Fig. UW-13.1, Sketch (l) interpretation

[jamesl]

In sketch (l), y looks like the offset between OD of head and OD of shell at tangent line. If a hemi head has the same OD as shell, then y equals 0. Does that mean tapered length l can be 0 (no taper)? In reality, at the weld joint, there is going to be big offset there.

 

[deanc]

You must always read the verbage. See UW-13b3,y merely moves to the opposite side. It still requires a 3to1 taper.

 

[jamesl]

In sketch (l), internal surface is not tapered. Even if y moves to the opposite side, there is no taper needed on internal surface.
I see some company standard defining y as measure from weld joint to OD of shell. I think it makes more sense than Sketch (l).

 

[deanc]

A taper is always required on butt welded unequal thickness parts. It does not matter if it is internal or external. Refer to UW-33b. If you doubt this check with your AIA.

 

[jamesl]

Thanks for reply. I never doubted that there has to be a taper when there is a thickness difference. One of my clients uses Sketch (l) to argue that, since the hemi head and shell has the same OD, y=0, so there is no need to put a taper on the external surface. I think the sketch (l) is misleading. The 3:1 taper shall be based on the offset at the weld joint, not based on the offset at tangent line. I am seeking the corret interpretation of the sketch itself.