Epoxy coal tar paint anticorrosive pipe

◎External anticorrosion measures of pipeline

       The outer sleeve of directly buried steam pipeline should ensure that the inner pipe and thermal insulation material operate in a strictly waterproof space. If the outer sleeve is damaged (caused by corrosion, mechanical damage, welding quality, etc.), the groundwater seeps into the insulation layer and evaporates into steam after the inner pipe is heated, which makes the interface temperature of the thermal insulation material and the outer surface temperature of the outer sleeve difficult to control, In serious cases, it can cause insulation and corrosion failure of the whole line and pipeline scrapping. Therefore, it is very important to take anti-corrosion measures for the outer wall of the steel jacket steam pipe. The following is a brief introduction of several anti-corrosion forms adopted by our company:

◎Coal tar epoxy paint

       It is composed of epoxy resin and coal tar asphalt. It is a (epoxy) B (curing agent) two-component coating. It combines the advantages of epoxy resin (high strength) and asphalt (good anti-corrosion performance). It has stable anti-corrosion performance, long service life, high temperature resistance (below 110 ℃), high coating strength, convenient construction, and can be semi mechanized or manual production, The coating cost is low, which is suitable for the requirements of anti-corrosion coating for directly buried steam pipe jacket. But in production, the following problems exist: curing is greatly affected by temperature, low temperature (below 10 ℃) curing is slow, and construction in northern winter is limited. Especially when the coating is repaired on site, the coating has a long curing time, which is difficult to guarantee the construction period。

◎ Glass fiber reinforced plastics    

        Epoxy resin or phenolic resin is used as the main raw material.

        Performance features: high strength, high hardness, impact resistance, smooth surface, high corrosion resistance, semi mechanized or manual production, short curing time.

◎ Fusion bonded epoxy powder

       Fusion bonded epoxy powder is a one-time film-forming production process with thermosetting powder coating. It has excellent corrosion resistance, good chemical corrosion resistance, aging resistance, high strength, smooth surface, wear resistance and high temperature resistance (up to 100 ℃), and its service life can exceed 40 years. Its patching adopts two-component liquid epoxy, which can be completely cured in 2 hours, which can greatly improve the construction speed. Due to its high cost, the domestic manufacturers of directly buried steam pipe use this technology less. With the gradual decline of its price, it has great development potential and application prospects.

◎ Polyethylene three layer structure      

         Polyethylene three-layer structure protective layer, also known as three-layer PE, is an advanced external anti-corrosion technology introduced from abroad in recent years. Its full name is fusion bonded epoxy / extruded polyethylene structural protective layer, and the structure is composed of the following three layers: the bottom layer is fusion bonded epoxy (≥ 80 μ m）； The middle layer is adhesive (170-250) μ m）； The surface layer is extruded polyethylene (about 2mm); The total thickness of protective layer is about 1.8-3.7mm. In the three-layer structure, the main functions of epoxy primer are: to form a continuous film, directly bond with the steel pipe surface, and have good chemical corrosion resistance and cathodic stripping resistance; It reacts with the active group of the intermediate layer adhesive to form a chemical bond, which ensures that the overall anti-corrosion coating has good adhesion at a higher temperature. The intermediate layer is usually a copolymer binder, the main component of which is polyolefin. The polar functional group of the copolymer adhesive can react with the epoxy group of the epoxy primer to form hydrogen bond or chemical bond, which makes the middle layer form a good bond with the bottom layer; The non-polar ethylene part has a good affinity with the surface polyethylene, so the middle layer and the surface also have a good bonding performance. The main function of the polyethylene surface is to play a role of mechanical protection and anti-corrosion.

        The three-layer PE coating combines the excellent properties of fusion bonded epoxy powder coating and extruded PE coating, and combines the interface characteristics and chemical resistance of fusion bonded epoxy powder coating with the mechanical protection characteristics of extruded PE coating, so as to significantly improve their respective properties. In addition, it adopts the heat shrinkable tape or cold winding tape joint mode in the joint repair mode, which is simple and easy to operate, and the construction period is short, so it is very superior as the external protective layer of the buried pipeline. The application of three-layer PE is mainly limited by temperature, and the cost ratio is low

        At present, polypropylene three-layer structure anticorrosive coating has been developed, and its cost is equal to that of three-layer PE. Its application temperature can reach 104 degrees, which solves the problem of high temperature resistance and has broad application prospects.

        Note: in addition to the above anticorrosive methods, polyurea coatings and rigid polyurethane foam anticorrosion are widely used.

◎The necessity of surface treatment

        As the saying goes, "three materials, seven construction" is not too much, especially the surface treatment of this process, often overlooked, it can be said that the importance of surface treatment is no less than coating, through the surface treatment of steel, remove the original adhesion. Increasing the surface roughness can greatly improve the adhesion between the steel surface and the coating.

        Our company has shot blasting production equipment, which can ensure the quality of steel surface treatment, and can reach Sa21 / 2 near white standard. After cleaning, there is almost no visible oil, grease, lime soil, oxide scale, rust and old coating on the steel surface, so as to ensure the bonding strength between the anti-corrosion coating and steel and prolong the anti-corrosion life.

◎ cathodic protection

       Cathodic protection is one of the electrochemical protection methods in metal anti-corrosion process. Different from other anti-corrosion processes, it makes the electrode potential of the protected metal move negatively by applying electric current to the protected metal body, and makes the metal lose the tendency of spontaneous change from atomic state to ionic state. Therefore, it fundamentally inhibits the occurrence of corrosion. The perfect combination of cathodic protection and pipeline preservatives is recognized as the best anti-corrosion scheme at present.