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

T91 steel pipe is a type of high-performance martensitic heat-resistant steel developed by the United States National Laboratories, such as the Shuling Laboratory and the Combustion Engineering Corporation's Metallurgical Materials Laboratory. It was designed based on 9Cr1MoV steel but with reduced carbon content, strict control over sulfur and phosphorus levels, and the addition of small amounts of vanadium and niobium to enhance its properties. The alloying process significantly improves the high-temperature strength and oxidation resistance compared to 12Cr1MoV steel, although it presents challenges in terms of weldability. One of the key issues with T91 steel is its susceptibility to cold cracking during welding. To mitigate this, preheating to 200–250°C and maintaining an interpass temperature of 200–300°C are recommended, which effectively reduces the risk of cold cracks. After welding, proper heat treatment is essential. The steel must be cooled to 100–150°C and then reheated for at least one hour before tempering at 730–780°C for a minimum of one hour. These steps ensure optimal mechanical properties and structural integrity. T91 steel has been successfully applied in the manufacturing of 200 MW and 300 MW boilers, delivering excellent results and significant economic benefits. Steel pipes, in general, are hollow cylindrical structures without any seams, widely used for transporting fluids like oil, natural gas, coal gas, water, and even certain solid materials. Compared to solid steel sections, they offer greater strength-to-weight ratios, making them more economical and efficient for many applications. Steel pipes are commonly used in the production of structural components such as oil drilling pipes, car drive shafts, and bicycle frames. They are also essential in construction for scaffolding and support structures. Manufacturing ring-shaped parts from steel tubes can improve material efficiency, simplify production processes, and reduce both material and labor costs—examples include bearing rings and hydraulic jacks. In addition to industrial uses, steel pipes play a critical role in military equipment, such as gun barrels and other weapon systems. Depending on their cross-sectional shape, steel tubes can be round or shaped. Circular tubes are most common due to their superior fluid flow capacity and uniform stress distribution under internal or external pressure. This makes them the preferred choice in most piping applications. Steel pipes continue to be a vital component across various industries, from energy and construction to transportation and defense. Their versatility, strength, and cost-effectiveness make them an indispensable material in modern engineering.

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