External corrosion situation and cause analysis
The corrosion challenges faced by oil storage tanks and pipeline facilities are quite significant. Varied seasons, geographical locations, specific areas, and diverse humidity and temperature conditions contribute to corrosion effects on oil storage tanks and their associated pipelines. This encompasses several specific aspects.
External corrosion of oil tank
The occurrence of external corrosion on oil tanks is a prevalent issue. This is attributed to the use of steel materials for the external surface of oil tanks, especially within the vault area, where a substantial steel structure is exposed to the surrounding environment. The applied anti-corrosive coating on the surface is susceptible to peeling off under the influence of external factors. For instance, increased water on the top or periphery of oil tanks, often due to rainwater, leads to prolonged corrosion, causing the coating around oil tanks to peel off in windy conditions, exacerbating external corrosion.
Corrosion at the bottom of oil storage tanks is also common. The steel plate at the bottom, being the stressed component of the tank, experiences uneven settlement under the influence of oil pressure, leading to grooves between the tank bottom and the concrete base over time. These grooves become gathering places for accumulated water, fostering corrosion due to heat expansion and cold contraction. Data analysis indicates that bottom corrosion is severe, with accumulated water mainly originating from rain flowing down the tank wall. The presence of grooves impedes water evaporation, providing conditions for bacterial and plant growth, further intensifying corrosion.
Additionally, the widespread peeling off of coating by wind is a recurring issue. During monsoon seasons, the anticorrosive coating on the tank body is prone to peeling off due to strong winds, significantly impacting the tank's anticorrosive performance. Water accumulation at the top of an oil tank is also prevalent, particularly in low-lying areas around the tank top. This often leads to steel rusting as the exposed steel plate undergoes cracking due to wind and sun exposure. Moreover, a considerable amount of water accumulation results in electrochemical corrosion on the steel surface.
Corrosion of Oil Pipelines is likewise common, particularly in the supporting base. Corrosion tends to manifest on the lower and upper surfaces of the pipeline, influenced by mechanical vibrations during operation. The coating on the steel support base can peel off due to wind exposure. The corrosion of steel support bases is typical in oil transportation processes, where steel bases are densely set up to distribute pressure evenly. These steel bases, connected to concrete caps, undergo anti-corrosion treatment. However, water accumulation between the steel base and the concrete pile cap, caused by mechanical vibrations, leads to corrosion on the lower surface of the pipeline. The lower surface corrosion is characterized by peeling off and warping of the white coating, resulting in corrosion in these areas. The upper surface of the pipeline is also prone to corrosion, evidenced by the cracking of the white coating and the presence of brown rust. Atmospheric conditions and coating degradation contribute to this phenomenon, allowing rainwater and the atmosphere to contact the steel surface, inducing chemical corrosion.
Mechanism analysis of the external corrosion process
External corrosion in pipelines and oil tanks often involves varying degrees of chemical reactions. In managing this process, engineers and relevant technical personnel play a crucial role in enhancing equipment performance through meticulous on-site control. The underlying mechanism is as follows.
Upon analyzing and assessing the external corrosion observed in oil tanks and pipelines, it becomes apparent that, due to the prevalence of steel materials in these structures, applying suitable anti-corrosion coatings during the initial construction phase is imperative. However, when corrosion occurs, it is often accompanied by the cracking or peeling of organic coatings. This results in direct contact between the steel surface and the atmospheric environment, eventually leading to corrosion. Moreover, if the organic coating fails, the bonding strength between the coating and the steel surface diminishes, causing the coating to detach and the steel structure to corrode. In essence, during the process of external corrosion, direct contact between steel and water vapor typically induces corresponding electrochemical corrosion, culminating in rust formation.
Over time, organic coatings on oil pipelines and tanks are subjected to the prolonged effects of the external water and light environments. Due to inherent differences in their physical characteristics within specific conditions, these coatings are prone to pulverization and cracking, leading to eventual peeling away from the steel plates. Moreover, the distinct thermal expansion coefficients of organic coatings and steel contribute to the risk of cracking under stress induced by excessive temperature differences. This results in the exposure of the steel structure. In cases of subpar construction quality, organic coatings may detach or warp, especially under the influence of freezing temperatures and other external natural factors.
Analysis reveals that the failure of organic coatings on the surfaces of oil pipelines and tanks can be attributed to thermal expansion and contraction stresses. Simultaneously, changes in the physical and chemical characteristics of organic coatings occur due to external factors such as strong winds, high temperatures, and direct sunlight, leading to cracking and detachment of the coating. Regardless of the type of organic coating failure, atmospheric water seeps between the coating and the steel surface, creating a water film. Over time, the area of coating detachment expands, exacerbating the corrosion effect. Additionally, external mechanical vibration or wind affecting oil tanks or pipelines diminishes the binding force between the coating and the steel structure, further intensifying the corrosion phenomenon.
Upon the detachment or cracking of the organic coating, atmospheric moisture reacts with the steel structure, giving rise to a water film. This water film contains hydrogen ions and hydroxide ions, forming an electrolytic solution. This initiates an electrochemical reaction in which the steel, serving as the anode, is converted into iron ions and electrons. Meanwhile, at the cathode, oxygen, water, and iron ions undergo reactions, ultimately producing hydroxide ions. The overall reaction involves the interaction of iron with oxygen and water to produce ferric hydroxide, which, upon dehydration, forms rust. Rust exhibits unstable chemical and physical properties, leading to its detachment and exacerbating the degree of surface corrosion on steel.
Furthermore, the water film formed between the coating and the steel surface continually absorbs sulfur dioxide and ammonia gas from the air. This results in alkaline or acid corrosion on the steel surface, further elevating the working pressure of oil pipelines or tanks composed of the affected steel materials over time. Ultimately, this can lead to equipment failure, posing a serious risk of safety accidents.
Countermeasures and suggestions
To achieve effective corrosion control for oil storage tanks and transportation pipelines, a targeted and refined corrosion treatment approach is essential. In this undertaking, engineers and relevant designers should employ a top-level design strategy. This involves analyzing and assessing the existing mechanism of external corrosion in oil storage tanks and pipelines, with a specific emphasis on managing electrochemical corrosion. The objective is to strengthen the adhesion between anti-corrosion coatings and pipelines, thereby achieving enhanced corrosion control effects. Simultaneously, construction units need to elevate the overall construction quality of the project to optimize the impact of corrosion control.
Control the construction quality of the organic coating
Based on the preceding analysis, it is evident that the application of suitable organic coatings on material surfaces enhances the service life of oil tanks and pipelines. The quality of applied organic coatings directly influences the effectiveness of corrosion prevention. Ensuring high construction quality of organic coatings involves maximizing the adhesion between these coatings and steel surfaces. A robust bond prevents the formation of a water film between steel and organic coatings, thereby preventing electrochemical reactions. As depicted in the chemical reaction formula, the presence of an electrolyte is crucial for electrochemical reactions between the anode and cathode. Optimal binding force between organic coatings and steel surfaces prevents electrolyte connection, inhibiting chemical battery formation and subsequent chemical reactions.
Controlling the binding force requires meticulous attention to surface rust removal, which accounts for nearly 60% of quality defects in anti-corrosion coatings. In oil depot construction, the construction party must undertake targeted treatment of steel tanks and pipelines. Stringent qualification checks for construction units are crucial to ensuring the availability of requisite construction technology. Adequate introduction of professional anti-corrosion management personnel is necessary to evaluate the entire project's anti-corrosion performance and conduct corresponding protective acceptance. During the organic anti-corrosion coating process, third-party organizations should be engaged to test pipeline anti-corrosion performance using professional equipment, enhancing construction quality and efficiency. Surface treatment of equipment involves pre-cleaning the steel surface oxide, ensuring the required surface roughness to augment contact area between anti-corrosion coatings and steel. In the acceptance management of organic coatings, vigilance is necessary to ensure coatings are in good condition. Any identified non-compliance in organic coatings mandates rectification before acceptance to guarantee coating quality.
Optimize the structure and prevent water accumulation
After conducting a comprehensive field investigation and analysis, it can be inferred that the peeling of organic coatings is closely linked to water immersion, exacerbating the corrosion of steel surfaces. Water immersion predominantly occurs in areas surrounding the bottom of oil storage tanks and the supporting base of oil pipelines. It holds significant practical importance to eliminate accumulated water and implement effective preventive measures and treatments to enhance corrosion resistance. In this context, designers play a crucial role in optimizing the structure to prevent water accumulation at the top and bottom of oil tanks and the base of oil pipelines.
Generally, it is imperative to establish intercepting ditches around the top of oil tanks, controlling drainage pipes to minimize the corrosion of the tank wall's organic coating due to vertically descending rain. Simultaneously, engineers and relevant designers should install protective umbrellas around the bottom steel plate of the tank to mitigate rainwater accumulation on the steps of the bottom steel plate. Additionally, specific water diversion devices need to be deployed in particularly damp areas to channel rainwater to the surface, preventing the freezing of the pipeline bottom during winter.
Thermal spraying technology anticorrosion
Thermal spraying technology primarily involves utilizing a heat source to elevate the coating's temperature until it reaches a molten or semi-molten state. Subsequently, the molten or semi-molten coating is atomized using high-speed airflow, and the resulting atomized raw materials are sprayed onto the surface of steel components. This process facilitates the construction of a corresponding anti-corrosion coating, ultimately achieving effective corrosion control and enhancing wear resistance. The application of thermal spraying technology is characterized by its efficiency, simplicity, economic feasibility, and flexibility in both technology and equipment. Consequently, it finds wide-ranging applications in various aspects of anti-corrosion control for engineering projects.
In recent years, thermal spraying technology has undergone significant advancements, enabling the effective control of corrosion in steel structural materials with diverse shapes. In comparison to traditional coating methods, this technology offers advantages such as raw material savings. Furthermore, it ensures the formation of a robust bonding force between the coating and the steel surface, thereby providing effective protection to steel structures.
To manage the external corrosion of oil storage tanks and pipelines, engineers and relevant technical professionals should engage in top-level design, optimize various anti-corrosion control measures, enhance equipment operational efficiency, embrace lean and refined management principles, reinforce anti-corrosion measures for pipeline projects and oil storage tanks, intensify quality inspections, and establish explicit control standards. This approach aims to elevate the operational quality and efficiency of the equipment.
