Stainless Steel Coil Tube (盘管) – Water-Jacket Furnace Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous tube product wound into a coil configuration, specifically designed for high-temperature industrial applications including water-jacket furnaces (WJF), heat exchangers, and thermal processing systems. This product is produced under internal reference Item No. 1371 and is categorized within the technical literature and learning reference series.
Unlike straight-length seamless or welded tubes, coil tubes are delivered in continuous coiled form, which offers significant advantages in terms of material utilization, reduced cutting waste, ease of handling in long-run installations, and compatibility with automated forming and welding equipment. The coil form factor also enables efficient storage and transportation logistics for large-scale industrial projects.
This product line is particularly distinguished by its suitability for water-jacket furnace (Water Jacket Furnace, WJF) applications, where the coil tubes serve as critical heat-exchange elements that require robust weld integrity, thermal fatigue resistance, and dimensional stability under prolonged cyclic thermal loading conditions.
2. Material & Properties
2.1 Base Material Grades
The stainless steel coil tube is available in a range of standard and specialty austenitic and austenitic-ferritic grades, selected based on application-specific requirements:
- Austenitic Grades: SUS304 / AISI 304, SUS316L / AISI 316L, SUS321 / AISI 321, SUS310S / AISI 310S
- Super-Austenitic Grades: SUS904L / UNS N08904, Alloy 20 equivalents
- Heat-Resistant Grades: SUS314, SUS309S (for extreme temperature environments)
2.2 Key Mechanical Properties
- Tensile Strength: ≥ 520 MPa (for SUS304 at room temperature); ≥ 600 MPa (for SUS310S)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Elongation: ≥ 35% (minimum, at break)
- Hardness: ≤ 217 HB (annealed condition)
- Thermal Conductivity: 14.9–16.3 W/(m·K) (austenitic grades, at 20°C)
- Maximum Service Temperature: 870°C (SUS304); 1150°C (SUS310S)
- Cold Forming Capability: Excellent; suitable for cold bending, roll forming, and coiling without pre-heating
2.3 Chemical Composition (Typical – SUS304 Grade)
| Element | Specification (wt%) |
|---|---|
| C (Carbon) | ≤ 0.08 |
| Mn (Manganese) | ≤ 2.00 |
| P (Phosphorus) | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 |
| Si (Silicon) | ≤ 1.00 |
| Cr (Chromium) | 18.00 – 20.00 |
| Ni (Nickel) | 8.00 – 10.50 |
| N (Nitrogen) | ≤ 0.10 |
2.4 Corrosion Resistance
The chromium-rich passive oxide layer (Cr₂O₃) formed on the surface provides exceptional resistance to atmospheric corrosion, acidic environments, and chloride-induced pitting (particularly in SUS316L grades containing molybdenum). The material exhibits a critical pitting temperature (CPT) of ≥ 30°C in 3.5% NaCl solution for SUS316L grade, making it suitable for aggressive chemical processing environments.
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ108.0 mm | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 4.0 mm | ASTM A269 / GB/T 14976 |
| Coil Inner Diameter (ID) | Φ300 mm – Φ1200 mm | Custom / Project-Specific |
| Coil Length per Piece | 30 m – 300 m (continuous) | Manufacturer Standard |
| OD Tolerance | ±0.10 mm (≤ Φ25 mm); ±0.15 mm (> Φ25 mm) | ASTM A213 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A269 |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm); Baquelite pickled; 2B; No.4 brushed | ASTM A473 / GB/T 12770 |
| Heat Treatment | Solution annealed (1050°C – 1150°C) + water quench | ASTM A213 |
| End Condition | Plain cut; beveled; threaded; flanged (custom) | Project-Specific |
| Coating / Packaging | Protective film wrap; wooden pallet; steel drum | ISO 11607 |
| Applicable Standards | ASTM A213, ASTM A269, ASME SA-213, GB/T 12771, GB/T 14976, JIS G4806, EN 10216-5 | Multi-Standard Compliance |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Inspection: Stainless steel coil stock (SSR, Cold-Rolled Coil) is sourced from certified mills. Incoming material undergoes 100% chemical composition verification via Optical Emission Spectroscopy (OES) and mechanical property testing (tensile, hardness).
- Slitting & Edge Trimming: The master coil is slit to the required strip width using high-precision slitting lines with laser-guided edge trimming to ensure dimensional accuracy within ±0.05 mm.
- Forming (Tube Making): The slit strip is fed into a roll-forming machine (Hedgerman or similar type) where sequential rolls progressively bend the flat strip into a near-circular tube blank. This process is performed at room temperature (cold forming) to preserve the metallurgical integrity of the annealed austenitic structure.
- Welding (Longitudinal Seam): The formed tube blank undergoes continuous longitudinal seam welding. Two primary welding methods are employed:
- TIG Welding (Gas Tungsten Arc Welding, GTAW): Used for higher-grade and thicker-wall tubes. Argon shielding gas (purity ≥ 99.99%) is applied on both inside and outside of the seam to prevent oxidation. Typical welding parameters: 120–350 A, 10–25 V, travel speed 5–15 mm/s.
- IG Welding (Induction Welding): Used for high-volume production of thinner-wall tubes. High-frequency induction heating (frequency 200–400 kHz) achieves rapid, localized heating of the seam area followed by cap-roller pressure closure. This method offers superior speed and weld consistency.
- Heat Treatment (Post-Weld Annealing): The welded coil tube is subjected to solution annealing at 1050°C – 1150°C followed by rapid water quenching. This step dissolves any carbide precipitates formed in the Heat-Affected Zone (HAZ) during welding, restoring full corrosion resistance and eliminating residual stresses. The grain structure is refined to ASTM E112 grain size of 6–8.
- Pickling & Passivation: The annealed tube undergoes chemical pickling (HNO₃/HF mixed acid bath) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive film. The resulting surface achieves a minimum chromium enrichment ratio of 18:1 (Cr:Fe) in the passive layer.
- Coiling & Winding: The processed tube is wound onto a coil mandrel using a controlled winding machine that applies uniform tension to prevent kinking, ovality, or coil instability. The coil is stabilized with tension-controlled layers and secured with steel strapping.
- Final Inspection & Testing: Comprehensive quality verification is performed (see Section 6 for details).
- Packaging & Dispatch: Coils are wrapped with protective PE film, placed on wooden pallets or in steel drums, and prepared for export or domestic delivery.
4.2 Water-Jacket Furnace Coil Tube Welding – Special Considerations
The welding of coil tubes for water-jacket furnace (WJF) applications presents unique technical challenges that require specialized expertise. Key considerations include:
- Thermal Fatigue Resistance: WJF coil tubes experience repeated thermal cycling between high-temperature furnace zones (up to 900°C) and relatively cooler water-jacket sections. The weld seams must maintain integrity over thousands of thermal cycles without cracking. This necessitates strict control of weld bead geometry, interpass temperature (≤ 150°C), and post-weld heat treatment parameters.
- Stress Relief: Residual welding stresses in WJF coil tubes can accelerate fatigue failure. A post-weld stress relief anneal at 650°C – 750°C for 1–2 hours is recommended for critical applications, though this must be balanced against potential sensitization (carbide precipitation) risks in 300-series grades.
- Weld Quality Verification: 100% visual inspection, dye penetrant testing (DPT) per ASTM E709, and periodic radiographic testing (RT) per ASTM E94 are mandatory. For critical furnace applications, ultrasonic testing (UT) per ASTM E747 is also performed on the longitudinal seam.
- Dimensional Stability: Coil tubes in WJF applications must maintain their coiled geometry under thermal expansion. The tube's minimum bend radius must be ≥ 3× OD to prevent ovality under thermal cycling.
5. Applications
5.1 Primary Applications
- Water-Jacket Furnaces (WJF): Primary application. Coil tubes serve as heating elements and heat-exchange surfaces in batch and continuous WJF systems used for heat treatment of metals, glass tempering, and ceramic sintering.
- Industrial Heat Exchangers: Shell-and-tube heat exchangers, air heaters, and recuperators in chemical, petrochemical, and power generation industries.
- Boiler & Steam Systems: Superheater tubes, economizers, and evaporator tubes in industrial boilers operating at elevated temperatures and pressures.
- Food & Pharmaceutical Processing: Sanitary-grade coil tubes (mirror polished, Ra ≤ 0.25 μm) for pasteurization, sterilization, and CIP (Clean-In-Place) systems.
- Chemical Processing: Reactor internals, distillation column internals, and heat transfer coils in aggressive chemical environments (SUS316L / SUS904L grades).
- Petrochemical & Oil Refining: Crude oil distillation coils, hydrotreater internals, and reformer tubes.
- Automotive & Aerospace: Exhaust system components, catalytic converter substrates, and thermal management systems.
5.2 Unique Selling Points (USPs)
- Specialized WJF Expertise: Wenzhou Jixing Metal Materials possesses deep technical knowledge in water-jacket furnace coil tube welding, gained through extensive project experience and continuous technical learning. This expertise translates into superior weld integrity, thermal fatigue performance, and long-term operational reliability.
- Continuous Coil Delivery: The coil form eliminates the need for butt-welding multiple straight tube sections, reducing potential failure points and installation labor. This is particularly advantageous for large-scale WJF installations requiring hundreds of meters of tube.
- Multi-Grade Flexibility: Availability in multiple stainless steel grades (304, 316L, 321, 310S, 904L) allows precise material selection matched to the specific thermal, chemical, and mechanical demands of each application.
- Precision Dimensional Control: Tight OD and wall thickness tolerances (±0.10 mm) ensure consistent heat transfer performance and compatibility with precision-fitted mounting hardware in furnace applications.
- Comprehensive Quality Assurance: Multi-stage inspection protocol including chemical analysis, mechanical testing, non-destructive testing (NDT), and dimensional verification ensures every coil meets or exceeds specification requirements.
- Custom Engineering Support: Capability to produce custom OD, wall thickness, coil diameter, and surface finish configurations tailored to specific project requirements, including special beveling, threading, and end-finishing.
- Cost Efficiency: The coil tube format reduces material waste by up to 15% compared