Xuejun Bai

Research and Development Into Low Temperature Toughness of Large Diameter Heavy Wall X80 Pipeline Steel at Shougang Steel

In recent years the trend in oil and gas transmission pipelines has been toward higher operating pressures. This trend, while the desire to keep steel costs low, has resulted in an increased demand for large diameter heavy wall X80 with good low temperature toughness. It is well known that improving the low temperature toughness with increasing wall thickness of the pipeline is very difficult. To overcome the difficulty of producing consistent low temperature toughness in heavy wall pipe Shougang Steel Research in cooperation with the Shougang Steel Qinhuangdao China (Shouqin) 4.3 m heavy wide plate mill research was conducted.This paper describes the background, composition design and process strategy to produce good low temperature toughness in heavy wall API plate. The importance of the slab reheating schedule and recrystallized rolling process/schedule that occurs during the roughing process will be discussed. The effect of per pass reductions and work roll speed rotation on the strain introduced was analyzed by means of the numerical simulation technology. Furthermore, the center thickness microstructure and low temperature toughness of plate under the different rolling schedules were researched. The results showed a low reheating temperature and slow rough rolling speed should be implemented. The per pass reductions during recrystallized rough rolling should be increased in a steady fashion, with special emphasis on the reduction of the final roughing pass prior to the intermediate hold (transfer thickness for finishing). When the final roughing pass had a per pass reduction of more than 15%, the main microstructure of plate consists of uniform (surface to center) fine ferrite/acicular ferrite with a small volume fraction of M-A constituent. This fine uniform microstructure results in good low temperature fracture toughness in heavier plate thicknesses. Results of this research and development work will be discussed.Copyright

Effects of Heat Treatment Process on Microstructure and Mechanical Properties for Extra-Thick High-Strength Steel Plate

To develop thickness>60mm, yield strength>550MPa high-strength steel plate, the effects of heat treatment process on the microstructure and mechanical properties of plate specimens were investigated on the same controlled rolling and cooling process. The research results showed that, a single time-quenching and tempering heat treatment were conducted to obtain the bainite + free ferrite and residual austenite, the grain size was large and the impact toughness was low. Twice-quenching and a tempering heat treatment could refine the microstructure grain size and increase the soft ferrite proportion to obviously improve the mechanical properties and impact toughness. Taking reasonable intercritical quenching after tempering, the mechanical properties of plate are significantly improved.

Development and Production of Heavy Gauge X80 and High Strength X90 Pipeline Steels Utilizing TMCP/Optimized Cooling Process

Along with the increasing demand of oil and natural gas by various world economies, the operating pressure of the pipeline is also increasing. Large diameter heavy wall X80 pipeline steel is widely used in the long distance high pressure oil and gas transportation in China today. In addition, development of X90/X100 has begun in earnest to support the growing energy needs of China. With the wide use of X80 steels, the production technology of this grade has become technically mature in the industry. Shougang Group Qinhuangdao Shouqin Metal Materials Co., Ltd. (SQS) since 2008 has been steadily developing heavier thicknesses and wider plate widths over the years. This development has resulted in stable mass production of X80 pipeline steel plate in heavy wall thicknesses for larger pipe OD applications.The technical specifications of X80 heavy wall thickness and X90/X100 14.8–19.6 mm wall thicknesses, large OD (48″) requiring wide steel plates for the 3rd West-to-East Natural Gas Transmission Pipeline Project and the third line of Kazakhstan-China Main Gas Pipeline (The Middle Asia C Line) and the demonstration X90/X100 line (part of the 3rd West-East Project) in China required changes to the SQS plate mill process design. Considering the technology capability of steelmaking and the plate mill in SQS, a TMCP+OCP (Optimized Cooling Process) was developed to achieve stable X80 and X90/X100 mechanical properties in the steel plates while reducing alloy content.This paper will describe the chemistry, rolling process, microstructure and mechanical properties of X80 pipeline steel plates produced by SQS for 52,000 mT of for the 3rd West-to-East Natural Gas Transmission Pipeline Project and 5,000 mT for the Middle Asia C Line Project along with 1000 tons of 16.3 mm X90/X100 for the 3rd West-East demonstration pipeline. The importance of the slab reheating process and rolling schedule will be discussed in the paper. In addition, the per pass reductions logic used during recrystallized rough rolling, and special emphasis on the reduction of the final roughing pass prior to the intermediate holding (transfer bar) resulting in a fine uniform prior austenite microstructure will be discussed. The optimized cooling (two phase cooling) application after finish rolling guarantees the steady control of the final bainitic microstructure with optimum MA phase for both grades. The plates produced by this process achieved good surface quality, had excellent flatness and mechanical properties. The pipes were produced via the JCOE pipe production process and had favorable forming properties and good weldability. Plate mechanical properties successfully transferred into the required final pipe mechanical properties. The paper will show that the TMCP+OCP produced X80 heavy wall and 16.3 mm X90 wide plates completely meet the technical requirements of the three pipeline projects.Copyright

Research and Development of Heavy Wall X80 Transmission Pipeline Steel With High Deformation Characteristics for Polar Environments at Shougang Steel

Oil and gas transmission pipeline steels with high deformation capability are required for environments (earthquake zones, permafrost zones, forest heave, deep sea applications, etc.) where large strata movement may occur. When large strata movement occurs the pipeline is exposed to large plastic deformations that can result in failure. Transmission pipelines that must operate in these environmental conditions utilize a strain based design strategy to protect the pipeline from failure. This strain based design strategy for these transmission pipeline environments requires that the steel design used for pipe production must not only have the capability to withstand the high internal operating pressure but must also have good deformation resistance characteristics.Shougang Steel has conducted research into the metallurgical design required for heavy wall X80 transmission pipeline steel with high deformation and good low temperature mechanical property characteristics. This research coupled with the production capability of the Shougang Steel’s Qinhuangdao China (Shouqin) 4.3 m heavy wide plate mill has resulted in the successful production of a cost effective low C-Nb X80 alloy design with good deformation and low temperature toughness capabilities suitable for applications such as the natural gas TCPL/ExxonMobil proposed Alaskan Pipeline Project. This paper will discuss Shougang Steel’s research and development of heavy wall X80 pipeline steel. Key process parameter and equipment capabilities of the Shouqin 4.3 m wide heavy plate mill along with heavy wall X80 production results will be discussed.Copyright