304 Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The 304 Stainless Steel Coil Tube (Coiltube) is a continuous-length, coiled austenitic stainless steel tube supplied in the form of a helical coil, designed for downstream processing, forming, and fabrication into end products such as heat exchangers, condensers, evaporators, and fluid transfer assemblies. This product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd. and conforms to international standards including ASTM A213/A213M, ASTM A269/A269M, and EN 10217-7.
The coiltube format offers significant advantages over straight-length tubes: it enables continuous automated processing, reduces material waste through seamless coil-to-product conversion, minimizes handling and welding joints, and allows for efficient storage and transportation in compact bundles. The inherent corrosion resistance, thermal stability, and mechanical integrity of the 304 grade make this product suitable for demanding industrial and commercial applications across multiple sectors.
Particular attention has been given to the Cracking Failure Analysis (开裂失效分析) of 304 stainless steel coil tubes. Understanding the root causes of cracking — including stress corrosion cracking (SCC), intergranular corrosion (IGC), hydrogen embrittlement, and cold-work-induced residual stresses — is critical for ensuring product reliability. This analysis has informed enhanced quality control protocols and material selection criteria adopted in the manufacturing process.
2. Material & Properties
2.1 Chemical Composition (ASTM A213 Type 304)
| Element | Specification (wt%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 0.75 |
| Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
2.2 Mechanical Properties (Annealed Condition)
| Property | Value | Unit |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 515 | MPa |
| Yield Strength (0.2% Proof) | ≥ 205 | MPa |
| Elongation (at Break) | ≥ 40 | % |
| Hardness (Rockwell B) | ≤ 95 | HBR |
| Thermal Conductivity (at 20°C) | ~16.3 | W/m·K |
| Thermal Expansion Coefficient (20–100°C) | 17.3 | ×10⁻⁶/K |
| Density | 8.00 | g/cm³ |
2.3 Corrosion Resistance Characteristics
- Atmospheric Corrosion: Excellent resistance to atmospheric oxidation and mild chemical environments.
- Acid Resistance: Good resistance to dilute sulfuric, phosphoric, and organic acids.
- Chloride Resistance: Moderate resistance to chloride-induced pitting; not recommended for high-chloride environments (consider 316L for such applications).
- Stress Corrosion Cracking (SCC) Susceptibility: 304 grade is susceptible to chloride SCC above 60°C; material selection and design considerations must account for this limitation.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | 304 Stainless Steel Coil Tube (Coiltube) |
| Material Grade | ASTM A213 Type 304 / 304L (Low Carbon) |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (customizable up to 100 mm) |
| Wall Thickness | 0.5 mm – 3.0 mm (customizable) |
| Coil Length | 15 m – 50 m per coil (adjustable per order) |
| Coil Inner Diameter (ID) | 300 mm – 500 mm (standard) |
| Surface Finish | BA (Bright Annealed), No. 4 Brushed, Matte, or Custom |
| Tolerance (OD) | ± 0.10 mm (standard); ± 0.05 mm (precision grade) |
| Tolerance (Wall Thickness) | ± 10% (standard); ± 5% (precision grade) |
| Straightness | ≤ 1.5 mm/m (per ASTM A269) |
| Heat Treatment Condition | Fully Annealed (Solution Annealed) |
| Delivery Form | Coiled, bundled, with protective end caps |
| Applicable Standards | ASTM A213/A213M, ASTM A269/A269M, EN 10217-7, GB/T 12771 |
4. Manufacturing Process
The production of 304 stainless steel coil tube follows a rigorous multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip (coil) conforming to ASTM A240/A240M is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) for chemical composition verification and mechanical testing.
- Slitting & Edge Trimming: The wide strip is slit to the required width for tube forming. Edge quality is inspected to prevent surface defects and roll marks during forming.
- Tube Forming (Cold Roll Forming): The strip passes through a series of progressively die-shaped rollers to form the tube cross-section. The forming process is optimized to minimize residual stress and avoid cracking at the weld seam.
- Welding (Autogenous TIG Welding): The longitudinal seam is welded using inert gas (Argon) shielded Tungsten Inert Gas (TIG) welding. A back-purge of Argon ensures a clean, oxide-free weld interior. Weld parameters are precisely controlled to prevent overheating and sensitization.
- Post-Weld Heat Treatment (Solution Annealing): The welded tube is solution-annealed at 1050°C – 1100°C followed by rapid cooling (water quench or air cool) to dissolve any carbides formed during welding, restore full austenitic structure, and eliminate residual stresses. This step is critical for preventing intergranular corrosion and stress corrosion cracking.
- Pickling & Passivation: The annealed tube undergoes acid pickling (typically nitric-hydrofluoric acid blend) to remove oxide scales, followed by passivation to restore the protective chromium oxide layer.
- Surface Finishing: Depending on specification, the tube may receive additional surface treatments including bright annealing in a controlled-atmosphere furnace, mechanical polishing, or brushing.
- Coiling & Packaging: The finished tube is coiled onto a protective core, wrapped in moisture-barrier packaging, and labeled with material certification traceability data.
4.1 Failure Analysis Informed Process Improvements
Based on the 304 Stainless Steel Coil Tube Cracking Failure Analysis (304不锈钢盘管开裂失效分析), the following process enhancements have been implemented:
- Residual Stress Monitoring: X-ray diffraction (XRD) residual stress measurement is performed at critical process stages to ensure stress levels remain below cracking thresholds.
- Weld Heat Input Control: Precise welding parameters (current, voltage, travel speed) are maintained within narrow windows to prevent localized sensitization and chromium carbide precipitation at grain boundaries.
- Hydrogen Embrittlement Prevention: Dehydrogenation treatment (baking at 200°C – 300°C) is applied post-forming to remove dissolved hydrogen that could cause delayed cracking.
- Grain Boundary Engineering: Heat treatment cycles are optimized to maintain a stable austenitic microstructure with minimal delta-ferrite content (target < 5% delta-ferrite), reducing susceptibility to intergranular corrosion.
5. Applications
The 304 Stainless Steel Coil Tube is widely used across multiple industries due to its balanced combination of corrosion resistance, mechanical strength, weldability, and formability:
- Heat Exchangers & Condensers: Coil tubes are ideal for manufacturing shell-and-tube heat exchangers, air-cooled condensers, and evaporators in chemical, petrochemical, and power generation plants.
- Food & Beverage Industry: Used in dairy processing equipment, beer brewing systems, and food-grade piping where hygienic surfaces and corrosion resistance are paramount (FDA-compliant).
- Pharmaceutical Industry: Employed in CIP (Clean-In-Place) systems, process piping, and sterilization equipment requiring high-purity fluid handling.
- Automotive Industry: Used in exhaust system components, turbocharger housings, and fuel injection lines.
- Oil & Gas: Applied in subsea production manifolds, gas gathering lines, and offshore platform piping (in non-sour environments).
- Construction & Architectural: Used for structural tubes, handrails, decorative elements, and facade systems.
- Medical Equipment: Utilized in surgical instrument handles, medical gas piping, and diagnostic equipment housings.
- Home Appliance Manufacturing: Coil tubes are fed directly into automated manufacturing lines for water heaters, refrigeration coils, and washing machine components.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure consistent quality and regulatory compliance:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking (EN 10217-7) | Compliance with European Union machinery and materials directives |
| ASME Section IX | Welding procedure qualification for pressure vessel and piping applications |
| EN 10204 3.1 | Material Test Certificate (MTC) issued by authorized inspection personnel |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
| ASTM A213/A213M | American standard for seamless and welded austenitic stainless steel tubes for high-temperature service |
| ASTM A269/A269M | American standard for austenitic stainless steel welded tubing |
6.1 Quality Control Measures
- Incoming Material Inspection: 100% chemical composition verification via Optical Emission Spectroscopy (OES); sampling for mechanical testing (tensile, hardness, impact).
- In-Process Inspection: Real-time monitoring of forming dimensions, weld quality (visual, dye penetrant testing), and coil geometry.
- Final Product Testing: Hydrostatic pressure testing (per ASTM A269), dimensional inspection (OD, wall thickness, straightness), surface finish verification, and corrosion testing (salt spray per ASTM B117, intergranular corrosion per ASTM A262 Practice E).
- Traceability: Each coil is individually identified with a unique heat number and batch code, enabling full traceability from raw material to finished product.
- Third-Party Inspection: Independent inspection by organizations such as SGS, BV (Bureau Veritas), or TÜV is available upon customer request.
7. Unique Selling Points
- Cracking-Resistant Design: Informed by comprehensive failure analysis, the manufacturing process specifically addresses stress corrosion cracking, intergranular corrosion, and hydrogen embrittlement risks through optimized heat treatment, residual stress management, and microstructural engineering.
- Continuous Coil Format: Enables seamless integration into automated manufacturing lines, reducing waste by up to 30% compared to straight-length tube, and eliminating field welding joints.
- Customizable Specifications: Flexible range of OD, wall thickness, coil length, and surface finish options to meet specific customer requirements.
- Full Traceability: Complete material certification with heat number traceability from mill to end product, supporting regulatory compliance and quality assurance.
- Global Standards Compliance: Products meet ASTM, EN, GB, and ASME standards, suitable for international markets.
- Post-Sales Technical Support: Dedicated engineering support for application-specific material selection, failure analysis consultation, and process optimization guidance.
8. Ordering & Technical Support
For detailed quotations, custom specification development, and technical consultation regarding the 304 Stainless Steel Coil Tube, contact Wenzhou Jixing Metal Materials Co., Ltd. Our engineering team provides expert guidance on material selection, dimensional tolerances, heat treatment requirements, and application-specific design considerations to ensure optimal product performance and reliability.