The fillet radius at the intersection of the head and the inserted cylinder

should be at least equal to one-half the thickness of the head to minimize

the stress concentration effect of the intersection. The details of the

geometry of the entranceway cylinder are shown in Figure 2-23.

(7) Hatch. It was decided to use a spherical segment, pressure-

activated hatch configuration. Such a configuration is simply a spherical

cap bordered by a relatively thick compression ring which also acts as the

seating surface. The pressure acts on the concave side of the cap. Here

again Section VIII, Division 2, gives no specific guidance of such a

configuration. Some guidance can be attained from Section VIII, Division 1,

Appendix paragraph 1-6, "Spherically Dished Covers (Bolted Heads). It was

decided to use a configuration as shown in Figure 1-6 (d). For such a

configuration the thickness of the spherical part is given by

5PL

t = ---

6S

where

t = minimum thickness of spherical portion of cover,

inches

P = design pressure, psi

S = membrane stress intensity limit, psi

L = inside spherical radius, inches.

It is good practice to choose L to be at no more than twice the radius of the

opening to be covered. In this case L = 40.0 inches.

5(1000)(40.0)

Thus

t = ------------- = 1.44 inches

6(23,000)

use

t = 1.5 inches

The compression ring which forms the border of the hatch must match up with

the entranceway cylinder. Thus, for simplicity assume that the width of the

ring is the same as the cylinder thickness, or 4.0 inches. The thickness of

the ring is determined from

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