Spiral Coil Tube for Large-Scale Industrial Heating Furnaces
Product Model: JX-CT Series Spiral Coil Tube | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Reference No.: 1542
1. Product Overview
The JX-CT Series Spiral Coil Tube is a precision-engineered stainless steel tube product specifically designed for integration into large-scale industrial heating furnaces, process heating systems, and heat exchanger assemblies. Unlike conventional straight or bent tubes, spiral coil tubes offer a significantly higher surface-area-to-volume ratio within a compact footprint, making them indispensable for applications requiring intense thermal exchange under spatial constraints.
These coil tubes are manufactured through advanced helical forming techniques and subsequently subjected to on-site heat treatment procedures to ensure metallurgical integrity, dimensional stability, and long-term service reliability under extreme thermal cycling conditions. The product line encompasses a wide range of coil diameters, pitch configurations, and wall thicknesses to accommodate diverse process parameters across the petrochemical, power generation, and metallurgical industries.
2. Material & Properties
2.1 Available Material Grades
- 304 / 304L (UNS S30400 / S30403): General-purpose austenitic stainless steel offering excellent corrosion resistance and formability. Suitable for moderate-temperature service up to approximately 870°C (1600°F).
- 316 / 316L (UNS S31600 / S31603): Molybdenum-enhanced austenitic grade providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments. Service temperature up to approximately 870°C (1600°F).
- 321 / 321H (UNS S32100 / S32109): Titanium-stabilized austenitic steel with excellent resistance to intergranular corrosion and thermal cracking. Recommended for sustained service temperatures between 650°C and 1100°C (1200°F–2000°F).
- 347 / 347H (UNS S34700 / S34709): Niobium-stabilized austenitic grade suitable for high-temperature applications up to approximately 1150°C (2100°F) with outstanding resistance to sensitization.
- 310 / 310S (UNS S31000 / S31008): High-chromium, high-nickel austenitic steel designed for extreme-temperature environments up to 1150°C (2100°F), with exceptional oxidation and scaling resistance.
2.2 Key Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 / 321H | 347 / 347H | 310 / 310S |
|---|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 515 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 8.00 | 8.00 | 8.00 | 8.00 | 8.00 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 16.3 | 14.6 | 14.6 | 26.2 |
| Thermal Expansion (μm/m·K, 100°C) | 17.2 | 16.0 | 17.2 | 17.2 | 18.0 |
| Maximum Service Temperature (°C) | 870 | 870 | 1100 | 1150 | 1150 |
2.3 Chemical Composition (Typical, wt%)
| Grade | C | Mn | S | P | Cr | Ni | Mo | Ti | Nb |
|---|---|---|---|---|---|---|---|---|---|
| 304 | ≤ 0.08 | ≤ 2.0 | ≤ 0.03 | ≤ 0.045 | 18.0–20.0 | 8.0–10.5 | — | — | — |
| 316 | ≤ 0.08 | ≤ 2.0 | ≤ 0.03 | ≤ 0.045 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — | — |
| 321 | ≤ 0.08 | ≤ 2.0 | ≤ 0.03 | ≤ 0.045 | 17.0–19.0 | 9.0–12.0 | — | 5×C–0.70 | — |
| 347 | ≤ 0.08 | ≤ 2.0 | ≤ 0.03 | ≤ 0.045 | 17.0–19.0 | 9.0–13.0 | — | — | 9×C–1.00 |
| 310 | ≤ 0.20 | ≤ 2.0 | ≤ 0.03 | ≤ 0.045 | 24.0–26.0 | 19.0–22.0 | — | — | — |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ14 mm – Φ159 mm | ASTM A213 / A269 |
| Wall Thickness | 0.5 mm – 6.0 mm | ASTM A213 / A269 |
| Coil Mean Diameter (CMD) | Φ200 mm – Φ3,000 mm (customizable) | Project-specific |
| Coil Pitch (Center-to-Center) | 15 mm – 150 mm (adjustable) | Project-specific |
| Coil Length (Developed Length) | Up to 12,000 mm per continuous coil | Project-specific |
| Number of Coils per Assembly | 1 – 500 (configurable) | Project-specific |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm); Polished (Ra ≤ 0.4 μm) available | ASTM A403 |
| End Condition | Plain, Beveled, Threaded, or Weld Prep | ASME B1.20.1 |
3.2 Tolerance Standards
| Dimension | Tolerance |
|---|---|
| Outer Diameter | ± 0.05 × OD (or ± 0.5 mm, whichever is greater) |
| Wall Thickness | ± 10% of nominal (or ± 0.05 mm, whichever is greater) |
| Coil Diameter | ± 1.0% of nominal CMD |
| Coil Pitch | ± 0.5 mm |
| Straightness (per end section) | ≤ 1.0 mm/m |
3.3 Applicable Standards & Codes
- ASTM A213: Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-Temperature Service
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for Chemical and Heat-Transfer Applications
- ASTM A213/A213M: Metric equivalent for international procurement
- ASME BPVC Section I & VIII: Boiler and Pressure Vessel Code
- EN 10216-5: Non-alloy and alloy steel tubes for pressure purposes — Heat-resistant austenitic stainless steels
- GB/T 12771: Chinese National Standard for Stainless Steel Tubes for Heat Exchange and Heat Transfer
- ISO 3506: Stainless steel tubes for general purposes
4. Manufacturing Process
4.1 Process Flow Summary
- Raw Material Procurement & Inspection: Hot-rolled or cold-rolled stainless steel strip/skew-butt seamless pipe stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification), mechanical testing, and visual inspection to verify compliance with the specified grade and condition.
- Dimensional Cutting & End Preparation: Raw tube stock is cut to required developed lengths using precision plasma or mechanical sawing. End faces are deburred, chamfered, and cleaned to prepare for subsequent forming and welding operations.
- Helical Coiling / Spiral Forming: The straight tube is fed into a programmable helical coiling machine (also referred to as a spiral tube former). The forming head rotates the tube around a mandrel of the specified Coil Mean Diameter (CMD) while advancing it longitudinally at a controlled rate to achieve the desired pitch. Modern CNC-controlled coiling systems ensure uniform curvature, minimize plastic deformation, and prevent wall thinning or ovality exceeding tolerance limits.
- Intermediate Heat Treatment (Solution Annealing): After coiling, the tube assembly is subjected to solution annealing at temperatures between 1010°C and 1150°C (depending on grade), followed by rapid air or water quenching. This process dissolves carbide precipitates, restores full austenitic microstructure, relieves forming-induced residual stresses, and maximizes corrosion resistance and ductility.
- Pickling & Passivation: The annealed coil tube is immersed in a mixed acid bath (typically HNO₃ + HF) to remove oxide scale and mill scale. Subsequently, a nitric acid passivation treatment establishes a chromium-rich passive film on the surface, ensuring long-term corrosion protection.
- Welding & Assembly: Individual coil sections are welded to headers, manifolds, or support structures using Gas Tungsten Arc Welding (GTAW/TIG) or Metal Active Gas Welding (MAG) with appropriate filler metals (e.g., ER308L, ER316L, ER321, ER347, ER310). Weld procedures are qualified in accordance with ASME Section IX or AWS D1.6.
- On-Site Heat Treatment (Post-Weld Heat Treatment — PWHT): For large-scale furnace installations, coil tube assemblies are often transported to the job site and integrated into the furnace structure. In-situ post-weld heat treatment is then performed using induction