Seamless steel pipes have been widely used in construction, chemical and other industries due to their excellent performance, but cracking will also occur in the application, which will not only cause waste of materials and increase costs but also lead to decreased production efficiency and delays construction period. The article introduces the
seamless steel pipe and analyzes the reasons for its cracking, which is for reference only.
1.
Introduction of seamless steel pipes
Seamless steel pipes can be divided into hot-rolled pipes, cold-rolled pipes, extruded pipes, and cold-drawn pipes according to different production processes. According to the cross-sectional shape of seamless steel pipes, they can be divided into two types, that is, round pipes and heterosexual pipes. Seamless steel pipes are mainly used in construction machinery, petrochemical and other fields, with a wide range of applications and excellent performance. The wide application of seamless steel pipe can improve the utilization rate of materials, simplify the manufacturing process and save manufacturing time, which is a type of steel pipe that is widely used in industrial production at present.
2.
Analysis of causes of cracking of seamless steel pipes
2.1
Defects in original materials
(1)
Non-metallic inclusions and effects of cracking
Seamless steel pipes are usually made of cold-rolled or hot-rolled tube blanks or billets, and tube blanks are the main raw material for seamless steel tubes. The defects of the tube blank are various due to the influence of various factors such as the manufacturing process of the tube blank and the production environment, mainly including non-metallic inclusions and chemical composition segregation. The original material of the seamless steel pipe will contain a certain amount of oxides or sulfides, which makes the cleanliness of the raw steel not so good, and reduces the continuity of the steel, making the steel structure uneven, leading to cracking in the seamless steel pipe. The non-metallic inclusions of seamless steel pipe’s manufacturing raw materials can be divided into four categories, the first category is sulfide, the second category alumina, the third category silicate, and the fourth category spherical oxides. Different types of non-metallic inclusions will show different colors, for example, sulfides are gray and appear as strips. The manufacturing process of seamless steel pipe is very complicated, including perforation, rolling and annealing treatment; it will come into contact with oxygen to form oxide inclusions. With the continuous improvement of modern production technology, higher requirements are put forward for the production quality of seamless steel pipes, especially the cleanliness of steel, which has become an important standard for evaluating steel quality.
(2)
Chemical composition segregation and cracking effects
Chemical composition segregation refers to the phenomenon that the constituent elements of alloy materials are not uniformly distributed during crystallization. The problem of chemical composition segregation in seamless steel pipes is mainly due to errors in casting technology or casting parameters, which lead to the failure of some chemical components in the alloy material to distribute and diffuse in time and complete solidification, resulting in uneven distribution of chemical elements, no segregation of chemical composition of seam steel pipes. Different chemical components in seamless steel pipes have different properties. Therefore, if there is chemical composition segregation in seamless steel pipes, it will make the distribution of partial chemical composition of seamless steel pipes uneven, resulting in abnormal mechanical properties of seamless steel pipes, forming concentrated stress, which causes seamless steel pipes to crack during applications.
2.2
Defects in the metallographic structure
The metallographic structure is the microstructure of metal materials, which needs to be observed and analyzed by optical metallographic microscopes or electron microscopes. Metallographic structure analysis is the focus of analysis of metal materials, including analysis of band structure, and Widmanstatten structure. The metallographic defects of seamless steel pipes play a key role in the cracking of steel pipes. It is necessary to start from the microstructure of seamless steel pipes and focus on the cracking of seamless steel pipes caused by metallographic structural defects to formulate scientific and effective preventive measures. Among them, the banded structure is a defect structure that appears inside the metal material. The banded orientation is parallel to the processing direction of the material. It usually appears in low-carbon hot-rolled steel structures, which will affect the mechanical properties of the steel structure, and reduce the toughness of the steel structure, and reduction of area will also be reduced. The Widmanstatten structure defect is caused at a certain temperature and cooling rate, and it will not directly affect the material properties, but the coarse structure defect will reduce the plasticity of the material and increase the brittleness of the material.
