Stainless Steel Coil Tube with Intergranular Corrosion Resistance Certification
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. manufactures high-performance stainless steel coil tubes engineered for demanding industrial applications where corrosion resistance and long service life are critical. These coil tubes are supplied in continuous coil form, enabling seamless integration into automated forming, bending, and fabrication processes. The product range is designed to meet the most stringent international standards for dimensional accuracy, metallurgical quality, and chemical composition.
A defining feature of this product line is the rigorous quality assurance protocol, particularly the advanced intergranular corrosion testing methodology employed. Each batch undergoes accelerated intergranular corrosion screening using the Oxalic Acid Electrolytic Etching method (GB/T 4334 Method A), a rapid and highly reliable technique that delivers definitive results in as little as 1.5 minutes. This ensures that only tubes demonstrating superior resistance to intergranular corrosion—caused by chromium carbide precipitation at grain boundaries—reach the end user.
Material & Properties
The coil tubes are available in a comprehensive range of austenitic and duplex stainless steel grades, selected to deliver optimal combinations of mechanical strength, corrosion resistance, and formability:
- Grade 304 / 304L: General-purpose austenitic stainless steel offering excellent corrosion resistance in a wide range of chemical environments. The 304L variant features reduced carbon content (≤0.03% C), providing superior resistance to sensitization during welding.
- Grade 316 / 316L: Molybdenum-enhanced austenitic grades with enhanced resistance to pitting and crevice corrosion, ideal for marine, chemical, and pharmaceutical applications.
- Grade 321: Titanium-stabilized austenitic steel with excellent resistance to intergranular corrosion, suitable for high-temperature service up to 870°C (1,598°F).
- Grade 347: Niobium-stabilized variant offering similar high-temperature performance to Grade 321 with improved weldability.
- Grade 904L: High-alloy austenitic grade with outstanding resistance to concentrated sulfuric acid and other aggressive oxidizing media.
All grades are supplied in the annealed and pickled condition, ensuring a clean, oxide-free surface and a uniform, fully recrystallized microstructure that maximizes ductility and corrosion performance.
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 159.0 mm (0.118 in – 6.260 in) |
| Wall Thickness | 0.3 mm – 6.0 mm (0.012 in – 0.236 in) |
| Coil Inner Diameter | 102 mm – 508 mm (4.0 in – 20.0 in) |
| Coil Length per Spool | Up to 2,000 m (6,562 ft) continuous |
| Surface Finish | No. 1 Annealed, 2B, BA (Bright Annealed), Pickled & Passivated |
| Surface Roughness (Ra) | ≤ 0.5 μm (BA finish), ≤ 0.8 μm (2B finish) |
| Chemical Composition | Per ASTM A213 / ASTM A269 / EN 10217-7 |
| Dimensional Tolerance | OD: ±0.1 mm; Wall: ±10% (per ASTM A213) |
| Delivery Condition | Annealed, Pickled & Passivated (APP) |
| Intergranular Corrosion Test | GB/T 4334 Method A (Oxalic Acid Electrolytic Etching) |
Manufacturing Process
The production of Wenzhou Jixing stainless steel coil tubes follows a tightly controlled, multi-stage manufacturing process designed to ensure consistent quality and performance:
- Raw Material Selection: Only certified virgin or re-melted stainless steel wire rod from approved mills is accepted, with full chemical analysis verification (including spectrographic analysis) prior to processing.
- Wire Drawing: The selected wire rod is cold-drawn through precision tungsten carbide dies to achieve the target inner diameter and wall thickness, with intermediate annealing cycles to restore ductility.
- Tube Forming (ERW/ODW): The drawn wire is formed into seamless or electric resistance welded (ERW) tubes on high-speed forming lines. For premium applications, orbital diffusion welding (ODW) provides a weld quality approaching seamless performance.
- Heat Treatment: Tubes are solution-annealed at temperatures between 1,020°C and 1,120°C (1,868°F – 2,048°F), followed by controlled cooling to ensure full grain homogenization and maximum corrosion resistance.
- Pickling & Passivation: The annealed tubes are pickled in a mixed acid solution (HNO₃/HF) to remove surface oxide scale, followed by passivation in dilute nitric acid to form a protective chromium oxide film.
- Coiling: The finished tubes are wound onto precision coils at controlled tension to prevent kinking, ovality, or surface damage.
- Quality Inspection & Packaging: Each coil undergoes comprehensive non-destructive testing (EDD/ECT), dimensional verification, and intergranular corrosion screening before being packaged for shipment.
Quality Assurance: Intergranular Corrosion Testing
Wenzhou Jixing Metal Materials Co., Ltd. employs a two-tier intergranular corrosion verification protocol that combines speed with thoroughness, ensuring that every coil tube batch meets the highest standards of metallurgical integrity.
Primary Screening: Oxalic Acid Electrolytic Etching (GB/T 4334 Method A)
The primary quality gate for intergranular corrosion resistance is the Oxalic Acid Electrolytic Etching test, performed in accordance with GB/T 4334 Method A. This technique is recognized internationally for its ability to rapidly detect sensitization—the precipitation of chromium carbides at grain boundaries that degrades corrosion resistance in the heat-affected zone and base metal.
- Test Principle: A prepared coupon is subjected to electrolytic etching in an oxalic acid solution (3% H₂C₂O₄) for 2 minutes at a current density of 2 A/dm². The resulting grain boundary contrast is examined under optical microscopy at 100× magnification.
- Rapid Results: The method delivers definitive pass/fail results in approximately 1.5 minutes, enabling real-time quality decisions on the production floor.
- Acceptance Criteria: A tube is deemed acceptable if no continuous intergranular attack is observed along grain boundaries. Discontinuous or localized attack is evaluated per the standard's severity classification.
- Decision Logic: Tubes that pass the oxalic acid electrolytic etching test are exempt from further immersion testing, significantly reducing turnaround time and cost. Tubes that fail or show marginal results are subjected to the full immersion test (GB/T 4334 Method C, 63% HNO₃ at 100°C for 24 hours) for definitive verification.
This tiered testing approach—rapid screening followed by comprehensive verification only when required—provides customers with the confidence that every coil tube batch has been rigorously evaluated for intergranular corrosion resistance, while optimizing production efficiency.
Additional Quality Checks
- Chemical Analysis: Full spectrographic analysis per ASTM E415 for every heat.
- Mechanical Testing: Tensile strength, yield strength, and elongation verified per ASTM A213/A269.
- Hardness Testing: Rockwell B or Vickers hardness to confirm annealed condition.
- Non-Destructive Testing: Electromagnetic detection (EDD) scanning for internal and external defects along the full tube length.
- Hydrostatic Testing: Pressure testing at 2.5× working pressure to verify weld integrity and dimensional conformity.
Applications
Wenzhou Jixing stainless steel coil tubes are specified across a broad spectrum of industries where corrosion resistance, formability, and long-term reliability are paramount:
- Heat Exchangers & Boilers: Coil tubes are ideal for hairpin and serpentine heat exchanger configurations in power generation, HVAC, and process heating systems.
- Food & Beverage Processing: Hygienic-grade BA finish tubes used in dairy processing, brewing, and pharmaceutical equipment where CIP/SIP compatibility is essential.
- Chemical & Petrochemical: 316L and 904L coil tubes resist aggressive acids, alkalis, and halide-containing process streams.
- Marine & Offshore: Molybdenum-bearing grades provide reliable performance in seawater and brackish environments.
- Automotive & Aerospace: Precision-diameter coil tubes for fuel systems, exhaust components, and hydraulic lines.
- Medical Devices: Biocompatible 316L tubes for endoscopes, surgical instruments, and implant manufacturing.
- Architectural & Decorative: BA and mirror-finish coil tubes for handrails, balustrades, and facade applications.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system aligned with international standards:
- ISO 9001:2015 – Quality Management System certification
- ISO 14001:2015 – Environmental Management System
- EN 10204 3.1 – Material Test Reports with third-party inspection available
- EN 10217-7 – Heat exchanger tubes and pipes
- ASTM A213 / A269 – Seamless and welded austenitic stainless steel tube
- GB/T 4334 – Intergranular corrosion testing (Methods A, C, and F)
- PED 2014/68/EU – Pressure Equipment Directive compliance available
- NACE MR0175 – Sulfide stress cracking resistance for sour service (select grades)
Unique Selling Points
- 1.5-Minute Intergranular Corrosion Screening: The GB/T 4334 Method A rapid test provides immediate pass/fail results, reducing quality control cycle time by up to 95% compared to traditional 24-hour immersion methods—while maintaining full technical rigor.
- Two-Tier Verification Protocol: Pass results are accepted outright; marginal results trigger comprehensive immersion testing, ensuring zero-risk quality assurance without unnecessary cost or delay.
- Full-Length Coil Supply: Continuous coils up to 2,000 m (6,562 ft) eliminate butt-welds, reducing leak points and improving production efficiency in downstream fabrication.
- Wide Grade Availability: From standard 304L to super-austenitic 904L, customers can source specialized alloys from a single supplier with consistent quality documentation.
- End-to-End Traceability: Every coil is traceable to its heat number, with full chemical, mechanical, and corrosion test data provided in EN 10204 3.1 format.
- Precision Dimensional Control: Tight tolerances on OD and wall thickness ensure seamless integration into automated forming and bending lines without secondary machining.
Conclusion
Wenzhou Jixing Metal Materials Co., Ltd. delivers stainless steel coil tubes that combine premium metallurgical quality, rigorous intergranular corrosion verification, and manufacturing precision. The implementation of the GB/T 4334 Method A rapid screening protocol represents a commitment to both quality excellence and operational efficiency—ensuring that every coil tube supplied meets the most demanding specifications while minimizing lead times and quality-related costs for the end user.