From Table 2-3: "Maximum Stress Intensities in Model No. 1", for Part 10, "at
the inner corner of the nozzle", P1 + Pb + Q + F is shown as 39,750 psi.
This value is accurate, thus the stress Index Method has generated
conservative results. Experience has shown that this is always so.
(8) Design Changes. In the normal process of design by analysis,
it would be expected that the initial design would be inadequate in several
locations from the viewpoint of the stress intensity limitations. In this
example, only two of the vessel's components were found inadequate, i.e., the
flanges for the "door." The next step in this procedure would be to go back
to the original design, change the thickness or geometry of the shell at its
point of inadequacy and reanalyze the structure. This will not be done here
for the example of the procedure would simply be a repeat of all of the
preceding. However, this process is continued until the vessel can be shown
to be entirely adequate as regards all the stress intensity limitations.
(9) Viewport Design Considerations. The viewports themselves were
not analyzed in this example for two reasons: (1) for the high pressure
operation considered such viewports would be massive, intricate affairs that
would probably require experimental evaluation; and (2) they fall into the
category of Appurtenances and are treated in Chapter 3 of this manual.
However, the designer is cautioned that the viewports do form
a part of the main pressure boundary of the vessel and as
such should be evaluated according to the provisions of
Section VIII, Division 2.
If it is decided to analyze the viewports separately from the vessel (as was
partially done here) then the designer must ensure that continuity conditions
are maintained between the contact boundaries of the viewport and those of
the viewport penetrations. Only a constraint against rotation was imposed on
the inner boundary of the 10.0 inch viewport penetration. This constraint
developed a 15,500 -----
bending moment on the edge and a radial
displacement of 4.8 mils at this location. In the design of the viewport
such conditions must be applied to the model developed for this component,
For instance, if the viewport is to be connected to the reinforcement ring by
means of bolts then provision must be made to ensure at least a 5.0 mil
clearance around the bolts when the vessel is under load so as to prevent
them from acting in a shear load carrying capacity. Further, the seal design
must incorporate provision for such a relative displacement between the
viewport and the mounting ring. Finally, the effects of the bolt holes and
the exact geometry of the viewport mounting ring interface must be carefully
examined as to their impact upon the local stress picture.
(10) Door Closing Mechanism.
The "door" closing mechanism was
only simulated in this example by the two 11,000 --- ring loads as explained.
This component, too, is considered an appurtenance. However, what was said
about the viewports is true here. The interaction between the flanges and
the means of securing the "door," whether bolts or, more probably, a "c" type
clamp is of extreme importance from the viewpoints of both proper sealing and