Valve End Loads 1

[BHMech]

Does anyone have any information on acceptable valve end loading due to piping stesses? We have customers who often ask for the allowable loads that valve ends can withstand.
Alternatively, is there any guidelines to show the expected load that a given pipe may exhort on a valve due to pressure or temperature?

 

[Zapster]

It is my understanding that when evaluation pipe stress that valves are considered rigid bodies. This is because their strength/rigidity is much greater than the pipe system they are attached to. So, the only way a correctly specified valve could be loaded past its design values is if it is not connected to a pipe.. Typically, valves are specified by ASME, AWWA, or API by class. If the piping wall thickness is a reasonable selection for a given pressure class, a valve of the same pressure class will be much stronger than the piping system. One possible problem (though not realistic if it is an engineered system) could arise if for some reason a pipe schedule is selected that is much greater than the pressure class would require with fabricated connection. At this point you should be concerned with stress in the valve body. The big key here is fabricated/unlisted components. There are other ways that valve bodies can be overstressed; however, your question stated due to pipe stress.

 

[Cockroach]

You have a very common question, one that is an issue to the end user on the pipeline.

With valves that I've done, typically fracture mechanics on the body will dictate extreme loads. Naturally this depends on the type of valve and exact placement of steel thus comprising the body. The closure(s) must also be taken into account, it is possible to crush these babies long before the valve body yields.

According to the API specification, and for obvious reasons, the valve CANNOT compromise the integrity of the pipeline. To start with, performing a simple calculation on yield strength on the pipeline cross section per unit length would give you MINIMUM expectations. I design to a factor of safety of three (3), sometimes four (4) depending on the exact nature of the application.

Note that finite element is the best approach to yield meaningful estimates. Due to the exact nature of the valve geometry, pipeline conditions, environmental properties, etc, there is no single equation to help you out. Your valve manufacturer should have this information as part of the customer documentation package, phone him!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada