Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
Product Code: No. 587 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Continuous-Length Stainless Steel Tubing
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length, coiled stainless steel tubing product manufactured to precision engineering standards. Unlike cut-length seamless or welded pipes, coil tubes are produced in a helically wound configuration, enabling downstream users to cut to length on demand, thereby minimizing material waste and optimizing logistics efficiency. This product category encompasses both seamless coil tubes and longitudinally welded coil tubes, available in austenitic, ferritic, and duplex stainless steel grades.
Coil tubes are particularly valued in applications requiring high surface-to-volume ratios, such as heat exchangers, condensers, evaporators, and fan coil units (FCU), where the coiled geometry facilitates compact thermal transfer assemblies. The continuous production format also ensures uniform microstructural properties along the tube length, free from the weld discontinuities inherent in butt-welded pipe sections.
2. Material Grades & Properties
2.1 Available Grades
- Austenitic Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), AISI 321 (UNS S32100)
- Ferritic Grades: AISI 430 (UNS S43000), AISI 409 (UNS S40900)
- Super-Austenitic / Duplex Grades: 2205 (UNS S32205), 2507 (UNS S32750)
- Custom Alloys: Available upon specification for specialized corrosion or temperature environments
2.2 Mechanical Properties (Typical for Grade 316L)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ASTM A270 / EN 10217 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A270 / EN 10217 |
| Elongation (% A) | ≥ 35% | ASTM A270 / EN 10217 |
| Hardness (HV) | ≤ 210 HV | ASTM A923 |
| Operating Temperature Range | −196 °C to +870 °C | — |
| Corrosion Resistance (Pitting, PREN) | ≥ 24 (Grade 316L) | ASTM G48 |
2.3 Chemical Composition (Grade 316L — Typical)
| Element | C | Si | Mn | P | S | Cr | Ni | Mo | N |
|---|---|---|---|---|---|---|---|---|---|
| Max (%) | 0.030 | 1.00 | 2.00 | 0.045 | 0.030 | — | — | — | 0.100 |
| Range (%) | — | — | — | — | — | 16.5–18.5 | 10.0–14.0 | 2.00–3.00 | — |
3. Dimensions & Specifications
3.1 Dimensional Parameters
| Parameter | Specification Range | Tolerance Standard |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 mm – Φ 159.0 mm | ASTM A270 / EN 10217-7 |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm | ASTM A270 / EN 10217-7 |
| Coil Length (per spool) | 50 m – 200 m (standard); up to 500 m (special order) | — |
| Coil Weight | Up to 3,000 kg per coil | — |
| OD Tolerance | ± 0.05 mm (precision); ± 0.10 mm (commercial) | ASTM A270 |
| WT Tolerance | ± 0.02 mm (precision); ± 0.05 mm (commercial) | ASTM A270 |
| Surface Finish (Ra) | 0.1 μm (electropolished) – 1.6 μm (pickled & passivated) | ASTM A967 |
| End Condition | Plain cut, beveled, or capped | Per customer drawing |
3.2 Applicable Standards
- ASTM A270 — Standard Specification for Seamless and Wrought Stainless Steel Tubing for Boilers, Heat Exchangers, and Similar Heat-Transfer Applications
- ASTM A554 — Standard Specification for Seamless Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- EN 10217-7 — Non-alloy, Alloy and Stainless Steel Tubes for Mechanical and Technical Purposes — Part 7: Seamless Tubes for Heat Exchangers
- GB/T 14976 — Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- ASME BPV Section VIII — Pressure Vessel Code (when applicable)
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorously controlled multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: High-purity stainless steel ingots or continuously cast slabs from certified mills (e.g., Outokumpu, POSCO, or domestic equivalents) with full mill test certificates (MTC) per EN 10204 Type 3.1.
- HOT Rolling & Annealing: Billets are reheated to 1150–1250 °C and hot-rolled into hollow perforated tubes. Intermediate annealing in controlled-atmosphere furnaces (dew point ≤ −40 °C) prevents carbide precipitation at grain boundaries.
- Piercing & Sizing: The hot tube is pierced through a mandrel to achieve the target wall thickness and outer diameter, followed by sizing rolls for dimensional refinement.
- Pickling & Passivation: Tubes are immersed in a mixed acid bath (HNO3 + H2SO4) at 60–80 °C to remove mill scale and restore the passive chromium oxide layer (Cr2O3). Post-pickling, tubes undergo passivation per ASTM A967.
- Cold Drawing / Cold Rolling: Tubes pass through a series of progressively reducing dies to achieve final dimensions and enhanced mechanical properties. Drawing speed is controlled to prevent work-hardening beyond specification limits.
- Intermediate Annealing: At specified reduction stages, tubes are solution-annealed at 1050–1100 °C followed by controlled cooling to restore ductility for subsequent forming.
- Coiling: Finished tubes are helically wound onto precision steel coils with controlled lay angle to prevent ovality and kinking. Coil inner diameter (ID) is matched to downstream uncoiling equipment.
- Final Inspection & Packaging: Each coil undergoes hydrostatic testing (per ASTM A270, typically 2× working pressure), eddy current inspection (ECI) for internal defects, and visual surface assessment. Coils are wrapped in moisture-proof film, strapped with steel bands, and packed on wooden pallets or in export-grade crates.
5. Applications
5.1 Primary Application Domains
- HVAC & Refrigeration: Coil tubes serve as the core heat-transfer elements in fan coil units (FCU), air handling units (AHU), condensers, and evaporators. The continuous coil format enables compact serpentine coil assemblies that maximize heat exchange area within minimal envelope volume.
- Heat Exchangers & Boilers: Used in shell-and-tube heat exchangers, plate heat exchanger channels, and fire-tube boilers where corrosion resistance and thermal cycling resistance are critical.
- Chemical & Petrochemical Processing: Reactor internals, distillation column downcomers, and process piping in aggressive chemical environments (chloride-containing media, acidic process streams).
- Food & Pharmaceutical Industry: Sanitary process piping, milk processing equipment, and pharmaceutical CIP (Clean-in-Place) systems requiring electropolished surfaces (Ra ≤ 0.4 μm).
- Automotive & Aerospace: Exhaust system components, fuel delivery lines, and cryogenic fuel storage tubing.
- Energy-Saving Systems: As referenced in industry literature on fan coil unit energy efficiency, coil tubes with optimized geometry and high-thermal-conductivity alloys contribute to reducing coefficient of performance (COP) losses in building HVAC systems.
5.2 Energy Efficiency Considerations
Research on fan coil unit energy-saving measures highlights that the geometry, material thermal conductivity, and surface finish of coil tubes directly influence heat transfer efficiency. Stainless steel coil tubes with optimized wall thickness and enhanced surface roughness patterns can improve convective heat transfer coefficients by 15–25%, reducing fan power consumption and overall system energy use.
6. Quality Assurance & Certifications
6.1 Quality Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- EN 10204 3.1 — Mill Test Certificate (third-party inspection available)
- NADCAP — National Aerospace and Defense Contractors Accreditation Program (for aerospace-grade tubing)
- PED (Pressure Equipment Directive 2014/68/EU) — CE marking for pressure applications
- NSF/ANSI 61 — Drinking Water System Components (for food-grade applications)
6.2 Inspection & Testing Protocols
| Test Type | Standard | Frequency |
|---|---|---|
| Hydrostatic Pressure Test | ASTM A270 / EN 10217-7 | 100% of production |
| Eddy Current Inspection (ECI) | ASTM E309 / EN 10217-7 | 100% continuous online |
| Tensile & Hardness Testing | ASTM A923 / EN 10204 | Per heat lot |
| Chemical Analysis (OES / Spark) | ASTM E415 | Per heat lot |
| Intergranular Corrosion (IGC) Test | ASTM A276 Annex A3 / ASTM G150 | Per heat lot (low-carbon grades) |
| Pitting Corrosion (ASTM G48 Method B) | ASTM G48 | On request / qualified grades |
| Dimensional Verification (CMM / Laser) | ASTM A270 / Customer drawing | Per coil (sampled) |
7. Unique Selling Points
- Zero-Waste Coiled Format: The continuous coil configuration eliminates butt-weld joints, reducing material waste by up to 8% compared to cut-length pipe delivery, and eliminating potential leak points in pressure systems.
- Precision Dimensional Control: Cold-drawing processes achieve tolerances as tight as ± 0.02 mm on wall thickness, enabling reliable press-fit assemblies and consistent hydraulic performance in heat exchangers.
- Superior Surface Integrity: Electropolishing capability delivers Ra values as low as 0.1 μm, meeting FDA and pharmaceutical GMP requirements for sanitary applications.
- Wide Grade Selection: From standard 304/316L to super-austenitic alloys (e.g., Alloy 2507), providing solutions for the most aggressive corrosion environments.
- Energy Efficiency Optimization: Geometrically optimized coil profiles contribute to improved heat transfer coefficients in HVAC and industrial heat exchange applications, supporting energy-saving objectives in line with industry research on fan coil unit performance.
- Full Traceability: Every coil is traceable to its heat number, with complete documentation including MTC, chemical analysis, mechanical test reports, and non-destructive examination (NDE) records.
8. Packaging & Delivery
- Standard Packaging: Each coil is wrapped in VCI (Vapor Corrosion Inhibitor) film, protected with moisture-barrier inner wrapping