Knowledge is key to sourcing the most effective replacement coatings, says Garret Haeglin

part of the routine maintenance schedule and the quality of the new coatings is dependent on attention to detail and the expertise of the refurbishment team. With a high level understanding of the processes, it is possible for operators to assess this expertise and select the most suitable suppliers. Tere are a number of features and processes used when applying high- quality coatings: and attention to detail is essential for optimum performance. Many gas turbines are used to support national power grids, generating electricity especially at times of peak demand. As such, their continued reliability offers that reassurance that when we flick the switch, the lights will come on.

I Components in an industrial gas turbine

are subjected to high temperatures that can cause oxidation, corrosion and even fatigue within their microstructure. Tese degradation mechanisms can be a limiting factor in not only the operating interval of the gas turbine, but also the overall life of

ndustrial gas turbines rely on specialised coatings in order to deliver continued performance and reliability. Renewing these protection systems is an important

the component. Specialised coatings have been developed to protect these components and extend their operational life as well as improve the overall performance of the gas turbine. Te process of replacing these protection systems requires expert knowledge and state-of- the-art equipment to ensure that the new coating performs equal to, if not better, than the original. An attention to detail down to microscopic levels is required in a continuous and rigorous quality control strategy. However, finding the most appropriate coatings supplier requires the turbine operator to have a certain amount of knowledge about the process. By asking a number of insightful questions, it is possible to determine what level of expertise and quality controls are at the disposal of the potential vendor.

METHODOLOGY Industrial gas turbine coatings require an array of application methods that involve specific processes and equipment. High

Flow checks ensure cooling passages remain operational after coatings have been applied

Robotic equipment delivers a more uniform application 18

velocity oxygen fuel (HVOF), plasma, arc wire, combustion, air spray and chemical vapour deposition (CVD) are all used in the refurbishment of gas turbine components. Different coatings have slightly varied bonding properties with different substrates, so it is essential to understand the conditions required to achieve a perfect bond. A coatings bond is one of the most critical aspects of its success in service. As such, it should be in focus during all processes associated with coating. Furthermore, the remaining range of properties of the finished coating must be sufficient for the application – the hardness value is an indicator of the proper application of wear coatings while the surface roughness will have a major impact on flow efficiency. By inspecting the microstructure and mechanical properties of the coating it is possible to verify that it was applied to required specifications and that it will provide all of the expected benefits in operation. In every refurbishment project, establishing the process foundation is essential to the long-term success and durability of the coating. Tis involves

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