PSV Reaction Forces 4

[kurtz]

Please look at the picture. Is it necessary to assume any other force from opening the safety valve?
I've seen some people add force directly at the outlet of the safety valve.

 

[1503-44]

AndyW The reducer and expander around a valve is because the valve only needs a very small relative opening area in order to control the typical high to maximum flowrate of any given pipe size, hence it seldom if ever, I could just about almost say "always never", needs to be the same size as the pipe into which it is placed.

"because the action time for the out of balance force is very small" I think that statement may only apply to relief valves that open, blow off a relatively slight overpressure very quickly and then immediately close, however some relief valves located in certain remote areas have been known to be continuously active for a day or two before a crew arrives to remedy whatever situation that set them off.

Alex, There was a program that was supposed to be able to distribute momentum and surge forces developed within the piping to the pipe's supports, but I am afraid that I saw it such a long time ago that I cannot recall its name. Not sure, but I think it may have been written in Delft, Holland. Sorry that I can't be more help.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[Alex Matveeff]

ax1e, do you remember it's name?

I'm the PASS/START-PROF Pipe Stress Analysis Software Developer

 

[saplanti]

The other thing in this kind of configuration is the control of the back pressure of the safety valve to be able to discharge in accordance with the specification. Any additional bend will increase the back pressure in addition to the pressure loss in the discharge pipe, and pressure drop in the possible silencer.

In my experience with steam we needed to discharge straight up just after the discharge bend with adequate supports to take forces. I have not tried the same application with hydrocarbons but it should not be so different, I guess.

 

[saplanti]

Additionally, every change of direction will introduce reaction which needs to be taken by either structure or the safety valve nozzle. The angle cut at the discharge will introduce two directional force (or force normal to the cut plane). In the first picture that littleich attached, the vertical reaction force and horizontal reaction could not be taken by the bend connection to the safety valve and connected inlet pipe as well as by the lateral stiffness of the portal frame, therefore the structure and pipe system failed all together.

Especially the safety valve in the picture should dischage the full capacity of the inlet piping, therefore the reaction forces are a lot higher. I feel that the report does not mention any of these. It feel that there was a miscommunication issue on the forces created and the directions from the design side. I guess everything was left to the structural engineer to design a structure.

 

[1503-44]

saplanti, you make an excellent point about the angle cut introducing a horizontal thrust component.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"