Find the reasons for the different corrosion on the outer wall of the oil storage tank

Is this tank constantly in a half-filled state, resulting in differential corrosion caused by differences in temperature and medium contact?

Since other storage tanks have insulation layers, it’s likely that this tank also has one, right? After removing the insulation from the upper and lower tank sections, it was found that rusting was more severe on the upper side than on the lower side. I suspect that the sealing performance of the insulation layer on the upper side was not adequate, which allowed rainwater to seep in over time and cause corrosion of the tank. Furthermore, the thickness of the anti-corrosion coating on the upper tank body probably doesn’t meet the requirements either, right? Of course, this is just a guess in one direction, for reference only

The water sprayed contains too much rust, and it is blocked by the reinforcement ring, so it cannot flow to the lower part.

Looking at the picture, is there a reinforcement ring around the waist of the storage tank? Using this as a boundary, the upper part suffers severe corrosion while the lower part is relatively less affected. There are more short circuits and attachments such as those on the upper fence, which indicates localized corrosion; this creates greater possibilities for gap corrosion and electrochemical corrosion. Either strengthen the ring, intentionally or unintentionally, so that at least the outer surface of the lower part of the storage tank is not as moist and covered in liquid as the upper part.

Gas tank, with no insulation on the tank body.

The metal surface was exposed to water for too long. As can be seen from the diagram above, there are no rain protection measures on the top of the tank; during rainy seasons, rainwater flows down along the top and sides of the tank. When there is a wind-resistant ring in the middle, rainwater can only flow down along the outer edge of the wind-resistant ring, without coming into contact with the tank wall. When it is raining and there is wind, even with an anti-wind ring in place, contact with rainwater is inevitable; however, compared to the overall time that the tank wall is exposed to rainwater, the metal surface beneath the anti-wind ring is exposed to rainwater for a much shorter period of time. When a metal surface is in prolonged contact with water, electrochemical corrosion is more likely to occur. Due to [2], the entire electrochemical reaction relies primarily on the depolarization effect of oxygen; since oxygen diffusion is easier under thin liquid film conditions, it is also easier for the anti-corrosion coatings on the metal surface and the metal’s passivation layer to be damaged. A metal rust layer was formed. Corrosion of metals beneath scale is accelerated due to the autocatalytic effect of their inherent electrochemical corrosion. Once a corrosion layer is formed, the rust layer acts as a reservoir for water and oxygen, accelerating the corrosion of the metal surface. It is recommended that, based on the above analysis and the corrosion condition of the oil storage tank’s surface, installing a rain guard strip 50–100 mm wide around the edge of the tank roof can prevent rainwater from adhering to the metal surface of the tank. Alternatively, reducing the time that rainwater remains on the surface of the tank wall can shorten the period of electrochemical corrosion of that wall, thereby extending the lifespan of the anti-corrosion coating and indirectly protecting the metal of the tank wall from corrosion. It can extend the service life of storage tanks.

1. Gas tanks can also serve as insulation layers; the iron sheet covering the outside of the tank protects it from the effects of rain, snow, wind, frost, and intense sunlight. Additionally, the tank itself is coated with anti-corrosion paint, and these two measures work together to maximize the tank’s service life and extend the time before it needs to be recoated with anti-corrosion material. 2. If no insulation layer is used, it is still necessary to apply high-quality anti-corrosion paint in sufficient quantities and of good quality, and to carry out spraying again in accordance with the standards. 3. The anti-corrosion protection provided by the coating also has a limited lifespan; it is necessary to renew it after a few years or when the tank develops extensive rust.