Safe life approach considering creep-fatigue interaction and Weibull statistics for crack growth evaluation based on field feedback applied to a GT first stage blade

Abstract

The increased flexibility that the energy market requires makes the service condition of gas turbine (GT) components more and more critical in terms of creep-fatigue interaction. A new lifing strategy has been developed in order to evaluate the expected life of blades and vanes in this demanding service condition taking into consideration creep-fatigue interaction. The developed lifing methodology has been applied to the first stage blade of an Ansaldo Energia F-class GT and the life map has been compared with the available field feedback. With this procedure crack initiation in the base material is considered as the lifing criteria. So, the critical locations have been correctly identified and the number of predicted cycles correspond to service experience. The available field feedback has been treated by using Weibull statistics. The statistical treatment of crack size for the critical locations provides a crack initiation evaluation that is in good agreement with the lifing strategy. Moreover, the available field feedback on the first stage blade allows the correlation of the linear crack size with its depth. This relationship has been used to define the maximum allowable crack length for safe operation of this component.