Why do seamless steel pipes crack in production

During the processing of cold-drawn precision steel pipes, there are cold hardening and hydrogen embrittlement, which are the key reasons for the cracking of cold-drawn seamless steel pipes.

Harm of cold work hardening Seamless steel pipes cause a lot of plastic deformation during cold drawing, resulting in significant changes in lattice constants, which in turn increase the kinetic energy of lattice constants, and metal materials can be improved, resulting in uneven internal stress of metal materials, resulting in residual thermal stress. This will increase the hardness of the metal and reduce the ductility. The higher the hardness of the metal, the greater the residual thermal stress during cold drawing, and the more pronounced the cold work hardening. When the internal stress reaches a certain standard value, the metal material will be torn along a certain column of crystal pages, resulting in the crack of the seamless steel pipe.

Hazards of hydrogen embrittlement state In the whole process of removing scale with acid solution, hydrochloric acid and iron produce reflected dissolved radon gas. Hydrogen penetrates into the steel in the form of molecules or positive ions, resulting in a solid solution. The hazard of hydrogen to the physical properties of steel is typically manifested in hydrogen embrittlement.

The raw material of the thick-walled cold-drawn seamless steel pipe is the round finishing tube. The round steel tube blank is processed by laser cutting of an automatic cutting machine to produce a blank with a length of about one meter, and is sent to the melting furnace by the conveyor belt for heating. The slabs are sent to a melting furnace for heating at about 1200°C. The fuel is radon or acetylene gas. Temperature control in the furnace is a crucial problem.

The round finishing tube is pierced by a piercing machine. Generally, the more common punching machine is the conical roller punching machine. This kind of punching machine has high production efficiency, good product quality, large amount of hole breaking and diameter expansion, and can wear a variety of steel grades. After the hole is broken, the round finishing tube is successively rolled by three rolls, continuous rolling or extrusion. After extrusion, the die should be removed from the tube. According to the high-speed operation of the conical twist drill, the die machine enters the steel blank to open the hole to produce the seamless steel pipe.

The inner diameter of the seamless steel pipe is determined by the diameter of the twist drill of the die machine. After the seamless steel pipe is sizing, it enters the cooling tower. According to the sprinkler cooling, after the seamless steel pipe is cooled, it needs to be straightened. After straightening, the seamless steel pipe is sent to the metal material flaw detector (or pressure test) by the conveyor belt for internal flaw detection. If there are cracks, bubbles and other problems inside the seamless steel pipe, it will be detected. After the quality inspection of the seamless steel pipe, the serial number, specification and model, production date, etc. are sprayed with paint. And lifted into the warehouse by the crane.

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