Stainless Steel Helical Coil Tube — Winch-Assisted Bending System
Product Code: No. 717 | Classification: Literature & Technical Learning | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
1. Product Overview
The Stainless Steel Helical Coil Tube (also referred to as a Coil Tube or Spiral Coil Tube) is a precision-engineered tubular component formed by winding a straight stainless steel pipe into a continuous helical geometry. This product category represents a critical intermediate form in the stainless steel pipe industry, bridging the gap between straight pipe stock and finished helical assemblies used in heat exchangers, reactors, and process equipment.
The technical learning document "Application of Winch in Helical Coil Tube Bending" (《卷扬机在螺旋盘管弯制中的应用》) provides a comprehensive study of the mechanical bending methodology employed in the manufacturing of helical coil tubes. The winch-assisted bending technique is a hallmark process at Wenzhou Jixing Metal Materials Co., Ltd., representing a specialized approach that combines traditional mechanical tension with controlled rotary forming to achieve precise helical geometries without compromising the metallurgical integrity of the stainless steel material.
The coil tube product line encompasses a wide range of configurations, including single-helix coils, double-helix coils, and multi-layer spiral assemblies, each tailored to specific thermal, hydraulic, and structural requirements of the end application.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 / ASTM 304 (UNS S30400): The most widely used austenitic stainless steel grade for coil tube applications. Offers excellent general corrosion resistance, formability, and weldability. Chromium (Cr) content: 18–20%; Nickel (Ni) content: 8–10.5%.
- AISI 304L / ASTM 304L (UNS S30403): Low-carbon variant (C ≤ 0.03%) specifically designed for improved resistance to intergranular corrosion during welding. Preferred for applications involving extensive welding operations.
- AISI 316 / ASTM 316 (UNS S31600): Molybdenum-bearing austenitic stainless steel with superior resistance to pitting and crevice corrosion. Molybdenum (Mo) content: 2–3%. Ideal for chemical processing and marine environments.
- AISI 316L / ASTM 316L (UNS S31603): Low-carbon variant of 316 grade, offering enhanced weldability and resistance to sensitization.
- AISI 321 / ASTM 321 (UNS S32100): Titanium-stabilized austenitic stainless steel with excellent resistance to intergranular corrosion at elevated temperatures. Suitable for high-temperature coil tube applications.
- AISI 310S / ASTM 310S (UNS S31008): High-temperature austenitic grade with exceptional oxidation resistance and thermal stability up to 1100°C (2012°F).
- Custom Alloy Grades: Including 904L, 2205 Duplex, 2507 Super Duplex, and Hastelloy variants for highly aggressive chemical environments.
2.2 Mechanical Properties (Typical for AISI 304 in Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (74.7 ksi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29.7 ksi)
- Elongation at Break: ≥ 40% (ASTM A270)
- Hardness (Brinell): ≤ 217 HB
- Density: 8.0 g/cm³
- Thermal Conductivity (20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
- Maximum Service Temperature: 870°C (1598°F) — continuous; up to 1150°C in oxidizing atmosphere
2.3 Surface Finish Options
- 2B (Cold Rolled & Annealed): Matte, non-directional finish; Ra ≤ 0.5 μm. Standard industrial finish.
- No. 4 (Brushed): Directional satin finish with fine parallel lines; Ra ≤ 0.8 μm.
- No. 8 (Mirror): Polished to a mirror-like reflective surface; Ra ≤ 0.1 μm.
- Electropolished (EP): Electrochemical polishing to achieve Ra ≤ 0.25 μm with enhanced surface cleanliness and corrosion resistance.
- Pickled & Passivated: Removal of mill scale followed by chemical passivation to restore chromium oxide passive layer.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Outside Diameter (OD) | 6.0 mm – 168.3 mm (¼" – 6") | ASTM A269 / A270 / A554 |
| Wall Thickness (WT) | 0.5 mm – 8.0 mm (0.020" – 0.315") | ASTM A269 / A270 |
| Coil Pitch (Helix Pitch) | 10 mm – 150 mm (0.39" – 5.9") | Custom / Customer Specification |
| Coil Diameter (Mean) | 100 mm – 3000 mm (3.9" – 118") | Custom / Customer Specification |
| Coil Length (Total Unwound) | 1 m – 200 m (3.3 ft – 656 ft) | Custom / Customer Specification |
| Number of Turns | 1 – 5000+ (continuous) | Custom / Customer Specification |
| OD Tolerance | ± 0.1 mm (± 0.004") | ASTM A269 |
| WT Tolerance | ± 10% of nominal | ASTM A269 |
| Pitch Tolerance | ± 0.5 mm (± 0.020") | ISO 13070 |
| Coil Diameter Tolerance | ± 1.0% of nominal | ISO 13070 |
| Roundness | ≤ 0.5% of OD | ASTM A269 |
| End Configuration | Plain, Beveled, Threaded, Flanged, or Weld Prep | ASME B1.20.1 / ASME B16.5 |
3.2 Geometric Configuration Types
| Configuration Type | Description | Typical Application |
|---|---|---|
| Single Helix Coil | Single continuous spiral winding with uniform pitch and diameter | Heat exchangers, air conditioning coils, condensers |
| Double Helix Coil | Two intertwined helical strands forming a figure-eight cross-section path | High-efficiency heat exchangers, chemical reactors |
| Multi-Layer Spiral | Multiple concentric layers of helical winding stacked vertically | Large-capacity heat exchangers, shell-and-coil assemblies |
| Conical Spiral | Helical winding with progressively changing diameter (tapered) | Specialized process equipment, separators |
| Flat Spiral (Planar) | Coil wound in a single plane with minimal vertical displacement | Plate heat exchangers, gasket sealing, sensors |
| Variable-Pitch Coil | Helical winding with non-uniform pitch for controlled flow distribution | Precision fluid distribution, specialized reactors |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Procurement & Inspection: Sourcing of certified stainless steel seamless or welded pipe stock from approved suppliers. Incoming inspection includes visual examination, dimensional verification, chemical composition analysis (OES — Optical Emission Spectroscopy), and mechanical testing.
- Material Preparation: Straightening of coiled pipe stock, cutting to required lengths, deburring of ends, and surface preparation (cleaning, pickling, passivation as required).
- Helical Coil Forming (Winch-Assisted Bending): The core forming operation utilizing a winch-driven mechanical bending system to convert straight pipe into a precise helical coil geometry.
- Post-Forming Stress Relief: Controlled annealing to relieve residual stresses introduced during the bending process, ensuring dimensional stability and restoring full mechanical properties.
- Welding & Assembly: TIG (Tungsten Inert Gas) welding of coil ends, joining to headers, manifolds, or end fittings as required by the final assembly design.
- Surface Treatment: Final surface finishing (brushing, polishing, electropolishing) and passivation treatment to ensure corrosion resistance.
- Quality Inspection & Testing: Comprehensive dimensional, visual, and non-destructive testing (NDT) to verify compliance with specifications.
- Packaging & Shipping: Protective wrapping, wooden crate packing, and dispatch with full documentation.
4.2 Winch-Assisted Helical Bending — Detailed Technical Description
The Winch-Assisted Bending Method (卷扬机弯制法) represents a specialized and highly effective technique for forming helical coil tubes from straight stainless steel pipe stock. This method, documented extensively in the technical learning literature at Wenzhou Jixing Metal Materials Co., Ltd., leverages the controlled tensile force generated by an industrial winch to achieve precise, consistent helical geometries.
4.2.1 Principle of Operation
The winch-assisted bending process operates on the following mechanical principles:
- Tensile Force Application: An industrial winch (卷扬机) applies a controlled and adjustable tensile force to one end of the straight pipe stock. The winch reel diameter and gear ratio determine the pulling force and speed.
- Rotary Mandrel Contact: The pipe is guided over a rotating mandrel or bending die of the desired coil diameter. As the winch pulls the pipe, the mandrel forces the pipe to follow a circular path, forming the helical shape.
- Pitch Control: The helical pitch is controlled by the relative linear speed of the winch pull versus the rotational speed of the mandrel. A feed mechanism (linear actuator or screw drive) advances the mandrel axially during rotation to create the helical offset.
- Continuous Forming: Unlike incremental bending methods, the winch-assisted technique allows for continuous, uninterrupted forming of long coil lengths, significantly improving production efficiency.
4.2.2 Key Process Parameters
| Parameter | Typical Range | Influence on Product |
|---|---|---|
| Winch Pulling Force | 5 kN – 80 kN (1,124 – 17,988 lbf) | Determines bending moment; insufficient force causes slippage, excessive force causes material thinning or cracking |
| Mandrel Rotation Speed | 0.5 – 5.0 RPM | Affects forming speed and surface quality; higher speeds may cause surface marking |
| Axial Feed Rate | 0.5 – 10 mm/rev | Directly determines coil pitch; must be precisely synchronized with mandrel rotation |
| Bending Temperature | Ambient (20–25°C) or Warm (300–500°C) | Warm bending reduces required force and improves formability for larger diameters or thicker walls |
| Minimum Bending Radius | ≥ 4D (4× pipe OD) for cold bending | Below this ratio, material may crack or develop excessive thinning on the inner bend surface |
| Lubrication | Food-grade or specialty lubricant applied to pipe surface | Reduces |