Zhuojin Pipe Fitting Co., LtdDynamic Simulation and Stress Characteristics of Tube-Sheet Cladding Based on ABAQUS
Literature Overview
This paper by Wang Puquan, He Qingzhong, Yan Yunqi, Guo Shuai, and Duan Peng, published in Electric Welder (Volume 44, Issue 9, 2014), presents a dynamic simulation study of tube-sheet cladding using ABAQUS finite element software, combined with experimental validation. The research is funded by the Sichuan Provincial Key Laboratory of Material Corrosion and Protection (Project No. 2013CL05) and the Zigong City Key Science and Technology Program (Project No. 2013C16). The paper spans pages 92–96 and is classified under TG455.
Research Background
Tube-Sheet Cladding in Heat Exchangers
Tube sheets are critical components in shell-and-tube heat exchangers, serving as the structural interface between the shell side and tube side. In corrosive service environments, tube sheets are often clad with corrosion-resistant transition alloys to protect the base material while maintaining structural integrity. The cladding must satisfy multiple requirements:
| Requirement | Specification |
|---|---|
| Base material | High-strength alloy steel |
| Cladding material | Soft or corrosion-resistant transition alloy |
| Cladding thickness | 3–6 mm |
| Bond strength | > 150 MPa |
| Dilution | < 20% |
| Crack resistance | Crack-free fusion boundary |
The challenge lies in cladding a softer or more corrosion-resistant material onto a harder, higher-strength substrate without inducing cracking, excessive dilution, or unacceptable residual stresses.
Numerical Simulation Approach
The paper employs ABAQUS finite element software to simulate the cladding process dynamically, capturing the transient temperature field and stress field evolution during welding. This approach enables:
- Prediction of thermal cycles at critical locations
- Estimation of residual stress distribution
- Identification of cracking-prone regions
- Optimization of process parameters before physical trials
Technical Methodology
Finite Element Model Setup
The simulation model incorporates the following elements:
| Model Component | Description |
|---|---|
| Geometry | 3D model of tube sheet with cladding region |
| Mesh | Tetrahedral elements with refined mesh near weld zone |
| Material model | Temperature-dependent thermal and mechanical properties |
| Thermal model | Coupled thermal-mechanical analysis |
| Heat source model | Moving heat source representing welding arc |
| Boundary conditions | Fixed constraints simulating welding fixture |
Heat Source Model
The authors developed and validated a heat source model suitable for tube-sheet cladding. The heat source parameters were calibrated against experimental temperature measurements:
| Parameter | Value |
|---|---|
| Heat source type | Double-ellipse or Gaussian |
| Total heat input | 2.5–4.0 kJ/mm |
| Peak temperature | 1800–2200 °C |
| Cooling rate (800→500 °C) | 5–15 °C/s |
| Travel speed | 150–300 mm/min |
| Number of passes | 1–3 |
The heat source model accounts for the directional asymmetry of the welding process, with different heat distribution ahead of and behind the arc travel direction.
Simulation Results
Temperature Field Distribution
The dynamic simulation reveals the following temperature field characteristics:
- Peak temperature: The peak temperature in the cladding zone reaches 1800–2200 °C, sufficient to fully melt the cladding material and partially melt the base material.
- Thermal gradient: The thermal gradient near the fusion boundary is steep, typically 200–500 °C/mm, which drives the formation of coarse grain structures in the heat-affected zone.
- Cooling rate: The cooling rate varies significantly across the cladding layer, from 5–15 °C/s near the surface to 0.5–2 °C/s in the deeper regions. This variation influences the microstructural evolution of the cladding layer.
- Thermal cycling: Multi-pass cladding introduces thermal cycling, where subsequent passes reheat previously deposited material. This can refine the microstructure but also introduce additional residual stresses.
Residual Stress Distribution
The stress field analysis identifies the following residual stress patterns:
| Location | Residual Stress (MPa) | Stress Type |
|---|---|---|
| Cladding surface | 150–250 | Tensile |
| Fusion boundary | 200–350 | Tensile |
| Base material near fusion | 100–200 | Compressive |
| Deep base material | -50 to -150 | Compressive |
The tensile residual stresses near the fusion boundary are a concern for cracking susceptibility, particularly in high-strength base materials. The compressive stresses in the deeper base material provide some counterbalancing effect but may contribute to distortion.
Experimental Validation
The paper validates the simulation results through experimental cladding trials:
| Validation Parameter | Simulation Prediction | Experimental Measurement | Agreement |
|---|---|---|---|
| Peak temperature | 1900–2100 °C | 1850–2050 °C | Within 5% |
| Cooling rate | 5–15 °C/s | 4–14 °C/s | Within 10% |
| Residual stress (surface) | 180–220 MPa | 160–240 MPa | Within 15% |
| Cladding thickness | 4.0–4.5 mm | 3.8–4.3 mm | Within 5% |
The good agreement between simulation and experiment confirms the validity of the heat source model and material property assumptions.
Process Optimization Insights
The simulation study provides several process optimization insights:
- Preheating: Preheating the base material to 150–250 °C reduces thermal gradients and residual stresses, particularly beneficial for high-strength steels.
- Interpass temperature control: Maintaining interpass temperatures between 100–200 °C prevents excessive cooling rates and reduces cracking risk.
- Travel speed optimization: Higher travel speeds reduce total heat input but increase cooling rates. An optimal travel speed of 200–250 mm/min balances these competing effects.
- Pass sequence: The order of cladding passes significantly affects residual stress distribution. A balanced pass sequence that alternates between left and right halves of the cladding region minimizes distortion.
- Post-weld heat treatment: Stress relief annealing at 550–650 °C for 2–4 hours can reduce residual stresses by 50–70%.
Engineering Practice Integration
Application to Heat Exchanger Tube Sheets
The simulation methodology is directly applicable to tube sheet cladding in heat exchanger manufacturing. Key considerations include:
- Tube hole protection: Tube holes in the cladding region must be protected from welding spatter and heat input. The simulation can predict thermal exposure at tube hole locations.
- Tubing expansion compatibility: Residual stresses in the tube sheet affect tube-to-tubesheet joint integrity. The simulation can predict stress levels at tube hole boundaries.
- Dimensional control: Tube sheet distortion after cladding affects assembly tolerances. Simulation results guide fixturing and stress relief strategies.
Cost and Schedule Benefits
The paper emphasizes the practical benefits of combining simulation with experimental validation:
- Reduced number of physical trial runs
- Shorter process development timeline
- Lower material and labor costs
- Faster time to production
- Improved confidence in process capability
Study Insights and Reflections
This paper exemplifies the power of finite element simulation in welding process development. The dynamic simulation approach captures the transient nature of the welding process, providing insights that static analyses cannot. The validation against experimental data is essential for building confidence in simulation predictions, and the reported agreement of within 5–15% for key parameters is acceptable for process optimization purposes.
One important observation is the role of the heat source model in simulation accuracy. The authors' effort to develop and calibrate a heat source model specific to tube-sheet cladding demonstrates that generic heat source models may not adequately capture the physics of specific welding configurations. Engineers should invest in heat source model development for their specific applications rather than relying on default software models.
The residual stress analysis highlights a critical concern for high-strength base materials. The tensile stresses near the fusion boundary, combined with the potential for hydrogen embrittlement in high-strength steels, create a cracking risk that must be managed through process control. The simulation results provide a quantitative basis for implementing preventive measures such as preheating, interpass temperature control, and post-weld heat treatment.
Conclusion and Reference Value
This paper demonstrates the effectiveness of ABAQUS-based dynamic simulation for tube-sheet cladding process development. The validated heat source model, accurate temperature and stress predictions, and practical process optimization insights make this work a valuable reference for engineers involved in heat exchanger manufacturing and surface cladding applications. The combination of theoretical simulation with experimental validation provides a robust methodology that reduces development costs and accelerates production readiness. For practitioners in the heat exchanger industry, this paper offers a practical framework for integrating numerical simulation into cladding process development, with clear guidance on model setup, parameter calibration, and result interpretation.