Finite Element Simulation of Temperature Field in Strip Electrode Submerged Arc Surfacing on Thick Plates

Literature Overview

The paper by Wang Zhifeng, Chen Peiyin, Wu Wei, Chen Yan, Chen Jianmin, and Bao Hong, published in The Journal of Welding (2009, Vol. 30, No. 1, pp. 89-92), presents a finite element simulation of the temperature field during strip electrode submerged arc surfacing (SESAS) on thick plates. The authors are affiliated with the Harbin Welding Research Institute of the Chinese Academy of Mechanical Sciences and China First Heavy Industries Group. This work addresses the challenge of modeling the unique thermal characteristics of strip electrode surfacing, which differs significantly from conventional wire electrode processes.

Core Technical Content

Strip Electrode Submerged Arc Surfacing Process

Strip electrode submerged arc surfacing is a high-deposition-rate process that uses a flat strip electrode (typically 20-50 mm wide) instead of a conventional wire electrode. Key process characteristics include:

Parameter	Strip Electrode Surfacing	Conventional SAW Surfacing
Electrode Form	Flat strip (20-50 mm wide)	Round wire (1.6-4.0 mm diameter)
Welding Current	1000-3000 A	300-800 A
Arc Voltage	25-35 V	25-35 V
Travel Speed	100-400 mm/min	200-600 mm/min
Deposition Rate	5-20 kg/h	1-5 kg/h
Heat Input	High	Medium
Typical Application	Thick plate surfacing, large components	General surfacing

The high deposition rate makes SESAS particularly suitable for surfacing thick plates and large components where efficiency is critical, such as large pressure vessel linings, wear plate overlays, and heavy machinery components.

Heat Source Model Development

The authors developed a heat source model for SESAS based on the Goldak double-ellipsoidal model, modified to account for the strip electrode geometry. The key modifications include:

Heat source shape: The conventional double-ellipsoid model is adapted to represent the elongated arc shape produced by a strip electrode. The heat source is modeled as a series of discrete heat source elements distributed along the strip width.
Heat flux distribution: The heat flux is assumed to be non-uniform across the strip width, with higher heat flux near the center and lower flux at the edges, reflecting the actual arc distribution.
Moving heat source implementation: The model was implemented using FORTRAN subroutines within the MSC.MARC finite element software platform. The moving heat source is applied through a user-defined subroutine that calculates the heat flux at each node based on the current position of the electrode.

Simulation Results and Validation

The simulation was validated against experimental measurements of:

Validation Parameter	Method	Agreement
Weld bead geometry	Optical measurement	Good agreement
Thermal cycle curves	Thermocouple measurement	Reasonable agreement
Temperature distribution	Infrared thermography	Acceptable agreement

The results confirmed that the proposed heat source model accurately represents the thermal characteristics of strip electrode submerged arc surfacing. The simulation captured the key features of the temperature field, including:

High peak temperatures in the weld zone
Wide heat-affected zone due to high heat input
Asymmetric temperature distribution ahead of and behind the moving electrode
Thermal cycle characteristics with relatively low cooling rates due to high heat input and thick plate geometry

Process Parameters and Their Influence

The simulation framework enables systematic analysis of the influence of process parameters on the temperature field:

Parameter	Effect on Temperature Field	Engineering Implication
Welding current	Increases peak temperature and HAZ width	Must be controlled to avoid excessive grain growth
Travel speed	Decreases peak temperature, increases cooling rate	Higher speed may promote harder microstructure
Strip width	Increases heat input per unit length	Wider strips require higher travel speeds to maintain cooling rate
Plate thickness	Increases thermal mass, reduces cooling rate	Thick plates may require post-weld heat treatment
Preheat temperature	Increases base temperature, reduces thermal gradient	Critical for preventing cracking in thick sections

Engineering Practice Integration

Application to Thick Plate Surfacing

The simulation framework developed in this paper has direct application to several industrial scenarios:

Large pressure vessel lining: Surfacing of corrosion-resistant alloys on thick carbon steel pressure vessels for chemical processing applications. The high deposition rate of SESAS makes it economically attractive for large surface areas.
Wear plate overlay: Surfacing of hardfacing materials on thick steel plates for mining, cement, and power generation applications. The simulation can predict the thermal cycle to optimize the microstructure and hardness of the overlay.
Repair welding: Repair of thick plate components with damaged surfacing. The simulation can guide the selection of welding parameters to minimize distortion and residual stress.

Residual Stress Prediction

While the paper focuses on temperature field simulation, the thermal analysis provides the foundation for residual stress prediction. The sequence of analysis would be:

Thermal analysis: Calculate temperature field as a function of time and position (as demonstrated in this paper).
Thermo-mechanical analysis: Use the temperature field as input to calculate residual stresses, accounting for thermal expansion, plastic deformation, and phase transformations.
Post-processing: Evaluate residual stress distribution, identify high-stress regions, and recommend stress relief procedures.

Comparison with Other Modeling Approaches

Approach	Advantages	Limitations
Goldak double-ellipsoid model	Well-established, widely validated	May not accurately represent strip electrode geometry
Cylindrical heat source model	Simple, computationally efficient	Poor representation of asymmetric heat distribution
Point heat source model	Very simple, fast	Inaccurate for wide welds
Modified Goldak model (this paper)	Accounts for strip geometry, validated	More complex implementation

Study Insights

The development of a validated finite element model for strip electrode submerged arc surfacing is a significant contribution to welding simulation technology. The modification of the Goldak heat source model to account for the strip electrode geometry demonstrates the flexibility of this approach and its applicability to non-conventional welding processes.

The implementation of the moving heat source through FORTRAN subroutines within MSC.MARC is a practical approach that can be adapted to other finite element software platforms. This modular approach allows for easy modification of the heat source model without requiring changes to the core finite element solver.

The validation of the simulation against experimental thermal cycle curves is particularly valuable, as it provides confidence in the model's predictive capability. The reasonable agreement between simulated and measured thermal cycles indicates that the model can be used to predict the thermal characteristics of SESAS for different process parameters and plate geometries.

For engineers involved in thick plate surfacing operations, this paper provides a valuable tool for process optimization. By simulating the temperature field before actual welding, engineers can select process parameters that minimize distortion, control residual stress, and achieve the desired microstructure in the overlay weld.

Summary

This paper presents a validated finite element model for simulating the temperature field during strip electrode submerged arc surfacing on thick plates. The modified Goldak heat source model, implemented through FORTRAN subroutines in MSC.MARC, accurately captures the thermal characteristics of this high-deposition-rate process. The simulation framework provides a valuable tool for process optimization, enabling engineers to predict temperature distributions, thermal cycles, and residual stresses before actual welding. The work contributes to the advancement of welding simulation technology and provides practical guidance for thick plate surfacing applications in heavy industry.