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

Paper in proceeding, 2018

For boilers manufacturers and operators, smart selection of materials is important. Thus, the understanding of corrosion mechanisms involved in the degradation of metallic components of the boiler is of great interest. In order to address corrosion problems in the boiler, probe exposures are performed in research and industrial projects. Valuable information is obtained from this test, such as material corrosion rates and deposit formation. However, due to the complex environment in the boiler, it is complicated to identified and study the corrosion mechanisms taking place. Therefore, laboratory exposures simplifying the conditions in the boiler can be used to study the corrosion mechanisms in more detail.
In order to correlate corrosion behavior between field and laboratory exposure, samples of same material were exposed in both field and laboratory scale. Field exposures were performed in a waste fired CFB boiler with horizontal design. Air-cooled test probes were used in order to control the temperature of the 347H sample materials to 600 °C. Pre-oxidized samples were exposed for 24 and 144 hours and compared to laboratory studies. Special focus was given to the study of the mechanism of chlorine induced corrosion.
After field exposure, optical examination of samples showed that the deposit material was easily detached form the samples surface. Chemical analysis of the deposit material shows that the deposit was rich in chlorine. Cross sectional views of all the samples show similar corrosion attack for both field and laboratory but more extensive attack was observed in the field samples. Presence of metal chlorides were detected at the oxide/metal interface of both types of exposures same as corrosion attack at the grain boundaries. The well-controlled laboratory exposures gave the opportunity to a more detailed characterization resulting in a better understanding of the propagation of the corrosion attack observed in the field exposures.