The effect of defect introduction vs. load application sequencing on defect-induced stress distributions in steel samples

This study examines the effect of altering the sequence of defect introduct ion vs. load application on the defect-induced stress distributions in stee l samples loaded under conditions of uniaxial tension. The stresses in the samples were measured using neutron diffraction and Magnetic Barkhausen Noi se (MBN). In addition, the samples were scanned using Magnetic Flux Leakage (MFL) to determine the effect of sequencing on the MFL signal amplitude an d trend with changing applied loads. At loads resulting in local plastic deformation at the defect edge, studies show distinct differences in the defect-induced stress distributions betwe en through-holes milled prior to the application of load (pre-drilled), com pared to those milled while the sample was held at-load (in situ). The cons equences of these findings are discussed in light of MFL tool calibration a nd the subsequent determination of the Maximum Allowable Operating Pressure (MAOP) for in-service pipelines. The implications with regards to the hole -drilling technique for stress measurement are also discussed. (C) 2000 Els evier Science Ltd. All rights reserved.