Turbine Disk Rim Inspection and LPRimLife Analysis

This presentation addresses the challenging decisions utility owners/operators are facing relative to cracking in turbine rotor disk rim blade attachment dovetails. As the turbine fleet ages, indications of significant cracking in the dovetails are occurring at an increasing rate. Repair options are expensive, and replacement options even more so. Consequently, utilities are frequently challenged to justify when it is appropriate to repair or replace and, on the other hand, when continued operation for a specified interval is justified on the basis of acceptable risk of failure.

The presentation will discuss various ultrasonic inspection techniques used for the detection of indications the attachment region of LP rotors. Examples of the ultrasonic indications will be presented, including specific examples of single indications occurring on a single hook and regions where two or more hooks had indications stacked at the same circumferential location. Sizing means will be shown as well.

The analytical portion the presentation will discuss the use of the LPRimLife code used in the lifetime analysis of blade attachments. LPRimLife assesses the risk of attachment failure from stress corrosion cracking as a function of continued operation. SI developed LPRimLife under an EPRI research contract, and has since provided assessments services to numerous power producers. The impact of several analysis variables will be discussed including the proximity of indications to the notch block; single hook versus stacked indications; and, overspeed trip limits.

Presented on: December 10, 2009

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