Stainless Steel/Nickel-Based Strip Electrode Submerged Arc and Electroslag Weld Overlay Technology (60×0.5 / 90×0.5 mm)
1. Definition and Operating Principles
Strip electrode submerged arc welding (SAW) and electroslag welding (ESW) are advanced solid-state welding processes that employ a continuous ribbon or strip electrode—typically 60 mm or 90 mm wide with a uniform thickness of 0.5 mm—to achieve exceptionally high deposition rates for weld overlay applications. Unlike conventional wire-fed processes such as TIG or MIG, the strip electrode delivers a significantly larger cross-sectional area of filler metal per unit time, translating into deposition rates that can reach 8–15 kg/h, which is 3 to 6 times greater than equivalent wire-based processes.
The fundamental principle of strip electrode SAW involves the strip electrode being fed continuously through a contact tip into a molten flux-covered arc. The wide electrode geometry creates a broad, shallow weld bead with excellent lateral coverage. The flux layer serves multiple critical functions: it shields the arc and molten pool from atmospheric contamination, stabilizes the arc, provides alloying additions, and acts as a thermal insulator that promotes controlled solidification. In electroslag welding mode, the process transitions from arc heating to resistive heating of the slag pool, allowing extremely high deposition rates (up to 20–30 kg/h) for thick overlay builds on flat or vertical surfaces.
For stainless steel and nickel-based overlay applications, the strip electrode composition is specifically engineered to resist sensitization, cracking, and corrosion in aggressive service environments. The 0.5 mm thickness of the strip provides a favorable balance between thermal input control and mechanical integrity during feeding, while the 60 mm and 90 mm widths allow operators to select the appropriate coverage rate based on the geometry and area requirements of the target component.
2. Category and Business Positioning
Within the welding materials (焊材) category of Cladding Technology Shanxi Co., Ltd.'s capability portfolio, strip electrode technology occupies a unique and strategically important position. It bridges the gap between high-precision, low-deposition-rate processes (such as TIG weld overlay) and bulk metallurgical bonding techniques (such as explosion welding and hydraulic explosive bonding). This positioning enables the company to serve customers across a wide spectrum of overlay requirements:
- Low-volume, high-precision overlays: Addressed by TIG/MIG weld overlay processes using wire electrodes
- Large-area, high-efficiency overlays: Addressed by strip electrode SAW/ESW processes (this technology)
- Bulk cladding with metallurgical bond: Addressed by explosion welding and hydraulic explosive bonding
The strip electrode technology is particularly valued in the power generation, petrochemical, and nuclear industries where large-diameter pressure vessels, heat exchanger tube sheets, and reactor internals require extensive overlay coverage with tight metallurgical quality requirements. The company's capability in this area directly supports EPC contractors, OEM equipment manufacturers, and end-user operators seeking to extend asset life and improve corrosion resistance through cost-effective overlay solutions.
3. Technical Purpose and Value
The primary technical purpose of stainless steel and nickel-based strip electrode overlay is to achieve large-area, high-efficiency deposition of corrosion-resistant alloy layers on carbon steel or low-alloy steel substrates. The value proposition is multi-dimensional:
3.1 Economic Efficiency
Strip electrode processes achieve deposition rates of 8–15 kg/h (SAW) or 20–30 kg/h (ESW), dramatically reducing labor hours, machine time, and overall project cost per square meter of overlay. For a typical 2000 mm diameter pressure vessel requiring 3 mm overlay on the entire inner surface, strip electrode SAW can reduce overlay time by 60–70% compared to conventional MIG processes, while maintaining comparable metallurgical quality.
3.2 Metallurgical Quality
The flux-shielded environment of SAW provides superior protection against nitrogen and oxygen pickup compared to gas-shielded processes. This results in lower intergranular corrosion susceptibility, reduced porosity, and more consistent mechanical properties in the overlay metal. The controlled cooling rates associated with the flux blanket also promote fine-grained microstructures with good toughness.
3.3 Geometric Flexibility
The 60 mm strip width is ideal for cylindrical surfaces with diameters below 1000 mm and for confined spaces within vessel internals. The 90 mm strip width provides superior coverage efficiency for large flat surfaces such as heat exchanger tube sheets, head plates, and large-diameter vessel walls. Both widths accommodate multi-pass builds with consistent bead overlap and dilution control.
3.4 Process Automation Compatibility
Strip electrode SAW and ESW are inherently amenable to mechanization and automation. The stable arc, predictable bead geometry, and high deposition rate make these processes ideal for robotic or CNC-controlled overlay systems, enabling consistent quality across large production runs with minimal operator intervention.
4. Key Process Parameters and Implementation Points
4.1 Submerged Arc Welding (SAW) with Strip Electrode
| Parameter | 60×0.5 mm Strip | 90×0.5 mm Strip | Notes |
|---|---|---|---|
| Welding Current (DC) | 400–700 A | 600–1000 A | Higher current for thicker builds |
| Arc Voltage | 22–28 V | 24–30 V | Stable voltage critical for bead uniformity |
| Travel Speed | 200–400 mm/min | 150–350 mm/min | Inversely proportional to current |
| Flux Coverage | 3–5 mm layer | 3–5 mm layer | Uniform flux distribution essential |
| Deposition Rate | 6–10 kg/h | 8–15 kg/h | Depends on current and speed |
| Typical Bead Width | 50–70 mm | 75–95 mm | May exceed strip width due to lateral spread |
| Typical Bead Height | 2–4 mm | 2–5 mm | Multi-pass for full build-up |
| Dilution Rate | 5–15% | 5–15% | Controlled by preheat and pass strategy |
4.2 Electroslag Welding (ESW) with Strip Electrode
| Parameter | 60×0.5 mm Strip | 90×0.5 mm Strip | Notes |
|---|---|---|---|
| Welding Current | 600–1200 A | 800–1600 A | Higher current than SAW mode |
| Slag Pool Temperature | 1200–1400°C | 1200–1400°C | Resistive heating of slag |
| Travel Speed | 50–150 mm/min | 40–120 mm/min | Slower than SAW due to thicker deposits |
| Deposition Rate | 12–20 kg/h | 15–30 kg/h | Up to 3× SAW deposition rate |
| Typical Bead Height | 5–10 mm | 8–15 mm | Single pass can build significant thickness |
| Orientation | Vertical (upward) | Vertical (upward) | Gravity-assisted slag flow |
4.3 Preheat and Interpass Temperature Control
Preheat temperatures of 100–200°C are typically applied to carbon steel substrates prior to overlay to reduce dilution and minimize the risk of cold cracking. Interpass temperatures should be maintained below 250°C for austenitic stainless steel overlays (304L, 309L, 316L) to prevent sensitization in the heat-affected zone. For nickel-based overlays (Alloy 625, Alloy 617, Alloy 600), interpass temperatures should generally be kept below 150°C to preserve the precipitation-strengthened microstructure of the overlay metal.
4.4 Multi-Pass Build Strategy
A typical overlay build for pressure vessel internals follows a structured multi-pass sequence:
- Transition Layer (1st pass): A high-dilution-resistant alloy such as 309L or 309Cb is deposited first to buffer the composition difference between the carbon steel substrate and the final overlay alloy. This layer typically achieves 15–25% dilution and serves as a metallurgical bridge.
- Intermediate Layer (2nd pass): A composition-matched alloy (e.g., 316L for 316L final overlay) is deposited to reduce dilution to below 10%. This pass establishes the correct alloy chemistry for the final overlay.
- Final Overlay Layer (3rd pass): The target overlay alloy is deposited to achieve the required thickness and corrosion resistance. Dilution in this pass should be below 5% for optimal performance.
4.5 Flux Selection and Management
Flux selection is critical to overlay quality. Rutile-type fluxes (e.g., AWS A5.17 ARN70) provide excellent arc stability and smooth bead appearance but may require additional deoxidation. Basic fluxes (e.g., AWS A5.17 ARN437) offer superior mechanical properties and lower sulfur pickup but require careful moisture control. For stainless steel and nickel-based overlays, fluxes must be selected to minimize iron pickup and maintain the required alloy composition in the deposited metal. Flux storage must comply with AWS A5.17 requirements for moisture control, with storage temperatures maintained above 10°C and humidity below 60% RH.
5. Applicable Standards and Acceptance Criteria
5.1 Material Standards
- AWS A5.9 (SAE/AWS Specification for Submerged Arc Welding Electrodes): Governs the composition, mechanical properties, and performance requirements for strip electrodes used in SAW overlay applications. Covers consumable classifications including E309L, E316L, E309Cb, and nickel-based equivalents.
- AWS A5.23 (SAE/AWS Specification for Nickel and Nickel Alloy Welding Electrodes and Rods): Specifies requirements for nickel-based strip electrodes including Alloy 600, Alloy 625, Alloy 617, and Alloy 800H compositions. Defines minimum tensile strength, elongation, and corrosion resistance criteria.
- AWS A5.17 (SAE/AWS Specification for Submerged Arc Welding Fluxes): Classifies fluxes by type (rutile, basic, fluorite) and specifies moisture content, melting point, and slag composition requirements.
- GB/T 12470: Chinese national standard for submerged arc welding consumables, applicable when projects follow Chinese specifications.
- GB/T 5117: Chinese standard for non-cored welding wires and rods, relevant for auxiliary processes.
5.2 Process and Qualification Standards
- ASME Section IX, QW-400 (Submerged Arc Welding): Governs WPS and PQR qualification requirements for SAW processes, including strip electrode variants. Defines essential variables including current, voltage, travel speed, flux type, and electrode composition.
- ASME Section IX, QW-26 (Electroslag Welding): Provides qualification requirements for ESW processes, including strip electrode configurations.
- ASME Section II, Part D: Covers material specifications for overlay metals and substrate materials referenced in pressure vessel codes.
- ASME Section VIII, Division 1, UW-25 (Weld Overlay): Defines requirements for weld overlay on pressure vessels, including minimum thickness, hardness limits, and inspection criteria.
- ASME Section VIII, Division 3, UCS-66: For nuclear applications, specifies overlay requirements including qualified WPS, hardness testing, and NDE coverage.
- API 510 / API 570: For inspection and repair of in-service pressure equipment, defines overlay repair procedures and acceptance criteria.
- ISO 14732: International standard for welding procedure qualification by mechanical testing, applicable to SAW and ESW processes.
- NB/T 20469 (TSG R0004): Chinese national standard for welding procedure qualification in pressure vessel manufacturing.
5.3 NDE and Acceptance Criteria
- ASME Section V, Article 4 (Radiographic Testing): RT examination of overlay welds to detect internal defects including porosity, lack of fusion, and inclusions. Acceptance criteria typically follow T-274 for overlay welds.
- ASME Section V, Article 5 (Magnetic Particle Testing): MT examination of overlay surfaces to detect surface-breaking defects including cracks and lack of fusion at the overlay-substrate interface.
- ASME Section V, Article 7 (Liquid Penetrant Testing): PT examination for non-ferromagnetic overlay surfaces (nickel-based alloys) to detect surface indications.
- ASME Section V, Article 2 (Ultrasonic Testing): UT examination for dilution measurement and subsurface defect detection. Dilution is typically measured using the Fe-65 activation technique or the Fe-59 dilution method per ASME Section V, Article 22.
- Hardness Testing: Overlay hardness must comply with ASME Section VIII, UW-25(b)(3), typically limited to 350 HV max for austenitic stainless steel overlays and 250 HV max for nickel-based overlays (unless otherwise specified by the design authority).
- Corrosion Testing: Intergranular corrosion testing per ASTM A262 (Practice A, B, or E) for austenitic stainless steel overlays. Pitting and crevice corrosion testing per ASTM G48 for nickel-based overlays.
6. Common Risks and Control Measures
| Risk | Cause | Control Measure |
|---|---|---|
| Excessive dilution | High travel speed, low current, insufficient preheat, inadequate transition layer | Optimize current/speed ratio; apply 100–200°C preheat; use multi-pass build with dedicated transition layer; verify dilution by UT or Fe-59 method |
| Cracking (hot/cold) | High sulfur/phosphorus content, rapid cooling, hydrogen pickup | Use low-sulfur fluxes; control interpass temperature; apply preheat; use consumables with controlled S/P content per AWS A5.9/A5.23 |
| Porosity | Moisture in flux, contaminated strip electrode, inadequate arc stability | Store flux per AWS A5.17 moisture requirements; inspect strip electrode for surface contamination; maintain consistent arc parameters |
| Lack of fusion | Low current, excessive travel speed, oxide scale on substrate | Ensure adequate current for strip width; grind substrate to bright metal before overlay; maintain consistent travel speed |
| Weld undercut | High travel speed, low current, improper electrode alignment | Reduce travel speed; increase current; ensure proper electrode stick-out and alignment |
| Distortion | High thermal input, constrained geometry, asymmetric heat input | Use back-step welding sequence; apply backing bars; use balanced heat input strategy; consider temporary stiffeners |
| Flux inclusions | Incomplete slag removal between passes, insufficient slag fluidity | Ensure complete slag removal between passes; select flux with appropriate melting point; maintain proper slag coverage |
7. Application Scenarios Across Technology Routes
7.1 Integration with TIG/MIG Weld Overlay
Strip electrode SAW/ESW technology complements TIG/MIG weld overlay in a multi-process overlay strategy. TIG overlay is typically employed for:
- Small-diameter components: Tubes, nozzles, and small-bore pipes where strip electrode equipment cannot be accommodated
- Complex geometries: Internal corners, weld seams, and irregular surfaces requiring precise electrode control
- Final finishing passes: Surface preparation and final thickness adjustment after bulk deposition by strip electrode SAW
- Transition layers on critical welds: Where dilution control is paramount and low thermal input is required
The typical workflow involves strip electrode SAW for bulk deposition (achieving 70–80% of the required overlay thickness), followed by TIG finishing passes to achieve the final surface profile and ensure complete coverage of any geometric irregularities.
7.2 Integration with Hydraulic Explosive Bonding
Hydraulic explosive bonding (HEB) is primarily used for producing clad plate with a metallurgical bond between the cladding layer and the base plate. Strip electrode overlay technology serves as a complementary process for:
- Post-bonding surface repair: Repairing surface defects or minor bonding failures on HEB-produced clad plates
- Overlay on HEB-clad components: Adding additional corrosion-resistant layers on HEB-clad pipe or plate for enhanced protection in aggressive environments
- Edge preparation: Preparing clad plate edges for welding by overlaying the cut edges with a compatible alloy to prevent base metal contamination in subsequent welds
The combination of HEB for bulk cladding and strip electrode SAW for finishing and repair creates a synergistic process chain that leverages the strengths of both technologies.
7.3 Integration with Explosion Welding
Explosion welding (EW) produces clad plate, pipe, and tube with a high-integrity metallurgical bond achieved through controlled detonation. Strip electrode overlay technology integrates with EW in the following ways:
- Overlay on EW-clad pipe: When EW-clad pipe is fabricated into pressure vessels, the internal surfaces may require additional overlay for corrosion resistance. Strip electrode SAW provides the high deposition rate needed for large-diameter vessel internals.
- Weld seam overlay: Longitudinal and circumferential weld seams in EW-clad pipe require overlay to restore the corrosion-resistant surface. Strip electrode SAW can efficiently overlay these seams while maintaining metallurgical compatibility.
- Thick overlay builds: When overlay thicknesses exceed 5 mm, strip electrode ESW provides the deposition rate advantage over wire-based processes, making it the preferred method for thick overlay builds on EW-clad components.
8. Qualification Building and Customer Value
8.1 WPS/PQR Qualification Strategy
Building a comprehensive WPS/PQR matrix for strip electrode overlay is essential for customer qualification and project bidding. The company should develop qualified procedures covering:
- Substrate materials: P-No. 1 (carbon steel), P-No. 3A (Cr-Mo steels), P-No. 5 (stainless steels), and P-No. 15 (nickel alloys) per ASME Section IX
- Overlay alloys: 309L, 316L, 321, 347H, Alloy 625, Alloy 617, Alloy 800H, Alloy 825 per AWS A5.9/A5.23
- Process variants: SAW with 60 mm strip, SAW with 90 mm strip, ESW with 60 mm strip, ESW with 90 mm strip
- Positional qualifications: Flat, horizontal, vertical (as required by ASME Section IX QW-400)
- Thickness range: Qualify for the full range of overlay thicknesses from 1.5 mm to 10 mm
8.2 Customer Value Proposition
The strip electrode overlay capability delivers measurable customer value through:
- Reduced project cost: 40–60% reduction in overlay labor cost compared to wire-based processes for large-area applications
- Shorter project timelines: 50–70% reduction in overlay cycle time, enabling faster project execution and earlier asset commissioning
- Improved overlay quality: Lower porosity rates, more consistent dilution, and better metallurgical homogeneity compared to manual or semi-automatic wire processes
- Enhanced asset life: Superior corrosion resistance of the overlay extends the service life of critical pressure vessels and heat exchangers, reducing unplanned shutdowns and maintenance costs
- Regulatory compliance: Qualified WPS/PQR packages that meet ASME, API, and NB requirements, facilitating regulatory approval and customer audits
8.3 Competitive Differentiation
The combination of strip electrode SAW and ESW capabilities, supported by qualified WPS/PQR packages and NDE infrastructure, positions Cladding Technology Shanxi Co., Ltd. as a preferred supplier for large-scale overlay projects in the power generation, petrochemical, and nuclear industries. The ability to offer both 60 mm and 90 mm strip widths provides geometric flexibility that addresses the full range of customer component sizes, from small-diameter heat exchanger tube sheets to large-diameter reactor pressure vessel internals.
9. Conclusion
Stainless steel and nickel-based strip electrode submerged arc and electroslag weld overlay technology represents a high-value, high-efficiency capability within the cladding and overlay manufacturing domain. By leveraging the superior deposition rates, metallurgical quality, and process stability of strip electrode SAW and ESW, Cladding Technology Shanxi Co., Ltd. can deliver large-area overlay solutions that meet the demanding requirements of ASME, API, and NB codes while providing significant cost and schedule advantages over conventional wire-based processes. This technology, when integrated with the company's TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding capabilities, creates a comprehensive overlay and cladding solution set that addresses the full spectrum of customer needs across the power, petrochemical, and nuclear industries.