Investigations on high temperature corrosion of wire enameling oven

The oven belonging to a wire enameling plant was heavily oxidized resulting in the contamination of the final product. The heating chamber of the oven therefore had to be removed prematurely from service and was replaced by a new one. Investigation carried out showed high phosphorous contents in the oxide scale of service exposed AISI 321. Service exposed AISI 321 subjected to the oxidation test in laboratory did not show phosphorous in the oxide scales. The phosphorous presence obstructed the chromia layer from protecting the underlying surface. Formation of coarse chromium carbide and sigma phase in the stainless steel was observed within a short exposure time. This reduced the chromium content below the critical limit required for protective chromia formation. These were the possible reasons of early service failure of the oven.