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RESEARCH PAPERS

Metallurgical Failure Analysis of a Rotating Blade in the Compressor Section of a Gas Turbine

[+] Author and Article Information
Fred V. Ellis

 Tordonato Energy Consultants, Inc., 4156 South Creek Road, Chattanooga, TN 37406tectn@aol.com

J. Pressure Vessel Technol 128(4), 632-637 (Dec 22, 2005) (6 pages) doi:10.1115/1.2172617 History: Received August 15, 2005; Revised December 22, 2005

A metallurgical failure analysis was performed for the stage 17 gas turbine rotating blade and stationary vane. Four pieces, including the failed rotating and stationary blades, were removed from the air-compressor section of a gas turbine. The damaged components were found during a borescope examination. The objectives were to determine the failure mechanism and to estimate an inspection interval. The measured chemical compositions of the rotating blade and stationary vane are consistent with that of 403 stainless steel. The failure mechanism for the rotating blade is fatigue based on the beach marks on the fracture surface and the transgranular cracking. The fatigue crack initiated at the trailing edge of the blade. The crack at the trailing edge is due to impact damage. The probable root cause of failure for the rotating blade is the loss of axial clearance between the stationary and rotating blades. Fatigue crack growth calculations were performed using the NASGRO computer program and the corner cracked plate geometry to estimate the inspection interval. The estimated inspection interval is of order of magnitude hours to days for failure by high-cycle fatigue crack growth.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Documentation of the four pieces removed from the air-compressor section of a gas turbine

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Figure 2

Failed stage 17 rotating blade fracture surface

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Figure 3

Cracking at trailing edge of stage 17 rotating blade

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Figure 4

Detailed photograph of fracture surface at leading edge showing ductile overlaod and fatigue crack tip (∼4.4×)

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Figure 5

Photographs of fracture surface at the center of beach marks and flat fracture (∼4.4×)

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Figure 6

Photograph of fracture surface at trailing edge of rotating blade, crack initiation site (∼4.4×)

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Figure 7

Photograph of metallurgical mount for rotating blade

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Figure 8

Crack on trailing edge of rotaing blade due to impact damage (150×)

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Figure 9

Microstructure of rotating blade at center of beach-mark fracture (300×)

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Figure 10

Documentation of damage to stationary blade attachment

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Figure 11

Tip of stationary vane is the unidentified airfoil remnant based on matching fracture faces, dimensions, and goodness of fit-up

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Figure 12

Faceted impact surface for unidentified airfoil piece and elongated grains indicating gross deformation (60×)

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Figure 13

Calculated crack growth as a function of cycles for the corner crack geometry and bending stress of 121MPa

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