Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-loop piping product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1679). Unlike straight-length seamless or welded pipes that require cutting, threading, and field welding, the coil tube is supplied in a pre-formed helical or spiral configuration, enabling seamless integration into systems demanding complex routing, high flexibility, and rapid installation.
This product category is extensively studied and deployed in thermal energy storage systems, particularly Ice Coil Tube Energy Storage Systems (ICTES), where the coiled geometry maximizes heat transfer surface area within a confined volume. Research literature, including the analytical study titled "Analysis of the Melting Process of Ice Coil Tube Energy Storage Systems", has demonstrated the superior thermal performance and operational reliability of stainless steel coil tubes in phase-change energy storage applications.
2. Material & Properties
Wenzhou Jixing Metal Materials Co., Ltd. manufactures coil tubes using a range of austenitic and duplex stainless steel grades, selected according to the specific service environment and performance requirements of the end application.
2.1 Commonly Available Grades
- ASTM A312 TP304 / TP304L — General-purpose corrosion resistance; suitable for food processing, chemical handling, and moderate-temperature thermal storage.
- ASTM A312 TP316 / TP316L — Enhanced resistance to chlorides and pitting corrosion; preferred for marine environments and aggressive chemical media.
- ASTM A312 TP321 / TP347 — Stabilized grades with titanium or niobium additions; suitable for elevated-temperature service up to 870°C (1600°F).
- ASTM A790 S31803 / S32205 — Duplex stainless steels offering approximately twice the yield strength of 300-series grades with superior resistance to stress corrosion cracking.
2.2 Key Mechanical Properties (Typical — Grade 304/304L)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation: ≥ 40% (in 50 mm gauge length)
- Hardness: ≤ 92 HRB / ≤ 100 HV
- Operating Temperature Range: −196°C to 870°C (−321°F to 1598°F)
2.3 Key Physical Properties
- Density: 8.0 g/cm³ (0.29 lb/in³)
- Thermal Conductivity (20°C): 16.3 W/(m·K) (0.94 BTU/(ft·hr·°F))
- Specific Heat: 500 J/(kg·K)
- Linear Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 168.3 mm (¼" – 6½") | ASTM A312 / EN 10216-5 |
| Wall Thickness (WT) | 0.5 mm – 12.7 mm (0.020" – 0.500") | ASTM A312 / EN 10216-5 |
| Coil Diameter (CD) | 150 mm – 2000 mm (6" – 80") | Manufacturer Standard |
| Coil Length | Custom (typically 50 m – 500 m per coil) | Manufacturer Standard |
| Inside Diameter (ID) Tolerance | ± 0.05 mm – ± 0.13 mm | ASTM A312 |
| OD Tolerance | ± 0.05 mm – ± 0.13 mm | ASTM A312 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A312 |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm) / Polished (Ra ≤ 0.4 μm) / Electropolished (Ra ≤ 0.2 μm) | ASTM A967 / ISO 11404 |
| End Condition | Plain End / Beveled End / Threaded End / Custom Fitting | Per Customer Specification |
3.2 Applicable Standards & Codes
| Standard | Description |
|---|---|
| ASTM A312 / A312M | Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Pipes, Tubing, and Shapes |
| ASTM A213 | Standard Specification for Seamless Austenitic Chromium-Chromium-Nickel Alloy Steel Tubing for Heat-Transfer and Reformer Applications |
| EN 10216-5 | Non-ferrous metallic tubes — Technical delivery conditions — Part 5: Technical delivery conditions for austenitic stainless steel tubes |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Cold-rolled and Hot-rolled Processes |
| ASME B31.3 / B31.5 | Pressure Piping — Process Piping / Institutional Piping |
| ISO 11404 | Stainless Steel Tubes — Chemical Cleaning and Passivation |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality.
4.1 Process Flow
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Raw Material Selection & Inspection:
High-purity stainless steel billets or strip are sourced from certified mills. Incoming material undergoes spectroscopic analysis (e.g., optical emission spectrometry) to verify chemical composition compliance with the specified grade. Heat number traceability is maintained throughout production.
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Coil Forming (Rolling/Bending):
Flat stainless steel strip or pre-formed pipe blanks are fed through precision roll-forming or bending machines that apply controlled plastic deformation to create the desired helical coil geometry. Computer Numerical Control (CNC) systems ensure consistent coil pitch, diameter, and alignment throughout the production run.
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Welding (for Welded Coil Tubes):
Where welded construction is specified, longitudinal seams are formed using Automated Tungsten Inert Gas (ATIG) welding, Laser Beam Welding (LBW), or Orbital Welding. Weld parameters are continuously monitored to achieve full penetration with minimal heat-affected zone (HAZ) distortion.
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Heat Treatment & Annealing:
Coil tubes are subjected to solution annealing (typically at 1050°C – 1150°C for austenitic grades) followed by controlled cooling to restore full solution-stabilized microstructure, eliminate residual stresses, and maximize corrosion resistance. For duplex grades, intercritical annealing is performed at 1000°C – 1100°C to optimize the austenite-ferrite phase balance.
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Pickling & Passivation:
The annealed product is immersed in a mixed acid bath (nitric acid/hydrofluoric acid or citric acid) to dissolve the mill scale and oxide layer. A subsequent passivation treatment with nitric acid or citric acid forms a stable, protective chromium oxide (Cr₂O₃) passive film on the surface, enhancing long-term corrosion resistance.
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Surface Finishing (Optional):
Depending on application requirements, additional finishing steps such as mechanical polishing, electropolishing, or sandblasting may be applied to achieve specified surface roughness values.
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Quality Control & Non-Destructive Testing (NDT):
Each coil tube undergoes comprehensive inspection including:
- Dimensional verification using laser diameter gauges and ultrasonic wall thickness gauges
- Eddy Current Testing (ECT) per ASTM E709 for weld seam integrity and surface defect detection
- Hydrostatic Testing per ASTM A312 (typically at 1.5× working pressure) for leak tightness
- Visual Inspection (VT) for surface defects, weld appearance, and marking verification
- Chemical Analysis via Optical Emission Spectroscopy (OES) or Inductively Coupled Plasma (ICP) analysis
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Packaging & Dispatch:
Finished coil tubes are wound onto protective cores, wrapped with moisture-absorbent desiccant paper and protective film, and secured with steel strapping. Each coil is labeled with a unique heat number, product specification tag, and Certificate of Conformity (CoC) reference.
5. Applications
The versatility of stainless steel coil tubes enables deployment across a broad spectrum of industrial, commercial, and research applications:
5.1 Thermal Energy Storage Systems (TES)
Ice Coil Tube Energy Storage Systems (ICTES) represent one of the most significant applications. As analyzed in the research study "Analysis of the Melting Process of Ice Coil Tube Energy Storage Systems", coil tubes immersed in ice slurry or packed ice beds facilitate efficient thermal energy absorption during off-peak hours and controlled release during peak demand. The coiled geometry provides:
- Maximum heat transfer surface area per unit volume
- Uniform flow distribution minimizing thermal stratification
- Reduced pressure drop compared to equivalent straight-pipe configurations
- Compact footprint suitable for modular system design
Stainless steel's combination of thermal conductivity, corrosion resistance, and mechanical durability makes it the material of choice for these demanding thermal cycling applications.
5.2 Additional Application Domains
- Heat Exchangers & Refrigeration Coils: Evaporator and condenser coils in air conditioning, HVAC, and industrial refrigeration systems.
- Food & Beverage Processing: Sanitary-grade coils for dairy, brewing, pharmaceutical, and chemical processing lines where hygiene and corrosion resistance are critical.
- Automotive & Transportation: Fuel lines, brake lines, exhaust system components, and hydrogen fuel cell manifolds.
- Oil & Gas: Subsea production tubing, wellhead flowlines, and offshore platform piping systems requiring resistance to chloride-induced stress corrosion cracking.
- Petrochemical & Chemical Processing: Aggressive chemical transfer lines, reactor internals, and distillation column internals.
- Power Generation: Boiler tubes, superheater coils, and steam generator elements in fossil-fuel and nuclear power plants.
- Medical & Laboratory Equipment: Gas supply lines, autoclave components, and analytical instrument tubing.
- Structural & Architectural: Decorative railings, handrails, and architectural elements requiring both formability and aesthetic finish quality.
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:
6.1 Management System Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- ISO/IEC 17025 — Testing and Calibration Laboratory Competence (where applicable)
6.2 Product Certifications & Compliance
- CE Marking — Conformity with European Union directives including PED 2014/68/EU (Pressure Equipment Directive)
- NACE MR0175 / ISO 15156 — Materials for use in H₂S-containing environments in oil and gas production
- ASME Section IX — Welding Qualification compliance for pressure-containing applications
- EN 10204 3.1 / 3.2 — Inspection and Test Certificates
- Mill Test Reports (MTR) — Provided with every shipment, documenting chemical composition, mechanical properties, heat treatment records, and NDT results
- EN 10216-5 / EN 10217-7 — European technical delivery conditions compliance
- GB/T 14976 / GB/T 12771 — Chinese national standard compliance