Shaped seamless steel pipe is a general term for seamless steel pipes of other cross-sectional shapes other than round pipes. According to the different shapes and sizes of the steel tube section, it can be divided into equal wall thickness shaped seamless steel tubes (code D), unequal wall thickness shaped seamless steel tubes (code BD), and variable diameter shaped seamless steel tubes (code BJ). Shaped seamless steel tubes are widely used in various structural parts, tools and mechanical parts. Compared with round pipes, special-shaped pipes generally have larger moments of inertia and section modulus, and have greater resistance to bending and torsion, which can greatly reduce the weight of the structure and save steel.

Shaped pipes are generally distinguished according to their cross-sections. According to materials, they can be divided into seamless steel pipe shaped pipes, aluminum alloy shaped pipes, and plastic shaped pipes. The following mainly introduces the special-shaped steel pipe. Steel tube shaped pipe can be divided into oval shaped seamless pipe, triangular shaped seamless pipe, hexagon shaped seamless pipe, diamond shaped seamless pipe, octagonal shaped seamless pipe, semi-circular shaped steel circle, unequal side six Angle shaped seamless pipe, five petal plum shaped seamless pipe, double convex shaped seamless pipe, double concave shaped seamless pipe, melon shaped seamless pipe, conical shaped seamless pipe, corrugated shaped seamless pipe tube.