Stainless Steel Intermediate Cooler Coil Tube (Coil Tube)
1. Product Overview
The Stainless Steel Intermediate Cooler Coil Tube, manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered heat exchange component designed for use in intermediate cooling systems within industrial compression, refrigeration, and process engineering applications. The coil tube serves as the primary heat transfer medium in intermediate coolers, facilitating the reduction of compressed gas temperatures between compression stages, thereby improving thermodynamic efficiency, reducing energy consumption, and extending the operational lifespan of downstream equipment.
The energy-saving mechanism of the intermediate cooler coil tube is rooted in the fundamental thermodynamic principle that cooling the working fluid between compression stages reduces the compression work required in subsequent stages. By employing high-conductivity stainless steel alloys with corrosion-resistant properties, these coil tubes achieve superior heat transfer performance while maintaining structural integrity under prolonged exposure to aggressive chemical media and elevated temperatures.
2. Material & Properties
2.1 Primary Material Grades
- 304 (UNS S30400 / AISI 304): Austenitic stainless steel with excellent general-purpose corrosion resistance, formability, and weldability. Suitable for moderate-temperature service up to approximately 870 °C in non-oxidizing environments.
- 316 (UNS S31600 / AISI 316): Molybdenum-enhanced austenitic stainless steel offering superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments and chemical processing applications.
- 316L (UNS S31603 / AISI 316L): Low-carbon variant of 316L, designed for improved weldability and resistance to sensitization in welded joints, recommended for cryogenic and high-purity applications.
- 321 (UNS S32100 / AISI 321): Titanium-stabilized austenitic stainless steel with enhanced resistance to intergranular corrosion, suitable for high-temperature service up to 900 °C.
- 310S (UNS S31008 / AISI 310S): High-temperature austenitic stainless steel with superior oxidation resistance, applicable in extreme thermal environments up to 1150 °C.
2.2 Key Physical and Mechanical Properties
| Property | 304 Grade | 316 Grade | 321 Grade | 310S Grade |
|---|---|---|---|---|
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 8.03 |
| Thermal Conductivity (W/m·K, 20 °C) | 16.3 | 14.6 | 16.3 | 14.2 |
| Specific Heat (J/kg·K, 20 °C) | 500 | 500 | 500 | 500 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100 °C) | 17.3 | 16.0 | 17.3 | 18.0 |
| Tensile Strength (MPa, min.) | 515 | 515 | 515 | 515 |
| Yield Strength (MPa, min.) | 205 | 205 | 205 | 205 |
| Elongation (% min.) | 40 | 40 | 40 | 35 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
2.3 Corrosion Resistance Characteristics
- General Corrosion: Resistance to dilute acids, alkalis, and atmospheric conditions; 316/316L grades exhibit enhanced resistance in marine and chloride-rich environments.
- Pitting and Crevice Corrosion: Governed by the Pitting Resistance Equivalent Number (PREN); 316 grade achieves a PREN of approximately 24–26, providing robust protection against localized attack.
- Intergranular Corrosion: Mitigated through titanium stabilization (321) or low-carbon composition (316L), preventing chromium carbide precipitation at grain boundaries in the sensitization temperature range of 425–870 °C.
- Stress Corrosion Cracking (SCC): Austenitic stainless steels demonstrate inherent resistance to chloride-induced SCC, although susceptibility increases above 60 °C in concentrated chloride solutions.
3. Specifications
| Parameter | Specification / Range | Applicable Standard |
|---|---|---|
| Tube Outer Diameter (OD) | 6.0 – 50.8 mm (¼" – 2") | ASTM A213 / GB/T 12771 |
| Tube Wall Thickness | 0.5 – 4.0 mm | ASTM A213 / GB/T 12771 |
| Coil Winding Diameter | 150 – 2000 mm (configurable) | Customer-specific / OEM |
| Coil Length (Developed) | 5 – 500 m (per assembly) | Customer-specific / OEM |
| Surface Finish | 2B, BA (Bright Annealed), Pickled & Passivated, or Custom | ASTM A473 |
| Surface Roughness (Ra) | ≤ 0.8 μm (BA finish); ≤ 1.6 μm (2B finish) | ISO 1302 |
| End Condition | Plain, Beveled, Threaded, Flanged, or Welded Fittings | ASME B1.20.1 / Customer Drawing |
| Design Pressure | Up to 3.0 MPa (typical); up to 6.4 MPa (custom) | ASME BPV Code Section VIII |
| Design Temperature Range | −196 °C to +870 °C (grade-dependent) | ASTM A213 |
| Tolerance (OD) | ±0.05 mm (precision); ±0.10 mm (standard) | ASTM A213 / GB/T 12771 |
| Tolerance (Wall Thickness) | ±10% of nominal (standard); ±5% (precision) | ASTM A213 / GB/T 12771 |
| Winding Tolerance | ±1.5% of nominal coil diameter | ISO 13070 |
4. Manufacturing Process
4.1 Raw Material Preparation
High-purity stainless steel billets or slabs conforming to the specified grade composition are sourced from certified primary producers. Incoming materials undergo spectroscopic verification (Optical Emission Spectrometry, OES) and chemical analysis to confirm compliance with ASTM and GB/T chemical composition requirements.
4.2 Seamless Tube Production
- Piercing: Billets are heated to 1100–1200 °C and pierced through a mandrel to form hollow tubes.
- Rolling / Drawing: Tubes are cold-rolled or warm-drawn through calibrated dies to achieve precise outer diameter and wall thickness dimensions with tight tolerances.
- Pilot Insertion: Internal mandrels (pilots) are inserted to maintain bore geometry during subsequent forming operations.
- Intermediate Annealing: Tubes are solution-annealed at 1050–1150 °C followed by controlled cooling to restore ductility and dissolve precipitation phases.
4.3 Coil Forming
- Coil Winding: Tubes are wound around precision mandrels using CNC-controlled coil winding machines to achieve the specified coil diameter and pitch. The winding process is performed at ambient temperature for standard applications or at elevated temperatures (up to 200 °C) for enhanced formability with thicker-wall tubes.
- Spring-Back Compensation: Numerical control systems compensate for elastic spring-back during winding to ensure dimensional accuracy of the final coil geometry.
- End Sealing: Coil ends are secured using welded saddle plates, mechanical clamps, or threaded fittings to prevent unraveling during transport and installation.
4.4 Heat Treatment and Surface Processing
- Solution Annealing: Final heat treatment at 1050–1150 °C with rapid water quenching to achieve a fully austenitic microstructure free of carbide precipitation.
- Pickling: Immersion in a hydrochloric acid–nitric acid mixed acid solution to remove oxide scale formed during heat treatment.
- Passivation: Treatment with nitric acid or citric acid solution to enrich the surface chromium oxide layer, enhancing passive film integrity and corrosion resistance.
- Electropolishing (Optional): Electrochemical polishing to achieve ultra-smooth surface finish (Ra ≤ 0.4 μm) for sanitary or high-flow applications.
4.5 Quality Inspection
- Dimensional Inspection: Laser scanning and coordinate measuring machine (CMM) verification of OD, wall thickness, coil diameter, and length.
- Non-Destructive Testing (NDT): Eddy current testing for wall thickness and surface defect detection; radiographic testing (RT) or ultrasonic testing (UT) for weld integrity verification.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the design pressure for a minimum hold time of 30 seconds to verify leak-tightness.
- Chemical Analysis: Spectrometric verification of final material composition.
- Microstructural Examination: Metallographic analysis to confirm austenitic grain structure and absence of detrimental phases.
5. Applications
5.1 Intermediate Coolers in Multi-Stage Compression Systems
The primary application of the intermediate cooler coil tube is in multi-stage reciprocating and centrifugal compressor systems. By cooling the compressed gas between stages, the coil tube reduces the specific compression work according to the polytropic compression equation, achieving energy savings of 10–20% compared to uncooled single-stage compression. This is particularly significant in:
- Air and gas compression for industrial processes
- Refrigeration and liquefied natural gas (LNG) systems
- Process gas compression in petrochemical and natural gas processing
5.2 Heat Exchanger Applications
- Shell-and-tube heat exchangers for process cooling
- Plate heat exchangers with welded stainless steel channels
- Double-pipe heat exchangers for high-pressure applications
- Condensers and evaporators in HVAC and refrigeration systems
5.3 Industrial Process Applications
- Petrochemical Industry: Reactor effluent cooling, distillation column condensers, and process fluid temperature control.
- Pharmaceutical Industry: Sanitary-grade heat transfer in CIP (Clean-in-Place) compatible systems for pharmaceutical and bioprocess applications.
- Food and Beverage Industry: Pasteurization, sterilization, and temperature control in hygienic processing lines.
- Power Generation: Steam condensate recovery and feedwater preheating systems.
- Marine Engineering: Seawater-cooled heat exchangers where chloride resistance is critical.
5.4 Energy-Saving Mechanism
The intermediate cooler coil tube reduces the temperature of compressed gas between compression stages, thereby lowering the volumetric flow rate entering the subsequent stage. According to the thermodynamic relationship for multi-stage compression, the total compression work is minimized when the temperature ratio per stage is equal. The coil tube ensures this optimal condition is met, yielding measurable reductions in specific energy consumption (kWh/kg of compressed gas) and extending equipment service life by reducing thermal stress on compressor components.
6. Quality Certifications and Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control. |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices. |
| ISO 45001:2018 | Occupational Health and Safety Management System certification. |
| EN 10204 Type 3.1 | Inspection Certificate based on specific inspection and testing procedures with verification by a designated person. |
| EN 10204 Type 3.2 | Test Report with detailed material and product testing data. |
| ASTM A213 / A269 | Standard specifications for seamless and welded austenitic stainless steel tubes. |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes. |
| GB/T 13296 | Chinese national standard for welded stainless steel tubes. |
| ASME BPV Code Section VIII | American Society of Mechanical Engineers Boiler and Pressure Vessel Code compliance for pressure-containing applications. |
| PED 2014/68/EU | European Pressure Equipment Directive compliance for CE marking. |
| NSF/ANSI 61 |