CLADDING TECHNOLOGY SHANXI CO., LTDThermal-Mechanical Coupled Simulation and Parameter Optimization of Narrow-Gap TIG Oscillating Welding Sidewall
Literature Overview
This study, published in Ordnance Materials and Engineering (2026) by researchers from Beijing Institute of Petrochemical Technology, investigates the thermal-mechanical coupled behavior of narrow-gap TIG oscillating welding sidewalls and develops parameter optimization strategies. The work is conducted at the Beijing Advanced Connection Technology Center for Energy Engineering. Narrow-gap welding represents a significant advancement in thick-section welding efficiency, reducing filler metal consumption by 50–70% compared to conventional multi-pass welding.
Narrow-Gap TIG Oscillating Welding Process
Narrow-gap welding involves machining a narrow V-groove (typically 3–8 mm width) in thick plates and filling it with multiple passes of oscillating TIG welding. The oscillation motion of the torch or workpiece spreads the heat input laterally, enabling wider bead coverage within the narrow groove.
Key Process Parameters
| Parameter | Typical Range | Effect on Process |
|---|---|---|
| Groove width | 3–8 mm | Determines pass count and filler volume |
| Groove depth | 20–100 mm | Affects plate thickness capability |
| Oscillation amplitude | 5–20 mm | Controls bead width |
| Oscillation frequency | 1–5 Hz | Affects heat distribution |
| Welding current | 100–250 A | Controls penetration per pass |
| Travel speed | 3–8 cm/min | Manages heat input rate |
| Shielding gas | Ar or Ar-5%He | Arc stability and penetration |
Thermal-Mechanical Coupled Behavior
The narrow-gap geometry creates unique thermal-mechanical challenges:
- Thermal confinement: The narrow groove acts as a thermal channel, concentrating heat and increasing peak temperatures
- Residual stress accumulation: Each successive pass heats and cools the previously deposited material, creating complex residual stress patterns
- Sidewall distortion: Differential thermal expansion between the groove sidewalls and the surrounding bulk material induces warpage
- Interpass temperature management: Maintaining interpass temperature below 200°C for structural steels or below 300°C for stainless steels is critical
Simulation Methodology and Results
The thermal-mechanical coupled simulation typically employs a sequential coupled approach:
- Thermal analysis: Moving heat source model (double-ellipsoidal Goldak model) with oscillating trajectory
- Mesh remapping: Layer-by-layer element activation/deactivation to simulate multi-pass welding
- Mechanical analysis: Elastic-plastic material behavior with temperature-dependent properties
- Residual stress calculation: Release of thermal stresses upon cooling
Key Simulation Findings
The residual stress distribution in narrow-gap welds exhibits characteristic patterns:
| Location | Residual Stress (MPa) | Character | Engineering Concern |
|---|---|---|---|
| Weld centerline | 200–350 (tensile) | Longitudinal tensile | Cracking susceptibility |
| Groove sidewall | 150–250 (tensile) | Transverse tensile | Distortion initiation |
| HAZ (near sidewall) | 100–200 (tensile) | Mixed | Grain growth and softening |
| Base metal (far field) | -50 to -150 (compressive) | Compressive | Generally benign |
| Root area | 250–400 (tensile) | High tensile | Root cracking risk |
Parameter Optimization Results
The study demonstrates that optimization of oscillation parameters significantly reduces residual stress and distortion:
- Optimal oscillation amplitude: 8–12 mm for 5 mm groove width (amplitude-to-width ratio of 1.6–2.4)
- Optimal oscillation frequency: 2–3 Hz for structural steel applications
- Optimal travel speed: 5–6 cm/min balances deposition rate and cooling rate
- Interpass temperature: 150–200°C for carbon steel, maintaining HAZ properties
Engineering Practice Applications
For bimetal pressure vessel fabrication, narrow-gap TIG oscillating welding offers significant advantages:
- Material savings: Reduces overlay or base metal consumption by 50–70% compared to conventional V-groove welding
- Weld quality: The confined geometry promotes better penetration and reduced porosity
- Productivity: Fewer passes required for thick sections, reducing welding time
- Distortion control: The symmetric heat input pattern produces less angular distortion than conventional welding
Quality Assurance Considerations
| Inspection Method | Acceptance Criteria | Standard Reference |
|---|---|---|
| Visual examination | No undercut >1 mm, no slag inclusion | ASME Section V, Article 1 |
| RT (Radiographic testing) | No linear indications >3 mm | ASME Section V, Article 2 |
| UT (Ultrasonic testing) | No indications above background +6 dB | ASME Section V, Article 4 |
| MT (Magnetic particle testing) | No surface discontinuities | ASME Section V, Article 7 |
| Hardness survey | ≤350 HV for carbon steel HAZ | NB/T 47014 |
Study Insights and Engineering Recommendations
The thermal-mechanical coupled simulation approach provides a powerful tool for predicting and mitigating residual stress and distortion in narrow-gap welding operations. For pressure vessel fabrication, where dimensional accuracy and structural integrity are paramount, the simulation-guided parameter optimization can significantly reduce the need for post-weld mechanical straightening and stress relief.
From a practical standpoint, the narrow-gap TIG oscillating welding process is particularly well-suited for:
- Hydrogenation reactor shell fabrication with stainless steel overlay
- Thick-wall heat exchanger tube sheet welding
- Spherical tank pole cap welding where distortion must be minimized
- Cladding of thick base plates where groove preparation cost must be controlled
The research validates that systematic parameter optimization, guided by numerical simulation, can achieve residual stress levels below 200 MPa in the weld zone, which is critical for preventing hydrogen-induced cracking and sulfide stress corrosion in hydrogen service applications.