Thin-Wall Internal Threaded Stainless Steel Coil Tube (Coil Tube)
1. Product Overview
The Thin-Wall Internal Threaded Stainless Steel Coil Tube is an advanced precision-engineered product developed through rigorous research and manufacturing optimization. This coil tube is supplied in continuous coil form (盘管, Coiltube), enabling high-efficiency downstream processing with minimal material waste. The product integrates seamless tubular integrity with precision internal threading, achieving superior fluid flow characteristics, enhanced mechanical strength, and extended service life in demanding industrial environments.
Wenzhou Jixing Metal Materials Co., Ltd. has dedicated extensive R&D resources to the research and production of thin-wall internal threaded seamless coil tubes, establishing industry-leading manufacturing capabilities that combine metallurgical expertise with precision cold-forming technology.
2. Material & Properties
2.1 Base Material Composition
- Primary Grades: SUS304, SUS316, SUS316L (AISI 304, 316, 316L equivalent)
- Chromium Content (Cr): 18.0% – 20.0% — provides exceptional corrosion resistance
- Nickel Content (Ni): 8.0% – 13.0% — enhances austenitic stability and ductility
- Molybdenum Content (Mo): 2.0% – 3.0% (for 316/316L grades) — imparts superior pitting and crevice corrosion resistance
- Carbon Content (C): ≤ 0.08% (304) / ≤ 0.03% (316L) — minimizes sensitization and intergranular corrosion risk
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (annealed condition)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation (A₅₀): ≥ 35% — ensures excellent formability for thread rolling
- Hardness (HB): 120 – 180 (annealed state)
- Thin-Wall Advantage: Reduced wall thickness (typically 0.3 – 1.2 mm) provides favorable strength-to-weight ratio while maintaining structural integrity
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, aqueous solutions, and mild chemical environments
- Superior resistance to pitting and crevice corrosion (316/316L grades)
- Non-magnetic in annealed condition (austenitic microstructure)
- Maintains corrosion performance after cold working and thread forming
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ38.1 mm (customizable) | GB/T 14976, ASTM A554 |
| Wall Thickness | 0.30 mm – 1.20 mm (thin-wall configuration) | GB/T 14976 |
| Internal Thread Pitch | 0.5 mm – 1.5 mm (selectable) | ISO 286-1, GB/T 227 |
| Thread Depth | 0.15 mm – 0.60 mm | ISO 286-1 |
| Coil Inner Diameter (ID) | Φ300 mm – Φ500 mm | Manufacturer standard |
| Coil Length per Spool | 100 m – 300 m (continuous) | — |
| Surface Finish | 2B / BA (Bright Annealed) / Polished | ASTM A480 |
| Dimensional Tolerance | ±0.05 mm (OD), ±0.02 mm (wall thickness) | GB/T 14976 |
| Temperature Range | −196°C to +870°C | — |
| Maximum Working Pressure | Up to 4.0 MPa (grade-dependent) | ASME B31.3 |
| Helix Angle (Coil) | 2° – 5° (controlled winding) | — |
| Helix Diameter | 150 mm – 400 mm (for coil spring configurations) | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel billets or strip are procured with certified chemical composition, undergoing incoming spectral analysis (OES) for verification.
- Hot Rolling & Pickling: Billets are hot-rolled into seamless tube blanks, followed by acid pickling and descaling to remove oxide scale and surface impurities.
- Cold Drawing (Seamless Tube Forming): The seamless tube blanks undergo multi-pass cold drawing through precision tungsten carbide dies to achieve the target thin-wall dimensions with tight tolerances.
- Intermediate Annealing: Periodic solution annealing (1050°C – 1100°C) is performed to relieve cold-work hardening, restore ductility, and maintain austenitic microstructure.
- Coil Winding (Coiltube Forming): The drawn seamless tube is wound into a continuous coil form using a precision coil winding machine with controlled helix angle and tension parameters.
- Internal Thread Rolling (Key Innovation): A specialized internal thread rolling process is applied to the thin-wall coil tube. This involves:
- Use of precision-machined thread rolling plugs (punches) with controlled deformation parameters
- Multi-stage progressive thread forming to prevent wall thinning beyond acceptable limits
- Real-time monitoring of thread depth, pitch accuracy, and dimensional consistency
- Optimized lubrication and cooling to manage friction heat during cold deformation
- Final Annealing & Pickling: Stress-relief annealing (850°C – 900°C) eliminates residual stresses introduced during thread rolling, followed by final pickling and passivation treatment.
- Coil Re-winding & Packaging: The finished threaded coil tube is re-wound onto protective spools with moisture barrier packaging for shipment.
4.2 Key Manufacturing Challenges & Solutions
| Challenge | Solution |
|---|---|
| Wall thinning during internal thread rolling on thin-walled tube | Progressive multi-stage rolling with controlled deformation ratios; finite element analysis (FEA) optimization of thread geometry |
| Maintaining dimensional accuracy in continuous coil form | Online laser diameter measurement with closed-loop control feedback |
| Preventing surface defects during cold working | Precision die polishing, controlled lubrication, and inter-pass inspection |
| Coil spring-back and shape stability | Optimized winding tension profile and post-forming stabilization annealing |
| Thread quality uniformity over long coil lengths | Automated thread gauging at fixed intervals; statistical process control (SPC) monitoring |
5. Applications
- Heat Exchanger Coils: Internal threading significantly increases the effective heat transfer surface area (up to 30%–50% enhancement), making these coils ideal for compact heat exchanger designs in HVAC, refrigeration, and industrial process heating/cooling systems.
- Refrigeration & Air Conditioning: Evaporator and condenser coils requiring high thermal efficiency with minimal refrigerant charge.
- Automotive Industry: Radiator cores, intercoolers, and transmission oil coolers where weight reduction and thermal performance are critical.
- Chemical Processing: Corrosion-resistant coil assemblies for heat transfer in aggressive chemical environments.
- Food & Pharmaceutical Industry: Sanitary-grade heat exchange coils meeting hygienic design standards (CIP/SIP compatible).
- Power Generation: Condenser tubes and economizer coils in power plant auxiliary systems.
- Oil & Gas: Downhole heating coils and subsea heat exchanger components.
6. Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality
- ISO 14001:2015 — Environmental Management System certification
- EN 10204 3.1 — Third-party material certification with full traceability
- ASME BPV Code — Compliance for pressure vessel and piping applications
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- ASTM A554 — Standard specification for austenitic stainless steel tube
- EN 10217-7 — European standard for cold-drawn seamless stainless steel tubes
- Mill Test Reports (MTR): Provided with every batch, including chemical analysis, mechanical test results, dimensional verification, and NDT reports
- Non-Destructive Testing (NDT): 100% eddy current inspection (ECI) for wall integrity; ultrasonic testing (UT) for internal defects
- Intergranular Corrosion Testing: ASTM A262 Practice E (oxalic acid test) or Practice F (ASTM A955) for sensitization verification
7. Unique Selling Points
Industry-First Thin-Wall Internal Threaded Coil Technology: Wenzhou Jixing Metal Materials Co., Ltd. has pioneered the integration of precision internal threading into thin-wall seamless stainless steel coil tubes — a technology that was previously limited to thicker-walled straight tubes. This breakthrough enables:
- 30%–50% Heat Transfer Enhancement: Internal thread geometry disrupts the boundary layer, dramatically increasing convective heat transfer coefficients without requiring larger tube diameters or additional surface treatments.
- Continuous Coil Supply: Unlike traditional straight tubes, coil form eliminates butt-weld joints, reducing leak points and improving overall system reliability.
- Weight Reduction: Thin-wall construction combined with enhanced heat transfer performance enables 20%–35% weight reduction compared to conventional smooth-wall coils of equivalent thermal capacity.
- Cost Efficiency: Continuous coil processing reduces material waste, minimizes fabrication labor, and accelerates production throughput in downstream coil winding operations.
- Design Flexibility: Customizable thread pitch, depth, and helix parameters allow optimization for specific fluid types, flow velocities, and thermal loads.
- Extended Service Life: The combination of austenitic stainless steel corrosion resistance and stress-relieved thread geometry ensures reliable performance over extended operational cycles.
8. Conclusion
The Thin-Wall Internal Threaded Stainless Steel Coil Tube represents a significant advancement in precision tubing technology, combining the corrosion resistance and formability of austenitic stainless steel with the thermal performance enhancement of internal thread geometry. Through rigorous research, process optimization, and quality control, Wenzhou Jixing Metal Materials Co., Ltd. delivers a product that meets the most demanding requirements of modern heat transfer applications while maintaining cost-effectiveness and dimensional precision.