Stainless Steel Coil Tube — High-Temperature Al-Based Sacrificial Anode & Coating Combined Protection System
Product Overview
The Coil Tube (盘管) produced by Wenzhou Jixing Metal Materials Co., Ltd. represents an advanced tubular product engineered for high-temperature environments where aggressive corrosive media are present. This product integrates a dual-layer corrosion protection strategy: an Aluminum (Al)-based sacrificial anode system coupled with a high-performance protective coating. This combined protection approach significantly extends the service life of the coil tube in demanding industrial applications, including petrochemical processing, power generation, and marine engineering.
The coil tube is manufactured from austenitic stainless steel grades and is supplied in a continuous coil form, enabling efficient downstream forming, cutting, and installation. The product is catalogued under item number 518 and is classified within the technical literature and learning reference category for corrosion engineering applications.
Material & Properties
The base material of the coil tube is typically selected from the following austenitic stainless steel grades:
- 304 (UNS S30408) — General-purpose grade with excellent corrosion resistance and formability.
- 316L (UNS S31603) — Low-carbon variant with molybdenum (Mo) addition for superior resistance to pitting and crevice corrosion in chloride-containing environments.
- 321 (UNS S32100) — Stabilized with titanium (Ti) for enhanced resistance to intergranular corrosion at elevated temperatures.
- 310S (UNS S31008) — High-temperature grade with elevated chromium (Cr) and nickel (Ni) content for sustained strength above 1000°C.
The Al-based sacrificial anode system utilizes aluminum alloys (commonly Al-Zn-In or Al-Zn-Si systems) that exhibit a more negative electrochemical potential than the stainless steel substrate. In the presence of an electrolyte, the aluminum anode preferentially corrodes, thereby providing cathodic protection to the underlying coil tube surface.
The protective coating layer is typically composed of:
- Thermal spray aluminum (TSA) or aluminized coating (thickness: 50–150 µm)
- Organic topcoat (epoxy or polyurethane-based, thickness: 200–400 µm)
This dual-layer system ensures that even if the organic topcoat is locally damaged, the underlying metallic aluminum layer continues to provide galvanic protection.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Coil Tube (盘管) — Item No. 518 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Base Material | 304 / 316L / 321 / 310S Stainless Steel |
| Outer Diameter (OD) | 19.05 mm – 114.3 mm (3/4" – 4-1/2") |
| Wall Thickness | 1.0 mm – 6.35 mm |
| Coil Length | Up to 50 m per coil (customizable) |
| Surface Finish | Bright annealed / Pickled & Passivated |
| Al Anode Layer Thickness | 50 – 150 µm |
| Organic Topcoat Thickness | 200 – 400 µm |
| Maximum Service Temperature | Up to 600°C (316L/321); Up to 1000°C (310S) |
| Corrosion Protection Mechanism | Al-based Sacrificial Anode + Barrier Coating (Dual-System) |
| Applicable Standards | ASTM A213 / ASME SA-213 / GB/T 12771 |
Manufacturing Process
- Coil Slitting & Straightening: The stainless steel strip coil is slit to the required width and straightened to ensure dimensional accuracy and flatness prior to forming.
- Tube Forming (Seamless or Welded): The straightened strip is formed into the desired tube geometry via cold-rolling or hydraulic expansion methods. For welded coil tubes, a TIG (Tungsten Inert Gas) welding process is employed to create a hermetic longitudinal seam.
- Heat Treatment & Annealing: The formed tube undergoes solution annealing (typically at 1050°C – 1100°C for austenitic grades) followed by rapid quenching to achieve the desired microstructure and mechanical properties.
- Pickling & Passivation: The tube surface is acid-pickled (using a mixed HNO₃/HF solution) to remove oxide scale, followed by passivation to restore the chromium oxide passive film.
- Surface Preparation for Coating: The tube surface is cleaned, degreased, and lightly abraded (grit-blasted to Sa 2½ per ISO 8501-1) to ensure optimal coating adhesion.
- Aluminum Anode Application: Thermal spray aluminum (TSA) coating is applied via flame or plasma spraying, or the tube is processed through a hot-dip aluminizing furnace. The aluminum layer is deposited to a controlled thickness of 50–150 µm.
- Organic Topcoat Application: A primer layer (zinc-rich or epoxy) is applied, followed by a mid-coat and finish coat (polyurethane or epoxy-based), each cured according to the manufacturer's technical data sheet.
- Quality Inspection: Each batch undergoes dimensional verification, coating thickness measurement (per ISO 2360), adhesion testing (per ISO 2409 cross-cut method), and electrochemical potential testing to confirm cathodic protection effectiveness.
Applications
- Petrochemical Industry: Heat exchanger coil tubes, reboilers, and distillation column internals exposed to high-temperature corrosive process streams.
- Power Generation: Boiler economizer tubes, superheater coils, and condensate recovery systems in coal-fired and gas-fired power plants.
- Marine & Offshore Engineering: Seawater cooling coils, desalination plant heat exchangers, and offshore platform piping systems.
- Chemical Processing: Reactor cooling coils and heat transfer tubes handling aggressive chemical media at elevated temperatures.
- Food & Pharmaceutical Processing: Sanitary-grade coil tubes requiring high corrosion resistance and ease of cleaning.
Quality Certifications & Compliance
- Material Certifications: ASTM A213, ASME SA-213, GB/T 12771, EN 10217-7
- Coating Standards: ISO 12944 (Corrosion protection of steel structures by paint systems), NACE No. 2 / SSPC No. 1 (Steel Preparation for Painting)
- Cathodic Protection: ISO 12473 (Cathodic protection of steel structures in contact with soil or water)
- Quality Management: ISO 9001:2015 certified manufacturing process
- Environmental Compliance: RoHS compliant coating formulations available upon request
Unique Selling Points
The integration of an Al-based sacrificial anode with a high-performance organic coating system on stainless steel coil tubes represents a synergistic corrosion protection strategy that outperforms either method used independently. Key advantages include:
- Dual-Barrier Protection: The organic topcoat provides a physical barrier against corrosive media ingress, while the aluminum layer offers active galvanic (cathodic) protection at any point where the topcoat is compromised.
- Extended Service Life: Field studies and accelerated corrosion testing (per ASTM B117 salt spray testing) demonstrate that the combined system can extend service life by 3–5 times compared to bare stainless steel in equivalent environments.
- High-Temperature Capability: Unlike conventional organic coatings that degrade above 200°C, the aluminized layer maintains its protective function at temperatures up to 600°C, making this system uniquely suited for high-temperature industrial applications.
- Cost-Effective Maintenance: The sacrificial anode design reduces the frequency of inspection and maintenance interventions, lowering total cost of ownership (TCO) over the asset lifecycle.
- Continuous Coil Form: Supply in coil configuration enables efficient downstream processing, minimizing material waste and reducing fabrication time compared to straight-length tube supply.
- Customizable Protection: Coating thickness, aluminum alloy composition, and topcoat chemistry can be tailored to specific environmental exposure conditions (e.g., C5-M per ISO 12944 for extreme marine environments).
Technical Reference
This product specification is derived from technical literature on "High-Temperature Al-Based Sacrificial Anode and Coating Combined Protection for Coil Tube Anti-Corrosion Technology" (高温Al基牺牲阳极与涂层联合保护的盘管防腐技术), as documented in the learning and reference materials catalogued by Wenzhou Jixing Metal Materials Co., Ltd. The technology addresses the critical challenge of maintaining structural integrity and corrosion resistance in stainless steel coil tubes operating under simultaneous high-temperature and aggressive chemical exposure conditions.