Pressure-temperature ratings for aluminum alloy flanges made from ASTM B247 3003-H112 and 6061-T6 materials are covered in ASME B31.3 Appendix L since 1995. They were previously included in ANSI B16.5 between 1960 and 1968, and in ANSI B16.31 Non-ferrous Alloy Flanges from 1968 and until it was withdrawn in 1981.

In 2018, Xu and Rana [PVP 2018-84076] used a modified version of the rules for establishing the pressure-temperature rating from ASME B16.5 Steel Flanges to re-assess the pressure-temperature rating of aluminum alloy currently listed in ASME B31.3 Appendix L. Based on their work, they recommended raising the pressure-temperature ratings for Classes 150, 300 and 600, as well as expanding rating to cover Classes 900 and 1500.

In this paper, the author will revisit this topic, explain the background of why ANSI B16.31 was withdrawn and the drawbacks of higher pressure-temperature rating of aluminum alloy flanges. The author will also explain the concept of “ceiling pressure” used in B16 standards to cap the maximum pressure rating for flanges and valves, and significant difference in the modulus of elasticity between Carbon Steel and Aluminum alloys, and its impact on flange rigidity and leak tightness, and will propose alternative rules for establishing the pressure-temperature ratings for aluminum alloy flanges.

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