Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous-length tubing product supplied in coiled form for downstream forming, bending, and fabrication processes. Unlike cut-length pipe, coil tube is delivered in a continuous helical coil, offering significant advantages in material utilization, processing efficiency, and dimensional consistency. This product category is particularly critical in the HVAC (Heating, Ventilation, and Air Conditioning) industry, where large-scale chiller coil assemblies and air-cooled heat exchangers demand high-performance tubing with reliable thermal and mechanical properties.
Based on field failure analyses conducted on large chiller coil assemblies — such as those documented in industrial metro infrastructure projects (e.g., Line 10 Phase II large chiller coil failure analysis) — the selection of appropriate stainless steel coil tube is essential to prevent corrosion-induced degradation, thermal fatigue cracking, and flow-induced vibration failures in critical heat exchange applications.
2. Material & Properties
2.1 Available Material Grades
- AISI 304 / ASTM A213 TP304 — General-purpose austenitic stainless steel; excellent corrosion resistance and formability
- AISI 316 / ASTM A213 TP316 — Enhanced corrosion resistance with molybdenum (Mo) addition; ideal for aggressive environments
- AISI 316L / ASTM A213 TP316L — Low-carbon variant of 316; superior resistance to intergranular corrosion after welding
- AISI 321 / ASTM A213 TP321 — Titanium-stabilized; excellent resistance to high-temperature oxidation and intergranular corrosion
- AISI 304L / ASTM A213 TP304L — Low-carbon version of 304; improved weldability and post-weld corrosion resistance
2.2 Mechanical Properties (Typical Values)
| Property | 304 / 304L | 316 / 316L | 321 | Unit |
|---|---|---|---|---|
| Tensile Strength (Minimum) | 515 | 515 | 515 | MPa |
| Yield Strength (0.2% Offset, Minimum) | 205 | 205 | 205 | MPa |
| Elongation (Minimum) | 40 | 40 | 40 | % |
| Hardness (Maximum) | 217 | 217 | 217 | HB |
| Thermal Conductivity (at 300°C) | 16.3 | 14.6 | 16.3 | W/(m·K) |
| Thermal Expansion Coefficient (20–800°C) | 17.2 | 17.4 | 17.2 | ×10⁻⁶ /°C |
2.3 Chemical Composition (Typical)
| Element | 304 | 316 | 321 |
|---|---|---|---|
| Carbon (C) Max | 0.08 | 0.08 | 0.08 |
| Chromium (Cr) | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 |
| Nickel (Ni) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 |
| Molybdenum (Mo) | — | 2.0–3.0 | — |
| Titanium (Ti) | — | — | 5×C to 0.70 |
| Iron (Fe) Balance | Balance | Balance | Balance |
3. Product Specifications
| Parameter | Specification Range | Applicable Standard |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.25 mm – 3.0 mm | ASTM A213 / GB/T 14976 |
| Surface Finish | No. 1, 2B, BA (Bright Annealed), Matte, Custom | ASTM A478 / GB/T 12771 |
| Coil Core Diameter | 200 mm – 600 mm (configurable) | — |
| Coil Weight | 200 kg – 2,000 kg (per coil) | — |
| Manufacturing Method | Seamless (Hot/Cold Rolled) or Welded (ERW / Laser Welded) | ASTM A213 / EN 10216-5 |
| Tolerance (OD) | ±0.05 mm – ±0.2 mm (depending on diameter) | ASTM A213 |
| Tolerance (Wall Thickness) | ±10% (standard) / ±5% (precision grade) | ASTM A213 |
| Available Lengths | Continuous coil (no cut-off loss) | — |
| End Condition | Plain, Beveled, or Threaded (upon request) | — |
4. Manufacturing Process
The production of stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection — Ingot or strip material sourced from certified mills (e.g., Outokumpu, POSCO, Taigang); incoming material undergoes spectroscopic analysis (Spectrometer) for chemical composition verification and mechanical testing.
- Hot Rolling / Forging — For seamless tubing: billets are heated to 1,150–1,250°C and pierced to form hollow blanks. For welded tubing: precision cold-rolled strip is fed into the forming line.
- Cold Drawing / Cold Rolling — Tubes are drawn through precision tungsten carbide (WC) dies to achieve tight dimensional tolerances and improved mechanical properties. Multi-pass drawing may be employed for thin-wall products.
- Welding (for Welded Coil Tube) — Longitudinal seam welding via Electric Resistance Welding (ERW) or High-Power Laser Welding (HPLW) with in-line seam inspection.
- Heat Treatment & Annealing — Tubes are solution annealed at 1,050–1,150°C followed by controlled cooling to achieve a fully austenitic grain structure, relieve residual stresses, and restore corrosion resistance.
- Pickling & Passivation — Acid pickling removes oxide scale and decarburized layers; passivation treatment forms a stable chromium oxide (Cr₂O₃) passive film to enhance corrosion resistance.
- Precision Sizing & Straightening — Final sizing through calibrated mandrel or roll sizing systems; straightening and leveling before coiling.
- Non-Destructive Testing (NDT) — 100% eddy current testing (ECT) for internal and external defect detection; hydrostatic pressure testing for seam integrity verification.
- Coiling & Packaging — Continuous tube is coiled onto precision-wound cores, wrapped in protective film, and palletized for shipment.
5. Applications
5.1 HVAC & Refrigeration Systems
- Large chiller coil assemblies (evaporator and condenser coils)
- Air-cooled heat exchangers and condenser units
- Chilled beam and fan coil unit (FCU) tubing
- Refrigeration condenser and evaporator tubes
5.2 Industrial Heat Exchangers
- Shell-and-tube heat exchangers
- Plate-fin and microchannel heat exchangers
- Process cooling and heating circuits
5.3 Infrastructure & Transportation
- Metro and railway HVAC coil systems (as referenced in Line 10 Phase II chiller coil applications)
- Automotive radiators and intercooler tubes
- Marine air conditioning systems
5.4 Additional Applications
- Food and beverage processing (sanitary tubing)
- Pharmaceutical and biotechnology equipment
- Chemical processing heat exchangers
- Gas and fluid transport systems
6. Unique Selling Points
- Failure-Informed Engineering — Product specifications are informed by real-world failure analyses of large chiller coil assemblies in demanding infrastructure environments, ensuring enhanced reliability against corrosion fatigue, flow-induced vibration (FIV), and thermal cycling degradation.
- Continuous Coil Supply — Elimination of butt welds in downstream fabrication; improved structural integrity and reduced leakage risk in welded coil assemblies.
- Precision Dimensional Control — Tight OD and wall thickness tolerances ensure optimal fit in automated tube-forming and fin-tube brazing equipment.
- Comprehensive Grade Selection — Availability of multiple stainless steel grades (304, 316, 316L, 321) allows precise matching to specific service environments and corrosion challenges.
- Full Traceability — Each coil is accompanied by a Mill Test Certificate (MTC) with heat number traceability, chemical analysis, and mechanical test data.
7. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A213 / A269 | Standard specification for seamless and welded austenitic stainless steel tubing |
| EN 10216-5 | European standard for seamless and welded heat exchanger tubes |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
| TÜV / SGS Testing | Independent third-party inspection and material verification available upon request |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 certificate provided with each shipment |
8. Technical Recommendations for Chiller Coil Applications
Based on failure analysis of large chiller coil assemblies in metro infrastructure (Line 10 Phase II), the following recommendations are provided for optimal coil tube selection and application:
- Material Selection: For water-cooled chiller coils exposed to treated water with chlorides, AISI 316L is recommended over 304 to mitigate pitting and crevice corrosion risks.
- Wall Thickness: Minimum wall thickness of 0.5 mm is recommended for tubes with OD ≤ 12 mm to resist flow-induced vibration fatigue under turbulent flow conditions.
- Support Spacing: Coil tube assemblies should incorporate adequate tube support plates with maximum unsupported span not exceeding 15× OD to prevent vibration-induced fretting corrosion.
- Water Quality Control: Implement rigorous water treatment protocols including pH control (8.5–9.5), inhibitor dosing, and periodic microbiological monitoring to prevent corrosion under deposit (CUD).
- Inspection Protocol: Conduct periodic eddy current testing and visual inspection of coil assemblies during preventive maintenance intervals to detect early-stage corrosion or mechanical degradation.
9. Ordering Information
Customers are advised to specify the following parameters when placing an order:
- Material grade (e.g., 304, 316L, 321)
- Outer diameter (OD) and wall thickness
- Surface finish requirement (2B, BA, matte, custom)
- Coil core diameter and preferred coil weight
- Applicable standard (ASTM, EN, GB)
- Special requirements (e.g., specific NDT methods, packaging, delivery schedule)
Wenzhou Jixing Metal Materials Co., Ltd is committed to delivering high-performance stainless steel coil tube products that meet the most demanding industrial specifications, backed by rigorous quality control and comprehensive technical support.