Most flanges arc in accordance with listed standards, such as ASME B 16.5, and for larger flanges, ASME B 16.47. Appendix L is provided in ASME B31.3 to cover aluminum Flanges because they are not included in ASME B16.5. When a custom flange is required, design by analysis is permitted by para. 304.5.1. ASME B31.3 refers to the rules for flange design contained in ASME BPVC Section VITI, Division 1, Appendix 2, but using the allowable stresses and temperature limits of ASME B31.3. For flanges with metal-to-metal contact outside of the bolt circle, the rules of ASME BPVC Section VIII, Division 1, Appendix Y are referenced. #Little_pEng.