CLADDING TECHNOLOGY SHANXI CO., LTDESAB Strip Cladding Technology Application in Industrial Practice
Literature Overview
The 2013 technical literature on ESAB strip cladding technology application provides a comprehensive overview of submerged arc strip cladding (also known as multi-wire submerged arc welding or SA-CLAD) as applied to large-diameter pressure vessels, piping systems, and structural components requiring corrosion-resistant or wear-resistant surface layers. This technology, developed and commercialized by ESAB Corporation, represents one of the most productive and cost-effective methods for achieving uniform overlay layers on carbon steel and low-alloy steel substrates. The document discusses the fundamental principles, equipment configuration, consumable selection, and quality control measures associated with this process, drawing upon industrial experience accumulated over decades of commercial application.
Core Technical Principles and Process Parameters
Strip cladding operates on the principle of submerged arc welding (SAW) but employs a continuous strip of alloy material as the consumable electrode rather than discrete wires. The strip is fed through a water-cooled contact tip at a controlled rate while an arc is struck between the strip end and the workpiece, with flux covering the molten pool to protect against atmospheric contamination. The key advantage lies in the extremely high deposition rate, typically ranging from 5 to 20 kg/h, which is significantly higher than conventional multi-wire SAW overlay processes.
| Parameter | Typical Range | Notes |
|---|---|---|
| Deposition rate | 5-20 kg/h | Dependent on wire diameter and current |
| Arc voltage | 22-30 V | Strip width dependent |
| Welding current | 300-1200 A | DC or AC, depending on consumable |
| Travel speed | 0.5-3.0 m/min | Higher than conventional SAW |
| Strip width | 12-30 mm | Common commercial widths |
| Strip thickness | 1.5-3.0 mm | Affects dilution and penetration |
| Flux coverage | Continuous | Granular flux, typically low-silica type |
The process parameters must be carefully balanced to achieve the desired dilution rate, which is typically between 5% and 15% for single-pass applications and can be reduced to below 5% with multiple passes. The dilution rate is critically important as it directly affects the chemical composition and microstructure of the final cladding layer. For stainless steel overlays on carbon steel substrates, dilution exceeding 20% may compromise the corrosion resistance of the overlay layer.
Consumable Selection and Metallurgical Considerations
The ESAB strip cladding system offers a wide range of strip consumables covering carbon steel, low-alloy steel, stainless steel, nickel-based alloys, and specialty alloys. The selection of the appropriate strip material depends on the service environment, mechanical requirements, and the substrate material. Common applications include:
- 309L/310L strips: Used for stainless steel overlay on carbon steel substrates where dilution is expected to be significant, providing a buffer layer with adequate Cr and Ni content to resist sensitization.
- 316L strips: Applied where chloride resistance is required, though higher dilution rates may necessitate multi-pass deposition.
- Ni-based alloy strips: Employed for extreme corrosion environments or where galvanic compatibility is critical.
- Cr-Mo alloy strips: Used for high-temperature service applications in power generation and petrochemical industries.
The metallurgical behavior of strip cladding is influenced by the rapid solidification rate, which typically produces a columnar dendritic microstructure with finer grain sizes compared to conventional welding. This results in improved mechanical properties but may also introduce residual stresses that require post-weld heat treatment (PWHT) to mitigate. The solidification rate in strip cladding is generally higher than in conventional SAW, leading to reduced grain growth and potentially improved hardness and wear resistance.
Quality Control and Inspection Requirements
Quality assurance in strip cladding applications requires adherence to established standards such as ASME Section IX, ASTM A263, and relevant national standards. The inspection regime typically includes:
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Visual inspection (VT) | Surface defects, undercut, porosity | ASME BPV Code Sec V Art 1 |
| Magnetic particle testing (MT) | Surface and near-surface cracks | ASME BPV Code Sec V Art 7 |
| Ultrasonic testing (UT) | Bond strength, lack of fusion | ASME BPV Code Sec V Art 4 |
| Hardness testing | Dilution control, microstructure verification | Specified range per material spec |
| Chemical analysis | Compositional verification | ASTM A263/A264 requirements |
| Tensile/shear testing | Bond strength verification | Minimum 150 MPa for clad plate |
The bond strength between the cladding layer and the substrate is a critical quality parameter. For most applications, a minimum shear bond strength of 150 MPa is required, with some critical applications demanding values exceeding 200 MPa. The dilution rate can be verified through hardness profiling across the clad layer, where a gradual transition from substrate hardness to overlay hardness indicates acceptable dilution control.
Engineering Practice and Process Optimization
In practical applications, strip cladding has been extensively used for the internal lining of hydrogenation reactors, ammonia synthesis loops, and petrochemical processing equipment. The process offers significant advantages over explosion cladding and roll-bonding for large-diameter vessels where the cladding area exceeds practical limits for mechanical bonding methods. However, several challenges must be addressed:
- Residual stress management: The high deposition rate generates significant thermal stresses that may exceed the yield strength of the substrate, necessitating careful PWHT procedures to prevent stress corrosion cracking.
- Warping control: For thin-walled components, the asymmetric heat input can cause significant distortion, requiring fixture design and back-heat techniques.
- Porosity control: Inadequate flux coverage or excessive travel speed can lead to gas porosity, particularly in the first pass. Proper flux management and consistent arc length control are essential.
- Crack susceptibility: High dilution rates or inappropriate consumable selection can lead to hot cracking or cold cracking, particularly in high-strength substrates.
Process optimization often involves the use of multi-pass strategies, where a transition layer (e.g., 309L) is applied first to reduce dilution in subsequent passes of the final overlay material (e.g., 316L). This approach allows for the use of higher-performance overlay materials while maintaining acceptable dilution levels.
Study Insights and Reflections
The ESAB strip cladding technology represents a mature and highly productive method for achieving corrosion-resistant overlays in industrial applications. The key insight from this literature is that the process's effectiveness depends not only on proper parameter selection but also on systematic quality control and process discipline. The high deposition rate, while advantageous for productivity, introduces challenges related to residual stress, dilution control, and defect prevention that must be managed through rigorous procedure qualification and operator training. For engineers involved in bimetal pressure vessel fabrication, understanding the fundamental metallurgical behavior and quality requirements of strip cladding is essential for ensuring long-term service reliability. The technology continues to evolve with improvements in consumable metallurgy and process control systems, offering expanding application possibilities in emerging industries such as hydrogen energy and advanced nuclear systems.