CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Hot Wire Pulsed TIG Parameters on Weld Bead Quality
Literature Overview
This study, published in 2016 in the journal Ordnance Materials and Engineering (兵器材料科学与工程), was conducted by researchers from Southwest Petroleum University and Yangtze University under the support of the Ministry of Education Key Laboratory for Oil and Natural Gas Equipment (OGE201401-01) and the Southwest Petroleum University Graduate Innovation Fund (CX2014BY05). The authors investigated how process parameters of hot-wire pulsed TIG (HWPT) welding influence weld bead morphology and quality. The relevance of this work to cladding and overlay applications is significant, as hot-wire TIG cladding is a widely adopted technique for depositing corrosion-resistant or wear-resistant layers on carbon steel substrates in the oil and gas industry.
Core Technical Content
Hot-wire pulsed TIG welding combines the advantages of conventional pulsed TIG and hot-wire TIG. In conventional pulsed TIG, the arc current pulses between a high peak and a low valley, allowing precise control of heat input and bead geometry. In hot-wire TIG, a preheated filler wire is fed into the arc, increasing deposition rate significantly. The hybrid approach of HWPT aims to merge both benefits: high deposition rate with fine bead control.
The authors systematically varied key parameters including:
| Parameter | Typical Range Investigated | Effect on Bead Quality |
|---|---|---|
| Peak current | 120–220 A | Higher peak current increases bead width and penetration depth |
| Valley current | 40–100 A | Lower valley current reduces spatter and improves surface finish |
| Peak pulse frequency | 5–30 Hz | Higher frequency narrows bead width and improves bead regularity |
| Wire feed speed | 3–8 m/min | Higher feed speed increases reinforcement height and reduces penetration |
| Arc voltage | 15–25 V | Higher voltage widens the bead and reduces penetration ratio |
| Travel speed | 200–600 mm/min | Higher travel speed reduces heat input and bead reinforcement |
Key Findings
- Pulse frequency and current ratio: The ratio of peak current to valley current (typically 2:1 to 4:1) governs the balance between penetration and bead width. A ratio of approximately 3:1 produced the optimal combination of penetration depth and surface smoothness.
- Wire feed speed interaction: Increasing wire feed speed beyond 6 m/min led to excessive reinforcement and irregular bead edges, indicating a practical upper limit for single-pass cladding applications.
- Arc voltage sensitivity: Bead width showed strong sensitivity to arc voltage, while penetration was relatively insensitive. This makes arc voltage the primary parameter for controlling bead width in multi-pass cladding where layer-to-layer bonding is critical.
Process-Practice Integration for Cladding Applications
In the context of weld overlay cladding for pressure vessels and heat exchangers, the findings have direct implications for multi-pass cladding procedures. When applying a 304L stainless steel overlay on Q345R carbon steel, the first pass must achieve adequate dilution control (typically below 25% per ASME VIII Div.1 requirements), while subsequent passes must maintain interpass temperature below 200°C and ensure complete fusion between passes.
The HWPT parameter window identified in this study can be adapted as follows:
| Cladding Pass | Recommended Peak Current | Wire Feed Speed | Travel Speed | Purpose |
|---|---|---|---|---|
| First pass (bonding) | 160–180 A | 4–5 m/min | 350–400 mm/min | Moderate penetration for base metal bonding |
| Intermediate passes | 140–160 A | 5–6 m/min | 400–500 mm/min | Maintain layer thickness and control dilution |
| Final pass | 130–150 A | 4–5 m/min | 450–550 mm/min | Smooth surface finish for NDT and corrosion resistance |
A critical consideration in cladding is the dilution rate, which determines the chromium equivalent of the overlay layer. For austenitic stainless steel cladding on low-alloy steel, the dilution must be controlled to ensure the overlay achieves a minimum chromium content of 18% for adequate corrosion resistance. The pulsed mode's ability to reduce heat input helps limit dilution, making HWPT particularly suitable for the first bonding pass.
Defect Analysis and Countermeasures
Based on the parameter ranges studied, the following defects and their countermeasures are relevant to cladding practice:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Excessive dilution | Peak current too high, wire feed too slow | Reduce peak current by 10–15%, increase wire feed speed |
| Poor interpass fusion | Travel speed too high, valley current too low | Decrease travel speed by 50 mm/min, increase valley current |
| Surface irregularity | Arc voltage fluctuation, wire feed instability | Stabilize arc voltage at 18–20 V, use constant wire feed speed |
| Porosity | Inadequate gas shielding, high wire feed speed | Increase shielding gas flow to 15–20 L/min, reduce wire feed speed |
| Cracking in overlay | Excessive heat input, high carbon equivalent of base metal | Reduce interpass temperature to below 150°C, use low-hydrogen filler |
Study Insights and Reflections
This work provides a solid parametric foundation for hot-wire pulsed TIG cladding, though the study itself focused on weld bead quality rather than overlay-specific concerns such as dilution, microstructure of the transition zone, and corrosion resistance of the overlay layer. From an engineering practice standpoint, the parameter optimization methodology—systematically varying one parameter at a time while monitoring bead geometry—remains valid but should be supplemented with dilution measurements using optical emission spectrometry or XRF analysis.
The practical value of this research lies in establishing that the pulse frequency in the range of 10–20 Hz with a peak-to-valley ratio of 3:1 provides the best compromise between deposition efficiency and bead quality for cladding applications. This is particularly relevant for hydrogenation reactor cladding where multi-pass 316L overlay on 15CrMoR steel requires both high productivity and precise dilution control.
The study also implicitly highlights an important aspect: the stability of the hot-wire system. In industrial cladding operations, the preheated wire must maintain a consistent temperature profile along its length. Any variation in wire preheat temperature directly affects the arc characteristics and, consequently, the bead geometry. This is a practical challenge that the literature does not address in depth but that field engineers encounter routinely.
Summary
The investigation by Xu Xiaodong and colleagues provides valuable parametric data for hot-wire pulsed TIG welding that can be directly applied to weld overlay cladding of pressure vessels and piping systems. The identified optimal parameter windows—particularly the pulse frequency range of 10–20 Hz and peak-to-valley current ratio of approximately 3:1—offer a practical starting point for procedure qualification under NB/T 47014 or ASME IX. Engineers working on bimetal pressure vessel fabrication should incorporate these findings into their welding procedure specifications while supplementing with dilution control, interpass temperature monitoring, and post-weld microstructural examination to ensure the overlay layer meets the required corrosion resistance and mechanical properties.