Authors: Mitchell, K. C.; Spink, G. M.; Martin, R.

Source: Energy Materials: Materials Science and Engineering for Energy Systems, Volume 2, Number 3, September 2007 , pp. 191-196(6)

Publisher: Maney Publishing

Included in the following Connect Compilations:

• Volume 2, Number 3: 7th Charles Parsons Turbine Conference

Abstract:

Work performed to refurbish last stage blades (LSBs) with articulated tip struts on low pressure steam turbine rotors is described. During the late 1990s, a series of erosion shield failures occurred on these high twist last stage blades, resulting in significant damage to tip struts and blades and causing generation downtime. Metallurgical investigation revealed the shield braze bond had degraded during cyclic service, resulting in shield detachment from the blade. Repair options considered included welding of Stellite bar to the blade leading edge, deposition of hardfacing weld metal on the blade leading edge and replacement of the complete blade tip with a laser hardened blade insert. From initial stress corrosion cracking tests, the laser hardened insert was selected. Trials to optimise welding parameters, joint set-up and weld bead deposition sequence are reported. The completed joint requires post-weld heat treatment to reduce residual stress and produce acceptable hardness across the weldment. Further high cycle fatigue and stress corrosion cracking testing of the aerofoil weld confirmed the suitability of this repair method. The susceptibility of the laser hardened insert to fatigue and environmentally assisted cracking was also found to be acceptable. Examples of the successful application of this patented repair technique are given.

Keywords: REFURBISHMENT; LASER HARDENED INSERT; WELDING; LP BLADES

Document Type: Case Report

DOI: http://dx.doi.org/10.1179/174892408X373554

Publication date: 2007-09-01

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