Dynamic Stress and Residual Stress Analysis During Overlay Welding of Large Frame Structures

Literature Overview

This 2010 study published in the Welding Journal by researchers from Baosteel Equipment Maintenance and Machinery Factory addresses the complex stress state that develops during the overlay welding process applied to large-scale frame structures. The investigation combines numerical simulation with experimental validation to characterize both the dynamic (transient) stress field during welding and the final residual stress distribution in the completed overlay. This work is particularly significant given the growing industry demand for extending the service life of large steel structures through weld overlay rather than replacement.

Core Technical Findings

The study reveals that overlay welding on large frame structures introduces a unique stress state that differs fundamentally from conventional welding of smaller components. The key findings include:

• High tensile residual stresses develop in the overlay layer, with peak values reaching 350-450 MPa near the weld centerline
• Compressive residual stresses form in the adjacent base metal regions, creating a self-equilibrating stress system
• Stress gradients are most severe at the weld toe and weld root, where geometric discontinuities amplify local stress concentrations
• Sequential welding of multiple overlay passes creates a complex superposition of thermal and mechanical stress fields

Residual Stress Distribution Characteristics

The numerical simulation results, validated by X-ray diffraction and hole-drilling measurements, reveal the following residual stress patterns:

The longitudinal residual stress in the overlay layer is consistently higher than the transverse component, reflecting the directional nature of the welding heat input and the constraint imposed by the surrounding cooler base metal.

Dynamic Stress Analysis During Welding

The transient stress analysis reveals that peak thermal stresses develop during the welding arc passage and are subsequently partially relieved through plastic deformation. The stress evolution follows a characteristic pattern:

1. Heating phase: Thermal expansion of the weld zone is constrained by surrounding cold material, generating compressive thermal stresses
2. Cooling phase: Thermal contraction of the solidifying weld metal generates tensile residual stresses that become locked in upon full solidification
3. Multi-pass superposition: Each subsequent overlay pass modifies the existing stress field, with later passes partially relieving stresses from earlier passes through thermal cycling

The study demonstrates that the final residual stress state is not simply additive but represents a complex interaction between the thermal history of each pass and the accumulated plastic strain in the weld zone.

Process Optimization Recommendations

Based on the stress analysis results, the following process optimization strategies are recommended for overlay welding of large frame structures:

• Welding sequence optimization: Implementing a back-step or symmetric welding sequence reduces angular distortion and peak longitudinal residual stresses by up to 30%
• Preheating: Moderate preheating to 100-150°C reduces thermal gradients and consequently lowers peak residual stresses
• Interpass temperature control: Maintaining interpass temperatures below 200°C prevents excessive grain growth while still providing some stress relief through thermal cycling
• Post-weld stress relief: A controlled stress-relief annealing at 550-620°C for 2 hours per 25 mm thickness can reduce residual stresses by 50-70%

Engineering Practice Integration

For large frame structures in the steel and heavy industry sectors, the stress analysis findings have direct implications for structural integrity assessment and service life prediction. Engineers should incorporate residual stress measurements into their fitness-for-service evaluations, particularly when overlay welding is applied to components subject to cyclic loading or fatigue-critical applications. The study also highlights the importance of considering stress relief requirements in the overall repair strategy, as unmitigated residual stresses can significantly reduce fatigue life and promote stress corrosion cracking in aggressive environments.

The practical application of these findings requires careful balance between the benefits of stress relief treatment and the potential for distortion or microstructural changes that may compromise the overlay layer's intended performance characteristics.

Key Questions and Reflections

An important question arising from this study is the optimal balance between residual stress reduction and distortion control. While stress-relief heat treatment effectively reduces harmful tensile stresses, it may introduce angular distortion in thin-walled frame structures. Engineers must therefore evaluate whether mechanical stress relief methods such as vibration stress relief or shot peening might be more appropriate for certain geometries. Additionally, the study raises the question of how residual stress measurements should be incorporated into acceptance criteria for overlay welds on safety-critical structures.

Study Insights and Conclusions

The dynamic and residual stress analysis of overlay welding on large frame structures provides essential quantitative data for predicting weld integrity and service performance. The study confirms that peak tensile residual stresses in the overlay layer can approach or exceed the yield strength of the base material, creating a condition that is highly susceptible to fatigue cracking and stress corrosion initiation. For engineers involved in the repair and maintenance of large industrial structures, this research underscores the critical importance of welding sequence design, preheat control, and post-weld stress relief in ensuring the long-term reliability of overlay-welded components. The integration of numerical simulation with experimental validation offers a powerful methodology that should be adopted as standard practice for critical overlay welding applications.