Assessment of a premature failure in a gas turbine part

A premature failure of an inlet guide vane in a gas turbine has been the su bject of a rigorous study and the present paper describes it in detail. It was established that failure occurred by fatigue crack growth which was ini tiated from a surface defect, in the form of a non-metallic inclusion clust er, at the vane root location where working stresses were highest. From a careful fractographic study and fatigue data, it was assessed that t he fatigue stress range for this failure was from 260 to 530 MPa. Strain ga uge measurements indicated a real working stress range of 210-450 MPa and d emonstrated the usefulness of the fractographic predictions. It was recommended that (a) the guide vane root be increased in thickness s uch that the working stresses be reduced by some 40% and (b) the Vane be fa bricated from a forged steel rather than a casting. The latter reduced the extent and size of non-metallic inclusions and it was assessed that fatigue crack growth would not be initiated from the worst inclusion cluster obser ved in the forged steel guide vane component. (C) 2000 Elsevier Science Ltd . All rights reserved.