Tests were conducted on the thermal fouling of 8.71 mm i.d. type 304 stainless tubes by flowing suspensions of ferric oxide in water over concentrations of 0-3750 ppm, Reynolds nabers of 10,100-37,600 and heat fluxes of 0-292 kW/m². Deposits were subjected to microscopic examination and electron microprobe analysis. The results were explained by invoking electrochemical crevice corrosion as the mechanism governing the fouling.