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	Typical TMF cracks in a Frame 7EA bucket

Failure Modes

To evaluate the life of components, it is essential to identify the probable failure modes for a given component. The possible failure modes for hot section components include thermal mechanical fatigue (TMF), hot corrosion, creep, and coating oxidation and degradation.

The engineers at SwRI examine the parts using state-of-the-art laboratory facilities. They examine hot section parts failed in service and identify the most probable cause of failure.

Life Evaluation Methodology

In gas turbines, the life and integrity of the coatings, applied to protect the components from environmental attack and degradation, govern the life and maintenance intervals of hot section components. SwRI has developed state-of-the-art coating and TMF life prediction methods for several substrate/coating systems. The TMF model has been calibrated with service experience and can be used to predict the life of a specific coating on turbine blades in service.

Through an industry consortium program, GTD LIFE software was developed to calculate the remaining life of GE MS5002 engine first-stage buckets. This software is available to turbine users.

Coating Oxidation	Coating Degradation
Photomicrographs showing bond coating oxidation and degradation

Photograph of a corrosion-attacked area on a Frame 5 blade after 40,000 hours of service		Flow diagram shows the tasks required to develop a life management system for determining the life of gas turbine components. SwRI is one of the few organizations capable of performing each step in the development of these systems.

Metallography Results						COATLIFE Calculation
Click photo for larger image		Click photo for larger image
In-service degraded coating of a 7FA blade (left) and a 9FA blade (right) after 21,000 hours of service
					COATLIFE validation for Frame 7/9FA blades (GT29+ coating). Model prediction is in good agreement with metallographic results.

Typical interface cracking and crack growth as a function of time		Cracking at the bond coat/ thermal barrier coating (TBC) interface leads to TBC spallation. The results generated at SwRI show that these cracks form at the early stages of component life.

SwRI can offer you a full range of capabilities and experience in gas turbine technology including becoming an extension of your engineering department. For more information about SwRI gas turbine technology life evaluation studies or how you can contract with SwRI, please contact Klaus Brun, Ph.D. at kbrun@swri.org or (210) 522-5449.
 

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

August 29, 2008