First, what are the classifications of coating methods for large-diameter plastic-coated steel pipes?
Coating methods for large-diameter plastic-coated steel pipes using coating equipment are divided into two categories: simultaneous internal and external coating, and separate internal and external coating.
The process coating methods for large-diameter plastic-coated steel pipes are also divided into two categories: internal coating first, then external coating; external coating first, then internal coating.
There are five types of internal coating methods for large-diameter plastic-coated steel pipes: well coating, electrostatic gun with extended rod spraying, electrostatic powder pump push-pull rod spraying, powder coating, and vacuum suction coating.
There are four types of external coating methods for large-diameter plastic-coated steel pipes: well coating, electrostatic spraying, fluidized bed dip coating, and waterfall spraying.
Simultaneous internal and external coating for large-diameter plastic-coated steel pipes mostly fall into two categories: well coating (internal and external coating) and fluidized bed dip coating (external dip coating, internal electrostatic powder, pump, push-pull rod spraying).

Secondly, what are the pretreatment requirements for large-diameter plastic-coated steel pipes?
Plastic-coated steel pipes usually refer to double-sided plastic coating, also known as internally and externally plastic-coated steel pipes. For composite steel pipes, the initial rust removal technology plays a crucial role in the quality of the finished plastic-coated steel pipes. Therefore, when selecting newly arrived steel pipes, galvanizing is not required, but rust must be removed. Any remaining rust spots inside the plastic-coated steel pipe also need to be thoroughly cleaned. All rust must be removed to meet the St2 or Sa1 level requirements for electric rust removal. To remove oil stains from the surface of the steel pipe, acetone can be used for cleaning.