Stainless Steel Coil Tube (Coiltube) — Model 823
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), designated as Product No. 823 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-form tubular product manufactured through cold-drawing or cold-rolling processes. Unlike conventional straight-length stainless steel pipes, coil tubes are delivered in continuous wound coils, offering superior material utilization, reduced cutting waste, and enhanced supply-chain efficiency for high-volume fabrication environments.
This product category is particularly critical in applications demanding precise thermal management, including constant temperature and humidity control units (恒温恒湿机组), where coil tubes serve as the core heat exchange elements. The critical coil tube operation mode analysis demonstrates that the geometric and metallurgical integrity of the coil tube directly governs the thermodynamic performance envelope of HVAC systems, refrigeration circuits, and industrial process cooling loops.
2. Material Composition & Mechanical Properties
2.1 Base Alloy Grades
Coil tubes are predominantly fabricated from austenitic stainless steel grades, selected based on the specific service environment:
- 304 (UNS S30400) — General-purpose austenitic grade with excellent corrosion resistance and formability; carbon equivalent ≤ 0.08%.
- 316 (UNS S31600) — Molybdenum-enhanced grade (2.0–3.0% Mo) offering superior resistance to pitting and crevice corrosion in chloride-containing environments.
- 316L (UNS S31603) — Low-carbon variant (C ≤ 0.03%) optimized for welding applications and critical coil tube configurations requiring post-fabrication thermal treatment.
- 321 (UNS S32100) — Titanium-stabilized grade suitable for elevated-temperature service (up to 870 °C) in thermal exchange applications.
2.2 Mechanical Properties (Typical Values — Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa |
| 0.2% Proof Stress (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 |
| Thermal Conductivity (λ, 20 °C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 16.3 W/(m·K) |
| Thermal Expansion (α, 20–100 °C) | 17.3 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K |
2.3 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr₂O₃, typically 2–5 nm thickness) formed on the austenitic surface provides a self-healing barrier against atmospheric and aqueous corrosion. In the context of constant temperature and humidity unit operation, the coil tube is exposed to condensate, humid air, and potential chemical contaminants. The 316L grade's molybdenum addition shifts the pitting resistance equivalent number (PREN) from approximately 19 (304L) to approximately 25, significantly extending service life in aggressive condensate environments.
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Category | Stainless Steel Coil Tube (盘管 / Coiltube) | — |
| Product Number | 823 | — |
| Outer Diameter (OD) | 6.0 – 50.8 mm (1/4" – 2") | ASTM A778 / GB/T 12771 |
| Wall Thickness | 0.5 – 3.0 mm | ASTM A778 / GB/T 12771 |
| Coil Length (Continuous) | 20 – 200 m per coil | Manufacturer specification |
| Coil Diameter (Wound) | 600 – 1,200 mm (outer) | Manufacturer specification |
| Surface Finish | No. 4 Brushed / 2B Annealed / Electropolished (Ra ≤ 0.4 μm) | ASTM A967 |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) | ASTM A778 |
| Dimensional Tolerance (Wall) | ±0.02 mm (precision grade); ±0.05 mm (standard grade) | ASTM A778 |
| Roundness | ≤ 2% of nominal OD | ASTM A778 |
| Straightness (per 1 m) | ≤ 1.5 mm | ASTM A778 |
| Operating Temperature Range | −196 °C to +870 °C (grade-dependent) | ASME BPV Code |
| Maximum Working Pressure | Grade and dimension dependent; typically ≤ 10 MPa | ASME B31.3 |
| Packing | Wooden reel with moisture-proof inner wrapping; export-grade pallet available | ISO 4180 |
4. Manufacturing Process
4.1 Process Flow
- Steel Billet Preparation — Vacuum Induction Melting (VIM) or Argon Oxygen Decarburization (AOD) refining of the base alloy to achieve target chemistry with controlled sulfur, nitrogen, and carbon levels.
- Hot Rolling — The refined billet is hot-rolled into seamless tube blanks or welded pipe stock with controlled wall thickness uniformity.
- Pickle and Anneal — The hot-rolled tube undergoes acid pickling (HNO₃/HF blend) to remove mill scale, followed by solution annealing at 1050–1150 °C with controlled cooling to restore full austenitic microstructure and maximize corrosion resistance.
- Cold Drawing / Cold Rolling — The annealed tube is drawn through precision tungsten carbide or hardened steel dies to achieve final dimensions. For coil tube production, continuous cold-drawing is employed to maintain the continuous form.
- Intermediate Annealing — Multiple drawing reductions may require intermediate annealing cycles (1050–1100 °C) to relieve work-hardening and prevent cracking.
- Coiling — The finished tube is wound onto a reel using a controlled tension system to prevent ovalization, kinking, or surface marking. The coiling tension is calibrated based on the tube's elastic modulus and minimum bend radius.
- Final Annealing (if required) — For applications demanding maximum ductility (e.g., critical coil tube configurations in HVAC systems), a final stress-relief anneal at 1050 °C followed by controlled air cooling is performed.
- Quality Inspection & Packing — Each coil undergoes comprehensive non-destructive testing before packaging.
4.2 Critical Process Parameters for Coil Tube Integrity
The analysis of critical coil tube operation modes in constant temperature and humidity units reveals that the manufacturing quality of the coil tube directly impacts system performance. Key process parameters include:
- Minimum Bend Radius: ≥ 3D (where D = outer diameter) during coiling to prevent wall thinning at the inner bend radius.
- Coiling Tension Control: Maintained within 15–25% of the material's yield strength to ensure uniform spring-back characteristics.
- Surface Roughness: Internal surface Ra ≤ 0.8 μm is critical for minimizing flow resistance and preventing biofilm accumulation in HVAC condensate circuits.
5. Applications
5.1 Constant Temperature and Humidity Control Systems (HVAC)
The primary application domain for this product involves constant temperature and humidity units (恒温恒湿机组), where coil tubes function as the core evaporator and condenser elements. The continuous coil configuration enables optimized surface-area-to-volume ratios, maximizing heat transfer efficiency. Critical operation mode analysis demonstrates that the coil tube's thermal conductivity, flow channel geometry, and surface condition collectively determine the unit's dew-point control precision, which is essential for pharmaceutical, electronics manufacturing, and laboratory environments.
5.2 Additional Application Domains
- Refrigeration and Air Conditioning — Evaporator coils, condenser coils, and heat exchanger circuits.
- Food and Beverage Processing — Pasteurization equipment, CIP (Clean-in-Place) systems, and sanitary-grade fluid transfer lines.
- Pharmaceutical Manufacturing — GMP-compliant fluid handling, sterilization circuits, and process cooling systems.
- Chemical Processing — Reactor cooling jackets, distillation column internals, and corrosive fluid transfer.
- Automotive and Aerospace — Fuel lines, hydraulic circuits, and heat management systems requiring lightweight, corrosion-resistant tubing.
- Water Treatment — Reverse osmosis (RO) systems, ultrafiltration membranes, and desalination plants.
6. Quality Certifications & Testing Protocols
6.1 Applicable Standards
- ASTM A778 — Standard Specification for Seamless and Wrought Stainless Steel, Nickel Alloy, and Copper-Nickel Alloy Tube, Pipe, and Fittings for General Applications.
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Gas-Related Applications.
- GB/T 12771 — Technical Conditions for Cold-Rolled Stainless Steel Seamless Tubes.
- ISO 3506 — Stainless Steel Fasteners — General Specifications for Materials.
- EN 10217 — Technical Delivery Conditions for Cold Drawn Stainless Steel Tubes.
6.2 Quality Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing processes.
- ISO 14001:2015 — Environmental Management System certification.
- EN 10204 3.1 — Material Test Certificate (MTC) issued by an authorized quality assurance body.
- CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU) where applicable.
- Mill Test Reports (MTR) — Full chemical composition and mechanical property data for each heat lot.
6.3 Non-Destructive Testing (NDT) Methods
| Test Method | Purpose | Standard |
|---|---|---|
| Eddy Current Testing (ECT) | Detection of surface and near-surface defects (cracks, laps, seams) | ASTM E709 / E3093 |
| Magnetic Particle Testing (MT) | Surface defect detection on ferromagnetic materials (ferritic grades) | ASTM E709 |
| Visual Inspection | Surface condition verification, dimensional spot-check | ASTM A778 |
| Hydrostatic Pressure Test | Verification of weld integrity (welded tubes) and dimensional conformance | ASTM A269 |
| Intergranular Corrosion Test | Verification of sensitization resistance (ASTM A967 compliance) | ASTM A967 / GB/T 4334 |
7. Unique Selling Points
The Model 823 Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through several key technical advantages:
- Continuous-Form Efficiency: Delivered in coils up to 200 meters in length, eliminating butt-weld joints and reducing fabrication time by up to 40% compared to straight-length pipe delivery.
- Precision Dimensional Control: Tolerances as tight as ±0.02 mm on wall thickness ensure consistent flow characteristics and predictable pressure drop in critical HVAC and refrigeration circuits.
- Multi-Grade Availability: Comprehensive range from 304L to 316L and 321 grades allows engineers to select the optimal alloy for specific corrosion and temperature environments without changing suppliers.
- HVAC-Optimized Surface Finish: Internal electropolished finish (Ra ≤ 0.4 μm) reduces flow resistance by up to 15% and inhibits biofilm formation, extending maintenance intervals in constant temperature and humidity applications.
- Full Traceability: Each coil is accompanied by a complete Mill Test Report (MTR) with heat-number traceability, chemical analysis, mechanical test data, and NDT results, ensuring full supply-chain accountability.
- Custom Coil Configuration: Coil diameter, winding direction, and end-protection can be customized to match downstream uncoiling equipment specifications, minimizing handling damage.
8. Conclusion
The Stainless Steel Coil Tube (Model 823) represents a technically sophisticated product that bridges metallurgical science and applied engineering. Its design, material selection, and manufacturing methodology are specifically calibrated to meet the demanding