Stainless Steel Boiler Coil Tube — Nickel-Plated Phosphated Anti-Corrosion Series
1. Product Overview
The Stainless Steel Boiler Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a high-performance piping solution engineered specifically for boiler and thermal-fluid systems. This product line incorporates an advanced Nickel-Plated Phosphating Anti-Corrosion Coating Technology (Ni-Plated Phosphating Anti-Corrosion Technology), which has been formally appraised and certified through a technical evaluation conducted in Jiujiang. The coil tube is designed to deliver exceptional resistance to corrosion, thermal fatigue, and mechanical wear under the demanding conditions found in industrial boiler environments, power generation facilities, and chemical processing plants.
Unlike conventional stainless steel tubing, this product integrates a dual-layer surface treatment system combining nickel electroplating with phosphating conversion coating, creating a synergistic barrier against aggressive chemical media, high-temperature oxidation, and electrochemical degradation. The coiled configuration allows for efficient heat exchange surface area utilization while maintaining structural integrity under cyclic thermal loading.
2. Material & Properties
2.1 Base Material Composition
The base tube material is fabricated from austenitic stainless steel conforming to recognized international standards. The primary alloy grades include:
- 304 (UNS S30400) — General-purpose austenitic stainless steel with 18% Cr and 8% Ni
- 316L (UNS S31603) — Low-carbon variant with 2–3% Mo for enhanced chloride resistance
- 321 (UNS S32100) — Stabilized with titanium for high-temperature applications
2.2 Surface Treatment System
The proprietary surface treatment comprises two sequential layers:
- Nickel Electroplating Layer — A uniform nickel deposit (typical thickness: 15–25 μm) applied via electrochemical plating, providing a noble potential barrier that prevents galvanic corrosion initiation. The nickel layer exhibits a microhardness of 180–220 HV and excellent ductility.
- Phosphating Conversion Coating — A zinc-manganese mixed phosphating layer (thickness: 1.5–4.0 μm) applied over the nickel plating, creating a crystalline phosphate film that enhances adhesion, improves chemical passivation, and provides an additional diffusion barrier against corrosive species.
2.3 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa | ASTM A213 / GB/T 14976 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A213 / GB/T 14976 |
| Elongation | ≥ 35% | ASTM A213 / GB/T 14976 |
| Hardness (Base Tube) | ≤ 200 HV | ASTM E18 |
| Operating Temperature Range | -40°C to 870°C | — |
2.4 Corrosion Resistance
| Corrosion Test | Result | Standard |
|---|---|---|
| Pitting Corrosion (3.5% NaCl, 60°C, 72h) | No pitting observed | ASTM G48 |
| Intergranular Corrosion | Pass (no intergranular attack) | ASTM A262 Practice E |
| Cyclic Corrosion (CASS Test) | ≥ 500h without red rust | ASTM B117 |
| High-Temperature Oxidation (800°C, 100h) | Weight loss < 1.5 mg/cm² | GB/T 10125 |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Boiler Coil Tube (Nickel-Plated Phosphated) |
| Material Grade | SUS304 / SUS316L / SUS321 |
| Outer Diameter (OD) | φ12 mm – φ89 mm (customizable) |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Inner Diameter (Coil ID) | φ200 mm – φ1,200 mm |
| Coil Length per Roll | 10 m – 500 m (as required) |
| Surface Finish | 2B / BA / Nickel-Plated Phosphated |
| Nickel Plating Thickness | 15 – 25 μm |
| Phosphating Layer Thickness | 1.5 – 4.0 μm |
| Tolerance (OD) | ±0.10 mm |
| Tolerance (Wall Thickness) | ±10% of nominal |
| Applicable Standards | ASTM A213 / ASME SA-213 / GB/T 14976 / EN 10216-5 |
| Maximum Operating Pressure | Up to 3.5 MPa (design-dependent) |
| Maximum Operating Temperature | 870°C (321 grade) / 600°C (304, 316L grade) |
| Coating Adhesion | ≥ 5B (ASTM D3359 cross-cut test) |
4. Manufacturing Process
The production of this specialized coil tube follows a rigorous multi-stage process flow to ensure dimensional accuracy, metallurgical quality, and coating integrity:
- Coil Uncoiling & Straightening — Cold-rolled stainless steel strip is uncoiled and precision-straightened to eliminate residual stress and ensure uniform flatness prior to forming.
- Tube Forming (ERW/ODW) — The strip is formed into tube using Electric Resistance Welding (ERW) or Optimized Double-Weld (ODW) technology, with precise control of weld heat input to minimize grain growth in the Heat Affected Zone (HAZ).
- Weld Cleaning & Pickling — The weld seam is mechanically cleaned and then subjected to acid pickling (HNO₃/HF mixture) to remove oxide scale and achieve a uniform passive surface.
- Passivation Treatment — Nitric acid passivation (20–30% HNO₃) is applied to enrich the surface chromium oxide layer, establishing a stable passive film with a minimum free Cr content of 15%.
- Coil Winding — The formed tube is wound onto a precision mandrel at controlled tension to produce the required coil geometry, ensuring uniform bend radius and preventing ovality or kinking.
- Nickel Electroplating — The coiled tube undergoes nickel electroplating in a sulfamate or Watts-type nickel bath at 45–60°C with current density of 4–8 A/dm². Anode efficiency is maintained at ≥95% to ensure uniform deposit thickness.
- Phosphating Conversion Coating — A zinc-manganese mixed phosphating solution is applied (immersion method, 55–65°C, 10–20 min dwell time), forming a crystalline Zn₃(PO₄)₂ / Mn₃(PO₄)₂ composite layer on the nickel surface.
- Post-Coating Treatment — The coated tube is dried, optionally wax-sealed or oil-passivated, and inspected for coating continuity and adhesion before packaging.
- Quality Inspection & Testing — Comprehensive final inspection including hydrostatic testing (1.5× working pressure), dimensional verification, coating thickness measurement (eddy current method), and surface defect examination.
5. Applications
The Nickel-Plated Phosphated Stainless Steel Boiler Coil Tube is designed for the following industrial applications:
- Industrial Boilers — Water tubes, superheater tubes, economizer tubes, and air preheater coils in fired boilers operating under high thermal cycling conditions.
- Power Generation — Steam generator tubing and condenser coils in thermal power plants requiring extended service life in high-temperature, high-pressure environments.
- Chemical Processing — Heat exchanger coils in chemical reactors where resistance to acidic or alkaline media is critical.
- Petrochemical Industry — Furnace tube coils in cracking units and reformers where thermal fatigue and carburization resistance are paramount.
- Marine & Offshore — Boiler systems on marine vessels and offshore platforms operating in chloride-rich environments.
- Food & Pharmaceutical — Steam sterilization systems and process heating coils where hygienic surface finish and corrosion resistance are required.
- Heating Systems — Coil-based heating elements in district heating networks and industrial process heating applications.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and holds the following certifications:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- ASME "S" Stamp — Sectional Construction of Boilers and Pressure Vessels
- PED 2014/68/EU — Pressure Equipment Directive Compliance (CE Marking)
- TUV / SGS — Independent Third-Party Inspection and Certification
- Technical Appraisal Certification — The Nickel-Plated Phosphating Anti-Corrosion Technology has been formally appraised and recognized through a technical evaluation panel, validating the innovation and performance superiority of the coating system.
7. Unique Selling Points
- Patented Dual-Layer Coating Technology — The combination of nickel electroplating with phosphating conversion coating provides a synergistic corrosion protection mechanism that significantly exceeds the performance of single-layer treatments.
- Extended Service Life — Field testing demonstrates a 3–5× improvement in service life compared to uncoated stainless steel tubing under equivalent operating conditions.
- Formally Appraised Innovation — The technology has undergone independent technical appraisal, providing verified performance data and third-party validation of the coating system's effectiveness.
- Customizable Coil Geometry — Flexible manufacturing capability allows coil dimensions to be tailored to specific boiler design requirements, minimizing on-site fabrication waste.
- Comprehensive Standards Compliance — Products meet or exceed requirements of ASTM, ASME, EN, and Chinese national standards (GB), facilitating global market acceptance.
- Cost-Effective Lifecycle Solution — While the initial coating investment is modest, the dramatic reduction in replacement frequency and unplanned downtime delivers significant total cost of ownership (TCO) advantages.
Technical Note: The Nickel-Plated Phosphating Anti-Corrosion Technology employed in this product line has been recognized through formal technical appraisal conducted in Jiujiang, confirming its innovation level, technical advancement, and industrial applicability. This certification serves as independent validation of the coating system's performance claims and supports its adoption in critical infrastructure applications.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Catalog No.: 1401
Classification: Technical Literature / Engineering Reference