Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuously wound, pre-formed tubular product manufactured from high-grade austenitic stainless steel. Unlike straight-length tubing, coil tubes are produced in long, uninterrupted helical coils, eliminating the need for field welding or joint connections during installation. This design fundamentally enhances structural integrity, thermal efficiency, and leak resistance in applications where fluid containment and heat transfer performance are critical.
Coil tubes are predominantly employed in heat exchanger assemblies, including condensers, evaporators, reboilers, and shell-and-tube heat exchangers. The continuous coil geometry maximizes heat exchange surface area within a compact footprint, making it an indispensable component in industrial process engineering, HVAC&R (Heating, Ventilation, Air Conditioning & Refrigeration), petrochemical, and pharmaceutical manufacturing systems.
Wenzhou Jixing Metal Materials Co., Ltd. produces coil tubes through a specialized manual tube bending process, utilizing a dedicated manual coiling and bending apparatus (Manual Tube Bending Device) to achieve precise, uniform curvature with minimal material deformation or wall thinning.
2. Material and Properties
2.1 Base Material Grades
- SAE 304 / AISI 304 (UNS S30400): The most widely specified austenitic stainless steel for general-purpose coil tubes. Offers excellent corrosion resistance, formability, and weldability. Suitable for food-grade, chemical, and atmospheric environments.
- SAE 316 / AISI 316 (UNS S31600): Enhanced molybdenum content (2.0–3.0%) provides superior resistance to pitting and crevice corrosion in chloride-containing environments. Preferred for marine, pharmaceutical, and aggressive chemical service.
- SAE 316L (UNS S31603): Low-carbon variant of 316 (C ≤ 0.03%) to prevent sensitization during welding. Ideal for welded heat exchanger assemblies.
- SAE 321 / AISI 321 (UNS S32100): Titanium-stabilized grade with excellent resistance to intergranular corrosion at elevated temperatures (up to 870°C). Suitable for high-temperature process applications.
- SAE 347 / AISI 347 (UNS S34700): Niobium-stabilized grade offering superior high-temperature strength and creep resistance compared to 321.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property |
SAE 304 |
SAE 316 |
SAE 321 |
SAE 347 |
| Tensile Strength (MPa) |
≥ 515 |
≥ 515 |
≥ 515 |
≥ 515 |
| Yield Strength (0.2% Proof Stress, MPa) |
≥ 205 |
≥ 205 |
≥ 205 |
≥ 205 |
| Elongation (% in 50 mm) |
≥ 40 |
≥ 40 |
≥ 40 |
≥ 40 |
| Hardness (HBW) |
≤ 217 |
≤ 217 |
≤ 217 |
≤ 217 |
| Density (g/cm³) |
7.93 |
8.00 |
7.90 |
7.90 |
| Thermal Conductivity at 100°C (W/m·K) |
16.3 |
16.3 |
16.3 |
16.3 |
| Maximum Service Temperature (°C) |
870 |
870 |
900 |
900 |
2.3 Chemical Composition (wt%, Typical)
| Element |
SAE 304 |
SAE 316 |
SAE 321 |
SAE 347 |
| C (Carbon) |
≤ 0.08 |
≤ 0.08 |
≤ 0.08 |
≤ 0.08 |
| Cr (Chromium) |
18.0–20.0 |
16.0–18.0 |
17.0–19.0 |
17.0–19.0 |
| Ni (Nickel) |
8.0–10.5 |
10.0–14.0 |
9.0–12.0 |
9.0–13.0 |
| Mo (Molybdenum) |
— |
2.0–3.0 |
— |
— |
| Ti (Titanium) |
— |
— |
5×(C−0.02) to 0.70 |
— |
| Nb (Niobium) |
— |
— |
— |
10×(C−0.01) to 1.00 |
| Si (Silicon) |
≤ 1.00 |
≤ 1.00 |
≤ 1.00 |
≤ 1.00 |
| Mn (Manganese) |
≤ 2.00 |
≤ 2.00 |
≤ 2.00 |
≤ 2.00 |
| P (Phosphorus) |
≤ 0.045 |
≤ 0.045 |
≤ 0.045 |
≤ 0.045 |
| S (Sulfur) |
≤ 0.030 |
≤ 0.030 |
≤ 0.030 |
≤ 0.030 |
3. Product Specifications
3.1 Dimensional Specifications
| Parameter |
Specification Range |
Standard Reference |
| Outer Diameter (OD) |
3.18 mm – 25.40 mm (1/8" – 1") |
ASTM A213 / ASME SA-213 |
| Wall Thickness |
0.50 mm – 1.65 mm (0.020" – 0.065") |
ASTM A213 / ASME SA-213 |
| Coil Inner Diameter |
150 mm – 600 mm (6" – 24") |
Customer Specification |
| Coil Length (Continuous) |
50 m – 500 m (164 ft – 1,640 ft) |
Customer Specification |
| Bend Radius (Minimum) |
3D – 5D (3× to 5× Outer Diameter) |
ASTM A213 |
| OD Tolerance |
± 0.05 mm (± 0.002") |
ASTM A213 |
| Wall Thickness Tolerance |
± 10% of nominal |
ASTM A213 |
| Roundness Tolerance |
≤ 0.5% of OD |
ASTM A213 |
| Straightness (per 1,000 mm) |
≤ 3.0 mm |
ASTM A213 |
3.2 Surface Finish Options
| Finish Type |
Ra (μm) |
Application |
| Pickled & Passivated |
0.4 – 0.8 |
General industrial, chemical processing |
| Commercial Polished |
0.2 – 0.4 |
Food & beverage, pharmaceutical |
| Mirror Polished |
≤ 0.1 |
Decorative, high-purity applications |
| Electropolished |
0.05 – 0.1 |
Biomedical, semiconductor |
3.3 End Condition Options
- Plain Ends: Straight-cut ends without additional treatment.
- Beveled Ends: 37.5° ± 1° bevel per ASME B16.25 for butt-weld connections.
- Threaded Ends: NPT (National Pipe Taper), BSP (British Standard Pipe), or custom thread per customer drawing.
- Flanged Ends: Weld-neck or slip-on flanges per ASME B16.5.
- Pre-formed Coil Ends: Coil ends pre-bent to specified radius for direct insertion into tube sheets.
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Procurement: High-purity stainless steel seamless or welded tube stock is sourced from certified mills. Incoming material undergoes full chemical analysis (spectrometric) and mechanical property verification prior to acceptance.
- Material Inspection & Certification: Each heat lot is verified against ASTM/ASME standards. Material Test Reports (MTR) are generated and archived.
- Tube Straightening & Cutting: Raw tube coils are straightened using a hydraulic straightening machine to achieve the required straightness tolerance. Tubes are then cut to specified lengths using a precision tube saw.
- End Preparation: Ends are deburred, chamfered, or beveled according to the specified end condition. Internal and external burrs are removed to prevent fluid flow obstruction and ensure proper welding fit-up.
- Manual Coil Bending (Coiling): The straightened tube is fed into a Manual Tube Bending Device (Manual Coiling Machine) to form the helical coil shape. The bending process is executed with the following critical parameters:
- Bend Radius: Precisely controlled at 3D–5D (minimum) to prevent wall thinning and ovalization.
- Tooling: Matching bend mandrel and die sets are selected based on the tube OD and wall thickness to minimize cross-sectional deformation.
- Bending Speed: Controlled at a slow, uniform rate to ensure even material flow and prevent springback.
- Support Roller System: Multi-point support rollers maintain tube alignment throughout the bending path, preventing kinking or buckling.
- Dimensional Verification: Each coil is inspected for OD, wall thickness, coil diameter, bend radius uniformity, and overall length using calibrated measuring instruments (micrometers, calipers, coil diameter gauges).
- Pickling & Passivation: Bended coils are subjected to acid pickling (nitric/hydrofluoric acid blend) to remove oxidation scale formed during bending. Subsequent passivation treatment (citric or nitric acid) forms a protective chromium oxide layer, enhancing corrosion resistance.
- Surface Finishing (Optional): Additional polishing or electropolishing is performed per customer specification.