Broadly speaking corrosive nature of the material is due to the role of environmental factors in causing the surrounding metal and non-metallic material damage. Solely in terms of metal, it is the expression of metal compounds into elemental state chemical changes in state and electrochemical consumption, namely the nature of metal corrosion is reduced from the state to the common elements of natural phenomena natural state of ore. The presence of a metal tend to emit energy into a lower energy, more stable state of the ore. This release of energy is the driving force generated corrosion, the corrosion process is the release of energy in the process. Corrosion of metal pipes is a manifestation of this widespread natural phenomenon.
Refers to the destruction of chemical corrosion of metal and non-electrolytes occurs directly caused by the chemical action. Corrosion process is a pure redox processes, namely corrosive oxidant corrosion products formed directly reducing surface atoms interacting with the metal, the metal is oxidized to corrosive media are restored. For example occurred in the high-temperature oxidation of iron casting, rolling and heat treatment process is metal in high-temperature gas chemical corrosion. Chemical corrosion can be divided into non-gas corrosion and corrosion in the electrolyte solution. Characterized in the reaction process is not current. Metal due to corrosion in the electrolyte solution electrochemical reaction that occurs is called galvanic corrosion. It is the most common metal corrosion in a form, which is characterized by a current flowing in the corrosion process. Corrosion of metal occurs in seawater, industrial water, various acids, alkaline solutions are all electrochemical corrosion. Electrochemical corrosion process by the cathodic process, the electron transfer process and a part of the composition of the anode. Corrosion types of electrochemical corrosion of metal pipes is based atmospheric corrosion, soil erosion, water and corrosion solution, stray current corrosion. In addition, bacterial corrosion.
Steel plating using electroplating, plating, hot dip, diffusion coating technology, the corrosion-resistant metal plating to the steel surface. Plating anode and cathode of the species. If the surface of galvanized steel, tin and other metals, plating potentials more negative potential than the matrix of iron, is anodic coating. This coating can play the role of the sacrificial anode, which is not smooth for the steel surface is applicable, even if porous, defect, still better protection of the steel pipe, the other is a potential corrosion inhibiting coating metal than steel potentials are cathodic coating, such as lead, tin, copper, and nickel. Cathodic deposit generally only complete enough, in order to better protect the steel, otherwise it will accelerate the corrosion of steel. Corrosion protection layer insulation of large underground pipe, such as oil and gas pipelines, pipe wall corrosion serious, often with anti-corrosion insulation engineering. The anti-corrosion coating evenly coated in dense steel wall by rust, and corrosion environment so isolated, cut off the corrosion cell circuitry to protect the pipeline from corrosion. Such as pipelines, pipe wall is coated with rust epoxy asphalt coating, and then wrapped in fiberglass cloth, several layers alternately construction, corrosion formed over the insulating layer thickness. And steel which is characterized by good adhesion, good electrical insulation properties, high mechanical strength and flexibility, waterproof, heat resistance, high chemical stability.
In petroleum, chemical and other industrial sectors, the steel pipe wall corrosion can not be ignored. Inner wall coating is one of the effective anti-corrosion measures. Commonly used anti-corrosion coating with epoxy paint, phenolic resin modified epoxy paint aimed month, polyurethane vinegar anticorrosive paint, epoxy polyurethane paint. The anti-corrosion paint is also often add some special fillers such as glass flake, the magnetic iron oxide powder, zinc powder, asbestos powder activity to improve the anti-corrosion effect. It features sophisticated construction technology, simple and low cost. Pipe wall corrosion protection as well as rubber linings, plastic liners such as polyethylene, polyvinyl chloride, polystyrene, Teflon, nylon, etc., FRP Lining, enamel linings. These health measures difficult, there are some limitations.
Pipeline corrosion coating metal corrosion cell is increased loop resistance, reducing the corrosion current to inhibit corrosion. In practice, however, due to various factors, intact coating is difficult to achieve, especially in long-distance pipeline buried, often missing in the coating deposited at the office or corrosion damage. So, in some cases, a simple anti-corrosion coatings, has not yet reached the purpose of preventing corrosion occurred. According to the principle of electrochemical corrosion of metal corrosion cell cathode corrosion does not occur, it is only the anode corrosion. The method makes use of certain metals into the protected cathode to prevent metal corrosion generation, this method is called cathodic corrosion protection, usually in the depot for the protection of buried pipelines. Cathodic protection into the impressed current cathodic protection and sacrificial anode protection.
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