Seamless steel pipes are used widely and are usually rolled from ordinary carbon structural steel, low alloy structural steel, etc., which are made of a single piece of metal with no seams on the surface and have good applications. However, seamless steel pipes crack when used due to the influence of original material defects and metallographic structure defects, which has a serious impact on stability and safety. It is necessary to find effective preventive measures to prevent them from improving their application effect.
 
1.1 Preventive measures for defects of raw materials
(1) Preventive measures for non-metallic inclusions
To prevent cracking caused by non-metallic inclusions, the source of non-metallic inclusions in raw materials of seamless steel pipes must first be clarified. There are mainly two sources of non-metallic inclusions, namely internal sources and external sources, and it is necessary to carry out targeted prevention and control for different sources. For the prevention and control of external sources, some high-quality refractory materials can be selected, or some excellent crystalline casting powder can be used to control the entry of casting powder into liquid steel and reduce the existence of non-metallic inclusions from external sources. To solve the problem of cracking caused by internal sources, deoxidizers should be used reasonably, because different deoxidizers will produce different contents of inclusions in the blank during use. At the same time, for different tundishes, whether to blow nitrogen is also a preventive measure to reduce non-metallic inclusions. For example, blowing nitrogen into the magnesium tundish can reduce the inclusion content, while blowing nitrogen into the silicon tundish will increase the inclusion content. Therefore, when smelting and casting seamless steel pipes, it is necessary to strictly control, reduce the mixing of external and internal non-metallic impurities, and improve their performance.
 
(2) Preventive measures for chemical composition segregation
The preventive measures for chemical composition segregation need to be formulated according to the cause of segregation. During the preparation of seamless steel pipes, the chemical composition segregation is mainly carbon segregation, which is caused by the untimely distribution of carbon during the solidification of liquid steel. Therefore, to effectively prevent the problem of carbon segregation in seamless steel pipes, it is necessary to strictly control the composition of liquid steel, strictly control the preparation temperature, casting speed, and cooling method according to the production and preparation process, and effectively control the carbon segregation. However, carbon segregation cannot be eliminated. In addition to carbon segregation, chemical composition segregation such as sulfur and phosphorus will also occur. It is necessary to control the content of these elements that are prone to chemical segregation, that is, to improve the purity of liquid steel and control the chemical composition segregation within a certain range. In short, the chemical composition segregation of seamless steel pipes is directly related to the casting speed, cooling method, and mixing technology of liquid steel. It is necessary to prepare for the preparation process and improve the production quality.
 
1.2 Preventive measures for metallographic defects
There are two reasons for banded structure; one is composition segregation, and the other is that the temperature is not suitable during processing. Therefore, in the process of preventing banded structure, the control of component segregation can be done well during the production of tube blanks; the cooling rate of liquid steel can be appropriately increased; the concentration difference of components in steel can be reduced, and the soaking temperature or time of blanks can also be improved, which promotes the uniform diffusion of elements in steel. In addition, for the banded structure caused by the processing technology, an appropriate heat treatment process can be selected to solve it, such as normalizing operation. Widmanstatten defect grains are coarse; the toughness of the steel is reduced, and the mechanical properties are deteriorated. The main reason is that the heating temperature of the tube blank is too high, the holding time is too long, or the cooling rate of the steel drops too fast. The defects of Widmanstatten structure can be eliminated by means of normalizing or annealing heat treatment, for example, prolonging the holding time at a lower heating temperature can eliminate the defects of Widmanstatten structure.
 
2. Conclusion
In short, although the seamless steel pipe has excellent performance, it will crack due to factors such as raw materials and processing technology, which will affect its mechanical properties and toughness. Therefore, in the preparation process of seamless steel pipes, effective preventive measures should be taken for specific cracking reasons to improve production efficiency and quality, increase its toughness, improve mechanical properties, and prolong the service life of seamless steel pipes.