Correlation between field and laboratory exposures for boiler corrosion test – mechanistic study of chlorine induced corrosion.

For boilers manufacturers and operators, smart selection of materials is important. Thus, the\ua0understanding of corrosion mechanisms involved in the degradation of metallic components of the boiler\ua0is of great interest. In order to address corrosion problems in the boiler, probe exposures are performed\ua0in research and industrial projects. Valuable information is obtained from this test, such as material\ua0corrosion rates and deposit formation. However, due to the complex environment in the boiler, it is\ua0complicated to identified and study the corrosion mechanisms taking place. Therefore, laboratory\ua0exposures simplifying the conditions in the boiler can be used to study the corrosion mechanisms in\ua0more detail.In order to correlate corrosion behavior between field and laboratory exposure, samples of same\ua0material were exposed in both field and laboratory scale. Field exposures were performed in a waste\ua0fired CFB boiler with horizontal design. Air-cooled test probes were used in order to control the\ua0temperature of the 347H sample materials to 600 \ub0C. Pre-oxidized samples were exposed for 24 and\ua0144 hours and compared to laboratory studies. Special focus was given to the study of the mechanism\ua0of chlorine induced corrosion.After field exposure, optical examination of samples showed that the deposit material was easily\ua0detached form the samples surface. Chemical analysis of the deposit material shows that the deposit\ua0was rich in chlorine. Cross sectional views of all the samples show similar corrosion attack for both field\ua0and laboratory but more extensive attack was observed in the field samples. Presence of metal\ua0chlorides were detected at the oxide/metal interface of both types of exposures same as corrosion\ua0attack at the grain boundaries. The well-controlled laboratory exposures gave the opportunity to a more\ua0detailed characterization resulting in a better understanding of the propagation of the corrosion attack\ua0observed in the field exposures