Laboratory Testing of the Atmospheric Corrosion of Steel

Abstract

AbstractThe atmospheric corrosion of a mild steel (0.09 C) has been studied in flowing atmospheres containing 1, 10 and 100ppm SO2 at 80, 85, 90 and 96% relative humidity. The flow rate was varied to give SO2‐supplies ranging between 0.4 and 250 μg SO2 cm−2 h−1. After an exposure period of 300 h testing was continued up to 5000 h in atmospheres free from SO2 at 85–100% relative humidity. Some of the samples were sprayed with distilled water to simulate wetting by rain or condensation. The corrosion attacks were followed by successive weighings. The composition of the corrosion products was studied using X‐ray diffraction, IR‐spectrometry and ESCA‐technique. The flow rates of the SO2‐containing atmospheres were found to have a marked influence on the corrosion attack. The corrosion rates could not therefore be related to the SO2 concentration of the atmosphere alone but rather to the supply of SO2 per unit surface area and time. Exposures performed at high SO2‐supply resulted in formation of corrosion products more protective than those formed at lower SO2‐supply. ESCA‐analysis proved formation of suphide containing corrosion products at SO2‐supply. ESCA‐analysis proved formation of sulphide containing corrosion products at SO2‐supplies ≥ 8 μg SO2 cm−2 h−1. Periodic spraying of the samples with distilled water were found to cause a drastic increase in corrosion attack.