Quality defects of cold-rolled (drawn) seamless pipes and their prevention

Quality defects of cold-rolled (drawn) seamless pipes and their prevention:

⒈ Seamless steel pipe cold processing methods: cold rolling, cold drawing, spinning

a. Cold rolling and cold drawing are mainly used for: precision, thin-walled, small diameter, abnormal cross-section and high-strength pipes
b. Spinning is mainly used for: the production of large diameter, thin wall or super large diameter, ultra-thin wall steel pipes, and has a tendency to be replaced by welded pipes (steel strip, welding, heat treatment, etc.)

⒉ The main process flow of producing seamless steel pipes by cold rolling (drawing) method:
Pipe blank preparation → Cold rolling (drawing) of steel pipe → Finishing and processing of finished steel pipe → Inspection

⒊ Characteristics of seamless pipe production by cold rolling (drawing) method (compared with hot rolling process)
① The outer diameter of the steel pipe becomes smaller until capillary tubes can be produced
② The steel pipe wall is thinner
③ The steel pipe has higher dimensional accuracy and better surface quality
④ The cross-sectional shape of the steel pipe is more complex, and variable cross-section and special-shaped steel pipes can be produced
⑤ Steel pipe performance is superior

⑥ High production costs, large tool and mold consumption, low yield, small output, and higher environmental protection requirements

1) Quality defects of cold drawn seamless pipes and their prevention

The quality defects of cold-drawn seamless pipes mainly include: uneven wall thickness of steel pipes, out-of-tolerance outer diameter, surface cracks, surface straight lines and scratches, etc.

① The uneven wall thickness of cold-drawn steel pipes is related to the wall thickness accuracy of the tube blank, pipe drawing method, drawing center line offset, hole shape, deformation process parameters and lubrication conditions, etc.

① The uneven wall thickness of cold-drawn steel pipes is related to the wall thickness accuracy of the tube blank, pipe drawing method, drawing center line offset, hole shape, deformation process parameters and lubrication conditions, etc.
a. Improving the wall thickness accuracy of the tube blank is an important prerequisite for improving the wall thickness accuracy of the cold drawn steel pipe.
b. The main purpose of extubation without mandrel is to reduce diameter and deformation
c. The hole shape is an important factor affecting the uneven wall thickness of cold drawn steel pipes.
d. It is also an effective method to ensure the pickling quality of the tube blank, remove the iron oxide scale on its surface, and improve the lubrication quality.

②During the production process, great attention should be paid to the wear and tear of fitting and drafting
③In order to reduce cracks on the surface of the steel pipe after pulling, qualified pipe blanks should be selected, and surface defects of the pipe blanks should be ground. When pickling the pipe blanks, it is necessary to prevent over-pickling to avoid pitting or hydrogen embrittlement, and to To prevent lack of pickling and incomplete cleaning of the oxide scale, ensure the annealing quality of the tube blank during use, adopt a reasonable tube drawing method, select appropriate deformation process parameters and tool shape, and strengthen the adjustment and inspection of the drawing center line.

④ Improving the pickling quality and lubrication quality of the pipe blank, ensuring the tool hardness, uniformity and surface finish will help reduce the occurrence of straight lines and scratches on the steel pipe.

2) Quality defects of cold-rolled seamless pipes and their prevention

The main quality defects of cold-rolled seamless pipes include: uneven wall thickness of steel pipes, excessive outer diameter, surface cracks, wrinkles, rolling folds, etc.

① Improving the wall thickness accuracy of the tube blank is an important condition to ensure uniform wall thickness of cold-rolled steel pipes.
② Ensuring the wall thickness accuracy of the tube blank and the pickling quality, lubrication quality and surface finish of the tube rolling tool are important guarantees for improving the wall thickness accuracy of the cold-rolled tube. The tube blank should be prevented from being over-pickled or under-pickled, and the surface of the tube blank should be prevented from being damaged. If pitting or residual iron oxide scale is produced, strengthen the cooling of pipe rolling tools and inspection of tool surface quality, and promptly replace unqualified mandrel rods and rolling groove blocks.

③ All measures to reduce the rolling force are conducive to improving the outer diameter accuracy of the steel pipe, including annealing the tube blank, reducing the rolling deformation, improving the lubrication quality of the tube blank and the surface finish of the tube rolling tool, etc., using Use materials with high strength and hardness to make pipe rolling tools, and strengthen the cooling and inspection of pipe rolling tools. Once the pipe rolling tools are found to be severely worn, they should be replaced in time to prevent the outer diameter of the steel pipe from exceeding the tolerance.
④ Surface cracks on steel pipes produced during the cold rolling process are caused by uneven deformation of the metal. In order to prevent surface cracks in the steel pipe during cold rolling, the tube blank should be annealed when necessary to eliminate work hardening of the metal and improve the plasticity of the metal.

⑤ The amount of rolling deformation has a crucial impact on the surface cracks of cold-rolled steel pipes. Appropriately reducing the amount of deformation is a very effective method to reduce the surface cracks of steel pipes.
⑥ Improving the surface finish of pipe rolling tools and the lubrication quality of pipe blanks are active measures to prevent cracks in steel pipes.

⑦ By annealing and heat treating the tube blank to reduce the deformation resistance of the metal, reduce the amount of deformation, and improve the quality of the tube rolling tools and lubrication quality, etc., it is beneficial to reduce the occurrence of steel pipe rolling folding and scratch defects.

Tips: ASTM A106 seamless pressure pipe (also known as ASME SA106 pipe) is commonly used in the construction of oil and gas refineries, power plants, petrochemical plants, boilers, and ships where the piping must transport fluids and gases that exhibit higher temperatures and pressure levels.