The effect of cleaning procedures on corrosion coupon surface topography

Several standardised procedures are available to corrosion researchers for preparing, cleaning, and evaluating corrosion test specimens in experimental investigations using coupon mass loss to measure corrosivity. These procedures may be mechanical, chemical or electrolytical in nature and are designed to remove corrosion products from coupons, ostensibly without significant loss of base metal. However, recent very detailed short-term corrosion experiments suggested that some of the procedures may interfere with the mass loss estimation and also may cause unexpected surface characteristics. The latter is problematic if the topography of the cleaned surfaces is of interest, for example in the investigation of the corrosion of mild steel surfaces exposed to marine immersion conditions for which, typically, corrosion is not uniform. This paper reports on a comparative study of the effect, on surface images, of the mechanical, chemical and electrolytic corrosion product removal procedures. It presents scanning electron microscopy images and the differences of final surface topography corresponding to each cleaning methods. This has implications for the selection of cleaning technique for specific investigations.