Stress Classification Plane and Its Application in Finite Element Analysis

The stresses within pressure vessels and internals, etc. are categorized into membrane, bending, and peak stresses in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, as well as many other design codes of different countries. The total stress results calculated from a finite element analysis, which is the most commonly utilized tool in the component design, have to be classified into these categories to be compared to the design code criteria. The stress classification line (SCL) method has been developed to linearize the stresses along a line cutting through the thickness of the component. However, the SCL method tends to overestimate or underestimate the linearized stresses if the stress distribution of the cross-section is not axisymmetric. Since the design code criteria are given over a cross-section, this article proposes a stress classification plane (SCP) method in stress linearization. An SCP is defined as a cross-section that cuts through a solid 3-D finite element model. The element nodes do not need to lie on the SCP. The stresses are linearized over the entire cross-section that defines the SCP. Therefore, the linearized stresses obtained using this method are consistent with the design code definitions. The SCP approach provides an accurate and convenient tool when comparing the finite element results to the Code criteria during the component design and analysis process. As an example, the applications of the SCP method using ANSYS^® are also given in this article.