Stainless Steel Coil Tube (Coiltube) — Technical Product Specification

1. Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. through precision cold-drawing and coiling processes. Unlike conventional straight stainless steel pipes, Coiltube is delivered in continuous helical or spiral coil configurations, offering superior flexibility, reduced installation labor, and enhanced dimensional consistency. This product is engineered for demanding applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, heat exchangers, industrial fluid conveyance, and specialized process engineering where corrosion resistance, thermal conductivity, and mechanical integrity are critical performance parameters.

The Coiltube product line represents a significant advancement in tubular manufacturing technology, combining the inherent advantages of austenitic and duplex stainless steel alloys with the geometric efficiency of coiled delivery. The continuous coil configuration eliminates the need for field welding and joint fabrication, thereby reducing potential failure points and improving overall system reliability.

2. Material & Properties

2.1 Base Alloy Composition

The Coiltube product is manufactured from high-grade austenitic stainless steel conforming to international metallurgical standards. The primary alloy grades available include:

2.2 Mechanical Properties

Property Specification (AISI 304/316) Test Method
Tensile Strength (Ultimate) ≥ 515 MPa (74,700 psi) ASTM A370
Yield Strength (0.2% Offset) ≥ 205 MPa (29,700 psi) ASTM A370
Elongation (at Rupture) ≥ 40% (in 50 mm / 2 in.) ASTM A370
Hardness (Brinell) ≤ 201 HB ASTM A262
Impact Strength (Charpy V-Notch, -40°C) ≥ 47 J (35 ft-lb) ASTM A370

2.3 Physical Properties

Property Value
Density 8.0 g/cm³ (499 lb/ft³)
Thermal Conductivity (at 100°C) 16.3 W/(m·K) (9.5 BTU/hr·ft·°F)
Thermal Expansion Coefficient (20–100°C) 17.3 × 10⁻⁶ /°C
Specific Heat 0.50 J/(g·K)
Electrical Resistivity (at 20°C) 7.2 × 10⁻⁷ Ω·m
Maximum Service Temperature 870°C (AISI 304); 870°C (AISI 316)
Cryogenic Service Temperature Down to −196°C (−321°F)

2.4 Corrosion Resistance Characteristics

3. Specifications

3.1 Dimensional Specifications

Parameter Specification Tolerance
Outside Diameter (OD) 6.00 mm – 108.00 mm (¼" – 4") ± 0.1 mm (± 0.004")
Wall Thickness 0.50 mm – 6.00 mm (0.020" – 0.236") ± 10% of nominal
Coil Diameter (Major) 500 mm – 2,000 mm (20" – 80") ± 25 mm (± 1")
Coil Length (Continuous) 50 m – 500 m (164 ft – 1,640 ft) As specified by purchaser
Coil Height (Width) 50 mm – 200 mm (2" – 8") ± 5 mm (± 0.2")
Surface Finish No. 4 Brushed / 2B Annealed / Mirror Polished (Ra ≤ 0.4 μm) Per customer specification
End Configuration Open ends / Flat-cut / Beveled / Threaded (optional) Per customer specification

3.2 Applicable Standards and Specifications

3.3 Coiling Parameters

Parameter Specification
Minimum Bend Radius ≥ 3 × OD (for cold bending)
Maximum Number of Coils per Spool As per coil diameter and tube OD
Coil Packing Method Layer-wound with protective interleaving
Protective Packaging Wooden pallet / steel drum / stretch-wrap with desiccant
Maximum Coil Weight ≤ 5,000 kg (11,023 lbs)

4. Manufacturing Process

4.1 Process Flow Overview

The manufacturing of stainless steel Coiltube involves a multi-stage, precision-controlled production sequence:

  1. Raw Material Preparation: Selection of certified stainless steel ingots or continuously cast billets conforming to the specified alloy grade. Incoming material is subjected to chemical analysis (spectrometric verification) and mechanical testing.
  2. Piercing and Hot Rolling: Billets are heated to approximately 1,150–1,250°C and pierced to produce seamless hollow blanks. Hot rolling reduces the cross-section to near-final dimensions.
  3. Heat Treatment (Solution Annealing): The hot-rolled tube is solution-annealed at 1,040–1,150°C followed by rapid water quenching to achieve a fully austenitic, stress-free microstructure with optimal corrosion resistance.
  4. Pickling and Descaling: Removal of oxide scale through controlled acid pickling (typically using a mixture of hydrofluoric and nitric acids or citric acid-based solutions) to achieve a clean, uniform surface.
  5. Cold Drawing / Cold Rolling: The tube is cold-worked through calibrated dies to achieve precise final dimensions (OD and wall thickness) with tolerances within ±0.1 mm. This step also imparts beneficial work hardening and improves surface finish quality.
  6. Intermediate Annealing: Periodic annealing at 1,000–1,100°C is performed between cold-drawing passes to restore ductility and prevent cracking during subsequent deformation.
  7. Precision Coiling: The finished tube is fed through a precision coiling head that forms the continuous coil with controlled bend radius, coil diameter, and coil pitch. The coiling process employs hydraulic tension control to prevent ovality and surface damage.
  8. Final Heat Treatment (if required): Post-coiling stress-relief annealing may be applied for applications requiring specific mechanical properties or for preventing spring-back effects.
  9. Surface Finishing: Final surface treatment options include mechanical polishing, electropolishing, passivation (per ASTM A967), or specialized surface treatments as required.
  10. Quality Inspection: Comprehensive non-destructive testing (NDT) including eddy current testing, hydrostatic pressure testing, and dimensional verification.
  11. Packaging and Dispatch: Finished coils are packaged with protective wrapping, corrosion inhibitors, and labeled with full traceability documentation.

4.2 Key Manufacturing Advantages

5. Applications

5.1 HVAC (Heating, Ventilation, and Air Conditioning) Systems

The Coiltube finds extensive application in HVAC systems, particularly in the manufacture of:

5.2 Industrial Heat Exchange

5.3 Chemical and Petrochemical Processing

5.4 Food and Pharmaceutical Industry

5.5 Energy and Power Generation