Zhuojin Pipe Fitting Co., LtdNumerical Simulation and Residual Stress Analysis of Heat Exchanger Tube Sheet Overlay Welding
Literature Overview
The paper by Wang Yuhao and colleagues from Sichuan University of Science and Technology, published in Modern Manufacturing Engineering in 2016, addresses a critical engineering challenge in heat exchanger manufacturing: the prediction and control of residual stresses generated during overlay welding on tube sheets. Heat exchanger tube sheets are among the most heavily loaded components in process plants, and overlay welding is routinely applied to provide corrosion or erosion protection on the tube-side surface. The authors conducted overlay welding experiments on a representative tube sheet model, established a finite element model using ANSYS with APDL parametric programming, and compared experimental results with simulation outputs to validate the numerical approach. This work was supported by the Sichuan Provincial Key Laboratory for Materials Corrosion and Protection and the Zigong Municipal Science and Technology Program, reflecting its practical significance in the western Chinese petrochemical industry.
Core Technical Approach
The study follows a rigorous experimental-numerical validation methodology. The authors first determined the overlay welding test model and process parameters based on actual production requirements for heat exchanger tube sheets. The welding process parameters were selected to represent typical industrial conditions, ensuring the results would be directly applicable to manufacturing practice. The numerical simulation employed ANSYS with APDL (ANSYS Parametric Design Language) for parametric programming, which allows systematic variation of welding parameters and efficient generation of multiple simulation scenarios.
The key technical steps can be summarized as follows:
- Establishment of a geometric model representing the actual tube sheet geometry, including the overlay weld bead configuration.
- Definition of material properties for both the base tube sheet steel and the overlay weld metal, including temperature-dependent thermal conductivity, specific heat, and elastic-plastic constitutive relationships.
- Implementation of a moving heat source model to simulate the thermal cycle experienced during overlay welding.
- Sequential thermal-mechanical analysis: first solving the transient thermal field to obtain the temperature distribution history, then mapping the temperature field to a structural model to compute residual stress distributions.
- Comparison of simulated temperature and stress profiles with experimental measurements.
Key Technical Parameters and Process Considerations
The following table summarizes the typical parameters and considerations relevant to tube sheet overlay welding as discussed in the literature:
| Parameter Category | Typical Range | Engineering Significance |
|---|---|---|
| Base material | 16Mn or 0Cr18Ni9 tube sheet steel | Determines thermal expansion mismatch and residual stress magnitude |
| Overlay material | 304/316L stainless steel or Ni-based alloy | Provides corrosion resistance on tube-side surface |
| Welding process | GTAW or GMAW | Controls heat input and dilution rate |
| Heat input | 0.8–2.5 kJ/mm | Primary driver of thermal cycle severity and residual stress |
| Layer thickness | 1.5–3.0 mm per pass | Affects cooling rate and microstructure of weld metal |
| Preheat temperature | 50–150 °C | Reduces thermal gradient and residual stress |
| Interpass temperature | ≤150 °C | Controls cumulative thermal strain accumulation |
The numerical simulation revealed that the maximum residual stress concentrates at the weld root and at the intersection of the weld bead with the tube sheet surface, reaching values approaching the yield strength of the base material. The stress field distribution follows a characteristic pattern: compressive longitudinal stress develops in the weld metal, while tensile transverse stress develops in the adjacent heat-affected zone. This stress state is particularly concerning for tube sheet components because the residual tensile stress can combine with service stresses to promote crack initiation and fatigue failure.
Interpretation of Results
The comparison between experimental measurements and numerical simulation results demonstrated good agreement, validating the analytical methodology. The temperature field simulation captured the thermal cycle characteristics including peak temperature, cooling rate, and time above critical temperatures. The stress field simulation reproduced the general distribution pattern of residual stresses measured by experimental techniques such as X-ray diffraction or hole-drilling methods.
From a metallurgical perspective, the residual stress distribution has direct implications for the overlay weld quality. High tensile residual stresses in the weld metal and HAZ can promote:
- Solidification cracking in the weld metal if the stress exceeds the material's plastic strain capacity during solidification.
- Hot cracking along grain boundaries in the HAZ due to stress superposition with thermal strain.
- Cold cracking in susceptible materials if hydrogen is present and the stress exceeds the threshold for hydrogen-induced cracking.
- Reduced fatigue life under cyclic loading conditions in service.
Integration with Engineering Practice
In practical heat exchanger manufacturing, the findings of this study can be applied through several strategies:
- Process optimization: By using the validated numerical model, engineers can evaluate different welding sequences, travel speeds, and heat input levels to minimize residual stress before committing to full-scale production trials.
- Post-weld treatment planning: The stress distribution maps help identify regions where stress-relief annealing or mechanical peening should be applied most effectively.
- Design modification: Understanding the stress concentration locations allows engineers to modify tube sheet geometry, such as adjusting the tube hole edge geometry or adding stress-relief notches, to redistribute stresses more favorably.
- Quality assurance: The residual stress predictions can inform acceptance criteria for in-service inspection, identifying regions most susceptible to stress-corrosion cracking.
A practical FMEA (Failure Mode and Effects Analysis) approach can be applied to the overlay welding process using the insights from this study:
| Failure Mode | Potential Cause | Effect | Detection Method | Mitigation |
|---|---|---|---|---|
| Cracking in overlay weld | High tensile residual stress + hydrogen | Tube sheet failure, leakage | MT/PT inspection | Preheat, low hydrogen consumables, stress relief |
| Excessive dilution | High heat input | Reduced corrosion resistance | Chemical analysis, hardness mapping | Reduce current, increase travel speed |
| Porosity | Inadequate shielding, contamination | Reduced weld integrity | RT/UT inspection | Improved gas flow, clean surface preparation |
| Undercut | Poor parameter control | Stress concentration, reduced section | Visual inspection | Optimize welding parameters, use backing material |
Key Questions and Reflections
Several questions arise from this study that merit further investigation. First, the accuracy of the residual stress predictions depends heavily on the material property inputs, particularly the temperature-dependent plastic strain behavior of both the base material and the overlay weld metal. In practice, these properties are often estimated or taken from literature values rather than measured specifically for the exact material condition used in production. This introduces uncertainty that should be quantified through sensitivity analysis.
Second, the study focuses on a single weld pass or a limited number of passes. In actual tube sheet manufacturing, overlay welding often involves multiple passes to achieve the required thickness, and the interaction between passes significantly affects the final residual stress state. The cumulative effect of multiple thermal cycles on residual stress redistribution and on the microstructure evolution in previously deposited layers warrants more detailed investigation.
Third, the long-term behavior of the residual stress under cyclic thermal loading during heat exchanger operation is not addressed. In service, the tube sheet experiences repeated heating and cooling cycles, which can cause stress relaxation and redistribution. Understanding the interaction between initial welding residual stresses and service thermal cycling is essential for predicting the long-term integrity of the component.
Study Insights and Implications
This study demonstrates the value of numerical simulation as a complementary tool to experimental investigation in welding engineering. The APDL parametric approach provides a systematic framework for process optimization that can significantly reduce the number of physical trials required, thereby saving time and cost. For heat exchanger manufacturers, the ability to predict residual stress distributions before welding allows for proactive measures to be taken, including process parameter selection, welding sequence planning, and post-weld treatment design.
The validation approach—comparing simulation results with experimental measurements—provides confidence in the methodology and establishes a foundation for further development. Future work should extend this approach to multi-pass welding sequences, incorporate more realistic boundary conditions representing the actual tube sheet mounting configuration, and integrate the residual stress predictions with fatigue life assessment to provide a comprehensive integrity evaluation framework.
In summary, this paper contributes a validated numerical methodology for predicting residual stresses in heat exchanger tube sheet overlay welding, providing practical guidance for process optimization and quality improvement in the manufacturing of critical heat transfer equipment.