In 1974, the Level D Service Limits for Section III, Division 1, Class 1 components were published in Non-Mandatory Appendix F titled “Rules for Evaluation of Service Loading with Level D Service Limits”. Over the past 40 years, the scope of Appendix F has been expanded to be applicable to certain Class 1, Class 2 and Class 3 components and supports in Division 1 as well as in Division 3 and Division 5. With each addition, the organization and implementation of the rules in Appendix F became more cumbersome for the user and consistency between the Appendix and the Code Books1 was not maintained. At the same time, the use of these rules has evolved to the point where the non-Mandatory Appendix is essential the default for Level D Service Limits. Starting in the 2017 Code edition, the component design rules will reference Mandatory Appendix XXVII when Design by Analysis is used to determine Level D Service Limits. This paper describes the methodology utilized to convert Non-Mandatory Appendix F to Mandatory Appendix XXVII which includes the history of the Level D Rules in the ASME Code, the philosophy taken to convert Non-Mandatory Appendix F to Mandatory Appendix XXVII, and an overview of the new Appendix XXVII. The approaches to ensure identical safety margins are maintained and the basis for adding or clarifying three allowable stress limits are also included.

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