Condition Assessment Study of A-286 Alloy Gas Turbine Wheel

Abstract

Life extension programs for rotating and nonrotating gas turbine components are popular and widely practiced in the industry. It is often possible to extend the life of the component beyond the design life through life assessment studies. The life assessment study generally includes a combination of nondestructive and destructive tests. Considering the life assessment approach, a Frame 5002 unit gas turbine wheel was examined nondestructively. The material of the turbine wheel is A-286, which is an iron-based super alloy. This turbine wheel has accumulated more than 200,000 service hours. The objective for nondestructive testing of this wheel was to check for any material degradation and any surface cracking in order to ensure extended service hours. The nondestructive tests included eddy current test, ultrasonic flaw detection, replica metallography, and portable hardness test. As such, no significant abnormalities were detected in the nondestructive tests performed. The replica metallography revealed excessive carbide precipitation. It was recommended to retire the turbine wheel from service. The significant test result findings of replica metallography are presented and discussed in this paper.