Stainless Steel Helical Coil Tube — Cryogenic Heat Exchanger Grade

Product Overview

The Stainless Steel Helical Coil Tube (Product No. 529) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product specifically designed for cryogenic heat exchanger applications. This coil tube is optimized for convective heat transfer performance under extreme low-temperature conditions, particularly in helium (He) circulation systems where thermal conductivity, mechanical integrity, and dimensional stability are paramount.

Unlike conventional straight tubing, the helical coil geometry provides a significantly increased heat transfer surface area within a compact envelope. The curvature of the coil induces secondary flow patterns (Dean vortices) that enhance turbulent mixing, thereby improving the convective heat transfer coefficient — a critical advantage validated through rigorous numerical simulation studies of cryogenic helium flow in helical coil heat exchangers.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional resistance to thermal cycling, cryogenic embrittlement, and oxidation under vacuum or inert gas environments.

Base Material Options

SAE 304 (UNS S30400) — General-purpose cryogenic service; excellent formability and weldability
SAE 316L (UNS S31603) — Enhanced corrosion resistance; preferred for applications involving trace halide or chloride contamination
SAE 310S (UNS S31008) — High-temperature oxidation resistance; suitable for combined thermal cycling scenarios

Key Mechanical Properties (at Cryogenic Temperature, 4.2 K)

Tensile Strength: ≥ 720 MPa (at 4.2 K; increases with decreasing temperature)
Yield Strength: ≥ 310 MPa (at 4.2 K)
Elongation: ≥ 35% (maintains ductility at cryogenic temperatures — no brittle fracture transition)
Impact Toughness: Retains full toughness; no ductile-to-brittle transition temperature (DBTT) within the operational range
Thermal Conductivity: 20–25 W/(m·K) at 4.2 K (significantly higher than at ambient temperature, facilitating efficient heat transfer)
Linear Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /K (300 K → 4.2 K)
Specific Heat: 1000–1300 J/(kg·K) at cryogenic temperatures

Corrosion & Environmental Resistance

Excellent resistance to pitting and crevice corrosion in cryogenic liquid environments
Immune to intergranular corrosion (IGC) when properly stabilized (L-grade or stabilized variants)
Non-magnetic or low-magnetic (≤ 0.5 gauss after cold working), suitable for sensitive instrumentation environments
Hygienic surface finish available (Ra ≤ 0.4 μm) for pharmaceutical or food-grade applications

Specifications

Parameter	Specification / Range	Standard Reference
Product Name	Stainless Steel Helical Coil Tube (Coil Tube)	—
Product No.	529	—
Outer Diameter (OD)	3.0 mm – 50.8 mm (customizable)	ASTM A213 / A269
Wall Thickness	0.3 mm – 3.0 mm	ASTM A213
Coil Diameter (Helix Diameter)	50 mm – 500 mm (D/D ratio: 3 – 30)	Custom per application
Pitch (Helix Pitch)	5 mm – 50 mm (adjustable for flow rate optimization)	Custom per application
Coil Length	1 m – 50 m per coil (continuous)	—
Surface Finish	Bright Annealed (BA), 2B, or Polished (Ra ≤ 0.4 μm)	ASTM A213
Operating Temperature Range	4.2 K (−269 °C) to +800 °C	—
Maximum Operating Pressure	Up to 100 bar (depending on OD and wall thickness)	ASME B31.3
Applicable Fluids	Cryogenic Helium (He), Nitrogen (N₂), Hydrogen (H₂), LNG, Water, Steam	—
End Connections	Butt-welded, Threaded (BSPP/NPT), Flanged (ASME B16.5)	ASME B16.5
Tolerance (OD)	±0.1 mm (standard); ±0.05 mm (precision grade)	ISO 1307
Tolerance (Wall Thickness)	±10% of nominal	ASTM A213

Manufacturing Process

The production of cryogenic-grade stainless steel helical coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:

Raw Material Selection & Inspection:
Virgin stainless steel seamless tubes (ASTM A213 TP304/316L/310S) are procured from certified mills. Each batch undergoes spectrographic analysis (PMI — Positive Material Identification) to verify chemical composition, and ultrasonic testing (UT) for internal defects.
Precision Cutting & End Preparation:
Raw tubing is cut to specified lengths using plasma or laser cutting systems. End faces are deburred and chamfered to ensure uniform wall thickness and facilitate subsequent welding operations.
Helical Coiling (Cold Forming):
The straight tube is fed into a CNC-controlled coiling machine equipped with precision-diameter mandrels and forming rollers. The coil diameter, pitch, and number of turns are controlled to within ±1% tolerance. The D/D ratio (helix diameter to tube OD) is optimized to balance heat transfer enhancement with acceptable pressure drop.
Stress Relief Annealing:
After coiling, the helical coil undergoes a controlled annealing cycle (typically 1050–1100 °C for 304/316L; 1050–1150 °C for 310S, followed by water quench) to eliminate residual stresses introduced during cold forming. This step is critical for preventing stress-corrosion cracking (SCC) and ensuring dimensional stability at cryogenic temperatures.
Pickling & Passivation:
The annealed coil is subjected to acid pickling (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation to form a protective chromium oxide layer (Cr₂O₃). This ensures maximum corrosion resistance and surface purity.
Welding & End Connection Fabrication:
End connections (butt welds, threaded fittings, or flanges) are fabricated using inert gas shielded welding (TIG/GTAW — Tungsten Inert Gas / Gas Tungsten Arc Welding) under argon or helium back-purge to prevent internal oxidation. Weld seams are radiographically inspected (RT) or ultrasonically tested (UT) per ASME Section IX.
Final Quality Inspection:
Each coil tube assembly undergoes comprehensive inspection including:
- Dimensional verification (OD, wall thickness, coil diameter, pitch) using calibrated gauges and laser measurement
- Surface finish measurement (profilometry) to confirm Ra values
- Pressure testing (hydrostatic at 1.5× operating pressure) for leak integrity
- Visual inspection (VT) of welds and surface condition
- Helium leak testing (for cryogenic applications) using mass spectrometer-based leak detectors (sensitivity ≤ 1 × 10⁻⁹ Pa·m³/s)

Applications

The cryogenic-grade stainless steel helical coil tube is engineered for demanding thermal management applications where high heat transfer efficiency, mechanical reliability, and resistance to extreme temperature differentials are essential:

Primary Applications

Cryogenic Helium Heat Exchangers:
Used in superconducting magnet cooling systems (e.g., MRI, NMR, particle accelerators such as the LHC) where liquid helium (LHe) at 4.2 K must be efficiently warmed or cooled. The helical geometry enhances convective heat transfer of supercritical helium (SHe) through Dean vortex generation, as demonstrated in numerical simulation studies of cryogenic helium flow in helical coil heat exchangers.
Liquefied Natural Gas (LNG) Processing:
Employed in LNG cooling trains and vaporizers where efficient heat exchange between process streams at −162 °C and ambient-temperature fluids is required. The corrosion resistance of 316L grade makes it ideal for LNG service.
Liquid Nitrogen (LN₂) and Liquid Hydrogen (LH₂) Systems:
Used in industrial gas processing, aerospace propulsion systems, and hydrogen fuel cell infrastructure for cryogenic fluid storage and heat management.
Superconducting Magnet Cryostats:
Integrated into cryostat thermal shields and cold heads for maintaining stable cryogenic temperatures in research and medical imaging equipment.

Secondary Applications

Pharmaceutical and biotechnology cold-chain storage and processing
Food industry cryogenic freezing and quick-freeze systems
Chemical process heat exchangers requiring corrosion-resistant materials
Solar thermal energy systems (high-temperature variant using 310S grade)
Oil and gas industry subsea cryogenic processing
Research and development facilities for low-temperature physics experiments

Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring full traceability and compliance with international standards:

Management System Certifications

ISO 9001:2015 — Quality Management Systems
ISO 14001:2015 — Environmental Management Systems
ISO 45001:2018 — Occupational Health and Safety Management
ISO 3834-2:2021 — Quality Requirements for Fusion Welding of Metallic Materials

Product & Material Certifications

EN 10204 Type 3.1 — Material Test Certificate (independent third-party inspection)
EN 10204 Type 3.2 — Inspection Certificate (available upon request)
ASME Section IX — Welding qualification and certification
ASME B31.3 — Process piping design compliance
ASTM A213 / A269 — Seamless austenitic stainless steel tube specifications
CE Marking (PED 2014/68/EU) — Pressure Equipment Directive compliance (for pressure-rated assemblies)
NSF/ANSI 61 — Drinking water system components (for potable water applications)

Testing & Inspection Protocols

100% Positive Material Identification (PMI) via XRF or optical emission spectrometry
100% hydrostatic pressure testing at 1.5× maximum operating pressure
100% dimensional inspection with calibrated instruments (traceable to national standards)
Helium mass spectrometer leak testing for cryogenic applications (detection limit: 1 × 10⁻⁹ Pa·m³/s)
Non-Destructive Testing (NDT): Visual Testing (VT), Ultrasonic Testing (UT), Radiographic Testing (RT), Magnetic Particle Testing (MT) as applicable
Cryogenic qualification testing (thermal cycling: −269 °C to +25 °C, minimum 100 cycles) available upon request

Unique Selling Points

1. Cryogenic-Optimized Helical Geometry: The coil tube geometry is specifically engineered for cryogenic helium heat exchanger applications, with D/D ratios and pitch configurations validated through numerical simulation of convective heat transfer under extreme low-temperature conditions. This provides a demonstrable heat transfer enhancement of 30–60% over equivalent straight-tube configurations.

2. Full Metallurgical Integrity at 4.2 K: The austenitic stainless steel microstructure maintains full ductility and toughness at helium temperatures, with no ductile-to-brittle transition — a critical requirement for supercritical helium (SHe) flow systems where pressure drops and flow instabilities can be severe.

3. Precision Manufacturing Tolerances: CNC-controlled coiling with ±1% dimensional accuracy ensures uniform flow distribution and predictable thermal performance, essential for high-precision cryogenic applications.

4. Comprehensive Quality Traceability: Full batch traceability from raw material mill certificates through final