Stainless Steel Coil Tube — Plasma Arc Welded (PAW) Process
Product Overview
The Plasma Arc Welded Stainless Steel Coil Tube is a precision-engineered seamless-appearance welded tube manufactured using the Plasma Arc Welding (Plasma Arc Welding, PAW) process. Produced by Wenzhou Jixing Metal Materials Co., Ltd, this product leverages the exceptional energy density and penetration capability of plasma arc technology to deliver high-integrity welded joints in medium-to-thick wall stainless steel coil tubes. The PAW process distinguishes itself from conventional Tungsten Inert Gas (TIG) welding through superior thermal efficiency, deeper weld penetration, and significantly higher deposition rates — making it the preferred method for producing thick-walled stainless steel coil tubes with outstanding metallurgical properties.
Material & Properties
These coil tubes are fabricated from high-grade austenitic and duplex stainless steel strip, offering exceptional corrosion resistance, mechanical strength, and dimensional stability across a wide range of operating environments.
- Grade Options: 304 (AISI), 304L, 316L (AISI), 321, 347, 904L, Duplex 2205, and custom alloy specifications
- Base Strip Material: Cold-rolled stainless steel coil with tight thickness tolerance (±0.02 mm)
- Weld Metal: Consumable filler wire matched to base metal chemistry (e.g., ER308L, ER316L, ER321) to ensure metallurgical homogeneity at the weld seam
- Corrosion Resistance: Excellent resistance to intergranular corrosion, pitting, and crevice corrosion in aggressive chemical environments
- Mechanical Properties: Tensile strength ≥ 520 MPa (Grade 304), Yield strength ≥ 205 MPa, Elongation ≥ 40%
- Surface Finish: BA (Bright Annealed), 2B, No.4 Brushed, or custom finishes available
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108.0 mm | ASTM A269 / ASME SA-269 |
| Wall Thickness | 0.5 mm – 6.0 mm (medium to thick wall) | ASTM A269 / ASME SA-269 |
| Coil Length | Custom (typically 50 m – 500 m per coil) | Customer specification |
| OD Tolerance | ±0.05 mm | EN 10217-7 |
| Wall Thickness Tolerance | ±10% (minimum ±0.05 mm) | ASTM A269 |
| Welding Process | Plasma Arc Welding (PAW) | ISO 14555 |
| Weld Penetration Depth | Full penetration (up to 6.0 mm wall thickness) | — |
| Welding Speed | 1.5× – 2.5× faster than conventional TIG | — |
| Shielding Gas | Argon (Ar) or Ar/CO₂ mixture | — |
| Heat-Affected Zone (HAZ) | Narrow & controlled (< 2 mm) | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (BA finish) | — |
| Maximum Operating Temperature | 870°C (Grade 304), 925°C (Grade 316L) | — |
| Minimum Operating Temperature | −196°C (cryogenic service) | — |
Manufacturing Process
3.1 Plasma Arc Welding (PAW) — Process Principle
The Plasma Arc Welding process utilizes a high-velocity, highly ionized plasma jet generated by forcing an electric arc through a constricting nozzle (torche nozzle). This produces an energy density of approximately 1,000 – 10,000 W/mm², significantly exceeding that of conventional TIG welding (~100 – 1,000 W/mm²). The resulting arc is characterized by:
- Extreme Energy Concentration: The plasma jet achieves temperatures up to 30,000 K, enabling rapid and complete melting of the base metal and filler wire.
- Deep Weld Penetration: The narrow, high-energy arc achieves full-penetration welds in medium-to-thick wall sections (up to 6.0 mm) in a single pass, eliminating the need for multi-pass welding.
- High Travel Speed: Welding speeds are 1.5× to 2.5× greater than TIG, dramatically improving production throughput and reducing manufacturing cycle time.
- Narrow Heat-Affected Zone (HAZ): The concentrated thermal input minimizes the HAZ width to less than 2 mm, reducing thermal distortion and preserving the base metal's mechanical properties.
3.2 Production Workflow
- Strip Preparation: Cold-rolled stainless steel coil strip is uncoiled, slit to precise width, and edge-trimmed to ensure consistent bevel geometry for the welding process.
- Forming: The flat strip is fed through a series of progressive roll-forming stations, gradually bending it into the desired circular cross-section. Precision hydraulic forming ensures tight dimensional control.
- Plasma Arc Welding: The formed tube blank is continuously welded using the PAW process. A consumable tungsten electrode generates the plasma arc, while matched filler wire is fed into the weld pool. Shielding gas (Argon) protects the weld from atmospheric contamination.
- Post-Weld Heat Treatment: The welded coil tube undergoes solution annealing (typically 1050°C – 1150°C) followed by controlled cooling to restore full austenitic microstructure, eliminate residual stresses, and maximize corrosion resistance.
- Pickling & Passivation: The tube surface is chemically pickled to remove oxide scale, then passivated to form a protective chromium oxide layer, ensuring superior corrosion performance.
- Dimensional Calibration: Final sizing passes through precision mandrel dies to achieve exact OD and wall thickness tolerances.
- Quality Inspection: Comprehensive non-destructive testing (NDT) including eddy current inspection, hydrostatic pressure testing, and visual weld seam examination.
- Coiling & Packaging: Finished coil tubes are wound onto protective cores and packaged with moisture-barrier wrapping for shipment.
3.3 PAW vs. TIG — Comparative Advantages
| Performance Metric | Plasma Arc Welding (PAW) | Tungsten Inert Gas (TIG) |
|---|---|---|
| Energy Density | 1,000 – 10,000 W/mm² | 100 – 1,000 W/mm² |
| Welding Speed (medium-thick wall) | 1.5× – 2.5× faster | Baseline |
| Penetration Depth (single pass) | Up to 6.0 mm | Up to 3.0 mm |
| Heat-Affected Zone Width | < 2 mm | 3 – 5 mm |
| Weld Bead Geometry | Narrow, deep, uniform | Wider, shallower |
| Productivity (thick wall tubes) | Significantly higher | Moderate |
Applications
The Plasma Arc Welded Stainless Steel Coil Tube finds extensive use across demanding industrial sectors where high-integrity weld seams, thick wall sections, and superior corrosion resistance are critical:
- Chemical Processing: Reactor piping, heat exchanger tubes, and process lines handling aggressive chemicals (acids, alkalis, chlorides)
- Oil & Gas Industry: Downstream processing piping, separator internals, and high-pressure transport lines
- Pharmaceutical & Biotechnology: CIP/SIP-compatible process piping, fermentation vessel internals, and sanitary-grade transfer lines
- Food & Beverage Processing: Hygienic transfer lines, pasteurization equipment, and CIP systems requiring smooth, weld-free interior surfaces
- Petrochemical & Refining: Crude oil distillation columns, catalytic converter housings, and high-temperature process lines
- Power Generation: Boiler feedwater piping, steam lines, and heat recovery systems
- Marine & Offshore: Ballast systems, seawater intake piping, and offshore platform infrastructure
- Aerospace: Hydraulic lines, fuel systems, and structural tubing requiring high strength-to-weight ratios
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and adheres to international standards throughout the manufacturing process:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control
- ISO 14555 — Specification for plasma arc welding processes, ensuring standardized PAW parameters and weld quality
- ASTM A269 / ASME SA-269 — Standard specification for welded austenitic stainless steel tube
- EN 10217-7 — European standard for cold-drawn or cold-rolled stainless steel tubes
- PED (Pressure Equipment Directive 2014/68/EU) — Compliance for pressure-containing applications
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 or Type 3.2 certification available upon request
- NDT Inspection: 100% eddy current testing (ECT), hydrostatic pressure testing, and visual inspection per ASTM E309
- Material Traceability: Full heat number traceability from raw material to finished product
Unique Selling Points
Why Choose PAW-Welded Stainless Steel Coil Tubes from Wenzhou Jixing?
- Superior Weld Integrity: The plasma arc's extreme energy concentration produces full-penetration welds with minimal porosity, ensuring weld seams that match or exceed the strength of the base metal.
- High Productivity for Thick Walls: PAW welding efficiency for medium-to-thick wall tubes significantly outperforms conventional TIG — reducing manufacturing time by up to 60% while maintaining weld quality.
- Minimal Thermal Distortion: The narrow heat-affected zone preserves the tube's dimensional accuracy and mechanical properties, critical for precision applications.
- Single-Pass Full Penetration: Eliminates the need for multi-pass welding, reducing residual stresses and improving overall weld reliability.
- Coil Form Factor Advantage: Delivered in continuous coil configuration, enabling downstream users to minimize cutting waste, reduce installation labor, and optimize material utilization.
- Customization Capability: Flexible in diameter, wall thickness, grade selection, surface finish, and coil length to meet specific project requirements.