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ASM Failure Analysis Case Histories

Handbook of Case Histories in Failure Analysis

Edited by
Khlefa A. Esaklul
Khlefa A. Esaklul
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ASM International
Volume
2
ISBN electronic:
978-1-62708-215-0
Publication date:
1993
Book Chapter

Cracking in a Steam Turbine Rotor Disk

By
Richard L. Colwell
Richard L. Colwell
Air Products and Chemicals
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Published:
1993
Page range:
277 - 279

Abstract

An A-470 steel rotor disk was removed from the high-pressure portion of a steam turbine-powered compressor after nondestructive testing revealed cracks in the shoulder of the disk during a scheduled outage. Samples containing cracks were examined using various methods. Multiple cracks, primarily intergranular were found on the inlet and outlet faces along prior-austenite grain boundaries. The cracks initiated at the surface and propagated inward. Multiple crack branching was observed. Many of the cracks were filled with iron oxide. X-ray photoelectron spectroscopy indicated the presence of sodium on crack surfaces, which is indicative of NaOH-induced stress-corrosion cracking. Failure was attributed to superheater problems that resulted in caustic carryover from the boiler. Two options for disk repair, installing a shrink-fit disk or applying weld buildup, were recommended. Weld repair was chosen, and the rotor was returned to service; it has performed for more than 1 year without further incident.

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Richard L. Colwell, 1993. "Cracking in a Steam Turbine Rotor Disk", Handbook of Case Histories in Failure Analysis, Khlefa A. Esaklul

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