Coatings for Advanced Large Frame Combustion Turbines for Power Generation

Use of metallic coatings for protecting hot section blades and vanes of combustion turbines for power generation has been a common practice for the last three decades. Since these coatings have to be optimized both with respect to different forms of corrosion and operation (base load vs. peak load) their performance can be machine specific. Power company users generally do not have sufficient knowledge of the failure mechanisms of the coatings and the basis for selecting coatings to suit their specific requirements. This paper describes the evolution of metallic coatings, discusses failure mechanisms, and describes a methodology for comparing and selecting machine-specific coatings. The methodology, which can be used to rank and predict the remaining life of coatings and for optimizing operation, forms the basis of a computer code known as COATLIFE. The ingredients of this methodology, i.e., degradation modeling and thermomechanical fatigue life (TMF) prediction, are reviewed in the paper.