Stainless Steel Coil Tube (Coiltube) — Finned & Layered Configuration

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.  |  Product No.: 804  |  Category: Technical Literature & Engineering Reference

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured in continuous coil form, designed for applications requiring high thermal efficiency, corrosion resistance, and mechanical durability. This product line encompasses both plain-wall and finned (刺片式) coil tube configurations, the latter incorporating thin-walled fins or ribs to significantly enhance the surface-area-to-volume ratio and thereby improve heat transfer performance. The coil tube is supplied in continuous coil form to facilitate downstream processing such as straightening, cutting, bending, and fin-insertion without introducing work-hardening or residual stress concentrations.

A critical engineering consideration for finned coil tubes is the determination of dynamic boundary conditions under operational loading. The layered testing methodology — which involves progressive loading of finned coil tube assemblies in discrete stages — enables accurate characterization of boundary forces, moments, and displacement constraints at each fin interface. Sensitivity analysis conducted on these layered test results identifies which geometric and material parameters exert the greatest influence on structural response, thereby guiding optimization of fin geometry, tube wall thickness, and coil winding parameters.

Material & Properties

The coil tube is fabricated from austenitic stainless steel grades selected for their combination of corrosion resistance, formability, and weldability. The following material grades are typically available:

Key Mechanical Properties (Cold-Wound Coil Condition):

Surface Finish Options:

Specifications

Parameter Specification Range Standard / Reference
Outer Diameter (OD) Φ3.0 mm – Φ108.0 mm ASTM A213 / ASTM A269
Wall Thickness 0.30 mm – 6.00 mm ASTM A213
Coil Winding Diameter 150 mm – 800 mm (configurable) Manufacturer Specification
Coil Length 5 m – 500 m (continuous) Manufacturer Specification
Fin Height (Finned Variant) 0.5 mm – 3.0 mm ISO 21815 / Custom
Fin Pitch / Spacing 1.5 mm – 12.0 mm ISO 21815 / Custom
Fin Material Matching tube grade or aluminum (dissimilar) ASTM A240 / ASTM B209
Dimensional Tolerance (OD) ±0.05 mm (precision); ±0.10 mm (standard) ASTM A213
Dimensional Tolerance (Wall) ±10% of nominal ASTM A213
Roundness Tolerance ≤ 0.5% of OD ASTM A213
Heat Treatment Solution Annealed (1050 °C – 1150 °C, water quench) ASTM A213
Packaging Wooden pallet with moisture-proof wrapping; VCI paper protection ISO 4180

Manufacturing Process

The production of stainless steel coil tubes involves a multi-stage process chain designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:

  1. Slit-to-Coil (Slitting): Cold-rolled stainless steel strip is slit to the required coil width using precision slitting lines. Edge quality and strip flatness are verified at this stage.
  2. Forming & Welding: The slit strip is formed into a tubular configuration via cold-rolling dies. A continuous longitudinal weld is produced using either Automatic Submerged Arc Welding (SAW), Tungsten Inert Gas Welding (TIG/GTAW), or Laser Welding. The weld seam is subsequently ground or mechanically finished to achieve flush surface continuity.
  3. Heat Treatment (Solution Annealing): The welded coil tube is solution-annealed at 1050 °C – 1150 °C followed by rapid water quenching. This eliminates welding-induced sensitization, restores full austenitic microstructure, and ensures maximum corrosion resistance. A subsequent pickling and passivation step removes oxide scale and establishes the passive chromium oxide film.
  4. Dimensional Calibration & Sizing: The annealed coil tube passes through cold-sizing rolls to achieve final OD and wall thickness within specified tolerances. Roundness and straightness are verified by automated optical or laser measurement systems.
  5. Finning (for Finned Coil Tube Variant): Fins are applied to the tube surface using either:
    • Insert Fin Method: Pre-formed fin stock is inserted into the tube bore and mechanically expanded, creating a tight metal-to-metal bond.
    • Welded Fin Method: Fins are welded to the tube OD using resistance welding or friction welding.
    • Slit Fin Method: A solid fin material is slit and mechanically expanded onto the tube OD.
  6. Quality Inspection: Each coil lot undergoes comprehensive inspection including:
    • Visual inspection for surface defects, weld seam quality, and fin integrity
    • Dimensional verification (OD, wall thickness, fin height, fin pitch) using ultrasonic thickness gauges and calibrated micrometers
    • Chemical composition verification via Optical Emission Spectrometry (OES)
    • Hydrostatic pressure testing (typically 1.5× working pressure) to verify weld seam integrity
    • Mechanical property testing (tensile, hardness) on representative samples per ASTM A213
  7. Coiling & Packaging: The finished coil tube is wound onto a protective core, wrapped with moisture-proof material, and secured for shipping on wooden pallets in compliance with ISO 4180.

Dynamic Boundary Condition Analysis & Sensitivity Study

A defining engineering feature of the finned coil tube (刺片式盘管) is the rigorous characterization of its dynamic boundary conditions through layered testing (分层试验). This methodology is essential for applications where the coil tube assembly is subjected to cyclic thermal, pressure, or mechanical loading.

Layered Testing Methodology:

The layered testing approach involves the progressive application of load to the finned coil tube assembly in discrete increments (layers), with instrumentation at each interface to record the evolution of boundary forces, moments, and displacements. The procedure follows these steps:

  1. Baseline Measurement: The unfinned (bare) coil tube is subjected to reference loading to establish baseline boundary conditions.
  2. Incremental Fin Loading: Fins are introduced in successive layers, with each layer representing a defined fin density or fin height increment. At each stage, strain gauges, displacement transducers, and pressure transducers record the boundary response.
  3. Full-Assembly Characterization: The complete finned coil tube assembly is tested under operational loading conditions (thermal cycling, pressure cycling, or combined loading) to capture the full dynamic boundary condition set.

Sensitivity Analysis:

The sensitivity analysis quantifies the influence of key design parameters on the dynamic boundary conditions. Parameters typically evaluated include:

The sensitivity coefficients (∂y/∂xᵢ) are computed for each parameter xᵢ with respect to key output variables y (e.g., maximum interface force, displacement at fin root, stress concentration factor). Parameters with the highest absolute sensitivity values are identified as critical design variables, enabling targeted optimization of the finned coil tube geometry for improved structural performance and fatigue life.

Applications

The Stainless Steel Coil Tube (Coiltube) finds extensive application across multiple industries due to its versatile configuration and superior material properties:

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and standards compliance:

Unique Selling Points