Prior to 1988, coverage of metallic bellows expansion joints in ASME B31.3 was very limited. Bellows were required to be designed in accordance with the rules for pressure design of unlisted components (par. 304.7.2) and the Standards of the Expansion Joint Manufacturers Association, Inc. (EJMA Standards). Appendix X was added in 1988, and has undergone several significant revisions in subsequent years. It provides specific Code coverage for metallic bellows expansion joints by adopting, with exceptions and additions, a widely used industry standard for expansion joints, the EJMA Standards.
The overall philosophy of Appendix X was to adopt the EJMA Standards with modifications that the Code Committee felt were necessary to make the EJMA Standards into Code requirements suitable for ASME B31.3 piping. This differs somewhat from the approach taken in ASME BPVC, Section VIII, Division 1, Appendix 26 (formerly Appendix BB), Pressure Vessel and Heat Exchanger Expansion Joints, where the design equations from the EJMA Standards were directly incorporated into the Code. The background behind these bellows stress analysis equations and comparison with detailed analysis and test results are provided in Becht (1985), Becht and Skopp (1981a), Osweiller (1989), and Broyles (1994).
The most significant of these modifications to the EJMA Standards were in requirements for pressure design, fatigue design, and hydrotest. It should be noted that both the EJMA Standards and the ASME B31.3 Code are living documents. For example, EJMA revised the pressure design requirements in the Sixth Edition, issued in 1993. This Edition was adopted by ASME B31.3 in the 1994 Addenda. Some of the pressure design requirements in Appendix X could now be dropped, because they are now adequately addressed in the EJMA Standards. However, they have been left in for emphasis of certain considerations.
