(a)
AD-160.1, "Operating Experience." The designer is
cautioned that certain design features are inherently poor from the viewpoint
of fatigue. Specifically mentioned are:
o
Nonintegral construction, such as the use of pad
type reinforcements or of fillet-welded attachments
as opposed to integral construction
o
Use of pipe threaded connections
o
Stud bolt connections
o
Major abrupt thickness changes between adjacent members.
These considerations take on added emphasis when considered from the
viewpoint of corrosion. Each of the above geometries can present locations
for the action of either crevice corrosion or corrosion due to the entrapment
of corrosive agents. It is for these reasons that such construction
practices are not recommended for use in pressure vessels in hyperbaric
facilities.
(6) AD-160.2, "Rules to Determine
Need for Fatigue Evaluation of
Integral Parts of Vessels." The designer is
cautioned that all parts of
Condition A or all parts of Condition B must
be met for a vessel constructed
in such a manner to be exempt from a fatigue
evaluation.
b.
Article D-2, "Shells of Revolution Under Internal Pressure." This
article is quite clear in its exposition and needs no further interpretation.
The equations contained therein, together with Table AD-150.1 can assist the
designer in the setting of the initial shell thicknesses for his preliminary
design. Inherent in the term, "minimum thickness," used throughout this
article should be the understanding, "in the as-corroded condition." Note
carefully, that the formulae presented deal almost solely with internal
pressure and that paragraphs AD-200.1 through AD-206 require that provision
be made for other types of loading. These types may encompass local moment
loads, thermal stress, and others. By and large the Code leaves the manner
of determining the additional thickness required for such loadings to the
designer.
c.
Article D-3, "Shells of Revolution Under External Pressure."
Generally, the normal loading for pressure vessels forming parts of
hyperbaric facilities will be internal pressure. However, there may be
instances particularly in the case of multi-chambered vessels, where a
pressure differential may exist such that one vessel or part of one vessel
could be subjected to an effective external pressure. In such an instance,
the provisions of this article together with the data found in Appendix 2 of
the Code should be applied.
d.
Article D-4, "Welded Joints." This article classifies the types
of welded joints which may be incorporated into a Code-approved vessel. The
classifications are primarily intended to correlate with inspection
procedures but also present good engineering practice. In this article, as
in others, the designer is urged to keep his design "smooth"; that is, free
from sharp local discontinuities and the use of fillet or partial penetration
welds in the main pressure wall of the vessel. Particular attention should
be directed to Paragraph AD-420 and Figure AD-420.2 which deal with material
thickness transition zones.
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