Protection of metal piping from corrosion

Pipes made of iron and steel, after installation is exposed to soil corrosion. The main causes of soil corrosion, may be chemical, electrochemical and electrical factors. The chemical corrosion of the gradual destruction of the metal of the pipe is made, due to the action of liquids, non-electrolytes, and corrosive gases. In this case, the wall of the pipe is usually uniformly thinning, and thus the probability of through injury in this type of corrosion is small. The main cause of corrosion in the soil is electrochemical corrosion. Metal pipe then becomes an electrode and ground water with dissolved salts in them are the electrolyte. Danger of galvanic corrosion is the narrow focus of its action, which can lead to local ulceration and cavities in the walls of the pipeline, which can eventually turn into a through-hole and violate the integrity of the pipeline. Permanent effect on the pipeline of stray currents (generated, for example, as a result of leaks from rail electrified transport in the soil) can cause electrical corrosion associated with metal by electrolysis. This type of corrosion is very common in the city, especially near the traction substations trams and trolleybuses. The intensity of corrosion in the soil depends primarily on moisture content in the soil electrolytes (acids and salts) and air capacity of the soil to conduct electrical current. In dry soil corrosion is much slower than in the wet (the corrosion rate is maximal when the water content in soil ranges from 11 to 13%). Retards the corrosive destruction of pipes and low electrical conductivity of the soil. To protect metal pipes from corrosion often resorted to various methods of pipe insulation from the aggressive environment. As an insulator is usually used bitumen with additives of special fillers to increase strength of the coating. This mixture is called asphalt mastic, mostly in its composition injected cement or asbestos. More pipe insulation is provided by wrapping waterproofing. This - asbestos paper, which added 15 to 20% cellulose, saturated with bitumen. Another actual wrapping material for isolation of the pipeline - it brizol except bitumen in its composition includes waste out-of-use of vulcanized rubber. Preparations for the subsequent isolation of the pipeline is to clean the surface of the pipe to a metallic luster, and then pipe primed with a solution containing 1 part of petroleum bitumen and 2 parts of gasoline. When the primer coat has dried, the surface of the pipe causing a lot of hot bitumen mastic, alternating layers of mastic with layers of waterproofing or brizola. The number of layers of mastic and wrapping material determines the types of insulation. It may be normal, heavy and very heavy. What type of insulation to select the customer decides, based on the corrosiveness of the soil in which the planned pipeline.