Spiral Stainless Steel Coil Tube (Coiltube)

Product Overview

The Spiral Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured through the cold-bent spiral coiling process. This product represents a specialized form of stainless steel tubing that combines the structural integrity of seamless or welded pipe with the geometric flexibility afforded by spiral coiling configurations. The coil tube is supplied in continuous helical form, enabling efficient downstream processing, storage, and deployment across a wide range of industrial applications.

The cold-bending process introduces controlled plastic deformation in the tube material, resulting in a stable spiral geometry. However, the elastic recovery phenomenon — known as springback (回弹) — is an inherent and critical factor in the design and manufacturing of these products. Accurate prediction and compensation of springback are essential to achieving dimensional accuracy, geometric fidelity, and functional performance in the final coiled configuration.

Material and Properties

The Spiral Stainless Steel Coil Tube is fabricated from high-quality austenitic and duplex stainless steel grades, selected for their superior corrosion resistance, mechanical strength, and formability characteristics required during the cold-bending coiling process.

Common Material Grades

Key Mechanical Properties

Property 304 / 304L 316 / 316L SAF 2205
Yield Strength (0.2% Offset), MPa ≥ 205 ≥ 205 ≥ 450
Tensile Strength, MPa 515 – 720 515 – 720 550 – 800
Elongation (A50mm), % ≥ 40 ≥ 40 ≥ 25
Young's Modulus, GPa 193 193 200
Poisson's Ratio 0.29 0.29 0.29
Density, kg/m³ 8.00 8.03 7.85
Maximum Service Temperature, °C 870 870 300 (in oxidizing atmosphere)

Specifications

Parameter Range / Value Standard Reference
Outer Diameter (OD) 6.0 mm – 168.3 mm (¼" – 6") ASTM A269 / A213 / EN 10216-5
Wall Thickness 0.5 mm – 6.0 mm ASTM A269 / EN 10216-5
Coil Diameter (Helical) Custom — typically 100 mm – 500 mm —
Coil Pitch (Helix Pitch) Custom — typically 5 mm – 50 mm —
Tube Length per Coil Up to 100 m (continuous) —
Surface Finish Bright Annealed (BA), Pickled & Passivated, Mill Finish, 2B, No. 4 Brushed ASTM A480 / GB/T 4237
End Condition Plain, Beveled, Threaded, Flanged ASTM A269
Dimensional Tolerance (OD) ± 0.1 mm to ± 0.5 mm (per grade) ASTM A269 / EN 10216-5
Dimensional Tolerance (Wall) ± 10% of nominal (min ± 0.05 mm) ASTM A269 / EN 10216-5
Straightness (per 1 m) ≤ 0.5 mm EN 10216-5
Springback Control Calculated and compensated per cold-bending springback model Internal process specification

Manufacturing Process

The production of the Spiral Stainless Steel Coil Tube involves a multi-stage manufacturing sequence, with the cold-bending coiling operation being the defining process step. Each stage is subject to rigorous quality control to ensure dimensional accuracy, material integrity, and surface quality.

Process Flow

  1. Raw Material Procurement & Incoming Inspection — Seamless or welded stainless steel pipe stock is sourced from certified mills. Incoming material undergoes chemical composition analysis (via optical emission spectrometry, OES), mechanical property verification, and visual surface inspection in accordance with applicable standards.
  2. Pre-Processing (Cutting & Preparation) — Pipe stock is cut to required lengths using precision saws or laser cutting systems. Ends are deburred and prepared for the coiling operation. Surface preparation may include pickling and passivation to remove mill scale and establish a protective chromium oxide layer.
  3. Cold Bending & Spiral Coiling — The core forming operation. The tube is guided through a series of precision rollers and bending dies that impose a controlled helical deformation. This process relies on the plastic deformation regime of the material, where the bending moment exceeds the elastic limit of the tube cross-section. The springback phenomenon — the elastic recovery that occurs upon removal of the bending forces — must be precisely calculated and compensated for during tooling design. The springback angle (or springback amount) is determined by the following key parameters:
    • Bending radius to thickness ratio (D/t) — A lower ratio indicates more severe bending and greater plastic deformation
    • Yield strength (σ_y) — Higher yield strength results in greater elastic recovery
    • Young's modulus (E) — Governs the magnitude of elastic strain recovery
    • Strain hardening exponent (n) — Influences the distribution of plastic strain through the tube wall
    • Bend angle (θ) — The total angular deformation imposed

    The fundamental springback equation for a bent tube is expressed as:

    Δθ = (σ_y × L) / (E × R_f)

    where Δθ is the springback angle, σ_y is the yield strength, L is the neutral axis length, E is Young's modulus, and R_f is the final bending radius. In practice, advanced finite element analysis (FEA) models incorporating the Ramberg-Osgood stress-strain relationship are employed for accurate springback prediction, particularly for thin-walled tubes where the D/t ratio is low.

  4. Post-Coiling Stress Relief — If required by the application, the coiled tubes may undergo stress relief annealing to minimize residual stresses introduced during the cold-bending process. This is typically conducted at 650°C – 870°C in a controlled atmosphere to prevent oxidation.
  5. Dimensional Inspection & Quality Assurance — Final products are inspected for coil diameter accuracy, pitch uniformity, straightness, surface condition, and dimensional conformance. Non-destructive testing (NDT) methods such as eddy current testing and ultrasonic testing may be applied to detect internal defects.
  6. Packaging & Dispatch — Coiled tubes are secured on custom wooden or steel pallets, wrapped in protective film or paper, and packed for transport with appropriate handling documentation and material traceability certificates.

Applications

The Spiral Stainless Steel Coil Tube finds extensive application across multiple industrial sectors, leveraging the combination of stainless steel's corrosion resistance and the geometric advantages of spiral coiling:

Quality Certifications

The Spiral Stainless Steel Coil Tube is manufactured in accordance with internationally recognized quality management systems and industry standards:

Unique Selling Points