Material Anisotropy in ASME Boiler and Pressure Vessel Code Section VIII

Abstract There have been many revisions to the ASME Boiler & Pressure Vessel Code (BPVC), Section VIII, Divisions 1 (VIII-1) and 2 (VIII-2) [in combination referred to collectively as VIII] to address the issue of material anisotropy. Anisotropy is the behavior of a material such that its properties differ depending on the direction of the testing. This paper addresses the latest changes in the 2025 Edition of VIII (E25 VIII) addressing this technical topic. The general technical background and evolution of BPVC anisotropy rules until the E17 was presented at PVP 2018 and published in paper PVP2018-84823. Lab testing and its evaluation was presented virtually at PVP 2020 and in an unpublished draft paper submitted for PVP 2020. The results of these two papers are now codified in the E25 VIII. In the E25 VIII, significant editorial and technical revisions are published for the requirements for parts machined from bar: • Revised the tension test requirements. • Added permissions for additional types of components that can be machined from bar. • A Table and two Figures are added to provide clarity to the requirements. • The 50% penalty on design values is expanded in its scope of applicability. Also in the E25 VIII, rules addressing plate anisotropy are revised.