Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length, cold-formed tubular product supplied in coiled configuration, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for applications requiring high corrosion resistance, mechanical integrity, and dimensional consistency in HVAC (Heating, Ventilation, and Air Conditioning), fluid conveyance, and structural systems. The coil delivery format offers logistical efficiency, reduced material waste, and seamless integration into downstream fabrication processes such as bending, cutting, and welding.
This specification draws upon industry-standard failure analysis methodologies — particularly those documented in the study "Analysis of Leak Causes in Q215 Fan Coil Pipe" — to define critical quality parameters that prevent the leakage and degradation issues commonly observed in lower-grade tubular products used in fan coil units (FCUs) and air handling systems.
2. Material & Properties
2.1 Material Grades
- Primary Grades: SUS304 (AISI 304), SUS316 (AISI 316), SUS304L, SUS316L
- Equivalent Standards: GB/T 12771, ASTM A554/A554M, EN 10216-5
- Alternative Grades Available: SUS430, SUS321, SUS310S
2.2 Chemical Composition (Typical — SUS304)
| Element | Carbon (C) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Silicon (Si) | Chromium (Cr) | Nickel (Ni) | Iron (Fe) |
|---|---|---|---|---|---|---|---|---|
| Max/Min (%) | 0.08 / — | 2.00 / — | 0.045 / — | 0.030 / — | 1.00 / — | 18.0–20.0 | 8.0–10.5 | Balance |
2.3 Mechanical Properties
| Property | Specification (Annealed Condition) |
|---|---|
| Tensile Strength (Ultimate) | ≥ 520 MPa (75,400 psi) |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,730 psi) |
| Elongation (in 50 mm / 2 in.) | ≥ 40% |
| Hardness (Brinell) | ≤ 217 HB |
| Density | 7.93 g/cm³ |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C |
2.4 Key Performance Characteristics
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, freshwater, and moderate chemical environments; SUS316 grade provides superior resistance to chlorides and marine environments.
- Weldability: Fully weldable using TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and resistance welding methods without pre-heat or post-heat treatment.
- Formability: High ductility permits cold bending to radii as small as 2D (diameter) without cracking or wall thinning beyond acceptable limits.
- Hygienic Properties: Smooth inner surface finish (Ra ≤ 0.5 μm available) prevents bacterial adhesion, suitable for food-grade and pharmaceutical applications.
- Temperature Range: Operational from cryogenic temperatures (−196°C) to 870°C (SUS304) or 925°C (SUS316) without loss of mechanical properties.
3. Specifications
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm |
| OD Tolerance | ±0.10 mm (±0.004") |
| WT Tolerance | ±10% of nominal (min. ±0.05 mm) |
| Coil Length (Continuous) | 50 m – 500 m (custom lengths available) |
| Coil Weight | 200 kg – 1,500 kg per coil |
| Surface Finish | 2B (Cold Rolled), BA (Bright Annealed), No. 4 Brushed, Mirror (#8) |
| Inner Surface Roughness | Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (electropolished, optional) |
| End Condition | Plain cut, beveled (V-groove), or capped |
| Coiling Method | Centerless coiling with protective interlayer wrapping |
| Minimum Bend Radius | 2 × OD (cold bend, no mandrel) |
| Pressure Rating (Hydrostatic Test) | 2.5 × working pressure; minimum 1.0 MPa for all sizes |
3.1 Dimensional Tolerance Standards
- GB/T 14976 — Seamless steel tubes (dimensional reference)
- ASTM A554/A554M — Cold-worked stainless steel tubing
- ISO 1307 — Welded and seamless stainless steel tubes for heat exchangers
4. Manufacturing Process
4.1 Process Flow
- Strip Procurement: Cold-rolled stainless steel strip (CR+AN condition) sourced from certified mills, inspected for surface quality, dimensional accuracy, and chemical composition compliance.
- Strip Preparation: Edge trimming, surface cleaning (degreasing and descaling), and tensile leveling to eliminate coil set and ensure flatness within 0.1 mm/m.
- Forming (Pipe Making): Multi-roll cold forming using a combination of roll-passes (typically 15–20 passes) to progressively reduce the strip into a closed circular cross-section. This includes ovalizing passes for roundness correction.
- Welding: Continuous longitudinal welding using TIG (Tungsten Inert Gas) with high-purity argon shielding gas (≥ 99.999% purity). Weld parameters are precisely controlled to achieve full penetration with minimal heat-affected zone (HAZ).
- Weld Finishing: In-line grinding or orbital brushing of the weld seam to achieve surface continuity. For high-purity applications, internal orbital brushing achieves Ra ≤ 0.4 μm.
- Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by controlled cooling to relieve residual stresses, homogenize microstructure, and restore full corrosion resistance.
- Pickling & Passivation: Removal of mill scale and oxide films using controlled acid bath (nitric-hydrofluoric acid blend), followed by passivation to establish a stable chromium oxide protective layer.
- Coiling: Precision centerless coiling with controlled tension to prevent deformation. Coils are wrapped with protective film and secured with steel strapping.
- Final Inspection: Comprehensive quality assurance including dimensional verification, hydrostatic pressure testing, spectroscopic chemical analysis, and surface inspection.
4.2 Critical Quality Control Measures
Based on industry failure analysis — specifically the documented leakage mechanisms in Q215-grade fan coil piping — the following enhanced controls are implemented:
- Wall Thickness Uniformity: Continuous ultrasonic thickness monitoring ensures minimum wall thickness is maintained throughout the coil length, preventing thin-wall regions susceptible to corrosion-induced perforation.
- Weld Integrity Testing: 100% eddy current inspection of weld seams to detect porosity, incomplete fusion, or undercut defects that could serve as initiation points for leakage.
- Corrosion Resistance Verification: Salt spray testing (ASTM B117) for minimum 48 hours without red rust formation (SUS304); 240 hours for SUS316 grade.
- Hydrostatic Testing: Every coil subjected to hydrostatic pressure test at 2.5× the maximum working pressure with a minimum hold time of 60 seconds.
5. Applications
5.1 Primary Application Sectors
- HVAC Systems: Fan coil unit piping, air handling unit (AHU) distribution, chilled water loops, and refrigerant lines. The coil format enables efficient fabrication of U-bends and serpentine circuits.
- Food & Beverage Industry: Dairy processing lines, brewing systems, sanitary fluid transfer, and CIP (Clean-in-Place) systems. Electropolished versions meet FDA 3-A standards.
- Pharmaceutical & Biotechnology: Process piping for GMP (Good Manufacturing Practice) facilities, sterilization loops (SIP), and clean water systems.
- Chemical Processing: Acid transfer lines, reactor feed systems, and exhaust ducting where corrosion resistance is critical.
- Automotive & Aerospace: Exhaust systems, fuel lines, hydraulic circuits, and structural tubing requiring weight optimization and corrosion resistance.
- Domestic & Commercial Plumbing: Water supply lines, gas piping, and radiant heating systems.
- Construction & Architecture: Structural framing, handrails, decorative elements, and curtain wall systems.
5.2 Advantages of Coil Format
- Material Efficiency: Up to 30% reduction in material waste compared to straight-length tube due to elimination of cut-off losses and the ability to nest complex geometries.
- Logistical Efficiency: Reduced packaging volume, fewer handling operations, and optimized transportation loading.
- Production Continuity: Enables automated downstream processing (cutting, bending, welding) without manual tube transfer, reducing cycle time by 40–60%.
- Weld-Free Fabrication: Allows formation of continuous piping circuits (e.g., coil tubing for heat exchangers) without intermediate welds, eliminating potential leak points.
6. Quality Certifications & Compliance
6.1 System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- CE Marking — Compliance with European Union directives (PED 2014/68/EU where applicable)
- PED (Pressure Equipment Directive) — For pressure-containing applications
6.2 Product Testing & Inspection Standards
| Test | Standard | Purpose |
|---|---|---|
| Hydrostatic Pressure Test | GB/T 241, ASTM A554 | Verify weld integrity and structural soundness |
| Eddy Current Testing | ASTM E309 | Detect surface and near-surface weld defects |
| Salt Spray Test | ASTM B117 | Verify corrosion resistance |
| Spectroscopic Analysis | ASTM E415 | Confirm chemical composition compliance |
| Dimensional Inspection | ISO 1307 / ASTM A554 | Verify OD, WT, roundness, and straightness |
| Intergranular Corrosion Test | ASTM A240 Appendix (ASTM A923) | Verify weld sensitization resistance |
| Mechanical Testing | ASTM A370 / GB/T 228 | Verify tensile strength and elongation |
6.3 Documentation Provided
- Mill Test Certificate (MTC) / EN 10204 Type 3.1 Certificate
- Heat Traceability Record — linking each coil to specific mill heat numbers
- Batch Inspection Report with dimensional and mechanical test data
- Material Safety Data Sheet (MSDS)
- RoHS & REACH Compliance Declaration
7. Unique Selling Points
1. Engineering-Informed Design: This product line incorporates lessons learned from extensive field failure analysis of carbon steel fan coil piping (Q215 grade), resulting in enhanced wall thickness tolerances, superior weld integrity requirements, and rigorous corrosion resistance verification that directly address the root causes of premature leakage.
2. Precision Coil Technology: Advanced centerless coiling ensures uniform curvature with no kinks, ovality, or surface damage — critical for downstream automated processing and reliable system performance.
3. Multi-Grade Flexibility: Availability across SUS304, SUS316, and specialty grades from a single supplier streamlines procurement while maintaining consistent quality standards across all material options.
4. Full Traceability: Complete heat-to-coil traceability enables rapid root cause analysis in the event of field performance issues, supporting proactive maintenance strategies.