Stainless Steel Seamless Coil Tube — GB/T 13296 Heat Exchanger Tube

1. Product Overview

The Stainless Steel Seamless Coil Tube (also referred to as Coil Tube or Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for heat exchange applications. This product is manufactured in strict compliance with GB/T 13296 — the Chinese National Standard for Seamless Steel Tubes for Heat Exchangers and Heat Sinks. As a seamless coil tube, it is supplied in continuous coiled form, offering superior dimensional consistency, enhanced mechanical integrity, and superior thermal transfer performance compared to welded alternatives.

This product is classified under the Quality Standards category, specifically aligned with the Chinese National Standard (中国国标) for Heat Exchange Equipment (换热设备). The seamless construction eliminates weld seams that could serve as potential failure points under thermal cycling and pressure loading conditions, making it an ideal choice for demanding industrial heat exchanger environments.

2. Material & Properties

2.1 Material Grades

Seamless coil tubes conforming to GB/T 13296 are typically available in the following austenitic and austenitic-ferritic stainless steel grades:

• 06Cr19Ni10 (SUS304 / 304) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
• 022Cr17Ni12Mo2 (SUS316 / 316) — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion
• 022Cr19Ni10 (SUS304L / 304L) — Low-carbon variant with enhanced resistance to intergranular corrosion
• 022Cr17Ni12Mo2 (SUS316L / 316L) — Low-carbon molybdenum-bearing grade for demanding corrosive environments
• 06Cr13 (SUS410 / 410) — Martensitic grade for elevated-temperature applications with moderate corrosion resistance
• 06Cr17Ni12Mo2Ti (SUS321Ti / 321) — Titanium-stabilized grade for high-temperature service

2.2 Key Mechanical Properties

• Yield Strength (屈服强度): ≥ 205 MPa (minimum, per GB/T 13296)
• Tensile Strength (抗拉强度): 520–750 MPa (depending on grade and temper condition)
• Elongation (延伸率): ≥ 35% (indicating excellent ductility for forming and bending operations)
• Thermal Conductivity (导热系数): 14–16 W/(m·K) at 20°C (typical for austenitic grades)

2.3 Corrosion Resistance Characteristics

The seamless coil tube demonstrates outstanding resistance to a wide spectrum of corrosive media, including acidic solutions, alkaline environments, chloride-containing fluids, and high-temperature oxidation. The austenitic microstructure provides inherent resistance to stress corrosion cracking (SCC) under controlled conditions.

3. Technical Specifications

Parameter	Specification / Standard	Notes
Governing Standard	GB/T 13296 (Seamless Steel Tubes for Heat Exchangers and Heat Sinks)	Chinese National Standard
Product Form	Seamless Coil Tube (盘管 / Coiltube)	Continuous coiled delivery
Outer Diameter (OD)	6 mm – 50 mm (typical range)	Custom diameters available upon request
Wall Thickness (WT)	0.5 mm – 5.0 mm	Tolerance per GB/T 13296
Coil Length	Continuous coil, typically 100 m – 500 m per coil	Custom lengths negotiable
Surface Finish	Pickled and Passivated (酸洗钝化)	Available in No. 1, 2B, or BA finish
Manufacturing Method	Hot Rolling (热轧) / Cold Drawing (冷拔) / Cold Pilger (冷定径)	Seamless — no longitudinal or circumferential weld
U-Bend Test (U型弯管试验)	100% inspection per GB/T 13296	Bend radius and number of bends per standard
Intergranular Corrosion Test (晶间腐蚀试验)	100% inspection — Acetate Solution Test or Sulfuric Acid–Sulfuric Copper Test	Ensures resistance to sensitization
NDT Inspection Ratio (无损检测比例)	Elevated NDT coverage — 100% Eddy Current (涡流检测) + 100% Hydrostatic Test (水压试验)	Higher than industry average for heat exchanger applications
Hydrostatic Test Pressure (水压试验压力)	≥ 60 MPa (or as specified per GB/T 13296 formula)	Full-length testing on every coil
Temperature Range	−196°C to +800°C (depending on grade)	Full range cryogenic to elevated-temperature service
Pressure Rating	Up to 40 MPa (design pressure, depending on OD, WT, and grade)	Conforms to GB/T 151 heat exchanger design codes
Delivery Condition	Annealed (固溶处理 / Solution Annealed)	Full solution treatment at 1050°C – 1150°C with water quench

4. Manufacturing Process

The production of GB/T 13296 seamless coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing workflow designed to ensure material homogeneity, dimensional accuracy, and mechanical integrity:

1. Billet Preparation (坯料准备): High-purity stainless steel billets are procured from certified suppliers. Incoming material undergoes 100% chemical composition analysis (spectrometry) and ultrasonic inspection to confirm conformance with GB/T 13296 material requirements.
2. Hot Rolling / Hot Extrusion (热轧 / 热挤压): Billets are heated to 1100°C – 1250°C and processed through a hot rolling mill or extrusion press to produce seamless tube blanks. The seamless process ensures a uniform grain structure throughout the cross-section.
3. Heat Treatment — Solution Annealing (固溶处理): Tubes are reheated to 1050°C – 1150°C and rapidly quenched in water to achieve a fully austenitic microstructure, dissolve carbides, and restore maximum ductility and corrosion resistance.
4. Cold Drawing / Cold Pilgering (冷拔 / 冷定径): For tighter dimensional tolerances and superior surface finish, tubes undergo cold drawing through precision dies. This process refines the grain structure, improves mechanical properties, and achieves final OD and wall thickness dimensions to within ±0.05 mm tolerance.
5. Pickling and Passivation (酸洗钝化): Tubes are immersed in a pickling solution (typically a mix of nitric acid and hydrofluoric acid) to remove scale and surface contaminants. A subsequent passivation step forms a protective chromium oxide film on the surface, enhancing corrosion resistance.
6. Coiling (盘管成形): The finished tubes are wound into coils using a precision coiling machine that maintains consistent coil diameter and prevents surface damage or deformation during winding.
7. Quality Inspection (质量检验): Every coil undergoes comprehensive non-destructive testing and destructive testing as detailed in Section 5.

5. Quality Certifications & Inspection Protocol

Wenzhou Jixing Metal Materials Co., Ltd. implements a multi-layered quality assurance system that exceeds the baseline requirements of GB/T 13296, incorporating elevated inspection ratios and additional testing protocols to ensure the highest level of product reliability for heat exchanger applications.

5.1 Non-Destructive Testing (NDT) — 无损检测

The seamless coil tube is subjected to an elevated NDT inspection ratio compared to standard industry practice. This includes:

• 100% Eddy Current Testing (涡流检测 / ECT): The entire length of every coil is scanned using high-frequency eddy current probes capable of detecting internal and external defects as small as 0.1 mm. This ensures the absence of cracks, laminations, inclusions, and wall thinning.
• 100% Hydrostatic Pressure Test (水压试验): Every coil is pressure-tested at a minimum of 60 MPa (or the calculated test pressure per GB/T 13296) for a hold time of at least 10 seconds. This verifies the structural integrity of the entire tube length.
• Ultrasonic Testing (超声波检测 / UT): Applied to critical batches and customer-specified orders to detect internal volumetric defects and measure wall thickness with ±0.02 mm accuracy.
• Visual Inspection (目视检测): 100% inspection of tube ends, surface finish, coil condition, and dimensional accuracy.

5.2 U-Bend Test (U型弯管试验)

The U-Bend Test is a critical formability assessment mandated by GB/T 13296 for seamless heat exchanger tubes. This test evaluates the tube's ability to withstand repeated bending without cracking or deformation failure.

• Test Method: A sample tube is bent to a U-shape with a specified bend radius (typically 5× OD) around a mandrel, then the bent portion is heated to 870°C and water-quenched to simulate the thermal cycling conditions experienced in heat exchanger service.
• Acceptance Criteria: The tube must show no cracks, blisters, or other surface defects after the bending and thermal treatment cycle. Typically, a minimum of 3 bends is required for standard grades, with some applications requiring up to 5 or more.
• Significance: This test is particularly important for coil tubes, as they are routinely formed into hairpin bends, U-tubes, and other complex geometries during heat exchanger fabrication. A passing U-Bend test confirms that the tube can be formed into these shapes without compromising structural integrity.

5.3 Intergranular Corrosion Test (晶间腐蚀试验)

The Intergranular Corrosion (IGC) Test is a mandatory requirement under GB/T 13296 for austenitic stainless steel seamless tubes. This test verifies that the material has not been sensitized — a condition in which chromium carbides precipitate at grain boundaries during exposure to temperatures in the range of 450°C – 850°C, depleting adjacent regions of chromium and rendering them susceptible to corrosion.

• Test Methods:
  • Acetate Solution Test (醋酸溶液试验) — per ASTM A240 / GB/T 4334 Method A
  • Sulfuric Acid–Sulfuric Copper Test (硫酸-硫酸铜试验) — per GB/T 4334 Method C
  • 65% Boiling Sulfuric Acid Test — for 316L and other low-carbon grades
• Acceptance Criteria: The test specimen must show no visible intergranular attack after the prescribed immersion period. The microstructure must remain free of grain boundary corrosion.
• Significance: For heat exchanger applications, tubes are frequently exposed to elevated temperatures that can induce sensitization. The IGC test confirms that the solution-annealed microstructure and low-carbon composition (for L-grade materials) provide adequate resistance to this degradation mechanism.

5.4 Chemical Composition Verification

Every heat lot of steel is verified by optical emission spectrometry (OES) to confirm conformance with the specified chemical composition range per GB/T 13296. Key elements monitored include:

• Carbon (C): ≤ 0.08% (standard grades); ≤ 0.03% (L-grade, low-carbon)
• Chromium (Cr): 18.0% – 20.0% (for 304-type); 16.0% – 18.0% (for 316-type)
• Nickel (Ni): 8.0% – 10.5% (for 304-type); 10.0% – 14.0% (for 316-type)
• Molybdenum (Mo): 2.0% – 3.0% (for 316-type grades)
• Nitrogen (N): ≤ 0.10% (controlled to prevent excessive hardening)

5.5 Certification & Traceability

• Mill Test Certificate (MTC / 材质证明书): Every coil is accompanied by a comprehensive MTC (EN 10204 Type 3.1 or equivalent) detailing chemical composition, mechanical properties, NDT results, U-Bend test results, IGC test results, and hydrostatic test data.
• Heat Traceability (炉号追溯): Each coil is laser-marked or tag-identified with the heat number, coil number, and production date for full traceability from raw material to finished product.
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