ESAB Submerged Arc Surfacing (Flux-Cored Wire) Weld Overlay Technology
1. Definition and Technical Principles
ESAB Submerged Arc Surfacing (SAS) technology, as documented in the learning reflection on "Application of ESAB Flux-Cored Wire Surfacing Technology," refers to a specialized weld overlay process that utilizes tubular flux-cored wire (FCW) in a submerged arc welding (SAW) configuration to deposit corrosion-resistant, wear-resistant, or metallurgically compatible overlay layers onto base substrates. Unlike conventional solid-wire submerged arc welding, the ESAB SAS system employs a hollow wire electrode filled with a proprietary flux blend. This flux is released during arc combustion, creating a dual-shield environment—both from the externally applied granular flux blanket and the internally generated flux from the wire core—resulting in superior dilution control, enhanced deposit chemistry, and significantly higher deposition rates compared to traditional overlay methods.
The fundamental principle relies on the controlled melting of the flux-cored wire under a submerged arc, where the arc is shielded from atmospheric contamination by a thick layer of granular flux. As the wire advances through the welding torch, the internal flux core melts and mixes with the molten metal, refining the weld pool chemistry, reducing nitrogen and oxygen pickup, and enabling the deposition of overlay materials with compositions that would be difficult to achieve using solid wire alone. The process is characterized by high current density, deep penetration control, and the ability to build multi-layer overlays with precise dilution management.
2. Category and Business Positioning
Within the company's three core technology routes—TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding—ESAB SAS technology occupies a strategic position in the weld overlay domain, specifically serving as a high-productivity, large-scale overlay solution that complements the precision-oriented TIG and MIG processes. While TIG overlay excels in thin-walled components, transition layers, and critical joint quality, and MIG overlay provides versatile mid-range productivity, the ESAB SAS system addresses the demands of heavy-duty, large-area, and multi-pass overlay applications where deposition rate and economic efficiency are paramount.
The technology is positioned as a qualification-enabling process that expands the company's WPS (Welding Procedure Specification) portfolio, particularly for applications governed by ASME, API, and NACE standards where high-dilution-controlled overlay is required. It also serves as a bridge technology between conventional weld overlay and explosion welding, providing a viable alternative when explosion welding is impractical due to component geometry, size limitations, or customer specification constraints.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- High Deposition Rate: Achieve overlay deposition rates 3–5 times greater than conventional TIG or MIG processes, reducing cycle time for large-area applications such as pressure vessel internal linings, heat exchanger tube sheets, and structural steel wear surfaces.
- Dilution Control: Maintain dilution levels within specified limits (typically 10–30% for corrosion-resistant overlays) by leveraging the flux-cored wire's inherent dilution-reducing properties and the multi-layer build-up strategy.
- Deposit Integrity: Produce overlay layers with controlled microstructure, low porosity, minimal cracking susceptibility, and consistent mechanical properties across the entire overlay area.
- Scalability: Enable the overlay of large-diameter pipes, wide flat plates, and complex geometries that would be impractical or cost-prohibitive using manual or semi-automatic TIG/MIG processes.
3.2 Economic and Strategic Value
The adoption of ESAB SAS technology directly contributes to the company's competitive positioning by enabling cost-effective delivery of large-volume overlay work, reducing labor hours per unit of overlay area, and expanding the range of materials and specifications that can be qualified. The technology also strengthens the company's capability statement to customers in the oil, gas, chemical, and power generation sectors, where large-scale corrosion-resistant overlay is a recurring requirement.
4. Key Process and Implementation Points
4.1 Equipment Configuration
ESAB SAS systems typically employ a mechanized or semi-automated welding carriage with a dedicated flux-cored wire feeder, flux hopper and distributor, and a dual-wire or single-wire torch configuration. The system requires precise control over wire feed speed, travel speed, arc voltage, and flux coverage. The torch is designed to maintain a consistent arc length and to ensure adequate flux coverage ahead of and behind the arc to prevent atmospheric contamination.
4.2 Critical Process Parameters
| Parameter | Typical Range | Control Rationale |
|---|---|---|
| Wire Diameter | 2.0 mm – 3.0 mm (flux-cored) | Thicker wires increase deposition rate but may increase dilution; selection depends on overlay material and base metal |
| Travel Speed | 200 mm/min – 600 mm/min | Balances deposition rate with dilution control and bead profile; slower speeds increase penetration and dilution |
| Wire Feed Speed | 4 m/min – 10 m/min | Directly controls arc current; must be synchronized with travel speed for consistent bead geometry |
| Arc Current | 400 A – 800 A | Higher currents increase penetration and dilution; must be balanced against overlay composition requirements |
| Arc Voltage | 28 V – 40 V | Influences bead width and arc stability; higher voltages produce wider, flatter beads |
| Flux Coverage | Minimum 10 mm ahead of arc, 15 mm behind | Prevents oxidation and nitrogen pickup; ensures consistent shielding during the entire weld pass |
| Interpass Temperature | Below 150°C – 250°C | Controls cooling rate and dilution; excessive interpass temperature increases dilution and may cause microstructural degradation |
| Preheat Temperature | 50°C – 200°C (material-dependent) | Reduces cracking susceptibility in high-carbon or high-strength base metals; also controls thermal gradients |
4.3 Multi-Layer Build-Up Strategy
A hallmark of ESAB SAS overlay technology is the multi-layer build-up approach, which is essential for achieving acceptable dilution levels when overlaying dissimilar materials. The typical strategy involves:
- First Layer (High Dilution Layer): A transition layer is deposited with a material of intermediate composition between the base metal and the final overlay material. Dilution for this layer may be as high as 30–50%, but the composition is designed to absorb this dilution without compromising the final overlay performance.
- Second Layer (Intermediate Layer): A second layer is deposited with a composition closer to the target overlay material. Dilution is reduced to 15–25% due to the lower base metal influence from the first layer.
- Final Layer (Target Composition Layer): The final overlay layer is deposited with the specified overlay material. Dilution is controlled to within 10–15%, achieving the target corrosion or wear resistance properties.
4.4 Wire and Flux Selection
The selection of ESAB flux-cored wire and matching flux is critical to the success of the overlay process. ESAB offers a range of flux-cored wires for various overlay applications, including:
- Corrosion-Resistant Overlays: Cr-Ni austenitic compositions (e.g., equivalent to 309, 310, 321, and 625) for use on carbon steel and low-alloy steel substrates in corrosive environments.
- Wear-Resistant Overlays: High-carbon martensitic, austenitic, or carbide-reinforced compositions for applications involving abrasive or erosive wear.
- Transition Layers: Intermediate-composition wires designed to bridge between the base metal and the final overlay material, minimizing dilution-related performance degradation.
5. Applicable Standards and Acceptance Criteria
5.1 Governing Standards
| Standard | Scope | Relevance to ESAB SAS Overlay |
|---|---|---|
| ASME BPV Section IX | Welding, Brazing, and Fusing Qualifications | WPS qualification and welder/operator performance qualification for pressure vessel overlay applications |
| ASME BPV Section VIII, Div. 1 & 2 | Rules for Construction of Pressure Vessels | Acceptance criteria for overlay thickness, dilution limits, and NDE requirements |
| API 579 / API 570 | Fitting-Up and Welding of Piping / Piping Inspection | Overlay acceptance criteria for piping systems in oil and gas applications |
| NACE MR0175 / ISO 15156 | Materials for Use in H2S-Containing Environments | Hardness limits, microstructural requirements, and SSC resistance for overlays in sour service |
| ASTM A240 / ASTM A276 | Stainless Steel Plates / Bars | Chemical composition and mechanical property requirements for overlay materials |
| GB/T 985.1 | Welding Procedure Specification Preparation | Chinese standard for WPS development and qualification procedures |
| NB/T 47014 | Welding Procedure Qualification for Pressure Vessels | Chinese standard for WPS qualification in pressure equipment |
| ISO 9606-1 | Qualification Testing of Welders – Arc Welding | Welder performance qualification requirements for mechanized/automated processes |
5.2 Acceptance Criteria
- Dilution: Verified by chemical analysis of the overlay layer, typically required to be below 15–25% depending on the application and specification. For NACE MR0175 applications, dilution must be controlled to ensure hardness remains below 22 HRC.
- Overlay Thickness: Minimum and maximum thickness specified per drawing or standard (e.g., ASME Section VIII requires minimum 1.5 mm for corrosion allowance overlays). Thickness verified by ultrasonic testing (UT) or magnetic particle testing (MT) with thickness measurement.
- Surface Quality: No cracks, porosity, undercut, or excessive reinforcement. Surface roughness typically required to be within Ra 12.5 μm or as specified.
- NDT Requirements: Visual testing (VT) for 100% of overlay area; magnetic particle testing (MT) or dye penetrant testing (PT) for 100% of overlay surface; ultrasonic testing (UT) or radiographic testing (RT) for bond line and dilution verification as specified.
- Hardness: Verified by Rockwell C or Brinell hardness testing, with limits specified per the applicable standard (e.g., NACE MR0175 requires maximum 22 HRC for carbon equivalents above 0.6% in sour service).
- Corrosion Resistance: Verified by immersion testing, electrochemical testing, or field experience data as specified by the customer or applicable standard.
6. Common Risks and Controls
6.1 Process Risks
| Risk | Cause | Control Measure |
|---|---|---|
| Excessive Dilution | High travel speed mismatch, excessive current, insufficient multi-layer build-up, high interpass temperature | Implement multi-layer strategy with transition layers; control interpass temperature below 200°C; calibrate wire feed and travel speed synchronously; verify dilution by chemical analysis after qualification |
| Cracking (Hot or Cold) | High carbon equivalent of base metal, inadequate preheat, rapid cooling, hydrogen pickup | Apply preheat per WPS; use low-hydrogen flux and flux-cored wire; control interpass temperature; apply post-weld heat treatment (PWHT) where required |
| Porosity | Inadequate flux coverage, contaminated wire or flux, excessive travel speed, wire feeding irregularities | Ensure continuous flux coverage; store flux in controlled humidity environment (below 60% RH); inspect wire for surface contamination; maintain consistent wire feed speed |
| Inconsistent Bead Geometry | Torch misalignment, carriage vibration, wire feeding instability, flux distribution unevenness | Use precision-guided welding carriage; maintain torch-to-workpiece alignment; use flux distributor with consistent coverage; perform regular equipment calibration |
| Overlay Spallation / Poor Bond | Insufficient heat input, poor surface preparation, excessive dilution, thermal mismatch between layers | Ensure adequate surface preparation (grinding to bare metal, free of oxide, oil, and contaminants); use appropriate heat input per WPS; verify bond quality by UT or destructive testing during qualification |
6.2 Material and Environmental Risks
- Flux Moisture Absorption: ESAB flux is hygroscopic and must be stored in a controlled environment. If flux has absorbed excessive moisture, it must be re-dried at 250–300°C for 2–4 hours before use. Failure to do so results in hydrogen-induced porosity and cracking.
- Wire Surface Contamination: Flux-cored wire must be stored in a dry environment and protected from moisture, oil, and rust. Contaminated wire leads to inconsistent arc performance and deposit quality.
- Ambient Conditions: Wind, rain, and high humidity can compromise flux shielding. Indoor welding or wind shielding is required in outdoor environments. Relative humidity above 70% may require additional flux drying measures.
7. Application Scenarios Across the Company's Technology Routes
7.1 TIG/MIG Weld Overlay Integration
ESAB SAS technology is most effectively deployed in combination with TIG and MIG overlay processes within the company's production workflow. The typical integration strategy is as follows:
- Transition Layer via TIG: For critical applications requiring extremely low dilution (e.g., nuclear-grade stainless steel overlay on carbon steel), the first transition layer is deposited using TIG welding with precise heat input control. This ensures a metallurgically sound interface with minimal dilution.
- Bulk Overlay via ESAB SAS: Once the transition layer is established, the bulk of the overlay is deposited using ESAB SAS for high productivity. This approach combines the precision of TIG with the throughput of SAS.
- Final Finish Layer via MIG or TIG: Where surface finish quality is critical (e.g., Ra < 6.3 μm), the final layer is deposited using MIG or TIG welding to achieve superior surface quality that SAS cannot match.
- Small-Feature Overlay via TIG/MIG: For small-diameter pipes, thin-walled components, or complex geometries where SAS equipment cannot access, TIG or MIG overlay is used as the primary process, with ESAB SAS reserved for large flat or large-diameter areas.
7.2 Hydraulic Explosive Bonding Integration
While hydraulic explosive bonding (HEB) is a solid-state joining process that produces metallurgical bonds without melting, ESAB SAS technology serves as a complementary overlay process in the following scenarios:
- Post-Bonding Surface Repair: If HEB bonding produces localized defects (e.g., minor voids, surface irregularities, or bond line discontinuities), ESAB SAS can be used to repair and overlay the affected areas, restoring the required corrosion or wear resistance.
- Edge and End-Cap Overlay: HEB is typically applied to the main body of a clad plate or pipe. The edges, end caps, and areas not covered by HEB are overlaid using ESAB SAS to provide continuous corrosion protection across the entire component.
- Multi-Layer Clad Construction: In applications requiring multi-layer cladding (e.g., carbon steel base + stainless steel intermediate layer + Hastelloy or Inconel outer layer), HEB may be used for the first bond, and ESAB SAS for the subsequent overlay layers, combining the advantages of both processes.
- WPS Qualification Support: ESAB SAS qualification data can support the overall WPS for hybrid clad constructions, demonstrating that the overlay process is qualified and that the combined construction meets the required performance criteria.
7.3 Explosion Welding Integration
Explosion welding produces high-quality metallurgical bonds but is limited by component size, geometry, and the availability of explosion welding facilities. ESAB SAS technology complements explosion welding in the following ways:
- Large-Area Overlay Alternative: For components too large or too complex for explosion welding (e.g., large pressure vessel shells, wide structural steel plates), ESAB SAS provides a viable alternative for depositing corrosion-resistant or wear-resistant overlay layers.
- Post-Explosion Overlay: After explosion welding produces the primary clad bond, ESAB SAS can be used to deposit additional overlay layers on the clad surface for enhanced performance (e.g., adding a wear-resistant layer on top of a corrosion-resistant explosion-welded clad).
- Repair and Maintenance Overlay: For existing explosion-welded components that require field repair or re-overlay due to wear or corrosion, ESAB SAS provides a portable and scalable solution that does not require explosion welding facilities.
- Qualification Cross-Reference: ESAB SAS WPS qualifications can be cross-referenced with explosion welding qualification data to demonstrate the company's comprehensive overlay capability across multiple process routes.
8. Qualification Building and WPS Development
8.1 WPS Qualification Requirements
The ESAB SAS process must be qualified in accordance with the applicable code (ASME Section IX, NB/T 47014, or ISO 15614-1) before production use. The qualification procedure involves the following steps:
- WPS Development: Define all essential variables including process type (SAS), wire type and diameter, flux type, current range, voltage range, travel speed range, wire feed speed range, preheat temperature, interpass temperature, and post-weld treatment. Non-essential variables include torch angle, flux coverage thickness, and backing material.
- Test Coupon Preparation: Prepare test coupons matching the production material, thickness, and geometry. For overlay applications, the coupon must include a sufficient length to allow for multi-layer build-up and subsequent NDE and destructive testing.
- Welding Execution: Perform the multi-layer overlay weld on the test coupon using the parameters defined in the WPS. Record all process parameters, including actual current, voltage, travel speed, wire feed speed, preheat and interpass temperatures, and any deviations.
- NDT Inspection: Perform visual testing (VT), magnetic particle testing (MT) or dye penetrant testing (PT), and ultrasonic testing (UT) or radiographic testing (RT) on the test coupon to verify weld quality.
- Destructive Testing: Perform macrographic and micrographic examination to verify dilution, microstructure, and bond quality. Perform chemical analysis of the overlay layer to verify composition. Perform hardness testing to verify mechanical properties. Perform bend testing or peel testing to verify bond strength.
- Performance Testing: For corrosion-resistant overlays, perform immersion testing or electrochemical testing to verify corrosion resistance. For wear-resistant overlays, perform abrasion testing to verify wear resistance. For sour service applications, perform hardness testing and microstructural examination per NACE MR0175 / ISO 15156.
8.2 Welder Performance Qualification
Operators of ESAB SAS equipment must be qualified in accordance with ISO 9606-1 or the applicable national standard. The qualification test involves the operator setting up the equipment, adjusting parameters within the qualified WPS range, and performing a test weld that is inspected for visual quality, NDE, and dilution. The operator must demonstrate the ability to maintain consistent weld quality across multiple passes and to adjust parameters within the qualified range to accommodate variations in workpiece geometry and surface condition.
9. Quality Management and Inspection Protocol
9.1 Incoming Material Inspection
- Verify ESAB flux-cored wire and flux certificates of conformity against the WPS-specified material grade.
- Inspect wire for surface condition, diameter consistency, and absence of rust or contamination.
- Verify flux moisture content; if moisture content exceeds 0.5%, re-dry flux at 250–300°C for 2–4 hours before use.
- Verify base metal material grade, thickness, and surface condition; ensure surface is free of oxide, oil, paint, and other contaminants.
9.2 In-Process Inspection
- Monitor and record arc current, voltage, travel speed, and wire feed speed at regular intervals (e.g., every 30 minutes).
- Verify preheat temperature using calibrated infrared thermometer or contact thermocouple.
- Measure and record interpass temperature before each subsequent pass.
- Inspect flux coverage continuously; replenish flux as needed to maintain adequate coverage.
- Perform visual inspection of each weld pass for bead profile, surface quality, and absence of defects.
9.3 Final Inspection
- Perform 100% visual testing (VT) of the entire overlay area.
- Perform 100% magnetic particle testing (MT) or dye penetrant testing (PT) of the overlay surface.
- Perform ultrasonic testing (UT) or radiographic testing (RT) for bond line and dilution verification as specified in the WPS.
- Perform overlay thickness measurement using UT or magnetic thickness gauge.
- Perform hardness testing at specified intervals across the overlay area.
- Perform chemical analysis of the overlay layer to verify dilution and composition.
- Compile all inspection records into a traceable quality dossier for customer delivery.
10. Conclusion and Strategic Contribution
The ESAB Submerged Arc Surfacing technology, as documented in the company's learning reflection, represents a significant capability enhancement for Cladding Technology Shanxi Co., Ltd. The technology enables the company to deliver high-productivity, cost-effective overlay solutions for large-scale applications while maintaining the quality and compliance required by international standards such as ASME, API, NACE, and ISO. By integrating ESAB SAS with the company's existing TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding capabilities, the company can offer a comprehensive, multi-route overlay solution that addresses the full spectrum of customer requirements—from precision-critical applications to high-volume production work.
The qualification of ESAB SAS procedures under ASME Section IX, NB/T 47014, and ISO 15614-1 directly strengthens the company's WPS portfolio, enabling acceptance of contracts in regulated industries such as oil and gas, power generation, and chemical processing. The technology also enhances customer value by reducing delivery lead times, lowering production costs, and providing a scalable solution for both new construction and repair/maintenance applications. As the company continues to expand its technology portfolio, ESAB SAS technology serves as a critical enabler of competitive differentiation and market growth in the global cladding and weld overlay industry.