Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), catalog reference No. 1621, is a continuous-length tubular product supplied in coiled configuration. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is engineered for applications requiring flexible deployment, resistance to corrosion, and sustained structural integrity under thermal and mechanical loading. The coil form factor eliminates the need for butt-welded joints during installation, offering a seamless solution for fluid conveyance systems, heat exchangers, and pressure-containing assemblies.
Coiltube products occupy a critical niche in industrial piping systems where long, unbroken runs are required without intermediate supports or weld seams. The continuous geometry minimizes potential leakage points and reduces total installed weight compared to straight-length tube assemblies with welded couplings.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel conforming to recognized international standards. The primary grade options include:
- 304 (UNS S30400) — General-purpose austenitic grade with 18% Cr, 8% Ni; excellent corrosion resistance and formability.
- 316 (UNS S31600) — Molybdenum-enhanced austenitic grade with 2–3% Mo; superior resistance to pitting and crevice corrosion in chloride environments.
- 321 (UNS S32100) — Titanium-stabilized grade; enhanced resistance to intergranular corrosion at elevated temperatures (450–850 °C).
- 316L (UNS S31603) — Low-carbon variant of 316 (C ≤ 0.03%); optimized for welding applications and cryogenic service.
2.2 Mechanical Properties (Typical, Annealed Condition)
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 |
| Yield Strength (0.2% Offset) (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (% min., 50 mm gauge) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HRB max.) | 95 | 95 | 95 |
| Density (g/cm³) | 8.0 | 8.0 | 8.0 |
| Thermal Conductivity (W/m·K, 100 °C) | 16.3 | 16.3 | 16.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 |
2.3 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr₂O₃) formed on the alloy surface provides inherent resistance to atmospheric, acidic, and aqueous corrosion. The addition of molybdenum in Grade 316/316L significantly improves resistance to localized attack in chloride-bearing solutions, including seawater and industrial process fluids containing halides. The titanium stabilization in Grade 321 prevents chromium carbide precipitation at grain boundaries during sensitization-temperature exposure.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.18 mm – 159.0 mm (1/8" – 6") | ASTM A269 / ASME SA-269 |
| Wall Thickness | 0.25 mm – 6.35 mm (Schedule 5S – 80S) | ASTM A269 / EN 10217-7 |
| Coil Inner Diameter (ID) | 300 mm – 1,200 mm (adjustable per order) | Manufacturer standard |
| Coil Length | 100 m – 500 m per coil (typical) | — |
| Surface Finish | Pickled & Passivated (2B), Brushed, or Mirror (Ra ≤ 0.4 μm) | ASTM A270 / EN 10217-7 |
| End Condition | Plain cut, Beveled, Threaded, or Threaded with Fitting | ASME B1.20.1 (NPT) |
| Weld Type | Seamless or Welded (ERW / OA / AFW) | ASTM A554 / ISO 6507 |
| Heat Treatment | Solution Annealed (1050–1150 °C, water quench) | ASTM A269 |
| Temperature Range | −196 °C to +870 °C (grade-dependent) | — |
| Pressure Rating | Up to 40 bar (grade and schedule dependent) | ASME B31.3 |
| Tolerance (OD) | ± 0.05 mm (precision); ± 0.10 mm (standard) | ASTM A269 |
| Tolerance (Wall) | ± 10% of nominal thickness | ASTM A269 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Preparation: Hot-rolled stainless steel strip or hot-rolled coil is inspected for chemical composition and mechanical properties via spectroscopic analysis (OES) and tensile testing.
- Coil Slitting & Leveling: The master coil is slit to the required width using precision slitter-line equipment. Tension leveling ensures flatness and eliminates coil set.
- Forming (Tube Milling): The flat strip is fed through a series of progressive roll-forming stations (typically 12–16 passes) in a continuous tube mill. The strip is progressively curled and formed into a circular cross-section.
- Welding: For welded coil tube, the formed tube passes through a high-frequency induction (HFI) welding head or gas tungsten arc welding (GTAW/PTAW) station. Weld parameters are monitored in real time via in-line vision systems.
- Piercing & Sizing (Seamless Route): For seamless coil tube, billets are heated to 1,100–1,250 °C and pierced through a plug mandrel on a rotary piercing mill, followed by elongation, reduction, and sizing passes.
- Heat Treatment (Solution Annealing): The formed tube is solution-annealed in a continuous annealing furnace at 1,050–1,150 °C with rapid water quenching to dissolve carbides and restore full austenitic structure.
- Pickling & Passivation: Annealed tube is subjected to pickling (HNO₃/HF mixture or organic acid) to remove scale and heat-tint, followed by passivation (HNO₃ or citric acid) to restore the protective chromium oxide layer.
- Coiling & Packaging: The finished tube is coiled onto a steel coil core using a hydraulic coiler. Each coil is wrapped with VCI (Vapor Corrosion Inhibitor) paper and secured with steel strapping for shipment.
4.2 Key Process Control Points
- Weld seam quality verified by eddy current testing (ECT) and hydrostatic testing (typically 1.5× working pressure).
- Dimensional accuracy monitored via in-line laser measurement systems at the coil exit.
- Surface integrity assessed by magnetic particle inspection (MPI) for welded products.
- Chemical composition confirmed by spark OES on each heat lot.
5. Applications
5.1 Primary Application Sectors
- Pump & Piping Systems (盘管水泵): Coil tubes serve as the primary conveying element in coil-wound centrifugal pumps and submersible pump assemblies. The continuous coil geometry eliminates internal weld joints, reducing turbulence and improving hydraulic efficiency. This configuration is particularly advantageous in deep-well water extraction, chemical transfer, and slurry handling applications.
- Heat Exchangers & Boilers: Coiled stainless steel tubing is used in shell-and-coil heat exchangers, reboilers, and economizers where large surface-area-to-volume ratios are required for efficient thermal transfer.
- Food & Beverage Processing: Grade 316L coil tube is extensively used in sanitary piping systems (CIP-compatible) for dairy, beverage, and pharmaceutical processing lines where smooth, non-reactive surfaces are mandated.
- Chemical & Petrochemical Industry: Resistant to aggressive process chemicals, coil tube is deployed in acid storage, chemical dosing lines, and process fluid transfer where corrosion resistance is paramount.
- Marine & Offshore: Molybdenum-bearing grades (316/316L) provide reliable service in seawater cooling systems, ballast water circuits, and offshore platform piping.
- Automotive & Exhaust Systems: Grade 321 coil tube is used in exhaust manifolds and catalytic converter substrates, leveraging its resistance to high-temperature intergranular corrosion.
- Medical & Laboratory Equipment: Ultra-clean coil tubing (electropolished, Ra ≤ 0.25 μm) is used in fluid delivery systems for medical devices, chromatography, and analytical instrumentation.
5.2 Coil Pump (Coiltube Pump) — Special Application Note
The coil tube product is integral to the design of coil-wound centrifugal pumps (盘管水泵). In this configuration, the stainless steel coil tube is wound into a helical spiral around a central core, forming the impeller or volute of the pump. Key advantages of this design include:
- Elimination of internal weld seams, resulting in a smooth flow path with minimal turbulence and pressure drop.
- Enhanced resistance to cavitation due to uniform internal surface finish.
- Compact geometry enabling higher NPSH (Net Positive Suction Head) performance.
- Simplified maintenance — the entire coil assembly can be removed and replaced as a single unit.
6. Quality Certifications & Compliance
6.1 International Standards
| Standard | Description | Applicability |
|---|---|---|
| ASTM A269 / ASME SA-269 | Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubes for High-Temperature Service | Material & testing |
| ASTM A554 | Standard Specification for Small-Automatic Welded, Cold-Drawn, Seamless, and Heavy-Walled Austenitic Stainless Steel Tubes | Welded tube manufacturing |
| EN 10217-7 | Non-ferrous metal tubes for pressure purposes — Technical delivery conditions — Austenitic stainless steel tubes | European market compliance |
| ISO 6507-1 | Metallic materials — Vickers hardness test | Hardness verification |
| GB/T 14976 | Seamless stainless steel tubes for fluid transport (Chinese National Standard) | Domestic market compliance |
| GB/T 12771 | Welded stainless steel tubes for fluid transport | Domestic market compliance |
| ASME BPE | BioPharmaceutical Equipment & Systems (for sanitary-grade applications) | Pharmaceutical/food grade |
| 3-A Sanitary Standards | International Sanitary Construction Code | Food & dairy processing |
6.2 Quality Management System Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing and supply.
- ISO 14001:2015 — Environmental Management System compliance.
- ISO 45001:2018 — Occupational Health & Safety Management System.
- NACE MR0175 / ISO 15156 — Compliance for sour service (H₂S-containing environments) where applicable.
- PED 2014/68/EU — Pressure Equipment Directive compliance for pressure-containing applications in the European Economic Area.
6.3 Inspection & Testing Protocol
- Chemical Analysis: Spark OES on each heat lot; confirmed against ASTM/EN/GB chemical composition limits.
- Mechanical Testing: Tensile test (ASTM A370), hardness test (ASTM E92/E18), and bend test (ASTM A999) on representative samples per heat.
- Dimensional Inspection: Full-length OD and wall thickness measurement via in-line laser gauging; end-of-coil dimensional verification.
- Non-Destructive Testing (NDT): Eddy current testing (ASTM E727) for weld seam integrity; hydrostatic pressure test (ASTM A269 §8.5) at 1.5× maximum working pressure.
- Surface & Microstructure Examination: Grain size verification (ASTM E112), intergranular corrosion test (ASTM A923 Practice A) for stabilized grades, and pitting resistance assessment (ASTM G48