How much do you know about pipeline anti-corrosion?

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Introduction The underground pipe network is the "capillary" of a city, responsible for the daily life of people, and is closely related to the quality of the city and people's happiness. The types of urban pipeline projects mainly include water supply pipelines, drainage pipelines, gas pipelines, thermal pipelines, power cables, etc. For pipelines buried deep underground, corrosion prevention is a complex issue with many influencing factors. Pipeline anti-corrosion is a very niche and segmented industry, and it is extremely important to the development and safety of the city. Thermal pipelines are important infrastructure in the city. The focus of construction technology and construction quality monitoring is the insulation and anti-corrosion of thermal pipelines. The quality of thermal insulation and anti-corrosion of pipelines is related to the safety and efficiency of the use of thermal pipelines and the service life of the pipelines. Therefore, the thermal insulation and anti-corrosion construction of thermal pipelines must be done well. 1. Analysis of corrosion causes 1. Material reasons Since most heating management systems are laid underground, the pipe materials used are extremely susceptible to the corrosive effects of the soil itself. After entering summer, the metal elements in the pipe will be affected by the combined effects of temperature and soil, resulting in corrosion problems near the carbon steel welds on the pipe wall. In addition, the moisture in the pipes will also affect the heating pipes. If the Ph value of the hot water in the pipes does not meet the standard, the flowing hot water will accelerate the corrosion of the heating pipes. 2. Soil problems. Soil causes that can cause corrosion problems in heating pipes include: Soil oxidation, salinity, etc. The oxidation of soil refers to the strong oxidation in the soil, which can cause strong corrosion to heating pipes, and the permeability of the soil will also directly affect the redox reaction of the soil. If the soil has strong oxidizing ability and a certain degree of air permeability, the oxygen element in the soil will gradually increase, which will cause corrosion to the heating pipes. Salt in the soil can affect heating pipes. Salt will affect the corrosiveness of the soil. When the content of salt ions in the soil is high, it will increase the conductivity of the soil, thereby increasing the corrosion ability of the heating pipes. The salt ions that can cause an impact include chloride ions, magnesium ions, sulfate ions, etc. The main principle is that sulfate will cause a strong destructive effect on metal substances. 2. Anti-corrosion measures 1. Strengthen the external anti-corrosion of pipelines. During the actual burial process of heating pipelines, protective pipes and insulation layers need to be used for the layout of the pipelines. Direct burial can effectively reduce the probability of possible corrosion at the welding locations within the pipelines. Where welding is required, strict anti-corrosion measures should be taken to strengthen maintenance. ； Improve electrochemical anti-corrosion capabilities. The main purpose is to strengthen the anti-corrosion control of the insulation layer, use cathodic protection methods to control the overall current of the heating pipe, and maintain the potential in the metal elements of the heating pipe in a safe state, thereby improving the anti-corrosion capability of the heating pipe. 2. Strengthen the pipeline installation process. The installation process of thermal pipelines has a great impact on anti-corrosion and thermal insulation. If the installer does not follow the process requirements of pipeline installation, the insulation level and anti-corrosion capabilities of the pipeline will be reduced. The steps for installing thermal pipelines are very clear. The installation requirements for each process are relatively high, especially the foaming and shaping part of the insulation material. The installer needs to ensure the accuracy of the process in order to scientifically check the foaming quality and ensure the anti-corrosion and insulation treatment. 3. Improve management level Pipeline management (including daily inspection and maintenance of pipelines) can promptly detect defects in anti-corrosion and insulation measures in thermal pipelines, and then take effective repair treatments. During the construction of thermal pipelines, it is necessary to improve the management level and check whether the thermal pipelines have potential performance risks. For example: The lack of proper management in a certain thermal pipeline project led to many mistakes in the construction, which seriously affected the anti-corrosion and insulation treatment of the thermal pipeline. Some details in the thermal pipeline required anti-corrosion and thermal insulation treatment. However, due to lack of management, the treatment was insufficient, severe corrosion occurred in later applications, and the heat loss of the pipeline was excessive, reducing the economic benefits of the thermal pipeline. my country's long-distance natural gas pipelines are under construction for sustainable economic development, and energy consumption is increasing day by day. In order to deal with the environmental pollution problems caused by energy consumption, my country is continuously reducing the use of environmentally polluting fuels such as oil and coal. The demand for natural gas has increased significantly, which helps reduce atmospheric pollution. The use of natural gas depends on pipeline transportation, so it is necessary to increase the attention to natural gas transportation equipment, which directly affects the cost and safety of developing new energy. Pay attention to whether pipelines are prone to corrosion or to take measures to protect pipelines in advance. 1. Analysis of corrosion causes 1. Inner wall corrosion is caused by electrochemical reactions caused by moisture in natural gas. A layer of electrolyte solution film is covered on the internal surface of the pipeline. A galvanic reaction occurs, causing damage to the inner wall of the pipeline. Natural gas contains various substances that may directly react with the inner wall of the pipeline during transportation to destroy the metal structure. At the same time, it causes looseness and perforation damage to the inner wall of the pipeline. It cannot continue to withstand the transportation of natural gas and external pressure. 2. Exterior wall corrosion (1) Soil corrosion. Transportation pipelines are steel materials that have been buried underground for a long time. The soil is heterogeneous and inhomogeneous, loose and porous, and permeable to water and gas. The soil structure and humidity are different at different stages, and the oxygen permeability is also greatly different. Under the influence of soil, pipelines will have segmented thicknesses and even perforations, which can easily cause oil and gas leakage, threaten the ecological environment and personal safety, and easily lead to fuel explosions. ① Uneven oxygen causes corrosion. When pipelines are buried, due to different pipeline structures, different soil environments, and uneven aeration, oxygen concentration cells corrode. Metal pipes in sandy soil have high oxygen content, and metal pipelines in clay lack oxygen, forming oxygen concentration cells. The metal parts in the clay are extremely susceptible to corrosion. Different placements of transportation pipelines will also form cells with poor oxygen concentration. Transportation pipelines buried deep underground will be difficult to reach due to oxygen and are prone to corrosion. ②Corrosion from stray currents. Stray current is actually a leakage phenomenon. Stray current leaks from DC power equipment such as trains and subways. As long as it is underground equipment, it will be corroded by such stray current. The DC current penetrates from the track into the ground, enters a certain part of the pipeline, and then returns to the track from other parts of the pipeline. The stray current leaks out of the pipeline during the movement of the DC current. The leaked place is prone to corrosion damage, and the damage results are serious. ③Microbial corrosion. There are not many bacteria that can corrode steel in the biological world, but there are still influenza bacteria and hydrochloride-reducing bacteria. The living environment near transportation pipelines is humid and cold. There is a large amount of oxygen in the soil, which is suitable for the reproduction and survival of microorganisms. Elemental sulfur will appear during biological activities. The elemental flow is easily oxidized into sulfuric acid and exerts a corrosive effect on metals. ； Sulfate-reducing bacteria cultivated in sulfate soil will also exist during biological activities. Under the catalysis of organisms, the degree of corrosion of pipelines will be increased. Bacteria themselves do not have a corrosive effect on metal materials, but the life activities of bacteria can easily cause electrochemical reactions on metal materials, thereby corroding objects. For example, the metabolic activities of bacteria produce corrosive metabolites such as sulfuric acid and sulfide. Biological activities can also affect the electrode reaction and cause corrosion phenomena. Biological activities can also change the environmental conditions of metals and destroy the anti-corrosion coating on the metal surface. (2) Atmospheric corrosion. Atmospheric corrosion is humid atmospheric corrosion in which water vapor exists. When the concentration of water vapor is too high, corrosion will occur. In addition, acidic substances such as sulfur dioxide and nitrogen oxide gases dissolve into the water attached to the metal surface, forming a sulfuric acid or nitric acid solution. As a result, electrochemical and chemical corrosion phenomena occur, leading to accelerated corrosion. It may also be atmospheric corrosion under the visible liquid film. Corrosion will occur when the relative humidity of the air is very high and a water film can already be seen forming on the metal surface. 2. Anti-corrosion measures 1. Apply anti-corrosion coating When choosing an anti-corrosion coating, it needs to meet various conditions, such as strong insulation, water barrier properties, coating on pipelines that cannot hinder the transportation of natural gas, and can make up for coating defects to the greatest extent. It has good adhesion on the surface of the pipeline, can resist damage during transportation, does not pollute the environment, and is easy to repair damage later, etc. 2. Protective polarization current impressed current protection method is based on the external DC power supply to achieve cathodic polarization of the transportation pipeline to achieve protection measures. The negative electrode of the external DC power supply is connected to the transportation pipeline, the positive electrode is connected to the auxiliary anode, and the auxiliary anode forms a complete cathodic protection circuit. Its characteristic is that it requires the assistance of an external DC power supply ； It has high voltage drive, large power output, and large current protection. It can self-adjust under harsh environmental conditions, control the cathodic protection current, and expand the effective anode protection radius. However, it can easily cause over-protection and cause interference to nearby facilities. ； The number of anodes is small, the system is light in weight, and the service life is long. It can be used for cathodic protection for a long time. However, the number of anodes in the system is small and the protection current is uneven. ； Under harsh environmental conditions, the system is easily damaged by foreign objects, equipment installation and maintenance are complicated, and the use cost is high. 4. Stray current drainage protection When the distance between the long-distance natural gas pipeline and the high-voltage transmission line is small and in parallel, the operating status of the high-voltage transmission line and the electrified railway may affect the operation quality of the pipeline, thereby accelerating the pipeline corrosion rate. Therefore, the pipeline should be constructed as far away from AC and DC interference sources as possible. Apply drainage protection to the pipeline, specifically based on whether there is positive and negative polarity alternating current in the anode area of ​​the pipeline affected by the interference current, and then select the best drainage method. Under normal circumstances, the DC drainage protection method is used when there is a constant current in the anode of the pipeline, and the polarity drainage protection method is used when there is an alternating current. When the current in the anode area of ​​the pipeline is complicated and its nature is difficult to determine, the mandatory drainage protection method is suitable. After the construction workers laid the long-distance natural gas pipeline underground, they scientifically selected drainage measures based on the authenticity test results of stray current to ensure the quality of anti-corrosion work. Specifically, the stray current outflow ends were assembled to form zinc anodes, and construction measures were used to connect the fiberglass test piles and pipelines to achieve the goal of eliminating soil current in the natural gas long-distance pipeline and reducing its impact. Anti-corrosion measures during construction During the construction of long-distance natural gas pipelines, a series of processes such as pipeline transportation, pipeline disassembly, pipeline arrangement, assembly, and welding at the construction site must be implemented step by step in accordance with the construction technical specifications, and blind and rude construction behaviors must be avoided. In terms of the selection of spreaders, the best objects are nylon slings or rubber roller hanging baskets to prevent the direct use of wire ropes to pull pipelines. During the pipeline laying process, try to reduce the probability of collision with the trench wall. Under special circumstances, wooden boards or straw bags can be laid on the upper end of the trench wall. The purpose is to maintain the integrity of the anti-corrosion layer. If a long-distance natural gas pipeline is buried in a trench in a stone section, construction workers should pay special attention to laying 20.0cm thick fine soil at the bottom of the trench to avoid damage to the integrity of the anti-corrosion coating during the pipeline burial process. ； If construction workers find scratches or other damage to the coating, they must repair it according to the anti-corrosion coating repair procedures, so as to minimize the probability of corrosion of long-distance natural gas pipelines due to pipeline coating wear. Implement temporary cathodic protection measures for the entire long-distance natural gas pipeline. Temporary cathodic protection uses strip zinc anodes. The size of the anode area can be planned as follows: 8.5mm × 10.0mm, the length of natural gas long-distance pipeline laying is set to 20.0m per 1 km, so that the test pile evolves into a hub for effective connection between the anode belt and the pipeline. The implementation of the above-mentioned pipeline construction procedures has great advantages in reducing the probability of environmental corrosion of pipelines. If the long-distance natural gas pipeline to be laid passes through a river, then a pair of zinc alloy sacrificial anodes are installed at the current test piles on both sides of the pipeline. The anode group is usually composed of multiple prepackaged zinc anodes, and the net weight is controlled at about 80.0kg.