Zhuojin Pipe Fitting Co., LtdDynamic Simulation of Overlay Welding Thermal Stress Based on ANSYS Platform
Literature Overview
The paper by Wang Qiang and Li Donglin (2004), published in the Journal of Wuhan University of Technology (Transportation Science and Engineering Edition), presents a finite element analysis approach to simulating the transient temperature field and stress field during flat plate overlay welding. The authors developed an appropriate finite element model and used the ANSYS software with APDL (ANSYS Parametric Design Language) programming to implement the moving welding heat source. The study addresses residual stress and deformation after welding through dynamic simulation, which is a critical concern in overlay welding applications for corrosion-resistant and wear-resistant surface treatments on steel pipes and structural components.
Core Technical Approach
The methodology involves several key computational steps that are worth examining in detail for their applicability to industrial overlay welding scenarios:
- Moving heat source model: The authors implemented a Gaussian-type moving heat source using APDL scripting, which allows the heat input to follow the actual welding travel path. This is essential for accurately capturing the asymmetric thermal gradients that develop during single-pass or multi-pass overlay welding.
- Thermo-mechanical coupled analysis: The simulation couples the thermal transient analysis with structural analysis, meaning the temperature field calculated at each time step serves as a thermal load for the subsequent stress calculation. This sequential coupled approach is computationally efficient while maintaining reasonable accuracy for residual stress prediction.
- Element birth and death technique: As the weld pool advances, new material is deposited. The ANSYS element activation technique (element birth/death) is used to simulate the progressive addition of weld metal, which is fundamental to modeling multi-pass overlay builds.
Key Technical Parameters and Process Windows
| Parameter | Typical Value / Range | Significance |
|---|---|---|
| Welding current | 180–280 A (SMAW) | Controls heat input and dilution |
| Travel speed | 30–80 mm/min | Affects thermal gradient and HAZ width |
| Heat input | 0.8–2.5 kJ/mm | Critical for residual stress magnitude |
| Interpass temperature | 100–250°C | Controls cooling rate and microstructure |
| Base plate thickness | 10–30 mm | Influences constraint factor and stress |
| Weld layer thickness | 3–6 mm per pass | Determines stress distribution |
The simulation results typically reveal that the maximum residual stress develops in the weld metal and extends into the base material HAZ, often reaching values of 200–350 MPa in the transverse direction. The longitudinal residual stress shows a characteristic distribution with tensile stress in the weld zone transitioning to compressive stress in the base material away from the weld.
Interpretation of Technical Points
The use of APDL for automating the moving heat source implementation represents a significant methodological contribution. In practice, overlay welding on steel pipes (such as CRA overlay on carbon steel pipe for sour service) involves complex geometry where the heat source moves along a curved path. The APDL approach demonstrated here can be adapted for cylindrical geometries by modifying the coordinate system in which the heat source moves.
The temperature field simulation provides insight into the cooling rate distribution, which directly influences the microstructure of the overlay weld. For high-carbon martensitic overlays (common in wear-resistant applications), cooling rates exceeding 10°C/s in the weld metal can lead to brittle martensitic structures with high residual stress. The simulation allows prediction of these conditions before physical welding trials, reducing development time and cost.
Integration with Engineering Practice
In overlay welding applications for pipeline and pipe fitting manufacturing, the following practical considerations arise from the simulation methodology:
- Preheating optimization: The predicted thermal gradients can guide preheating temperature selection. For example, when overlay welding a hardfacing alloy on a 200 mm diameter pipe with 12 mm wall thickness, the simulation would indicate the required preheat to limit the maximum thermal gradient and prevent cracking.
- Post-weld stress relief: The residual stress distribution predicted by the simulation helps determine the effectiveness of stress relief annealing parameters. Typical stress relief for overlay welds involves heating to 550–650°C for 2 hours per 25 mm thickness, but the simulation can refine this based on the actual stress state.
- Weld sequence planning: For multi-layer overlay builds on large components, the simulation can evaluate different welding sequences to minimize distortion and residual stress accumulation.
Key Questions and Reflections
Several questions arise from studying this methodology:
- How well does the sequential coupled approach capture the elastic-plastic behavior during welding, particularly the stress relaxation that occurs during the high-temperature phase?
- What is the accuracy of the material property database used, especially for the temperature-dependent properties of overlay alloys?
- How does the simulation handle the complex phase transformations that occur in the HAZ and weld metal during cooling?
The 2004 timeframe of this publication means that modern ANSYS versions with advanced solidification models and phase transformation algorithms would provide significantly improved predictions. However, the fundamental methodology remains valid and is still widely used in industrial welding simulation today.
Study Insights and Implications
This literature demonstrates the power of numerical simulation in understanding and controlling overlay welding processes. For engineers working with corrosion-resistant overlay welds on pipeline components or wear-resistant overlays on rotating equipment, the ability to predict thermal and stress fields computationally is invaluable. The APDL programming approach provides flexibility that commercial welding simulation packages may not offer, allowing customization for specific geometries and process parameters.
The practical implication is that overlay welding process development can be accelerated by combining simulation with limited physical trials. This approach reduces the number of expensive test welds while providing detailed insight into the internal state of the weldment that is difficult to measure experimentally. For critical applications such as CRA overlay on sour service pipes or hardfacing on mill rolls, this methodology can significantly improve first-time success rates and reduce field failures.