Stainless Steel Coil Tube (Spiral Coil Pipe) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Spiral Coil Pipe or Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. in accordance with the principles outlined in the standard for Steel Shell-and-Coil Spiral Coil Heat Exchangers. This product is formed by continuously winding high-grade stainless steel seamless or welded pipe into a helical or spiral configuration, creating a compact and highly efficient heat transfer element. The coil tube is widely recognized for its superior thermal performance, structural integrity, and resistance to corrosion, making it an indispensable component in industrial heat exchange systems, chemical processing, and energy-intensive applications.
The coil tube design maximizes the surface-area-to-volume ratio, enabling more efficient heat exchange within a confined footprint compared to conventional straight-tube arrangements. This geometric advantage is particularly critical in shell-and-coil heat exchanger assemblies, where the spiral coil serves as the primary heat transfer medium within a pressure-containing shell.
2. Material & Properties
2.1 Base Materials
The coil tube is fabricated from austenitic and duplex stainless steel grades, selected based on the specific application requirements:
- ASTM A312 Type 304 (UNS S30400) — General-purpose corrosion resistance; excellent formability for coil winding
- ASTM A312 Type 316L (UNS S31603) — Enhanced resistance to pitting and crevice corrosion due to molybdenum addition; suitable for aggressive chemical environments
- ASTM A312 Type 321 (UNS S32100) — Titanium-stabilized grade; resistant to intergranular corrosion at elevated temperatures
- ASTM A312 Type 310S (UNS S31008) — High-temperature service grade; maintains mechanical strength up to 1100 °C
- ASTM A312 Type 904L (UNS N08904) — Super austenitic grade; exceptional resistance to sulfuric acid and mixed acid environments
- Duplex 2205 (UNS S32205) — Combined austenitic-ferritic microstructure; high yield strength and superior chloride stress corrosion resistance
2.2 Key Mechanical Properties (Typical for Grade 316L)
| Property | Specification |
|---|---|
| Tensile Strength (Ultimate) | ≥ 515 MPa (75 ksi) |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) |
| Elongation at Break | ≥ 40% |
| Density | 8.0 g/cm³ |
| Thermal Conductivity (at 100 °C) | 16.3 W/(m·K) |
| Thermal Expansion Coefficient (20–100 °C) | 17.3 × 10⁻⁶ /°C |
| Maximum Service Temperature | 870 °C (1598 °F) — non-oxidizing atmosphere |
| Minimum Service Temperature | -196 °C (LN₂ service) |
2.3 Corrosion Resistance
The austenitic stainless steel grades employed exhibit excellent resistance to atmospheric corrosion, dilute acids, alkaline solutions, and organic chemicals. The passive chromium oxide film (Cr₂O₃) self-repairs in the presence of oxygen, providing long-term durability without the need for additional protective coatings.
3. Specifications
3.1 Geometric Dimensions
| Parameter | Range / Options | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (¼" – 4") | Custom diameters available |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm (0.020" – 0.236") | Selected per pressure rating |
| Coil Diameter (Helix Mean Diameter) | 200 mm – 6000 mm | Dependent on shell size |
| Coil Length (Developed Length) | Up to 500 m continuous | Single-piece winding |
| Number of Turns | 10 – 500 turns | Configured per thermal duty |
| Coil Pitch (Turn-to-Turn Spacing) | 5 mm – 25 mm | Affects flow turbulence and ΔP |
| End Connections | Welded, Flanged, Threaded, or Brazed | Custom per installation |
| Surface Finish | 2B (Mill Annealed) / BA (Bright Annealed) / Electropolished (Ra ≤ 0.4 μm) | Electropolished for sanitary use |
3.2 Pressure & Temperature Ratings
| OD (mm) | WT (mm) | Max Working Pressure (bar) @ 20 °C | Max Working Pressure (bar) @ 200 °C |
|---|---|---|---|
| 12.7 | 1.65 | 60 | 42 |
| 19.1 | 1.65 | 55 | 38 |
| 25.4 | 2.11 | 70 | 48 |
| 38.1 | 2.77 | 85 | 58 |
| 50.8 | 3.05 | 80 | 54 |
| 76.2 | 3.96 | 82 | 56 |
| 108.0 | 4.57 | 78 | 53 |
Pressure ratings are calculated per ASME B31.3 / EN 13480 standards using the Barlow equation and are subject to final verification based on specific grade, temperature, and corrosion allowance.
3.3 Applicable Standards & Codes
- ASTM A312 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipes, Tubes, and Shapes
- ASME B31.3 — Process Piping Code
- ASME BPV Code Section VIII — Pressure Vessel Code (for heat exchanger integration)
- EN 10216-5 — Technical Delivery Conditions for Seamless Heat Exchanger Tubes
- GB/T 12771 — Chinese National Standard for Welded Stainless Steel Tubes for General Application
- GB/T 13296 — Chinese National Standard for Seamless Stainless Steel Tubes for Heat Exchangers
- GB/T 26121 — Steel Shell-and-Coil Spiral Coil Heat Exchangers
- ISO 1129 — Heat Exchangers — General Requirements
- TSG 21 — Chinese Safety Technical Supervision for Pressure Vessels
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel pipe (seamless per ASTM A312 or welded per ASTM A999) is inspected for chemical composition (via spark emission spectrometry), mechanical properties, and dimensional accuracy. Each heat lot is traceable via mill test certificates.
- Cutting & End Preparation: Pipe is cut to the required developed length using precision plasma or laser cutting. Ends are deburred and chamfered to facilitate welding and assembly.
- Pre-Forming (Optional): For large-diameter coils, the pipe may be pre-bent to an initial curvature to reduce residual stress during the final winding operation.
- Spiral Winding: The pipe is wound around a precision mandrel using a CNC-controlled coil winding machine. The mandrel diameter, pitch, and number of turns are programmed to exact specifications. The winding speed and tension are controlled to prevent ovalization, buckling, or plastic deformation.
- Post-Winding Heat Treatment: For grades susceptible to sensitization (e.g., 304, 316), solution annealing at 1010–1150 °C followed by rapid quenching may be applied to restore full corrosion resistance and relieve residual stresses induced during winding.
- End Connection Fabrication: Coil ends are prepared for connection — options include GTAW (Gas Tungsten Arc Welding) butt welds, flange welding, threaded fittings, or brazed joints. All welds are performed in accordance with ASME Section IX qualification procedures.
- Surface Treatment: Depending on application, the coil may undergo pickling and passivation (nitric acid or citric acid), electropolishing, or mechanical polishing to achieve the required surface roughness (Ra values).
- Non-Destructive Testing (NDT): Welded joints and coil integrity are verified through 100% visual inspection, dye penetrant testing (PT), and hydrostatic pressure testing per ASME B31.3 requirements. Radiographic testing (RT) or ultrasonic testing (UT) may be applied for critical welds.
- Hydrostatic Pressure Test: Each coil assembly is pressure-tested at 1.5× the maximum design working pressure, held for a minimum of 30 minutes with zero leakage tolerance.
- Final Inspection & Documentation: Dimensional verification, surface finish measurement, and compilation of the complete quality dossier including material certificates, NDT reports, pressure test records, and dimensional drawings.
4.2 Quality Control Measures
- In-process dimensional checks at every winding station using laser displacement sensors
- Ovality control maintained within 1% of nominal OD after winding
- Hardness testing (HV30) to verify post-winding mechanical properties
- Intergranular corrosion testing (ASTM A262 Practice E) for stabilized grades
- Full traceability from raw material heat number through to final coil serial number
5. Applications
5.1 Primary Application Domains
- Shell-and-Coil Heat Exchangers: The primary application domain; the spiral coil is housed within a cylindrical shell, serving as the heat transfer surface for liquid-liquid, liquid-gas, or condensing/evaporating service. The helical geometry induces secondary flow (Dean vortices), significantly enhancing the heat transfer coefficient compared to straight tubes.
- Chemical Processing: Reactor cooling, distillation column condensers, and heat recovery systems in petrochemical, pharmaceutical, and specialty chemical plants. Grades 316L and 904L are preferred for corrosive process fluids.
- Food & Beverage Industry: Pasteurizers, sterilizers, condensers, and evaporators. Electropolished 316L coil tubes with Ra ≤ 0.4 μm surface finish meet FDA and EHEDG sanitary requirements.
- Pharmaceutical Manufacturing: Clean-in-place (CIP) compatible coil assemblies for bioreactors, distillation systems, and thermal process equipment.
- Petrochemical & Oil Refining: Crude oil preheaters, crude fractionators, and heat recovery steam generators (HRSG).
- Power Generation: Economizers, feedwater heaters, and waste heat recovery systems in combined cycle power plants.
- Cryogenic Applications: LNG processing and cryogenic separation units using 304L/316L grades with proven low-temperature impact toughness.
- HVAC & Refrigeration: Compact condensers and evaporators for industrial and commercial refrigeration systems.
- Marine & Offshore: Seawater coolers, desalination plants, and ballast water treatment systems utilizing duplex 2205 for chloride resistance.
5.2 Performance Advantages in Heat Exchange
The spiral coil geometry generates Dean number (De)-dependent secondary flow patterns within the tube, which disrupt the thermal boundary layer and enhance turbulent mixing. This results in heat transfer coefficients that are typically 1.5× to 3.0× higher than those achieved in equivalent straight-tube configurations at the same flow velocity. The compact helical arrangement also allows for up to 50% reduction in equipment footprint compared to conventional shell-and-tube designs.
6. Quality Certifications & Compliance
6.1 Manufacturer Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- ASME "U" Stamp — Authorization for fabrication of pressure vessels and heat exchangers
- CE Marking (PED 2014/68/EU) — Conformity with European Pressure Equipment Directive
- TSG Certification — Chinese Technical Supervision Bureau approval for pressure equipment manufacturing
- API Q1 (ISO/TS 29001) — Quality Management Systems for Petroleum, Petrochemical, and Natural Gas Industries
- EN 10204 — Type 3.1 Test Certificates issued for every production lot
6.2 Third-Party Inspection
All coil tube assemblies are available for third-party inspection by internationally recognized inspection bodies including LRQA (Lloyd's Register Quality Assurance), TÜV, DNV, ABS, and CCIC. Inspection scope covers raw material verification, in-process monitoring, NDT witnessing, pressure test observation, and final dimensional/surface finish verification.