Neutron and X-Ray Diffraction Residual Stress Measurements on Power Generation Turbine Blades: Comparison with Finite Element Analysis

Abstract

The residual stresses in used and unused turbine blades from a 380 MW steam power generator were measured by neutron and X-ray diffraction techniques and modelled using finite element analysis computation. One of the main engineering problems with the turbine blades is the growth and propagation of fatigue cracks which may form around the lacing hole under the strain of cyclic rotation and vibration during the service life of the component. Careful analysis of the residual stress distribution is therefore important in assessing the fatigue-limited life of the turbine blades and improving the turbine blade design. The large penetration depth of neutrons compared with that for X-rays allowed us to measure the triaxial residual stress in the vicinity of the lacing hole, averaged over the whole thickness of the blade. Our measurements indicate the existence of triaxial residual stress in both used and unusued turbine blades. The neutron results have been complemented by the data measured, using a laboratory based X-ray facility, from points on the blade surface at locations corresponding to those for the neutron measurements.