Stainless Steel Coil Tube (Coiltube) — Solid Solution Treated
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. represents a high-performance, continuously formed tubular product engineered for demanding industrial applications. Unlike straight-length seamless or welded tubes, coil tubes are produced in continuous coil form, offering superior material utilization, reduced cutting losses, and enhanced logistics efficiency. The product undergoes rigorous solid solution treatment (Solution Annealing), a critical heat treatment process that homogenizes the microstructure, eliminates residual stresses introduced during cold forming, and restores optimal mechanical and corrosion resistance properties.
Coiltube products are particularly advantageous for downstream applications requiring continuous processing, such as heat exchanger tube drawing, capillary tube manufacturing, and precision instrument tubing. The solid solution treatment ensures the austenitic stainless steel matrix achieves full solubility of intermetallic precipitates, yielding a uniform single-phase austenitic structure with excellent ductility and toughness.
2. Material & Properties
2.1 Base Materials
- Austenitic Grades: AISI 304, AISI 304L, AISI 316, AISI 316L, AISI 321, AISI 310S
- Super Austenitic Grades: AISI 904L, Alloy 20
- Specialty Grades: Custom formulations per customer specification
2.2 Mechanical Properties (Post Solid Solution Treatment)
- Tensile Strength (UTS): ≥ 520 MPa (for 304/304L), ≥ 550 MPa (for 316/316L)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation: ≥ 40% (minimum)
- Hardness: ≤ 95 HRB (annealed condition)
- Impact Toughness: ≥ 47 J at −196 °C (cryogenic capable)
2.3 Corrosion Resistance
- Pitting Resistance (PREN): 18–20 (304 series), 24–26 (316 series), 42–45 (904L)
- Intergranular Corrosion Resistance: Passes ASTM A923 Practice A/B/C (100% austenitic, no carbide precipitation)
- Acid Resistance: Excellent in dilute sulfuric acid, acetic acid, and nitric acid environments
- Chloride Resistance: Superior resistance to stress corrosion cracking (SCC) in chloride-containing media
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 1.5 mm – 168.3 mm (adjustable per order) |
| Wall Thickness | 0.1 mm – 6.0 mm |
| Coil Weight | 500 kg – 5,000 kg per coil |
| Coil Inner Diameter | 500 mm – 1,200 mm |
| Surface Finish | 2B, BA (Bright Annealed), No. 4, Mirror (Ra ≤ 0.2 μm) |
| Dimensional Tolerance | OD: ±0.05 mm to ±0.10 mm; Wall: ±0.02 mm to ±0.05 mm |
| Solid Solution Treatment Temperature | 1010 °C – 1150 °C (grade-dependent) |
| Quenching Method | Rapid water quench / controlled atmosphere cooling |
| Standards Compliance | ASTM A269, ASTM A213, EN 10216-5, GB/T 12771, JIS G3459 |
| Maximum Straight Length (after coil cutting) | Up to 12,000 mm |
4. Manufacturing Process
4.1 Production Flow
- Raw Material Selection: High-purity stainless steel strip or wire rod from certified mills, with controlled chemistry (low carbon, low sulfur, low nitrogen).
- Forming: Continuous roll forming or welding (ERW/TIG) to produce the initial coil tube geometry.
- Piercing & Sizing: Multi-pass cold sizing to achieve precise dimensional tolerances.
- Solid Solution Treatment (Critical Step): The coil tube is heated uniformly in a controlled-atmosphere furnace to the prescribed austenitization temperature (typically 1050–1100 °C for 300-series grades), held for sufficient time to fully dissolve carbon and chromium carbides into the austenite matrix, then rapidly quenched (water or high-velocity air) to suppress precipitation.
- Pickling & Passivation: Removal of oxide scale via acid pickling (mixed HNO₃/HF), followed by passivation to restore the protective chromium oxide layer.
- Surface Finishing: Mechanical polishing or chemical bright annealing (BA) to achieve specified surface quality.
- Quality Inspection: Dimensional verification, spectrometric analysis, hydrostatic testing, and visual inspection.
- Coiling & Packaging: Rewinding into specified coil dimensions with protective wrapping.
4.2 Solid Solution Treatment — Technical Detail
The solid solution treatment is the defining metallurgical operation for this product. The process parameters are carefully calibrated to the specific alloy grade:
- Heating Rate: Controlled at 100–150 °C/hour to prevent thermal cracking and ensure uniform temperature distribution throughout the coil.
- Austenitization Hold Time: 2–4 hours (adjusted for coil thickness and mass) to ensure complete homogenization.
- Quench Rate: ≥ 100 °C/minute to suppress δ-ferrite and carbide precipitation at grain boundaries.
- Atmosphere Control: Inert gas (N₂ or Ar) or vacuum environment to prevent oxidation and carburization during treatment.
Key Advantage: Wenzhou Jixing employs a proprietary continuous solid solution treatment line capable of processing full coils without prior cutting, eliminating heat-affected zones at cut ends and ensuring uniform metallurgical properties along the entire tube length. This is a significant differentiator from batch-treated products.
5. Applications
- Heat Exchangers & Condensers: Refrigeration, HVAC, and chemical process heat exchangers requiring high thermal conductivity and corrosion resistance.
- Cryogenic Systems: Liquefied natural gas (LNG) pipelines, superconducting magnet cooling circuits, and aerospace cryogenic applications.
- Medical & Pharmaceutical: Hospital equipment tubing, pharmaceutical processing lines, and bioreactor components requiring sanitary-grade surface finishes.
- Food & Beverage Industry: Dairy processing, brewing, and beverage transfer systems compliant with FDA and 3-A Sanitary Standards.
- Chemical Processing: Acid-resistant piping, reactor internals, and evaporator tubes in aggressive chemical environments.
- Automotive & Aerospace: Exhaust system components, fuel lines, and hydraulic tubing requiring fatigue resistance and weight optimization.
- Oil & Gas: Downhole tubing, wellhead equipment, and offshore platform piping systems.
- Capillary & Precision Tubes: Downstream drawing for instrument tubes, medical needles, and hydraulic capillaries.
6. Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- EN 10204 3.1 — Inspection Certificates (Material Test Reports with product-specific data)
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking (for oil & gas applications)
- NSF/ANSI 61 — Drinking water system components (where applicable)
- 3-A Sanitary Standards — Dairy and food processing equipment compliance
- ASME Boiler & Pressure Vessel Code — Section I/IV/IX material compliance
7. Unique Selling Points
- Full-Coil Solid Solution Treatment: Continuous treatment of entire coils eliminates weld-line property variations and ensures metallurgical uniformity throughout — a capability not universally available in the industry.
- Ultra-Thin Wall Capability: Minimum wall thickness of 0.1 mm with controlled ovality and roundness, enabling downstream precision drawing without cracking.
- Multi-Grade Flexibility: Single production line accommodates standard austenitic through to super austenitic grades with grade-specific heat treatment protocols.
- Surface Quality Excellence: Bright annealed (BA) finish achieving Ra ≤ 0.4 μm without additional mechanical polishing, reducing downstream processing costs.
- Traceability & Documentation: Full heat-number traceability from mill certificate through to final coil delivery, with complete metallurgical and mechanical test data.