Stainless Steel Coil Tube — Coiltube (Series 695)

Product Overview

The Stainless Steel Coil Tube (Coiltube, Product No. 695) is a precision-engineered continuous-length tubular product supplied in coil configuration, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for heat exchanger and condenser applications, where the coiled geometry maximizes surface area within a compact footprint, thereby enhancing thermal transfer efficiency. The coil tube represents a critical component in optimized condenser designs, where geometric parameters—including coil diameter, pitch, tube wall thickness, and number of turns—are systematically tuned to minimize pressure drop while maximizing heat exchange capacity.

Unlike straight seamless or welded tubes, coil tubes are formed through a continuous coiling process that produces a uniform helical geometry with minimal residual stress. This inherent shape provides superior convective heat transfer coefficients due to the secondary flow (Dean flow) generated within the curved channel, which disrupts the thermal boundary layer and promotes turbulent mixing even at moderate Reynolds numbers.

Material & Properties

The coil tube is fabricated from austenitic stainless steel grades, selected for their combination of corrosion resistance, thermal stability, and formability. The primary material specifications are as follows:

Specifications

Parameter Specification
Product Designation Coiltube (Coil Tube), Series 695
Outer Diameter (Outer Diameter, OD) 3.18 mm – 50.8 mm (1/8" – 2")
Wall Thickness (Wall Thickness, WT) 0.25 mm – 3.00 mm (0.010" – 0.118")
Coil Diameter (Coil Diameter, CD) Custom; typical range 50 mm – 200 mm (2" – 8")
Coil Length (Coil Length, CL) Up to 3,000 m (continuous, custom-cut available)
Manufacturing Process Continuous Coiling / Rotary Draw & Bend (Rotary Draw and Bend, RDB)
Surface Finish Pickled & Passivated (Pickled and Passivated), Mirror Polish, or As-Rolled
End Condition Open ends, Beveled ends, or Custom-formed ends
Applicable Standards ASTM A213, ASTM A269, ASTM A778, EN 10217-7, GB/T 12771
Temperature Range −196°C to +870°C (−321°F to +1,598°F)
Pressure Rating Up to 40 MPa (5,800 psi), dependent on geometry and grade
Material Grades 304, 304L, 316, 316L, 321, 347, Duplex 2205 (on request)

Manufacturing Process

The production of high-precision stainless steel coil tubes follows a rigorous multi-stage process chain:

  1. Raw Material Preparation (Raw Material Preparation): Cold-rolled stainless steel strip or coil stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (Optical Emission Spectrometry, OES) to verify chemical composition within ASTM/EN specification tolerances.
  2. Tube Forming (Tube Forming): The strip is fed into a rotary draw and bend (Rotary Draw and Bend, RDB) machine or a continuous coiling mill. The strip is simultaneously formed into a tubular cross-section and coiled into a helical shape. The RDB process involves progressive reduction through multiple draw stations, each equipped with rotating tooling that maintains dimensional accuracy throughout the forming operation.
  3. Welding (Welding): A longitudinal seam weld is applied using Continuous Laser Welding (Continuous Laser Welding, CLW) or Pulse-Tungsten Inert Gas Welding (Pulse-Tungsten Inert Gas Welding, Pulse-TIG). The weld is subsequently ground and polished to achieve internal surface smoothness, critical for applications requiring low flow resistance.
  4. Heat Treatment (Heat Treatment): The welded coil tube undergoes solution annealing (Solution Annealing) at 1010–1150°C followed by rapid water quenching. This step homogenizes the microstructure, relieves residual welding stresses, and restores full corrosion resistance in the Heat-Affected Zone (Heat-Affected Zone, HAZ).
  5. Pickling & Passivation (Pickling and Passivation): The tube is immersed in a mixed acid bath (typically nitric-hydrofluoric acid solution) to remove oxide scale and contaminants. A subsequent passivation step with dilute nitric acid or citric acid promotes the formation of a protective chromium oxide film (passive film).
  6. Dimensional Inspection & Coiling (Dimensional Inspection and Coiling): Final dimensions—including outer diameter, wall thickness, coil diameter, and pitch—are verified using ultrasonic thickness gauges (Ultrasonic Thickness Gauges, UTG), laser profilometers, and optical measurement systems. The tube is then coiled onto a mandrel or core for shipping.

Applications

The Stainless Steel Coil Tube (Series 695) is deployed across a wide spectrum of industrial and commercial applications, particularly where compact, efficient heat exchange is required:

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications:

Unique Selling Points

Technical Notes on Coil Condenser Optimization

As referenced in the study "Optimized Design of a Coil Condenser", the performance of coil tubes in condenser applications is governed by the interplay of geometric parameters and fluid dynamics. Key optimization variables include:

  • Coil Diameter to Tube Diameter Ratio (Coil Diameter to Tube Diameter Ratio, D/d): Ratios between 15 and 60 typically yield the best balance of heat transfer enhancement and pressure drop.
  • Pitch (Pitch): The axial spacing between adjacent coil turns affects flow maldistribution and overall thermal-hydraulic performance.
  • Number of Turns (Number of Turns): Determines the total heat exchange area and must be optimized against manufacturing complexity and cost.
  • Tube Pass Configuration (Tube Pass Configuration): Multi-pass coil arrangements can be employed to increase residence time and improve condensation efficiency.

Wenzhou Jixing Metal Materials Co., Ltd. applies these optimization principles in the design and production of Series 695 coil tubes, ensuring that each product delivers peak thermal-hydraulic performance for its intended application.