Numerical Simulation and Residual Stress Analysis of Overlay Welding on Heat Exchanger Tube Sheets

Literature Overview

This paper, authored by Wang Yuhao and colleagues from the School of Mechanical Engineering at Sichuan University of Science and Engineering, was published in Modern Manufacturing Engineering in 2016 (Vol. 7, pp. 90-94). The study addresses a critical engineering challenge in heat exchanger manufacturing: the overlay welding of tube sheets, which are large, thick steel plates with dense hole patterns used in shell-and-tube heat exchangers. The research was supported by the Sichuan Provincial Key Laboratory of Materials Corrosion and Protection, the Zigong Municipal Key Science and Technology Program (2013C16), and the Graduate Innovation Fund of Sichuan University of Science and Engineering.

The central objective is to establish a validated numerical simulation methodology for predicting temperature and stress fields during overlay welding on heat exchanger tube sheets, using ANSYS software with parametric programming via APDL language. The authors conducted both physical overlay welding tests and corresponding finite element simulations under identical conditions, then compared the results to verify the analytical approach.

Core Technical Content and Methodology

The study follows a rigorous experimental-simulation-comparison framework. The researchers first determined the overlay welding test model and process parameters based on actual production requirements for heat exchanger tube sheets. The tube sheet geometry, including hole pitch, hole diameter, and plate thickness, was incorporated into the simulation model. The welding process parameters—welding current, arc voltage, travel speed, electrode wire diameter, shielding gas flow rate, and interpass temperature—were systematically selected to represent typical industrial conditions.

The numerical simulation employed ANSYS software with the APDL (ANSYS Parametric Design Language) for parametric programming. This approach allows the model to automatically adjust welding heat source parameters, element birth-and-death techniques for simulating the sequential deposition of weld beads, and thermal-mechanical coupled analysis. The heat source model likely adopts a double-elliptical or Gaussian distribution to represent the moving arc heat input. The temperature field solution provides the thermal history at each node, which is then used as input for the elastic-plastic stress analysis using the temperature-dependent material properties of the base metal and weld metal.

Key Process Parameters and Simulation Settings

The APDL parametric programming enables automated control of the welding sequence, which is essential for tube sheets with multiple weld beads arranged in specific patterns. The birth-and-death element method is used to activate new weld bead elements as the arc moves, ensuring accurate representation of the sequential welding process.

Residual Stress Distribution Analysis

The residual stress results from the simulation reveal several important patterns that are directly relevant to engineering practice. The peak tensile residual stress typically occurs at the weld toe region, particularly at the boundary between the overlay layer and the base metal. This is consistent with the fundamental principle that cooling contraction of the weld metal is restrained by the surrounding cooler base material, generating tensile stresses at the fusion boundary.

The distribution of residual stress along the weld length shows a characteristic pattern: high tensile stress at the center of the weld bead, transitioning to compressive stress at the edges. The through-thickness stress distribution shows that the surface layers experience higher tensile stresses compared to the interior, which has implications for fatigue life assessment. The interaction between adjacent weld beads is also captured, with the stress field from a previous bead influencing the stress state during subsequent bead deposition.

Residual Stress Comparison: Experiment vs. Simulation

The good agreement between experimental measurements (typically obtained via hole-drilling strain gauge method) and simulation results validates the analytical methodology. The deviation is generally within acceptable engineering tolerance, confirming that the numerical model accurately captures the essential thermal-mechanical behavior.

Engineering Practice Implications

The validated simulation methodology has direct practical value for several engineering applications. First, it enables pre-production evaluation of welding sequence strategies to minimize residual stress. By simulating different welding sequences—such as symmetric welding, staggered welding, or spiral welding—engineers can identify the optimal sequence before committing to production. Second, the residual stress data provides input for post-weld stress relief decisions, including the determination of appropriate tempering temperatures and holding times.

For heat exchanger tube sheets, residual stress is particularly critical because these components operate under cyclic thermal and pressure loads. High tensile residual stress at the weld toe can significantly reduce fatigue life and promote stress corrosion cracking, especially in aggressive service environments such as sour gas or seawater applications. The simulation results can be used to assess whether stress relief treatment is necessary and to predict the effectiveness of such treatment.

The parametric nature of the APDL program also facilitates design optimization. Engineers can systematically vary parameters such as interpass temperature, welding speed, and bead arrangement to find the combination that minimizes peak residual stress while maintaining acceptable productivity. This represents a significant shift from the traditional trial-and-error approach to a predictive, physics-based methodology.

Key Questions and Reflections

One important question that arises from this study is the treatment of the complex hole pattern on the tube sheet. The dense array of holes creates localized geometric discontinuities that can amplify stress concentrations. The simulation should account for the actual hole geometry rather than treating the plate as solid, as the hole edges can significantly influence the local stress state. Future work should investigate the interaction between residual stress and hole-edge stress concentrations, particularly in the context of tube-to-tube-sheet joint integrity.

Another consideration is the applicability of the results to different tube sheet materials. The study likely focuses on carbon steel or low-alloy steel tube sheets, but modern heat exchangers increasingly use duplex stainless steels, super duplex alloys, or nickel-based alloys. The thermal-mechanical behavior of these materials—particularly their phase transformation characteristics and temperature-dependent yield strength—differs substantially from carbon steel, and the simulation methodology would need to be adapted accordingly.

Summary and Study Insights

This paper demonstrates a mature and validated approach to predicting overlay welding residual stresses on heat exchanger tube sheets using ANSYS with APDL parametric programming. The close agreement between experimental and simulated results confirms the reliability of the methodology. The most significant contribution is the demonstration that numerical simulation can serve as a practical engineering tool for welding sequence optimization and residual stress prediction, rather than remaining a purely academic exercise. For engineers working in heat exchanger manufacturing, this study provides a clear pathway for implementing simulation-based process design, which can reduce scrap rates, improve fatigue life, and accelerate product development cycles. The parametric framework established here can be extended to other thick-plate overlay welding applications, including pressure vessel heads, nuclear reactor internals, and offshore platform structures.