Stainless Steel Coil Tube — Online Solution Heat Treatment (In-Line Solutionizing)
Product Overview
The Stainless Steel Coil Tube produced by Wenzhou Jixing Metal Materials Co., Ltd. features a proprietary Online Solution Heat Treatment (In-Line Solutionizing) process applied immediately after the welding stage. This advanced manufacturing technique involves rapid water quenching or gas quenching of the welded coil tube, ensuring that the weld zone and Heat Affected Zone (HAZ) are brought to a solution-treated condition in real time. The process is integral to maintaining the metallurgical integrity, corrosion resistance, and mechanical performance of the finished product.
The online solution heat treatment eliminates the need for post-manufacturing batch solution treatment, reducing energy consumption, production lead time, and the risk of oxide scale formation associated with re-heating in a furnace. This results in a superior surface finish and a more uniform microstructure throughout the tube length.
Material & Properties
Applicable Grades
- Austenitic Stainless Steels: 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), 321 (UNS S32100), 310S (UNS S31008)
- Super Austenitic Grades: 904L (UNS N08904), 254 SMO (UNS S31254)
- Duplex Stainless Steels: 2205 (UNS S31803), 2507 (UNS S32750)
- Custom Alloys: Available upon request based on customer specifications
Key Metallurgical Properties
- Corrosion Resistance: Full recovery of pitting resistance equivalent number (PREN) in the weld zone; resistance to intergranular corrosion (IGC) confirmed by ASTM A262 Practice E
- Mechanical Properties: Uniform tensile strength and elongation across the weld and base metal; no localized softening or embrittlement
- Microstructure: Homogeneous austenitic (or austenite-ferrite for duplex grades) structure with minimal chromium carbide (Cr₂₃C₆) precipitation at grain boundaries
- Hardness: Typically 150–220 HV (depending on grade), with no significant hardness differential between weld zone and base material
- Sensitization Resistance: Immunity to chromium depletion at grain boundaries, ensuring long-term service life in corrosive environments
Specifications
| Parameter | Specification / Range | Standard / Method |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 323.9 mm (¼" – 12") | ASTM A554 / EN 10217-7 |
| Wall Thickness | 0.5 mm – 12.7 mm (0.020" – ½") | ASTM A554 / EN 10217-7 |
| Coil Length | Up to 1,500 m (custom lengths available) | Manufacturer specification |
| Seam Welding Method | High-Frequency Induction (HFI) / TIG (GTAW) | ASME B31.3 / EN 12074 |
| Online Solution Treatment Method | Immediate Water Quenching / Gas Quenching (Nitrogen or Argon) | ASTM A999 / ASTM A313 |
| Quench Temperature Range | 1010 °C – 1150 °C (1850 °F – 2100 °F) | Grade-dependent |
| Quench Rate | > 100 °C/s (rapid cooling through sensitization range) | Manufacturer specification |
| Surface Finish | Mill Finish (BF), Bright Annealed (BA), 2B, or Polished | ASTM A580 |
| Intergranular Corrosion Test | Pass ASTM A262 Practice E (Acid Solution) | ASTM A262 |
| Residual Stress | ≤ 50 MPa (low residual stress after online solutionizing) | X-ray diffraction method |
| Applicable Standards | ASTM A554, A511, A313; EN 10217-7, EN 10216-5; ISO 13505 | International standards |
Manufacturing Process
Process Flow
- Coil Slitting & Leveling: Cold-rolled stainless steel strip coils are slit to the required width and leveled to ensure flatness and dimensional accuracy.
- Forming & Rolling: The strip is fed through precision rolls to form the desired tube cross-section (round, square, rectangular, or oval).
- Seam Welding: The formed strip is welded into a continuous tube using High-Frequency Induction (HFI) welding or Gas Tungsten Arc Welding (GTAW/TIG), depending on grade and wall thickness requirements.
- Online Solution Heat Treatment (Critical Step):
- The freshly welded coil tube passes through an in-line induction heating zone where the weld zone and HAZ are rapidly heated to the solution temperature range (1010–1150 °C).
- Immediately upon reaching the target temperature, the tube undergoes rapid quenching — either by direct water spray quenching or inert gas (nitrogen/argon) quenching — at a cooling rate exceeding 100 °C/s.
- This rapid thermal cycle dissolves all chromium carbides (Cr₂₃C₆) formed during welding and re-distributes alloying elements uniformly throughout the microstructure, fully restoring corrosion resistance in the weld zone.
- Piercing & Sizing: The coil tube passes through sizing rolls and a piercing station to achieve precise final dimensions.
- Coiling & Packaging: The finished coil tube is wound onto a mandrel, protected against surface damage, and packaged for shipment.
Why Online Solution Treatment Matters
During the welding process, the high thermal input causes chromium to combine with carbon at grain boundaries, forming chromium carbide precipitates (Cr₂₃C₆). This phenomenon, known as metallurgical sensitization, depletes chromium in the adjacent zone, reducing the local corrosion resistance significantly. Online solution treatment — performed immediately after welding — reverses this process by re-dissolving the carbides at elevated temperature and quenching rapidly enough to prevent their re-precipitation. The result is a weld zone with corrosion resistance equivalent to the base metal.
Unique Selling Points
- Real-Time Sensitization Prevention: By performing solution treatment immediately after welding, the product eliminates the risk of sensitization that occurs during conventional post-weld heat treatment delays or storage.
- Energy Efficiency: The in-line process leverages the residual heat from welding, significantly reducing the energy required compared to batch furnace solution treatment.
- Superior Surface Quality: No re-heating in a furnace means no secondary oxide scale formation, resulting in a cleaner, more uniform surface finish that requires less downstream processing.
- Consistent Microstructure: Continuous in-line processing ensures uniform solution treatment along the entire tube length, eliminating the variability associated with batch processing.
- Reduced Lead Time: The integration of welding and heat treatment into a single continuous process streamlines production, enabling faster delivery to customers.
- Environmental Advantage: Lower energy consumption and reduced oxide waste contribute to a smaller environmental footprint.
Applications
- Chemical & Petrochemical Industry: Heat exchangers, reactors, piping systems, and storage vessels handling aggressive chemicals
- Food & Beverage Processing: Hygienic piping, CIP (Clean-in-Place) systems, and processing equipment requiring high corrosion resistance
- Pharmaceutical Industry: GMP-compliant piping and equipment for drug manufacturing and sterile processing
- Oil & Gas (Upstream & Downstream): Subsea piping, wellhead equipment, and refinery systems exposed to chloride-containing environments
- Power Generation: Boiler tubes, condensers, and heat recovery steam generators (HRSG) in fossil fuel and nuclear plants
- Marine & Offshore: Propeller shafts, ballast systems, and offshore platform piping
- Architectural & Structural: Decorative cladding, structural components, and railings in coastal environments
Quality Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing
- EN 10204 3.1 — Third-party inspection and material certification for each production batch
- ASTM A262 Compliance — Intergranular corrosion resistance testing (Practice E, Acid Solution) confirming sensitization prevention
- ASME Section IX — Welding procedure qualification for all applicable grades and wall thicknesses
- NADCAP (where applicable) — Special process certification for aerospace and critical industrial applications
- CE Marking / PED 2014/68/EU — Conformity with European Pressure Equipment Directive for pressure-containing applications
Technical Notes
- For duplex stainless steel grades (e.g., 2205, 2507), the online solution treatment temperature is carefully controlled to maintain the optimal austenite-ferrite phase balance (typically 40–60% ferrite), preventing the formation of detrimental intermetallic phases (σ-phase, χ-phase).
- Gas quenching (using nitrogen or argon) is preferred for grades susceptible to water-induced stress cracking or where surface oxidation must be minimized. Water quenching provides a faster cooling rate and is suitable for most standard austenitic grades.
- Customers requiring additional post-treatment steps such as pickling & passivation or stress relief can request these as supplementary services.
- Full traceability is maintained from raw material coil to finished product, including heat numbers, welding parameters, and heat treatment logs.