Anisotropic Materials Use in the ASME Boiler and Pressure Vessel Code

Very few materials have all their properties behave the same in all orientations of the material. The term for this behavior is anisotropy or anisotropic properties. The properties that are affected and the degree of anisotropy they exhibit, depend on the material family, the alloy, and the processing of the material. This paper will only discuss metals, and limited to those metal specifications adopted in the ASME Boiler & Pressure Vessel Code (B&PVC) Section II, Parts A and B. The anisotropic properties of plate have been well recognized explicitly and implicitly in the B&PVC for a very long time. At issue, and the specific focus of this paper, is another wrought product form: bars. Bar, specifically round bar — also called rod, is a very useful starting material to manufacture pressure parts. The bar can be stocked at the largest feasible diameter and length, and then cost-effectively machined to whatever diameter and length is desired for the part. Due to the anisotropic properties of bar, there is a need for understanding and setting limitations for the use of such material in the B&PVC. This paper will explore the past history, current status and future directions of the Code requirements for bar.