Stainless Steel Coil Tube — TIG Autogenous Welding (No-Filler-Wire Process)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Category: Welded Stainless Steel Coil Tube | Forming Process: TIG Autogenous Welding (Tungsten Inert Gas)
1. Product Overview
The TIG Autogenous Welding Coil Tube is a precision-engineered stainless steel welded tube produced through a specialized no-filler-wire (self-welding) TIG process. In this method, the weld metal is derived exclusively from the base material of the coil strip, eliminating the introduction of exogenous filler alloys. This approach yields a weld seam of exceptionally high metallurgical purity, with minimal risk of compositional deviation, inclusion formation, or intermetallic precipitation along the weld zone.
As a coil tube (盘管 / Coiltube), the product is supplied in continuous coiled form, enabling downstream processors to achieve high utilization rates, minimize scrap loss, and streamline automated cutting and forming operations. The TIG autogenous welding process is recognized as the industry-standard welding methodology for thin-wall stainless steel tubes, particularly where internal surface integrity, corrosion resistance, and aesthetic weld quality are paramount.
2. Material & Properties
2.1 Base Material Grades
- 304 / 304L (UNS S30400 / S30403) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- 316 / 316L (UNS S31600 / S31603) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chlorinated environments.
- 321 (UNS S32100) — Titanium-stabilized austenitic grade suitable for elevated-temperature service.
- 310S (UNS S31008) — High-temperature austenitic grade for sustained operation above 900 °C.
- 443 / 444 — Ferritic stainless grades for cost-sensitive applications.
- 2205 Duplex (UNS S31803) — Dual-phase austenitic-ferritic grade combining high strength with outstanding chloride stress corrosion cracking (CSCC) resistance.
- 904L (UNS N08904) — High-alloy austenitic grade for aggressive chemical processing environments.
2.2 Key Metallurgical Properties
- Weld Purity: The autogenous (no-filler-wire) process ensures that the weld metal composition matches the base metal with negligible dilution variation, preserving the specified chromium (Cr), nickel (Ni), and alloying element ratios.
- Internal Surface Finish: The weld seam on the inner wall is exceptionally smooth and flat, typically achieving an internal surface roughness (Ra) of ≤ 0.8 μm after post-weld processing, critical for sanitary and pharmaceutical applications.
- Heat-Affected Zone (HAZ): The controlled heat input of TIG welding minimizes the HAZ width, reducing the risk of sensitization (chromium carbide precipitation) and preserving local corrosion resistance.
- Microstructure: The weld zone maintains a fine-grained, homogeneous microstructure with controlled grain boundary character, contributing to fatigue resistance and long-term durability.
3. Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 1.5 mm – 150 mm (custom sizes available upon request) |
| Wall Thickness (WT) | 0.05 mm – 3.0 mm (optimized for thin-wall applications) |
| OD Tolerance | ±0.05 mm (precision grades); ±0.10 mm (standard grades) |
| WT Tolerance | ±10% (standard); ±5% (precision grades) |
| Welding Process | TIG Autogenous (No Filler Wire / Self-Welding) |
| Shielding Gas | Pure Argon (Ar, ≥ 99.99%); Helium-Ar mixtures for thick-section variants |
| Weld Seam Type | Continuous longitudinal single-pass weld |
| Internal Surface Roughness | Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (electropolished / passivated) |
| External Surface Finish | No. 4 Brushed, 2B, Mirror (8K), Matte, or custom finishes |
| Supply Form | Coil (盘管 / Coiltube) — continuous length |
| Applicable Standards | ASTM A269, ASTM A554, EN 10217-7, EN 10216-5, GB/T 12771, GB/T 14976 |
| Heat Treatment | Solution Annealing (1050–1150 °C) + Rapid Quench; Pickling & Passivation available |
| Coil Weight | Up to 2,000 kg per coil (standard); custom weights available |
4. Manufacturing Process
4.1 Process Flow
- Coil Strip Uncoiling & Feeding: Precision cold-rolled stainless steel strip coil is fed through a high-speed servo-controlled uncoiling system, maintaining consistent strip tension and flatness.
- Edge Beveling (V-Notching): Strip edges are precision-notched to form a V-groove joint, ensuring uniform gap width and root penetration for the autogenous weld. Bevel angles and gap dimensions are optimized based on wall thickness.
- Forming & Shaping: The notched strip is passed through a series of progressively reducing rollers and forming dies to achieve the target circular cross-section. Multi-roller forming stations ensure dimensional accuracy and roundness.
- TIG Autogenous Welding: The formed tube is welded using a high-frequency (HF) or DC TIG arc under a protective atmosphere of pure argon. No filler wire is introduced; the arc melts the base metal at the joint to achieve full-penetration fusion. This is the defining characteristic of the process — the weld metal is 100% derived from the base strip, ensuring compositional fidelity.
- Post-Weld Sizing & Straightening: The welded tube passes through sizing rolls and straightening stations to achieve final OD and roundness tolerances.
- Heat Treatment (if applicable): Solution annealing is performed in a continuous furnace (typically 1050–1150 °C with rapid air or water quench) to dissolve carbides and restore full austenitic microstructure and corrosion resistance.
- Pickling & Passivation: The tube is treated with nitric-hydrofluoric acid solutions to remove heat tint, oxide scales, and residual contaminants, followed by passivation to establish a stable chromium oxide surface film.
- Internal & External Surface Finishing: Mechanical or chemical polishing (electropolishing) may be applied to achieve the required internal surface roughness specifications.
- Quality Inspection & Testing: Comprehensive dimensional, mechanical, chemical, and non-destructive testing (NDT) is performed (see Section 6).
- Coiling & Packaging: Finished tube is coiled onto precision-wound coil cores, wrapped in protective film, and packaged for shipment.
4.2 Why TIG Autogenous Welding for Thin-Wall Tubes?
- Zero Filler Contamination: By eliminating filler wire, the process avoids compositional mismatches, impurity introduction, and the risk of brittle phase formation in the weld zone.
- Superior Internal Wall Quality: The absence of filler metal means no internal weld bead protrusion, resulting in a smooth, laminar internal surface — critical for fluid flow, hygiene, and inspection.
- Precise Heat Input Control: TIG welding allows fine adjustment of arc current, travel speed, and gas flow, enabling minimal thermal distortion in thin-wall geometries.
- Consistent Weld Geometry: The autogenous process produces a uniform, symmetric weld seam with predictable dilution ratios, essential for repeatable quality in continuous production.
- Full Penetration Achievable: With proper bevel geometry and parameter optimization, full-penetration welds are consistently achieved even at wall thicknesses as low as 0.05 mm.
5. Applications
5.1 Food & Beverage Industry
Sanitary-grade coil tubes for dairy processing, brewing, juice production, and food-grade fluid conveying. The smooth internal weld seam prevents product accumulation and facilitates automated CIP (Clean-In-Place) procedures.
5.2 Pharmaceutical & Biotechnology
Process tubing for sterile fluid transfer, bioreactor connections, and pharmaceutical manufacturing lines requiring compliance with FDA 21 CFR Part 117 and EU GMP standards.
5.3 Chemical Processing
Corrosion-resistant tubing for aggressive chemical environments including sulfuric acid, hydrochloric acid, and organic solvent handling. Grades such as 316L, 904L, and 2205 Duplex are particularly suited.
5.4 Oil & Gas
Instrument tubing, control lines, and instrumentation connections in upstream and downstream petroleum facilities. The high weld integrity and corrosion resistance ensure long service life in demanding environments.
5.5 Medical Devices
Endoscope tubing, catheter manufacturing, and medical instrument components where biocompatibility (ISO 10993), internal surface smoothness, and weld purity are non-negotiable.
5.6 Automotive & Aerospace
Exhaust system tubing, fuel lines, hydraulic lines, and structural tubing where dimensional precision, fatigue resistance, and weight optimization are critical.
5.7 Architectural & Decorative
Ornamental tubing for handrails, balustrades, furniture components, and architectural features. Mirror-finish (8K) TIG-welded coil tubes offer a seamless, weld-free aesthetic.
5.8 Electronics & Semiconductor
Precision tubing for semiconductor equipment gas lines, vacuum systems, and ultra-pure fluid delivery where surface cleanliness and material purity are paramount.
6. Quality Certifications & Testing
6.1 Quality Management System
- ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification.
- ISO 45001:2018 — Occupational Health & Safety Management System.
6.2 Product-Specific Certifications
- EN 10204 3.1 / 3.2 — European Certificate of Conformity (inspection body certified for 3.2).
- NACE MR0175 / ISO 15156 — Compliance for sour service (H₂S-containing environments).
- ASME BPV Section VIII — Pressure vessel and piping component compliance (where applicable).
- NSF/ANSI 61 — Drinking water system components certification.
- 3-A Sanitary Standards — Food and dairy processing equipment certification.
6.3 Inspection & Testing Methods
| Test Category | Method | Standard |
|---|---|---|
| Chemical Composition | Spectroscopic Analysis (OES / XRF) | ASTM E415 / ASTM E1019 |
| Mechanical Properties | Tensile Test, Hardness Test | ASTM E8 / ASTM E92 |
| Weld Integrity (NDT) | Eddy Current Testing (ECT) / Ultrasonic Testing (UT) | ASTM E309 / ASTM E164 |
| Hydrostatic Pressure Test | Internal Pressure Testing (100% inline) | ASTM A269 / EN 10217-7 |
| Corrosion Resistance | Potentiodynamic Polarization, Salt Spray (ASTM B117) | ASTM G5 / ASTM B117 |
| Dimensional Inspection | Laser OD Measurement, Ultrasonic WT Gauge, Roundness Check | ISO 6508 / ASTM A554 |
| Surface Roughness | Contact / Non-Contact Roughness Profiling | ISO 4287 / ASTM B466 |
| Intergranular Corrosion | ASTM A269 Practice (Cupronitric / Ferric Sulfate) | ASTM A269 / ASTM A923 |
7. Unique Selling Points
"No filler wire. No compromise. Pure metallurgy."
- 100% Autogenous Weld Purity: The exclusive use of base metal as weld material