Stainless Steel Coil Tube (Helical Coil Pipe) — Model No. 1380
Product Overview
The Stainless Steel Coil Tube (Helical Coil Pipe), catalogued under product code 1380 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product formed by winding seamless stainless steel pipe into a continuous helical spiral configuration. Unlike conventional straight pipe segments, coil tubes are manufactured using specialized bending processes on standard pipe-bending machinery, enabling the production of consistent, high-tolerance helical geometries suitable for demanding industrial applications. This product category falls under advanced tubular fabrication literature and represents a significant advancement in coil-form manufacturing techniques.
Coil tubes are distinguished by their continuous spiral geometry, which provides superior heat transfer efficiency, compact volumetric footprint, and enhanced mechanical resilience compared to U-bend or hairpin tube arrangements. The manufacturing methodology documented under this product code emphasizes the adaptation of ordinary (conventional) pipe-bending machines to produce helical coil tubes — a process that reduces capital equipment investment while maintaining dimensional accuracy and structural integrity.
Material & Properties
Stainless steel coil tubes are predominantly manufactured from austenitic stainless steel grades, which offer excellent corrosion resistance, high-temperature strength, and superior formability — essential characteristics for the helical bending process. The following table summarizes the key material grades and their corresponding mechanical and physical properties:
| Property | 304 / 0Cr18Ni9 | 316L / 00Cr17Ni14Mo2 | 321 / 0Cr18Ni10Ti | 310S / 0Cr25Ni20 |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥520 | ≥485 | ≥520 | ≥520 |
| Yield Strength (MPa) | ≥205 | ≥170 | ≥205 | ≥205 |
| Elongation (%) | ≥40 | ≥40 | ≥40 | ≥40 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
| Corrosion Resistance | Good (general) | Excellent (chloride/pitting) | Good (intergranular) | Outstanding (oxidation) |
| Typical Density (g/cm³) | 8.0 | 8.0 | 8.0 | 8.0 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 16.3 | 16.3 | 16.3 |
Key Material Characteristics
- Formability: Austenitic stainless steels exhibit high ductility, enabling the pipe to be bent into tight helical radii without cracking or excessive thinning at the outer bend.
- Weldability: Low carbon variants (e.g., 316L) provide superior weldability, minimizing sensitization and intergranular corrosion risks at welded joints.
- Cryogenic Performance: Retains full mechanical properties at temperatures as low as −196°C (LN₂), making coil tubes suitable for cryogenic process applications.
- Non-magnetic Properties: Austenitic grades remain essentially non-magnetic in the annealed condition, critical for instrumented and electromagnetic applications.
Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ3 mm – Φ108 mm |
| Wall Thickness | 0.5 mm – 8.0 mm |
| Coil Diameter (Helix Diameter) | 100 mm – 3,000 mm |
| Pitch (Helical Spacing) | 5 mm – 200 mm (customizable) |
| Number of Turns | 2 – 5,000+ (application-dependent) |
| Minimum Bend Radius | ≥ 1.5 × OD (with proper tooling) |
| Tube Length (Pre-Coil) | Custom (typically 6,000 mm – 12,000 mm seamless pipe stock) |
| Surface Finish | Milled, Pickled, Polished (Ra ≤ 0.8 μm), or Passivated |
| End Condition | Plain, Beveled (37.5°), Threaded, or Flanged |
| Applicable Standards | ASTM A269 / A213, ASME SA-213 / SA-269, GB/T 12771, EN 10217-7 |
| Packaging | Wooden crate, export-grade carton, or custom protective wrapping |
Manufacturing Process
The production of stainless steel helical coil tubes on ordinary (conventional) pipe-bending machines represents a technically sophisticated adaptation of standard bending equipment. The process is documented as a specialized fabrication methodology and proceeds through the following sequential stages:
1. Raw Material Inspection and Selection
Seamless stainless steel tubes conforming to ASTM A269 (welded) or ASTM A213 (seamless) specifications are received and subjected to incoming quality control. Verification includes chemical composition analysis (per ASTM E415), dimensional measurement, surface inspection, and hydrostatic testing. Only material meeting full specification requirements proceeds to the forming stage.
2. Pre-Bending Preparation
- End Cleaning: Tube ends are deburred, chamfered, and cleaned to remove mill scale, oils, and contaminants that could interfere with the bending process or subsequent welding.
- Dimensional Verification: Pre-bend OD, wall thickness, and straightness are confirmed against the engineering drawing using calibrated micrometers and straightness gauges.
- Material Conditioning: Cold-worked tubes may undergo a stress-relief annealing cycle (typically 1050°C ± 15°C, followed by water quench) to restore full ductility prior to helical forming.
3. Helical Coiling on Ordinary Pipe-Bending Machine
This is the critical and most technically demanding step. The adaptation of an ordinary pipe-bending machine for helical coil production involves the following sub-processes:
- Tooling Configuration: The standard bending die set is supplemented with a helical guide mechanism — a rotating mandrel or rotary fixture that advances the tube axially in precise synchronization with the angular rotation of the bend head. This converts the conventional arc-bending motion into a continuous helical winding path.
- Pitch Control: The axial feed rate of the tube relative to the angular velocity of the bending head determines the helical pitch. Precision control of this ratio (typically governed by a mechanical or servo-driven feed mechanism) ensures uniform spacing between adjacent turns.
- Bend Radius Consistency: The die radius must be selected to accommodate the target helix diameter while maintaining a minimum bend radius of ≥ 1.5 × OD to prevent ovality distortion exceeding 5% and wall thinning at the outer fiber exceeding 15%.
- Progressive Winding: The tube is wound continuously over multiple turns. For large coil diameters or high-turn-count applications, the process may require multi-stage winding with intermediate stress-relief annealing to prevent accumulated residual stresses.
4. Post-Coiling Heat Treatment (if required)
Depending on the application and grade, the formed coil tube may undergo a solution annealing treatment to:
- Eliminate work-hardening effects from the cold bending process
- Restore full austenitic microstructure
- Relieve residual bending stresses that could lead to dimensional springback or stress-corrosion cracking (SCC) in service
Typical annealing parameters: 1040°C – 1120°C, held 15–30 minutes, followed by controlled cooling (air cool or furnace cool per specification).
5. Surface Treatment and Passivation
- Pickling: Immersion in a mixed acid solution (HNO₃ + HF) to remove oxide scale formed during heat treatment.
- Passivation: Treatment with 20–30% nitric acid or citric acid solution to enrich the surface chromium oxide layer, enhancing corrosion resistance.
- Polishing (optional): Mechanical or chemical polishing to achieve specified surface roughness (Ra ≤ 0.8 μm for sanitary applications).
6. Quality Inspection and Testing
- Dimensional Inspection: Helix diameter, pitch uniformity, OD, wall thickness, and total turn count verified against engineering drawings.
- Ovality Measurement: Cross-sectional roundness confirmed at multiple points along the coil (target: ≤ 5% ovality).
- Wall Thickness Measurement: Ultrasonic or micrometer measurement at bend apexes to confirm minimum wall thickness compliance.
- Visual Inspection: Surface examination for cracks, wrinkles, kinks, or deformation anomalies.
- Hydrostatic/Pneumatic Testing: Pressure testing at 1.5–2.0 × design pressure to verify leak-tightness and structural integrity.
- Spectroscopic Analysis: Spot-check of chemical composition via XRF or optical emission spectrometry.
Applications
Stainless steel coil tubes find extensive application across multiple industrial sectors where compact heat exchange, chemical resistance, and mechanical durability are paramount:
Heat Exchanger & Thermal Management
- Shell-and-Tube Heat Exchangers: Spiral coil tubes serve as the primary heat transfer surface in condensers, evaporators, and reboilers. The helical geometry increases surface area per unit volume, improving thermal efficiency.
- Air Cooled Heat Exchangers (ACHE): Coil tubes wound into serpentine or spiral configurations for gas-to-gas heat exchange in petrochemical and power generation facilities.
- Plate-Fin and Microchannel Exchangers: Precision coil tubes used in compact refrigeration and HVAC systems.
Chemical & Pharmaceutical Processing
- Reactor Cooling/Heating Jackets: Coil tubes embedded in reactor walls for precise temperature control of exothermic/endothermic reactions.
- Sanitary Heat Exchangers: 316L coil tubes with polished internal surfaces (Ra ≤ 0.5 μm) for dairy, beverage, and pharmaceutical processing under GMP (Good Manufacturing Practice) conditions.
- Distillation Columns: Internal coil tubes for reflux condensation and vapor management.
Oil, Gas & Petrochemical
- Subsea Heat Exchangers: 316L and duplex stainless steel coil tubes for subsea process applications requiring resistance to chloride-induced SCC.
- Upstream Separators: Spiral coil tubes for gas-liquid separation and cooling in wellhead equipment.
- Refinery Units: Condensers and coolers in atmospheric and vacuum distillation units.
Power Generation
- Boiler Economizers and Superheaters: 321 and 310S coil tubes for high-temperature flue gas heat recovery.
- Steam Turbine Bleed Coolers: Coil tubes for extraction steam cooling in condensing power plants.
Specialty Applications
- Cryogenic Systems: Stainless steel coil tubes in LNG (Liquefied Natural Gas) processing and liquid nitrogen/oxygen distribution systems.
- Food Processing: Sanitary-grade coil tubes for CIP (Clean-In-Place) compatible heat exchangers in food and beverage production.
- Automotive Exhaust Systems: Compact coil tubes for catalytic converter heat management and exhaust gas recirculation (EGR) cooling.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification framework ensuring full compliance with international and national standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — certified for design, manufacture, and supply of stainless steel tubular products |
| ISO 14001:2015 | Environmental Management System — ensuring environmentally responsible manufacturing practices |
| ASME SA-213 / SA-269 | American Society of Mechanical Engineers standards for seamless and welded austenitic stainless steel tubing |
| ASTM A213 / A269 | American Society for Testing and Materials specifications for seamless and welded stainless steel tube |
| EN 10217-7 | European standard for austenitic stainless steel seamless and welded tube for pressure applications |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes for general application |
| TÜV / SGS Inspection | Third-party quality inspection and material verification available upon request |
| Material Traceability | Full mill certification (EN 10204 3.1) with heat number traceability for each coil tube lot |
Unique Selling Points
- Cost-Efficient Manufacturing: The proprietary methodology enables helical coil tube production on ordinary pipe-bending machines, significantly reducing capital equipment costs compared to dedicated coil-winding machinery while maintaining dimensional accuracy.
- Customizable Geometry: Full customization of helix diameter, pitch, turn count, and end conditions to meet specific engineering requirements — from micro-coils (Φ3 mm OD) to large-diameter industrial coils (Φ108 mm OD).
- Multi-Grade Material Availability: Comprehensive range of austenitic stainless steel grades (304, 316L, 321, 310S, and specialty alloys) to address diverse corrosion, temperature, and mechanical performance requirements.
- Superior Thermal Efficiency: The helical coil geometry maximizes heat transfer surface area per unit volume, delivering 30–50% higher thermal performance compared to equivalent straight-tube configurations in compact heat exchanger designs.
- Full Traceability & Certification: Every production lot is accompanied by mill test certificates, chemical analysis reports, and dimensional inspection records, ensuring complete material traceability and regulatory compliance.
- Technical Expertise: The documented process knowledge — particularly the adaptation of conventional bending equipment for helical forming — reflects deep