Causes of corrosion in oil and gas pipelines and corrosion protection measures

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The corrosion of oil and gas pipelines is influenced by factors such as the external environment and the medium being transported. Its forms mainly include soil corrosion, stray current corrosion, atmospheric corrosion, and internal corrosion within the oil and gas pipelines. 1. Soil corrosion: 80%–90% of oil and gas transmission pipelines are buried underground, and the presence of corrosive substances in the soil, stray currents, and bacteria all have a direct impact on the corrosion rate of these pipelines. 2. Stray current corrosion: If underground metal components (such as oil and gas pipelines) are buried in areas where stray currents flow, these currents will enter and exit the metal components; a cathodic area is formed at the point of entry while an anodic area is formed at the point of exit, resulting in corrosion of the metal. 3. Atmospheric corrosion: Pipes located in an atmospheric environment, such as pipeline sections that span distances or those situated on station grounds, are subject to atmospheric corrosion. The degree of wetness on metal surfaces is the main factor determining atmospheric corrosion. 4. Internal corrosion of oil and gas pipelines: (1) Internal corrosion of oil transport pipelines: The corrosive components in crude oil are mainly water, hydrogen sulfide, carbon dioxide, bacteria, and various salts. However, for crude oil that has undergone treatments such as oil-water separation and sediment purification prior to long-distance transportation, the content of corrosive components is generally very low. The main components of refined oil are various hydrocarbons, and it is a non-electrolyte; therefore, internal corrosion in long-distance crude oil and refined oil pipelines proceeds at a relatively slow rate. In low-lying areas and bends of oil pipelines, some of the water and solid impurities such as sand contained in the oil precipitate, causing internal corrosion of the pipes, such as pitting corrosion. If corrosive bacteria are present in the oil, it will accelerate the electrochemical corrosion of the inner wall of the pipes. (2) Internal corrosion of gas pipelines: Natural gas contains components such as water, hydrogen sulfide, and carbon dioxide that can cause metal corrosion. During gas transmission, these components cause severe electrochemical corrosion on the inner walls of the pipes; in particular, hydrogen sulfide is a major threat to the pipes. Corrosion in oil and gas pipelines can lead to various leakage problems, issues related to the structural strength of equipment, reduced efficiency or even equipment failure, directly affecting the safe and continuous operation of enterprises while posing significant safety risks. It also results in a significant waste of resources and an increase in costs. Therefore, corrosion protection for oil and gas pipelines is an urgent task. Heavy-duty anti-corrosion coatings refer to a type of coating that, as compared to conventional anti-corrosion coatings, can be used in relatively harsh corrosive environments and provides a longer protection period than conventional anti-corrosion coatings. There are many types of anti-corrosion coatings commonly used for pipelines, such as epoxy asphalt paint, silicone high-temperature resistant paint, and acrylic polyurethane topcoats. The specific choice depends on the type of pipeline and the required anti-corrosion conditions. I believe they can be roughly divided into two categories: anti-corrosion for buried, enclosed pipelines, and anti-corrosion for exposed, open pipelines. The anti-corrosion coatings used for the inner and outer walls of buried pipelines are also different. The outer wall is generally coated with epoxy asphalt paint or solvent-free epoxy coatings for anti-corrosion purposes, while the inner wall uses different types of coatings depending on the specific conditions. For example, drinking water pipelines have their inner walls coated with IPN8710 series anti-corrosion paints, whereas oil pipelines use oil-resistant, conductive anti-corrosion paints; different types of pipelines require different anti-corrosion coatings. As an example of anti-corrosion for outdoor pipelines, epoxy zinc-rich primers combined with acrylic polyurethane topcoats can be used for the anti-corrosion of gas pipelines. For pipelines that need to withstand high temperatures, silicone-based high-temperature resistant coatings can be employed for anti-corrosion purposes, while epoxy resin coatings can be used for the anti-corrosion of indoor pipelines. Under many conditions, different anti-corrosion coatings exhibit varying properties, and naturally, they can serve different functions in preventing corrosion.