Stainless Steel Coil Tube — Joint Station Large Tank Heating Coil Tube
Product Overview
The Stainless Steel Coil Tube (Product No. 731) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heating element designed for integration into large-capacity storage tanks at oil and gas joint stations (joint processing facilities). This coil tube product represents the culmination of advanced metallurgical research focused on material selection optimization and structural design improvement for heating applications in demanding industrial environments.
Unlike conventional straight-tube heat exchangers, coil tubes leverage the inherent geometric advantages of a helical or spiral configuration to maximize heat transfer surface area within a confined volume. The coil tube is typically installed internally within large tanks (often exceeding 5,000 m³ in capacity) where heated transfer of viscous hydrocarbons, crude oil, or condensate is required to maintain adequate fluidity for downstream processing, transportation, and pipeline injection.
This product line has been specifically optimized through systematic research into material-property correlations, thermal stress analysis, and structural integrity under cyclic thermal loading conditions encountered in continuous industrial operation.
Material & Properties
The selection of stainless steel grade for joint station heating coil tubes is governed by a multi-criteria optimization framework that balances thermal conductivity, corrosion resistance, mechanical strength at elevated temperatures, and cost-effectiveness. The following grades are typically evaluated and recommended:
Primary Material Grades
- Austenitic Stainless Steel — 304 (UNS S30408 / 06Cr19Ni10): The baseline material offering excellent general corrosion resistance, good formability, and adequate thermal conductivity. Suitable for non-chloride environments with moderate temperature exposure.
- Austenitic Stainless Steel — 316 (UNS S31608 / 06Cr17Ni12Mo2): Preferred grade for applications involving chloride-containing media (e.g., crude oil with H₂S and Cl⁻ content). The addition of 2–3% Molybdenum significantly enhances pitting and crevice corrosion resistance.
- Super-Austenitic Stainless Steel — 316L (UNS S31603 / 022Cr17Ni12Mo2): Low-carbon variant (C ≤ 0.03%) recommended where intergranular corrosion resistance is critical, particularly in environments susceptible to sensitization at elevated operating temperatures (450–850°C range).
- Duplex Stainless Steel — 2205 (UNS S32205 / S31803): Selected for high-pressure, high-chloride, and high-temperature differential applications. Offers approximately double the yield strength of 316L with superior resistance to chloride stress corrosion cracking (Cl-SCC).
Key Material Properties
| Property | 304 (UNS S30408) | 316L (UNS S31603) | Duplex 2205 (UNS S32205) |
|---|---|---|---|
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 | 13.0 |
| Yield Strength (MPa, 20°C) | ≥ 205 | ≥ 170 | ≥ 450 |
| Tensile Strength (MPa) | 515–720 | 485–620 | 620–800 |
| Maximum Operating Temperature (°C) | 870 | 870 | 350 (continuous) |
| PREN (Pitting Resistance Equivalent Number) | 19 | 25 | 34 |
| Chloride SCC Resistance | Moderate | Good | Excellent |
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Designation | Coil Tube — Joint Station Heating Type |
| Product Number | 731 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Outer Diameter (OD) | Φ 25 mm – Φ 89 mm (customizable) |
| Wall Thickness | 1.5 mm – 4.0 mm (tolerance ±10%) |
| Coil Diameter (Helix) | Φ 300 mm – Φ 2,000 mm (as designed) |
| Coil Pitch | 20 mm – 100 mm (optimized for heat transfer) |
| Tube Length (per coil) | 10 m – 50 m (continuous coil) |
| Applicable Standards | ASTM A213 / ASME SA-213 / GB/T 14976 / GB/T 13296 |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm) |
| Heat Treatment | Solution Annealed at 1050–1100°C, followed by rapid water quench |
| Maximum Operating Temperature | ≤ 350°C (design dependent) |
| Design Pressure | Up to 2.5 MPa (heating medium side) |
| Corrosion Allowance | ≥ 0.5 mm (for service life extension) |
Manufacturing Process
The production of high-integrity coil tubes for joint station heating applications follows a rigorous multi-stage manufacturing protocol:
- Raw Material Procurement & Inspection: Certified stainless steel seamless tubes or welded tubes are sourced from approved mills. Incoming material undergoes full spectrographic analysis (PMI — Positive Material Identification), mechanical property verification, and ultrasonic flaw detection (UT) per ASTM A999.
- Dimensional Preparation: Tubes are cut to specified lengths and undergo end-preparation (beveling, deburring) to ensure uniformity prior to coil forming.
- Coil Forming / Helical Bending: Using computerized numerical control (CNC) coil forming machinery, straight tubes are precisely bent into the designed helical geometry. The forming process is executed at controlled temperatures (cold-forming for OD ≤ 50 mm; warm-forming for larger diameters) to avoid work-hardening effects and residual stress concentration.
- Heat Treatment (Post-Forming): Cold-formed coils undergo solution annealing at 1050–1100°C followed by rapid quenching to restore full austenitic microstructure, eliminate residual stresses introduced during forming, and maximize ductility.
- Pickling & Passivation: Chemical pickling removes oxide scale; subsequent passivation treatment forms a stable chromium oxide (Cr₂O₃) protective film on the surface to ensure optimal corrosion resistance.
- Welding & Fabrication: Coil tube segments are joined to inlet/outlet headers via orbital TIG (Tungsten Inert Gas) welding or pulsed arc welding. Weld procedures are qualified per ASME Section IX or AWS D10.9.
- Non-Destructive Testing (NDT): Completed assemblies undergo:
- Visual inspection (VT) per ASME Section V, Article 1
- Penetrant testing (PT) on all welds
- Hydrostatic pressure testing at 1.5× design pressure
- Random ultrasonic testing (UT) for wall thickness verification
- Final Inspection & Packaging: Dimensional verification, surface quality assessment, and protective packaging for shipping to project site.
Applications
The stainless steel coil tube is primarily deployed in the following industrial scenarios:
- Joint Station Large Tank Heating: Internal heating of crude oil, heavy oil, condensate, and bitumen storage tanks at oil and gas joint processing stations to maintain fluid viscosity within transportable limits.
- Oil & Gas Processing Facilities: Heating of upstream production separators, buffer tanks, and transfer tanks where thermal management is essential for process continuity.
- Chemical Processing Plants: Corrosive medium heating in chemical reactors, mixers, and holding tanks where stainless steel corrosion resistance is mandatory.
- Marine & Offshore Applications: Seawater-resistant heating elements for offshore platform tank systems.
- Power Generation: Auxiliary heating systems in thermal power plants for feedwater preheating and condensate warming.
Structural Optimization Advantages
Research findings from the "Joint Station Large Tank Heating Coil Tube Material Selection Optimization and Structural Optimization Research and Application" study demonstrate that the optimized coil tube design offers:
- 30–50% reduction in heat transfer area compared to conventional flat-tube heat exchangers for equivalent thermal duty
- Enhanced natural convection due to helical geometry promoting fluid circulation within the tank
- Reduced thermal stress concentration at tube-to-header junctions through optimized transition geometry
- Extended service life (target: ≥ 10 years) through proper material selection matched to the specific corrosive environment
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications ensuring product compliance with international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- API Q1 (API Spec Q1) — Quality Management System for Oil and Gas Industry (where applicable)
- NADCAP — National Aerospace and Defense Contractors Accreditation Program (for specialized heat treatment processes)
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- ASME "U" Stamp — Authorized for fabrication of pressure vessels and components (where certified)
- Material Traceability: Full mill test certificates (MTC) per EN 10204 Type 3.1 or ASTM A999 for all supplied material
Unique Selling Points
1. Research-Driven Material Optimization: Each coil tube design is backed by systematic metallurgical research correlating material grade selection with actual operating conditions (temperature, medium composition, pressure), ensuring optimal performance-to-cost ratio.
2. Geometry-Optimized Heat Transfer: Proprietary structural optimization methods maximize the heat transfer coefficient while minimizing pumping power requirements and mechanical vibration risks in large tank installations.
3. Full Lifecycle Reliability: From raw material certification through NDT verification to post-installation support, the product lifecycle is managed to ensure minimum unplanned downtime and maximum operational safety.
4. Customization Capability: Flexible design parameters (OD, wall thickness, coil diameter, pitch, length) allow precise adaptation to specific tank dimensions, thermal loads, and spatial constraints at the installation site.
5. Corrosion-Resistant Engineering: Material selection protocols incorporate chloride stress corrosion cracking (Cl-SCC) risk assessment, ensuring long-term integrity even in aggressive hydrocarbon service environments containing dissolved water, H₂S, CO₂, and chlorides.
Document Classification: Technical Product Specification — Literature Study Reference Series
Product Reference: No. 731 | Stainless Steel Coil Tube for Joint Station Large Tank Heating
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)