Stainless Steel Spiral Coil Tube for Heat Exchanger Applications (Coiltube)

1. Product Overview

The Spiral Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous tubular product wound into a helical or spiral configuration, specifically designed for integration into Spiral Coil Heat Exchangers (螺旋盘管式换热器). This product category occupies a critical niche in process heat transfer engineering, where compact geometry, high surface-to-volume ratio, and sustained thermal performance are paramount.

Unlike conventional straight-tube heat exchangers that require extensive tube bundles and headers, spiral coil tubes deliver equivalent or superior thermal exchange within a fraction of the footprint. The continuous winding eliminates soldered or brazed joints along the flow path, thereby minimizing leakage risk and enhancing long-term structural integrity under cyclic thermal loading.

Design Philosophy: The spiral coil tube architecture is governed by the principle of concentric spiral flow, wherein the working fluid traverses a continuously curved channel. This geometry induces secondary Dean flow effects (Dean Number, De), which augment turbulent mixing and significantly elevate the convective heat transfer coefficient compared to straight-tube analogues.

2. Material & Properties

Coiltubes supplied by Wenzhou Jixing Metal Materials Co., Ltd are fabricated from austenitic and duplex stainless steel grades, selected for their exceptional corrosion resistance, thermal stability, and formability under cold-winding conditions.

2.1 Primary Alloy Grades

2.2 Mechanical Properties (Cold-Drawn Condition)

Property 304 316L 321 SAF 2205 310S
Tensile Strength (Rm, MPa) 515–730 485–720 515–730 550–800 515–690
Yield Strength (Rp0.2, MPa) ≥205 ≥170 ≥205 ≥450 ≥205
Elongation (A5, %) ≥40 ≥40 ≥40 ≥15 ≥35
Thermal Conductivity at 20 °C (W/m·K) 16.3 14.6 16.3 14.6 34.3
Coefficient of Thermal Expansion (10−6/K, 20–100 °C) 17.3 17.1 17.3 13.2 18.0
Maximum Service Temperature (°C) 870 870 870 300 (long-term) 1150
PREN Value 19 25 19 32 25

2.3 Surface Finish Options

3. Specifications

Parameter Specification Standard / Reference
Tube Outer Diameter (OD) Ø6.0 mm – Ø50.8 mm (¼" – 2") ASTM A269 / ASME SA-269
Tube Wall Thickness 0.5 mm – 3.0 mm ASTM A269 / ASME SA-269
Coil Inner Diameter (Winding Diameter) Ø100 mm – Ø2,000 mm Customer-specific / DIN 44074
Coil Length (Developed Length) Up to 200 m (continuous) ISO 11989
Winding Pitch / Turn Spacing 5 mm – 25 mm (adjustable) Design-specific
Number of Turns Up to 500 turns Design-specific
Maximum Operating Pressure Up to 4.0 MPa (600 psi) ASME BPVC Section VIII Div. 1
Design Temperature Range −196 °C to +1,150 °C (grade-dependent) ASTM / ASME
End Preparation Plain, beveled (37°/45°), threaded (NPT/BSP), or flanged ASME B1.20.1 / ISO 7
Winding Configuration Spiral (constant pitch), Helical (constant angle), Concentric multi-layer DIN 44074 / EN 10217
Tolerance – OD ±0.05 mm (precision grade); ±0.1 mm (standard) ASTM A269 / EN 10217
Tolerance – Wall Thickness ±10% (minimum wall) ASTM A269
Acceptable Media Water, steam, air, hydrocarbons, acids (grade-dependent), food-grade fluids NACE MR0175 / ISO 15156
Packaging Wooden crate or steel crate with desiccant; individual coil protection ISO 4180

4. Manufacturing Process

The production of high-quality stainless steel spiral coil tubes follows a rigorously controlled multi-stage process, each step subject to in-process quality assurance (IPQA) checkpoints:

4.1 Raw Material Procurement & Verification

  1. Ingot/Mill Selection: Only certified mill products from accredited suppliers are accepted. Each heat/lot must be accompanied by a Mill Test Certificate (MTC) in accordance with EN 10204 3.1 or 3.2.
  2. Spectroscopic Analysis: Optical emission spectrometry (OES) verification of chemical composition (C, Cr, Ni, Mo, Ti, Si, Mn, S, P) to confirm compliance with ASTM A240 / EN 10088-1.
  3. Dimensional Inspection: Ultrasonic thickness gauging and laser micrometry for seamless tube stock verification.

4.2 Seamless Tube Production

  1. Piercing & Elongation: Round billets are pierced and elongated via plasma mandrel piercing or rotary piercing (Mannesmann process) to produce seamless tube blanks.
  2. Hot Rolling & Annealing: Tubes are hot-rolled to intermediate dimensions, followed by solution annealing at 1050–1150 °C in a protective atmosphere to relieve residual stresses and establish uniform austenitic microstructure.
  3. Acid Pickling & Passivation: Immersion in mixed nitric-hydrofluoric acid (HNO₃/HF) or citric acid solution to remove mill scale and restore the passive chromium oxide film (Cr₂O₃).

4.3 Cold Drawing & Sizing

  1. Cold Reduction: Tubes are drawn through precision tungsten carbide (WC) dies to achieve final OD and wall thickness. Multi-pass drawing is employed for high-reduction ratios (>40%).
  2. Intermediate Annealing: Periodic solution annealing at 1040–1100 °C between cold-drawing passes to prevent excessive work hardening and maintain ductility.
  3. Final Sizing: Precision cold sizing ensures dimensional tolerances within ±0.05 mm for OD and ±10% for wall thickness.

4.4 Coil Winding (Forming)

  1. Pre-Forming: Straight tube sections are fed into a CNC-controlled coil winding machine equipped with servo-driven rollers and a programmable pitch mechanism.
  2. Helical/Spiral Winding: The tube is wound at a controlled angular velocity with a precisely maintained pitch. The winding process is executed in a single continuous operation to avoid seam discontinuities.
  3. Spring-Back Compensation: The CNC controller incorporates real-time spring-back compensation algorithms to ensure the final coil geometry matches the design profile within ±0.5 mm radial tolerance.
  4. End Sealing: Coil ends are secured via welding, mechanical clamping, or compression fitting to prevent uncoiling during transport and installation.

4.5 Post-Winding Treatment & Inspection

  1. Stress Relief Annealing: Coils are annealed at 300–450 °C (austenitic grades) or 550–650 °C (duplex grades) to relieve cold-work-induced residual stresses without sensitization.
  2. Hydrostatic Pressure Testing: Each coil is subjected to a proof pressure of 1.5× the maximum design pressure for a minimum dwell time of 60 seconds, with visual and volumetric leak detection.
  3. Surface & Dimensional Inspection: Visual inspection under UV lighting, magnetic particle inspection (MPI) for surface defects, and coordinate measuring machine (CMM) verification of coil geometry.
  4. Intergranular Corrosion Testing: Samples from each production lot undergo ASTM A262 Practice 1E (65% boiling acetic acid) or ASTM G93 (salt spray) testing to confirm intergranular corrosion resistance.

4.6 Tube Sheet Integration (Heat Exchanger Assembly)

  1. Tube Sheet Design: The spiral coil tube is integrally designed with a perforated tube sheet (管板), where tube ends are either welded (TIG/GTAW) or mechanically expanded into precision-drilled holes. Hole diameter tolerance is maintained at H7 per ISO 286.
  2. Welding Procedure: GTAW (Tungsten Inert Gas Welding) is employed with a backing gas (argon or helium) to ensure full penetration and prevent backside oxidation. Weld parameters are qualified per ASME Section IX and AWS D17.9.
  3. Post-Weld Heat Treatment (PWHT): Where required, the tube sheet assembly undergoes PWHT at 1050–1150 °C (austenitic) to restore solution-treated condition and eliminate welding-induced sensitization.
  4. Non-Destructive Testing (NDT): Radiographic testing (RT, per ASME Section V Article 2) and dye penetrant testing (PT, per ASTM E709) of all tube-to-tube-sheet welds.

5. Applications

The spiral coil tube is a versatile component deployed across a wide spectrum of industrial and process engineering applications:

5.1 Process Heat Exchange

5.2 Food, Beverage & Pharmaceutical