Spiral Coiled Stainless Steel Tube (Coiltube) — Technical Specification

1. Product Overview

The Spiral Coiled Stainless Steel Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Unlike conventional straight seamless or welded pipes, the Coiltube is formed into a continuous helical spiral configuration, enabling its deployment in compact heat exchanger designs where space efficiency, thermal performance, and flow dynamics are critical parameters.

This product category falls under the classification of literature-based engineering study products, derived from in-depth academic analysis and design methodology documented in the technical study titled "Analysis and Design of Tube Sheets for Spiral Coiled Tube Heat Exchangers". The product embodies the culmination of theoretical research, finite element analysis (FEA), and practical manufacturing know-how, positioning it as a technically advanced solution for demanding thermal management applications.

2. Material & Properties

2.1 Base Material Grades

The Coiltube is predominantly fabricated from austenitic stainless steel grades selected for their superior corrosion resistance, mechanical integrity, and formability under cold coiling conditions:

• SAE 304 / 1.4301 (AISI 304) — General-purpose austenitic stainless steel with excellent oxidation resistance up to 870 °C in intermittent service.
• SAE 316L / 1.4404 (AISI 316L) — Low-carbon variant with molybdenum addition (2–3%) providing enhanced resistance to pitting and crevice corrosion in chloride-containing environments.
• SAE 321 / 1.4541 (AISI 321) — Titanium-stabilized grade suitable for sustained high-temperature applications where sensitization resistance is required.

2.2 Key Mechanical Properties (Typical for 304 Grade, Annealed Condition)

• Tensile Strength (UTS): ≥ 520 MPa
• Yield Strength (0.2% Offset): ≥ 205 MPa
• Elongation at Break: ≥ 40%
• Hardness: ≤ 217 HB (Brinell)
• Density: 7.93 g/cm³
• Thermal Conductivity (20 °C): 16.3 W/(m·K)
• Thermal Expansion Coefficient (20–100 °C): 17.3 × 10⁻⁶ /K

2.3 Microstructural Characteristics

The austenitic microstructure, stabilized through solution annealing at 1050–1150 °C followed by rapid quenching, ensures full non-magnetic behavior, high ductility, and absence of phase transformation during service. The low carbon content (≤ 0.03% for 316L) minimizes intergranular carbide precipitation, preserving intergranular corrosion resistance (IGCR) as verified by ASTM A262 Practice E.

3. Specifications

Parameter	Specification / Range	Standard Reference
Outer Diameter (OD)	6.0 mm – 50.8 mm (⅛" – 2")	ASTM A269 / EN 10216-5
Wall Thickness (WT)	0.5 mm – 3.0 mm	ASTM A269 / EN 10216-5
Coil Diameter (Mean)	100 mm – 1,500 mm	Custom / Project-Specific
Coil Pitch	15 mm – 120 mm	Custom / Project-Specific
Number of Turns	2 – 50 (typical)	Design-Specific
Tubular Length (Uncoiled)	Up to 200 m per coil	—
Surface Finish	Mill finish / Pickled & Passivated / Brushed	ASTM A473
Surface Roughness (Ra)	0.8 µm – 1.6 µm (internal)	ASTM A269
End Preparation	Plain end / Beveled (37.5°) / Threaded	ASME B31.3
Manufacturing Method	Seamless (Cold Drawn) / ERW Welded + Weld Annealing	ASTM A269 / A554
Applicable Standards	ASTM A269, ASTM A554, EN 10216-5, GB/T 12771, JIS G3459	—

4. Manufacturing Process

4.1 Seamless Tube Production Route

1. Billet Preparation: Vacuum arc remelted (VAR) or electro-slag remelted (ESR) stainless steel billets are inspected for homogeneity and inclusion content.
2. Piercing & Hot Rolling: Billets are heated to 1,100–1,200 °C and pierced to produce hot-rolled tube blanks (typically 6–25% oversize).
3. Cold Drawing / Cold Pilgering: Hot-rolled blanks are cold-worked through multiple passes to achieve precise dimensional tolerances (±0.05 mm on OD) and the required grain structure refinement.
4. Solution Annealing: Tubes are annealed at 1,050–1,150 °C in protective atmosphere (argon or endothermic gas) to relieve cold-work stresses, restore ductility, and achieve the fully austenitic condition.
5. Pickling & Passivation: Acid pickling (HNO₃/HF blend) removes scale and surface contaminants; passivation forms a chromium oxide layer (Cr₂O₃) for corrosion protection.

4.2 Coiling / Spiraling Operation

1. Coil Forming: The annealed tube is fed through a precision coiling head with calibrated mandrels and guide rollers to produce the desired helical geometry. The process is performed at ambient temperature (cold coiling) to avoid work-hardening.
2. Springback Compensation: FEA-based springback models (developed per the referenced study) are applied to pre-bend angles, ensuring the final coil geometry meets tolerance requirements (±2% on coil diameter, ±1 mm on pitch).
3. Stress Relief (Optional): For applications requiring minimal residual stress, post-coiling tempering at 400–500 °C may be applied.
4. Tube Sheet Fabrication: The spiral coil is welded or mechanically fixed to a fabricated tube sheet (typically 304/316L plate, 20–80 mm thick). The tube sheet design incorporates FEA-optimized hole patterns, reinforcing rings, and stress-relief features as detailed in the referenced analytical study.

4.3 Quality Control During Manufacturing

• Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of coil geometry and tube dimensions.
• Hydrostatic Testing: Pressure testing at 1.5× working pressure per ASTM A269 to verify weld integrity and wall uniformity.
• Visual & Dye Penetrant Inspection (PT): Per ASTM E709 for surface defect detection.
• Eddy Current Testing (ET): Per ASTM E3092 for internal flaw detection on seamless tubes.
• Chemical Analysis: Spark OES (Optical Emission Spectroscopy) for compositional verification per ASTM E415.

5. Applications

5.1 Heat Exchanger Systems

The primary application domain is spiral coiled tube heat exchangers, where the helical geometry provides the following engineering advantages:

• Enhanced Heat Transfer: The curvature induces secondary Dean flow vortices, increasing the turbulent heat transfer coefficient by 20–50% compared to straight tubes at equivalent Reynolds numbers.
• Compactness: Spiral arrangement reduces the volumetric footprint by up to 40% compared to shell-and-tube designs with equivalent heat duty.
• Uniform Flow Distribution: Continuous spiral path eliminates bypass flow and dead zones, ensuring consistent thermal performance across the exchanger.

5.2 Industry-Specific Applications

• Oil & Gas Industry: Subsea heat exchangers, wellhead cooling systems, gas processing units, and cryogenic separation trains.
• Petrochemical: Reactor effluent coolers, distillation column condensers, and polymerization heat removal systems.
• Power Generation: Feedwater preheaters, condenser sections, and waste heat recovery units.
• Marine & Offshore: Seawater coolers, ballast water treatment systems, and LNG (Liquefied Natural Gas) cooling circuits.
• Pharmaceutical & Food Processing: Sanitary heat exchangers requiring hygienic surface finishes and CIP (Clean-in-Place) compatibility.
• Chemical Processing: Acid concentrators, solvent recovery units, and corrosive fluid heat exchange.

6. Quality Certifications & Compliance

6.1 Product Certifications

• ISO 9001:2015 — Quality Management System certification for manufacturing processes.
• ISO 3834-2 — Quality requirements for fusion welding of metallic materials (where welding is involved in tube sheet assembly).
• NACE MR0175 / ISO 15156 — Compliance for oil and gas industry materials resistant to sulfide stress cracking.
• ASME Section VIII, Div. 1 — Pressure vessel code compliance for heat exchanger design and fabrication.
• EN 10204 Type 3.1 — Third-party inspection certificate for material verification.

6.2 Testing & Inspection Certifications

• Mill Test Reports (MTR): Full chemical composition and mechanical property data provided for each heat lot.
• NDE (Non-Destructive Examination): Radiographic testing (RT) per ASTM E94 for weld joints; ultrasonic testing (UT) per ASTM E747 for wall thickness verification.
• Corrosion Testing: Pitting Resistance Index (PREN ≥ 19 for 316L) verified per ASTM G48; intergranular corrosion per ASTM A262 Practice E.
• Hydrostatic Test Certificate: Individual tube hydrostatic test results documented per ASTM A269.

6.3 Third-Party Inspection

All production batches are subject to third-party inspection by accredited organizations (e.g., TÜV, DNV, Lloyd's Register) upon customer request, ensuring full traceability from raw material mill certification through final product release.

7. Unique Selling Points

Engineering Excellence Through Analytical Design: The Coiltube product line is distinguished by its foundation in rigorous academic analysis — specifically the referenced study on "Analysis and Design of Tube Sheets for Spiral Coiled Tube Heat Exchangers." This analytical heritage ensures that every coil geometry, tube sheet configuration, and stress distribution is optimized through finite element simulation prior to fabrication, yielding products with superior fatigue life and mechanical reliability.

• FEA-Driven Design: Pre-production finite element analysis of tube sheet stress concentrations, thermal expansion mismatches, and cyclic loading scenarios ensures design margins exceed ASME code requirements by 25–40%.
• Precision Coiling Capability: In-house coiling equipment with CNC-controlled pitch and diameter control achieves geometric tolerances unattainable by conventional methods.
• Full Material Traceability: From ingot heat number to final coil serial number, complete traceability documentation is maintained per ISO 10002.
• Custom Engineering Support: Dedicated engineering team provides application-specific design consultation, thermal performance modeling, and FEA-based validation for bespoke projects.
• Multi-Grade Availability: Comprehensive material portfolio spanning 304, 316L, 321, 347, and duplex 2205 grades to address diverse corrosion and temperature requirements.

8. Conclusion

The Spiral Coiled Stainless Steel Tube (Coiltube) from Wenzhou Jixing Metal Materials Co., Ltd represents a convergence of advanced metallurgical science, precision manufacturing, and analytical engineering design. Backed by peer-reviewed technical research into tube sheet mechanics and spiral coil heat transfer optimization, this product delivers exceptional thermal efficiency, mechanical durability, and design flexibility for the most demanding industrial heat exchange applications worldwide.