Zhuojin Pipe Fitting Co., LtdFinite Element Simulation of Temperature Field in Strip Electrode Submerged Arc Overlay Welding of Thick Plates
Literature Overview
This paper by Wang Zhifeng and colleagues, published in the Welding Journal in 2009 (Vol. 30, Issue 1, pp. 89-92), presents a finite element simulation of the temperature field during strip electrode submerged arc overlay welding (SAW) on thick plates. The authors developed a heat source model based on the Goldak model theory, implemented it through FORTRAN subroutines on the MSC.MARC platform, and validated the simulation results against experimental thermal cycle curves and weld geometry measurements.
Technical Background and Significance
Strip electrode submerged arc welding (also known as twin-wire or wide-arc submerged arc welding) is a specialized process that uses a strip-shaped electrode instead of conventional wire electrodes. This geometry produces a wider, flatter weld bead with lower heat input per unit width compared to conventional submerged arc welding. The process is particularly suited for overlay welding applications where wide, uniform deposits are required on thick plate components, such as large pressure vessels, mining equipment, and structural components requiring corrosion or wear-resistant surfaces.
The thermal history during overlay welding is critical because it determines the microstructure, residual stress state, and mechanical properties of both the overlay layer and the heat-affected zone. For thick plate applications, the temperature field is complex due to three-dimensional heat flow, multi-pass welding sequences, and the cumulative thermal effects of successive passes.
Heat Source Model Development
The authors adapted the Goldak elliptical heat source model for strip electrode SAW. The Goldak model represents the heat source as an elliptical distribution with different energy densities in the leading and trailing regions of the arc, which better captures the asymmetric nature of welding heat input compared to simpler cylindrical or point models.
| Model Parameter | Description | Typical Value Range |
|---|---|---|
| Arc Efficiency (η) | Fraction of electrical energy transferred to workpiece | 0.70-0.90 |
| Longitudinal Decay (α) | Energy distribution along welding direction | Process-dependent |
| Transverse Decay (β) | Energy distribution across weld width | Process-dependent |
| Leading/Trailing Asymmetry | Ratio of front to rear energy density | 1.2-2.0 |
The implementation through FORTRAN subroutines on MSC.MARC represents a standard approach in computational welding mechanics. The subroutine approach allows dynamic modification of material properties, boundary conditions, and heat source parameters during the simulation, which is essential for capturing the transient nature of welding thermal cycles.
Validation and Results
The simulation was validated against two experimental benchmarks: weld geometry measurements and thermal cycle curves obtained from embedded thermocouples. The authors report good agreement between simulated and experimental results, confirming the suitability of the proposed heat source model for strip electrode SAW process simulation.
Thermal cycle validation is particularly important because peak temperature, time at elevated temperature, and cooling rate (particularly the t800-t600 cooling rate) directly determine the microstructure of the weld metal and HAZ. For overlay welding applications, the thermal cycle also affects the dilution ratio and the interface bonding quality between overlay layers.
Engineering Applications and Implications
The finite element simulation approach presented in this paper has several important engineering applications:
- Process optimization — identifying parameter combinations that minimize cracking susceptibility while maintaining acceptable deposition rates
- Residual stress prediction — thermal analysis provides the input for subsequent mechanical analysis to predict residual stress distributions
- Distortion prediction — understanding thermal deformation patterns to design fixture and restraint strategies
- Procedure qualification — extending validated simulation results to untested parameter ranges with reduced experimental cost
- Multi-pass planning — optimizing pass sequencing and interpass temperatures for complex overlay geometries
From my experience with computational welding mechanics, the accuracy of temperature field simulations is fundamentally limited by the accuracy of the heat source model and material property data. The Goldak model, while widely used, has known limitations for certain welding processes and parameter ranges. For strip electrode SAW, the wider arc geometry may require modified decay parameters compared to conventional wire electrode processes.
Study Insights and Reflections
This paper represents an important contribution to the computational welding mechanics literature, particularly for the specialized case of strip electrode SAW. The validation approach — comparing both thermal cycles and weld geometry — is methodologically sound and provides confidence in the simulation results. However, engineers should recognize that temperature field simulation is only the first step in a complete welding analysis; mechanical analysis for residual stress and distortion prediction requires additional material property data and computational effort.
The practical value of this work extends beyond academic interest. For manufacturers of thick plate overlay welded components, validated thermal simulation models can reduce the cost and time of procedure qualification, enable optimization of welding sequences for complex geometries, and provide insights into process parameters that are difficult to measure experimentally. As computational resources continue to improve, real-time thermal simulation integrated with welding equipment control systems represents a promising direction for process optimization and quality assurance.