jacketed vessels' high enough to raise steam in your cooling system should a couple of isolation valves be inadvertently left blocked in? Then possibly you may have a different problem to consider.

 

[zerosum]

See thread 'High Temperature Thermal Relief' on this forum, below, for related postings.