Pipeline Thermal Relief Valves

[SamSnead]

Hi All,

I have seen and read posts that say rule of thumb is to install a thermal relief valve for every 500 liters of liquid. I have a 24 in pipeline that is 1000 ft long. Does this mean I have to install a TRV every 6 ft? That’s 167 TRVs. IMO, that seems like a lot of TRV for a straight pipe.

Can anyone help clarify this? I appreciate all help.

Sam.

 

[zdas04]

In my experience thermal relief volume requirements are really tiny (unless you have a very abnormal heat source). Most discussions of them on eng-tips.com puts them at launchers and receivers with none in the body of the system. That has been the direction I've gone for the last few decades too.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[pennpiper]

Sam,
What is the Fluid?

Sometimes its possible to do all the right things and still get bad results

 

[bimr]

You have the rule of thumb incorrect.

The rule of thumb is that if equipment is operating full of liquid, the equipment should be provided with a thermal relief valve if the volume of blocked-in liquid is greater than 0.5 m3. The rule of thumb does not say a thermal relief for every 500 liters of liquid.

Review this document:

http://www.chemwork.org/PDF/papers/what you should know about liquid thermal_expansion.pdf

 

[TD2K]

< I have seen and read posts that say rule of thumb is to install a thermal relief valve for every 500 liters of liquid >

That makes no sense. I've seen some guidelines about installing thermal relief valves if a section of piping that can be blocked in is greater than a certain distance but not on a straight volume. The real question is can the pipeline be blocked in and exposed to a heat source. I would not overlook Zdas's comments.

 

[SamSnead]

The fluid is crude oil.

 

[SamSnead]

Here is a sample post that mentions the 500 liters as a rule of thumb: [URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=83163[/url]

And, I've read 4 or 5 similar posts.

 

[bimr]

In the post that you reference, it states "As a rule of thumb, pipe containing more than 500 lts. of liquid or more than 45 m length (whichever is lower) which could be normally blocked in should be provided with TRV."

You are misreading it. It does not say one TRV for every 500 liters. This means that the threshold for installing a TRV is a minimum of 500 liters in an individual piece of equipment.

 

[zdas04]

bimr,
Are you saying that it a threshold as in "if you have more than 500L you need thermal relief"? Rather than a valve for every 500 L. That makes much more sense.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[bimr]

Correct

 

[LittleInch]

Sam,

The general rule for thermal relief is that you need to allow for this where volumes of liquid can become isolated between valves AND exposed to temperature ranges which give rise to a pressure rise which exceeds the pressure rating of the pipe or equipment. This temperature rise can be quite small, <10C in many instances. The amount kg liquid to relieve this pressure is very small. The 500l guide is the minimum volume where thermal relief is justified, not a fixed volume. The key point is the ability for an operator to isolate sections of pipe or equipment. If this cannot happen as there are no valves there then you don't need more than a single TRV.

For most pipelines, the temperature rise is very low as they are long and normally buried. Your description sounds much more like a piece of pipe as 300m is not normally designated as a "pipeline".

Unless you have lots of intermediate valves a dibble TRV would seem to be justified

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