Effects of Key Engineering Soil Parameters on the Surface of Pipeline Steel Under Different Environmental Exposures

Abstract

Pipeline steel (PS) electrodes were buried in seven different soil samples (SSs), and they characterized by weight loss (WL), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). WL measurements confirmed previous electrochemical measurements in terms of excessive corrosion rates under acidic media (SS 4). The SEM/EDX analysis also revealed a severe ulcerous corrosion attack on the entire surface of the electrode in SS 4. In fact, the retrieved steel surface was covered by a black layer of corrosion products; and the XRD analysis on corrosion products encompassed iron phases: goethite, hematite, and ferryhidrite. These oxides are the habitats of most acidic soils, and cause re-acidification of the soils during hot climatic conditions. Overall, analysis showed that the corrosion of buried PSs differ from environment to environment, and the corrosion rates more closely related to pH and soil resistivity. Distinctively, corrosion rates were least under neutral environment (soil with pH 7.7) and higher in soil with pH value of 3.1.