SEM-EDX and AFM analysis for the surface corrosion morphology structure and roughness on embedded X70 external pipeline in acidic soil (peat) environment

The corrosion of underground pipelines, especially on external surfaces, is generally influenced by soil properties and surrounding environmental conditions. Corrosion of the external oil and gas pipeline could result in a catastrophic incident in the oil refinery sectors due to friable points and corrosion prevention failure, restricting pipeline performance under high-pressure situations. Furthermore, this issue could cause substantial financial costs for the industry, notably in pipeline maintenance. In this study, an investigation was done focusing on the surface morphology change of this external pipeline under a series of exposure times (14, 30 and 60 days) at ambient and acidic peat environments. Organic peat with a pH range of 4.5–5.5 was chosen, as it can potentially induce surface deterioration on this pipeline external surface. SEM images revealed the production of dispersive corroded deposits form and tiny irregular porosity on the surface of X70 steel, while EDX proved the presence of Fe, O, and C elements associated with corrosion products. Meanwhile, AFM measurements verified that the average surface roughness value increased between 0.06 μm and 5.9 µm, indicating an acidic attack by these acidic soil particles leading to the heterogeneous formation with some defects at random positions on this pipeline surface. The intergranular corrosion mainly contributed to this phenomenon along this pipeline and resulted in a progressive induction of non-uniform and pitting corrosion products.