UW-13(c)(1) Intermediate Head - Close Fit Definition

[MrPDes]

For an intermediate head in accordance with Fig UW-13.1(e), Section UW-13(c)(1) says:

"...the outside diameter of the head skirt is a close fit inside the overlapping ends
of the adjacent length of cylinder."

Does anyone know if there is a definition for "close fit"?

Shaft tolerance tables have "close running fit" and "close slidding fit" but I don't think this is what is being referred to.

 

[gr2vessels]

I don't think you'll find a tabulated listing of allowable tolerances for the close fit. It has too many variables and allowances, to enable some figures to be put against it. The idea is to have a minimal gap for the welding purposes, but sufficient also for a slide fit of the head inside the shell. You take in consideration the out of roundness of the shell and the head, small local (allowed) deformations on the edges of the head and shell, possible thickness variations, imperfections of the head straight flange, and the list could go even further. I believe it depends on the fabricator's experience to work things together, rather than relying on a table of numbers. Once he jammed a head inside the shell in the wrong position and had to cut it open, he learned quickly what is the meaning of 'close fit'.
Cheers,
gr2vessels