Stainless Steel Serpentine Coil Tube (Coiltube) — Product Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product No.: 766
Category: Literature Study / Technical Reference
1. Product Overview
The Stainless Steel Serpentine Coil Tube (also referred to as Coiltube or Helical Coil Tube) is a precision-formed tubular product characterized by its continuous serpentine geometry, engineered to maximize heat transfer surface area within a compact volumetric footprint. This product category is extensively studied and applied in high-efficiency thermal systems, particularly in boiler economizers (省煤器), waste heat recovery units, and process heat exchangers.
The serpentine coil tube represents a critical component in modern power generation and industrial heating systems. Unlike straight tubes arranged in parallel banks, the coil configuration enables cross-flow heat exchange (横向冲刷换热), significantly enhancing convective heat transfer coefficients by disrupting boundary layer development along the tube outer surface.
Reference Study: "Research on the Manufacturing Process of Economizer Serpentine Coil Tubes" — This foundational study examines the full manufacturing chain from raw material preparation through final coil forming, dimensional verification, and performance validation.
2. Material Composition & Mechanical Properties
2.1 Common Grades
| Grade (GB/T) | Grade (ASTM) | Grade (UNS) | Key Composition (%) | Typical Application |
|---|---|---|---|---|
| 06Cr19Ni10 | 304 / 304L | S30400 / S30403 | Cr 18–20, Ni 8–10.5, C ≤ 0.08 | General heat exchange, moderate corrosion |
| 022Cr17Ni12Mo2 | 316L | S31603 | Cr 16–18, Ni 10–14, Mo 2–3, C ≤ 0.03 | High-corrosion environments, marine/chemical |
| 06Cr25Ni20 | 310S | S31008 | Cr 24–26, Ni 19–22, C ≤ 0.08 | High-temperature service (≤ 1150 °C) |
| 06Cr17Ni12Mo2Ti | 321 | S32100 | Cr 17–19, Ni 9–12, Ti ≥ 5×C | High-temperature economizer sections |
2.2 Mechanical Properties (Solution-Annealed Condition)
| Property | 304 / 304L | 316L | 310S | 321 |
|---|---|---|---|---|
| Tensile Strength (Rm, MPa) | ≥ 520 | ≥ 485 | ≥ 515 | ≥ 520 |
| Yield Strength (Rp0.2, MPa) | ≥ 205 | ≥ 170 | ≥ 205 | ≥ 205 |
| Elongation (A, %) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HV10) | ≤ 210 | ≤ 210 | ≤ 210 | ≤ 210 |
| Maximum Service Temperature (°C) | 870 | 870 | 1150 | 980 |
2.3 Physical Properties
- Density: 7.93 g/cm³ (304), 8.00 g/cm³ (316L)
- Thermal Conductivity (λ): 16.3 W/(m·K) at 20 °C; 30.4 W/(m·K) at 800 °C
- Linear Expansion Coefficient (α): 17.3 × 10⁻⁶ /K (20–100 °C)
- Specific Heat (c): 500 J/(kg·K) at 20 °C
- Electrical Resistivity (ρ): 0.72 × 10⁻⁶ Ω·m at 20 °C
3. Technical Specifications
3.1 Tube Dimensions
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 19.0 mm – 57.0 mm (custom available) | GB/T 12771, ASTM A213 |
| Wall Thickness | 1.0 mm – 4.0 mm | GB/T 12771, ASTM A269 |
| Coil Diameter (Pitch) | 150 mm – 500 mm (adjustable per design) | Project-specific |
| Coil Length (Developed) | Up to 30 m continuous (splicing available) | — |
| Number of Turns | 10 – 100+ turns per section | Design-dependent |
| Tube End Condition | Plain end, flared end, or threaded (per drawing) | ASME B31.4 / B31.5 |
| Surface Finish | Ra ≤ 0.8 μm (polished); Ra ≤ 1.6 μm (standard) | ASTM A270 |
3.2 Performance Requirements
| Test Item | Acceptance Criteria | Test Method |
|---|---|---|
| Hydrostatic Pressure Test | No leakage or visible deformation at 1.5× design pressure | GB/T 241, ASTM A269 |
| Flattening Test | No cracks or splits after flattening to specified ratio | GB/T 14977 |
| Corrosion Test (Intergranular) | Grade 1 (no intergranular attack) — 100 h, 65% HNO₃ | GB/T 4334, ASTM A240 |
| Dimensional Tolerance | OD: ±0.1 mm; Wall: ±0.05 mm; Coil pitch: ±2 mm | GB/T 12771 |
| Coil Roundness Deviation | ≤ 0.5% of coil diameter | Project specification |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Inspection (原材料检验): Incoming seamless or welded stainless steel tube undergoes visual inspection, dimensional verification, chemical composition analysis (spectrometry), and mechanical property testing.
- End Preparation & Cleaning (端部加工与清理): Tube ends are deburred, chamfered, and cleaned to ensure uniform feed into the forming equipment.
- Heat Treatment / Solution Annealing (固溶处理): Tubes are solution-annealed at 1050–1150 °C followed by rapid water quenching to achieve a fully austenitic microstructure, eliminate carbide precipitation, and restore ductility.
- Coil Forming (盘管成型): The straight tube is fed through a precision bending machine equipped with a rotary die and bending roller system. The tube is formed into the serpentine/helical geometry at controlled bend radii (typically R ≥ 3D to prevent ovality and wall thinning).
- Fixturing & Stress Relief (定型与去应力): The formed coil is secured in a dedicated jig to maintain geometric accuracy. Optional stress-relief annealing at 300–400 °C may be applied to reduce residual bending stresses.
- Welding (焊接): For multi-section coils, butt-weld joints are fabricated using GTAW (Gas Tungsten Arc Welding / TIG) with argon gas shielding on both interior and exterior surfaces. Weld procedures are qualified per ASME Section IX.
- Final Inspection & Testing (最终检验): Includes hydrostatic testing, dimensional survey, surface inspection (visual + eddy current), and chemical verification.
- Packaging & Dispatch (包装发货): Coils are wrapped in protective film, placed in wooden crates or custom fixtures, and labeled with material certificates (MTC) and traceability information.
4.2 Key Process Control Parameters
| Parameter | Control Range | Significance |
|---|---|---|
| Bend Radius (R) | ≥ 3 × OD (typically 3D–6D) | Prevents wall thinning, ovality, and wrinkling |
| Bending Speed | 50 – 150 mm/min (material-dependent) | Controls springback and residual stress |
| Springback Compensation | 2° – 5° over-bend per turn | Ensures final geometry matches design |
| Weld Filler Wire | ER308L / ER316L (matched to base metal) | Prevents sensitization; ensures corrosion resistance |
| Argon Flow Rate | 5 – 10 L/min (root side); 8 – 12 L/min (fill side) | Prevents oxidation; ensures weld quality |
5. Applications
5.1 Primary Applications
- Boiler Economizers (省煤器): Serpentine coil tubes are the primary heat exchange element in coal-fired boiler economizers, recovering waste heat from flue gas to preheat feedwater, improving overall boiler thermal efficiency by 2–5%.
- Waste Heat Recovery Systems (余热回收系统): Used in industrial furnaces, cement kilns, and metallurgical processes for flue gas cooling and energy recovery.
- Process Heat Exchangers (工艺换热器): Applied in chemical processing, pharmaceutical, and food industries where stainless steel corrosion resistance is essential.
- Supercritical/Ultra-Supercritical Boilers (超临界/超超临界锅炉): High-grade materials (310S, 321) used in high-temperature economizer and reheater sections.
- Marine & Offshore Systems (海洋与 offshore 系统): 316L coil tubes for desalination plants and marine waste heat recovery.
5.2 Performance Advantages in Economizer Service
- Enhanced Heat Transfer: Cross-flow impingement on coil surfaces increases heat transfer coefficient by 20–40% compared to parallel-flow tube banks.
- Compact Footprint: Serpentine configuration reduces equipment volume by up to 30% for equivalent heat duty.
- Low Flue Gas Pressure Drop: Coil arrangement provides lower resistance compared to tube banks with the same heat transfer area.
- Anti-Fouling Characteristics: High gas velocity across coil surfaces promotes self-cleaning action, reducing ash deposition.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Scope |
|---|---|
| GB/T 12771 | Stainless steel seamless/welded tubes for general engineering |
| GB/T 21830 | Stainless steel seamless tubes for heat exchangers |
| ASTM A213 | Seamless austenitic stainless steel tubes for heat exchangers |
| ASTM A269 | Welded austenitic stainless steel tubes for chemical equipment |
| ASTM A312 | Welded austenitic stainless steel tubes for general applications |
| ASME BPV Code Section I | Boiler and Pressure Vessel Code — Power Boilers |
| EN 10216-5 | European standard for stainless steel tubes for heat exchangers |
6.2 Quality Assurance System
- ISO 9001:2015 — Quality Management System certification
- ISO 3834-2 — Quality requirements for welding of metallic materials
- EN 10204 3.1 / 3.2 — Inspection certificate (manufacturer's declaration / third-party inspection)
- Mill Test Certificate (MTC) — Full chemical composition and mechanical property documentation for each heat lot
- Welding Procedure Qualification (WPQ/WPS) — Qualified per ASME Section IX or ISO 15614
- NDT (Non-Destructive Testing): Eddy current (ET), penetrant testing (PT), and radiographic testing (RT) available upon request
6.3 Traceability
Each coil tube assembly is assigned a unique batch number linked to the original steel mill heat number, ensuring full material traceability from raw material through to final installation. Traceability marks are laser-etched or stamped at both ends of the tube assembly.