Non-axially loaded plate with holes

[idesign73]

I am working on a design for vertically conductivity probes for boiler applications. Basically, I have an endcap for a pipe and I need to drill and tap holes in the end of it to allow the probes to be threaded in. I need to perform calculations to determine how many holes I can put in the end cap before the integrity of the cap is compromised beyone the allowable stress given in ASME Boiler and Pressure Vessel Code Section IID. I can find all kinds of references that state what the stress concentration factor is if the plate is axially loaded, but in my case, the pressure inside the tube will be acting perpendicular to the holes, not in the axial direction. I know that the orientation of the holes will make a difference as well, but I am unsure how to take this into account with non-axial loading. Also, how do I take into account that a probe (SA-479 309H) will be threaded into the hole? Below is a very basic diagram of what I have. Please let me know if there is any additional information needed to help.
Any suggestions are much appreciated.
Thanks!

-------------------|
Pressure |
----------> |
Pipe |<--Endcap
-------------------|

 

[jdkuhndog]

In most of the stress concentration books they have stress concentration factors for plates with a moment applied to them. Isn't this what you have? Figure out the moment created in the plate due to the distributed pressure on the face of the end cap and then get the factors from the charts.

 

[arto]

Maybe analyze it as a flat head with an opening per ASME Sec VIII?

 

[JRScan2003]

i Would calculate the surface area the threads have in contact with the plate and after adding in the required safty factor use the pressure on the plate and figue out how many threades it would need and increse the plate thickness,or if you could weld the pipe to the plate.

 

[prex]

I'm not sure to understand your setup: are the holes drilled at the periphery of the end cap with their axes parallel to the faces of the end cap (and presumably at mid thickness)?
If it is so, you might consider the following points (but actual figures would be required for further help):
- stress concentrations are only relevant to fatigue analysis and before performing a fatigue analysis you need to ensure that the basic primary stress is within the allowables. Of course if you limit the peak stress to the code allowable you would have a very conservative design
- no account should be taken for anything that is inserted into the tapped holes
- a way to account for the holes could be to calculate with an equivalent reduced thickness of the flat head, determined on the basis of how much metal is cut out in the holes; how to do that critically depends on the hole pattern
- in a flat end cap the governing stress is normally at the center of the plate: if you have no holes there you could take advantage of this
- if you need to satisfy a specific code, then forget all the above: an analysis per code should be conducted by an expert and this will likely lead to FEM or even to the conclusion that what you want to do cannot be done, as this situation is quite uncommon with respect to normal code rules.



prex

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