nonintegral connections. Incorporated in this Article and deeply
imbedded in the philosophy of Section VIII, Division 2, is an
emphasis on the creation of a pressure vessel as free as possible
from sharp, local, geometric stress risers such as notches, fillet
welds, and partial welds. This is seen continually throughout the
design and fabrication sections of the Code. The avoidance of such
discontinuities from pressure vessels to be employed in hyperbaric
facilities takes on even more importance when corrosion effects are
considered.
3.
DESIGN REQUIREMENTS. Part AD, "Design Requirements" of Section VIII,
Division 2, contains 10 articles, each of which deals with specific design
requirements for a Code-approved vessel. These 10 articles are listed below
and selected items are discussed.
a.
Article D-1, "General."
(1) AD-115, "Corrosion." The designer is cautioned that he must
make allowance for the loss of material due to corrosion effects, and that he
must consider effects for the entire lifetime of the vessel. This loss must
be compensated for by the addition of material to the wall thicknesses of the
vessel above that needed to meet the stress intensity limitations as
determined by analysis. Throughout the Articles dealing with design, it is
emphasized that the analysis to be carried out should deal with the vessel
geometry in the "as-corroded" condition.
(2) AD-140, "Design Criteria." Particular attention should be
given to paragraph AD-140(c), where the definition of primary local membrane
stress is given.
(3) AD-150, "Load Combinations." The designer should become
familiar with Table AD-150.1, "Stress Intensity Limits for Various Load
Combinations" Table 2-2 in this manual. The information contained in this
table will be of use to the designer in the initial steps of his design
procedure, and for setting test pressure limits.
(4) AD-155, "Minimum Permissible Temperatures for Ferrous
Materials Other Than Austenitic." This paragraph, basically, sets the lower
limit of test, design, or operating temperature for such materials. This
limitation on temperature is solely based on toughness requirements. If the
design of the vessel calls for operation at low temperatures, it is the
absolute obligation of the designer to show that the material he chooses has
the required toughness at the lowest temperatures to be seen by the chamber
during its operational life.
(5) AD-160, "Fatigue Evaluation." This paragraph specifies the
conditions under which a vessel may be exempted from the necessity of being
evaluated for fatigue. Further, it makes a particular point of the dele-
terious effect that certain construction features may have upon the fatigue
life of a vessel.
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