Estimation of Residual Stresses in Pipe-Ring Specimens by Incremental Hole Drilling and X-Ray Diffraction Method

Abstract

Residual stresses are usually not considered in engineering calculations of components and structures, however, they are present more or less in most of components, such as castings, welded components, components produced by rolling, bending, etc. The main objective of presented research is to determine the residual stresses in seamless thin-walled pipes, i.e. in ring specimens cut out from hot-rolled pipes. Pipe Ring Notched Bend specimens cut out from a pipe are considered as an alternative to the standardized Single Edge Notched Bend specimen used for determination of pipe material fracture toughness. In this research, residual stresses in ten ring specimens are measured by two methods: Incremental Hole Drilling Method (IHDM) and X-Ray Diffraction (XRD). Hoop residual stress is considered as the most important one in pipes. Principal stresses, as well as orientation of principal coordinate system, are determined by IHDM, and subsequently, hoop residual stress is calculated. Direct residual stress in hoop direction is measured by XRD. All results are shown on diagrams up to the depth of 1 mm from outer surface of each ring. Direct comparison of results referring to residual stresses obtained by both methods of measurement is presented to conclude that measurement with XRD shows uncertainty at some depths of measurement, since that method of measurement gives results with some large local oscillations.