Numerical Simulation and Residual Stress Analysis of Heat Exchanger Tube Plate Surfacing Welding

Literature Overview

This paper by Wang Yuhao, He Qingzhong, and colleagues from the College of Mechanical Engineering, Sichuan University of Science & Engineering, published in Modern Manufacturing Engineering (2016, Issue 7, pp. 90-94), addresses the critical problem of residual stress distribution in heat exchanger tube plate surfacing operations. The study was supported by the Sichuan Provincial Key Laboratory of Material Corrosion and Protection (Grant 2013CL05), Zigong Municipal Key Science and Technology Program (2013C16), and the Graduate Innovation Fund of Sichuan University of Science & Engineering (y2014037). The authors combined experimental surfacing trials with finite element numerical simulation using ANSYS software and APDL parametric programming to characterize the temperature and stress field evolution during multi-pass surfacing welding of heat exchanger tube plates.

Core Technical Approach and Methodology

The researchers first established a representative surfacing test model based on actual heat exchanger tube plate geometries and service conditions. They determined appropriate welding process parameters through trial runs, then performed full-scale surfacing experiments under controlled conditions. In parallel, a numerical simulation was conducted using ANSYS with identical geometry and process parameters. The APDL (ANSYS Parametric Design Language) was employed for parametric programming, enabling systematic simulation of multi-pass welding sequences and accurate capture of the coupled thermal-mechanical behavior.

The numerical model incorporated the following key elements:

The multi-pass surfacing process was modeled as a sequential thermal loading-unloading cycle. Each weld pass was simulated as a moving heat source, with the thermal history from previous passes serving as initial conditions for subsequent passes. This approach captures the cumulative thermal cycling effect that governs the final residual stress state.

Key Findings and Technical Insights

The comparison between experimental measurements and numerical simulation results demonstrated good agreement in both temperature field and residual stress field distributions, validating the reasonableness of the analytical methodology. The study revealed several important patterns:

• The residual stress distribution exhibits strong anisotropy, with maximum tensile residual stresses typically occurring in the weld centerline region and along the longitudinal direction of welding.
• Transverse residual stresses are generally lower than longitudinal residual stresses but still significant enough to influence fatigue life and dimensional stability.
• The depth profile of residual stresses shows a characteristic pattern where tensile stresses near the surface transition to compressive stresses at greater depths, maintaining overall force equilibrium.
• Multi-pass surfacing introduces complex stress superposition effects that cannot be predicted from single-pass analysis alone.

Engineering Significance for Tube Plate Applications

Heat exchanger tube plates are critical components in petrochemical, power generation, and process industries. They are subject to cyclic thermal loads, pressure fluctuations, and corrosive media. The surfacing layer is applied to enhance corrosion resistance or wear resistance of the tube plate surface, particularly at tube holes and sealing surfaces. Understanding the residual stress state is essential because:

1. High tensile residual stresses can accelerate stress corrosion cracking (SCC) in chloride-containing environments.
2. Residual stresses contribute to distortion during subsequent machining operations, affecting the flatness and hole alignment of the tube plate.
3. Fatigue crack initiation sites are preferentially located at regions of high residual tensile stress, reducing the effective fatigue life of the component.

Reflections and Practical Implications

This study provides a valuable framework for predicting and controlling residual stresses in tube plate surfacing operations. The validated numerical model can be directly applied to optimize welding sequences, select appropriate post-weld stress relief procedures, and evaluate the effectiveness of different process parameter combinations. For engineers working on heat exchanger design and fabrication, this methodology offers a cost-effective alternative to full-scale experimental trials when evaluating process changes. The parametric approach using APDL programming allows systematic investigation of the influence of heat input, welding speed, interpass temperature, and pass sequence on the final residual stress state, facilitating data-driven process optimization rather than trial-and-error approaches.

The study also highlights the importance of integrating numerical simulation with experimental validation in welding engineering practice. While finite element analysis provides detailed spatial and temporal information that is difficult to obtain experimentally, experimental verification remains essential to ensure model accuracy and predictive reliability. Future work should extend this approach to include the effects of stress relief treatments, multi-material interactions between the base steel and surfacing alloy, and long-term creep-relaxation behavior under service temperatures.