First, the processing technology of EP inner and PE outer anti-corrosion steel pipe:
The EP inner and PE outer anti-corrosion combination process of large-diameter water pipeline is to combine the characteristics of thermosetting epoxy resin powder coating and polyethylene powder coating and the processing technology, and cleverly combine the single-layer polyethylene coating with the fused epoxy powder coating technology to provide good protection for the corrosion protection of buried steel pipes. After continuous research and improvement in the market, the EP coating inside the pipeline and the PE coating outside are a good anti-corrosion combination solution for steel pipe anti-corrosion. At present, it has become a widely used product for large-diameter water pipelines in the market.

Second, the coating method of EP inner and PE outer anti-corrosion steel pipe:
1. There are five types of internal coating methods for EP inner and PE outer anti-corrosion steel pipes: well coating, non-static gun extension rod spraying, non-static powder pump push-pull rod spraying, buckle powder, and vacuum suction coating.
2. There are four types of external coating methods: well coating, electrostatic spraying, fluidized bed dipping, and waterfall coating.
3. There are two types of internal and external coating at the same time: well coating (internal and external coating) and fluidized bed dipping (external dipping, internal non-electrostatic powder pump push-pull rod spraying).

Methods of well coating for anti-corrosion steel pipes with EP inside and PE outside:
The well coating method (internal and external coating) for internal and external coating at the same time is the basic form introduced to China in the 1990s. Now most of them have been eliminated. Some are still used in some places, but they are basically used for the plastic coating of threading pipes, and the inside and outside are mostly PE powder. This form requires the use of fluidized wells, so deep wells need to be dug in the factory, generally exceeding the usual specifications of steel pipes by 6m, and 8.5m deep wells are dug. Fluidized plates or fluidized cloths are arranged 500 mm above the well. The fluidized cloths are generally arranged in 16 layers. A high tower is added to the side of the well, and a high-speed winch is configured below. The winch line speed reaches 120 meters/minute. For overweight steel pipes and large-size steel pipes DN500-DN800, the winch line speed is 90 meters/minute. The speed of the winch is too slow, the steel pipe is immersed in the fluidized well for too long, and the thickness difference of the coating on the upper and lower ends of the steel pipe is large. In this way, compressed air needs to be introduced under the fluidized plate or fluidized cloth to make the powder in the well form a fluidized state.

When the EP-inner and PE-outer anti-corrosion steel pipe is immersed in the fluidized well, the lower end of the steel pipe coating is thick and the upper end is thin because the lower end of the steel pipe is first in and then out. The productivity is fast, and it takes about 10 seconds to coat a steel pipe. In actual production, when producing PE threading pipe coated steel pipe, the powder coating on the upper and lower ends of the steel pipe differs by 300 microns.