Development and Application of Metallurgical Key Technologies for High-Strength and Toughness Underwater Pipeline Steel

underwater pipelines, as a tool for transporting fluid media, possess numerous advantages including continuous operation, prompt delivery, and high throughput. the technical requirements for underwater pipeline steel pipes are extremely high, necessitating not only high resistance to atmospheric and seawater corrosion but also high strength, toughness, and weldability.

steel pipes must meet high strength standards while also ensuring low-temperature toughness down to -30°c. due to various reasons, the development of seamless underwater pipes in china started relatively late, with lower-grade steels such as x52qo and x60qo being the main grades used. higher grades such as x65qo are still in the trial stage and have not been widely adopted.

in response to the characteristics of high-strength and toughness requirements for underwater pipeline steel, this project has researched and developed a series of metallurgical key technologies for x65qo underwater pipeline steel, effectively addressing difficulties in smelting, continuous casting, and quality control of x65qo steel.

the main tasks include:

（1）studying the technical requirements and composition design principles of underwater pipeline steel. the focus is on the development of x65qo underwater pipeline pipes. independent composition design for x65qo steel has been carried out with narrow composition control technology. control measures ensure c ≤ 0.12%, with appropriate amounts of cr, ni, mo elements for solid solution strengthening and nb as a microalloy for grain refinement. x65qo steel pipes achieve high strength, toughness, good weldability, and corrosion resistance, with impact values exceeding 300j at -30°c.

（2）investigating the development status of deep desulfurization slag systems. a deep desulfurization slag system containing bao and li2o has been developed: ω(cao) 45%–55%, ω(sio2) 3%–10%, ω(al2o3) 18%–30%, ω(bao) 5%–12%, ω(li2o) 0.2%–2%, ω(mgo) 3%–8%. this system is used in producing ultra-low sulfur steel, playing a crucial role in controlling the s content during the smelting of x65qo steel.

（3）developing electromagnetic acceleration technology for round billets to improve the low magnification quality of x65qo continuous castings.

（4）researching the variation laws of inclusions in steel. a precise calcium treatment technology has been developed, controlling ω[ca]/ω[s] between 1.5 and 2.5. this treatment promotes the modification of inclusions in steel.

（5）developing and using ultra-pure steel control technologies to improve the purity of x65qo steel.

（6）studying the main quality defects of pipeline steel billets.

from 2017 to 2019, a total of 75,107 tons of x65qo and other marine pipes were produced, generating an additional sales revenue of ¥560.47 million and a profit of ¥155.56 million. the project has obtained patents for inventions such as "method for producing ultra-low sulfur steel using a deep desulfurization slag system containing bao and li2o" and "method for continuous casting using a combination of continuous casting mold and dummy bar assembly," as well as a utility model patent for "whole tundish submerged nozzle device," and published 10 related papers including "development of hsl450s underwater pipeline."

utilizing products developed from this project, hengyang valin steel achieved international advanced levels in physical quality, and the x65qo underwater pipeline was successfully used for the first time in a domestic project at a depth of 1500 meters, filling a technological gap in china.

centerway steel co., ltd. has established a good cooperative relationship with the famous domestic professional seamless pipe manufacturer--"hengyang valin steel tube" enterprise. it is the first-level agent of hengyang valin steel tube co.,ltd and provides you with one-stop total pipe solutions.

centerwayis committed to providing one-stop service for steel pipe products to customers around the world.