Stainless Steel Coil Tube (Coiltube) — Product Technical Specification

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.

Product Category: Stainless Steel Coil Tube / Spiral Wound Tube (盘管)

Reference No.: 1288

1. Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product formed by cold-rolling or hot-forming a straight stainless steel pipe into a continuous helical or spiral coil configuration. Unlike conventional straight-length tubing, the Coiltube is delivered in a pre-coiled state, enabling significant advantages in space utilization, thermal efficiency, and installation logistics. This product represents a specialized segment within the stainless steel pipe industry, designed for applications demanding high surface-area-to-volume ratios, enhanced heat transfer performance, and corrosion resistance.

Wenzhou Jixing Metal Materials Co., Ltd. has developed proprietary manufacturing processes and dedicated tooling (工装) for the production of circular-section coil tubes, addressing critical challenges in dimensional accuracy, coil geometry consistency, and surface integrity preservation during the coiling operation.

2. Material & Properties

2.1 Base Materials

2.2 Mechanical Properties (Typical Values for Annealed Condition)

Property 304 / 304L 316 / 316L 321 904L 2205
Tensile Strength (UTS) [MPa] ≥ 515 ≥ 515 ≥ 515 ≥ 550 ≥ 550
Yield Strength (0.2% offset) [MPa] ≥ 205 ≥ 205 ≥ 205 ≥ 220 ≥ 450
Elongation (A50) [%] ≥ 40 ≥ 40 ≥ 40 ≥ 35 ≥ 30
Density [kg/m³] 8.00 8.03 8.00 8.10 7.80
Thermal Conductivity @ 100°C [W/(m·K)] 16.3 14.6 16.3 11.4 12.5
Maximum Service Temperature [°C] 870 870 900 1100 350

2.3 Surface Finish Options

3. Specifications

3.1 Geometric Dimensions

Parameter Specification Range Standard Reference
Outer Diameter (OD) 6.0 – 114.3 mm (¼" – 4") ASTM A554, EN 10217, GB/T 14976
Wall Thickness (WT) 0.5 – 6.0 mm —
Coil Inner Diameter (CID) 100 – 1500 mm (customizable) —
Coil Outer Diameter (COD) 200 – 2000 mm —
Coil Height (Coil Length along axis) 50 – 3000 mm —
Coil Pitch (Center-to-center spacing) 15 – 200 mm —
Number of Turns 2 – 500 turns —
Overall Tube Length (developed length) Up to 300 m per coil —
OD Tolerance ±0.1 mm (precision grades) ASTM A554
WT Tolerance ±10% of nominal ASTM A554
Coil Pitch Tolerance ±1.0 mm —

3.2 Applicable Standards

4. Manufacturing Process

The manufacturing of stainless steel coil tubes is a multi-stage process requiring specialized equipment and precise process control. Wenzhou Jixing Metal Materials Co., Ltd. employs a proprietary methodology that integrates advanced forming technology with rigorous quality assurance at each stage.

4.1 Process Flow

  1. Raw Material Selection & Inspection:

    Seamless or welded stainless steel pipes are sourced from certified mills. Incoming material undergoes full chemical composition analysis (spectrometry), mechanical property verification, and visual inspection per ASTM A554 requirements.

  2. Pre-Treatment:

    The straight pipe is cleaned, degreased, and subjected to a pre-heat treatment (solution annealing at 1050–1150°C followed by controlled cooling) to ensure uniform microstructure and optimal formability. Surface scale is removed via pickling (HNO₃/HF mixture) and passivation.

  3. Coil Forming (Primary Process):

    The straight tube is fed into a precision coiling machine equipped with custom-designed tooling (工装) consisting of:

    • Forming rollers: Multiple roller stations with adjustable pressure to progressively bend the tube without wall thinning or ovalization
    • Support mandrels: Internal or external mandrels to prevent cross-sectional distortion during bending
    • Pitch control mechanism: CNC-controlled feed system ensuring consistent coil pitch throughout the entire forming length
    • End-stop & trim stations: Precision cutting at both ends to achieve exact coil height and developed length

    Two primary forming methods are employed:

    • Cold Coiling: The tube is bent at ambient temperature using progressive roller forming. Suitable for smaller ODs (≤ 32 mm) and thinner walls. Produces superior surface finish and dimensional accuracy.
    • Hot Coiling: The tube is heated to 950–1100°C (intercritical or austenitic range) before forming. Enables larger ODs and tighter coil radii without cracking. Followed by post-annealing to restore mechanical properties.
  4. In-Process Inspection:

    During coiling, real-time monitoring of bend radius, pitch accuracy, wall thickness reduction, and ovality is performed. Critical parameters include:

    • Minimum bend radius ≥ 5D (cold forming) or ≥ 3D (hot forming)
    • Maximum allowable wall thinning ≤ 15%
    • Maximum ovality ≤ 1.5% of nominal OD
  5. Post-Forming Heat Treatment:

    For cold-formed coils, a stress-relief annealing (800–900°C, 1–2 hours) or full solution annealing (1050–1150°C) may be applied to relieve residual stresses introduced during forming and restore full ductility.

  6. Final Surface Treatment:

    Pickling and passivation to remove any heat tint or oxide scale. Optional electropolishing for critical applications requiring ultra-clean surfaces.

  7. Final Quality Control:
    • Dimensional verification (OD, WT, coil geometry) using CMM (Coordinate Measuring Machine) and laser scanning
    • Chemical analysis confirmation (spectrometric)
    • Mechanical testing on representative samples
    • Non-Destructive Testing (NDT): Eddy current (ET) for wall thickness and defect detection; hydrostatic pressure testing per ASTM A554
    • Surface roughness measurement (Ra values)
  8. Packaging & Shipping:

    Coils are wrapped in protective plastic film, secured with steel bands, and placed on wooden pallets or crates. Moisture absorbers are included. Each shipment is accompanied by a Mill Test Certificate (MTC/EN 10204 3.1) and packing list.

4.2 Key Process Innovations

Proprietary Tooling Design: Wenzhou Jixing Metal Materials Co., Ltd. has developed specialized forming tooling (工装) that addresses the unique challenges of coil tube manufacturing, including:

  • Multi-stage progressive bending to minimize localized plastic deformation
  • Integrated cooling channels in tooling to prevent work-hardening in austenitic grades
  • Quick-change die sets enabling rapid changeover between different coil geometries
  • Anti-scuff coatings on roller surfaces to prevent surface damage to the tube

5. Applications

The stainless steel coil tube finds extensive application across multiple industries due to its unique combination of compact geometry, high heat transfer efficiency, and corrosion resistance:

5.1 Heat Exchangers & Condensers

5.2 Refrigeration & Air Conditioning (HVAC/R)

5.3 Chemical & Petrochemical Industry

5.4 Food & Beverage Industry

5.5 Power Generation

5.6 Marine & Offshore

5.7 Automotive & Transportation

6. Quality Certifications