Hot-rolled seamless steel pipes are irreplaceable, high-safety basic raw materials used in nuclear and thermal power, oil and gas drilling, equipment manufacturing, and other fields. However, due to the high-temperature hot rolling process and the annular cross-section, the controlled rolling and cooling (CR+CC) technology, which is widely applied in the plate industry, is difficult to apply in hot-rolled seamless steel pipe production. As a result, improving the performance of pipes has traditionally relied on adding alloying elements and offline heat treatment. Over the past forty years, both domestic and international efforts have been made to develop controlled cooling technology for steel pipes. However, due to the inability to control uniform temperature during the pipe cooling process, there have been few successful precedents, making this an international challenge in the field. Breaking through the bottleneck of online control of microstructure and performance has become the key to achieving high-quality and green production of hot-rolled seamless steel pipes.

Since 2013, Northeastern University and Baosteel have collaborated, and after seven years of effort, they finally overcame this global challenge. They were the first to develop controlled cooling technology and equipment for hot-rolled seamless steel pipes that enables rapid and uniform cooling of both inner and outer walls, as well as direct quenching. This technology was the first to achieve stable industrial application globally. It was applied to the PQF460 unit, enabling controlled cooling and direct quenching of all 10-36m lengths of steel pipes after rolling. The team developed an automated system for online controlled cooling of hot-rolled seamless steel pipes based on an online cooling temperature control model, a dynamic self-adaptive temperature algorithm for the full length of the pipe, and a multi-process control strategy. This system achieved efficient (matching the fastest rolling pace of 40 seconds), uniform (temperature control accuracy of ±20°C along the length and circumference), and stable production, with excellent pipe shape and straightness (ovality < 1% D, straightness < 5mm/m).

Based on the online controlled cooling and quenching equipment, the production process was re-engineered to achieve short-process production with online microstructure control, leading to the development of entirely new compositions and process technologies for high-grade casing, line pipes, and structural pipes. This enabled series production of three major categories of hot-rolled seamless steel pipes in all specifications. Compared to traditional processes, grain size improved by 1-3 levels on average, impact toughness increased by 20-100J, and for 110ksi anti-sulfur pipes, the Kissc value of anti-sulfur indicators in the online controlled cooling + offline tempering process was 10% higher compared to the traditional secondary offline tempering process, reaching over 30MPa·m1/2. This successfully replaced the traditional secondary offline tempering process, significantly reducing the cost per ton of steel.

The proposal for “using online controlled cooling technology for seamless oil well casing production” passed the American Petroleum Institute (API) standard revision application, marking a breakthrough in which a Chinese steel pipe manufacturing enterprise led the revision of an API standard for the first time. The achievements have become a platform technology for Baosteel.