Hair pulling and torispherical heads 4

[roadapple]

Concerning the rules in Sect. VIII, Div. 2: for torispherical heads.

Step 2 page 4-50

0.7 <=L/D<=1.0 (eq. 4.3.5) or go to Part 5.

I am designing a vessel out of 8 inch pipe with torispherical heads.
The D=7.625 in and the L=8.625.
Because the inside crown radius equals the outside diameter of the skirt (UG-32 (e)) and the D equals the inside diameter of the head (shcd. 80).

I know I am making a mistake and am willing to air it out in public - but by my numbers these will never satisfy the equation 4.3.5 as it will always be larger than 1.

Can someone please shine some light before I am completely bald?

roadapple

 

[Thermodom]

I intend to let you guys know what the AI says during the audit but my understanding is that the shape is to be checked. Not just the thickness.

I spoke to a heads manufacturer and he confirms that cut-outs are used to check the shape. He also confirms that the ellipsoidal 2:1 heads are made to match an ellipse of D/4 height inside (based on inside diameter).

He further informed me that the cut-outs are hung in the shop to show the AI but are rarely used, the issue only comes up at audit time.

My calc showing almost 1/4" tolerance on a 8"NPS STD pipe cap made sense to him, confirming that the mill undertolerance has a big play in it. THat also confirms that changing head thickness would require another cut-out.

Overall, my impression is that the best checking is by looking for the D/4 depth and seeing that visually it looks like an ellipse (no sharp change or flats), of course check for the rest of the required markings, UG and UCS stuff.

THanks again,

Thermodom