Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous-tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for thermal-fluid transfer applications in power generation, industrial heating, and process engineering. Unlike straight-segment piping systems, coil tubes are formed into helical, spiral, or serpentine configurations that maximize heat transfer surface area within a compact footprint. This product is particularly renowned for its performance in steam heating systems, where it serves as the core heat exchange element in boilers, economizers, superheaters, and condensers.
The Coiltube product line draws upon extensive engineering knowledge accumulated through real-world operational scenarios, including detailed analyses of water hammer (water hammer phenomenon) in steam heating coil tube systems. This operational insight informs the product's design philosophy, ensuring enhanced resistance to transient pressure surges, thermal cycling fatigue, and fluid-structure interaction (FSI) loads.
2. Material & Properties
Stainless steel coil tubes are fabricated from austenitic, ferritic, and duplex stainless steel grades, each selected based on the specific thermal, chemical, and mechanical demands of the application environment.
2.1 Commonly Used Grades
- Austenitic Grades: SUS304 (UNS S30408), SUS316 (UNS S31608), SUS321 (UNS S32108), SUS347 (UNS S34708) — offering excellent corrosion resistance, high-temperature strength, and superior formability for coil winding.
- Ferritic Grades: SUS430 (UNS S43008), SUS444 (UNS S44400) — providing enhanced resistance to chloride stress corrosion cracking (SCC) and thermal cracking.
- Duplex Grades: SUS31803 (UNS S31803), SUS32205 (UNS S32205) — delivering approximately twice the yield strength of standard austenitic grades with excellent resistance to pitting and crevice corrosion.
2.2 Key Material Properties
- Corrosion Resistance: Passive chromium oxide film (Cr₂O₃) provides long-term protection against oxidation, acid exposure, and chloride environments.
- Thermal Stability: Maintains mechanical integrity at operating temperatures ranging from cryogenic (−196°C) to elevated temperatures exceeding 870°C (depending on grade).
- Mechanical Strength: Yield strength ranging from 205 MPa (annealed 304) to 550 MPa (duplex 2205), with tensile strength up to 800 MPa.
- Formability: Austenitic grades exhibit excellent cold-forming characteristics, enabling tight coil diameters without cracking or excessive work hardening.
- Thermal Conductivity: 14.9–21.5 W/(m·K), with enhanced heat transfer performance when combined with internal coil geometry.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ159.0 mm |
| Wall Thickness | 0.3 mm – 12.0 mm |
| Coil Diameter | Φ50 mm – Φ2000 mm (customizable) |
| Coil Length (per unit) | 1.0 m – 50.0 m (continuous) |
| Coil Pitch (spacing) | 5 mm – 100 mm (adjustable per design) |
| Number of Turns | 1 turn – 200+ turns |
| Surface Finish | 2B, BA (Bright Annealed), No.4 Brushed, Mirror (Ra ≤ 0.4 μm) |
| Applicable Standards | ASTM A213, ASTM A269, ASTM B437, EN 10217-7, GB/T 12771, JIS G3459 |
| Operating Temperature Range | −196°C to +870°C |
| Operating Pressure | Up to 40.0 MPa (design dependent) |
| Coil Configuration | Helical, Spiral, Serpentine, Multi-pass, Pin-fin enhanced |
| Tolerance on OD | ±0.05 mm – ±0.15 mm (per ASTM/EN) |
| Tolerance on Wall Thickness | ±10% of nominal |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous, multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:
- Raw Material Selection & Inspection: Hot-rolled stainless steel coils or seamless tubes are sourced from certified mills. Incoming materials undergo spectroscopic analysis (OES), mechanical testing, and visual inspection to verify grade compliance and absence of surface defects.
- Tube Drawing / Pipe Forming: For seamless coil tubes, the raw steel billet is heated and pierced into a hollow shell, then cold-drawn through a series of reducing dies to achieve the target outer diameter and wall thickness with high dimensional precision.
- Intermediate Annealing: Tubes are subjected to solution annealing (typically at 1050°C–1150°C) to relieve cold-work stresses, restore ductility, and ensure uniform microstructure prior to coiling.
-
Coil Winding / Bending: Using precision CNC bending machinery, the straight tube is formed into the specified coil geometry. The bending process is carefully controlled to avoid:
- Ovalization of the tube cross-section (controlled to < 5% for critical applications)
- Wall thinning at bend apex (monitored to remain within ±10% of nominal)
- Residual stress accumulation that could compromise fatigue life
- Post-Coiling Annealing & Pickling: The coiled assembly undergoes stress-relief annealing followed by acid pickling and passivation to remove scale, restore the protective chromium oxide layer, and achieve the specified surface finish.
- End Fitting & Welding: Coil tube ends are prepared and welded (TIG/Argon arc welding, GTAW) to headers, supports, or connectors. Welds undergo visual inspection, and critical welds are subjected to dye penetrant testing (PT) or radiographic testing (RT).
- Non-Destructive Testing (NDT): Comprehensive inspection including hydrostatic pressure testing, eddy current testing (ECT) for internal defects, and dimensional verification using laser scanning or coordinate measuring machines (CMM).
- Final Inspection & Packaging: Each coil tube unit receives a unique traceability identifier, material certificate (Mill Test Report / MTR), and is packaged with protective end caps and moisture barriers for shipment.
5. Applications
The stainless steel coil tube is a versatile component deployed across a broad spectrum of industrial and commercial applications:
5.1 Power Generation & Steam Systems
- Steam Heating Coil Tubes: Primary heat exchange elements in power station steam systems, where the coil geometry maximizes convective heat transfer between steam and process fluid.
- Economizers & Air Preheaters: Spiral coil configurations used to recover waste heat from flue gases.
- Water Hammer Mitigation: Coil tube designs incorporate natural pressure-wave dampening characteristics; engineering analyses of water hammer phenomena (transient pressure surges caused by rapid valve closure or steam condensation) inform the selection of appropriate wall thickness, material grade, and support spacing to prevent fatigue failure and tube rupture.
5.2 Industrial Process Engineering
- Chemical reactor jacket coils for temperature control
- Distillation column reboilers and condensers
- Oil & gas heat exchangers (sour gas service with SUS316L / duplex grades)
- Food & beverage pasteurization and sterilization coils (hygienic BA finish)
5.3 Building Services & HVAC
- Plate-fin coil heat exchangers for commercial air conditioning
- Radiant floor heating coil loops
- Dryer and dehumidifier heat recovery coils
5.4 Marine & Offshore
- Seawater cooling coils (SUS316L with enhanced pitting resistance)
- Ballast water treatment heat exchange units
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following standards:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System — covers design, manufacturing, testing, and delivery of all coil tube products |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASME Section IX | Welding qualification and procedure specifications |
| EN 10204 3.1 | Inspection Certificate — material and product conformity documentation |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for applicable coil tube assemblies |
| GB/T 12771 | Chinese National Standard for stainless steel seamless tubes |
| ASTM A213 / A269 | Material and dimensional specifications for seamless austenitic stainless steel tubing |
7. Unique Selling Points
- Water Hammer Resilience by Design: Informed by detailed field analyses of steam heating coil tube failures caused by water hammer, the product incorporates optimized wall thickness profiles, strategic support bracket placement, and material selection strategies that mitigate transient pressure surge damage — reducing unplanned downtime and extending service life.
- Precision CNC Coiling: Computer-controlled bending ensures repeatable coil geometry with minimal cross-sectional distortion, enabling seamless integration into modular heat exchanger designs.
- Full Traceability: Every coil tube unit is linked to its mill test report, heat number, and manufacturing batch, enabling complete supply chain traceability for critical infrastructure applications.
- Custom Engineering Capability: The product line supports fully customized coil configurations — including non-standard diameters, variable pitch designs, multi-pass arrangements, and hybrid geometries — tailored to specific thermal-hydraulic performance requirements.
- Wide Material Palette: Availability across austenitic, ferritic, and duplex stainless steel grades enables optimal material matching for diverse chemical and thermal environments, from mild aqueous service to aggressive sour gas applications.
- Comprehensive NDT Protocol: Multi-method non-destructive testing (hydrostatic, eddy current, radiographic, dye penetrant) ensures defect-free products suitable for high-pressure and safety-critical applications.
8. Summary
The Wenzhou Jixing Metal Materials Co., Ltd. Stainless Steel Coil Tube represents a high-performance, engineering-driven solution for thermal-fluid transfer applications. Grounded in practical operational experience — including rigorous analysis of water hammer failure mechanisms in power station steam heating systems — the product combines advanced material science, precision manufacturing, and comprehensive quality assurance to deliver reliable, long-life performance across power generation, chemical processing, food safety, marine, and HVAC sectors worldwide.