Characteristics of hot-rolled seamless steel pipes

Hot-rolled seamless steel pipes are produced from steel billets through a series of cold and hot rolling, cold drawing, and other processing methods conducted at high temperatures. Compared to ordinary seamless steel pipes, hot-rolled seamless steel pipes offer distinct advantages:

- Smooth inner and outer surfaces with high precision.

- Strong pressure-bearing capacity and excellent tensile strength.

- Stable chemical composition, free from defects such as oxides, impurities, and inclusions.

Advantages:

The hot-rolling process refines the grain structure of the steel, enhancing its density and improving its mechanical properties by breaking down the casting structure of the ingot. This enhancement is primarily observed in the rolling direction, making the steel less isotropic. Additionally, defects such as bubbles, cracks, and porosity formed during casting can be welded together under the influence of high temperature and pressure.

Disadvantages:

Layering:

During hot rolling, non-metallic inclusions (such as sulfides, oxides, and silicates) within the steel may be elongated into thin sheets, leading to delamination. This layering weakens the tensile properties of the steel along its thickness, potentially causing interlayer tearing when welds shrink. The local strain caused by weld shrinkage can far exceed the strain from the applied load.

Residual Stress:

Uneven cooling after hot rolling induces residual stress—internal stress that exists without external forces. This stress is common in hot-rolled steel sections, particularly in those with larger cross-sectional areas. While residual stress is self-balancing, it can adversely affect the performance of steel components under external forces, leading to issues such as deformation, reduced stability, and diminished fatigue resistance.

Dimensional Inaccuracy:

Due to thermal expansion and contraction, hot-rolled steel products often face challenges in maintaining precise dimensions in terms of thickness and width. Although the dimensions may meet standards initially, a certain degree of shrinkage occurs during cooling, resulting in a negative deviation. This deviation is more pronounced in larger steel sections, affecting the precision of width, thickness, length, angle, and side lines.

Overall, hot-rolled seamless steel pipes are known for their high strength, precision, corrosion resistance, and pressure resistance, making them suitable for a wide range of applications. When selecting steel pipes, it's essential to consider the appropriate standards and specifications based on specific application needs to ensure optimal performance and safety.