the designer. If the program is a well known and well used one such
input loads and boundary conditions applied. In other cases, the
justification may require full documentation of the program and examples of
analyses carried out by the use of the program that can be easily checked by
"classical" analysis, "exact" analysis, or data existing in the literature.
b. Stress Intensity Limits. There are two mandatory appendices of
Section VIII, Division 2, which form the entire basis of the concept of
design by analysis. These are Appendix 4, Design Based on Stress Analysis
and Appendix 5, Design Based on Fatigue Analysis. A detailed understanding
of these two appendices is necessary to understand Section VIII, Division 2.
Both appendices deal with the establishment of "stress intensity limits" and
the interpretation of stresses calculated by the designer to meet these
limits. Appendix 4 gives such information as pertains to vessels that are to
be loaded either statically or cyclically, while Appendix 5 gives further
information to be applied to vessels that are to be loaded cyclically. Note
carefully that the data presented in Appendix 4 must be applied in all cases
(1) Appendix 4, Article 4-1 Design Based on Stress Analysis.
article presents the methods that a designer should use in:
Classifying the type of stresses that he has calculated;
Converting these classes of stress into "stress
(c) Comparing the calculated "stress intensities" to the
Code-allowable "stress intensity limits" for the material from which the
vessel is fabricated.
A brief description is given below of part of the information found in
Article 4-1. The designer is urged to read and fully understand the complete
c. Types of Stresses.
In Article 4-1 stresses are broadly categorized
into three groups:
(1) Primary stress. Such a stress is imposed by loading which is
necessary to satisfy equilibrium and which is not self-limiting. That is, as
the loading increases, the distortion of the area over which this stress acts
continues to increase until failure.
(a) Primary general membrane stress. This is a membrane
stress existing in a shell at a position removed from any gross geometric
(b) Primary local membrane stress. This is a membrane
stress existing close to a geometric discontinuity which decreases rapidly
away from that location.