Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Reconditioning Technologies for Film Cooled Single Crystal Turbine Blading

[+] Author and Article Information
Alexander Stankowski

Alstom (Switzerland) Ltd.,
7 Brown Boveri Street,
Baden 5417, Switzerland

Hans Bissig

Alstom (Switzerland) Ltd.,
40 Zentralstrasse,
Birr 5242, Switzerland

Contributed by International Gas Turbine Institute (IGTI) division of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received July 25, 2012; final manuscript received August 13, 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 052101 (Apr 23, 2013) (8 pages) Paper No: GTP-12-1300; doi: 10.1115/1.4007774 History: Received July 25, 2012; Revised August 13, 2012

Increased availability, reliability, and performance combined with reduced maintenance costs are key factors for the success of gas turbine users. This paper focuses on the reconditioning of film cooled single crystal (SX) components used in the GT24 and GT26 fleet and the latest enabling technologies. The general reconditioning strategy is based on a thorough analysis of the accumulated field experience with SX parts and a controlled, stepwise introduction of new techniques. Reconditioning processes have been developed for different damage scenarios for components. This would include the most technically challenging SX “heavy” scope reconditioning. This paper gives an overview about the reconditioning sequence for SX components and some of its key process steps. As an example, the crack braze repair process is described in detail and several novel SX welding techniques for crack repairs and blade tip and temperature controlled leading edge wall thickness restoration are shown. This covers different processes such as tungsten inert gas (TIG) welding or laser metal forming (LMF) of SX components. During the last few years, highly automated production solutions and innovative production tools have been implemented, which enable high capacity and consistently high quality of reconditioning. After their successful validation and a limited phase of monitored production, these techniques are applied on rotating and stationary SX turbine parts. Validation criteria and the experience gained during the first years of commercial production and operation in the field will be presented.

Copyright © 2013 by ASME
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Fig. 1

An approach to turbine component reconditioning

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Fig. 2

Selected steps of the heavy scope reconditioning cycle for SX turbine components, example of an HPT vane

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Fig. 3

CT picture of location of insufficient wall-thickness at the leading edge

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Fig. 4

US measuring device for, e.g., GT24/GT26 HPT blades lifted above water basin

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Fig. 5

US measurement showing the clear detection of the first (main) reflexion peak

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Fig. 6

Comparison of NDT results (in mm) obtained by different test methods on the same HPT blade (measured at three different heights)

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Fig. 7

Example cracks on surface and cross section of SX base material (after oxide removal)

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Fig. 8

100% oxide removal in crack tip after FIC

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Fig. 9

Metal-concentration profile after FIC treatment and after brazing

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Fig. 10

SX cracks brazed, dendrite structure, and wide gap brazing

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Fig. 11

Good condition of frontrunner SX crack braze repaired HPT vanes after ∼5 kEOH engine operation

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Fig. 12

Industrial LMF tip repair process and below the resulting near net-shape weld buildup after LMF processing

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Fig. 13

Integrated photogrammetric tip geometry capturing made from 3D vision system.

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Fig. 14

Weld path generation by fully automated adjustment of preprogrammed weld tracks

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Fig. 15

Result of leading edge wall thickness restoration by temperature controlled LMF, with corresponding temperature and laser power recordings

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Fig. 16

Excellent condition of frontrunner SX weld repaired HPT blades after ∼12 kEOH



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