Let’s talk about the corrosion of storage tanks

Thread Content

Corrosion of storage tanks: 1. Corrosion of tank walls and roofs ⑴ Carbon steel tanks: Uniform corrosion, pitted corrosion, and spot corrosion occur simultaneously on the inner wall; when corrosion generates a large amount of rust scale, severe under-scale corrosion can result. The inner wall of the main surface tank develops a large amount of rust; local corrosion occurs in certain areas, especially at the weld seams and in their heat-affected zones. In severe cases, leaks may occur in the tank walls. ⑵Stainless steel tank: Severe pitting on the inner wall, as well as cracks in the welds and heat-affected zones. The corroded areas were treated by patch welding to address the pitting, but even after this treatment, it is not possible to ensure that all pitted areas are identified and welded properly; thus, corrosion risks still remain. 2. Corrosion of the tank bottom plate: During actual use, the degree of corrosion varies in different parts of an oil storage tank. Overall, the bottom of the tank is the most severely affected by corrosion, which directly impacts the tank’s service life and the quality of the product. The specific forms of corrosion include pitting, ulcerated surfaces, and uniform thinning. It generally occurs in areas where the bottom plate is sunken, at sites of mechanical plastic deformation and at areas damaged during construction; pitting and stress corrosion cracking tend to occur there as well. This type of corrosion is mainly caused by water remaining on the bottom plate. In water, it is affected by dissolved oxygen, hydrogen ion concentration, chloride concentration, and temperature. The main areas affected by corrosion, as well as the causes of this corrosion, are the lower part of the tank wall (usually within 1 meter below the tank bottom) and the upper surface of the tank bottom. These areas suffer the most severe corrosion in oil tanks; electrochemical corrosion occurs there, and the form of corrosion is pitting. It is mainly caused by the water accumulated at the bottom of the tank; corrosion is resulting from chloride ions, dissolved oxygen, and sulfate-reducing bacteria in this accumulated water. Salts and organic silt in the sediments inhibit oxygen diffusion due to their viscosity. Corrosion is caused by the formation of an oxygen concentration cell.