Brief Introduction of Coating Process of Conveying Pipe Anticorrosive Coating

China's natural gas transmission pipeline from west to East is 4169km long, with 20 billion cubic meters of gas per day Coating and cathodic protection are used to protect the outer wall of the pipeline This kind of pipeline coating has the following varieties (1) petroleum asphalt has been used for more than 30 years in China The process is hot coated petroleum asphalt, wrapped with glass cloth and covered with plastic film, with low cost It is often used in petroleum sector, with simple construction Its disadvantages are high water absorption, poor heat resistance, use range of 0-40 ℃, not resistant to soil microorganisms, easy to be penetrated by plants, and gradually eliminated in Europe and the United States (2) the technology of coal tar pitch "enamel" is to first apply a thin coal tar pitch primer to wet the surface, reheat and apply solvent-free coal tar pitch "enamel", and then wrap the tape Its advantages are low water absorption, applicable to the temperature range of - 30 ~ 95 ℃, good corrosion resistance, resistance to soil bacteria, resistance to plant root penetration, and low cost The disadvantage is that the flue gas during construction is harmful to workers' health, and the compatibility with cathodic protection is poor In the early 1920s, this coating was used in Wuhan water pipeline in China After excavation and recheck in the 1950s, the steel pipe is still metallic luster without corrosion (3) the fusion bond epoxy system powder coating has been used in foreign countries for 30 years It has strong adhesion and corrosion resistance with steel pipes, and can be used in the range of - 60 ~ 110 ℃ The disadvantage is poor waterproof, easily damaged by impact, and high cost The operation is shot blasting and derusting to Sa2.5 level, electrostatic spraying epoxy powder (novolac epoxy resin plus phenolic curing agent) with induction ring heating to 230 ~ 260 ℃, the pipe rotating binding force on the operation line for 2 ~ 3min, making the powder level and solidified, then spraying water for quenching, the film thickness is 400um (4) the epoxy asphalt coating has been used in foreign countries for 40 years, the United States started in 1959, Japan started in 1967, and has been used in China for 20 years The utility model has the advantages of strong adhesion, good water resistance, microorganism resistance and plant root penetration resistance, which can be used in the environment of - 60 ~ 110 ℃ and can be solidified at room temperature The disadvantage is that the two-component is inconvenient, the coating is brittle, the VOC of solvent pollutes the environment, and it can be used in the branch project with small scale and small pipeline diameter (5) the three-layer protection zone of epoxy / polyethylene is a technology developed more than ten years ago The operation is to first coat the molten epoxy powder coating (FBE) and then combine it with extruded polyethylene: epoxy powder coating + copolymer + polyethylene This system is not only corrosion-resistant, but also has excellent mechanical properties The disadvantage is the high cost This technology is applied to the outer wall of large-diameter gas transmission pipeline from Shaanxi to Beijing in China There are still projects from Korla to Shanxian, Jingbian to Xi'an, etc Lu bocen of Kailin paint factory introduced that the coating process for underground pipeline supplied by the factory is as follows: sand blasting up to Sa2.5 level, under 85% relative humidity, ambient temperature not less than 5 ℃, substrate temperature higher than 3 ℃ above dew point before construction; the first epoxy zinc rich primer 80um; the second epoxy mica iron oxide antirust paint 100um; the third epoxy asphalt paint 200um The thickness of coating film shall be measured after each coating is dry The total thickness shall be measured after the completion of the whole coating system More than 90% of the measuring points must reach the specified value If the film thickness does not reach the specified value, it shall not be less than 90% of the specified value, otherwise, it shall be coated or added with a value This system has been widely used in underground water and gas pipeline projects in Shanghai, Hunan and Shantou, Guangdong for 15 years, and is still in normal use At present, 5 pipelines in China are operated with domestic coal tar enamel paint, and the quality of anticorrosive pipeline fully meets the requirements of SY / t0079-93 standard Coal tar enamel is made of coal tar pitch, coal powder, anthracene oil and mineral filler by boiling Its formula is: coal tar pitch 20% ~ 35% anthracene oil 25% ~ 35% coal powder 20% ~ 30% mineral filler 25% ~ 40% by boiling, pay attention to dehydration, the whole process takes 10 ~ 12h Lu Weizhong introduced the application of anti-corrosion technology in the water supply pipeline system, and also mentioned that the anti-corrosion coating for the outer wall of the pipeline includes petroleum asphalt, coal tar pitch celadon paint, adhesive tape, extruded polyethylene, epoxy asphalt and fusion bonded epoxy Extruded polyethylene is easy to produce stress cracking if it is coated on large-diameter pipes with a diameter of more than 508mm (20 inches) The corrosion of the inner wall of the water supply pipe is more serious than that of the outer wall In the late 1980s in China, fusion bonded powder coatings were produced from abroad The corrosion Institute of Chinese Academy of Sciences has developed fusion bonded epoxy powder (SEBF) and solventless high performance composite liquid epoxy coating (SLF) since 1990s, which has excellent corrosion resistance.