Stainless Steel Coil Tube — Offline Whole-Length Solution Annealing Process
1. Product Overview
The Stainless Steel Coil Tube (Coil Tube / Coil Pipe) is a continuous-length tubular product supplied in a coiled configuration, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product distinguishes itself through the application of Offline Whole-Length Solution Annealing (离线整体固溶处理), a premium heat treatment process in which the entire length of the coil tube is loaded into a controlled-temperature furnace as a single unit. This approach ensures complete and uniform thermal treatment across the full product length, effectively eliminating all residual stresses and delivering the most homogeneous mechanical and metallurgical properties achievable in industrial coil tube manufacturing.
Unlike segmented or partial heat treatment methods, the offline whole-length solution annealing process guarantees that every section of the tube — from the innermost coil layer to the outermost — undergoes identical thermal cycling, resulting in superior dimensional stability, corrosion resistance, and mechanical consistency.
2. Material & Properties
2.1 Common Material Grades
- Austenitic Stainless Steels: 304 (UNS S30400/S30408), 304L (UNS S30403), 316 (UNS S31600/S31608), 316L (UNS S31603), 321 (UNS S32100), 347 (UNS S34700)
- Super-Austenitic Grades: 904L (UNS N08904), 254 SMO (UNS S31254)
- Other: Custom alloy compositions upon request
2.2 Key Metallurgical Properties (Post-Solution Annealing)
- Crystal Structure: Fully austenitic (Face-Centered Cubic, FCC) — solution-annealed condition
- Hardness: Typically ≤ 220 HV (annealed condition); ≤ 200 HV for low-carbon grades
- Tensile Strength (Rm): 500–700 MPa (grade-dependent)
- Yield Strength (Rp0.2): 200–310 MPa (annealed condition)
- Elongation (A50): ≥ 40% (typical minimum)
- Corrosion Resistance: Maximum resistance achieved through complete carbide dissolution and uniform grain structure
- Magnetic Permeability: Non-magnetic to weakly magnetic (≤ 3 μ relative permeability)
2.3 Unique Selling Points
- 100% Residual Stress Elimination: The whole-length furnace treatment ensures that no localized stress concentrations remain, which is critical for applications subject to cyclic loading or cryogenic temperatures.
- Superior Property Uniformity: Unlike partial or sectional annealing, this process delivers consistent mechanical properties along the entire tube length — no weak zones or property gradients.
- Optimal Corrosion Resistance: Complete dissolution of chromium carbides (Cr23C6) prevents intergranular corrosion susceptibility, maximizing service life in aggressive environments.
- Maximum Ductility & Formability: Ideal for downstream cold-forming operations including bending, flanging, and deep drawing.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Product Form | Coil Tube (continuous coil configuration) |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (typical); custom sizes available |
| Wall Thickness | 0.5 mm – 3.0 mm (typical range) |
| Surface Finish | 2B (cold-rolled and annealed), BA (Bright Annealed), Pickled & Polished |
| Coil Weight | 100 kg – 1,000 kg (standard); custom upon request |
| Solution Annealing Temperature | 1050°C – 1150°C (grade-dependent) |
| Heating Rate | Controlled: 50°C – 150°C/hour |
| Soak Time | 10 – 30 minutes (depending on wall thickness and coil weight) |
| Quenching Medium | Air cooling or forced-air cooling (controlled rate) |
| Applicable Standards | ASTM A269, ASTM A213, EN 10216-5, GB/T 12771, GB/T 21830 |
| Tolerance (OD) | ± 0.1 mm or ± 1% (whichever is greater) |
| Tolerance (Wall) | ± 10% of nominal wall thickness |
4. Manufacturing Process
4.1 Process Flowchart
- Coil Straightening & Cutting: The stainless steel strip coil is unwound, straightened, and slit to the required wall thickness and width.
- Forming & Welding: The strip is roll-formed into a tube and longitudinally welded (TIG welding or automatic orbital welding), producing a continuous coil tube.
- Coil Winding: The continuous tube is wound into a large-diameter coil for bulk handling and transport.
- Offline Whole-Length Solution Annealing (Core Process):
- The entire coil tube assembly is loaded into a controlled-atmosphere or vacuum furnace as a single unit.
- The furnace is heated at a controlled rate (50°C–150°C/hour) to the solution annealing temperature (1050°C–1150°C), depending on the alloy grade.
- The coil is held at temperature for the required soak time to ensure complete carbide dissolution and austenitization throughout the entire cross-section and length.
- Controlled cooling (air or forced-air) follows to preserve the austenitic microstructure.
- Pickling & Descaling: Post-annealing oxide scale is removed via acid pickling (nitric-hydrofluoric acid blend) to restore the passive chromium oxide layer.
- Final Surface Treatment: Optional polishing, passivation, or bright annealing to achieve the specified surface finish.
- Quality Inspection & Packaging: Dimensional verification, surface inspection, mechanical testing, and protective packaging prior to shipment.
4.2 Process Advantages of Offline Whole-Length Treatment
The offline whole-length solution annealing method is the gold standard in stainless steel tube heat treatment. By processing the entire tube as a single furnace charge, this process achieves:
- Zero thermal gradient across the tube length — eliminating property variation
- Complete and uniform carbide dissolution — maximizing corrosion resistance
- Total elimination of cold-work residual stresses — enhancing fatigue life and dimensional stability
- Consistent grain size and microstructure throughout the entire product
5. Applications
The offline whole-length solution annealed stainless steel coil tube is specified in demanding applications where material uniformity, corrosion resistance, and mechanical reliability are paramount:
- Petrochemical & Refining Industry: Process piping, heat exchanger tubes, and reactor components exposed to corrosive media
- Food & Beverage Processing: Hygienic piping systems, CIP (Clean-In-Place) compatible tubing, and sanitary equipment
- Pharmaceutical Industry: GMP-compliant fluid transfer systems, reactor internals, and sterilization circuits
- Cryogenic Applications: Liquefied natural gas (LNG) systems, helium cooling lines, and low-temperature service (maintains ductility at −196°C)
- Automotive & Aerospace: Fuel lines, hydraulic tubing, exhaust components, and structural tubing requiring high strength-to-weight ratios
- Medical Equipment: Endoscopy tubing, instrument shafts, and implant-grade components
- Construction & Architecture: Decorative handrails, structural supports, and building facade elements
- Downstream Cold Forming: Tubing intended for secondary bending, flanging, or deep-drawing operations where maximum formability is required
6. Quality Certifications & Testing
6.1 Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001 — Environmental Management System
- ISO/IEC 17025 — Testing and Calibration Laboratory Competence (in-house lab)
- NACE MR0175 / ISO 15156 — Oil & Gas Service Compliance (where applicable)
- EN 10204 3.1 — Material Test Certificates
6.2 Inspection & Testing Regime
| Test Type | Standard | Frequency |
|---|---|---|
| Chemical Composition Analysis (Spectroscopy) | ASTM E415 | Per heat / per coil |
| Tensile Testing | ASTM A370 / EN 10002-1 | Per coil |
| Hardness Testing (Rockwell B / Vickers) | ASTM E18 / ASTM E92 | Per coil |
| Intergranular Corrosion (IGC) Test | ASTM A269 / ASTM G28 | Per heat |
| Hydrostatic Pressure Test | ASTM A269 | Per coil |
| Dimensional Verification | Per applicable product standard | 100% online + sampling |
| Surface Defect Inspection | Visual + eddy current | 100% continuous |
| Grain Size & Microstructure | ASTM E112 | Per heat (on request) |
6.3 Traceability
Every coil tube batch is fully traceable from raw material mill certificate through the solution annealing furnace log to final shipment documentation. Heat numbers, furnace batch records, and test results are maintained in a digital quality database for lifetime product traceability.
Wenzhou Jixing Metal Materials Co., Ltd. — Precision stainless steel coil tube solutions with industry-leading whole-length solution annealing technology.