Thermal Spraying with Diode Lasers

Abstract Boiler tubes in biomass and incineration plants are exposed to extreme operating conditions. To create vapor pressure within the pipes that makes an effective drive of the power‐plant turbines possible, flue gas temperatures of up to 1000 °C must be realized within the combustion chamber of the boiler. No pipe‐material will sustain the chemical processes induced in this way for very long. Already at temperatures of 350 °C, the chlorine in the flue gas increasingly reacts with the iron of the ferritic pipe materials. A rapid and progressive oxidation process begins and reduces the wall thickness of the pipes, which can lead – using unprotected pipes – to tube leakage in some cases within less than one year (Fig. 1). In order to improve the lifetime of pipes, many power plant operators count on metallic or ceramic corrosion‐protection coatings. With their help, the material decomposition process can be delayed and the lifetime of the pipes can be tripled or even quadrupled. However, the investment in a coating in most cases is profitable already if lifetime of pipes is doubled because the exchange of corroded pipes requires new tubes plus a temporary shutdown of the whole boiler system.