Stainless Steel Coil Tube (Coiltube) — Resistance-Heated Solution Treatment Product Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product No.: 935
Category: Literature Study & Technical Reference
Document Focus: Solution Treatment of Stainless Steel Coil Tubes Based on Resistance Heating
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coiltube) is a continuously formed, uncut length of stainless steel tubing wound into a compact coil configuration, serving as a critical intermediate product in the manufacturing supply chain. Unlike straight-length tubes, coil tubes are supplied in continuous lengths—often exceeding 50 meters per coil—enabling high-throughput downstream processing such as cutting, forming, bending, and machining with minimal material waste.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production and treatment of stainless steel coil tubes, with particular expertise in resistance-heated solution treatment (电阻加热固溶处理). This thermal process is the defining differentiator of the product, ensuring optimal microstructural homogeneity, superior corrosion resistance, and maximum mechanical performance across austenitic and ferritic stainless steel grades.
Key Differentiator: The application of resistance heating for solution treatment of coil tubes represents an advanced thermal processing methodology that overcomes the limitations of conventional furnace-based approaches, delivering uniform heating rates, precise temperature control, and energy efficiency across the entire coil length without requiring the coil to be unwound.
2. Material Composition & Properties
The coil tubes are fabricated from high-quality stainless steel wire rod or seamless tube stock, predominantly from the following austenitic and duplex grades:
- A182 F304 / F304L — Low-carbon austenitic stainless steel with excellent formability and corrosion resistance
- A182 F316 / F316L — Molybdenum-bearing austenitic grade offering superior resistance to pitting and crevice corrosion
- A182 F321 — Stabilized austenitic grade with titanium addition for enhanced resistance to sensitization
- A182 F316Ti — Titanium-stabilized variant of F316 for high-temperature applications
- A182 F310 / F310S — High-temperature austenitic grade with elevated chromium and nickel content
2.1 Chemical Composition (Typical — ASTM A182 F316L)
| Element | Specification | Function |
|---|---|---|
| Carbon (C) | ≤ 0.030% | Low carbon prevents sensitization during heat treatment |
| Chromium (Cr) | 16.0 – 18.0% | Primary corrosion-resistant alloying element; forms passive Cr₂O₃ film |
| Nickel (Ni) | 10.0 – 14.0% | Stabilizes austenitic microstructure; enhances ductility |
| Molybdenum (Mo) | 2.0 – 3.0% | Improves pitting and crevice corrosion resistance |
| Nitrogen (N) | ≤ 0.10% | Minor solid-solution strengthening element |
| Silicon (Si) | ≤ 1.0% | Deoxidizer; improves high-temperature strength |
| Manganese (Mn) | ≤ 2.0% | Partial austenite stabilizer; improves hot workability |
2.2 Mechanical Properties (Post Solution Treatment)
| Property | Typical Value (F316L) | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 485 MPa (70 ksi) | ASTM A262 / ASTM E8 |
| 0.2% Yield Strength (YS) | ≥ 170 MPa (25 ksi) | ASTM E8 |
| Elongation at Break | ≥ 40% | ASTM E8 |
| Hardness (HB) | ≤ 200 HB | ASTM E10 |
| Impact Energy (Charpy V-Notch, RT) | ≥ 47 J | ASTM E23 |
2.3 Microstructural Characteristics
Following resistance-heated solution treatment, the microstructure of the coil tube exhibits:
- Single-phase austenite (FCC crystal structure) with minimal to no retained ferrite in austenitic grades
- Homogeneous grain distribution — uniform grain size across the coil cross-section and length, with no localized overheating or underheating zones
- Absence of carbide precipitation at grain boundaries — the solution treatment dissolves chromium carbides (Cr₂₃C₆) formed during prior cold working or welding, restoring full corrosion resistance
- Equiaxed grain morphology — promoting isotropic mechanical properties and improved fatigue performance
3. Product Specifications
| Parameter | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 – 50.0 mm | Custom diameters available upon request |
| Wall Thickness (WT) | 0.3 – 3.0 mm | Tolerance per ASTM A213 / ASME B36.19 |
| Coil Length | 20 – 100 m (continuous) | Dependent on diameter and grade |
| Coil Weight | 0.5 – 5.0 tons | Varies by specification |
| Surface Finish | Pickled & Passivated (P&P) / Bright Annealed (BA) / 2B | Ra ≤ 0.8 μm for BA finish |
| Surface Roughness | Ra 0.4 – 1.6 μm | Polished finishes available |
| Heat Treatment Condition | Solution Treated (固溶处理) | Resistance heating method |
| Solution Treatment Temperature | 1010 – 1150°C | Grade-dependent; F316L typically 1050°C |
| Cooling Method | Water Quench / Forced Air Quench | Rapid cooling to suppress carbide precipitation |
| Applicable Standards | ASTM A213, ASTM A269, ASME SA-213, EN 10216-5, GB/T 12771 | Multi-standard compliance |
| End Condition | Plain End / Beveled / Threaded | Custom end preparation available |
| Delivery Condition | Coiled, shrink-wrapped, or palletized | Moisture-proof packaging for export |
4. Manufacturing Process — Resistance-Heated Solution Treatment
The defining manufacturing process for this product is the resistance-heated solution treatment (电阻加热固溶处理), a specialized thermal processing technique that addresses the unique challenges of treating coiled tubing without unwinding.
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel wire rod or seamless tube stock undergoes chemical composition analysis (OES spectroscopy), mechanical testing, and visual surface inspection to ensure conformance with ASTM/ASME specifications.
- Coil Forming: The tube stock is continuously formed into a coil configuration using automated coiling machinery with precise diameter and pitch control to prevent kinking, deformation, or surface damage.
- Coil Loading & Electrical Contact Preparation: The formed coil is loaded onto the resistance heating fixture. Conductive contact pads or spring-loaded electrodes are applied to the coil to ensure uniform current distribution across the entire length of the tubing.
- Resistance Heating: A controlled electric current is passed through the coil, generating Joule heating (I²R heating) directly within the tube material. This method provides:
- Heating rates of 50–150°C/min (significantly faster than conventional furnace heating of 20–50°C/min)
- Temperature uniformity of ±15°C across the coil, achieved through multi-zone current control and thermocouple feedback
- Minimal thermal mass of the heating apparatus, reducing energy consumption by 30–50% compared to batch furnace methods
- Temperature Monitoring & Holding: Embedded thermocouples (Type K or Type N) monitor the coil temperature in real time. Once the target solution treatment temperature (typically 1010–1150°C, grade-dependent) is reached, the current is modulated to maintain a precise holding period (typically 5–30 minutes) for complete carbide dissolution and microstructural homogenization.
- Rapid Quenching: Immediately upon completion of the holding period, the coil is rapidly cooled via:
- Water quench: Immersion or spray quenching with deaerated water (cooling rate > 200°C/min)
- Forced air quench: High-velocity air cooling for applications requiring reduced residual stress
- Pickling & Passivation: The coil is subjected to acid pickling (typically nitric-hydrofluoric acid blend or citric acid for environmental compliance) to remove oxide scale, followed by passivation to restore the protective chromium oxide film.
- Final Inspection & Testing: Comprehensive quality verification including dimensional measurement, surface inspection, mechanical testing, corrosion testing (ASTM A262 Practice E — Intergranular Corrosion), and spectrographic analysis.
- Packaging & Dispatch: The treated coil is wound onto protective cores, wrapped in moisture-barrier film, and palletized for shipment.
4.2 Advantages of Resistance Heating Over Conventional Furnace Treatment
| Parameter | Resistance Heating | Conventional Batch Furnace |
|---|---|---|
| Heating Rate | 50–150°C/min | 20–50°C/min |
| Temperature Uniformity | ±15°C | ±25–40°C |
| Processing Time (per coil) | 30–60 minutes | 3–8 hours |
| Energy Consumption | Low (direct resistive heating) | High (indirect furnace heating) |
| Atmosphere Control | Not required (no furnace) | Requires controlled atmosphere (vacuum or protective gas) |
| Suitability for Coiled Product | Excellent (no unwinding needed) | Poor (requires unwinding and re-coiling) |
| Environmental Impact | Minimal (no combustion gases) | Higher (fuel combustion, off-gas treatment) |
5. Applications
The solution-treated stainless steel coil tube finds extensive application across demanding industrial sectors where corrosion resistance, mechanical integrity, and hygienic performance are paramount:
5.1 Process Industries
- Chemical Processing: Heat exchanger tubes, reactor piping, and process lines handling aggressive chemicals, acids, and chlorides
- Petrochemical & Oil & Gas: Downstream processing equipment, distillation columns, and transfer lines
- Pharmaceutical Manufacturing: Clean-in-place (CIP) tubing systems, bioreactor components, and hygienic piping (BA finish)
- Food & Beverage Processing: Sanitary-grade tubing for dairy, brewing, and beverage production lines
5.2 Energy & Power Generation
- Nuclear Power: Instrumentation and control tubing in reactor systems
- Solar Thermal: Heat transfer tubing in concentrated solar power (CSP) systems
- Power Plant: Desulfurization and denitrification (SCR) system components
5.3 Marine & Offshore
- Offshore Platforms: Fluid transfer lines, ballast water system tubing, and corrosion-resistant structural components
- Shipbuilding: Seawater cooling systems, ballast tanks, and marine piping
5.4 Medical & Laboratory
- Medical Devices: Tubing for dialysis machines, infusion pumps, and surgical instruments
- Laboratory Equipment: Chromatography columns, analytical instrument tubing
5.5 Architectural & Decorative
- Architectural Features: Handrails, balustrades, and decorative elements in high-end commercial and residential buildings
- Automotive Trim: Exhaust system components, decorative trim tubing
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all coil tube products meet international standards:
| Certification / Standard | Description |
|---|---|
| ISO 90 |