Stainless Steel Coil Tube — GB/T 24592 Welded Heat Exchange Tubes
Product Overview
The Stainless Steel Coil Tube (Product No. 73) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered welded tubing product designed specifically for heat exchange equipment applications. This product is manufactured in strict compliance with GB/T 24592 — the Chinese National Standard for Welded Heat Exchange Tubes (焊接换热管). As a coiled tube configuration, this product offers superior flexibility in installation and heat transfer surface utilization compared to straight-tube alternatives, making it particularly advantageous for compact heat exchanger designs.
The defining characteristic of this product line is its enhanced non-destructive testing (NDT) requirements for weld seam integrity. Unlike standard fluid transport tubes, the RT (Radiographic Testing) and UT (Ultrasonic Testing) sampling ratio for weld seams in these tubes is significantly elevated, ensuring exceptional reliability in thermal cycling and pressure-bearing environments.
Material & Properties
These coil tubes are fabricated from austenitic stainless steel grades commonly specified under GB/T 24592, including but not limited to:
- 304 (06Cr19Ni10) — General-purpose corrosion resistance with excellent weldability
- 316 (06Cr17Ni12Mo2) — Enhanced pitting and crevice corrosion resistance via molybdenum addition
- 316L (022Cr17Ni12Mo2) — Low-carbon variant for superior weld zone integrity
- 321 (06Cr18Ni11Ti) — Titanium-stabilized grade for elevated-temperature service
Key material properties include:
- Operating temperature range: −196°C to +800°C (depending on grade)
- Corrosion resistance: Excellent against water, steam, atmospheric, and mildly aggressive media
- Mechanical properties: Tensile strength ≥ 520 MPa (minimum, per grade specification)
- Thermal conductivity: 14–16 W/(m·K) typical for austenitic grades
- Surface finish: Passivated and pickled interior/exterior surfaces for corrosion resistance
Specifications
| Parameter | Specification |
|---|---|
| Applicable Standard | GB/T 24592 (Welded Heat Exchange Tubes) |
| Product Form | Coil Tube (盘管) |
| Outer Diameter (OD) | 6.0 mm – 25.0 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm |
| Coil Diameter | ≥ 200 mm (minimum bend diameter per material grade) |
| Weld Type | Continuous longitudinal seam weld (TIG / resistance welding) |
| Weld Seam NDT — RT | Sampling ratio: ≥ 10% (elevated vs. fluid tube requirements) |
| Weld Seam NDT — UT | Sampling ratio: ≥ 10% (elevated vs. fluid tube requirements) |
| Pressure Rating | Up to 4.0 MPa (typical for heat exchanger duty) |
| Surface Treatment | Acid pickling and passivation; Ra ≤ 0.8 μm interior finish |
| Delivery Condition | Coiled, heat-treated (solution annealed), pickled |
| Material Grades | 304, 304L, 316, 316L, 321, 310S (per order) |
Manufacturing Process
The production of GB/T 24592 compliant coil tubes follows a rigorous multi-stage manufacturing sequence:
- Strip Preparation — Cold-rolled stainless steel strip is slitted to precise dimensions and inspected for surface defects.
- Forming & Welding — The strip is formed into a tubular configuration and joined via continuous longitudinal seam welding (typically TIG welding for seamless weld quality or resistance welding for high-speed production).
- Coiling — The welded tube is cold-formed into a coil configuration using precision rollers, ensuring uniform bend radius and avoiding work-hardening or cracking.
- Heat Treatment (Solution Annealing) — The coiled tube undergoes solution annealing at 1050–1150°C followed by rapid cooling to restore full austenitic microstructure and eliminate welding-induced sensitization.
- Pickling & Passivation — The tube is treated with a mixed acid solution to remove oxide scale, followed by passivation to form a protective chromium oxide layer.
- Non-Destructive Testing (NDT) — Weld seams undergo Radiographic Testing (RT) and Ultrasonic Testing (UT) at sampling rates exceeding those required for fluid transport tubes, ensuring weld integrity critical for heat exchange service.
- Hydrostatic Pressure Testing — Each coil is subjected to hydrostatic proof testing at 1.5× the maximum working pressure.
- Final Inspection & Packaging — Dimensional verification, surface inspection, and protective packaging for shipment.
Applications
These welded heat exchange coil tubes are engineered for demanding thermal management applications, including:
- Air-Conditioning & Refrigeration Systems — Evaporator and condenser coils in commercial HVAC units
- Process Heat Exchangers — Shell-and-tube heat exchangers in chemical, petrochemical, and pharmaceutical industries
- Power Generation — Feedwater heaters, economizers, and condensers in thermal power plants
- Marine Systems — Seawater coolers and heat recovery units on vessels
- Food & Beverage Processing — Hygienic heat exchangers requiring corrosion-resistant, food-grade tubing
- Automotive Radiators — Compact heat exchange assemblies for engine cooling systems
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality assurance framework for this product line:
- GB/T 24592 Compliance — Full conformance to the Chinese National Standard for welded heat exchange tubes, including all dimensional tolerances, mechanical property requirements, and testing protocols.
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality and traceability.
- Elevated NDT Standards — The RT and UT weld seam inspection sampling ratio exceeds that of standard fluid tubes, providing an additional margin of safety for heat exchange applications where weld integrity is critical to preventing thermal leakage and pressure failure.
- Mill Test Certificates (MTC) — Each batch is accompanied by EN 10204 Type 3.1 material test certificates with full chemical composition and mechanical property data.
- Third-Party Inspection — Available upon request (SGS, BV, TUV, or client-designated inspector).
Key Differentiator: The enhanced weld seam NDT protocol — with RT and UT sampling ratios deliberately set above those of standard fluid tubes — reflects the critical safety demands of heat exchange service. In thermal applications, a single weld defect can lead to cross-contamination between fluids, thermal efficiency loss, or catastrophic pressure failure. This product's elevated inspection standard provides end-users with verified confidence in long-term operational reliability.