Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd.

1. Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for use in a wide range of industrial, HVAC (Heating, Ventilation, and Air Conditioning), and thermal management applications. The coil tube is supplied in a continuous helical winding configuration, which facilitates downstream processing operations such as bending, forming, and cutting while minimizing material waste and production cycle time.

Research into the thermal performance of fan coil units (FCU) has demonstrated that environmental humidity significantly affects the accuracy of heat transfer measurements in coil-based heat exchangers. This finding underscores the critical importance of material selection, surface finish quality, and dimensional precision in coil tube products used within HVAC systems. The stainless steel coil tube offered by Wenzhou Jixing addresses these concerns through rigorous material specifications, consistent dimensional tolerances, and controlled surface treatments that ensure reliable thermal conductivity and long-term operational stability under variable humidity conditions.

2. Material and Properties

2.1 Base Material Grades

2.2 Key Mechanical Properties

2.3 Corrosion Resistance

The austenitic stainless steel grades used in this product exhibit excellent resistance to atmospheric corrosion, pitting corrosion (particularly SUS316 and SUS316L due to molybdenum content of 2.0–2.5%), and intergranular corrosion. The materials comply with ASTM A270 and ASTM A778 standards for corrosion resistance testing, including salt spray testing (ASTM B117) with minimum 1,000 hours of resistance for SUS316L grades.

2.4 Surface Finish Options

3. Technical Specifications

Parameter Specification Standard Reference
Outer Diameter (OD) 6.0 mm – 50.8 mm (custom sizes available) ASTM A778
Wall Thickness 0.3 mm – 3.0 mm ASTM A270
Diameter Tolerance ±0.05 mm – ±0.15 mm (depending on size range) ISO 1307
Wall Thickness Tolerance ±10% of nominal ASTM A270
Coil Width (Flat) Standard: 100 mm – 600 mm Custom
Coil Inner Diameter (ID) 300 mm – 1,200 mm Custom
Coil Length (Uncoiled) 100 m – 5,000 m per coil (continuous) —
Maximum Operating Temperature 870°C (SUS304); 870°C (SUS316) ASME BPV Section II
Minimum Operating Temperature −196°C (cryogenic capable) ASTM A270
Welding Method Resistance Welding (RW) or Laser Welding (LW) ASTM A270
Weld Seam Strength ≥90% of parent material UTS ASTM A270
Hydrostatic Test Pressure 1.5 × maximum working pressure (per coil) ASTM A270
Edge Condition Smooth, burr-free; optional slitting ISO 1307
Material Condition Annealed (A), Cold Worked (CW), Solution Treated ASTM A270
Product Standard ASTM A270 / ASTM A778 / EN 10217-7 / GB/T 12771 Multi-standard compliance

4. Manufacturing Process

4.1 Process Flow

  1. Raw Material Selection and Inspection: Ingot or hot-rolled coil material is received and subjected to spectroscopic analysis (OES) to verify chemical composition compliance with ASTM/EN standards. Incoming quality control includes visual inspection, dimensional verification, and mechanical property testing.
  2. Hot Rolling and Annealing: Steel strip is hot-rolled to preliminary dimensions, then annealed at 1,050–1,150°C followed by controlled cooling to achieve the desired austenitic microstructure with uniform grain size.
  3. Cold Reduction: The annealed strip undergoes multi-stand cold rolling to achieve final thickness within tight tolerances. Interpass annealing may be applied for reductions exceeding 60% to prevent work hardening.
  4. Coil Slitting: The cold-rolled coil is slit to the required tube blank width using precision slitting lines with automatic edge trimming and tension control systems.
  5. Forming (Tube Making): The slit strip is fed through a series of progressive rollers in a cold forming mill, gradually shaping the flat strip into a round tube profile. The forming process is controlled to maintain uniform wall thickness and roundness.
  6. Welding: The formed tube is welded along the longitudinal seam using either high-frequency resistance welding (HF-RW) or laser welding (LW). Weld parameters are continuously monitored via in-line vision systems to ensure seam quality.
  7. Heat Treatment: Welded tubes undergo solution annealing (1,050°C for SUS304/SUS316) in a protective atmosphere (nitrogen or vacuum) to restore corrosion resistance, relieve welding stresses, and achieve the final mechanical properties.
  8. Pickling and Passivation: Tubes are chemically pickled in a mixed acid solution (HNO₃ + HF or HNO₃ + H₂SO₄) to remove scale, followed by passivation treatment per ASTM A967 to establish a protective chromium oxide layer.
  9. Dimensional Inspection: Automated optical measurement systems verify OD, wall thickness, roundness, and straightness. Hydrostatic testing is performed at 1.5× maximum working pressure to confirm weld integrity.
  10. Coiling and Packaging: Qualified tubes are coiled onto precision mandrels, wrapped with protective film, and packaged for shipment. Each coil is labeled with material grade, dimensions, heat number, and certification reference.

4.2 Process Control Points

5. Applications

5.1 HVAC and Fan Coil Units

Stainless steel coil tubes are extensively used in fan coil unit (FCU) heat exchangers, where they serve as the primary heat transfer medium between chilled water or hot water and the ambient air stream. Research has demonstrated that humidity levels in the operating environment significantly influence the accuracy of heat transfer measurements in FCU systems. The use of high-quality stainless steel coil tubes with consistent wall thickness and controlled surface finish minimizes thermal resistance variations, thereby improving the reliability of heat exchange performance and energy efficiency ratings.

5.2 Food and Beverage Industry

5.3 Chemical and Pharmaceutical Processing

5.4 Building Services and Plumbing

5.5 Cryogenic and Low-Temperature Applications

6. Quality Certifications and Compliance

6.1 International Standards

6.2 Quality Management Systems

6.3 Product Testing and Documentation

7. Unique Selling Points

7.1 Superior Corrosion Resistance: The use of premium austenitic stainless steel grades with controlled molybdenum and nitrogen content provides exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking, extending service life in aggressive environments including high-humidity HVAC applications.

7.2 Precision Dimensional Consistency: Advanced cold forming and welding technology ensures uniform wall thickness and tight dimensional tolerances throughout the coil length, minimizing thermal resistance variations and ensuring consistent heat transfer performance in fan coil unit applications.

7.3 Environmental Humidity Resilience: Based on research findings regarding humidity effects on heat measurement accuracy in FCU systems, the surface passivation treatment and controlled oxide layer formation on these coil tubes ensure stable thermal conductivity regardless of ambient humidity fluctuations, maintaining energy efficiency ratings over the product lifecycle.

7.4 Continuous Supply Configuration: The coil format enables downstream fabricators to perform cutting, bending, and forming operations without interruption, reducing production cycle time and material waste by up to 15% compared to straight-length tube supply.

7.5 Full Traceability and Certification: Every coil is backed by complete material documentation, mechanical test certificates, and hydrostatic test records, providing comprehensive quality assurance for regulated industries including pharmaceutical, food, and pressure vessel applications.

7.6 Customization Capability: Wenzhou Jixing offers flexible customization of dimensions, material grades, surface finishes, and coil configurations to meet specific project requirements, supported by