Aqueous Corrosion of Deformed Steel Under Simulated Diluted Bitumen

Abstract

The effect of predeformation on corrosion of ASTM A106B pipeline steel exposed to 1.7 mM sodium chloride droplets covered by simulated diluted bitumen was evaluated. The microstructures of ASTM A106B pipeline steel with and without predeformation were examined by electron backscatter diffraction and optical microscope. Corrosion of pipeline steel under the chloride droplet covered by simulated diluted bitumen for 5 min was studied with and without predeformation using scanning electron microscopy. Corrosion was initiated at the surface of ASTM A106B pipeline steel after 5 min of exposure. The predeformation increased the number of pits initiated at the steel surface and the number of partially dissolved inclusions. Scanning electron microscopy, profilometry, and x-ray photoelectron spectroscopy measurements were used to characterize the corrosion of the specimens with and without prior deformation after 24 h of exposure to an oil-covered droplet. The corrosion products coalesced and formed a small circular ring which deviated from the geometric center of the droplet. The diameters of the circular rings for the unbent and pre-bent specimens were 2.371±0.125 mm and 2.465±0.046 mm, respectively; the distances between the circular ring centers and droplet centers were 0.599±0.124 mm and 0.620±0.190 mm, respectively. The average corrosion penetration of the predeformed specimen was 1.18±0.09 times higher than that of the specimen without predeformation.