| Summary: | The following report investigates the use of abradable seal technology in industrial steam turbine applications. Abradable seals are a highly adaptable, widely applicable and cheap method of improving seal performance. By retrofitting abradable coatings to existing labyrinth seals, improvements in the range of 0.5% - 1% power output are seen with cost returns within two years [1]. The intention of this investigation was to develop fundamental understanding of the seal degradation process. A Multi Oxidation and Incursion Steam Test (MOIST) rig was designed from concept, through detailed design and finally commissioned. During commissioning the capabilities of the MOIST rig were defined. Although flowing steam operation was not achieved during this investigation, a theoretically proofed steam system is in place for future development. High temperature operation was achieved, although not reliably. Reliable, repeatable atmospheric tests were developed, representative of the start-up and shut-down operations of an industrial steam turbine. These tests produced relative velocities up to 121ms-1 between coatings and blades, and incursion rates up to 50μms-1. ST12T, Nimonic 80A and Nimonic 101 blade materials were tested against a bentonite-NiCrAl abradable coating. The results suggest that the bentonite-NiCrAl abradable coating tested was highly suitable as an abradable coating for all blade materials. Additionally, high temperature tests are necessary to fully prove the use of blade materials against coating systems. Simultaneously, non-MOIST rig oxidation testing was performed in the range of 580˚C - 800˚C in static air and 580˚C in flowing steam for exposure times up to 5000 hrs. Bentonite-NiCrAl top coat - NiAl bond coat and either a STG-9T or IN625 substrate were analysed to devise mechanistic models for the oxidation of the top coat, bond coat, substrate and all associated interfaces. It was concluded that steam oxidation is intrinsically different to air oxidation and that adapting the bond coat to include Cr would significantly improve the oxidation resistance and service life of the coating system investigated.
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