Source: https://www.dfctank.com/news/analysis-of-external-corrosion-mechanism-of-oil-tank-and-pipeline.html

The external corrosion phenomenon of oil tank pipelines is relatively common. In the process of managing and controlling related corrosion problems, engineers and related technical personnel should analyze and evaluate the operating environment and operating principle of the equipment in combination with lean and refined on-site management, so as to enhance the operating quality and efficiency of the equipment.
 
External corrosion situation and cause analysis
The corrosion problems of oil storage tanks and pipeline facilities are relatively serious, and at the same time, in different seasons, different regions, different places, and different humidity and temperature environments, it will cause corrosion effects on the oil storage tanks and corresponding oil pipelines, specifically including the following aspects.
 
External corrosion of oil tank
The phenomenon of external corrosion of oil tanks is relatively common. Because the external surface of oil tanks is usually combined with the use of steel materials, at the same time, there is a large steel structure area in the vault area of oil tanks, and the relevant areas are also relatively affected by the surrounding environment. The anti-corrosive coating applied on the surface will also fall off and peel off under the influence of external adverse factors. For example, when the water on the top or periphery of oil tanks increases, it will lead to corrosion for a long time, and the large area of coating around oil tanks will peel off by the wind, which will further aggravate the impact of external corrosion of oil tanks. Corrosion around the bottom of the oil storage tank is also relatively common. The steel plate at the bottom of the oil storage tank is the stress part of the whole oil storage tank and during oil storage.

Under the influence of oil pressure, its internal structure will appear uneven settlement, which will lead to corresponding grooves between the tank bottom and the concrete base over time. Under the influence of heat expansion and cold contraction, the grooves will provide a gathering place for the surrounding accumulated water, eventually causing serious corrosion. Through data investigation and analysis, it can be seen that the corrosion phenomenon at the bottom of the oil storage tank is relatively serious, and the accumulated water at the bottom of the oil storage tank mainly comes from the rainwater flowing vertically from the tank wall, which leads to the steel plate and coating at the bottom being soaked in water for a long time. Because there are corresponding grooves at the bottom, the accumulated water inside is difficult to evaporate, which finally provides external conditions for the growth of bacteria and plants, and aggravates the corrosion at the bottom of the oil storage tank. Secondly, the phenomenon of large-area coating peeling off by wind is relatively common. In the monsoon season, due to the influence of wind, the anticorrosive coating coated on the tank body will also be affected by the corresponding peeling-off, which will ultimately have a great impact on the anticorrosive performance of the tank body. In addition, the phenomenon of water accumulation at the top of an oil tank is relatively common. Generally, the corrosion of water accumulation at the top of the oil tank is mainly concentrated in the relatively low-lying position around the top of the oil tank, often accompanied by steel rusting. Because the steel plate is exposed to the wind and sun, it is cracked under the joint action of water accumulation. In addition, a large amount of water accumulation around the top of the oil tank leads to serious electrochemical corrosion on the steel surface.
 
Corrosion of Oil Pipelines Corrosion of oil pipelines is also relatively common. Oil pipeline corrosion is mainly manifested in the corrosion of the supporting base, and the corresponding corrosion parts are usually on the lower and upper surfaces of the pipeline. Moreover, the pipeline is affected by mechanical vibration during operation, and the coating will peel off due to the wind. Generally speaking, the corrosion of steel support bases is relatively common. In the process of oil transportation, due to the uneven distribution of pressure on the pipeline, in order to avoid excessive concentration of pressure and ensure the safety of the transportation line, it is often necessary to set up a dense steel support base. The steel base is connected to the concrete cap, and after the steel base is set up, it also needs to be treated with anti-corrosion. Usually, white coating is used to effectively isolate the steel base from the outside air and moisture. However, if there are related areas, Generally speaking, the water accumulation between the steel base and the concrete pile cap is caused by the mechanical vibration in the oil transportation process of the oil pipeline, which makes the relevant areas low-lying, while the corrosion phenomenon on the lower surface of the pipeline is mainly reflected in the situation that the white coating falls off and becomes warped, which leads to the corrosion phenomenon in the area where the coating falls off. The fundamental reason for this phenomenon is that the lower surface of the pipeline is relatively wet, and it is difficult for both sides of the pipeline to gather or accumulate excessive water. However, under the stress of the pipeline, it is easy to collect rainwater, and the relevant areas will condense into ice in winter when the temperature is relatively low, and the white coating will crack under the influence of thermal expansion and cold contraction. In addition, the upper surface of the pipeline is often corroded, which is reflected in the cracking of the white coating, accompanied by brown rust. The reason for this phenomenon is that when the pipeline coating is affected by the atmospheric environment. However, the phenomenon of pulverization and cracking occurs. Finally, rainwater and the atmosphere contact the surface of pipeline steel through the cracked part, resulting in corresponding chemical corrosion.
 
Mechanism analysis of the external corrosion process
External corrosion of pipelines and external corrosion of oil tanks are usually accompanied by different degrees of chemical reactions. In this process, engineers and related technical personnel should enhance the service performance of equipment through meticulous on-site control. The related mechanism is as follows.
 
Through the analysis and evaluation of the external corrosion phenomenon of oil tanks and oil pipelines, it can be seen that due to the fact that oil tanks and oil pipelines have more steel materials, it is necessary to apply corresponding anti-corrosion coatings to the surface of oil tanks and oil pipelines in the initial construction process. However, after the corrosion phenomenon occurs, it is usually accompanied by the cracking or cocking of the organic coating, which leads to the direct contact of the steel surface with the atmospheric environment and finally leads to corrosion. In addition, in this process, if the organic coating fails, the bonding force between the coating and the steel surface will be reduced, and the coating will fall off and the steel structure will be corroded. In a word, in the process of external corrosion, it is usually the direct contact between steel and water vapor that leads to the corresponding electrochemical corrosion and finally generates rust.
 
Organic coating failure
Organic coatings are affected by the external water environment and light environment for a long time in the process of use. Due to the corresponding differences in their physical characteristics in specific environments, it is easy to appear the phenomenon of pulverization and cracking, which eventually leads to the phenomenon of peeling off between coatings and steel plates. In addition, there are different thermal expansion coefficients between organic coating and steel. In the case of excessive temperature difference, it is easy for the organic coating to crack under the influence of stress, which eventually leads to the steel structure being exposed. Due to the unqualified construction quality, the organic coating will fall off or become warped under the influence of freezing and external natural factors. Through analysis, it can be concluded that on the one hand, the failure of the organic coating on the surface of oil pipelines and oil tanks is due to the stress of thermal expansion and contraction, on the other hand, the physical and chemical characteristics of the organic coating have changed due to external environments such as strong wind, high temperature and direct sunlight, and finally the coating cracks and falls off. No matter which kind of organic coating fails, the water in the atmosphere will enter between the coating and the steel surface, and finally, the corresponding water film will be produced. Over time, the shedding area of the organic coating will be further expanded, and the corrosion effect will be further aggravated. In addition, when the oil tank or oil pipeline is affected by external mechanical vibration or wind, the binding force between the coating and the steel structure will be reduced, and finally, the corrosion phenomenon will be further aggravated.
 
Principle of atmospheric corrosion of steel surface
When the organic coating falls off or cracks, the moisture in the atmosphere will react with the steel in the structure, forming a water film. There are hydrogen ions and hydroxide ions in the water film, thus forming a corresponding electrolytic solution, which makes the steel undergo an electrochemical reaction. Generally, the steel will be used as an anode to be converted into iron ions and electrons, while at the cathode, oxygen, water and iron ions will react, eventually generating corresponding hydroxide ions. The total reaction is that iron contacts with oxygen and water to form the ferric hydroxide, and finally, related substances are dehydrated to form rust, which has unstable chemical and physical properties, and will fall off, eventually making steel.

The degree of surface corrosion is further aggravated. In addition, the water film formed between the coating and the steel surface will constantly absorb sulfur dioxide and ammonia gas in the air, eventually causing corresponding alkaline corrosion or acid corrosion to the steel surface, which will lead to a further increase in the working pressure of oil pipelines or oil tanks of related steel materials over time, and eventually lead to equipment failure, resulting in serious safety accidents.
 
Countermeasures and suggestions
In order to realize the anti-corrosion control of oil storage tanks and transportation pipelines, it is necessary to combine directional and refined anti-corrosion treatment. In this process, engineers and related designers should adopt the top-level design, analyze and evaluate the current mechanism of external corrosion of oil storage tanks and pipelines, focus on controlling electrochemical corrosion, and enhance the binding force between anti-corrosion coating and pipelines, so as to achieve the anti-corrosion control effect. At the same time, the construction unit also needs to improve the construction quality of the project and enhance the anti-corrosion control effect.
 
Control the construction quality of the organic coating
From the above analysis and evaluation, it can be seen that the application of corresponding organic coatings on the surfaces of related materials will enhance the service life of oil tanks and oil pipelines, and the application quality of related organic coatings will also affect the service life of anti-corrosion. To control the construction quality of organic coatings, it is necessary to maximize the binding force between organic coatings and steel surfaces. If they have good binding force, there will be no corresponding water film between steel surfaces and organic coatings, and thus no corresponding electrochemical reaction will occur. From the chemical reaction formula, it can be seen that only after the electrolyte is connected can the corresponding electrochemical reaction take place between the anode and the cathode. If the organic coating and the steel structure have good binding force, the electrolyte will not be connected. If there is a corresponding binding force difference between them, the electrolyte will eventually be connected to form a chemical battery, which will lead to a chemical reaction. To control the binding force between organic coating and steel surface, it is necessary to
Through data analysis, it can be seen that nearly 60% of the quality defects of anti-corrosion coating are related to surface rust removal. In the oil depot construction activities, the construction party needs directional treatment of steel oil storage tanks and oil pipelines. In the early stage of construction, the enterprise needs to check the qualification of the construction unit to ensure that the construction unit has the corresponding construction technology and the construction operation can be carried out normally and stably. If the qualification examination of the construction unit is not strict, it will be difficult to guarantee the improvement of the construction quality. At the same time, the construction party and the project party also need to introduce professional anti-corrosion management personnel in time to evaluate and judge the anti-corrosion performance of the whole project and make corresponding protection acceptance. In the subsequent process of coating the organic anti-corrosion coating on the steel structure surface, the enterprise needs to actively invite third-party organizations and staff to test the anti-corrosion performance of pipelines through professional equipment. Ensure the quality and efficiency of organic coating construction can be effectively improved. In the process of surface treatment and control of related equipment, the oxide on the steel surface needs to be cleaned in advance before the corresponding anticorrosive coating can be applied. At the same time, it is also necessary to ensure that the roughness of the whole surface can meet the corresponding requirements, so as to increase the contact area between anticorrosive coating and steel, and then increase the binding force between them. In the process of acceptance management of organic coatings, it is also necessary to ensure that the coatings are in good condition. If unqualified organic coatings are found, they need to be rectified, and then accepted to ensure that the coatings are qualified.
 
Optimize the structure and prevent water accumulation
Through field investigation and analysis, it can be concluded that there is a great correlation between the shedding of organic coating and the soaking in water, which further aggravates the corrosion of steel surfaces. The soaking in water mainly occurs in the areas around the bottom of the oil storage tank and the supporting base of an oil pipeline. Therefore, it is of great practical significance to eliminate the accumulated water and realize effective prevention and treatment of accumulated water for improving corrosion resistance. In this process, the designer needs to optimize the structure to prevent the corresponding water accumulation at the top and bottom of the oil tank and the base of the oil pipeline. In general, it is necessary to set intercepting ditches around the top of the oil tank to control the drainage pipes at the top of the tank, so as to reduce the corrosion of the organic coating on the tank wall caused by the vertical downward rain.
Ring; On the other hand, engineers and relevant designers also need to set up corresponding protective umbrellas around the bottom steel plate of the tank to reduce the rainwater accumulated on the steps of the bottom steel plate. In addition, corresponding water diversion devices should be set up at particularly wet parts to guide the rainwater to the surface, so as to avoid freezing the bottom of the pipeline in winter.
 
Thermal spraying technology anticorrosion
Thermal spraying technology mainly uses a heat source to heat the coating until it is molten or semi-molten, then atomizes it with high-speed airflow, and then sprays the corresponding atomized raw materials to the surface of steel parts, so as to construct the corresponding anti-corrosion coating, and finally achieves the control effect of anti-corrosion and wear resistance. Thermal spraying technology has relatively efficient application characteristics, and the related technology and equipment are simple, economical and flexible, so it can be widely used in all aspects of anti-corrosion control of engineering projects. In recent years, thermal spraying technology has also made great progress, which can control the anti-corrosion of steel structural materials with different shapes. Compared with traditional coating technology, this technology can save raw materials, and at the same time, it can ensure that the coating forms a good bonding force with the steel surface, thus realizing effective protection of steel structures.

Conclusion
 
In the process of controlling the external corrosion of oil storage tanks and pipelines, engineers and related technical personnel should carry out top-level design, optimize various anti-corrosion control work, improve the operation efficiency of equipment, combine lean and refined management ideas, strengthen the anti-corrosion control of pipeline projects and oil storage tanks, strengthen quality inspection, and formulate clear control standards, so as to improve the operation quality and efficiency of the equipment.
 

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