Performance of JCOE Longitudinal Submerged-Arc Welded Steel Pipe Manufactured from Hot-Rolled Coils

Literature Overview

This 2008 paper published in Oil and Gas Storage and Transportation by Yang Yanhua, Yang Zhuanzhao, Ding Yi, Li Yunlong, Ma Qiurong, and Wei Yaqiu provides a comprehensive overview of the manufacturing process and mechanical performance of JCOE longitudinal submerged-arc welded (LSAW) steel pipes produced from hot-rolled coils. The research was conducted by Xi'an Aeronautical Technical College, China Petroleum Materials Research Institute, and PetroChina Tarim Oilfield Company. The study evaluates the pipes against DNV-OS-F101 (2000) and API SPC 5L specifications, which are critical standards for offshore pipeline applications.

Manufacturing Process Overview

The JCOE (J-C-O-E) manufacturing process involves several sequential forming steps:

1. J-form: Initial forming to create a J-shaped profile from the flat coil.
2. C-form: Further forming to create a C-shaped profile.
3. O-form: Expansion to form a nearly circular shape.
4. E-form: Final expansion and sizing to achieve the target diameter and ovality.

The process begins with hot-rolled coil (HRC) as the raw material, which undergoes leveling, cutting to length, and then the JCOE forming sequence. After forming, the pipe is longitudinally submerged-arc welded (LSAW) to close the seam, followed by post-weld heat treatment (PWHT) if required, and final inspection.

Key Technical Parameters and Performance Results

The DWTT (Drop Weight Tear Test) is particularly important for offshore pipeline applications, as it evaluates the resistance of the pipe material to crack propagation in the thickness direction, which is critical for preventing hydrostatic burst failures under internal pressure loading.

Engineering Practice Implications

For steel pipe manufacturing engineers, this study has several practical implications:

• Coil material selection: The quality of the hot-rolled coil directly affects the final pipe performance. Coil material should have controlled chemical composition, particularly low sulfur and phosphorus content, to ensure adequate weldability and toughness. The coil thickness should be selected based on the target pipe diameter and wall thickness, with consideration for the forming reduction ratio.
• JCOE forming parameters: The forming sequence and parameters (roll gap, forming angle, expansion ratio) must be carefully optimized to achieve the target pipe geometry with minimal residual stress and strain. Excessive forming strain can affect the material's mechanical properties and weldability.
• Welding process control: The longitudinal submerged-arc welding process requires precise control of welding parameters (current, voltage, travel speed, wire feed rate) to achieve consistent weld quality. The weld procedure qualification (WPQ) must be performed in accordance with ASME Section IX or ISO 15614, and production welds must be inspected using non-destructive testing (NDT) methods such as magnetic particle testing (MT) and ultrasonic testing (UT).
• Post-weld heat treatment (PWHT): For certain material grades and wall thicknesses, PWHT may be required to relieve welding residual stresses and improve the toughness of the heat-affected zone (HAZ). The PWHT parameters (temperature, holding time, cooling rate) must be carefully controlled to avoid adverse effects on the material properties.
• Hydrostatic testing: All pipes must undergo hydrostatic testing to verify the integrity of the weld and the overall pipe body. The test pressure is typically 1.5 times the specified minimum yield strength, with a minimum hold time based on the pipe diameter and wall thickness.

Quality Control Considerations

The quality control program for JCOE LSAW pipes should include the following elements:

The implementation of a robust quality control program is essential for ensuring the reliability of JCOE LSAW pipes in critical offshore applications, where failure can result in catastrophic consequences including environmental damage and loss of life.

Critical Reflections

The study provides valuable information on the performance of JCOE LSAW pipes manufactured from hot-rolled coils, demonstrating compliance with DNV-OS-F101 and API 5L specifications. However, several aspects could be further investigated:

1. The long-term performance of the pipes under cyclic loading and corrosion conditions, which are common in offshore environments.
2. The effect of the JCOE forming process on the microstructure and mechanical properties of the pipe material, particularly in the thickness direction.
3. The weldability of different coil grades and the effect of coil chemistry on weld quality.
4. The residual stress distribution after the JCOE forming and welding processes, and its effect on the pipe's resistance to stress corrosion cracking (SCC).

Study Insights and Reference Value

This research contributes to the understanding of JCOE LSAW pipe manufacturing technology and its application in offshore pipeline systems. For steel pipe manufacturers, the study reinforces the importance of process control, material selection, and quality assurance in producing pipes that meet the stringent requirements of offshore standards. The use of hot-rolled coils as the raw material offers cost advantages over plate material, but requires careful attention to the forming process to ensure that the material properties are maintained throughout the manufacturing sequence. The study also highlights the importance of comprehensive mechanical testing, including DWTT, to ensure that the pipes have adequate resistance to crack propagation in critical service conditions.