ow and medium pressure boiler tubes are made of steel ingots or solid tube billets through perforation into capillary tubes, which are then hot-rolled, cold-rolled or cold-drawn.It is suitable for the manufacture of high-quality carbon structural steel hot-rolled, hot-extruded, hot-expanded and cold-drawn, cold-rolled seamless steel pipes for various low and medium pressure boilers.

1. Scratches
Features: There are irregular scratches with different lengths and directions on the surface of low and medium pressure boiler steel pipes. Reasons: 1) Improper operation during annealing. 2) Scratched during lifting. 3) During the straightening process, the steel pipe is scratched at the sleeve.

Reasons: 1) Improper operation during annealing. 2) Scratches when lifting. 3) During the straightening process, the steel pipe was scratched at the sleeve.

2. Scribing: also known as drawing, brushing, straight, including blue line
Features: On the inner and outer surfaces of the low and medium pressure boiler steel pipes, there are longitudinally linear scratches of different lengths, most of which are groove-shaped. If the surface is damaged, it is a scribe, and if there is no damage on the surface, it is a blue line.

Causes: 1) There is a line on the capillary. 2) Iron oxide scale remains on the capillary. 3) The lubricant coating is poor, causing friction to increase, so that the mold heats up the welding metal. 4) The hardness of the inner and outer molds is insufficient or uneven, and the finish is poor. 5) The hammer head is not good, the transition part produces sharp edges and corners, the die is worn, and the scribe line is caused.

3. Shaking pattern: also known as corrugated, slub-shaped, annular
Features: On the outer surface of the low and medium pressure boiler steel pipe, there are full circle or half circle wave-shaped ring marks along the transverse direction. There are continuous, intermittent, and sometimes only superficial.

Causes: 1) There is residual iron oxide scale or dirt on the surface of the steel pipe, the friction force increases, and vibration occurs during drawing. 2) There are no small holes punched at the head. 3) Poor lubrication of steel pipes. 4) The hot-rolled steel pipe with uneven annealing and high carbon content cools too fast, resulting in hard steel. 5) The sizing position of the mold is incorrect. 6) The chain vibrates when pulling.

4, pits: including indentation
Features: The surface of the low and medium pressure boiler steel tube has local depressions with different areas, some are periodic, and some are irregular. The surface of the defect is damaged as a pit, and there is no damage on the surface of the indentation.

Causes: 1) Scrap iron, iron sheets or other dirt adheres to the surface of the steel pipe. After being pressed into the surface during drawing or rolling, it peels off and leaves an indentation. 2) Foreign matter adhered to the straightening roller, and the surface of the steel pipe was pressed into pits during the straightening process.

5. Pockmarks: also known as pockmarked noodles
Features: There are small dot-like depressions on the surface of low and medium pressure boiler steel pipes.

Causes: 1) The iron oxide scale on the surface of the steel pipe is serious. 2) The steel pipe is over-pickled, resulting in pitting corrosion on the surface. 3) Poor preservation, the steel pipe is seriously corroded.

6. Scars: including scales, warping skin, rolling skin
Features: The inner and outer surfaces of the low and medium pressure boiler steel tubes are partially separated from the metal, in the form of blocks or scales. Some are connected to the metal of the tube wall and are not easy to fall off, and some are not connected to the metal and are easy to fall off.

Causes: 1) Poor steel quality and subcutaneous bubbles. 2) Produced by hot rolling and taken to cold drawn or cold rolled tubes. 3) The inner diameter of the steel pipe is too large due to the bending of the tail of the steel pipe, and the uneven force during drawing will form an inner warping skin. 4) The steel pipe has deep lateral pits with edges and corners, which are formed after drawing.

7. Separation
Features: Layered rupture in the spiral direction in the tube wall of the low and medium pressure boiler steel tube.

Causes: 1) There are non-metallic inclusions and shrinkage cavity residues in the tube blank. 2) Serious looseness, etc.