The difference between plastic-lined steel pipe and plastic-coated steel pipe

first, definitions, classification, and terminology
1. plastic-lined steel pipe
1.1 definition: plastic-lined steel pipes are steel-plastic composite products with steel pipes as the base pipe, treated inner and outer surfaces, galvanized outside and painted or painted, and lined with polyethylene plastic or other anti-corrosion layers.
1.2 classification: plastic-lined steel pipes are divided into cold-water plastic-lined steel pipes, hot-water plastic-lined steel pipes, and rotomolded plastic-lined steel pipes.
1.3 lining plastic: polyethylene (pe), heat-resistant polyethylene (pe-rt), cross-linked polyethylene (pe-x), polypropylene (pp-r) rigid polyvinyl chloride (pvc-u), chlorinated polyvinyl chloride (pvc-c).
2. plastic-coated steel pipe
2.1 definition: plastic-coated steel pipe is a steel-plastic composite product with a steel pipe as the base pipe, plastic powder as the coating material, and a plastic layer or another anti-corrosion layer on the inner and outer surfaces.
2.2 classification: plastic-coated steel pipes are divided into polyethylene-coated steel pipes and epoxy resin-coated steel pipes according to different coating materials.
2.3 plastic coating materials: polyethylene powder and epoxy resin powder.

second, product labeling
1. plastic-lined steel pipe
1.1 the code of plastic-lined steel pipe for cold water is sp-c
1.2 the code of plastic-lined steel pipe for hot water is sp-cr
1.3 the outer plastic-lined steel pipe code for cold water is psp-c
1.4 plastic-lined plastic-lined steel pipes for hot water are code-named psp-cr
2. plastic-coated steel pipe
2.1 pe-coated steel pipe code sp-t-pe
2.2 epoxy resin coated steel pipe code sp-t-ep

third, product technology
1. plastic-lined steel pipe
1.1 plastic-lined process: after the pre-treatment of the steel pipe, apply the adhesive evenly on the outer wall of the plastic pipe, and then place it in the steel pipe to expand it to form a steel-plastic composite product.
1.2 rotational molding process: heat the steel pipe after pretreatment, roll and sprinkle polyethylene powder evenly on the inner wall while the steel pipe is rotating, and then perform curing treatment to form a steel-plastic composite product.
2. plastic-coating process: steel-plastic composite products are formed by heating the steel pipe after pre-treatment, high-speed plastic-coating treatment, and then curing treatment.

fourth, the implementation of standards
1. plastic-lined steel pipe
1.1 plastic-lined steel pipes for water supply shall meet the requirements of cj/t136 standard.
1.2 the adhesive between the outer plastic layer and the steel pipe should meet the requirements of sy/t0413 for adhesives.
1.3 the lining plastic of polyethylene (pe) steel pipes should meet the requirements of gb/t13663 for plastics.
1.4 the lining plastic of heat-resistant polyethylene (pe-rt) steel pipes should meet the requirements of cj/t175 for plastics.
1.5 the lining plastic of cross-linked polyethylene (pe-x) steel pipes should meet the requirements of gb/t18992.2 for plastics.
1.6 the lining plastic of polypropylene (pp-r) steel pipes should meet the requirements of gb/t18742.2 for plastics.
1.7 the lining plastic of rigid polyvinyl chloride (pvc-u) steel pipes should meet the requirements of gb/t10002.1 for plastics
1.8 the lining plastic of chlorinated polyvinyl chloride (pvc-c) steel pipes should meet the requirements of gb/t18993.2 for plastics
1.9 if the base pipe is a straight seam welded pipe, it shall meet the requirements of gb/t3091 for base pipes.
1.10 if the base pipe is a seamless welded pipe, it shall meet the requirements of gb/t8163 for base pipes.
1.11 if the base pipe is a spiral submerged arc welded pipe, it shall meet the requirements of sy/t5037 for the base pipe.
2. plastic-coated steel pipe
2.1 plastic-coated steel pipes for water supply shall meet the requirements of cj/t120 standards.
2.2 the performance of polyethylene powder should meet the requirements of the cj/t120 standard.
2.3 the performance of epoxy resin powder should meet the requirements of the cj/t120 standard.
2.4 if the base pipe is longitudinally welded, it shall meet the requirements of gb/t3091 for base pipes.
2.5 if the base pipe is a seamless welded pipe, it shall meet the requirements of gb/t8163 for base pipes.
2.6 if the base pipe is a spiral submerged arc welded pipe, it shall meet the requirements of sy/t5037 for base pipes.

fifth, model specifications
1. plastic-lined steel pipes are suitable for plastic-lined steel pipes for water supply with a nominal diameter not greater than 500mm.
2. plastic-coated steel pipes are suitable for water-supply plastic-coated steel pipes with a nominal diameter not greater than 1200mm.

sixth, the connection method
1. plastic-lined steel pipe
1.1 flange connection should meet the requirements of gb/t9119 standard.
1.2 groove connection shall meet the requirements of gb5135.11 standard.

2. plastic-coated steel pipe
2.1 the flange connection shall meet the requirements of the gb/t9119 standard.
2.2 groove connection should meet the requirements of the gb5135.11 standard.
2.3 the screw connection should meet the requirements of the gb/t7306.1 standard.

seventh, external anti-corrosion
1. if the external anti-corrosion of the base pipe is hot-dip galvanized, it shall meet the requirements of gb/t3091 for the galvanized layer.
2. if the external anti-corrosion of the base pipe is plastic-coated, it shall meet the requirements of cj/t120 for the plastic-coated layer.
3. if the outer anti-corrosion of the base pipe is covered with plastic, it should meet the requirements of sy/t0413 for the outer plastic layer.

eighth, plastic layer, coating thickness
1. the thickness of the plastic layer of the plastic-lined steel pipe should meet the requirements of the cj/t136 standard for the thickness of the plastic layer.
2. the coating thickness of plastic-coated steel pipes should meet the requirements of cj/t120 standards for coating thickness.

ninth, performance
1. performance of plastic layer of plastic-lined steel pipe
1.1 bonding strength: the bonding strength between steel and plastic-lined steel pipe for cold water should not be less than 0.3mpa (30n/cm2); the bond strength between steel and plastic-lined steel pipe for hot water should not be less than 1.0 mpa (100n/cm2).
1.2 peel strength of the outer covering layer: the peel strength should not be less than 0.35mpa (35n/cm2)
1.3 external anti-corrosion performance: the product that is baked or sprayed after galvanizing is soaked in 3% (weight ratio) sodium chloride aqueous solution for 24 hours at room temperature, and the appearance should be free from corrosion, whitening, peeling, and wrinkling.
1.4 flattening test: no cracks will occur after the plastic-lined steel pipe is flattened to 1∕3 of the outer diameter of the pipe, and there will be no separation between the steel and the plastic.

2. coating properties of plastic-coated steel pipes
2.1 pinhole test: the inner surface of the plastic-coated steel pipe is detected by an electric spark detector, and no electric spark is generated.
2.2 adhesion: the adhesion of polyethylene coating should not be less than 30n/10mm; the adhesion of epoxy resin coating should be grade 1-3.
2.3 flattening test: no cracks will occur after flattening 2∕3 of the outer diameter of the polyethylene-coated steel pipe and 4∕5 of the outer diameter of the epoxy-coated steel pipe, and there will be no peeling between the steel pipe and the coating.

installation
first, installation and construction
1. plastic-lined steel pipe
1.1 during the construction and installation of plastic-lined steel pipes, plastic-lined steel pipes cannot be cut on-site due to changes in construction technology. increase construction difficulty and cost.
1.2 the on-site construction of plastic-lined steel pipes cannot be prefabricated in advance, which will prolong the construction time.
1.3 plastic-lined steel pipes will shrink in diameter (relatively speaking), which will increase the design pressure of the piping system.
1.4 the plastic-lined steel pipe is relatively wear-resistant due to the relatively thick plastic lining.
2. plastic-coated steel pipe
2.1 the plastic-coated steel pipe can be cut to any length according to the needs of the construction site, and it can continue to be used after being repaired after cutting.
2.2 plastic-coated steel pipes can be prefabricated at the construction site in advance.
2.3 the plastic-coated steel pipe will not shrink due to the coating.

maintenance articles
plastic-lined steel pipes and plastic-coated steel pipes can meet the needs of owners after construction or later maintenance. the pipes and fittings are sufficient and appropriate, the maintenance is convenient, and the pipes and fittings can be replaced quickly without stopping the operation of the pipe system.