Session: 18-05 Metallurgy, Coating and Repair I

Paper Number: 126858

126858 - Metallurgical Investigation and Failure Analysis in GTD-111 Stage 2 Buckets From an Industrial F-Class Gas Turbine 

A utility experienced cracking in multiple row 2 blades in a large f-class power generation gas turbine after only ~7,000 hours and ~30 starts following a standard repair and rejuvenation heat treatment cycle. The blades were cast from a directionally solidified (DS) superalloy and the cracking was found in the shroud section of the blade in the Z-notch region. A detailed failure investigation was conducted to determine the failure mechanism and most likely contributing factors to root cause in terms of design, operation, fabrication, and metallurgy. Three blades, two with visible cracks and one without cracks, were subjected to non-destructive and destructive evaluation. Methods consisted of visual inspection, 3-D scanning, physical measurements, process compensated resonant testing (PCRT), chemical analysis, optical metallography, LED surface topological evaluation, and scanning electron microscopy. The failure mechanism was determined to be due to creep with damage propagating along the grain boundaries in a high stress concentration area. Evaluation of precipitate structure and size also confirmed this area exhibited the highest temperature during operations. Detailed chemical composition also determined metallurgical risk factors were a contributing factor due to differences in key elements between the different casting houses. The findings from this work will help better define key factors that influence the high temperature performance of nickel-base superalloys used in the hot section of industrial power generating turbines.

Presenting Author: Alex Bridges Electric Power Research Institute

Presenting Author Biography: Alex Bridges is a Sr. Team Lead at The Electric Power Research Institute (EPRI) in the Materials group. His primary role is to oversee the high temperature mechanical testing lab at EPRI in Charlotte, NC, which is equipped with >60 creep testing machines and several servo hydraulic frames for evaluating creep, fatigue and other damage mechanisms. His research has been focused on high temperature materials behavior, analysis of creep behavior, material property development, additive manufacturing of nickel-base superalloys, development of non-traditional testing methods, microstructural characterization, weld repair research and field test methods.

Authors:

Alex Bridges Electric Power Research Institute
John Shingledecker Electric Power Research Institute
Yongqing Wang Duke Energy