PE lining is made of thermoplastic plastic pipes such as polyethylene (PE), heat-resistant polyethylene (PE-RT), cross-linked polyethylene (PE-X), and so on, which are lined on the inner wall of steel pipe according to the requirements of the conveying medium, so it has the advantages of both steel pipe and plastic pipe.
Plastic-coated composite steel pipe is a steel-plastic composite product with steel pipe as the base material and plastic powder as the coating material, with a plastic layer melt-coated on the inner surface and a plastic layer or other material anti-corrosion layer melt-coated on the outer surface.
According to the different inner coating materials, there are two types, one is polyethylene-coated steel pipe. The other is epoxy resin-coated steel pipe.

Hot-dip galvanized square tubes are generally judged to be qualified based on the appearance of the product. If the outer wall of the square tube has plating defects, pitting, white spots, heavy skin, bubbles, greening, etc., and the frequency of occurrence is too high, it is judged as an unqualified product. However, the product standard has a specified range for the allowable deviation of the product, which should meet the design requirements and relevant standards.

1. Look at the color. Compared with 304 stainless steel cold-rolled plates, the surface of 201 stainless steel cold-rolled plates is white.
2. Feel the feel. The surface friction of 201 cold-rolled steel plate is smaller, and it feels smoother.
3. Test hardness. Find a 201 and 304 stainless steel plate of roughly the same thickness, and gently bend one corner of them with the same force. After letting go, the 304 stainless steel plate is more likely to bend and deform. 201 stainless steel has a higher hardness, but poor toughness, while 304 stainless steel has both hardness and toughness.
4. Look at the sparks. Use an angle grinder to grind 304 and 201 stainless steel respectively. The sparks formed by 201 are wide and long, while the sparks formed by 304 are narrow and short.
5. Look at the spray code. There is usually a spray code on the surface of the stainless steel plate to indicate its material, thickness, width, furnace (batch) number, and other information. 201 stainless steel is represented by "201" (some use "J1" or "J2" to represent its material), and 304 stainless steel is represented by "304" "SUS304" "06Cr19Ni10" "S30408" "1.4301" to represent its material.

1. From a distance, the surfaces of 304 and 201 stainless steel plates have the same gloss and matte color. However, we can identify them in other ways. If you observe directly with the naked eye at a close distance, the color of 304 is saturated and shiny, and it feels very smooth to the touch; while 201 will be slightly darker, with low color saturation, and it will feel a little rough to the touch. In the water test, the water stains on the surface of 304 are very easy to remove, while 201 is very troublesome to handle.
2. Distinguish by grinding machine: When grinding 304 stainless steel plates, the sparks are short and few; while 201 is the opposite, with sparks flying and many. When distinguishing by this method, keep the grinding force consistent.
3. Distinguish by stainless steel pickling paste: Apply the pickling paste on 304 and 201, and observe the color changes; if the color is white or does not change color, it is 304; on the contrary, it is 201 if it is black.