B31J

Stress Intensification Factors (i-Factors), Flexibility Factors (k-Factors), and Their Determination for Metallic Piping Component

This Standard sets forth an engineering procedure deemed appropriate for the determination of the fatigue capacity of a piping component or joint in most services, relative to a standard butt-welded joint. The B31 piping Codes provide stress intensification factors for the most common piping components and joints. This Standard presents an experimental method to determine stress intensification factors.

In 1990 The American Society of Mechanical Engineers (ASME) B31 Code for Pressure Piping Technical Committee on Mechanical Design (MDC) realized that there was a need for a standard method to develop stress intensification factors (SIFs or i-factors) for ASME piping components and joints. At the time, the B31 Code books provided SIFs for various standard fittings and joints but did not provide guidance on how to conduct further research on existing SIFs or how to establish SIFs for nonstandard and other standard fittings or joints. In 2001 the Committee realized that SIFs and k-factors in the various B31 Code books were not consistent or up to date, andsoASMEinitiateda researchproject completedby theMDCto incorporate recent researchandcurrentmanufacturing practices in the SIF and k-factor test procedures, to provide a consistent and up-to-date table of SIFs and k-factors for metallic piping components. Thisdocumentprovides a standardapproachfor thedevelopment of SIFs, k-factors, andsustainedstressmultipliers for piping components and joints of all types, including standard, nonstandard, and proprietary fittings. Sustained stress multipliers are used to multiply the nominal bending stress due to sustained loading and reflect the collapse capacity of the metallic piping component or joint. Multipliers of the nominal bending stress due to sustained loads currently exist explicitly in some, but not all, B31 books. Where more accurate sustained stresses are needed but an equation for the sustained stress is not given in theB31 Code book, nominal stresses due to sustained moments computed using the section modulus of the matching pipe should be multiplied by the appropriate sustained stress multiplier. Where the sustained stress is needed and an equation for the sustained stress is given in the Code book as a function ofthe SIF and provided in lieu of more applicable data, the sustained stress multipliers developed using the method in this Standard may be substituted as more applicable data and used with the nominal stress computed using the section modulus of the matching pipe. The most applicable currently available stress intensification and flexibility factors compiled from test and analysis data for standard commercially available metallic components are included in Table 1-1 and should be used with the section modulus of the matching pipe (not an “effective” section modulus). Nonmandatory Appendix A provides the standard method to develop stress intensification factors. Nonmandatory Appendix B provides the standard method to develop branch connection flexibility factors. Nonmandatory Appendix C demonstrates how the new branch connection k-factors should be used in the elastic analysis of piping systems, and Nonmandatory Appendix D provides a standard method to develop sustained stress factors. A procedure to develop k-factors for bends, elbows, and straight pipe is available inWRCBulletin 463,“Report 1: Standardized Method for Developing Flexibility Factors for Piping Components,” E. C. Rodabaugh and E. A. Wais (July 2001). In its development, this Standard has been reviewed by individuals and appropriate subcommittees of the Boiler and Pressure Vessel Code, B31, and B16 Committees. Comments resulting from the review have been considered and responded to, with revisions made to the Standard, as appropriate. The 2017 edition has been revised in its entirety. It was approved as an American National Standard by the American National Standards Institute on January 11, 2017.

Publish Date: 2017

Pages: 64

Language: English

ISBN: 9780791871508

https://www.asme.org/products/codes-standards/b31j-2017-stress-intensification-factors-ifactors