Factors affecting the corrosion of buried steel pipes
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Factors affecting the corrosion of buried steel pipes: The external factor for corrosion is the environment, and this external factor exerts its effect through internal factors. If external factors are absent, corrosion will not occur. In buried steel pipe systems, the section with a relatively more negative pipe-to-soil potential is the anodic zone, and it corrodes first. A. Areas that may cause galvanic corrosion: joints between different materials, and 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 pipes accelerate corrosion; damaged areas on coated pipes: exposed iron accelerates corrosion ； B. Areas on the metal surface subjected to different stresses: such as scratches, defects, elbows, threads, weld areas, etc. Stress on the metal surface in areas subject to force, such as mechanical stress, can accelerate corrosion in areas like elbows, scratches, defects, and threads ； Thermal stress: Corrosion is likely to accelerate at the weld area ； C. Differences caused by the external environment: oxygen concentration, salt concentration, temperature differences, pH value differences, bacteria, stray currents, etc. D. The corrosivity of soils with different compositions varies greatly in different geomorphic environments. (a) At the boundaries between clay, marshes, silt, slag, cinder, and adjacent sand, limestone, gravel, etc ； (b) Points crossing rivers, railways, and highways ； Pass through cement and concrete walls ； (c) At the surface-ground interface, near the waterline ； (d) Different salt concentrations (soils with a salt content of around 3 suffer the most severe corrosion) ； (e) Acidic soils cause more corrosion than neutral and alkaline soils ； (f) Higher temperatures cause more severe corrosion than lower temperatures; soils containing bacteria, such as sludge and humus soil, suffer more severe corrosion ； (d) Severe pipeline corrosion caused by stray current interference, etc.
Factors affecting the corrosion of buried steel pipes include: 1. Joints between different materials: areas such as coatings, rust layers, paint layers and bare metal, as well as scale and the metal surface itself; joints with such different surface conditions are prone to galvanic corrosion. 2. Areas on the metal surface that are subjected to different stresses: such as scratches, defects, bends, threads, weld areas, etc. These stress-prone areas are prone to accelerated corrosion. 3. External environmental factors: such as oxygen concentration, salt concentration, temperature differences, pH value differences, bacteria, stray currents, etc. – all of these factors can affect the corrosion rate. 4. Soil environment: Corrosivity varies greatly depending on the landscape and soil composition; for example, areas at the boundaries between clay, swamps, silt, slag, cinder, and adjacent sandy, calcareous, or gravelly soils are prone to corrosion. Passing through rivers, railways, roads, as well as through concrete and cement walls can also lead to corrosion. In summary, the corrosion of buried steel pipes is primarily influenced by factors such as the joints in the material, areas on the metal surface subject to stress, external environmental conditions, and the soil environment. .