Stainless Steel Coil Tube (Coiltube) – Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Coiltube or Coil Pipe) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product category encompasses both round and rectangular cross-sectional coil tubes designed for continuous bending into helical, serpentine, or spiral configurations. The coil tube is widely recognized in the industrial sector for its superior heat transfer efficiency, compact footprint, and resistance to corrosion under extreme operating conditions.
The product is manufactured in accordance with international standards including ASTM (American Society for Testing and Materials), EN (European Norms), JIS (Japanese Industrial Standards), and GB (Chinese National Standards). The manufacturing process draws upon advanced coil forming technology, including cold bending, heat treatment, and surface finishing techniques that ensure dimensional accuracy and mechanical integrity throughout the entire coil length.
2. Material & Properties
2.1 Available Material Grades
The coil tube is available in a comprehensive range of stainless steel grades, each selected to meet specific application requirements:
- 304 / 304L (UNS S30400 / S30403) – General-purpose austenitic stainless steel with excellent corrosion resistance and formability. The "L" designation indicates low carbon content (<0.03% C), suitable for welding applications requiring resistance to sensitization.
- 316 / 316L (UNS S31600 / S31603) – Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments.
- 321 (UNS S32100) – Columbium (niobium) stabilized grade providing excellent resistance to intergranular corrosion at elevated temperatures.
- 310S (UNS S31008) – High-temperature austenitic grade with outstanding oxidation resistance up to 1150°C.
- 316Ti (UNS S31635) – Titanium-stabilized variant of 316L with enhanced weldability and resistance to stress corrosion cracking.
- 904L (UNS N08904) – High-alloy austenitic grade with exceptional resistance to oxidizing and reducing acids.
- 2205 Duplex (UNS S31803) – Duplex austenitic-ferritic stainless steel offering yield strength approximately twice that of standard austenitic grades.
2.2 Mechanical Properties (Typical Values for Grade 304)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ASTM A213 / GB/T 12771 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A213 / GB/T 12771 |
| Elongation (A) | ≥ 40% | ASTM A213 |
| Hardness (HBW) | ≤ 217 | ASTM A262 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | ASTM E153 |
| Maximum Operating Temperature | 870°C (oxidizing atmosphere) | — |
| Maximum Operating Pressure | Up to 35 MPa (grade-dependent) | ASME B31.3 |
2.3 Chemical Composition (Grade 304 – Typical)
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 |
| Iron (Fe) | Balance |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification Range | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 168.0 mm | ±0.15 mm |
| Wall Thickness (WT) | 0.4 mm – 6.0 mm | ±10% |
| Rectangular Cross-Section | Min. 4×4 mm to Max. 100×100 mm | ±0.2 mm |
| Bend Radius (Min.) | 1.5 × OD (cold bending) | ±2% |
| Coil Length | 10 m – 500 m (continuous) | — |
| Coil Diameter (Winding) | 200 mm – 1200 mm | ±10 mm |
| Surface Finish | Ra ≤ 0.8 μm (electropolished); Ra ≤ 1.6 μm (standard) | ASTM A967 |
3.2 Available Standards
- ASTM A213 – Standard Specification for Seamless Austenitic Stainless Steel Tube for Heat-Transfer Exchangers and Similar Service
- ASTM A269 – Standard Specification for Seamless and Wrought Stainless Steel Tubing
- EN 10216-5 – Seamless heat-exchanger tubes of austenitic steels
- GB/T 12771 – Welded Stainless Steel Tubes for Fluid Transport
- GB/T 21832 – Seamless Stainless Steel Tubes for Heat Exchangers
- JIS G3459 – Austenitic Stainless Steel Tubes for Heat Exchangers
4. Manufacturing Process
The production of stainless steel coil tubes involves a multi-stage manufacturing sequence designed to ensure dimensional precision, metallurgical integrity, and surface quality. The following process flow illustrates the complete production chain:
4.1 Raw Material Preparation
- Ingot Casting & Hot Rolling: Primary stainless steel ingots are cast via vacuum arc remelting (VAR) or electro-slag remelting (ESR) to minimize impurity content. The ingots are subsequently hot-rolled into strip or plate stock.
- Acid Pickling & Descaling: The hot-rolled product undergoes pickling in mixed acid baths (HNO₃ + HF or HNO₃ + HCl) to remove oxide scale, restoring the passive chromium oxide layer essential for corrosion resistance.
4.2 Tube Forming
- Cold Forming / Roll Forming: The pickled strip is fed through a series of precision dies to form the desired cross-sectional profile (round, rectangular, or oval). For rectangular coil tubes, the forming process employs progressive die sets to achieve sharp corner radii without wall thinning or material cracking.
- Seam Welding (for welded tubes): The formed strip is welded using high-frequency induction welding (HF) or laser welding technology, achieving weld strength exceeding 90% of the base metal. Post-weld annealing eliminates residual stresses in the heat-affected zone (HAZ).
- Seamless Tube Production: For seamless variants, the hot-rolled billet is pierced (Mannesmann process), followed by cold drawing and mandrel drawing (ODT process) to achieve final dimensions with superior internal surface quality.
4.3 Coil Bending & Shaping
- Cold Bending: The straight tube is fed through a CNC-controlled coil bending machine equipped with hydraulic servo systems. The bending process employs a combination of rotary draw bending and push bending techniques to achieve uniform coil geometry with consistent bend radius.
- Springback Compensation: Advanced software algorithms compensate for elastic springback during bending, ensuring the final coil dimensions conform to design specifications within ±2% tolerance.
- Heat-Assisted Bending (for large OD): For tubes with OD > 50 mm or tight bend radii, localized induction heating is applied to reduce yield strength during the bending operation, preventing cracking and excessive work hardening.
4.4 Post-Processing
- Stress Relief Annealing: The coiled product is subjected to solution annealing at 1050°C – 1150°C followed by controlled cooling (water quench or air cool), restoring full austenitic microstructure and relieving residual bending stresses.
- Pickling & Passivation: Post-welding or post-forming acid pickling removes any discoloration or oxide buildup. Subsequent passivation treatment (citric acid or nitric acid) enhances the natural chromium oxide passive layer, improving corrosion resistance.
- Surface Finishing: Options include mechanical polishing, chemical polishing, electropolishing (achieving Ra ≤ 0.4 μm), and PVD (Physical Vapor Deposition) coating for specialized applications.
- End Finishing: Tube ends are cut to length, deburred, and beveled (where required) to facilitate welding or fitting installation.
4.5 Quality Inspection
- Dimensional Inspection: Coordinate Measuring Machine (CMM) verification of OD, wall thickness, and bend radius at multiple points along the coil length.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) for detecting surface and near-surface defects; ultrasonic testing (UT) for internal wall thickness verification; hydrostatic testing at 1.5× working pressure for leak detection.
- Microstructural Examination: Metallographic analysis to verify grain structure, absence of phase segregation, and proper weld fusion characteristics.
- Corrosion Testing: Salt spray testing (ASTM B117) for minimum 500 hours without pitting; intergranular corrosion testing per ASTM A262 Practice E for stabilized grades.
5. Applications
5.1 Heat Exchangers & Thermal Management
The coil tube's primary application domain is the manufacture of spiral-wound and plate-fin heat exchangers. The continuous coil configuration maximizes heat transfer surface area within a compact volume, making it ideal for:
- Oil coolers and water-to-air heat exchangers in automotive and HVAC systems
- Refrigeration evaporators and condensers
- Process heat exchangers in chemical and petrochemical industries
- Power plant feedwater heaters and condensers
5.2 Chemical & Pharmaceutical Processing
- Reactor coil inserts for jacketed vessel cooling
- Pharmaceutical CIP (Clean-In-Place) and SIP (Sterilize-In-Place) systems
- Corrosive chemical transfer lines and distribution manifolds
- Food and beverage processing equipment requiring hygienic-grade surfaces (Ra ≤ 0.8 μm)
5.3 Energy & Power Generation
- Solar thermal collector absorber tubes
- Geothermal heat extraction coils
- Nuclear reactor coolant loop components (specialized grades)
- Fuel cell bipolar plate manifolds
5.4 Marine & Offshore
- Ballast water treatment system piping
- Offshore platform heat exchangers (Grade 316L / 904L)
- Submarine cable protection and cooling systems
5.5 Aerospace & Defense
- Engine cooling circuit tubing
- Fuel system lines and hydraulic circuits
- Avionics thermal management coils
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management infrastructure ensuring that all coil tube products meet international regulatory and industry standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System – ensures consistent product quality and customer satisfaction |
| ISO 14001:2015 | Environmental Management System – sustainable manufacturing practices |
| ISO 45001:2018 |