CLADDING TECHNOLOGY SHANXI CO., LTDDynamic Simulation and Stress Characteristics of Tube-Sheet Cladding Based on ABAQUS
Literature Overview
This 2014 research publication from the School of Mechanical Engineering at Sichuan University of Science and Technology, authored by Wang Puquan, He Qingzhong, Yan Yunqi, Guo Shuai, and Duan Peng, presents a finite element analysis (FEA) study of tube-sheet cladding operations using the ABAQUS software platform. Funded by the Sichuan Provincial Key Laboratory of Materials Corrosion and Protection Open Fund (Project No. 2013CL05) and Zigong City 2013 Key Science and Technology Program (Project No. 2013C16), this work was published in the journal "Electric Welding Machine" and addresses a critical engineering challenge in heat exchanger manufacturing.
Core Technical Content
Tube sheets are critical structural components in shell-and-tube heat exchangers, serving as the structural interface between the tube bundle and the shell while providing leak-tight sealing for each tube. Cladding of tube sheets with corrosion-resistant materials (such as stainless steel or nickel-based alloys) is a common practice to protect the tube sheet surface from corrosive process fluids. The welding-induced residual stresses and deformations in tube sheets directly affect the long-term integrity of heat exchangers, particularly under cyclic thermal and pressure loading conditions.
ABAQUS Simulation Framework
The finite element analysis of tube-sheet cladding operations requires careful modeling of several physical phenomena:
| Modeling Aspect | Approach | Key Considerations |
|---|---|---|
| Thermal analysis | Transient heat transfer with moving heat source | Goldak heat source model; convection and radiation boundary conditions |
| Mechanical analysis | Sequential coupling (thermal-stress) | Temperature-dependent material properties; plastic deformation |
| Material model | Elasto-plastic with kinematic hardening | Yield surface evolution; Bauschinger effect |
| Mesh strategy | Adaptive mesh refinement at weld zone | Element size 0.5–2 mm near weld; 5–10 mm in far field |
| Boundary conditions | Symmetry and fixed constraints | Realistic constraint representation |
| Cladding process | Multi-pass deposition with remeshing | Pass sequence; interpass temperature control |
Typical Residual Stress Results
The FEA simulation of tube-sheet cladding typically reveals the following residual stress distributions:
- Peak longitudinal residual stresses of 300–500 MPa near the weld toe, approaching or exceeding the yield strength of the cladding material
- Transverse residual stresses of 150–300 MPa, generally lower than longitudinal stresses
- Through-thickness residual stresses that vary from compressive at the surface to tensile in the interior
- Stress relaxation in subsequent passes due to thermal cycling effects
- Distortion of the tube sheet, typically 0.5–2.0 mm out-of-plane deflection for sheets 50–100 mm thick
Engineering Practice Integration
Design Implications for Heat Exchangers
The residual stress state in clad tube sheets has direct implications for heat exchanger design and fabrication:
- Stress corrosion cracking (SCC) susceptibility — Tensile residual stresses in the weld overlay can promote SCC in susceptible materials, particularly in chloride-containing environments
- Fatigue life reduction — Residual stresses superimposed on cyclic service loads reduce fatigue life according to Miner's rule
- Creep-fatigue interaction — At elevated operating temperatures, residual stresses accelerate creep damage accumulation
- Hydrostatic test performance — Excessive residual stresses may cause permanent deformation or failure during hydrostatic testing
Stress Relief Strategies
Based on the simulation results and engineering experience, the following stress relief strategies are recommended:
| Strategy | Implementation | Effectiveness |
|---|---|---|
| Post-weld heat treatment (PWHT) | 550–650°C for 2–8 hours depending on thickness | High — reduces residual stresses by 70–90% |
| Vibration stress relief (VSR) | Mechanical vibration at resonant frequencies | Moderate — reduces stresses by 40–60% |
| Optimized weld sequence | Back-step welding; symmetric pass layout | Moderate — reduces peak stresses by 20–40% |
| Interpass temperature control | Limiting to 150–250°C | Low-Moderate — manages thermal cycling effects |
| Back gouging and filling | Removing weld root and refilling | Moderate — eliminates root defects and reduces stress |
Standards Compliance
Tube-sheet cladding for heat exchangers must comply with applicable standards including:
- GB/T 151 (Shell-and-tube heat exchangers) for design and fabrication requirements
- ASME VIII Div.1 or Div.2 for pressure vessel code compliance
- ASME IX for welding procedure and operator qualification
- TUBULAR (Tubular Exchanger Manufacturers Association) standards for tube sheet specifications
- NB/T 47014 for welding procedure qualification in Chinese nuclear and pressure vessel applications
Study Insights and Reflections
This research demonstrates the power of finite element analysis in predicting and optimizing the residual stress state in clad tube sheets. The ABAQUS-based simulation approach allows engineers to evaluate different welding sequences, parameter combinations, and stress relief strategies without the cost and time of physical trials. This computational capability is particularly valuable for large tube sheets where experimental investigation would be impractical.
From my engineering practice, I emphasize that while FEA provides valuable predictive capabilities, it must be validated against experimental data for critical applications. The accuracy of residual stress predictions depends on several factors: the fidelity of the heat source model, the accuracy of temperature-dependent material properties, the representation of material behavior during plastic deformation, and the boundary conditions applied. Validation through strain gauge measurements, X-ray diffraction, or neutron diffraction residual stress measurements is recommended for critical applications.
The research also highlights an important practical consideration: the interaction between tube-sheet cladding residual stresses and the subsequent tube-to-tubesheet jointing process (welding or expanded). The residual stress state established during cladding affects the quality and integrity of the tube joints, which are critical for pressure containment. Engineers must consider the entire fabrication sequence when evaluating the residual stress implications of tube-sheet cladding.
This 2014 publication remains relevant today as the demand for high-performance heat exchangers continues to grow in the petrochemical, power generation, and nuclear industries. The computational methods described can be adapted to current finite element software platforms, and the fundamental insights into residual stress behavior remain applicable regardless of the specific software used.