Stainless Steel Coil Tube (Coiltube) — Product Technical Specification

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.  |  Product Code: JX-1475  |  Classification: Literature & Technical Reference Series

1. Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered coiled piping component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed primarily for integration into Fan Coil Units (FCUs), heat exchangers, and thermal management systems, this product represents a critical component in air-side heat transfer applications. The coiltube is formed into a continuous spiral or serpentine geometry to maximize surface area-to-volume ratio, thereby enhancing convective and conductive heat exchange efficiency within confined equipment envelopes.

Based on the engineering study documented in the technical literature titled "Variation Laws of Fan Coil Unit Cooling Capacity with Respect to Inlet Wet-Bulb Temperature and Inlet Water Temperature", the Coiltube product line has been optimized to address the thermodynamic interdependencies that govern cooling performance under variable operating conditions. This research-driven approach ensures that the coil geometry, material selection, and dimensional tolerances are calibrated to deliver consistent and predictable thermal output across a broad range of environmental and operational parameters.

2. Material Composition & Physical Properties

2.1 Base Material

The Coiltube is fabricated from high-purity austenitic stainless steel, primarily conforming to the following industry-standard grades:

2.2 Key Physical & Mechanical Properties

Property Unit AISI 304 AISI 316 AISI 316L
Density (ρ) g/cm³ 8.00 8.03 8.03
Thermal Conductivity (k) at 20°C W/(m·K) 16.3 14.6 14.6
Specific Heat Capacity (cₚ) at 20°C J/(kg·K) 500 500 500
Tensile Strength (σ_b) MPa ≥520 ≥515 ≥485
Yield Strength (σ_0.2) MPa ≥205 ≥205 ≥170
Elongation (A₅) % ≥40 ≥40 ≥45
Maximum Service Temperature °C 870 870 870
Linear Thermal Expansion Coefficient (20–100°C) ×10⁻⁶/K 17.3 16.0 16.0

2.3 Chemical Composition (Typical, wt%)

Element C Si Mn P S Cr Ni Mo N
AISI 304 ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.030 18.0–20.0 8.0–10.5 — ≤0.10
AISI 316 ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.030 16.0–18.0 10.0–14.0 2.0–3.0 ≤0.10
AISI 316L ≤0.03 ≤1.00 ≤2.00 ≤0.045 ≤0.030 16.0–18.0 10.0–14.0 2.0–3.0 ≤0.10

3. Geometric & Dimensional Specifications

3.1 Coil Tube Dimensions

Parameter Specification Range Tolerance
Outer Diameter (OD) 6.0 mm – 19.0 mm ±0.15 mm
Wall Thickness (t) 0.50 mm – 1.50 mm ±0.05 mm
Inner Diameter (ID) 5.0 mm – 17.5 mm (derived) ±0.20 mm
Coil Pitch (center-to-center spacing) 8.0 mm – 25.0 mm ±0.30 mm
Coil Length (developed length) 1.0 m – 12.0 m ±50 mm
Coil Height (axial height of coil) 25 mm – 150 mm ±2.0 mm
Number of Turns 10 – 200 turns ±2 turns
End Forming Straight, flared, or crimped (per customer drawing) —

3.2 Performance Parameters (Typical Cooling Capacity)

Operating Condition Inlet Wet-Bulb Temp (T_wb,in) Inlet Water Temp (T_w,in) Cooling Capacity (Q) COP (Coefficient of Performance)
Standard Condition 18.0°C 7.0°C Baseline reference (100%) —
High Humidity Condition 21.0°C 7.0°C ≈ 92–95% of baseline —
Low Water Temp Condition 18.0°C 5.0°C ≈ 108–115% of baseline —
High Water Temp Condition 18.0°C 12.0°C ≈ 65–72% of baseline —

Note: The cooling capacity data above is derived from the thermodynamic analysis documented in the study "Variation Laws of Fan Coil Unit Cooling Capacity with Respect to Inlet Wet-Bulb Temperature and Inlet Water Temperature." The key finding established that cooling capacity exhibits a positive linear correlation with decreasing inlet water temperature and a negative correlation with increasing inlet wet-bulb temperature. The rate of capacity degradation per degree Celsius increase in wet-bulb temperature is approximately 3–5%, while a decrease of 1°C in inlet water temperature yields approximately 4–6% capacity improvement, within the standard operating envelope.

4. Manufacturing Process

4.1 Process Flow Overview

  1. Raw Material Inspection: Incoming stainless steel strip or seamless tube stock is subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with the specified grade.
  2. Surface Preparation & Cleaning: Material is degreased and pickled to remove surface oxides, scale, and contaminants, ensuring a clean substrate for subsequent forming operations.
  3. Coil Forming (Cold Bending): Precision CNC-controlled coil forming machines wind the straight tube into the specified spiral geometry. The forming process maintains a controlled bending radius (R ≥ 4 × OD) to prevent wall thinning, ovality, or cracking.
  4. Pitch Calibration: Automated laser measurement systems verify coil pitch consistency throughout the entire developed length, ensuring uniform heat transfer surface distribution.
  5. End Forming & Cutting: Tube ends are cut to precise length using cold sawing or laser cutting, followed by end-forming operations (flaring, crimping, or straightening) as specified in the customer drawing.
  6. Solid Solution Annealing (Optional): For applications requiring maximum ductility or stress relief post-forming, the coil tube may be subjected to solution annealing at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure.
  7. Surface Finishing: Final surface treatment includes electropolishing or mechanical polishing to achieve the required surface roughness (Ra ≤ 0.8 μm for hygienic applications; Ra ≤ 1.6 μm for standard HVAC applications).
  8. Final Quality Inspection: Each batch undergoes dimensional verification, visual inspection, and sampling for destructive and non-destructive testing (NDT).

4.2 Key Process Control Parameters

5. Applications

5.1 Primary Applications

5.2 Secondary Applications