Extension of Fatigue Exemption Rules in Section VIII, Division 2 Slightly Into the Creep Regime

Abstract

A number of alloys have applications slightly into the creep range that are in cyclic service, such as process reactors. The 2007 edition of Section VIII, Division 2 (2007, ASME Boiler and Pressure Vessel Code, Section VIII, Division 2, The American Society of Mechanical Engineers) provides allowable stresses for these materials, which may be controlled by creep properties. However, the fatigue design rules and fatigue exemption rules are not applicable, precluding the construction of vessels using these materials at temperatures above 370∘C (700∘F). This paper provides a simplified approach for the exemption of low chrome alloys that are slightly into the creep range from fatigue analysis. Part 1 of this paper (Becht, C., 2009, “Elevated Temperature Shakedown Concepts,” ASME J. Pressure Vessel Technol. 133 , p. 051203) describes shakedown concepts, which are the basis for the criteria evaluated in this paper.