Zhuojin Pipe Fitting Co., LtdApplication of Strip Electrode Surfacing Technology
Literature Overview
This paper by Martin Kubenka, Gabriellf Galazzi, and Solveig Rigdal from ESAB Welding & Cutting Supplies (Shanghai) Co., Ltd., published in Electric Welding Machine (Vol. 40, No. 8, 2010, pp. 59–63), provides a comprehensive overview of strip electrode surfacing technology, with particular emphasis on stainless steel strip electrode applications in chemical, petrochemical, and nuclear industries. The paper includes case studies from Italian manufacturers SICES and Ansaldo Camozzi.
Technical Principles of Strip Electrode Surfacing
Strip electrode surfacing is a variant of submerged arc welding (SAW) in which a continuous strip of welding metal replaces the conventional granular flux-covered wire. The strip electrode acts as both the filler metal and the flux carrier, with a special flux coating that melts during the welding process to provide shielding and alloying.
Process Variants
| Parameter | Strip Electrode SAW | Electroslag Surfacing |
|---|---|---|
| Power source | AC or DC | DC |
| Flux type | Flux-coated strip | Granular flux with wire electrode |
| Deposition rate | 5–15 kg/h | 15–50 kg/h |
| Layer thickness per pass | 3–6 mm | 8–15 mm |
| Surface quality | Good (light grinding) | Requires machining |
| Equipment complexity | Moderate | High |
| Cost per kg deposited | Lower | Higher |
| Typical application | Thin to moderate corrosion layers | Thick wear/corrosion layers |
Key Process Parameters
- Current density: 40–80 A/mm² (of strip cross-section)
- Strip thickness: 1.5–3.0 mm (standard range)
- Strip width: 15–35 mm
- Flux coating thickness: 1.0–2.0 mm
- Travel speed: 150–400 mm/min
- Preheat temperature: 150–250°C for low-carbon steel substrates; higher for alloy substrates
- Interpass temperature: Controlled to prevent excessive grain growth and cracking
Application Case Studies
Case 1: SICES Factory (Italy)
SICES, a major manufacturer of stainless steel plates and tubes, employs strip electrode surfacing to apply corrosion-resistant layers to carbon steel components that require stainless steel surface properties without the cost of fully stainless construction. The primary applications include:
- Heat exchanger tubesheets: Carbon steel tubesheets receive austenitic stainless steel (typically 316L or 321) surfacing layers to resist corrosion from process fluids while maintaining the structural integrity and lower cost of carbon steel construction.
- Vessel internals: Support structures and platform frames receive stainless steel surfacing at bolted joints and areas exposed to corrosive process media.
Case 2: Ansaldo Camozzi Factory (Italy)
Ansaldo Camozzi, a manufacturer of pressure vessels and heat exchangers for the petrochemical and nuclear industries, applies strip electrode surfacing in the following contexts:
- Nuclear-grade components: Austenitic stainless steel surfacing on carbon steel pressure vessel components where the nuclear-grade stainless steel cladding must meet stringent metallurgical requirements.
- Reactor internals: Wear and corrosion resistant surfacing on components exposed to high-temperature coolant environments.
- Multi-layer surfacing strategies: Combining a transition layer (duplex stainless steel) with a final austenitic stainless steel layer to minimize cracking in the weld metal.
Metallurgical Considerations
Dilution and Composition Control
A critical challenge in strip electrode surfacing is controlling substrate dilution, which directly affects the corrosion resistance of the final surface layer:
| Number of Passes | Typical Dilution (%) | Resulting Cr Content (316L strip on CS) |
|---|---|---|
| 1 | 30–50% | 14–18% |
| 2 | 15–25% | 18–21% |
| 3 | 8–15% | 20–23% |
| 4+ | <10% | >22% |
For nuclear applications, the final layer must typically achieve a minimum chromium content of 20% and nickel content of 12% to ensure adequate corrosion resistance and meet qualification requirements.
Heat-Affected Zone Concerns
- Low-carbon steel substrates: HAZ is generally acceptable; preheating to 150–200°C prevents cold cracking.
- Low-alloy steels (e.g., P91): Requires careful preheating (250–350°C) and post-weld heat treatment to avoid brittle HAZ microstructures.
- Stainless steel substrates: Must control intergranular sensitization; use L-grade strips (316L, 321) with low carbon content.
Residual Stress Management
Strip electrode surfacing introduces significant longitudinal and transverse residual stresses due to the high deposition rate and thick single-pass layers. Mitigation strategies include:
- Post-weld stress relief annealing (typically 600–650°C for stainless steel layers, 620–680°C for carbon steel substrates)
- Peening of the final surface layer
- Controlled layer thickness (limiting individual pass thickness to 5–6 mm)
- Strategic surfacing sequence to minimize constraint
Quality Control Requirements
For strip electrode surfacing in critical applications, the following quality control measures are essential:
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Visual examination (VT) | Surface defects, undercut, porosity | No defects >0.5 mm depth |
| Magnetic particle testing (MT) | Surface/subsurface cracks | No linear indications >3 mm |
| Radiographic testing (RT) | Internal porosity, lack of fusion | Per ASME Section V, T-274 |
| Ultrasonic testing (UT) | Bond quality, delamination | No indications above reference level |
| Hardness testing | Layer homogeneity, dilution assessment | Within specified range (e.g., HRB 80–100 for 316L) |
| Chemical analysis | Composition verification | Cr, Ni, Mo within specification |
| Corrosion testing | Functional verification | Per ASTM G48 (crevice) or ASTM G102 (intergranular) |
Standards Framework
- ASME B31.3: Process piping — requirements for overlay welding
- ASME B31.1: Power piping — overlay specifications
- AWS D10.9: Specification for submerged arc surfacing of ferrous materials
- EN 12547: Specification for submerged arc welding consumables
- NB/T 20011: Nuclear power plant piping — overlay welding requirements (Chinese standard)
- API 570: Piping inspection — assessment of overlay welds
Study Insights and Implications
The ESAB paper provides a valuable industrial perspective on strip electrode surfacing that complements the academic research in the other papers of this study set. The emphasis on economic efficiency—achieving corrosion resistance through a thin overlay rather than using expensive fully alloyed materials—is a fundamental principle in engineering design. The Italian case studies demonstrate that strip electrode surfacing is a mature, well-established technology with decades of successful industrial application.
From a quality assurance perspective, the paper highlights the importance of multi-pass surfacing strategies to achieve adequate alloy content in the final layer. In my experience with nuclear-grade components, achieving the required dilution control often requires four or more passes with careful interpass temperature control. The transition from carbon steel to austenitic stainless steel involves a metallurgical challenge that must be addressed through appropriate consumable selection and process parameter optimization. The paper's documentation of successful industrial applications provides confidence in the technology's reliability for critical service applications.