Stainless Steel Coil Tube — Aquaculture-Grade Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Catalogue No. 1501) is a precision-engineered tubular product designed for demanding marine and aquaculture applications. Unlike conventional straight-length seamless tubes, coil tubes are delivered in continuous, tightly wound coil configurations, enabling seamless integration into large-scale marine infrastructure such as raft-cultivated abalone cage systems, underwater pipeline networks, and offshore support frameworks.
This product line is specifically developed to address the critical challenge of biofouling prevention — particularly the mass attachment of tube worms (Tubificidae spp.) on raft-cultivated abalone cage structures. By leveraging the inherent corrosion resistance of austenitic stainless steel alloys and optimized surface finish characteristics, the coil tube significantly reduces biological adhesion in submerged marine environments, thereby extending service life and maintaining structural integrity under prolonged seawater exposure.
2. Material & Properties
2.1 Material Grades
- AISI 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance in marine atmospheres and fresh water environments. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31600) — Enhanced marine-grade austenitic stainless steel with the addition of 2–3% Molybdenum (Mo), providing superior resistance to chloride-induced pitting and crevice corrosion in seawater.
- AISI 316L (UNS S31603) — Low-carbon variant of 316 grade, offering improved weldability and reduced intergranular corrosion susceptibility, ideal for welded aquaculture cage assemblies.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade with enhanced resistance to intergranular corrosion, suitable for high-temperature process applications in aquaculture water treatment systems.
2.2 Key Mechanical Properties (Typical — AISI 316L Annealed Condition)
- Tensile Strength (Ultimate Tensile Strength, UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa (29,700 psi)
- Elongation (in 50 mm / 2 in): ≥ 40%
- Hardness (Brinell): ≤ 217 HB
- Impact Energy (Charpy V-Notch, −40°C / −40°F): ≥ 47 J
2.3 Corrosion Resistance Performance
- Pitting Resistance Equivalent Number (PREN): ≥ 24 (for 316L grade)
- Seawater Immersion Life: > 25 years (316L in tropical seawater, 35‰ salinity, 25–30°C)
- Surface Roughness (Ra): ≤ 0.8 μm (polished finish), minimizing biofilm nucleation sites
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Catalogue No. | 1501 |
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 8.0 mm |
| Coil Inner Diameter (Coil ID) | 300 mm – 1,200 mm |
| Coil Length per Roll | 50 m – 500 m (configurable) |
| Material Grades | AISI 304, 316, 316L, 321, 321L |
| Surface Finish | No. 4 Brushed, Mirror Polished (Ra ≤ 0.4 μm), Pickled & Passivated |
| Manufacturing Method | Seamless (Cold-Rolled / Hot-Rolled) or Welded (ERW / Autoclaved) |
| Applicable Standards | ASTM A213, ASTM A269, ASTM A554, EN 10216-5, ISO 13960 |
| Tolerance (OD) | ±0.05 mm (precision grade), ±0.1 mm (standard grade) |
| Tolerance (WT) | ±10% (standard), ±5% (precision) |
| Operating Temperature | −196°C to +870°C |
| Maximum Working Pressure | Up to 40 MPa (depending on OD/WT combination) |
| Minimum Order Quantity | 1 ton per grade |
| Customization | OD, WT, coil length, surface finish, and material grade available upon request |
4. Manufacturing Process
4.1 Seamless Coil Tube Production
- Raw Material Procurement & Inspection: High-purity austenitic stainless steel billets or slabs are sourced from certified mills (e.g., Outokumpu, Nippon Steel, Tsingshan). Incoming materials undergo spectrographic analysis (OES) and mechanical property verification per ASTM E415.
- Hot Rolling / Extrusion: Billets are heated to 1,150–1,250°C and hot-rolled or extruded through calibrated dies to produce seamless tube blanks with controlled dimensional tolerances.
- Pickling & Annealing: Tubes are acid-pickled in a mixed HNO₃/HF solution to remove oxide scales, followed by solution annealing at 1,050–1,150°C in a controlled-atmosphere furnace to achieve a fully recrystallized, stress-free microstructure.
- Cold Drawing / Cold Rolling: For precision-diameter requirements, annealed tubes undergo cold drawing or cold rolling to achieve final OD and wall thickness within ±0.05 mm tolerance.
- Coiling: The finished tube is wound onto precision coiling drums to form the coil configuration, with careful control of coil tension to prevent ovality or mechanical deformation.
- Passivation Treatment: A final nitric acid passivation step (per ASTM A967) is applied to enrich the surface chromium oxide layer, enhancing corrosion resistance and reducing microbial adhesion.
- Final Inspection & Packaging: Each coil undergoes dimensional verification, surface inspection, and hydrostatic pressure testing. Tubes are packaged with protective inner wrapping, moisture-absorbing desiccants, and outer steel strapping for shipment.
4.2 Anti-Biofouling Surface Engineering
A distinguishing feature of this product line is the biofouling-resistant surface treatment protocol. The combination of mirror polishing (Ra ≤ 0.4 μm) and chromium-enriched passive film formation creates a surface that minimizes initial bacterial adhesion — the critical first step in the biofouling cascade. This significantly reduces the colonization rate of tube worms (Tubificidae), barnacles, and other fouling organisms on submerged aquaculture structures.
5. Applications
5.1 Primary Application — Aquaculture Infrastructure
- Raft-Cultivated Abalone Cage Systems: Coil tubes serve as structural framing members, mooring line conduits, and water circulation piping in floating abalone farming rafts. The anti-biofouling surface treatment directly addresses the industry challenge of tube worm mass attachment, which can compromise cage structural integrity and reduce water flow efficiency.
- Seawater Intake & Distribution Systems: Used in submerged pipeline networks delivering filtered seawater to aquaculture pens and processing facilities.
- Underwater Support Structures: Deployed in offshore fish farm mooring systems and subsea anchoring frameworks.
5.2 Secondary Applications
- Chemical processing plant piping and heat exchanger tubes
- Food-grade sanitary processing equipment (dairy, beverage, pharmaceutical)
- Automotive exhaust system components and catalytic converter substrates
- Architectural decorative elements and handrail systems
- Medical and laboratory equipment tubing
- Energy sector — fuel cell components and solar thermal collector tubes
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System — Full production process |
| ISO 14001:2015 | Environmental Management System |
| EN 10204 3.1 | Third-party certified material test certificates for each batch |
| ASTM A213 / A269 / A554 | Material and dimensional compliance |
| EN 10216-5 | European seamless stainless steel tube standard |
| ISO 13960 | Welded stainless steel tubes — general requirements |
| NSF/ANSI 61 | Drinking water system components (for potable water applications) |
| 3-A Sanitary Standards | Food-grade surface finish compliance (mirror polished variants) |
| CE Marking | European Conformity for pressure equipment directives |
7. Unique Selling Points
- Anti-Biofouling Surface Technology: Proprietary mirror-polished and passivated surface finish engineered to minimize tube worm and biofilm attachment, directly addressing the critical pain point in raft-cultivated aquaculture systems.
- Continuous Coil Configuration: Eliminates the need for field welding in large-scale installations, reducing potential corrosion initiation points at weld joints and lowering installation labor costs by up to 40%.
- Full Material Traceability: Each coil is accompanied by a mill test certificate (MTC) per EN 10204 Type 3.1, with complete chemical composition, mechanical property data, and heat treatment records.
- Customizable Specifications: Flexible customization across OD, wall thickness, coil length, surface finish, and alloy grade to meet project-specific engineering requirements.
- Marine-Grade Durability: AISI 316L/316L-grade options provide >25-year design life in tropical seawater environments, significantly outperforming carbon steel alternatives that require costly cathodic protection and coating maintenance.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalogue Reference: No. 1501
Application Domain: Marine Aquaculture — Raft-Cultivated Abalone Cage Systems & General Industrial Use
Technical Documentation: Full material test reports, dimensional inspection records, and surface finish certification available upon request.