Stainless Steel Coil Tube (Coiltube) — High-Pressure Two-Phase Flow Helical Coil

Product Overview

The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered helically coiled piping system designed for demanding high-pressure, high-temperature environments where steam-water two-phase flow is prevalent. This product is specifically optimized for applications in High Temperature Reactors (HTR), nuclear thermal systems, supercritical power generation, and advanced industrial heat exchangers. The coil geometry provides superior heat transfer surface area-to-volume ratios compared to straight-tube configurations, making it indispensable in compact thermal management systems.

The product line is informed by rigorous experimental research on friction resistance characteristics of high-pressure steam-water two-phase flow in small-diameter helical coil tubes, as documented in studies conducted on HTR-10 reactor components. This foundational research ensures that the coil tube design accounts for complex multiphase flow dynamics, pressure drop behavior, and thermal-hydraulic performance under extreme operating conditions.

Material & Properties

Primary Material Grades

• AISI 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability; suitable for moderate-temperature applications up to 870°C.
• AISI 316L (UNS S31603) — Low-carbon variant with added molybdenum (Mo 2–3%) for enhanced resistance to pitting and crevice corrosion in chloride-containing environments; ideal for nuclear and marine applications.
• AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 900°C); preferred for high-temperature reactor internals.
• AISI 310S (UNS S31008) — High-temperature austenitic grade with elevated chromium and nickel content; designed for sustained operation above 1000°C in oxidizing atmospheres.

Mechanical & Thermal Properties

• Tensile Strength (UTS): 515–720 MPa (depending on grade and condition)
• Yield Strength: 205–310 MPa (0.2% offset)
• Elongation: ≥30% (minimum, per ASTM A213/A269)
• Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
• Thermal Expansion Coefficient: 16.0–18.0 × 10⁻⁶ /K (20–1000°C)
• Density: 7.93–8.03 g/cm³
• Operating Temperature Range: −196°C to +1200°C (grade-dependent)
• Maximum Design Pressure: Up to 100 MPa (pressure-rated per ASME VIII Div. 1/3)

Specifications

Parameter	Specification	Standard / Reference
Product Name	Stainless Steel Coil Tube (Coiltube)	—
Product Code	1469	Internal Catalog
Tube Outer Diameter (OD)	Φ6.35 mm – Φ50.8 mm (¼" – 2")	ASTM A213 / ASTM A269
Tube Wall Thickness	0.5 mm – 3.0 mm	ASTM A213
Coil Diameter (Helix Diameter)	100 mm – 2000 mm (adjustable per application)	ASME B31.1 / B31.3
Coil Pitch (Helical Spacing)	10 mm – 100 mm (customizable)	Design-Specific
Number of Turns	10 – 5000+ turns (per coil assembly)	Design-Specific
Surface Finish (Roughness)	Ra ≤ 0.4 μm (electropolished); Ra ≤ 1.6 μm (pickled)	ASTM A967 / ASME BPE
End Condition	Plain end, beveled end, or threaded connection	ASME B1.20.1
Heat Treatment	Solution annealed (1050–1150°C) + water quench	ASTM A213
Maximum Operating Pressure	Up to 100 MPa (design-rated)	ASME BPV Code Section I
Maximum Operating Temperature	Up to 1200°C (grade-dependent)	ASME BPV Code
Flow Regime Capability	Single-phase, two-phase (steam-water), and supercritical flow	HTR-10 Research Data
Corrosion Resistance	Resistant to oxidizing acids, chlorides, and high-temperature oxidation	ASTM G48 / NACE TM0169

Manufacturing Process

The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, mechanical integrity, and compliance with international standards.

1. Raw Material Procurement & Verification:

   High-purity stainless steel seamless tube stock is sourced from certified mills (e.g., Outokumpu, Sandvik, Tsingshan). Each lot undergoes spectrographic analysis (OES), chemical composition verification, and mechanical property testing per ASTM E415 and ASTM A213.

2. Cold Bending & Coil Forming:

   Tubes are cold-formed into helical coils using precision CNC-controlled coiling machinery. The bending process is carefully controlled to avoid excessive work hardening, micro-cracking, or ovality distortion. The coil diameter and pitch are maintained within ±0.5% tolerance through real-time feedback systems.

3. Interpass Inspection:

   During and after coiling, each tube section undergoes visual inspection (VT), eddy current testing (ET) per ASTM E309, and dimensional verification (laser scanning) to detect surface defects, wall thinning, or geometric deviations.

4. Welding & Joining:

   Tube-to-tube and tube-to-header joints are fabricated using Gas Tungsten Arc Welding (GTAW / TIG) or Orbital Arc Welding (OAW) to achieve fully fused, high-integrity welds. Weld quality is verified via Penetrant Testing (PT) per ASTM E165, Radiographic Testing (RT) per ASTM E94, and Ultrasonic Testing (UT) per ASTM E2715.

5. Pickling & Passivation:

   Post-welding, the coil assembly is subjected to acid pickling (HNO₃/HF mixture) and passivation treatment per ASTM A967 to remove oxide scale, restore the chromium-rich passive film, and enhance corrosion resistance.

6. Electropolishing (Optional):

   For applications requiring ultra-low surface roughness (e.g., nuclear, pharmaceutical), the interior surface is electropolished to achieve Ra ≤ 0.4 μm, removing surface contaminants and work-hardened layers.

7. Final Pressure & Leak Testing:

   Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the maximum design pressure (per ASME BPV Code) and helium leak testing (leak rate ≤ 1×10⁻⁹ Pa·m³/s) for nuclear-grade applications.

8. Non-Destructive Testing (NDT) Summary:

   A comprehensive NDT package including ET, PT, RT, and UT is performed at critical junctures. All test results are documented in a traceable quality dossier per ISO 9001:2015 requirements.

Applications

Primary Application Domains

• Nuclear Reactor Systems (HTR-10, HTGR):

  Coil tubes serve as steam generators, intermediate heat exchangers, and reactor coolant channels in High Temperature Gas-Cooled Reactors. The helical geometry enhances turbulent mixing and heat transfer coefficients under high-pressure steam-water two-phase flow conditions, as validated by HTR-10 experimental data on frictional pressure drop characteristics.

• Supercritical & Ultra-Supercritical Power Plants:

  Used in superheater and reheater sections where operating pressures exceed 25 MPa and temperatures exceed 600°C. The coil design accommodates thermal expansion while maintaining structural integrity.

• Industrial Heat Exchangers & Boilers:

  Compact spiral heat exchangers for chemical processing, petrochemical refining, and food processing industries where space-constrained, high-efficiency heat transfer is required.

• Oil & Gas Industry:

  Subsea coil tubing for well intervention, oilfield heat tracing, and high-pressure gas conditioning systems in offshore platforms.

• Power Generation Turbines:

  Steam coil piping for turbine bypass systems, feedwater heaters, and condenser tube bundles in conventional and combined-cycle power plants.

• Chemical & Pharmaceutical Processing:

  Reactors, distillation columns, and heat recovery systems requiring hygienic-grade (3-A/ASME BPE) surface finishes and resistance to aggressive chemical media.

• Marine & Offshore Systems:

  Scrubber systems, exhaust gas cleaning (EGC) systems, and marine auxiliary boiler coils operating in corrosive saltwater environments.

Quality Certifications & Compliance

Certification / Standard	Description
ISO 9001:2015	Quality Management System certification ensuring consistent product quality and process control.
ISO 14001:2015	Environmental Management System certification demonstrating sustainable manufacturing practices.
ASME BPV Code Section I	American Society of Mechanical Engineers Boiler and Pressure Vessel Code for power reactor components.
ASME BPV Code Section VIII Div. 1/3	Pressure vessel and piping design standards for industrial applications.
ASTM A213	Standard Specification for Austenitic Stainless Steel Seamless, Welded, and Heavy-Walled Tube for High-Temperature Service.
ASTM A269	Standard Specification for General Requirements for Seamless and Welded Austenitic Stainless Steel Tubing.
EN 10217-7	European standard for stainless steel tubes for pressure purposes.
GB/T 12771	Chinese national standard for stainless steel tubes for fluid transport.
NB (Nuclear Safety) License	Chinese nuclear equipment manufacturing license for reactor-related components.
ASME "N" Stamp	National Board Registration for nuclear pressure equipment manufacturing.
CE Marking (PED 2014/68/EU)	Conformity with European Pressure Equipment Directive for CE-marked products.
ASME BPE	Bioprocessing Equipment standard for pharmaceutical-grade surface finishes.

Unique Selling Points

1. Research-Validated Two-Phase Flow Performance: The coil tube design is informed by peer-reviewed experimental data from HTR-10 reactor studies on high-pressure steam-water two-phase flow friction resistance characteristics in helical coil geometries. This ensures accurate pressure drop prediction, optimal flow distribution, and reliable thermal-hydraulic performance under multiphase conditions.

2. Precision Helical Geometry: CNC-controlled coiling with ±0.5% dimensional tolerance ensures uniform heat transfer characteristics along the entire coil length, minimizing flow maldistribution and thermal stress concentrations.

3. Full Traceability: Each coil tube assembly carries a unique serial number with a complete material traceability chain from mill certificate through final NDT, enabling lifecycle quality management and regulatory compliance.

4. Nuclear-Grade Manufacturing Capability: ASME "N" stamped and NB-licensed manufacturing infrastructure ensures the product meets the rigorous quality assurance requirements of nuclear safety authorities (NNSA, IAEA).

5. Customizable Coil Configuration: Helix diameter, pitch, number of turns, tube diameter, and wall thickness are all customizable to meet specific thermal-hydraulic design requirements, enabling optimized system integration.

6. Comprehensive NDT Coverage: Multi-modal non-destructive testing (ET, PT, RT, UT) at every critical manufacturing stage provides confidence in structural integrity and defect-free performance.

Technical Notes & Design Considerations

When selecting the appropriate coil tube specification for a given application, the following engineering parameters should be carefully evaluated:

• Flow Regime: For two-phase (steam-water) flow applications, the Dittus-Boelter or Sieder-Tate correlation should be supplemented with helical coil-specific friction factor correlations (e.g., Iwamura, White, or HTR-10 empirical data) to accurately predict pressure drop.
• Thermal Expansion: The helical coil geometry inherently accommodates thermal expansion, but support structures and expansion loops should be designed per ASME B31.1/B31.3 guidelines.