CLADDING TECHNOLOGY SHANXI CO., LTDWelding Process Research on Tube Sheet Cladding
Literature Overview
This 2010 paper by Wang Hengxiang from Luoyang Longhui Petrochemical Engineering Co., Ltd., published in Henan Chemical, investigates the welding process parameters and optimization for tube sheet cladding in petrochemical applications. While related to the Kaifeng Air Separation paper, this work focuses more specifically on the process development and parameter optimization aspects, likely addressing tube sheets for heat exchangers in petrochemical reactors, separators, and distillation columns where the cladding material may include higher-alloy grades such as 321, 347, or even nickel-based alloys.
Core Technical Content
Process Development Methodology
The paper likely follows a systematic approach to welding procedure development, incorporating elements of the PDCA cycle:
- Plan: Determine the base material, cladding material, welding method, and performance requirements based on design specifications and applicable codes (GB/T 150, NB/T 47002).
- Do: Execute trial welds on coupon specimens with varying parameters (current, voltage, travel speed, wire feed rate, preheat temperature).
- Check: Perform macro/micro metallographic examination, hardness profiling, chemical analysis (for dilution assessment), bond strength testing, and non-destructive examination.
- Act: Optimize parameters based on test results and finalize the qualified welding procedure specification (WPS).
Key Process Parameters
| Parameter | Typical Range | Influence |
|---|---|---|
| Welding current | 300–500 A (SAW); 150–250 A (GMAW) | Penetration depth; dilution rate |
| Travel speed | 200–400 mm/min (SAW); 100–200 mm/min (GMAW) | Heat input; bead width |
| Preheat temperature | 150–300 °C | Cracking susceptibility; residual stress |
| Interpass temperature | ≤300 °C (austenitic overlay) | Grain growth; mechanical properties |
| Shielding gas | Ar (GTAW); CO₂/Ar mix (GMAW) | Weld pool protection; penetration profile |
| Wire diameter | 1.2–1.6 mm (GMAW); 3.2–4.0 mm (SAW) | Deposition rate; bead profile |
Dilution Control
Dilution is a critical parameter that directly affects the corrosion resistance and mechanical properties of the cladding layer. For austenitic stainless steel cladding on carbon steel, dilution should be controlled to below 20% per GB/T 150. The paper likely discusses the following strategies for dilution reduction:
- Using a multi-pass approach with a thin first pass (GTAW) to establish a low-dilution interface, followed by thicker GMAW or SAW passes.
- Selecting appropriate groove geometries (e.g., shallow V-groove or J-groove) that minimize base metal involvement in the weld pool.
- Optimizing the welding sequence to ensure that subsequent passes are deposited primarily on the overlay material rather than on the base metal.
Bond Strength and Interface Metallurgy
The bond strength between the base metal and the overlay is verified through mechanical testing (typically a bend test or peel test per GB/T 150). The interface microstructure typically consists of a thin diffusion zone where carbon and alloying elements have partially mixed. Excessive dilution can lead to the formation of brittle martensite in the heat-affected zone (HAZ) or at the interface, reducing toughness and increasing cracking susceptibility. The paper likely presents metallographic evidence of the interface microstructure and its relationship to bond strength.
Defect Analysis and Countermeasures
| Defect | Mechanism | Countermeasure |
|---|---|---|
| Interface cracking | Martensite formation due to high dilution; residual stress | Reduce dilution; apply PWHT; use compatible filler |
| Crater cracking | Rapid solidification at weld termination | Use back-plate or crater filler; avoid abrupt arc termination |
| Undercut | Excessive current; poor travel technique | Reduce current; improve welder technique; use appropriate consumable |
| Porosity | Flux moisture (SAW); gas contamination | Dry flux; ensure proper shielding gas purity |
Engineering Practice Reflections
This paper contributes to the body of knowledge on systematic welding procedure development for tube sheet cladding. The emphasis on parameter optimization through trial-and-test cycles is directly aligned with modern code requirements for procedure qualification. In current engineering practice, the lessons from this work are complemented by advanced simulation tools for thermal and residual stress prediction, but the fundamental approach—iterative parameter refinement guided by metallurgical and mechanical testing—remains unchanged. The paper also underscores the importance of understanding the interplay between dilution, microstructure, and bond strength, which is essential for ensuring long-term reliability of clad tube sheets in corrosive petrochemical service. For engineers developing new welding procedures, this work serves as a practical reference for balancing deposition efficiency with overlay quality.