Stainless Steel Coil Tube (盘管 / Coiltube) — Technical Product Specification

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)

Product Category: Stainless Steel Coil Tube / Fan Coil Tube (异程风机盘管)

Reference Document: Hydraulic Service Radius Study of Fan Coil Tube Systems with Differential Circulation Paths (《异程风机盘管系统水力服务半径研究》)

1. Product Overview

The Stainless Steel Coil Tube (盘管 / Coiltube) is a precision-engineered tubular product manufactured from austenitic stainless steel, designed primarily for hydronic heating, cooling, and ventilation systems. The coil tube is formed by cold-drawing or cold-rolling stainless steel strip into a seamless or welded tubular profile, which is subsequently coiled into a compact, space-efficient configuration suitable for integration into fan coil units (FCUs), air handling units (AHUs), and radiant heating/cooling panels.

This product is specifically engineered to address the hydraulic service radius challenges identified in differential-path fan coil tube systems (异程风机盘管系统). The study referenced in the accompanying technical literature demonstrates that conventional coil tube geometries can suffer from flow maldistribution when the hydraulic service radius exceeds certain thresholds. The coil tube produced by Wenzhou Jixing Metal Materials Co., Ltd. incorporates optimized dimensional tolerances, wall thickness uniformity, and coil geometry to mitigate these hydraulic imbalances, ensuring consistent thermal performance across extended service radii.

The term "Coiltube" (盘管) refers to a tube that has been mechanically coiled into a helical or serpentine arrangement, offering high surface-area-to-volume ratios ideal for heat exchange applications. The stainless steel material provides exceptional corrosion resistance, long service life, and compliance with sanitary and industrial standards.

2. Material & Properties

2.1 Base Material

The primary material grade used in the manufacture of this coil tube is Austenitic Stainless Steel (奥氏体不锈钢), with the following standard grades available:

2.2 Mechanical Properties (Typical Values for SUS 304 Grade)

Property Specification Test Standard
Tensile Strength (抗拉强度) ≥ 520 MPa (75,400 psi) ASTM A213 / ASTM A312
Yield Strength (屈服强度) ≥ 205 MPa (29,700 psi) ASTM A213 / ASTM A312
Elongation (延伸率) ≥ 40% (minimum 30% for thick-walled) ASTM A213
Hardness (硬度) ≤ 92 HRB (annealed condition) ASTM A262
Density (密度) 7.93 g/cm³ —

2.3 Physical & Thermal Properties

Property Value
Thermal Conductivity (热导率) at 100°C 16.3 W/(m·K)
Specific Heat Capacity (比热容) 0.50 J/(g·K) at 20°C
Thermal Expansion Coefficient (热膨胀系数) (20–100°C) 17.3 × 10⁻⁶ /K
Electrical Resistivity (电阻率) at 20°C 7.4 × 10⁻⁷ Ω·m
Melting Range (熔点范围) 1400–1450°C

2.4 Chemical Composition (SUS 304, wt%)

Element Specification
Carbon (C) ≤ 0.08%
Chromium (Cr) 18.0–20.0%
Nickel (Ni) 8.0–10.5%
Manganese (Mn) ≤ 2.0%
Silicon (Si) ≤ 1.0%
Phosphorus (P) ≤ 0.045%
Sulfur (S) ≤ 0.030%
Nitrogen (N) ≤ 0.10%

2.5 Corrosion Resistance

The austenitic stainless steel coil tube exhibits excellent resistance to a wide range of corrosive media. The passive chromium oxide film (Cr₂O₃) self-heals in the presence of oxygen, providing robust protection against:

3. Specifications

3.1 Dimensional Specifications

Parameter Specification Tolerance Standard Reference
Outer Diameter (OD) (外径) 6 mm – 25 mm (standard range); custom sizes available ±0.1 mm (for OD ≤ 12 mm); ±0.15 mm (for OD > 12 mm) ASTM A312 / GB/T 12771
Wall Thickness (壁厚) 0.3 mm – 2.0 mm (standard range) ±10% (for t ≤ 1.0 mm); ±0.1 mm (for t > 1.0 mm) ASTM A312
Coil Length (盘管长度) Custom per order; typical range 1 m – 15 m ±2% of specified length Customer specification
Coil Pitch (盘管螺距) 15 mm – 80 mm (adjustable per application) ±0.5 mm Internal standard
Coil Diameter (盘管外径) 100 mm – 800 mm ±1% Customer specification
Surface Finish (表面光洁度) No. 1 (annealed), 2B (cold-rolled & annealed), BA (bright annealed), or polished (Ra ≤ 0.4 μm) — ASTM A478

3.2 Hydraulic Performance Parameters

The following parameters are critical for the hydraulic service radius (水力服务半径) performance of the coil tube system, as referenced in the technical study literature:

Parameter Typical Value Notes
Maximum Operating Pressure (最大工作压力) 1.6 MPa (standard); up to 4.0 MPa (custom) Based on OD and wall thickness
Hydraulic Service Radius (水力服务半径) Up to 80 m (optimized differential-path configuration) Ref: 《异程风机盘管系统水力服务半径研究》
Flow Velocity (流速) 0.5 – 3.0 m/s (recommended range) For optimal heat transfer and pressure drop
Pressure Drop (压降) per meter 50 – 350 Pa/m (depending on flow rate and dimensions) Darcy-Weisbach equation applicable
Maximum Operating Temperature (最高工作温度) −196°C to 870°C (SUS 304); up to 925°C (SUS 321) Continuous service
Design Service Life (设计使用寿命) ≥ 25 years Under normal operating conditions

4. Manufacturing Process

The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:

  1. Raw Material Selection & Inspection (原材料筛选与检验):

    High-purity stainless steel strip or wire rod is procured from certified suppliers. Incoming material undergoes spectroscopic analysis (光谱分析) to verify chemical composition, along with mechanical property testing and visual inspection for surface defects.

  2. Strip Cold-Rolling (带材冷轧):

    The stainless steel strip is cold-rolled to the target thickness with precise control of rolling force, roll gap, and pass schedule. This step ensures uniform wall thickness and surface finish. Multiple rolling passes may be employed for thick-walled applications.

  3. Forming & Welding (成型与焊接):

    The cold-rolled strip is formed into a tubular profile using roll-forming (辊压成型) or press-forming techniques. For welded tube configurations, the edges are joined via TIG welding (钨极惰性气体保护焊) or laser welding (激光焊接) under inert gas shielding (argon/氩气). The weld seam is ground and smoothed to minimize flow disturbance.

  4. Cold Drawing (冷拉拔):

    For seamless tube configurations, the formed tube is cold-drawn through precision-die sets to achieve tight dimensional tolerances and improved mechanical properties. Cold drawing enhances tensile strength and reduces surface roughness.

  5. Coil Forming (盘管成型):

    The straight tube is mechanically coiled into the target helical or serpentine geometry using CNC-controlled coiling equipment. The coil pitch, coil diameter, and number of turns are precisely controlled per the engineering design. Springback compensation algorithms are applied to ensure dimensional accuracy post-forming.

  6. Solution Annealing (固溶退火):

    The formed coil tube is subjected to solution annealing (solution heat treatment) at temperatures between 1010°C and 1150°C, followed by rapid quenching. This process dissolves carbide precipitates, restores full austenitic structure, and maximizes corrosion resistance.

  7. Pickling & Passivation (酸洗钝化):

    The annealed tube is immersed in a mixed acid bath (typically nitric acid + hydrofluoric acid) to remove scale and oxide deposits. A subsequent passivation treatment in dilute nitric acid promotes the formation of a stable, protective chromium oxide passive film.

  8. Hydrostatic Testing (水压试验):

    Each coil tube is subjected to hydrostatic pressure testing at 1.5 times the maximum operating pressure for a minimum dwell time of 30 seconds to verify pressure integrity and detect any leaks or defects.

  9. Final Inspection & Quality Control (最终检验与质量控制):

    Comprehensive inspection includes dimensional measurement (OD, wall thickness, coil pitch, coil length), visual examination of weld seams and surface finish, and non-destructive testing (NDT) such as eddy current testing (涡流检测) or magnetic particle inspection (磁粉检测) for weld integrity.

5. Applications

The stainless steel coil tube is widely deployed across multiple industries, particularly in applications requiring corrosion-resistant, high-performance heat exchange components:

5.1 HVAC Systems (暖通空调系统)