Stainless Steel Coil Tube — Industrial Annealed Coil Pipe Product Specification
Wenzhou Jixing Metal Materials Co., Ltd. presents a premium-grade stainless steel coil tube (also referred to as coil pipe or coil tubing) engineered for demanding industrial applications. This product specification provides a comprehensive technical overview of the material composition, dimensional parameters, manufacturing methodology, and quality assurance framework governing the production of annealed stainless steel coil tubes.
Product Overview
Stainless steel coil tubes are continuous lengths of hollow, seamless or welded pipe formed into large coils for efficient handling, transportation, and downstream processing. Unlike cut-to-length pipe, coil tubes offer superior material utilization, reduced waste, and enhanced flexibility in fabrication workflows. The coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd. is manufactured in accordance with international standards including ASTM A269, ASTM A554, GB/T 14976, and EN 10216, ensuring consistent performance across global supply chains.
The coil tube is typically produced from austenitic stainless steel grades such as 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), 321 (UNS S32100), 310S (UNS S31008), and 316Ti (UNS S31635), each selected to meet specific corrosion resistance, mechanical strength, and temperature tolerance requirements.
Material Composition and Properties
Chemical Composition (Typical — ASTM A269)
| Grade | C (max) | Mn (max) | P (max) | S (max) | Si (max) | Cr | Ni | Mo | Ti |
|---|---|---|---|---|---|---|---|---|---|
| 304 / 304L | 0.08 / 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 18.00–20.00 | 8.00–10.50 | — | — |
| 316 / 316L | 0.08 / 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 16.00–18.00 | 10.00–14.00 | 2.00–3.00 | — |
| 321 | 0.08 | 2.00 | 0.045 | 0.030 | 0.75 | 17.00–19.00 | 9.00–12.00 | — | 5×C–0.70 |
| 310S | 0.08 | 2.00 | 0.045 | 0.030 | 1.50 | 24.00–26.00 | 19.00–22.00 | — | — |
Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | 310S |
|---|---|---|---|---|
| Tensile Strength (MPa, min) | 515 | 515 | 515 | 515 |
| Yield Strength (0.2% offset, MPa, min) | 205 | 205 | 205 | 205 |
| Elongation (min, %) | 40 | 40 | 40 | 40 |
| Density (g/cm³) | 8.0 | 8.0 | 8.0 | 8.0 |
| Thermal Conductivity (W/m·K, at 100°C) | 16.3 | 16.3 | 16.3 | 15.1 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
Dimensional Specifications
Standard Diameter and Wall Thickness Ranges
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 273.05 mm (¼" – 10") | ASTM A554 / EN 10216 |
| Wall Thickness (WT) | 0.50 mm – 6.35 mm (0.020" – 0.250") | ASTM A269 |
| Coil Length | 6 m – 20 m (typical) | Manufacturer Standard |
| Coil Weight | 500 kg – 3,000 kg (typical) | Manufacturer Standard |
| OD Tolerance | ±0.5% (per EN 10216-5) | EN 10216-5 |
| Wall Thickness Tolerance | ±10% (standard) / ±5% (tight) | ASTM A269 |
| Straightness | ≤ 1.5 mm/m | ISO 4413 |
| Surface Roughness (Ra) | ≤ 1.6 μm (pickled & passivated) | ASTM A380 |
Surface Finish Options
- 2B Finish: Cold-rolled, annealed, and pickled surface with a smooth, matte appearance. Suitable for general industrial use.
- No. 4 Brushed Finish: Uniformly brushed grain pattern providing aesthetic appeal with moderate corrosion resistance.
- Mirror (8K) Finish: Polished to a reflective surface (Ra ≤ 0.05 μm), used in food processing, pharmaceutical, and decorative applications.
- Pickled and Passivated (P&P): Chemical cleaning to remove scale and form a protective chromium oxide layer. Compliant with ASTM A380.
- Hairline Finish: Directional brushing for architectural and appliance applications.
Manufacturing Process
Production Workflow Overview
- Raw Material Procurement and Inspection: Stainless steel strip or hot-rolled coil is sourced from certified mills and subjected to incoming inspection for chemical composition (via Optical Emission Spectrometry — OES) and mechanical properties. Certificates of Analysis (CoA) are verified against ASTM or EN specifications.
- Coil Slitting and Leveling: The parent coil is slit to the required width using precision slitting lines with hydraulic tension control. The slit coil is then leveled through a precision leveling mill to ensure flatness and eliminate residual stresses.
- Forming (Roll Forming / Welding): The leveled strip is fed through a series of progressive forming rolls that gradually shape the flat strip into a circular cross-section. For welded coil tubes, a TIG (Tungsten Inert Gas) welding process is employed, utilizing high-purity argon (≥ 99.998%) as a shielding gas to prevent oxidation of the weld seam. The weld seam is subsequently ground and polished to achieve surface continuity.
- Annealing in All-Refractory Fiber Lined Roller Hearth Furnace: A critical process step involves the annealing of the coil tube in a specialized roller hearth furnace designed with full refractory fiber lining. This furnace technology offers significant advantages over conventional annealing furnaces:
Key Features of the All-Refractory Fiber Lined Roller Hearth Annealing Furnace:
- Refractory Fiber Lining: The furnace interior is fully lined with high-purity ceramic fiber modules (typically alumina-silica or zirconia-based), providing excellent thermal insulation, low thermal mass, and rapid heating/cooling cycles. This reduces energy consumption by up to 30% compared to conventional fired-brick furnaces.
- Roller Hearth Design: The coil tube is transported through the furnace on a roller hearth, ensuring uniform heat distribution and preventing localized overheating or deformation. The roller mechanism accommodates the coil geometry and allows continuous or semi-continuous processing.
- Atmosphere Control: The furnace operates under a controlled reducing or inert atmosphere (e.g., cracked ammonia, hydrogen, or argon) to prevent oxidation and decarburization during the annealing cycle. Oxygen potential is maintained below 10⁻¹⁵ atm to ensure a clean, oxide-free surface.
- Temperature Uniformity: The furnace achieves temperature uniformity within ±5°C across the working zone, critical for achieving consistent grain structure and mechanical properties throughout the coil.
- Thermal Profile: The typical annealing cycle involves heating to 1050°C – 1150°C (depending on grade), holding for 30–60 minutes to achieve complete solution treatment and grain recrystallization, followed by controlled cooling (air or forced air quench) to room temperature.
- Pickling and Passivation: Following annealing, the coil tube undergoes chemical pickling using a mixed acid solution (typically HNO₃ + HF or H₂SO₄ + HNO₃) to dissolve any residual oxide scale. Subsequent passivation with a nitric acid or citric acid solution forms a stable, adherent chromium oxide passive film (Cr₂O₃), enhancing long-term corrosion resistance. This process complies with ASTM A380.
- Hydrostatic Testing: Each coil tube is subjected to hydrostatic pressure testing to verify structural integrity and freedom from leaks. Test pressure is typically 1.5× the maximum working pressure or as specified per ASTM A269. The test medium is water at ambient temperature, with a minimum hold time of 3 seconds for tubes up to 100 mm OD.
- Dimensional Inspection: Outer diameter, wall thickness, and straightness are measured at regular intervals using laser micrometers, ultrasonic thickness gauges, and straightness gauges. Statistical Process Control (SPC) methods are applied to monitor dimensional consistency.
- Coiling and Packaging: The finished coil tube is wound onto a protective core, wrapped with moisture-barrier film, and secured with steel strapping. Each coil is labeled with a unique batch/heat number, grade designation, dimensional specification, and manufacturing date for full traceability.
Applications
Stainless steel coil tubes find extensive application across multiple industrial sectors owing to their corrosion resistance, mechanical strength, hygienic properties, and thermal stability:
- Food and Beverage Processing: Piping systems for dairy, brewing, winemaking, and juice processing. Grades 304L and 316L are preferred for their compliance with FDA 21 CFR and EU 1935/2004 food contact regulations.
- Pharmaceutical and Biotechnology: Clean-in-place (CIP) and sanitize-in-place (SIP) piping systems requiring electropolished surfaces (Ra ≤ 0.25 μm). Compliant with FDA 21 CFR Part 210/211 and EHEDG guidelines.
- Chemical and Petrochemical Processing: Corrosive fluid transport in acid, alkali, and solvent handling systems. Grades 316L and 316Ti offer superior resistance to chlorides and reducing acids.
- Oil and Gas Industry: Downhole tubing, wellhead components, and subsea piping systems. Resistant to sour gas (H₂S) environments when properly specified.
- Power Generation: Boiler tubes, heat exchanger tubes, and condensate lines in coal-fired, nuclear, and renewable energy plants. Grade 310S is used in ultra-high-temperature applications (up to 1150°C).
- Aerospace: Hydraulic lines, fuel system tubing, and exhaust system components. Aerospace-grade 304 and 316 with strict non-destructive testing (NDT) protocols.
- Medical Devices: Endoscopy tubing, implant-grade components, and sterilization equipment. Requires biocompatibility testing per ISO 10993.
- Automotive: Exhaust system components, turbocharger piping, and fuel delivery lines. Resistance to high-temperature exhaust gases and corrosive road salts.
- Architectural and Decorative: Handrails, balustrades, elevator interiors, and structural elements. Available in various surface finishes for aesthetic requirements.
- Heat Exchangers and Radiators: Coil tubes used as heat transfer elements in industrial and HVAC systems, leveraging their high thermal conductivity and corrosion resistance.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following standards:
Management System Certifications
- ISO 9001:2015 — Quality Management System (QMS)
- ISO 14001:2015 — Environmental Management System (EMS)
- ISO 45001:2018 — Occupational Health and Safety Management System (OHSMS)
- ISO/TS 22163 — Automotive Quality Management (IATF 16949, where applicable)
Product Standards and Compliance
| Standard | Description | Scope |
|---|---|---|
| ASTM A269 | Standard Specification for Seamless and Wrought Stainless Steel Tubing, Austenitic and Austenitic-Ferritic (Duplex) Cr-N |