Possible locations of corrosion points on buried steel pipes

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Possible locations of corrosion points in buried steel pipes: In buried steel pipes, the areas where the pipe-ground potential is relatively negative are the anodic zones, and corrosion occurs there first. 1. Areas that may cause galvanic corrosion: joints between different materials, as well as regions with varying surface conditions (such as coatings, rust layers, coatings on bare metal, oxide scales on the base metal) ； Iron-copper connections: iron accelerates corrosion; galvanized iron sheets: zinc accelerates corrosion; connections between old and new pipes: the new pipe accelerates corrosion; damaged areas on coated pipes: exposed iron accelerates corrosion. 2. Areas on the metal surface that are subjected to different stresses, such as scratches, defects, bends, threads, weld areas, etc. Corrosion accelerates easily on the parts of metal surfaces that are under stress, such as mechanically stressed elbows, scratches, defects, and threads. Thermal stress: It can accelerate corrosion at the weld area. 3. The external environment leads to variations in oxygen concentration, salt concentration, temperature differences, pH value differences, bacteria, stray currents, etc. The external factor of corrosion is the environment, and the external factor comes into play through internal factors. If external factors are absent, corrosion will not occur. The corrosivity of soils with different compositions varies greatly depending on the geomorphic environment. At the boundaries between clay, marshland, silt, slag, cinder, and adjacent sand, limestone, gravel, etc ； Points across rivers, railways, and highways ； Wearing cement and concrete walls ； At the surface-ground junction, near the waterline ； Different salt concentrations (soils with a salt content of around 3% suffer the most severe corrosion) ； Acidic soils cause more corrosion than neutral and alkaline soils ； Higher temperatures cause more severe corrosion than lower temperatures; soils containing bacteria, such as sludge and humus-rich soil, suffer more severe corrosion ； Pipeline corrosion is severe due to interference from stray currents, among other issues. Buried oil and gas pipelines can extend for thousands of kilometers, passing through various types of soil, rivers, and lakes. Due to the variability of the soil, freezing and thawing in winter and summer, changes in groundwater levels, plant roots that penetrate the coating, microorganisms, stray currents, and other complex conditions associated with burial, these pipelines are exposed to a challenging corrosion environment. Corrosion rates vary greatly across different regions in our country; the minimum rate is 0.004 mm/year, while the maximum can reach 1 mm/year or even higher. In the presence of stray currents or microorganisms, a 7-mm-thick steel pipe can be perforated within a few months.