Stainless Steel Coil Tube — Online Solution Treatment Process
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a continuous-length tubular product manufactured through advanced cold-drawing or cold-rolling techniques, subsequently formed into coil configurations for efficient storage and downstream processing. A defining characteristic of this product line is the implementation of Online Solution Treatment (在线固溶处理) — a critical heat treatment process performed immediately following the welding stage. This integrated thermal treatment is executed via rapid water quenching (水淬) or gas quenching (气淬), ensuring that the weld zone undergoes precise thermal cycling to restore full metallurgical integrity and corrosion resistance.
Online solution treatment represents a state-of-the-art approach in austenitic stainless steel tube manufacturing, distinguishing this product from conventionally treated alternatives. By embedding the solution treatment directly into the production line, the process eliminates the need for post-production batch heat treatment, thereby reducing thermal cycling exposure, minimizing intergranular corrosion susceptibility, and delivering a product with superior weld zone performance.
Material & Properties
Stainless steel coil tubes are predominantly manufactured from austenitic stainless steel grades, including but not limited to AISI 304 (UNS S30400), AISI 304L (UNS S30403), AISI 316 (UNS S31600), AISI 316L (UNS S31603), and AISI 321 (UNS S32100). These grades are characterized by their face-centered cubic (FCC) crystal structure, which provides excellent ductility, formability, and resistance to intergranular corrosion when properly solution-treated.
- Microstructure: Fully austenitic grain structure with dissolved carbon in solid solution — no carbide precipitation at grain boundaries
- Mechanical Properties: Tensile strength typically ranging from 515 MPa to 720 MPa; yield strength ≥ 205 MPa; elongation ≥ 40% (ASTM A213/A269)
- Corrosion Resistance: Restored to base metal equivalent after online solution treatment; pitting resistance equivalent number (PREN) of ≥ 19 for 316L grades
- Weld Zone Integrity: No sensitization (chromium carbide precipitation) in the Heat-Affected Zone (HAZ); full recovery of intergranular corrosion resistance per ASTM A262 Practice E/A
- Surface Condition: Seamless weld zone with uniform grain size; no visible quench marks or oxidation discoloration
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Form | Coil Tube (Continuous Coiled Tubing) | — |
| Applicable Grades | 304, 304L, 316, 316L, 321, 347, 904L, TP310, Duplex 2205 | ASTM A213, ASTM A269, ASTM A778 |
| Outer Diameter (OD) | 1.5 mm – 219.0 mm (0.06 in – 8.62 in) | ASTM A554, EN 10216 |
| Wall Thickness (WT) | 0.20 mm – 12.0 mm (0.008 in – 0.472 in) | ASTM A554, EN 10216 |
| Welding Method | Automatic Argon Arc Welding (TIG / GMAW) | ISO 6947, ASME B31.3 |
| Solution Treatment Temperature | 1010 °C – 1150 °C (1850 °F – 2100 °F) | ASTM A269, EN 10217-7 |
| Quenching Method | Online Water Quenching / Gas Quenching (Nitrogen / Air) | Manufacturer Process Specification |
| Quenching Rate | ≥ 50 °C/s through the critical sensitization range (800–550 °C) | ASTM A262 Practice E |
| Grain Size | ASTM E112 No. 5 – No. 8 (fine-grained austenitic) | ASTM E112 |
| Intergranular Corrosion | Passes ASTM A262 Practice E (65% HNO₃, 23% HCl, or 5% H₂SO₄ + CuSO₄) | ASTM A262 |
| Surface Finish | BA (Bright Annealed), Pickled & Polished, or Custom | ASTM A473 |
| Coil Configuration | Random cut coils or fixed-length coils with protective end caps | ISO 11612 |
| Applicable Standards | ASTM A213, A269, A778; EN 10216-5, EN 10217-7; GB/T 12771 | Multi-standard compliance |
Manufacturing Process
The production of stainless steel coil tubes with online solution treatment follows a rigorously controlled, integrated manufacturing sequence designed to maximize metallurgical quality while maintaining production efficiency:
- Raw Material Preparation: Cold-rolled stainless steel strip (coil) of certified grade is uncoiled and fed into the tube forming line. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm chemical composition compliance.
- Tube Forming (Forming & Sizing): The strip is guided through a series of progressively reducing rollers to form the desired tube cross-section (round, rectangular, or oval). Precision roller configurations ensure dimensional accuracy within ±0.05 mm tolerance.
- Welding: The formed strip is welded along the longitudinal seam using automatic shielded metal arc welding (SMAW), gas metal arc welding (GMAW), or gas tungsten arc welding (GTAW) under a controlled inert gas atmosphere (argon or argon-helium mixture). Weld parameters (current, voltage, travel speed, gas flow) are continuously monitored and logged.
- Online Solution Treatment (在线固溶处理): Immediately upon completion of the welding operation, the tube passes through an inline induction heating station or radiant tube furnace where it is rapidly heated to the solution treatment temperature range (1010–1150 °C). This step dissolves all precipitated chromium carbides (Cr₂₃C₆, Cr₇C₃) within the weld zone and heat-affected zone, returning the microstructure to a homogeneous single-phase austenitic state with carbon in solid solution.
- Immediate Quenching (水淬/气淬): Following the solution heat treatment, the tube is subjected to rapid quenching — either by direct water spray/immersion (water quenching) or by high-velocity inert gas flow (gas quenching with nitrogen, argon, or compressed air). The quenching rate must exceed 50 °C/s through the critical sensitization temperature range (800 °C to 550 °C) to prevent re-precipitation of chromium carbides at grain boundaries.
- Coiling: The solution-treated tube is wound into coils of specified diameter and length. Protective end caps and wrapping materials prevent surface damage during handling and storage.
- Quality Inspection & Testing: Each coil undergoes comprehensive testing including hydrostatic pressure testing (per ASTM A530), dimensional verification, surface inspection (visual and magnetic particle testing), and metallurgical evaluation including intergranular corrosion testing (ASTM A262 Practice E).
Process Advantages of Online Solution Treatment
Key Technical Rationale: In conventional manufacturing, welded stainless steel tubes are often solution treated in batch furnaces after coiling, requiring a second thermal cycle. This additional heating and cooling exposes the weld zone to repeated sensitization risk and potential grain coarsening. Online solution treatment eliminates this intermediate step, delivering a product with superior metallurgical uniformity, reduced total thermal exposure, and guaranteed weld zone corrosion resistance from the point of manufacture.
Applications
The combination of coil tube form factor and online solution treatment makes this product ideally suited for applications demanding high corrosion resistance, cleanability, and dimensional precision:
- Chemical Processing & Petrochemical Industry: Heat exchanger tubes, reactor piping, distillation columns, and process lines handling aggressive media (acids, halides, chlorides)
- Food & Beverage Processing: Hygienic piping systems, pasteurization lines, fermentation tanks, CIP (Clean-in-Place) systems — meeting 3-A Sanitary Standards and FDA compliance
- Pharmaceutical & Biotechnology: GMP-compliant process piping, clean steam lines, bioreactor connections, chromatography systems
- Power Generation: Boiler tubes, superheater elements, nuclear-grade components (when manufactured to ASME Section III)
- Oil & Gas (Offshore): Subsea piping systems, wellhead components, platform structural tubing — resistant to chloride-induced stress corrosion cracking (SCC)
- Medical Devices: Surgical instrument tubing, implant manufacturing feedstock, dialysis machine components
- Automotive & Aerospace: Exhaust systems, fuel lines, hydraulic tubing, structural components requiring high-temperature oxidation resistance
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems to ensure that online solution-treated stainless steel coil tubes meet international standards and regulatory requirements:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 — Type 3.1 Material Test Certificates (third-party inspected)
- ASTM — Compliance with ASTM A213, A269, A778, A262, A530, A473
- EN Standards — Compliance with EN 10216-5, EN 10217-7, EN 10204
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking for oil and gas applications
- ASME Section IX — Welding procedure qualification (where applicable)
- Mill Test Reports (MTR) — Full chemical analysis, mechanical test results, and heat treatment documentation provided with each shipment
Unique Selling Points
- Integrated Online Heat Treatment: Solution treatment and quenching performed inline immediately after welding — eliminating secondary batch heat treatment, reducing production cycle time by up to 40%, and ensuring zero sensitization in the weld zone
- Guaranteed Weld Zone Corrosion Resistance: Every coil is verified to pass ASTM A262 Practice E intergranular corrosion testing, providing documented proof of weld zone integrity
- Superior Metallurgical Uniformity: Single thermal cycle ensures consistent grain structure, hardness, and mechanical properties throughout the entire tube length — no variation between weld zone and base metal
- Reduced Carbon Footprint: Elimination of batch furnace reheat cycles reduces energy consumption and CO₂ emissions per ton of finished product
- Wide Grade and Dimensional Flexibility: Available in multiple austenitic, duplex, and super-austenitic grades across a broad OD and wall thickness range, enabling single-source procurement for diverse project requirements
- Full Traceability: Each coil is serialized with complete process documentation including welding parameters, solution treatment temperature profiles, quenching rate data, and third-party inspection reports