Residual Stress Analysis of Circumferential Butt Welds in Q460 High-Strength Steel Pipe

Literature Overview

This study focuses on the circumferential butt weld residual stress distribution in Q460-grade high-strength steel pipes, which are increasingly used in bridge towers, offshore platforms, and heavy-load transmission structures. The research employs both numerical simulation and experimental measurement techniques to characterize the residual stress field generated during the welding of thick-walled Q460 steel pipes. Understanding this residual stress is critical because it directly influences fatigue life, distortion control, and the overall structural integrity of the welded joint.

Core Technical Points

The study addresses several fundamental aspects of welding residual stress in Q460 steel pipes. First, Q460 steel belongs to the Q460GD series (GB/T 1591), with a yield strength of 460 MPa and tensile strength of 550–650 MPa. The high strength introduces significant challenges during welding, including elevated cooling rates, increased susceptibility to cold cracking, and complex residual stress patterns that differ markedly from conventional Q345 steel.

The circumferential butt weld configuration is typical in pipe manufacturing and field erection. During the welding process, the local thermal input creates a non-uniform temperature field. Upon cooling, differential thermal contraction between the weld zone, heat-affected zone (HAZ), and base metal generates residual stresses. The axial residual stress near the weld surface typically reaches tensile values approaching the yield strength of the material, while the hoop direction shows compressive stress to maintain equilibrium.

Key Parameters and Process Windows

Residual Stress Distribution Characteristics

The study reveals that the residual stress distribution follows a characteristic pattern. In the weld metal zone, the axial residual stress (σ_z) reaches approximately 350–420 MPa, which is close to but slightly below the yield strength of Q460 steel. The hoop residual stress (σ_θ) in the same region is compressive, typically ranging from −50 to −150 MPa. In the HAZ, the axial stress transitions from tensile to compressive at a distance of approximately 1.5–2 times the weld width from the weld centerline.

The radial residual stress (σ_r) is generally lower in magnitude compared to axial and hoop stresses but becomes significant in thick-walled sections where constraint effects are more pronounced. The study demonstrates that the residual stress magnitude increases with wall thickness, as thicker sections impose greater restraint on thermal deformation.

Comparison of Measurement Methods

Engineering Implications and Countermeasures

The elevated residual stress in Q460 steel pipe welds poses a serious risk to fatigue performance. Fatigue cracks initiating at the weld toe or internal weld defects can propagate rapidly under cyclic loading, especially when the residual stress approaches the yield strength. The study recommends several mitigation strategies:

1. Post-weld heat treatment (PWHT): Stress relieving at 550–620 °C for 1–3 hours can reduce residual stress by 50–70%, though this must be balanced against potential microstructural coarsening.
2. Peening treatment: Shot peening or ultrasonic impact treatment (UIT) at the weld toe introduces compressive residual stress that counteracts the tensile stress, extending fatigue life by 2–5 times.
3. Optimized welding sequence: For multi-segment pipe fabrication, adopting a symmetrical welding sequence and controlling the total heat input can minimize angular and longitudinal distortion.
4. Mechanical stretching: Post-weld cold stretching or warm stretching at 200–300 °C can effectively relieve axial residual stress in pipe sections.

Defect Analysis and Quality Control

Study Insights and Reflections

This research is particularly valuable because Q460 steel is becoming the standard material for large-scale infrastructure projects in China, including the Yangtze River Bridge towers and offshore wind turbine foundations. The residual stress analysis provides a quantitative basis for fatigue assessment under the GB/T 19885 and ISO 15614 frameworks. A key insight is that the interaction between residual stress and material strength is not linear—once the residual stress exceeds 0.8 times the yield strength, the beneficial compressive stress component is significantly reduced due to local yielding during service loading.

The study also highlights the importance of considering the anisotropic behavior of Q460 steel in the rolling direction. The residual stress pattern is influenced by the pipe's rolling direction relative to the weld orientation, which has implications for the selection of welding procedures in production environments. Engineers should pay close attention to the heat input control during multi-pass welding, as excessive heat input in the fill and cap passes can lead to grain coarsening in the HAZ and reduced impact toughness, which is especially critical for low-temperature applications.

In practical engineering, the combination of FEM simulation and experimental validation provides the most reliable approach for residual stress prediction. However, the accuracy of FEM results depends heavily on the input parameters, including the thermal-mechanical coupling model, material constitutive law, and boundary conditions. The study recommends using the elastic-plastic coupled model with kinematic hardening to capture the cyclic loading-unloading behavior during multi-pass welding.

This literature contributes significantly to the understanding of welding residual stress in high-strength steel pipes and provides actionable guidelines for engineers involved in the design, fabrication, and inspection of Q460 steel pipe structures. The findings underscore the necessity of implementing rigorous residual stress management strategies throughout the entire lifecycle of such structures.