6 replies to this topic

[GS84]

Dear all,

 

I have a doubt regarding the design pressure of piping systems protected with thermal relief valves.

 

The questioin is that when you pressurize an isolated (protected with a TRV) piping system by increasing its temperature, certain amount of liquid will be released.

 

When it cools down to normal temperature, the volume of the evacuated liquid must be filled with vapour, at a pressure equal to the vapour pressure of that liquid.

 

 I have seen that systems under steam out, must be designed for FV.

 

On the other hand, I am not so used to seeing systems (that may be isolated and packed with liquid) designed for this requirement. I am thinking for example of pipe filled with diesel or any liquid with a relatively low vapour pressure.

 

Am I wrong in any point of my question?

Are ASME16.3 piping normally designed for FV or is it capable of withstanding that effort by default?

 

 

Thank you in advance,

[shan]

Comparing with vacuum stress, piping internal pressure is the governing case.  The piping wall is more than strong enough to stand vacuum pressure if it is able to stand specified internal pressure.

[fallah]

 

Are ASME16.3 piping normally designed for FV or is it capable of withstanding that effort by default?

 

 

GS84,

 

Piping system resistance to external pressure depends on thickness and diameter...

 

If the pipe wall is thin compared to its diameter buckling of piping is possible.

 

If i rightly recall, there is a formula from Roark will give the possibility of pipe buckling due to vacuum.

 

As a rough but good estimation, for piping systems only when internal design pressure for most material to be around 500 psig or higher, the corresponding thickness can withstand vacuum conditions...
 

Edited by fallah, 04 May 2015 - 12:47 PM.

[GS84]

Thank you Fallah!

[kiansafaie]

Dear Mr fallah
Would you give a reference about Roark and 500 psig? I need it, we did not considere F.V for all of pipe and i realy interested to know condition of it.
Thanks

[fallah]

Dear Kian,

 

It's from "Piping Design Handbook" edited by John J. Mcketta...

[kiansafaie]

Thanks