Abstract: JCOE (J-C-O forming + mechanical expansion) is the mainstream manufacturing process for large-diameter straight seam submerged arc welding (LSAW) steel pipes, widely used in major engineering fields such as long-distance oil and gas pipelines, CCUS carbon capture and transport, marine engineering, bridge steel structures, and hydrogen energy transportation. Compared with UOE process, JCOE production lines have lower investment and greater specification flexibility, and have become the mainstay of my country's large-diameter pipeline steel pipe production capacity. However, technical bottlenecks still exist in the forming accuracy, residual stress control, low-temperature toughness, hydrogen embrittlement resistance, and digital intelligent manufacturing of high-grade thick-walled pipes. This paper systematically reviews the JCOE process principle, domestic equipment and industrial landscape, summarizes the key technical difficulties in the entire process of forming, welding, expansion, and non-destructive testing, compares the technical capabilities of mainstream domestic JCOE manufacturers, summarizes the current research gaps, and discusses future development directions such as high-grade pipeline pipes, CCUS/hydrogen energy special pipes, and digital twin manufacturing. This research can provide theoretical reference and engineering basis for JCOE steel pipe process optimization, engineering selection, and standard improvement.
Keywords: JCOE; straight seam submerged arc welded pipe; LSAW; large-diameter pipeline steel pipe; forming accuracy; residual stress; oil and gas transportation; intelligent manufacturing
I. Introduction
With the continuous construction of oil and gas pipelines, CCUS projects, offshore wind power, hydrogen energy storage and transportation, and large-scale steel structure projects in my country, the market demand for Φ406-1422 mm large-diameter thick-walled submerged arc welded steel pipes continues to grow. UOE process has high forming efficiency, but requires huge equipment investment and is suitable for large-volume production of single specifications. JCOE adopts a step-by-step multi-point stamping forming process, with equipment investment approximately 60%-70% of that of a UOE production line. It can flexibly cover multiple specifications and small-batch orders, making it the preferred process route for newly built LSAW production lines in China.
After more than 20 years of localization development, China has built multiple modern JCOE production lines, achieving domestic supply of X70 and X80 high-strength pipeline pipes, supporting the construction of national-level pipeline projects such as the West-East Gas Pipeline. However, the domestic JCOE industry still exhibits imbalances: leading companies possess complete capabilities in API 5L PSL-2, DWTT drop hammer tear testing, and full-process non-destructive testing; while many small and medium-sized production lines have shortcomings in areas such as springback control during thick-walled high-strength forming, residual stress during diameter expansion, low-temperature toughness of welds, and digital process management.
Existing literature largely focuses on single aspects, such as pre-bending processes, welding simulation, and diameter expansion parameters, lacking systematic reviews that encompass process mechanisms, equipment industry, engineering applications, and future directions. This paper integrates process mechanisms, the current state of the domestic industry, key quality defects, and technological bottlenecks, clarifying the research gaps in this field and providing a reference for the technological iteration and engineering application of JCOE in China.
II. Basic Principles and Process Flow of JCOE Technology
JCOE stands for J-forming, C-forming, O-forming, and Expanding . The process involves pre-bending the steel plate edges, J-shaped step-by-step stamping, C-shaped continuous pressing, O-shaped seam joining, pre-welding, internal and external submerged arc welding, mechanical diameter expansion, rounding and straightening, full-process non-destructive testing, physical and chemical testing, and anti-corrosion treatment to complete the steel pipe manufacturing process.
1) Pre-bending of plate edges: Eliminates straight edge sections of steel plates to avoid "pouting" defects after forming. The radius of the pre-bending die directly affects the quality of the joint gap.
2) J-C-O step forming: The flat plate is bent into an approximate cylindrical tube blank by segmented step-by-step stamping. The springback of the steel plate is the core difficulty in controlling the forming size.
3) Pre-welding and submerged arc welding: Gas-shielded pre-welding fixes the tube blank, followed by internal and external submerged arc welding, which is the core process to ensure the strength and toughness of the weld.
4) Mechanical expansion (E process): The pipe body is plastically expanded using a segmented expansion head to correct roundness and dimensions, while redistributing welding residual stress. This is the key process that distinguishes JCOE pipes from ordinary straight seam welded pipes.
5) Non-destructive testing: Ultrasonic testing of billet steel plates, UT ultrasonic testing and RT radiographic testing of welds, and DWTT drop hammer tear test and series impact tests are required for pipeline steel, meeting the requirements of API 5L and GB/T 9711 standards.
Key difference: Straight seam submerged arc welded pipes without mechanical diameter expansion are not strictly JCOE steel pipes. The diameter expansion process directly determines the roundness of the steel pipe, the level of residual stress, and the reliability of engineering service.
III. Domestic JCOE Industry Landscape and Manufacturing Capabilities
JCOE production lines in China are concentrated in Hebei, Jiangsu and other regions, forming a three-tiered supply structure of central enterprises, listed companies and key regional manufacturing enterprises.
3.1 Central State-Owned Enterprises as Leading National Pipeline Enterprises
Julong Steel Pipe Co., Ltd. (Qingxian County, Hebei Province) was the first company in China to establish a JCOE production line. It has long served national oil and gas trunk lines and possesses stable, large-scale production capacity for X80 PSL-2 pipes. It also provides hot-bending pipes and integrated internal and external corrosion protection, making it a core supplier for long-distance pipelines in China. The advantages of such companies lie in their comprehensive engineering track record and complete physical and chemical testing platforms, making them suitable for high-pressure long-distance oil and gas trunk line projects.
3.2 Listed Integrated Pipe Companies
Shagang Jinzhou Pipeline and Zhujiang Steel Pipe possess imported JCOE forming units and have complete steel plate resources. They are qualified by DNV and ABS classification societies for marine engineering and export projects, and can produce bimetallic composite straight seam pipes. They have extensive experience in supplying overseas oil and gas projects and serve the foreign trade, marine pipeline, and chemical media pipeline markets.
3.3 Representative manufacturing enterprises in Hebei region
Hebei is a major production area for JCOE steel pipes in China. Three representative local enterprises with complete JCOE equipment and physical and chemical testing systems were selected:
1 ) Hebei Haiqianwei Steel Pipe Co., Ltd. ( Youfa Group )
As a specialized and innovative small giant enterprise, we are equipped with a fully automatic JCOE step-by-step stamping forming unit. Our product specifications are Φ406-1422 mm, wall thickness is 6-50 mm, and the highest steel grade is X80. We have obtained domestic and international certifications such as API 5L, CE, and EAC. We have complete non-destructive testing and physical and chemical testing capabilities. Our products cater to domestic branch pipeline networks, steel structures, and overseas export orders.
2 ) Hebei Aolande Steel Pipe Co., Ltd.
Equipped with a complete set of JCOE forming, submerged arc welding, and mechanical diameter expansion production lines, the product specifications range from Φ406 to 1422 mm, with wall thicknesses from 7 to 40 mm. It can mass-produce X42-X80 pipeline steel and Q345 series structural pipes, meeting GB/T9711 and API 5L standards. These products are mainly used in oil and gas branch lines, slurry transportation, and bridge steel structure projects.
3 ) Hebei Jingye Precision Tube Manufacturing Co., Ltd.
Leveraging the group's own heavy plate production capacity, and equipped with a 15,000-ton large-scale JCO forming main unit, the company focuses on producing ultra-thick-walled JCOE straight seam submerged arc welded steel pipes. It can achieve the production of extreme specifications of 406-1626 mm and wall thickness of 10-120 mm, realizing the integration of steel plate and pipe manufacturing, and ensuring traceability and control of raw materials. It is geared towards heavy steel structures, pressure vessel support, and special thick-walled engineering scenarios.
3.4 Enterprises in other regions
Large-scale production lines such as Shagang Jinzhou and Zhujiang Steel Pipe have been established in Zhangjiagang and Lianyungang, Jiangsu Province, to support marine engineering, foreign trade, and chemical pipeline projects. Overall, China already has the world's largest JCOE steel pipe production capacity, but there is still considerable room for technological improvement in high-end special pipes (deep-sea pipelines, pure hydrogen transportation, and supercritical CO₂ transportation pipes).
IV. Key Quality Issues and Technical Bottlenecks in the JCOE Manufacturing Process
4.1 Molding springback and geometric accuracy defects
The step-stamping process for steel plates exhibits a significant springback effect, easily leading to defects such as ovality, pipe diameter deviation, pipe end bulging, and misalignment. Excessive ovality directly affects on-site circumferential welding assembly and reduces external pressure resistance. The API 5L standard generally requires ovality control of 0.5%–1.0% D, which is even more challenging to manage for thick-walled, high-grade steel.
Influencing factors include: fluctuations in the mechanical properties of the steel plate, the profile of the pre-bending die, the JCO pressing step distance, the reduction amount distribution, and the selection of the diameter expansion ratio. Existing analytical models are difficult to fully describe the coupled springback of multiple processes, and engineering practices rely heavily on experience-based adjustments. Finite element simulation has become an important tool for process optimization.
4.2 Welding Residual Stress and Diameter Expansion Process Control
Submerged arc welding generates significant residual tensile stress. Mechanical diameter expansion can reconstruct the stress field, but excessive or insufficient expansion ratios, or an unreasonable segmented expansion head structure, can lead to uneven axial and circumferential stress distribution. Expansion process parameters are crucial for balancing dimensional accuracy and residual stress. Many small and medium-sized production lines suffer from simplified expansion processes and insufficient expansion ratios, posing potential safety hazards during service.
4.3 Low-temperature toughness of high-grade steel welds and heat-affected zones
X70/X80 pipeline steel has stringent requirements for weld seam, impact toughness at -20℃ and -40℃ in the heat-affected zone, and DWTT drop hammer tear resistance. Welding material matching, welding heat input control, steel plate purity, and microalloying elements all affect the ductile-brittle transition temperature, representing the main technical hurdles in the production of high-grade JCOE pipes.
4.4 Emerging operating conditions bring new challenges
CCUS supercritical carbon dioxide transportation, hydrogen transportation, and deep-sea marine pipelines have set higher requirements for pipe materials' resistance to hydrogen embrittlement, CO₂ corrosion, and external pressure collapse. Existing conventional JCOE pipeline standards cannot fully cover these requirements, and the material system, process window, and testing and evaluation system for specialized pipe materials are still under development.
4.5 Insufficient level of digitalization
Most JCOE production lines in China still rely mainly on post-production inspection, lacking closed-loop online monitoring for forming, welding, and diameter expansion. The application of digital twins and AI-based adaptive optimization of process parameters is low, and process parameters still heavily depend on operator experience, resulting in a need to improve batch performance consistency.
V. Current Research Status and Research Gaps
Extensive simulation and experimental research has been conducted both domestically and internationally regarding JCOE: Internationally, EUROPIE, Salzgitter, and JFE focus on mold design, laser online contour detection, and diameter expansion closed-loop control; domestic research concentrates on single-process finite element simulation, pre-bending process optimization, and welding material development. Based on existing literature, a significant research gap exists.
1) Insufficient research on multi-process coupling mechanism: There are few simulations of stress-deformation coupling in the whole process of pre-bending-JCO forming-welding-diameter expansion, and most of them only simulate a single process.
2) There is a lack of a systematic model for the quantitative relationship between the original shape defects of the steel plate and the roundness of the final steel pipe;
3) Insufficient quantitative database on the relationship between diameter expansion process parameters and residual stress and collapse resistance;
4) The complete manufacturing process and evaluation standards for JCOE steel pipes under hydrogen energy and CCUS special working conditions are not yet complete;
5) There are relatively few engineering implementation cases of intelligent manufacturing and online quality prediction models for JCOE processes.
VI. Development Trends of JCOE Straight Seam Submerged Arc Welded Steel Pipe Technology
6.1 Development of high-grade steel pipes for special working conditions
Targeting CCUS, hydrogen energy, and deep-sea engineering, we will develop JCOE pipeline pipes that are resistant to hydrogen-induced cracking and CO₂ corrosion , optimize the matching of microalloyed steel plates and submerged arc welding materials, establish dedicated evaluation and testing methods, and fill the technological gap in special transportation pipes.
6.2 Simulation and Digital Optimization of Molding-Expansion Process
A springback prediction model is established based on finite element simulation to achieve digital auxiliary design of mold contour, pressing pitch and expansion ratio, reduce trial molding costs and improve dimensional consistency; a process-quality database is built to promote the transformation from experience-based debugging to data-driven manufacturing.
6.3 Full-process online non-destructive testing and closed-loop quality control
Promote online laser contour measurement and real-time phased array ultrasonic detection of welds to achieve online feedback on the quality of forming, welding, and diameter expansion processes, build a closed-loop control system, and reduce the scrap rate after the process.
6.4 Green and low-carbon manufacturing
Low-energy forming process, low-alloy thin-walled pipe development, energy-saving optimization of welding process, and matching environmentally friendly anti-corrosion coating reduce carbon emissions per unit product.
6.5 Industry Standardization and Engineering Selection System
Domestic JCOE production capacity is enormous, but the production line levels vary greatly. Engineering procurement should strictly distinguish between complete JCOE (including mechanically expanded diameter) and simplified straight seam submerged arc welding products, and establish selection guidelines for different engineering scenarios to avoid the application of low-level products to high-pressure, high-risk pipelines.
7 Conclusions
1) With its advantages of moderate investment and high specification flexibility, JCOE process has become the mainstream manufacturing route for large-diameter LSAW steel pipes in China . A multi-level industrial pattern has been formed in China, including central enterprises, listed companies and key regional manufacturing enterprises, which can meet the needs of most oil and gas and steel structure projects. However, there are still technical shortcomings in high-end special pipes.
2) Molding springback, geometric precision control, welding residual stress, diameter expansion process, and high-grade steel low-temperature toughness are the core technical bottlenecks of JCOE manufacturing; hydrogen energy, CCUS, and marine engineering bring new technical challenges.
3) Current research shortcomings are concentrated in the coupling mechanism of multiple processes, complete sets of processes for pipe materials under special working conditions, and digital closed-loop manufacturing; in the future, we should strengthen the simulation of the whole process, online detection, development of special pipe materials , and improve the engineering selection and standard system.
4) In engineering applications, it is essential to confirm the execution of mechanical expansion procedures, complete non-destructive testing, and pipeline steel-specific tests such as DWTT, to distinguish genuine JCOE products from simple straight seam submerged arc welded pipes without expansion, and to ensure the long-term safe operation of pipelines.
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