Stainless Steel Coil Tube with TIG Self-Fusion & Back-Side Argon Shielded Welding
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. (Catalog No. 221) presents a high-performance stainless steel coil tube (Coiltube) engineered specifically for installation and maintenance applications requiring superior welded connections. This product is classified under the welding connection subcategory of joint fabrication processes and is manufactured using TIG (Tungsten Inert Gas) self-fusion welding with back-side argon shielding. The resulting coil tube offers exceptional weld integrity, corrosion resistance, and long-term structural reliability for demanding industrial environments.
The coil tube is supplied in continuous coil form, enabling efficient downstream processing including mandrel bending, coil-to-straight conversion, and automated cut-to-length operations. This format minimizes material waste and provides consistent mechanical properties throughout the entire length of the tube.
Material & Properties
Base Material
The coil tube is fabricated from austenitic stainless steel, with 304/304L and 316L being the most commonly specified grades. These materials offer a balanced combination of corrosion resistance, formability, and weldability essential for the TIG self-fusion welding process employed in this product.
Key Properties
- Corrosion Resistance: Superior resistance to general corrosion, intergranular corrosion, and pitting in a wide range of chemical and environmental media, provided weld integrity is maintained.
- Weldability: Excellent weldability with TIG self-fusion process, producing clean, oxide-free weld seams when proper argon shielding protocols are followed.
- Mechanical Strength: Maintains full parent-metal strength at the weld zone with no filler metal dilution, ensuring uniform mechanical properties along the coil tube length.
- Hygienic Surface: The self-fusion weld produces a smooth, seamless interior surface with no crevice or gap that could harbor contamination — critical for food-grade and pharmaceutical applications.
- Temperature Resistance: Suitable for continuous service in elevated temperature environments typical of heat transfer and process piping applications.
Unique Selling Point — Back-Side Argon Shielding Integrity
Critical Quality Indicator: Inner wall oxidation (black discoloration) is a definitive sign of shielding gas failure. Once oxidation occurs on the weld interior, the corrosion resistance of the entire weld zone is permanently compromised. Wenzhou Jixing Metal Materials Co., Ltd. employs rigorous pre-purge and continuous back-side argon protocols to guarantee a bright, oxide-free interior weld surface, preserving full metallurgical integrity and service life.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Coil Tube (盘管) |
| Catalog Number | 221 |
| Category | Installation & Maintenance → Connection Process → Welded Connection |
| Welding Process | TIG Self-Fusion with Back-Side Argon Shielding |
| Shielding Gas | Pure Argon (Ar), ≥ 99.99% purity |
| Shielding Gas Flow Rate | 8–15 L/min |
| Pre-Purge Requirement | Advance gas flushing before arc initiation (pre-ignition purge) |
| Weld Interior Quality | Bright, oxide-free, no discoloration (silver-white appearance) |
| Failure Indicator | Inner wall oxidation / blackening = shielding failure = corrosion resistance loss |
| Typical Outer Diameters | 6.0 mm – 108.0 mm (0.24 in – 4.25 in) |
| Typical Wall Thickness | 0.5 mm – 3.0 mm (0.020 in – 0.118 in) |
| Material Grades | SUS304 / 304L / 316L / 321 / 316Ti (custom available) |
| Supply Form | Continuous coil |
| Surface Finish | Pickled & passivated (standard); electropolished (optional) |
Manufacturing Process
Step 1 — Coil Tube Forming
Flat stainless steel strip is precision-formed into coil tube geometry via cold-rolling or helical welding of strip into a continuous tubular coil. The coil form ensures consistent dimensional tolerances and eliminates the variability associated with individual straight-length tubes.
Step 2 — TIG Self-Fusion Welding Preparation
Where coil tube segments require joining (e.g., coil-to-straight conversion, butt joints for longer runs), the TIG self-fusion process is employed. This technique requires no filler rod — the base metal itself melts to form the weld joint. Critical preparation steps include:
- Surface Cleaning: Weld preparation area is mechanically and chemically cleaned to remove oils, oxides, and contaminants that would compromise argon shielding effectiveness.
- Gas Line Setup: Pure argon (≥ 99.99%) is routed through a back-side shielding fixture that ensures continuous gas coverage of the weld interior from the first moment of gas flow.
- Pre-Purge: Argon flow is initiated at 8–15 L/min before arc ignition (advance purge). This displaces atmospheric oxygen and moisture from the weld zone, preventing oxide formation during the critical arc-start phase.
Step 3 — Arc Welding Execution
The TIG arc is struck with a tungsten electrode, melting the base metal edges of the coil tube to form a self-fusion weld bead. The continuous back-side argon flow (maintained at 8–15 L/min) protects the molten weld pool from atmospheric contamination on the interior surface. The front-side (exterior) is simultaneously shielded by the standard TIG gas nozzle.
Step 4 — Post-Weld Gas Hold-Off
After the arc is extinguished, argon flow is maintained for a sufficient cool-down period to protect the still-hot weld zone from re-oxidation during solidification.
Step 5 — Quality Verification
Every weld joint undergoes visual inspection of the interior surface. A bright, silver-white appearance confirms successful shielding. Any evidence of yellow, blue, or black discoloration indicates shielding failure, and the joint is rejected and reworked. Additional non-destructive testing (dye penetrant, X-ray) may be applied per customer specification.
Step 6 — Pickling & Passivation
Following welding, the coil tube undergoes pickling and passivation treatment to remove any residual heat-affected zone discoloration, restore the chromium oxide passive layer, and maximize long-term corrosion resistance.
Applications
- Food & Beverage Processing: Hygienic piping systems, CIP/SIP lines, and heat exchanger coils requiring smooth, crevice-free weld interiors.
- Pharmaceutical & Biotech: Sterilizable process piping, reactor coils, and sanitary transfer lines where weld integrity directly impacts product purity.
- Chemical & Petrochemical: Process piping systems, heat exchanger tubes, and corrosion-resistant coil assemblies handling aggressive media.
- Power Generation: Boiler tubes, heat recovery steam generator (HRSG) coils, and condensate return systems.
- Automotive & Aerospace: Exhaust systems, fuel lines, and high-temperature structural tubing requiring precise weld quality.
- Heat Exchanger Manufacturing: Coil tubes for shell-and-tube, air-cooled, and plate heat exchangers where internal weld quality governs heat transfer efficiency and long-term reliability.
Quality Certifications & Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems to ensure every coil tube product meets international standards and customer requirements:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001 — Environmental Management System
- EN 10204 — Type 3.1 material test certificates available upon request
- ASTM A213 / A269 — Compliance with standard specifications for austenitic stainless steel tubes
- ASME SA-213 / SA-249 — Heat exchanger tube specifications
- ASME BPE — Bioprocessing Equipment guidelines (for pharmaceutical applications)
- 3-A Sanitary Standards — For food and dairy industry applications
Summary of Differentiators
- Zero-Filler Self-Fusion Welding: Eliminates filler metal dilution, preserving 100% base metal composition and corrosion resistance at the weld zone.
- Rigorous Back-Side Argon Protocol: Pre-purge, continuous shielding at 8–15 L/min, and post-weld hold-off ensure oxide-free interior weld surfaces every time.
- Coil Form Supply: Enables continuous processing, reduces scrap, and provides superior dimensional consistency compared to straight-length tube.
- Visible Quality Verification: The bright, silver-white weld interior serves as an immediate, unambiguous quality indicator — no hidden defects.
- Full Traceability: Mill certifications, heat numbers, and weld inspection records provided with every shipment.
Wenzhou Jixing Metal Materials Co., Ltd. stands as a trusted supplier of precision-engineered stainless steel coil tubes, delivering products that combine manufacturing excellence with uncompromising quality standards for the most demanding industrial applications worldwide.