Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog No.: 789
Standard Reference: GB/T 19232—2003 Fan Coil Units (with revision considerations)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tubular product formed into a coiled configuration, designed primarily for use in hydronic heating and cooling systems, particularly within Fan Coil Units (FCUs) governed by the Chinese national standard GB/T 19232—2003. The coil tube serves as the core heat exchange element, facilitating efficient thermal transfer between the circulating fluid (water or glycol solution) and ambient air.
Wenzhou Jixing Metal Materials Co., Ltd. produces these coil tubes to meet the rigorous performance, durability, and dimensional accuracy requirements specified in GB/T 19232—2003 and its proposed revisions, addressing known deficiencies in the original standard related to thermal efficiency metrics, material specification ambiguity, and long-term corrosion resistance requirements.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel conforming to ASTM A213/A213M or GB/T 14976 specifications
- Grade Options:
- 304 (UNS S30400) — General-purpose corrosion resistance; minimum 18% Cr, 8% Ni
- 316 (UNS S31600) — Enhanced pitting and crevice corrosion resistance; minimum 16% Cr, 10% Ni, 2% Mo
- 316L (UNS S31603) — Low-carbon variant for welding applications; C ≤ 0.03%
- 321 (UNS S32100) — Titanium-stabilized for high-temperature service
- Surface Finish: 2B (Cold-rolled and annealed), BA (Bright Annealed), or No. 4 brushed finish
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316 | Grade 316L |
|---|---|---|---|
| Tensile Strength (MPa, min.) | 515 | 515 | 485 |
| Yield Strength (MPa, min.) | 205 | 205 | 170 |
| Elongation (% , min.) | 40 | 40 | 40 |
| Hardness (HB, max.) | 217 | 217 | 217 |
| Density (g/cm³) | 8.00 | 8.00 | 8.00 |
| Thermal Conductivity (W/m·K @ 100°C) | 16.3 | 14.6 | 14.6 |
| Maximum Service Temperature (°C) | 870 | 870 | 870 |
2.3 Chemical Composition (Typical, % by weight)
| Element | Grade 304 | Grade 316 | Grade 316L |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.08 | ≤ 0.03 |
| Cr (Chromium) | 18.0–20.0 | 16.0–18.0 | 16.0–18.0 |
| Ni (Nickel) | 8.0–10.5 | 10.0–14.0 | 10.0–14.0 |
| Mo (Molybdenum) | — | 2.0–3.0 | 2.0–3.0 |
| Mn (Manganese) | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
| P (Phosphorus) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm, 8.0 mm, 9.53 mm, 10.0 mm, 12.0 mm, 12.7 mm, 15.0 mm, 19.0 mm, 25.0 mm | ±0.1 mm |
| Wall Thickness | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm | ±0.05 mm |
| Coil Outer Diameter | 300 mm – 1200 mm (customizable) | ±5 mm |
| Coil Inner Diameter | 50 mm – 150 mm | ±3 mm |
| Coil Length per Spool | 10 m – 50 m (standard); up to 200 m on request | ±1% |
| Coil Pitch (Spacing) | 10 mm – 25 mm (adjustable per application) | ±0.5 mm |
| Roundness | ≤ 0.1 × OD | — |
| Straightness (per 1000 mm) | ≤ 1.0 mm | — |
3.2 Performance Specifications (per GB/T 19232—2003)
| Performance Parameter | Requirement | Test Method |
|---|---|---|
| Heat Transfer Efficiency | ≥ 95% of rated capacity under design conditions | GB/T 19232—2003, Clause 6 |
| Pressure Drop (at rated flow) | ≤ 50 kPa (water side) | GB/T 19232—2003, Clause 7 |
| Hydrostatic Pressure Test | 1.5 × working pressure, held for 30 min with no leakage | GB/T 14976 |
| Corrosion Resistance (Salt Spray) | ≥ 1000 hours without red rust (Grade 316/316L) | ASTM B117 |
| Operating Pressure (max.) | 1.6 MPa (standard); 2.5 MPa (heavy-duty) | — |
| Operating Temperature Range | -40°C to +200°C (standard); up to 870°C (Grade 321) | — |
| Flow Velocity (recommended) | 0.5 – 3.0 m/s | — |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection: Cold-rolled stainless steel strip (coil form) sourced from certified mills (e.g., Outokumpu, POSCO, Baosteel) with mill test certificates (MTC) verifying chemical composition and mechanical properties.
- Strip Inspection & Preparation: Incoming strip undergoes dimensional verification, surface quality inspection (visual and magnetic particle testing), and chemical spot analysis to confirm grade compliance.
- Coil Forming (Cold-Forming): Precision cold-rolling and bending equipment shapes the strip into the desired tube diameter. The forming process maintains the metallurgical integrity of the austenitic structure without requiring heat treatment.
- Welding (if applicable): For welded coil tubes, orbital TIG (Tungsten Inert Gas) welding or automatic laser welding is employed. Welding is performed under argon shielding to prevent oxidation. Weld seam quality is verified via X-ray radiography or ultrasonic testing (UT).
- Coil Winding: The formed tube is wound into a precise coil configuration using CNC-controlled winding machinery. Coil pitch, inner/outer diameter, and total length are programmed to exact specifications.
- Surface Treatment: Final surface finishing includes pickling and passivation (HNO₃/HF acid blend) to remove mill scale and restore the chromium oxide passive film. Bright annealing may be applied for BA finish requirements.
- Quality Inspection: Comprehensive final inspection includes dimensional measurement (OD, wall thickness, coil diameter), hydrostatic pressure testing, leak testing, and visual surface examination.
- Packaging & Shipping: Coils are wrapped in protective film, placed on wooden pallets or steel cradles, and packed with desiccant for moisture protection during transit.
4.2 Process Control Parameters
| Process Step | Key Control Parameter | Target Value | Inspection Frequency |
|---|---|---|---|
| Coil Forming | Drawing ratio | ≤ 2.5:1 per pass | Every coil |
| Welding | Shielding gas flow rate | 8–12 L/min (Ar) | Continuous monitoring |
| Welding | Weld current | 120–200 A (TIG) | Every 30 minutes |
| Winding | Coil pitch uniformity | ±0.5 mm | Every coil |
| Passivation | Acid concentration (HNO₃) | 15–20% by volume | Per batch |
| Pressure Testing | Test pressure | 1.5 × design pressure | 100% of product |
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCUs): As the primary heat exchange element in air handling units governed by GB/T 19232—2003. The coil tube configuration maximizes surface area-to-volume ratio for optimal convective and radiative heat transfer.
- Commercial HVAC Systems: Used in chilled water and hot water distribution systems for office buildings, hospitals, hotels, and retail spaces.
- Residential Air Conditioning: Compact coil tubes for wall-mounted and cassette-type indoor units.
- Industrial Process Cooling: Heat exchangers in chemical processing, food and beverage manufacturing, and pharmaceutical production.
- Marine HVAC: Grade 316/316L coil tubes for saltwater-resistant air conditioning systems aboard vessels.