Stainless Steel Coil Tube — Double-Channel Heating Coil Tube (Coiltube)

1. Product Overview

The Double-Channel Heating Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered stainless steel coiled tube product designed for high-efficiency thermal energy transfer applications. This product category encompasses continuously formed, helically wound stainless steel tubes engineered to maximize surface-area-to-volume ratios, thereby enhancing convective and conductive heat exchange performance. The coil geometry allows for compact installation within heat exchangers, industrial furnaces, chemical reactors, and process heating systems where space constraints and thermal efficiency are critical design parameters.

The product line reflects advanced metallurgical formulation and precision manufacturing capabilities, incorporating optimized wall thickness distributions, consistent coil winding tolerances, and superior weld integrity. The double-channel configuration enables independent fluid circulation within two concentric or adjacent passages, facilitating simultaneous heating, cooling, or temperature differential management within a single structural unit.

2. Material & Properties

2.1 Base Alloy Composition

The primary material grade employed in the construction of this coil tube product is Austenitic Stainless Steel (奥氏体不锈钢), with the following typical chemical composition conforming to ASTM and EN standards:

Alternative grades including SUS316L (Low Carbon), SUS321 (Ti-stabilized), and SUS310S (High Temperature) are available upon specification for specialized service environments involving aggressive chemical media or extreme thermal cycling.

2.2 Mechanical Properties

2.3 Surface Finish & Corrosion Resistance

The coil tube surface is processed to a SAT (Solid Acid Pickled and Oiled) or BA (Bright Annealed) finish, achieving surface roughness (Ra) values of ≤ 0.8 μm. The chromium-rich passive film (Cr₂O₃) provides inherent resistance to atmospheric corrosion, mild acids, and organic solvents. Pitting corrosion resistance is quantified by a Critical Pitting Temperature (CPT) exceeding 30°C in 3.5% NaCl solution for SUS316L variants.

3. Specifications

Parameter Specification Range Standard / Reference
Outer Diameter (OD) Φ6.0 mm – Φ50.8 mm ASTM A213 / EN 10216-5
Wall Thickness 0.5 mm – 3.0 mm ±10% tolerance
Coil Winding Diameter Φ100 mm – Φ2000 mm Custom per application
Coil Length (展开长度) 3 m – 500 m (continuous) —
Number of Channels 2 (Double-Channel) —
Weld Type Continuous TIG / Orbital Weld ISO 13919
Weld Quality 100% Radiographic Testing (RT) Available EN ISO 17636
Surface Treatment Acid Pickled & Passivated (酸洗钝化) ASTM A967
End Condition Beveled / Plain / Threaded Per customer drawing
Coil Packing Layer-wound with protective interlayers —
Operating Pressure ≤ 4.0 MPa (design dependent) ASME BPV VIII Div.1
Heat Treatment Solution Annealing at 1050°C + Water Quench ASTM A213

4. Manufacturing Process

4.1 Process Flow Diagram

  1. Material Preparation (原材料准备): Selection of certified stainless steel seamless tube or welded tube blanks conforming to the specified grade. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) and mechanical property testing.
  2. Hot/Cold Forming (冷热成形): Seamless tube blanks are subjected to hot rolling or cold drawing to achieve the target OD and wall thickness. Cold drawing enhances dimensional precision and surface finish while improving yield strength through work hardening.
  3. Solution Annealing (固溶退火): Tubes are heated to 1020–1100°C in a controlled atmosphere furnace and rapidly quenched (water or forced air) to dissolve carbides, restore full austenitic structure, and relieve residual stresses from forming operations.
  4. Acid Pickling & Passivation (酸洗钝化): Immersion in mixed acid baths (HNO₃ + HF or H₂SO₄ + HNO₃) removes mill scale and oxide layers. Subsequent passivation treatment re-establishes the protective chromium oxide film.
  5. Coil Winding / Helical Forming (盘绕成形): The straight tube is fed through precision-guided mandrels and wound into the target helical geometry using CNC-controlled coiling machines. Winding parameters (pitch, coil diameter, number of turns) are programmatically controlled to ±0.5 mm tolerance. The double-channel configuration is achieved through either concentric tube-in-tube arrangement or parallel-wound dual passages with intermediate sealing.
  6. Welding (焊接): End joints and channel connections are fabricated using Gas Tungsten Arc Welding (GTAW/TIG) with argon shielding. Weld parameters are optimized for full penetration and minimal heat-affected zone (HAZ) distortion. Weld seams receive 100% visual inspection and are subject to non-destructive testing (NDT).
  7. Heat Treatment Post-Welding (焊后热处理): Stress-relief annealing at 870–920°C eliminates residual welding stresses and prevents sensitization (chromium carbide precipitation at grain boundaries).
  8. Non-Destructive Testing (无损检测): Radiographic Testing (RT) per EN ISO 17636, Eddy Current Testing (ECT) per ASTM E709, and Hydrostatic Pressure Testing (水压试验) at 1.5× working pressure for 30 minutes with zero leakage tolerance.
  9. Final Inspection & Packing (终检与包装): Dimensional verification using laser scanning or coordinate measuring machines (CMM). Surface quality assessment. Protective end caps, moisture-absorbing desiccants, and anti-corrosion wrapping applied prior to export-grade packing.

4.2 Double-Channel Heat Transfer Optimization

Based on the research framework outlined in the study "Optimization of Heat Transfer Effect Analysis Model for Double-Channel Heating Coil Tube" (《双通道加热盘管传热效应分析模型优化》), the thermal performance of this product is governed by the following analytical model:

The overall heat transfer coefficient (U-value) for the double-channel coil configuration is expressed as:

1/U = 1/h₁ + δ_w/λ_w + 1/h₂ + R_foul

Where:

The optimization model incorporates the Nusselt number (Nu) correlation for helical coil flow, modified by the Dean number (De) to account for secondary flow effects induced by the curvature of the coil:

Nu = 0.023 × Re⁰·⁸ × Pr⁰·⁴ × (1 + 0.4 × (De/1000)⁰·⁵)

This model enables precise prediction of heat transfer enhancement factors (typically 1.5–2.5× over straight tube equivalents) and guides the selection of optimal coil diameter, pitch, and flow velocity for specific thermal duty requirements.

5. Applications

6. Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring traceability and compliance with international standards:

All production batches undergo full traceability documentation including heat number (炉号), chemical analysis reports (化学成分分析报告), mechanical test results, and NDT records. Third-party inspection (TPI) by entities such as SGS, BV (Bureau Veritas), or TÜV is available upon customer request.

7. Unique Selling Points

  1. Optimized Double-Channel Architecture: The dual-passage design enables simultaneous heating and cooling within a single coil assembly, reducing footprint by up to 40% compared to parallel single-channel systems while maintaining or exceeding thermal duty capacity.
  2. Model-Driven Design Optimization: Leveraging the validated heat transfer analysis model (传热效应分析模型), each coil configuration is computationally optimized for maximum U-value and minimum pressure drop, ensuring energy efficiency and reduced pumping costs.
  3. Full-Length NDT Coverage: 100% radiographic and eddy current inspection of all weld seams eliminates the risk of latent defects in critical pressure-containing applications.
  4. Custom Geometric Configuration: CNC-controlled coiling enables precise realization of customer-specific coil diameters, pitches, and total developed lengths with ±0.5 mm dimensional tolerance.
  5. Wide Grade Availability: From standard SUS304/316L to specialty high-temperature (310S) and super-austenitic (904L, 254 SMO) grades, accommodating the full spectrum of corrosive and thermal service conditions.
  6. Supply Chain Traceability: Complete material pedigree from steel mill heat number through final product, supporting regulatory compliance in nuclear, aerospace, and pharmaceutical sectors.