Companion Guide to the ASME Boiler & Pressure Vessel Code, Volume 2, Second Edition: Criteria and Commentary on Select Aspects of the Boiler & Pressure Vessel and Piping Codes
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In Chapter 39, William J. O'Donnell, whose consulting services have covered all aspects of fatigue evaluations, covers fatigue evaluations with the Code design and evaluation for cyclic loading of Sections III and VIII. The author notes that fatigue “is recognized as one of the most frequent causes of failure in pressure vessels and piping components … for fatigue strength is sensitive to design details, such as stress raisers, and to a myriad of material and fabrication factors, including welding imperfections. Fatigue is also sensitive to such unforeseen operating conditions as flow-induced vibrations, high-cycle thermal mixing, thermal striations, and environmental effects. What is somewhat surprising is the number of fatigue failures that are directly related to poorly chosen design and fabrication details.” The ASME B&PV Code was one of the first Codes and Standards to treat explicitly the design for fatigue life.
Dr. O'Donnell covers the historical background of fatigue failures, giving pertinent references. He notes that Section III was the first to include fatigue in its 1963 Edition; Section VIII, Division 2 (Alternate Rules for Pressure Vessels) followed in 1968; and Section VIII, Division 1 (Rules for Construction of Pressure Vessels) still does not include explicit fatigue design life—evaluation methods. Fatigue in pressure vessels and piping is of considerable importance, for it operates in the low-cycle regime where local stresses are far in excess of yield. This chapter covers the use of strain-controlled fatigue data; stress—strain concentration effects; the effects of mean stress; fatigue failure data; the procedure for fatigue evaluation; cumulative damage; exemption from fatigue analyses; experimental verification of design fatigue curves; and fatigue data for pressure vessel alloys.
More than half of this updated Chapter is devoted to Current and Future Code fatigue design evaluation developments. High temperature water environmental effects are shown to be very important, and the available data is presented in numerous plots. New fatigue design curves proposed by the ASME Code Subgroup on Fatigue are included. Environmental fatigue is expected to be a major Code issue for decades. The Chapter includes an excellent bibliography.