Stainless Steel Coil Tube (Coiltube) — Solar Thermal Heat Exchange Application Series

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for high-efficiency heat exchange applications in solar thermal energy systems. This product is primarily utilized in indirect heating systems for oil storage tanks, where the coil tube serves as the critical heat exchange element within solar collectors, facilitating the transfer of thermal energy from concentrated solar radiation to the stored liquid medium.

Unlike conventional straight pipe assemblies, coil tubes offer a significantly higher surface-area-to-volume ratio, enabling more compact heat exchanger designs while maximizing thermal absorption and dissipation efficiency. The continuous spiral or helical geometry eliminates the need for mechanical joints or welds along the primary heat transfer path, thereby reducing potential leak points and enhancing long-term operational reliability.

Technical Reference: Based on the study "Calculation Research on Collector and Heat Exchange Coil Tube Areas for Solar Energy Indirect Heating Systems of Oil Storage Tanks," the coil tube geometry and surface area parameters are optimized to achieve a heat transfer coefficient (U-value) that meets or exceeds the thermodynamic requirements of large-scale industrial oil storage applications.

2. Material Composition & Properties

The coil tube is fabricated from austenitic stainless steel grades selected for their superior corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions.

2.1 Primary Material Grades

2.2 Key Mechanical and Thermal Properties (Typical — AISI 304)

2.3 Surface Finish

Available in 2B mill finish (standard cold-rolled and annealed), No. 4 brushed finish, or Mirror finish (8K) depending on application requirements. The internal surface can be specified with a roughness value (Ra) as low as 0.4 μm to minimize fluid flow resistance and fouling accumulation.

3. Technical Specifications

Parameter Specification / Range Standard Reference
Product Designation Stainless Steel Coil Tube (Coiltube) —
Material Grade AISI 304, 304L, 316, 316L, 321 ASTM A213 / A269
Outer Diameter (OD) 6 mm – 50 mm (customizable) ASTM A213
Wall Thickness 0.5 mm – 3.0 mm ASTM A213
Coil Inner Diameter (ID) 200 mm – 2000 mm Custom specification
Coil Length (per coil) 5 m – 500 m (continuous) Custom specification
Pitch (Coil Spacing) 1.5 × OD – 3.0 × OD (adjustable) Engineering design basis
Surface Finish 2B, No. 4 Brushed, Mirror (8K) ASTM A480
Internal Surface Roughness (Ra) 0.4 μm – 1.6 μm ISO 1302
Pressure Rating Up to 1.6 MPa (design pressure, depending on OD and wall thickness) ASME B31.3
Temperature Range −40°C to +450°C (continuous service) Material-dependent
End Forming Plain, Beveled, Threaded, or Fitted (custom) Per customer drawing
Packaging Wooden drum or steel frame with protective wrapping ISO 4180

4. Manufacturing Process

The production of precision stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality.

4.1 Process Flow

  1. Raw Material Procurement (原材料采购): Cold-rolled stainless steel strip is sourced from certified mills and undergoes incoming inspection for chemical composition (spectroscopic analysis), mechanical properties, and surface quality per ASTM A666.
  2. Strip Cleaning & Preparation (带材清洗与预处理): The stainless steel strip is degreased, descaled, and passivated using acid pickling and passivation (APP) treatment to remove mill scale and ensure a clean, corrosion-resistant surface prior to forming.
  3. Roll Forming / Coiling (卷制成型): The prepared strip is fed through a series of precision roller stations that progressively bend the material into the desired helical or spiral coil geometry. Computer Numerical Control (CNC) systems regulate feed rate, roller positioning, and bend radius to maintain dimensional tolerances within ±0.5 mm.
  4. Welding (焊接): Where continuous tube formation is required, the formed strip edges are joined using Continuous Automatic Argon Arc Welding (TIG/Inert Gas Welding) with full internal shielding gas protection. Weld parameters are controlled to minimize heat-affected zone (HAZ) distortion and ensure weld integrity.
  5. Post-Weld Heat Treatment (焊后热处理): If required by the application specification, the coil tube undergoes solution annealing at 1010–1150°C followed by rapid water quenching to restore full austenitic microstructure and maximize corrosion resistance.
  6. Passivation & Surface Treatment (钝化与表面处理): Final passivation treatment is applied using nitric acid or citric acid solutions to re-establish the passive chromium oxide layer on the weld and formed surfaces.
  7. Quality Inspection & Testing (质量检验与测试): Each coil tube batch undergoes comprehensive inspection including visual examination, dimensional verification (OD, wall thickness, coil pitch), pressure testing (hydrostatic or pneumatic), and non-destructive testing (NDT) including dye penetrant testing (DPT) or ultrasonic testing (UT) on weld seams.
  8. Packaging & Dispatch (包装与发货): Coiled tubes are wound onto protective wooden or steel drums, wrapped with moisture-proof material, and labeled with material certification documents.

5. Applications

The stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd is applicable across a broad spectrum of industrial, commercial, and energy-related sectors:

5.1 Primary Application — Solar Thermal Energy Systems

Oil Storage Tank Indirect Heating Systems: As demonstrated in the referenced academic study, coil tubes serve as the heat exchange medium in solar collector arrays designed to indirectly heat large-capacity oil storage tanks. The coil tube is integrated within the collector structure, absorbing concentrated solar radiation and transferring thermal energy to the working fluid (typically water or thermal oil), which then circulates to the oil storage tank via a heat exchange loop.

Key performance advantages in this application include:

5.2 Additional Applications

6. Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains adherence to international quality management and product standards, ensuring that every coil tube product meets the rigorous requirements of global industrial applications.

6.1 Quality Management System

6.2 Product & Material Standards

6.3 Testing & Inspection Certifications

7. Unique Selling Points

Conclusion: The Stainless Steel Coil Tube (Coiltube) product line from Wenzhou Jixing Metal Materials Co., Ltd represents a technically advanced, standards-compliant, and application-optimized solution for solar thermal heat exchange and broader industrial heat transfer applications. Its combination of precision manufacturing, material versatility, and academically validated design parameters positions it