b.
Materials and Initial Calculations. Carbon steel, ASTM
Specification A-516 grade 70, a Category 1 plate material, is chosen as the
material from which to fabricate both the chamber and the support cylinder.
From Table ACS-1 of Section VIII, Division 2*, the design stress intensity
value, Sm, is shown as 23,300 psi at 100 deg. F and 23,100 psi at 200 deg.
F. Linearly interpolating sets Sm at 150 deg. F at 23,200 psi. Based on
this, the Stress Intensity Limits for the vessel become (see para. 2.e of
this Section):
Pm < / = 23,200 psi
PL < / = 34,800 psi
Pm (or PL) + Pb < / = 34,800
PL + Pb + Q < / = 69,600 psi
(1) Stress Intensity Range. From Figure 5-110 1, for a life of
10,000 cycles, a permissible Sa = 37,000 psi. Thus, since the pressure
loading is from 0 to 1000 psig, the full allowable stress intensity range is
2Sa = 74,000 psi.
(2) Membrane Stress Intensity Limit. From Table AD-150-1, the
factor to apply to the Membrane Stress Intensity is 1.0.
(3) Minimum Shell Thickness. From paragraph AD-202 of Article
D-2, the minimum shell thickness of the sphere is calculated from:
0.5 PR
tsp =
(for internal pressure loading only)
S - 0.25P
where
tsp =
minimum required thickness of sphere, inches
P
=
design pressure, psi
R
=
inside radius of shell, inches
S
=
factor from Table AD-150-1 times Sm, in this case
1.0 Sm, psi
0.5 PR(1000.0)(90.0)
tsp =
23,200 - 0.25(1000.0)
tsp =
1.98 inches, use 2.0 inches.
(4) Total Dead Weight.
The weight of the seawater in the full
chamber would be approximately:
* Note: Henceforth all references to Tables and Figures made in this
analysis shall be assumed to be those found in Section VIII,
Division 2, unless otherwise noted.
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