Stainless Steel Coil Tube — Large Diameter Flexible Coil Tube Assembly System
Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a specialized class of continuously wound tubular products engineered for flexible deployment in heat exchange, process piping, and industrial fluid transport systems. Unlike conventional straight-length stainless steel tubes, coil tubes are wound into helical or spiral configurations that offer superior thermal performance, compact installation footprint, and enhanced mechanical flexibility.
This product line is particularly distinguished by its large-diameter flexible coil tube assembly technology (大直径柔性盘管套装工艺), which enables the production of coil tubes with outer diameters significantly exceeding standard industry limits while maintaining structural integrity, dimensional precision, and seamless continuity throughout the coil length. The advanced assembly methodology integrates precision cold-drawing, controlled bending, and multi-layer coiling techniques to achieve coil tubes that can be deployed in complex spatial configurations without kinking, buckling, or loss of flow capacity.
Material & Properties
Base Materials
- 304 (UNS S30400 / 1.4301) — Austenitic stainless steel with 18% chromium and 8% nickel; excellent general corrosion resistance and weldability.
- 316L (UNS S31603 / 1.4404) — Low-carbon austenitic grade with molybdenum addition (2–3% Mo); superior resistance to pitting and crevice corrosion in chloride-rich environments.
- 321 (UNS S32100 / 1.4541) — Titanium-stabilized austenitic grade; enhanced resistance to intergranular corrosion at elevated temperatures.
- 310S (UNS S31008 / 1.4845) — High-temperature austenitic grade with elevated chromium and nickel content; suitable for sustained service above 1000 °C.
- 904L (UNS N08904 / 1.4539) — High-alloy austenitic grade with 25% Ni and 4.5% Mo; exceptional resistance to reducing acids and aggressive chemical media.
Key Mechanical and Physical Properties
- Tensile Strength (UTS): 515–750 MPa (depending on grade and wall thickness)
- Yield Strength (0.2% Offset): 205–310 MPa
- Elongation at Break: ≥ 40% (annealed condition)
- Hardness: ≤ 230 HV (annealed), ≤ 350 HV (cold-worked)
- Thermal Conductivity (25 °C): 14–16 W/(m·K) for austenitic grades
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C (25–1000 °C)
- Maximum Continuous Service Temperature: 870–1150 °C (grade-dependent)
- Corrosion Potential (ASTM G5): ≥ 200 mV vs. SCE in 3% NaCl solution (for 316L and 904L)
Specifications
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 168.3 mm (¼" – 6½") | ASTM A269 / ASME B36.19M |
| Wall Thickness | 0.40 mm – 6.35 mm (0.016" – ¼") | ASTM A269 / EN 10217-7 |
| Coil Mean Diameter | 300 mm – 3000 mm | Manufacturer specification |
| Coil Length (Unwound) | 5 m – 120 m (continuous) | Customer requirement |
| Bend Radius (Minimum) | ≥ 3D (D = outer diameter) | ISO 1127 |
| Surface Finish | Ra ≤ 0.8 μm (electropolished); Ra ≤ 1.6 μm (industrial passivated) | ASTM A270 / ISO 14288 |
| Tolerance on OD | ± 0.05 mm (precision grade); ± 0.10 mm (standard) | ASTM A269 |
| Tolerance on Wall Thickness | ± 10% of nominal (standard); ± 5% (precision) | ASTM A269 |
| End Condition | Plain, beveled, threaded, or flanged | ASME B1.20.1 / B16.5 |
| Operating Pressure | Up to 40 MPa (PN40) depending on schedule | ASME B31.3 / EN 13480 |
| Operating Temperature Range | −196 °C to +1150 °C | Grade-dependent |
Manufacturing Process
1. Raw Material Selection and Incoming Inspection
Hot-rolled stainless steel strip or seamless tube blank material is sourced from certified mills and subjected to comprehensive incoming inspection including spectroscopic analysis (OES — Optical Emission Spectroscopy), ultrasonic testing (UT — Ultrasonic Testing) for internal defects, and visual surface examination in accordance with ASTM E1951 and ASTM E309.
2. Cold Drawing and Precision Forming
The raw tube blanks undergo multi-stage cold drawing through progressively reducing dies to achieve the target outer diameter and wall thickness with tight dimensional tolerances. The cold-drawing process imparts beneficial work hardening while maintaining the austenitic microstructure. Intermediate annealing cycles (solid solution treatment at 1050–1100 °C followed by controlled cooling) are performed between drawing stages to relieve accumulated residual stresses and restore ductility.
3. Large-Diameter Flexible Coiling Process
The proprietary large-diameter flexible coil tube assembly technology (大直径柔性盘管套装工艺) involves:
- Pre-forming: Controlled induction heating of the tube to a prescribed temperature window to reduce bending stresses and prevent work hardening at the coil bend radius.
- Spiral Winding: The tube is wound onto precision mandrels using CNC-controlled coiling machines that maintain constant tension and uniform bend radius throughout the coil length. Multi-axis servo systems ensure concentricity accuracy of ± 0.5 mm.
- Stress Relief: Post-coiling stress relief annealing (850–900 °C for 1–2 hours, followed by furnace cooling) eliminates residual bending stresses while preserving dimensional stability.
- Layer Assembly: For multi-layer coil configurations, individual coil layers are assembled and secured using precision-engineered retaining rings, welding, or mechanical clamping systems to maintain structural integrity during transport and installation.
4. Surface Treatment and Finishing
- Pickling and Passivation: Acid pickling (nitric/hydrofluoric acid blend) followed by passivation to remove oxide scale and establish a protective chromium oxide layer (ASTM A967).
- Electropolishing: Available for critical applications requiring Ra ≤ 0.4 μm surface finish (ASTM B923 / ASTM F86).
- Pickling Paste Application: For large-diameter coils where immersion pickling is impractical, high-efficiency pickling paste is applied and removed to achieve uniform passivation.
5. Non-Destructive Testing and Quality Verification
- Helical Eddy Current Testing: 100% coverage for detection of surface and near-surface defects (ASTM E309).
- Hydrostatic Pressure Testing: Each coil tested at 1.5× the maximum design pressure with a minimum hold time of 30 seconds (ASTM A269 / ASME B31.3).
- Dimensional Verification: Coordinate Measuring Machine (CMM) inspection of OD, wall thickness, and coil geometry at specified intervals.
- Spectroscopic Verification: Confirmed chemical composition via portable XRF (X-Ray Fluorescence) or laboratory OES analysis.
Applications
Industrial Heat Exchangers
Coil tubes are the preferred configuration for shell-and-coil heat exchangers, air-cooled condensers, and evaporators in the chemical, petrochemical, and pharmaceutical industries. The helical geometry provides enhanced turbulence and heat transfer coefficients (up to 30% improvement over straight tubes) while minimizing pressure drop and fouling tendency.
Process Piping Systems
In complex plant layouts where space constraints or seismic activity preclude straight-run piping, flexible coil tubes offer a single-piece solution that eliminates numerous welding joints, reducing potential leak points and simplifying installation. The continuous coil length eliminates the need for intermediate fittings and supports.
Cryogenic Applications
316L and 904L coil tubes are extensively used in LNG (Liquefied Natural Gas) processing, cryogenic air separation, and superconducting magnet cooling systems. The austenitic microstructure maintains excellent ductility and toughness at temperatures as low as −196 °C without embrittlement.
Food and Beverage Processing
Electropolished 304 and 316L coil tubes meet sanitary requirements for milk pasteurization, beer brewing, and pharmaceutical clean-in-place (CIP) systems. The smooth internal surface (Ra ≤ 0.4 μm) prevents product adhesion and facilitates automated cleaning.
Energy and Power Generation
Coil tubes are employed in supercritical and ultra-supercritical boiler designs, solar thermal collectors, and geothermal heat extraction systems where high-temperature resistance and thermal cycling durability are paramount.
Quality Certifications
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- EN 10204 Type 3.1 — Third-party inspection and certification for material conformity
- ASME PE Stamp — Authorization for pressure equipment manufacturing
- EU PED 2014/68/EU — Pressure Equipment Directive compliance (Categories I–IV)
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking for oil and gas applications
- NSF/ANSI 61 — Drinking water system components certification (for food-grade applications)
- CE Marking — European Conformity for pressure equipment and machinery directives
Unique Selling Points
Proprietary Large-Diameter Coiling Technology: Wenzhou Jixing Metal Materials Co., Ltd has developed and refined a proprietary assembly process for large-diameter flexible coil tubes that overcomes the industry-limiting challenges of coil stability, layer-to-layer alignment, and post-coiling dimensional accuracy. This technology enables coil mean diameters up to 3000 mm with concentricity tolerances of ± 0.5 mm — a significant advancement over conventional coiling capabilities limited to 1500 mm.
- Seamless Continuous Length: Single-piece coils up to 120 m eliminate welding joints, reducing leak risk and maintenance requirements by up to 60% compared to field-welded piping systems.
- Custom Geometry Engineering: Capability to produce variable-diameter coils, transition sections, and multi-layer assemblies tailored to specific process requirements.
- Full Traceability: Each coil is accompanied by a complete material traceability dossier including mill certificates, heat numbers, test reports, and dimensional inspection data.
- Extended Design Life: The combination of high-purity raw materials, controlled manufacturing, and comprehensive surface treatment ensures a design service life exceeding 25 years in aggressive chemical environments.
Standards and Specifications Compliance
| Standard | Scope |
|---|---|
| ASTM A269 / A269M | Welded Austenitic Stainless Steel Tubing for Boilers, Heat Exchangers, and General Heat Transfer Applications |
| ASTM A312 / A312M | Welded Austenitic Stainless Steel Seamless and Welded Tubing |
| ASME B36.19M | Welded Austenitic Stainless Steel Tube |
| EN 10217-7 | Non-alloy and Heat Resistant Steel Tubes for High Pressure Uses at High Temperatures — Part 7: Dimensions and Tolerances for Tubes |
| ISO 1127 | Steel Tubes — Technical Delivery Conditions |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard) |
Wenzhou Jixing Metal Materials Co., Ltd — Engineering Excellence in Stainless Steel Coil Tube Solutions