Steel pipe knowledge: T91 steel pipe is a kind of steel pipe

T91 steel pipe is a type of high-performance steel pipe developed by the United States National Laboratories, such as the Shuling Laboratory and the Metallurgical Materials Laboratory of Combustion Engineering Corporation. It is a new generation of martensitic heat-resistant steel that was created by modifying 9Cr1MoV steel. The carbon content was reduced, while sulfur and phosphorus levels were strictly controlled. Additionally, small amounts of vanadium and niobium were added to enhance its properties. The alloying principle of T91 steel focuses on incorporating trace elements like niobium and vanadium, which significantly improve its high-temperature strength and oxidation resistance compared to 12Cr1MoV steel. However, one drawback of T91 steel is its poor weldability. Welding tests have shown that it has a strong tendency to develop cold cracks. To prevent this, preheating to 200–250°C and maintaining an interpass temperature of 200–300°C is recommended, which effectively minimizes the risk of cracking during welding. After welding, T91 steel must be cooled to between 100–150°C and then reheated for at least one hour before tempering. The tempering temperature should be in the range of 730–780°C, ensuring proper microstructure and mechanical properties. These procedures have been successfully applied in the manufacturing of 200 MW and 300 MW boilers, delivering excellent results and significant economic benefits. Steel pipes are long, hollow metal tubes without joints around their circumference. They are widely used for transporting fluids such as oil, natural gas, coal gas, water, and even certain solid materials. Compared to solid steel products like round bars, steel pipes offer the same bending and torsional strength with less weight, making them an economical choice. They are commonly used in the production of structural components, such as oil drilling pipes, car transmission shafts, bicycle frames, and construction scaffolding. Moreover, steel tubes are ideal for manufacturing ring-shaped parts, as they allow better material utilization, simplify the production process, and reduce both material waste and labor costs. Examples include bearing rings and hydraulic jacks. Due to their versatility, steel pipes are essential in various industries, including defense, where they are used for weapon barrels and other critical components. Steel pipes can be classified into round tubes and shaped tubes based on their cross-sectional shape. Circular tubes are the most common because, for a given perimeter, they provide the largest cross-sectional area, allowing more fluid to pass through. Additionally, when subjected to internal or external radial pressure, circular sections distribute stress more evenly. This is why the majority of steel pipes are manufactured in a round shape.

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