A Proposal for a Simplified Assessment Procedure to API-579 Standard

Abstract

The objective of this research paper is to propose, to API 579 standard, a simplified assessment procedure for shakedown limit load determination. The proposed assessment procedure applies the Simplified Technique, replacing the existing iterative elastic–plastic API 579 assessment procedures. The technique applies only two analyses (elastic and elastic–plastic) to determine the elastic shakedown limit. The shakedown limit load is determined from the residual stress that is calculated from the scaled elastic stress and subtracted from the elastic–plastic. Finally, to determine the shakedown limit from the residual stress calculated. For the purpose of validating the new assessment procedure to be applied to locally thinned-wall components, the shakedown boundary of a locally thinned-wall pipe-branch connection subjected to a spectrum of steady internal pressures and cyclic bending moments is generated. The results of the proposed assessment procedure are successfully verified against the existing API 579 elastic and elastic–plastic assessment procedures. A parametric study is performed through changing both the depth and location of the local wall thinning within the pipe-branch connection. The results of the parametric study show good agreement in the shakedown limit boundary results with the API 579 elastic–plastic stress analysis procedure.