Coil Tube (盘管) — Technical Product Specification
1. Product Overview
The Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed in continuous coil form for downstream processing, fabrication, and installation in HVAC (Heating, Ventilation, and Air Conditioning), industrial fluid transport, and thermal management systems. This product line encompasses both stainless steel and carbon steel variants, with particular emphasis on fan coil pipe applications where long-term hydraulic integrity and dimensional accuracy are paramount.
Based on extensive field analysis — notably the documented study "Analysis of Leakage Causes in Q215 Fan Coil Pipe" (Q215风机盘管管道渗漏原因分析) — this product specification integrates lessons learned from real-world failure modes to deliver a superior, leak-resistant coil tube solution. The technical development process incorporates root-cause analysis of common leakage mechanisms including weld seam porosity, corrosion-induced wall thinning, thermal fatigue cracking, and assembly-induced mechanical stress at connection points.
2. Material & Properties
2.1 Available Material Grades
- Stainless Steel Grades: SUS304 (AISI 304), SUS316 (AISI 316), SUS304L, SUS316L, SUS321 (AISI 321), SUS310S (AISI 310S)
- Carbon Steel Grades: Q215 (GB/T 700), Q235 (GB/T 700), ASTM A106 Gr.B, ASTM A53 Gr.B
- Duplex Stainless Steel: SUS31803 (UNS S31803), SUS32205 (UNS S32205)
2.2 Key Mechanical Properties (Typical Values for SUS304)
- Tensile Strength (UTS): ≥ 520 MPa (75,400 psi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (Brinell): ≤ 210 HBW
- Density: 7.93 g/cm³
- Thermal Conductivity (20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
2.3 Chemical Composition Requirements (SUS304, wt%)
| Element | Specification (wt%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
2.4 Corrosion Resistance Performance
The stainless steel variants demonstrate exceptional resistance to atmospheric corrosion, pitting, and intergranular corrosion. The carbon steel variant (Q215) is available with internal/external protective coatings including epoxy phenolic lining, galvanized finish, and organic solvent-resistant coating to mitigate the leakage risks documented in field analyses.
3. Product Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | φ6.0 mm – φ108 mm (customizable) | GB/T 14976, ASTM A554 |
| Wall Thickness | 0.30 mm – 6.0 mm | GB/T 14975, ASTM A269 |
| OD Tolerance | ±0.10 mm (standard); ±0.05 mm (precision) | ISO 6508 |
| Wall Thickness Tolerance | ±10% (standard); ±5% (precision) | ISO 6508 |
| Coil Inner Diameter (ID) | φ150 mm / φ200 mm / φ300 mm / φ400 mm | Manufacturer standard |
| Coil Weight per Roll | 1,000 kg – 3,000 kg | — |
| Surface Finish | 2B, BA (Bright Annealed), No.4, HL (Hairline), Mirror (8K) | ASTM A480 |
| End Form | Plain end, beveled end, threaded end, U-bend | Customer specification |
| Hydrostatic Test Pressure | ≥ 2.0 MPa (carbon steel); ≥ 3.0 MPa (stainless steel) | GB/T 24511 |
| Operating Temperature Range | −196°C to +870°C (SUS304); −196°C to +1050°C (SUS310S) | ASME BPV Section II |
| Formability (Deep Drawing Ratio) | ≥ 3.5 (SUS304 annealed) | ASTM A240 |
4. Manufacturing Process
4.1 Production Flow
- Raw Material Selection & Inspection: Hot-rolled coil (HRC) or cold-rolled coil (CRC) sourced from certified mills. Incoming inspection includes spectroscopic analysis (OES), mechanical testing, and visual surface examination per ASTM E1011 and GB/T 223 series.
- Slitting & Leveling: Precision slitting to target width with edge quality control. Tension leveling ensures flatness within ±0.5 mm/m.
- Forming (ERW / FAW / Weldless):
- ERW (Electric Resistance Welding): High-frequency induction heating (30–400 kHz) with precise weld temperature control to prevent heat-affected zone (HAZ) degradation.
- FAW (Fusion Arc Welding): Argon arc welding for larger diameters, ensuring full-penetration weld integrity.
- Weldless (Seamless): Available for critical applications via hot-rolling or cold-drawing processes.
- Heat Treatment / Annealing: Solution annealing at 1050–1100°C followed by controlled cooling (air cooling for standard; water quenching for super-austenitic grades). For Q215 carbon steel, stress-relief annealing at 600–650°C to reduce residual forming stresses that contribute to fatigue cracking.
- Pickling & Passivation: Nitric acid–hydrofluoric acid pickling (HNO₃ + HF) followed by passivation treatment to establish a stable chromium oxide passive film. Critical for preventing intergranular corrosion.
- Coiling & Packaging: Controlled tension coiling with center-to-center alignment. Protective wrapping with VCI (Vapor Corrosion Inhibitor) paper and steel banding.
- Final Quality Control: 100% hydrostatic testing, dimensional verification (laser measurement), eddy current testing (ECT) for weld seam integrity, and PMI (Positive Material Identification) verification.
4.2 Anti-Leakage Design Features (Derived from Q215 Fan Coil Pipe Failure Analysis)
Field investigations into Q215 fan coil pipe leakage revealed five primary failure mechanisms. This product incorporates specific countermeasures:
- Weld Seam Defects: Implemented 100% eddy current testing (ECT) and ultrasonic testing (UT) on weld seams. Weld heat input controlled within ±5% of specification to minimize HAZ embrittlement and porosity.
- Corrosion-Induced Wall Thinning: Minimum wall thickness tolerance tightened to ±5% for precision grade. Optional internal PTFE (Polytetrafluoroethylene) or EPDM (Ethylene Propylene Diene Monomer) lining for aggressive media.
- Thermal Fatigue Cracking: Enhanced cyclic thermal fatigue resistance through controlled grain refinement (average grain size ≤ ASTM No. 7) and optimized chromium content (≥ 18.5% Cr for SUS304).
- Assembly Stress at Connections: Recommended use of flexible coupling joints or expansion loops. Product supplied with stress-relief annealing certificate to minimize cold-work hardening effects.
- Manufacturing Defects (Inclusions, Laminations): Ultra-sonic internal inspection of parent coil material. Rejection criteria for inclusions exceeding 0.5 mm equivalent diameter.
5. Applications
5.1 Primary Application Domains
- HVAC & Fan Coil Units: Water-cooled fan coil piping, chiller water supply/return lines, condenser tubing. The Q215 and SUS304 variants are specifically optimized for hydronic coil applications where thermal cycling and water quality variability are common.
- Building Services: Domestic hot water distribution, radiator piping, underfloor heating manifolds, solar thermal systems.
- Food & Beverage Industry: Process piping, CIP (Clean-In-Place) systems, steam lines, hygienic-grade coil tubing (SUS316L with electropolished finish).
- Chemical Processing: Reactor cooling coils, heat exchanger tubes, chemical transfer lines (SUS316, Duplex 2205 for chloride environments).
- Automotive & Industrial: Radiator core tubes, intercooler piping, hydraulic systems, pneumatic tubing.
- Marine & Offshore: Seawater cooling loops, ballast water systems (SUS316L with enhanced pitting resistance).
- Medical Equipment: Dialysis machine tubing, sterilization autoclave lines, pharmaceutical process piping.
5.2 Fan Coil Pipe — Specialized Application Notes
For fan coil unit (FCU) applications, the following engineering considerations are critical based on documented leakage failure analyses:
- Operating pressure: Typically 0.3–0.6 MPa (supply); 0.2–0.4 MPa (return)
- Operating temperature: 45–70°C (heating); 7–12°C (cooling)
- Thermal cycling frequency: 1,000–10,000 cycles over design life
- Water quality: Conductivity ≤ 1000 µS/cm; pH 7.0–8.5; dissolved oxygen ≤ 0.1 mg/L (recommended)
- Recommended material: SUS304 for standard applications; SUS316 for coastal/high-chloride environments
6. Quality Certifications & Standards Compliance
6.1 International Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- EN 10204 3.1 — Inspection Certificate (Mill Test Certificate)
- CE Marking — European Conformity (where applicable)
6.2 Product-Specific Standards
- GB/T 14976-2012 — Steel tubes for fluid transport
- GB/T 14975-2012 — Cold-rolled stainless steel tubes for fluid transport
- GB/T 12771-2019 — Cold-rolled stainless steel tubes for general purposes
- ASTM A554 — ERW steel tubes for fluid transport
- ASTM A269 — Austenitic stainless steel tubing (seamless, welded, and welded-then-heat-treated)
- ASTM A580 — Seamless and welded austenitic stainless steel tubing
- ASME SA-213 — Seamless austenitic stainless steel tubes for heat exchangers
- EN 10216-5 — Heat exchangers and related equipment — welded tubes
- GB/T 15375-2008 — Seamless and welded stainless steel tubes for heat exchangers
6.3 Inspection & Testing Protocols
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