Use of the term "vertical diameter"

[rww88]

Would anyone care to comment on the meaning of the term "vertical diameter" in the following passage from API 650?
"The minimum cross-sectional area of the required reinforcement shall not be less than the product of the vertical diameter of the hole cut in the shell and the nominal plate thickness . . ."
Is there a difference between the vertical diameter and horizontal diameter of a hole? Does this imply that the hole is not circular? If so, does it mean the dimension of the hole along the meridional axis irrespective of the largest dimension of the opening?

 

[LittleInch]

This should read just as "diameter of the hole cut into the shell", but someone was trying to be a little too precise.

It's basically an area replacement technique like B 31.3 and a few other codes looking at hole or branch reinforcement

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

If you have a hill-sided nozzle (not radial), the hole dimension in the horizontal plane will be larger than in the vertical plane.
If you use an elliptical manway, the hole dimension will vary in the vertical vs horizontal plane.
For larger tanks with regular nozzles, the arc dimension along the shell is essentially the same as the chord, but for small diameter tanks, there can be some minor variation there as well.

The assumption is that you're reinforcing it for hoop stress, so the dimension perpendicular to that is the dimension desired to base reinforcing on.

 

[rww88]

Thank you both for your responses. Sometimes I tend to make too much out of something that is quite simple.