Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous stainless steel tubing supplied in coiled form, designed for use in heat exchangers, air coolers, evaporators, condensers, and process piping systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product line is engineered to withstand demanding thermal cycling, corrosive environments, and mechanical stress conditions typical in industrial HVAC (Heating, Ventilation, and Air Conditioning), metro infrastructure, and chemical processing applications.
Coiltube is distinguished from straight seamless or welded tubing by its continuous coil configuration, which enables efficient coil winding onto headers and frames, reduces welding joints, and minimizes potential leak points in heat exchange assemblies. The product is particularly suited for large-scale table cooler (表冷器) units where reliability and thermal efficiency are critical, as demonstrated in real-world failure analysis studies on metro-grade cooling equipment (e.g., Line 10 Phase II large table cooler coil tube failure analysis).
2. Material & Properties
2.1 Available Grades
- AISI 304 / ASTM 304 / SUS 304 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- AISI 316 / ASTM 316 / SUS 316 — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion in chloride-containing environments.
- AISI 316L / ASTM 316L / SUS 316L — Low-carbon variant of 316 for enhanced resistance to intergranular corrosion during welding operations.
- AISI 321 / ASTM 321 / SUS 321 — Titanium-stabilized grade for high-temperature service resistance.
- AISI 310S / ASTM 310S / SUS 310S — High-temperature grade suitable for extreme thermal conditions.
2.2 Mechanical Properties (Typical for Grade 304)
| Property | Value | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa (74,700 psi) | ASTM A270 / ASTM A269 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A270 / ASTM A269 |
| Elongation (延伸率) | ≥ 40% | ASTM A270 / ASTM A269 |
| Density (密度) | 8.00 g/cm³ | — |
| Thermal Conductivity (热导率) @ 20°C | 16.3 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (热膨胀系数) @ 20–100°C | 17.3 × 10⁻⁶ /°C | ASTM E228 |
2.3 Chemical Composition (Typical for Grade 304)
| Element | Specification (%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Chromium (Cr) | 18.0 – 20.0 |
| Nickel (Ni) | 8.0 – 10.5 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 0.75 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Iron (Fe) | Balance |
3. Specifications
3.1 Geometric Dimensions
| Parameter | Range / Options | Tolerance |
|---|---|---|
| Outer Diameter (OD) (外径) | 1.0 mm – 50.8 mm (1/8" – 2") | ± 0.05 mm (± 0.002") |
| Wall Thickness (壁厚) | 0.10 mm – 3.00 mm (0.004" – 0.118") | ± 10% of nominal |
| Coil Length (盘长) | 10 m – 500 m (33 ft – 1,640 ft) per coil | As specified by customer |
| Coil Inner Diameter (盘圈内径) | 100 mm – 600 mm (4" – 24") | ± 10 mm |
| Coil Weight (盘重) | Up to 500 kg (1,100 lbs) per coil | — |
| Surface Finish (表面状态) | Bright Annealed (BA), No. 1, 2B, Pickled & Passivated, Custom | — |
3.2 Manufacturing Standards
| Standard | Description |
|---|---|
| ASTM A270 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Heat-Transfer Service |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Chromium Stainless Steel Pipe for High-Pressure Boilers |
| ASTM A778 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for General Service |
| ASME B36.19M | Standard for Welded and Seamless Wrought Stainless Steel Pipe |
| EN 10216-5 | Heat-Exchanger Tubes and Heat Sink Tubes — Seamless and Welded Tubes Made of Nickel and Nickel Alloys |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection (原材料选择): High-purity stainless steel strip or round bar from certified mills, with mill test certificates (MTC) verifying chemical composition and mechanical properties.
- Slitting & Leveling (分条与平整): Coil strip is slit to the required width and leveled to eliminate residual stress and ensure dimensional accuracy.
- Forming (成型): The strip is fed through precision roll-forming stations to create the desired tube cross-section (round, oval, or rectangular). For seamless tubes, the forming is followed by piercing and reduction.
- Welding (焊接): For welded coil tubes, high-frequency induction welding (HF welding) or orbital TIG welding is applied to create a continuous longitudinal seam with minimal heat-affected zone (HAZ).
- Heat Treatment / Annealing (热处理/退火): The formed tube is bright annealed in a protective atmosphere (H₂/N₂ or vacuum) to relieve forming stresses, restore ductility, and achieve the desired microstructure.
- Pickling & Passivation (酸洗钝化): Surface scale and weld discoloration are removed via citric acid or nitric-hydrofluoric acid pickling, followed by passivation to establish a stable chromium oxide film.
- Coiling (盘卷): The finished tube is wound onto a coil using a precision coiler with controlled tension to prevent deformation, kinking, or ovality.
- Quality Inspection (质量检验): Each coil undergoes non-destructive testing (NDT) including eddy current testing (ECT), ultrasonic testing (UT), and hydrostatic pressure testing to detect internal and external defects.
- Packaging & Dispatch (包装与发货): Coils are wrapped in protective film, packed in wooden or steel crates, and labeled with batch identification, MTC reference, and handling instructions.
4.2 Key Process Controls
- Dimensional Control: In-process laser measurement systems monitor OD and wall thickness with ± 0.05 mm accuracy at every forming station.
- Weld Quality: Weld seam geometry is verified by visual inspection and automated ECT; weld penetration is confirmed by 100% hydrostatic testing at 2× working pressure.
- Surface Integrity: Optical surface inspection systems detect scratches, dents, and inclusions at speeds up to 120 m/min.
5. Applications
5.1 Primary Application Domains
- Large-Scale Air Coolers / Table Coolers (大型表冷器): Coiltube is wound into finned coil assemblies for metro ventilation systems, commercial building HVAC, and industrial process cooling. The continuous coil configuration minimizes brazed or welded joints, significantly reducing the risk of refrigerant leaks — a critical concern highlighted in metro infrastructure failure analyses.
- Heat Exchangers (换热器): Shell-and-tube heat exchangers, plate-fin heat exchangers, and evaporator/condenser units in refrigeration and air conditioning systems.
- Chemical & Petrochemical Processing (化工与石化): Corrosion-resistant process piping, reactor cooling loops, and distillation column internals where resistance to chlorides, acids, and caustic solutions is required.
- Food & Pharmaceutical Industry (食品与制药): Hygienic-grade tubing for CIP (Clean-In-Place) systems, pasteurization equipment, and process water lines where food-grade surface finish and non-toxic materials are mandated.
- Power Generation (发电): Boiler tubes, steam generator tubes, and condensate recovery systems in power plants.
- Automotive & Transportation (汽车与交通): Radiator tubes, intercooler tubes, and exhaust system components requiring thermal cycling resistance.
- Marine & Offshore (海洋与海上): Seawater cooling systems, ballast water treatment equipment, and offshore platform piping where marine corrosion resistance is essential.
5.2 Case Study Reference
The reliability of coil tubes in large table cooler applications has been extensively validated through field performance studies. For instance, the "Line 10 Phase II Large Table Cooler Coil Tube Failure Analysis and Recommendations" study identified common failure modes including tube wall thinning from erosion-corrosion, fatigue cracking at coil bends, and sealant degradation at coil-to-header joints. These findings directly inform the enhanced manufacturing tolerances, material grade selection, and quality assurance protocols applied to the coiltube product line — ensuring that the tubes delivered meet or exceed the performance requirements of critical infrastructure projects such as metro systems.
6. Quality Certifications & Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 — Inspection Certificates verifying compliance with specified standards and test requirements.
- PED 2014/68/EU — European Pressure Equipment Directive compliance for pressure-containing applications.
- ASME Stamp (U/U1) — Where applicable, for pressure vessel and heat exchanger tube applications.
- NSF/ANSI 61 — Drinking water system component certification for food and beverage applications.
- 3-A Sanitary Standards — For dairy, beverage, and pharmaceutical industry applications.
6.2 Quality Assurance Protocol
| Inspection Stage | Method | Acceptance Criteria |
|---|---|---|
| Incoming Raw Material | Spectroscopic analysis (OES), MTC verification | Chemical composition within ASTM/EN limits |
| In-Process Dimensional | Laser micrometer, ultrasonic thickness gauge | OD ± 0.05 mm; Wall thickness ± 10% |
| Weld Seam Integrity | Eddy Current Testing (ECT), Visual Inspection (VT) | No cracks, lack of fusion, or undercut per ASTM E309 |
| Hydrostatic Testing | Water pressure test at 2× MAWP | No leakage or permanent deformation |
| Surface Condition | Visual + automated optical inspection | No scratches, dents, or surface defects per ASTM A270 |
| Final Product | Full MTC issuance, batch trace |