ASME International

DESIGN GUIDELINES FOR THE EFFECTS OF CREEP, FATIGUE & CREEP-FATIGUE INTERACTION WITH DESIGN-BY-ANALYSIS AND NONDESTRUCTIVE INSPECTION ACCEPTANCE CRITERIA
 N STP-PT-070

Annotation

As part of the modernization of Section I – Rules for Construction of Power Boilers of the ASME Boiler and Pressure Vessel Code (Section I), a project was established to develop design guidelines for the effects of creep-fatigue interaction and flaw size acceptance criteria within the overall framework of Design-By-Analysis (DBA). The existing methods within Section I, which are based around Design-By- Rule/Formula and do not explicitly consider creep, fatigue or their interaction. The oversimplifications involved are such that the safety of boilers operating at higher steam cycle conditions, and under cyclic service, has been questioned. Design-By-Analysis (as an alternative to Design-By-Rule/Formula) is gaining acceptance as a viable approach for design of components that will experience cyclic loading and which will operate at elevated temperatures where creep may occur. Such Design-By-Analysis approaches have been introduced into other international codes, including other sections of the ASME Boiler and Pressure Vessel Code (ASME Code) and the EN Code.

This report has been prepared to recommend design guidelines for components in Section I - Power Boilers. As such, it does provide a comprehensive review of issues. However, to properly introduce the context of the recommendations, some background is provided to a number of philosophical topics that surround Design-By-Analysis, Design-By-Formula, Design-For-Safety and Design-For-Lifetime. As several other recognized Codes and Standards have approaches that are relevant to Design-By-Analysis, or which provide methods for including creep-fatigue interaction effects, a summary of these documents is provided. In particular, the summary compares and contrasts key aspects to provide insight into benefits and shortcomings (or inconsistencies) associated with particular approaches. From this review it is evident that no single Code or Standard has a method that can be universally adopted, particularly when the methods have to be used in the context of other Sections of Codes, such as material properties, or standardized design features. That is, a particular Design-By-Analysis methodology needs to be developed that could be used within the overall context of the ASME Code (particularly Section I).