Stainless Steel Spiral Coiled Tube (Coiltube) — Heat Transfer & Pressure Drop Optimized Series

Product Code: JX-CT-913 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.

1. Product Overview

The Stainless Steel Spiral Coiled Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular component formed into a continuous helical or spiral configuration, designed specifically for high-efficiency heat exchange applications. Unlike straight tubes, the spiral geometry of the Coiltube induces secondary flow patterns — including Dean vortices — within the internal fluid stream. These secondary flows enhance turbulent mixing, significantly improving convective heat transfer coefficients while maintaining a compact volumetric footprint.

Based on extensive experimental research into water heat transfer and pressure drop characteristics within spiral coiled tubes, this product line has been optimized to achieve an optimal balance between thermal performance enhancement and hydraulic resistance. The spiral curvature generates centrifugal forces that intensify radial fluid motion, breaking thermal boundary layers and promoting uniform temperature distribution across the tube cross-section. This fundamental physical mechanism underpins the superior thermal-hydraulic performance of the Coiltube compared to conventional straight-tube heat exchangers.

Wenzhou Jixing Metal Materials Co., Ltd. leverages advanced metallurgical expertise and precision forming technology to deliver Coiltubes that meet the most demanding specifications in industrial heat exchange, refrigeration, and process engineering sectors.

2. Material & Properties

2.1 Base Material Grades

Austenitic Stainless Steels: AISI 304 (UNS S30400), AISI 316L (UNS S31603), AISI 321 (UNS S32100) — offering excellent corrosion resistance, formability, and thermal conductivity.
Super-Austenitic Stainless Steels: AISI 904L (UNS N08904), Alloy 20 (UNS N08200) — selected for aggressive chemical environments and high-temperature service.
Duplex Stainless Steels: 2205 (UNS S31803) — providing elevated yield strength and superior resistance to chloride-induced stress corrosion cracking.
Specialty Alloys: Inconel 625 (UNS N06625), Hastelloy C-276 (UNS N10276) — available upon request for extreme corrosion and temperature conditions.

2.2 Key Material Properties

Property	AISI 304 (UNS S30400)	AISI 316L (UNS S31603)	Duplex 2205 (UNS S31803)
Chromium Content (wt%)	18.0 – 20.0	16.0 – 18.0	22.0 – 23.0
Nickel Content (wt%)	8.0 – 10.5	10.0 – 14.0	4.5 – 6.5
Molybdenum Content (wt%)	—	2.0 – 3.0	3.0 – 3.5
Thermal Conductivity at 20°C (W/m·K)	16.3	14.6	18.0
Thermal Conductivity at 500°C (W/m·K)	26.2	24.5	29.0
Maximum Service Temperature (°C)	870	870	350 (Pitting Limit)
Yield Strength (MPa, min.)	205	170	450
Tensile Strength (MPa, min.)	515	485	620
Corrosion Resistance (Pitting)	Moderate	Good	Excellent

2.3 Surface Finish Options

Pickled & Passivated (P&P): Standard surface treatment for general chemical resistance; removes mill scale and forms a passive chromium oxide layer.
Electropolished (EP): Achieves Ra ≤ 0.25 μm surface roughness; preferred for pharmaceutical, food-grade, and semiconductor applications requiring hygienic fluid contact.
Acid-Pickled (AP): Enhanced corrosion resistance for aggressive aqueous environments.
Bead Blasted: Textured surface for aesthetic applications and enhanced thermal emissivity.

3. Technical Specifications

Parameter	Specification Range	Tolerance / Standard
Outer Diameter (OD)	6.0 mm – 108.0 mm (¼" – 4")	±0.15 mm
Wall Thickness (WT)	0.30 mm – 6.00 mm	±10% of nominal
Coil / Spiral Pitch	15 mm – 150 mm (configurable)	±0.5 mm
Coil Diameter (Center-to-Center)	80 mm – 1200 mm	±1.0 mm
Tube Length per Coil	5 m – 500 m (custom)	±1%
Curvature Radius Ratio (D/d)	3.0 – 50.0 (D = coil diameter, d = tube OD)	Per design specification
End Configuration	Plain, Beveled, Flanged, Threaded, Socket-Welded	Per customer drawing
Maximum Operating Pressure	Up to 40 MPa (design-dependent)	ASME B31.3 / EN 13480
Operating Temperature Range	−196°C to +870°C (grade-dependent)	Per material datasheet
Surface Roughness (Internal)	Ra 0.4 μm – 1.6 μm (standard); Ra ≤ 0.25 μm (EP)	ASTM A213 / ASTM A269
Standards Compliance	ASTM A213, ASTM A269, ASME B31.3, EN 10216-5, EN 13480, GB/T 12771, GB/T 21832	—

4. Manufacturing Process

The production of high-performance stainless steel spiral Coiltubes involves a precisely controlled multi-stage manufacturing sequence:

Raw Material Selection & Inspection: Cold-rolled stainless steel strip or seamless tube blanks are procured from certified mill suppliers. Incoming material undergoes spectrographic analysis (OES), mechanical testing (tensile, hardness), and visual inspection to verify compliance with the specified ASTM/EN/GB grade requirements.
Pre-Forming Annealing: Material is solution-annealed at 1050°C – 1150°C followed by controlled water quenching to relieve residual stresses and achieve a fully austenitic microstructure with optimal ductility for subsequent forming operations.
Spiral Coiling / Bending: Precision CNC-controlled coiling machines form the straight tube into the specified helical or spiral geometry. The bending process is carefully controlled to prevent:
- Excessive cross-sectional ovality (limited to ≤ 1.5% of nominal OD)
- Wall thinning at the outer bend radius (controlled to ≤ 12% reduction)
- Residual stress accumulation that could compromise fatigue life
Post-Forming Heat Treatment: Stress-relief annealing at 850°C – 950°C (grade-dependent) eliminates residual stresses induced during coiling, restores full mechanical properties, and ensures dimensional stability during service.
Surface Treatment: Pickling and passivation (or electropolishing) are performed to remove oxide scales, contaminants, and to establish a stable, corrosion-resistant chromium oxide passive film on the tube surface.
End Finishing & Assembly: Tube ends are cut, beveled, or fitted with flanges/threads per customer specification. Pressure testing (hydrostatic at 1.5× design pressure or pneumatic per ASME B31.3) verifies integrity.
Final Quality Control: Comprehensive dimensional inspection (laser scanning for spiral geometry), ultrasonic thickness testing (UT), eddy current inspection (ECI) for wall integrity, and surface roughness verification (profilometry) are performed prior to packaging and dispatch.

5. Thermal-Hydraulic Performance Characteristics

The defining engineering advantage of the spiral Coiltube lies in its enhanced heat transfer performance relative to straight tubes. Based on experimental research into water flow within helical channels, the following performance characteristics are established:

5.1 Heat Transfer Enhancement

The Dean number (De = Re × √(d/D)) governs the intensity of secondary Dean vortices. For typical Coiltube geometries (D/d = 10–30) and water flow conditions (Re = 10,000–100,000), De values of 300–1,500 are achieved, corresponding to Nusselt number enhancements of 20% – 60% over straight-tube baselines.
The Nusselt number correlation for turbulent flow in helical coils follows the form: Nu = C · Re^m · Prⁿ · (D/d)^p, where the curvature ratio term (D/d)^p captures the geometric enhancement effect.
Enhanced radial mixing eliminates thermal boundary layer stratification, ensuring uniform wall temperatures and reducing the risk of localized overheating or fouling deposition.

5.2 Pressure Drop Characteristics

The frictional pressure drop in spiral Coiltubes is governed by: ΔP = f · (L/D_h) · (ρv²/2), where the Darcy friction factor (f) is elevated relative to straight tubes due to secondary flow contributions.
Typical friction factor enhancement ratios (f_coil / f_straight) range from 1.1 to 1.8 depending on curvature ratio and Reynolds number regime.
The net performance metric — heat transfer enhancement per unit pressure drop penalty (ΔNu/Δf) — remains favorable across the operating range, making Coiltubes an efficient choice for compact heat exchanger designs.

5.3 Compactness Advantage

Spiral coiling achieves up to 85% volumetric space savings compared to equivalent-length straight tube bundles, enabling significantly more compact heat exchanger constructions.
The continuous helical path provides uniform flow distribution without the maldistribution issues common in multi-pass shell-and-tube designs.

6. Applications

6.1 Industrial Heat Exchange

Shell-and-Tube Heat Exchangers: Spiral tubes serve as the tube bundle element in compact heat exchangers for process heating, cooling, and condensation duty.
Plate Heat Exchanger Alternatives: Coiltube assemblies provide a cost-effective alternative for medium-pressure applications where plate designs are limited.
Reboilers & Condensers: Spiral tube configurations in distillation columns and vacuum systems.

6.2 Refrigeration & HVAC

Evaporators & Condensers: Spiral Coiltubes in air-cooled condensers, water-cooled chillers, and refrigeration evaporator coils.
Heat Pump Systems: High-efficiency compact coils for residential and commercial heat pump units.
Cryogenic Applications: Liquid nitrogen, liquid oxygen, and LNG service coils (304L/316L grades).

6.3 Chemical & Petrochemical Processing

Reactor Cooling/Heating Jackets: Internal spiral coils for jacketed reactor temperature control.
Process Feed Preheaters: Spiral tube preheating of process streams in chemical plants.
Corrosive Fluid Handling: 904L and Hastelloy C-276 Coiltubes for sulfuric acid, hydrochloric acid, and caustic soda service.