Stainless Steel Coil Tube for Water Jacket Furnace Applications
Product Code: 1371 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Classification: Industrial Heat Exchanger Components — Helical Coil Tube (盘管)
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Helical Coil Tube or Spiral Coil Tubing) is a specialized tubular component fabricated into a continuous helical or spiral geometry, designed primarily for use in water jacket furnaces (水套炉) within the petroleum refining, petrochemical, and natural gas processing industries. These coil tubes serve as critical heat transfer surfaces, carrying process fluids — including crude oil, natural gas, refinery streams, and heat transfer media — through the furnace combustion zone while the surrounding water jacket absorbs excess radiant heat, thereby protecting the tube material from thermal degradation.
Unlike straight pipe sections, coil tubes leverage their helical configuration to achieve compact volumetric heat exchange, enhanced convective heat transfer coefficients, and superior resistance to thermal cycling fatigue. The continuous spiral geometry eliminates the need for intermediate weld joints along the tube length, reducing potential leak points and improving long-term operational reliability.
Unique Selling Points
- Enhanced Heat Transfer Efficiency: The helical geometry induces secondary flow (Dean vortices) within the tube, increasing the internal heat transfer coefficient by 20–40% compared to equivalent straight pipe sections.
- Compact Footprint: Achieves equivalent heat exchange capacity in a fraction of the volume required by straight-tube bundles, optimizing furnace design and reducing capital expenditure.
- Thermal Fatigue Resistance: The continuous spiral configuration distributes thermal stresses uniformly, extending service life under cyclic heating and cooling conditions typical of furnace operations.
- Reduced Weld Integrity Risk: Fewer longitudinal weld seams per unit length of heat exchange surface, minimizing failure points in high-temperature service.
- Customizable Geometry: Coil diameter, pitch, tube count, and cross-sectional profile can be tailored to specific furnace design parameters and process requirements.
2. Material & Properties
2.1 Base Material Grades
Coil tubes for water jacket furnace applications are manufactured from a range of stainless steel and alloy steel grades, selected based on the operating temperature, fluid composition, and corrosion environment:
| Material Grade | UNS Designation | Equivalent Standard | Max. Operating Temperature (°C) | Primary Application |
|---|---|---|---|---|
| 304 / 304L | S30400 / S30403 | ASTM A213 TP304 | 870 | General corrosion-resistant heat exchange |
| 316 / 316L | S31600 / S31603 | ASTM A213 TP316 | 870 | Chloride-containing process streams |
| 310 / 310S | S31000 / S31008 | ASTM A213 TP310 | 1150 | High-temperature furnace tubes |
| 321 | S32100 | ASTM A213 TP321 | 1090 | High-temperature oxidation resistance |
| 347 | S34700 | ASTM A213 TP347 | 1090 | Stabilized austenitic service |
| 904L | S31803 (approx.) | ASTM A213 TP904L | 650 | Highly corrosive environments |
| 316Ti | S31635 | ASTM A213 TP316Ti | 870 | Welding fatigue-critical applications |
2.2 Mechanical Properties (Annealed Condition, Representative)
| Property | 304L | 316L | 310S |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 485 | ≥ 485 | ≥ 515 |
| Yield Strength (MPa) | ≥ 170 | ≥ 170 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 35 |
| Density (g/cm³) | 7.93 | 8.00 | 8.00 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 14.6 | 22.4 |
| Thermal Expansion Coefficient (×10⁻⁶/°C, 20–100°C) | 17.3 | 16.0 | 19.0 |
2.3 Corrosion Resistance
- Pitting Resistance: 316L and 316Ti grades offer superior resistance to pitting and crevice corrosion in chloride-bearing environments, with PREN (Pitting Resistance Equivalent Number) values of ≥ 24 and ≥ 26, respectively.
- Intergranular Corrosion Resistance: Low-carbon (L) grades maintain carbon content ≤ 0.030% to prevent chromium carbide precipitation at grain boundaries during welding and high-temperature exposure.
- Crevice Corrosion: Enhanced by molybdenum (Mo) and niobium (Nb) / titanium (Ti) stabilization elements in grades 316, 316Ti, and 347.
- High-Temperature Oxidation: 310S and 321 grades provide excellent resistance to scaling and oxidation up to 1100°C in oxidizing atmospheres.
3. Specifications
3.1 Tube Dimensions
| Parameter | Typical Range | Notes |
|---|---|---|
| Tube Outer Diameter (OD) | Φ14 mm – Φ102 mm | Custom sizes available upon request |
| Tube Wall Thickness | 1.5 mm – 12.0 mm | Selected based on pressure rating and temperature |
| Coil Mean Diameter | 200 mm – 3,000 mm | Determined by furnace geometry and support structure |
| Coil Pitch (Helix) | 20 mm – 200 mm | Affects heat transfer rate and pressure drop |
| Tube Length (Straight Equivalent) | 5 m – 200 m | Depends on coil diameter, pitch, and number of turns |
| Number of Turns | 10 – 500+ | Calculated per furnace heat duty requirement |
| End Preparation | Plain, Beveled, Threaded, or Flanged | Per customer specification |
| Tolerance on OD | ±0.2 mm (Standard) / ±0.1 mm (Precision) | Per ASTM A213 / EN 10216 |
| Tolerance on Wall Thickness | ±10% (Standard) / ±7.5% (Precision) | Per applicable manufacturing standard |
3.2 Applicable Standards
- ASTM A213: Standard Specification for Seamless Austenitic Stainless Steel Tube for High-Temperature Service
- ASTM A269: Standard Specification for Seamless and Wrought Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- EN 10216-5: Seamless heat-resistant steel tubes — Part 5: Technical delivery conditions for non-alloy and alloy tubes for high-temperature service
- GB/T 14976: Chinese National Standard — Seamless steel tubes of stainless steel
- ASME BPV VIII: Boiler and Pressure Vessel Code — Division 1, Section VIII (where applicable for pressure-containing coil assemblies)
- API 5CT: American Petroleum Institute specification (for oil and gas industry coil applications)
4. Manufacturing Process
4.1 Process Flow Diagram
- Raw Material Procurement: Selection of certified seamless stainless steel tubes (or cold-drawn tubes) conforming to ASTM A213 or equivalent standards. Each heat lot is accompanied by a Mill Test Certificate (MTC) verifying chemical composition, mechanical properties, and heat treatment history.
- Incoming Inspection: Dimensional verification, visual surface inspection for defects (pits, seams, inclusions), and hydrostatic pressure testing per ASTM A213 requirements. Ultrasonic testing (UT) may be applied for wall thickness verification on critical applications.
- Coil Forming: The straight tube is passed through a series of precision rollers (cold coiling) or heated and formed (hot coiling) to achieve the specified helical geometry. Key parameters controlled during forming include:
- Coil mean diameter (CMD)
- Pitch (axial advance per revolution)
- Number of turns
- Springback compensation
- Post-Forming Stress Relief: For cold-formed coils, stress relief annealing at 650–850°C followed by controlled cooling is performed to relieve residual stresses introduced during the coiling process, preventing distortion during subsequent welding and service.
- Welding of Coil Sections (if applicable): When the required coil length exceeds the maximum available straight tube length, multiple coil segments are welded together. This is the critical process addressed in the associated technical literature ("Welding of Water Jacket Furnace Coil Tubes"):
- Welding Process: Gas Tungsten Arc Welding (GTAW / TIG) is the preferred method for stainless steel coil tube welding due to its precise heat input control, minimal spatter, and superior weld quality. Shielded Metal Arc Welding (SMAW) or Metal Active Gas Welding (MAG) may be used for thicker wall sections.
- Filler Material: Consumable electrodes and wire matching the base metal grade (e.g., ER308L for 304L base metal, ER316L for 316L base metal, ER310 for 310S base metal) per AWS A5.9 / AWS A5.4 specifications.
- Pre-Weld Preparation: Beveling of tube ends to V-groove or U-groove configuration per ASME Section IX requirements. Surface cleaning with mechanical abrasion and solvent degreasing to remove oxide layers and contaminants.
- Shielding Gas: High-purity argon (≥ 99.99% Ar) or argon-helium mixtures (e.g., 75% Ar / 25% He) for enhanced penetration. Back-purging with argon on the internal surface is essential to prevent internal oxidation and sensitization.
- Heat Input Control: Strict limitation of heat input (typically 0.5–1.5 kJ/mm) to minimize the heat-affected zone (HAZ) width and prevent intergranular corrosion sensitization in the 450–850°C temperature range.
- Interpass Temperature: Maintained below 150°C for low-carbon (L) grades to reduce the risk of carbide precipitation.
- Weld Post-Treatment:
- Pickling: Immersion in a mixed acid solution (typically HNO₃/HF or HNO₃/HCl) to remove heat-tinted oxide layers from the weld zone, restoring the passive chromium oxide film.
- Passivation: Treatment with nitric acid or citric acid solution to re-establish the protective Cr₂O₃ passive film on the weld surface.
- Stress Relief Annealing: Optional solution annealing at 1050–110