321/347 Seamless Stainless Steel Coil Tube for Automotive EGR Coolers
Product Overview
The EGR Cooler Coil Tube is a precision-engineered seamless stainless steel tubing product specifically designed for Exhaust Gas Recirculation (EGR) cooling systems in automotive and heavy-duty transportation applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube is purpose-built to endure the most punishing conditions found within modern exhaust gas recirculation systems — where exhaust gases at temperatures ranging from 600°C to 800°C (1,112°F to 1,472°F) are routed through compact heat exchanger coils to reduce NOx emissions before recirculation into the intake manifold.
Unlike conventional heat exchanger tubes that face only thermal stress, EGR cooler coil tubes must simultaneously withstand extreme thermal cycling, aggressive condensation acid corrosion (sulfuric, hydrochloric, and phosphoric acids formed during aftertreatment), and continuous mechanical vibration from engine and exhaust system dynamics. This triple-threat environment demands a tubing solution that integrates superior thermal fatigue resistance, outstanding corrosion durability, and robust structural integrity — all in a coil configuration suitable for compact heat exchanger manufacturing.
Material & Properties
The EGR Cooler Coil Tube is fabricated from austenitic stainless steel grades 321 (UNS S32100) and 347 (UNS S34700), both titanium-stabilized alloys specifically selected for their exceptional resistance to sensitization, thermal fatigue cracking, and high-temperature oxidation. The titanium stabilization eliminates the intergranular corrosion susceptibility that affects standard 304 and 316 grades when exposed to prolonged temperatures above 450°C.
Key Material Properties
- Grade 321 (UNS S32100): Contains 0.2%–0.7% Ti stabilization, offering superior resistance to thermal fatigue cracking at temperatures up to 870°C (1,598°F) and excellent resistance to sulfuric acid condensation corrosion.
- Grade 347 (UNS S34700): Contains 0.6%–1.2% Ti stabilization with enhanced creep strength and superior resistance to intergranular corrosion in the 600°C–900°C (1,112°F–1,652°F) range. Provides improved mechanical properties under sustained high-temperature loading.
- Chromium Content: 17.0%–19.0% minimum, ensuring robust passive film formation and resistance to oxidation and acidic attack.
- Nickel Content: 9.0%–12.0%, providing stable austenitic microstructure and resistance to thermal cycling.
- Carbon Content: ≤0.08% maximum, minimizing carbon availability for carbide precipitation at grain boundaries.
- Maximum Service Temperature: 870°C (1,598°F) for Grade 321; 980°C (1,796°F) for Grade 347.
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 100°C, providing efficient heat transfer in EGR cooler applications.
Performance Under EGR Cooler Conditions
- Thermal Fatigue Resistance: Validated through accelerated thermal cycling tests simulating 10,000+ duty cycles between 20°C ambient and 800°C peak exhaust temperature, with zero evidence of crack initiation at weld or tube walls.
- Condensation Acid Corrosion Resistance: Demonstrated through immersion and spray tests using simulated EGR condensate (pH 2.0–3.5, containing H₂SO₄, HCl, and H₃PO₄), with corrosion rates below 0.02 mm/year (0.0008 in/year).
- Vibration Resistance: Endorsed for continuous operation under harmonic and random vibration spectra typical of diesel and gasoline engine exhaust systems (up to 500 Hz, 20g peak).
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Material Grade | ASTM A268 TP321 / TP347; EN 10216-5 | ASTM A268, EN 10216-5 |
| Tube Type | Seamless coil tube (pre-formed coil configuration) | ISO 1172 |
| Outer Diameter (OD) | 6.35 mm to 25.4 mm (0.250 in to 1.000 in) | ASTM A268 |
| Wall Thickness | 0.50 mm to 2.00 mm (0.020 in to 0.079 in) | ASTM A268 |
| OD Tolerance | ±0.10 mm (±0.004 in) | ASTM A268 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A268 |
| Coil Length | 10 m to 300 m (33 ft to 984 ft) per coil | — |
| Coil Inner Diameter | 150 mm to 500 mm (5.9 in to 19.7 in) | — |
| Min. Bend Radius | 1.5× OD (cold bending) | ISO 1172 |
| Surface Finish | Pickled & passivated; Ra ≤ 0.8 μm (32 μin) | ASTM A268 |
| Maximum Operating Temperature | 800°C (1,472°F) continuous | — |
| Maximum Operating Pressure | Up to 2.5 MPa (363 psi) gauge | — |
| End Condition | Plain ends; optional notched or formed ends | — |
Manufacturing Process
The production of EGR Cooler Coil Tube follows a rigorous, multi-stage manufacturing process designed to ensure dimensional precision, metallurgical integrity, and consistent performance under extreme operating conditions.
- Raw Material Selection: Only certified ingots and billets from approved mills meeting ASTM A268 chemical composition requirements are accepted. Each heat is verified through spectroscopic analysis for Ti, Cr, Ni, C, and S content compliance.
- Hot Rolling & Seamless Piercing: Billets are heated to 1,150°C–1,200°C (2,092°F–2,192°F) and pierced to form seamless hollow sections. Hot rolling reduces wall thickness and OD to near-final dimensions while ensuring uniform grain structure.
- Cold Drawing / Cold Rolling: Tubes undergo cold drawing or cold rolling to achieve precise final dimensions with tight tolerances. This process introduces beneficial strain hardening and refines grain structure for enhanced fatigue resistance.
- Solution Annealing: Tubes are annealed at 1,050°C–1,150°C (1,922°F–2,092°F) in a controlled atmosphere to dissolve carbides, restore full austenitic structure, and eliminate residual stresses from cold working. Rapid quenching prevents sensitization.
- Pickling & Passivation: Tubes are subjected to acid pickling (HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to establish a uniform, protective chromium oxide film essential for corrosion resistance.
- Coil Forming: Annealed tubes are fed through precision coil forming equipment to achieve the required coil configuration with consistent curvature and no kinking or flattening. Coil ID and pitch are controlled to specification.
- Non-Destructive Testing (NDT): Every coil undergoes 100% eddy current testing (ECT) for wall thickness uniformity and internal/external defect detection, supplemented by hydrostatic pressure testing at 3× maximum operating pressure.
- Final Inspection & Packaging: Dimensions are verified using calibrated micrometers and ultrasonic thickness gauges. Each coil is protected with VCI (Volatile Corrosion Inhibitor) paper wrapping, shrink-wrapped, and labeled with full traceability documentation.
Applications
Primary Application: EGR Cooler Systems
The EGR Cooler Coil Tube is the critical heat transfer element within Exhaust Gas Recirculation coolers used in:
- Heavy-Duty Diesel Engines: EGR coolers in trucks, buses, construction equipment, and marine engines (Euro VI / Tier 4 Final / China VI emission standards) where exhaust gases must be cooled from 600°C–800°C before recirculation to reduce combustion peak temperatures and NOx formation.
- Light-Duty Gasoline Engines: High-pressure EGR (HP-EGR) systems in passenger vehicles where compact coil-type coolers must withstand aggressive exhaust chemistry and thermal cycling.
- Off-Highway Equipment: Agricultural machinery, mining equipment, and industrial generators requiring robust EGR cooling under variable duty cycles.
Additional Applications
- Compact automotive oil coolers and transmission coolers
- Aftertreatment system heat exchangers (DPF regeneration circuits)
- Industrial heat recovery units operating at elevated temperatures
- Hydrogen fuel cell thermal management loops
Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd delivers the industry's most validated seamless coil tube solution for EGR cooler applications, combining dual-grade material options with comprehensive thermal fatigue and condensation acid corrosion verification — a combination unmatched in the market.
- Dual-Grade Availability (321/347): Offers customers the flexibility to select Grade 321 for cost-optimized applications or Grade 347 for premium-duty scenarios requiring enhanced creep resistance and higher temperature capability — all from a single, reliable supplier.
- Dual-Validation Protocol: Every production batch undergoes simultaneous thermal fatigue testing (simulating 10,000+ duty cycles) AND condensation acid corrosion testing (simulated EGR condensate exposure for 500+ hours), ensuring the tube performs under the combined stress conditions of real-world EGR operation — not just isolated laboratory tests.
- Seamless Construction: Eliminates weld-related failure points that plague welded coil alternatives, ensuring uniform wall integrity and superior resistance to stress corrosion cracking under thermal cycling.
- Compact Coil Configuration: Delivered in ready-to-use coil form, reducing heat exchanger assembly time by up to 40% compared to straight tube cutting and bending, while minimizing material waste.
- Full Traceability: Each coil is accompanied by a complete material traceability dossier including mill certificates, heat analysis reports, NDT records, and validation test results — meeting OEM audit requirements.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring consistent product excellence:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing operations
- ISO/TS 22163 (IATF 16949) — Automotive industry quality management system, demonstrating capability to supply automotive OEMs and Tier-1 suppliers
- ISO 14001:2015 — Environmental Management System certification
- ASTM A268 Compliance — Full conformance with ASTM A268 for seamless wrought austenitic stainless steel tubing
- EN 10216-5 Compliance — European standard for welded and seamless heat exchanger tubes
- PEP / SAE Material Certifications — Powertrain Emissions Program material qualification documentation
- Third-Party Inspection Available: SGS, Bureau Veritas, or TÜV inspection upon customer request
Testing & Validation Summary
| Test Category | Method | Acceptance Criteria |
|---|---|---|
| Chemical Composition | OES Spectrometry | ASTM A268 Grade 321/347 ranges |
| Mechanical Properties | Tensile & Hardness Testing | ASTM A268 minimum requirements |
| Intergranular Corrosion | ASTM A268 Practice (66°C Acetic Acid) | Pass — no intergranular attack |
| Thermal Fatigue | Accelerated thermal cycling (20°C↔800°C) | Zero cracking after 10,000 cycles |
| Condensation Acid Corrosion | Simulated EGR condensate immersion (pH 2.5) | Corrosion rate < 0.02 mm/year |
| Dimensional Accuracy | OD/wall measurement at 5 locations per coil | Within specified tolerances |
| Internal Defects | 100% Eddy Current Testing | No indications above threshold |
| Pressure Integrity | Hydrostatic test at 3× operating pressure | No leakage; no permanent deformation |
Conclusion
The 321/347 Seamless Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd represents the definitive material solution for next-generation EGR cooler systems. By combining titanium-stabilized austenitic stainless steel with rigorous dual-validation testing protocols and seamless coil manufacturing, this product ensures reliable performance under the combined assault of 600°C–800°C exhaust temperatures, aggressive condensation acid corrosion, and continuous mechanical vibration — meeting and exceeding the requirements of the world's most stringent emission regulations including Euro VI, Tier 4 Final, and China VI.