Stainless Steel Coil Tube — Thermal Oil Heater Grade (Coiltube Series 1503)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous tubular product designed specifically for high-temperature heat transfer applications, particularly within Coil-Type Thermal Oil Heaters (also known as Coiled Tubular Heat Carrier Furnaces). The product is supplied in continuous coil form, enabling seamless integration into complex heating circuits without the need for field welding at transition joints, thereby minimizing potential failure points in high-pressure, high-temperature service environments.
Based on the optimization design principles outlined in the referenced study "Optimization Design of Coil-Type Thermal Oil Heaters", this coil tube product is engineered to maximize heat transfer efficiency while maintaining structural integrity under sustained thermal cycling, pressure fluctuations, and chemical exposure conditions inherent to thermal fluid systems.
2. Material & Properties
2.1 Base Material Grades
The coil tube is fabricated from premium-grade austenitic and super-austenitic stainless steels, selected to ensure superior oxidation resistance, thermal stability, and mechanical strength at elevated operating temperatures:
- ASTM A269 / A213 — Type 304 (UNS S30400): General-purpose heat transfer service up to 870°C (1,600°F); excellent corrosion resistance and formability.
- ASTM A269 / A213 — Type 316 (UNS S31600): Enhanced chlorides and pitting resistance; suitable for aggressive thermal fluid environments; operating range up to 870°C (1,600°F).
- ASTM A269 / A213 — Type 316L (UNS S31603): Low-carbon variant for superior weldability and resistance to intergranular corrosion; preferred for applications requiring extensive welding.
- ASTM A269 / A213 — Type 321 (UNS S32100): Titanium-stabilized; excellent resistance to thermal fatigue and scaling; suitable for sustained high-temperature thermal cycling.
- ASTM A269 / A213 — Type 347 (UNS S34700): Niobium-stabilized; comparable to 321 with enhanced creep resistance; ideal for continuous high-temperature operation.
- ASTM A269 — Type 310S (UNS S31008): High-temperature grade with exceptional oxidation and scaling resistance; operating range up to 1,150°C (2,100°F).
2.2 Key Physical and Mechanical Properties
- Density: 8.0 g/cm³ (0.29 lb/in³)
- Thermal Conductivity (at 100°C): 16.3 W/(m·K) for Type 304; 14.6 W/(m·K) for Type 316
- Linear Thermal Expansion (20–100°C): 17.3 × 10⁻⁶ /°C
- Specific Heat Capacity: 0.50 J/(g·°C)
- Tensile Strength (Annealed): ≥ 515 MPa (74,700 psi) for Type 304; ≥ 515 MPa for Type 316
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation: ≥ 40% (minimum)
- Maximum Service Temperature: 870°C (Type 304/316/321/347); 1,150°C (Type 310S)
- Operating Pressure Range: Up to 6.0 MPa (870 psi) depending on wall thickness and coil configuration
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Category | Stainless Steel Coil Tube (Continuous Coiled Tubing) | — |
| Product Code | 1503 — Coiltube Series | — |
| Outer Diameter (OD) | 1/8" to 6" (3.18 mm – 152.4 mm) | ASTM A269 / A213 |
| Wall Thickness | 0.5 mm – 12.7 mm (Schedule 5S to Schedule 40 and custom) | ASTM A269 / ASME B36.19M |
| Coil Diameter | Custom — typically 500 mm to 2,000 mm (19.7" – 78.7") | Manufacturer Specification |
| Coil Length per Spool | 50 m – 500 m (164 ft – 1,640 ft) per coil; customizable | — |
| Surface Finish | Commercial (No. 1), 2B, BA (Bright Annealed), or Polished (220–400 grit) | ASTM A480 / A485 |
| End Condition | Plain, Beveled, or Threaded (BSP/NPT); custom cutting available | — |
| Tolerance — OD | ±0.5% (standard); ±0.3% (precision) | ASTM A269 |
| Tolerance — Wall Thickness | ±10% (standard); ±5% (precision) | ASTM A269 |
| Heat Treatment | Solution Annealed and Pickled | ASTM A269 |
| Maximum Operating Temperature | Up to 870°C (Type 304/316); Up to 1,150°C (Type 310S) | — |
| Maximum Operating Pressure | Up to 6.0 MPa (870 psi), subject to wall thickness | ASME B31.3 |
| Corrosion Resistance | Equivalent to or exceeding 304/316 grade standards; pitting resistance number (PREN) ≥ 19 for 316L | ASTM G48 |
| Standards Compliance | ASTM A269, ASTM A213, ASME SA-269, GB/T 12771, GB/T 21832 | — |
| Manufacturing Standard | ISO 9001:2015, ISO 3834 (Welding Quality) | — |
| Material Certifications | EN 10204 Type 3.1 (Mill Test Certificate); MTC with full chemical and mechanical analysis | EN 10204 |
| Minimum Order Quantity | Negotiable — single coil or bulk shipment | — |
| Lead Time | 15–30 days (standard); 30–45 days (custom specifications) | — |
| Packaging | Export-grade wooden crate or steel frame packaging with moisture-proof inner wrapping | — |
| Country of Origin | China (People's Republic) | — |
4. Manufacturing Process
The production of the Coiltube Series 1503 adheres to a rigorously controlled multi-stage manufacturing process, ensuring dimensional accuracy, metallurgical homogeneity, and surface integrity:
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Raw Material Procurement and Inspection:
Virgin stainless steel billets or continuous casting slabs are sourced from certified mills (e.g., Outokumpu, Nippon Steel, Taigang, or equivalent). Each batch undergoes incoming inspection including Positive Material Identification (PMI) via X-ray Fluorescence (XRF) spectrometry and spectrographic analysis to verify chemical composition against ASTM/EN specifications.
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Hot Rolling:
Steel slabs are reheated to 1,150°C–1,250°C (2,094°F–2,282°F) and hot-rolled into seamless tube blanks. The rolling process is optimized to achieve uniform microstructure and minimize internal defects. The hot-rolled tube undergoes intermediate annealing to relieve residual stresses.
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Piercing and Elongation:
The hot-rolled blanks are pierced through a mandrel to form hollow tubes. The tube is then elongated to the target outer diameter and wall thickness through controlled rolling or plug drawing, achieving the specified dimensional tolerances.
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Cold Drawing / Cold Rolling:
For precision dimensions and superior surface finish, the tubes undergo cold drawing through a hardened die and mandrel assembly. This process achieves:
- Dimensional tolerances as tight as ±0.3% for OD
- Wall thickness tolerances of ±5%
- Improved mechanical properties through work hardening (optional)
- Superior surface finish (2B or BA quality)
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Solution Annealing and Pickling:
The tubes are solution annealed at 1,050°C–1,150°C (1,922°F–2,094°F) followed by rapid water quenching. This eliminates cold work stresses, restores full ductility, and homogenizes the microstructure. Subsequent acid pickling (nitric/hydrofluoric acid blend) removes surface oxide scale, revealing the clean, corrosion-resistant austenitic surface.
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Coiling Operation:
The annealed and pickled tubes are wound into coils of specified diameter using a controlled-tension coiling head. The coiling process is engineered to prevent:
- Permanent deformation or ovality
- Surface scratches or marking
- Residual stress concentration at coil transitions
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Hydrostatic Pressure Testing:
Every coil is subjected to 100% hydrostatic pressure testing at 1.5 times the maximum design operating pressure (typically 1.5 × 6.0 MPa = 9.0 MPa / 1,305 psi) for a minimum dwell time of 10 seconds. This ensures the integrity of the entire tube length without any leaks, cracks, or deformation.
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Non-Destructive Testing (NDT):
Depending on the application criticality, additional NDT methods may be applied:
- Eddy Current Testing: Detection of surface and near-surface defects
- Ultrasonic Testing (UT): Detection of internal laminations and wall thickness verification
- Magnetic Particle Inspection (MPI): Surface defect detection (where applicable)
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Final Inspection and Certification:
Each coil is subjected to final dimensional inspection, surface quality assessment, and chemical/mechanical property verification. A comprehensive Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1 is issued, documenting full chemical composition, mechanical test results, heat treatment records, and NDT findings.
5. Applications
The Coiltube Series 1503 is specifically optimized for the following industrial applications:
5.1 Coil-Type Thermal Oil Heaters (Primary Application)
As referenced in the optimization design study, this coil tube is the core heat exchange element in Coil-Type Thermal Oil Heaters (also termed Coiled Tubular Heat Carrier Furnaces). The continuous coil configuration provides:
- Maximized Heat Transfer Surface Area: The coiled geometry achieves a high surface-to-volume ratio, enabling efficient heat absorption from combustion gases and transfer to the thermal oil medium.
- Reduced Thermal Stress Concentration: The continuous coil eliminates the need for butt welds between straight tube sections, reducing stress risers and potential failure points under thermal cycling.
- Optimized Fluid Dynamics: The curved geometry promotes turbulent flow of the thermal oil, enhancing convective heat transfer coefficients.
- Space-Efficient Installation: The compact coil form factor reduces the footprint of the heater unit compared to equivalent straight-tube designs.
5.2 Additional Applications
- Chemical Processing Plants: Heat exchangers, reboilers, and distillation column internals requiring corrosion-resistant, high-temperature tubing.
- Petrochemical and Refining Industries: Process heating circuits, vaporizers, and thermal oil loop piping.
- Pharmaceutical Manufacturing: Sterilization equipment, jacketed reactors, and CIP (Clean-in-Place) heating systems requiring BA or polished surface finishes.