Since the 1970s, due to the harsh natural environment encountered in pipeline construction, stricter requirements have been placed on the performance of the anti-corrosion coating. Therefore, in the research of pipeline anticorrosion materials, vigorously develop composite materials or composite structures, emphasizing that the anticorrosion layer must have good dielectric properties, physical properties, stable chemical properties and wide temperature adaptability in order to achieve multiple functions, such as Anti-corrosion, insulation, heat preservation and enhanced strength, the winding three-layer PE polyethylene anti-corrosion layer has been introduced from Europe for more than ten years.
In the past ten years, my country has also gradually realized the production and laying of 3PE anti-corrosion layer steel pipes. With the extension of the service time of the pipeline, the 3PE anti-corrosion layer has shown the main peeling phenomenon of cathodic stripping. The occurrence of cathodic stripping is caused by the defects of the anti-corrosion layer itself. It is caused by the interference of existence and external factors. At present, the maximum potential for cathodic protection of 3PE coated steel pipes has not been proposed at home and abroad, and the defect detection technology for buried pipelines without excavation is not perfect. The base materials of 3PE anti-corrosion steel pipes include seamless steel pipes, spiral steel pipes and straight seam steel pipes.
It has become the development direction of the outer anti-corrosion layer of the pipeline in the future. The 3PE anti-corrosion steel pipe enables the pipeline (steel pipe) to be used in different working environments, in order to slow down or prevent the pipeline from being exposed to the chemical and electrochemical effects of the external medium or the metabolic activities of microorganisms. If it is corroded and deteriorated, apply 2 or 3 layers of polyethylene (3pe) on its outer wall to achieve pipeline anticorrosion, and the service life of 3pe anticorrosion steel pipes will be extended by 3-5 times. The polyethylene three-layer structure protective layer, also known as three-layer PE (3pe), is an advanced anti-corrosion technology imported from abroad in recent years. The anti-corrosion of direct-buried heating pipelines does not need to build huge trenches, as long as the anti-corrosion pipes are buried in the dark . The coated three-layer PE anti-corrosion is currently considered as the external anti-corrosion technology of pipelines in the world, so it greatly increases the project area, increases the amount of earthwork excavation by more than 50%, and increases the amount of civil masonry and concrete by 90%. , Anti-corrosion pipe processing and on-site trenching are carried out in parallel. As long as on-site research is performed, the construction period can be shortened by more than 50%.
The 3PE anti-corrosion layer usually uses liquid epoxy or fusion-bonded epoxy powder as a primer. The epoxy powder is directly coated on the surface of the steel pipe through static electricity, and its function is to form a chemical bond with the copolymer adhesive, which has excellent corrosion resistance and resistance to cathodic disbonding. performance. The middle layer is a copolymer adhesive, which plays the role of bonding with the bottom epoxy powder and the outer polyethylene protective layer. It has excellent chemical adhesion to the epoxy powder base layer and is resistant to shear forces caused by soil movement and temperature changes. The outer layer is a high-density polyethylene protective layer, which has excellent moisture resistance and can protect the epoxy powder bottom layer and adhesive layer. This three-layer structure has chemical corrosion resistance and good impact resistance. Anti-corrosion pipelines can be divided into two categories, inner-lined anti-corrosion steel pipes and outer-inner anti-corrosion steel pipes. The anti-corrosion lining mainly includes cement mortar-lined anti-corrosion steel pipes, which are widely used and the cost is low. The cement mortar-lined anti-corrosion steel pipes use the cement anti-corrosion layer to play a role in anti-corrosion of the pipes.