Stainless Steel Coiltube for Evaporative Condensing Condenser Systems — Power Station Heat Exchanger Coil Unit
Product Overview
The Stainless Steel Coiltube (Product No. 586) is a precision-engineered continuous-wound tubular heat exchange element designed specifically for evaporative condensing condenser systems in thermal power generation facilities. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coiltube serves as the core heat transfer component within condensate recovery and cooling loops, enabling efficient rejection of waste heat from turbine exhaust steam through direct evaporative cooling mechanisms.
Unlike discrete finned tube bundles, the coiltube configuration provides a compact, continuous serpentine geometry that maximizes surface-area-to-volume ratio while minimizing pressure drop across the heat exchange circuit. The design philosophy, as documented in the technical study "Design of Heat Exchanger Coil Units for Evaporative Condensing Condensate Systems in Power Stations", integrates aerodynamic optimization, thermal hydraulic performance, and long-term corrosion resistance into a single integrated component.
Material & Properties
The coiltube is fabricated from austenitic stainless steel grades selected for their superior resistance to condensation-induced corrosion, thermal cycling fatigue, and chemical degradation in power station environments. The primary material specifications are as follows:
- Primary Grade: AISI 304 / 304L (UNS S30400 / S30403) — General-purpose corrosion-resistant austenitic stainless steel
- Enhanced Grade: AISI 316L (UNS S31603) — Molybdenum-bearing variant for chloride-rich or high-temperature condensate environments
- Alternative Grade: TP310S (UNS S31008) — High-temperature service applications exceeding 870°C
| Property | Specification |
|---|---|
| Tensile Strength (ASTM A213) | ≥ 515 MPa (75 ksi) minimum |
| Yield Strength | ≥ 205 MPa (30 ksi) at 0.2% offset |
| Elongation | ≥ 35% minimum in 2 inches (50.8 mm) |
| Thermal Conductivity (25°C) | 16.3 W/(m·K) — Grade 304; 14.6 W/(m·K) — Grade 316L |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /°C (10–500°C) |
| Chromium Content | 18.0–20.0 wt% |
| Nickel Content | 8.0–10.5 wt% |
| Molybdenum Content | 2.0–3.0 wt% (Grade 316L only) |
| Carbon Content | ≤ 0.08% (304L); ≤ 0.03% (316L) |
| Maximum Service Temperature | 870°C (1600°F) — Grade 304/316L; 1093°C (2000°F) — TP310S |
| Corrosion Resistance | PIT (Pitting) Resistance Equivalent Number (PREN) ≥ 19 (304); ≥ 24 (316L) |
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 12.7 mm (1/2") to 50.8 mm (2") — customizable |
| Tube Wall Thickness | 1.0 mm to 3.0 mm (standard); 0.8 mm to 4.0 mm (special order) |
| Coil Pitch (Center-to-Center Spacing) | 15 mm to 40 mm (adjustable per thermal design) |
| Coil Turn Diameter | 200 mm to 1500 mm (based on unit footprint) |
| Coil Length (Unwound) | 5 m to 120 m per continuous coil assembly |
| Heat Transfer Surface Area | Up to 850 m² per coil unit (dependent on geometry) |
| Maximum Operating Pressure | 1.6 MPa (standard); 4.0 MPa (reinforced wall thickness) |
| Design Pressure (ASME VIII Div.1) | 1.5 × Maximum Operating Pressure |
| Design Temperature | –40°C to 450°C (standard range); –196°C to 870°C (special grade) |
| Surface Finish | 2B (Mill Annealed); No. 4 Brushed; Electropolished (Ra ≤ 0.4 μm); Passivated |
| End Condition | Plain end; Beveled end (37°); Flanged connection; Socket-weld (SW) fitting |
| Applicable Standards | ASTM A213 / A269; ASME SA-213; EN 10216-5; GB/T 12771; JIS G3459 |
| Heat Exchanger Design Code | TEMA (Tubular Exchanger Manufacturers Association) Standards, R/C Series |
| Pressure Test Standard | ASME BPV Code Section VIII; Hydrostatic test at 1.5× design pressure |
Manufacturing Process
The production of the stainless steel coiltune follows a rigorous multi-stage manufacturing protocol ensuring dimensional accuracy, metallurgical integrity, and performance reliability:
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or seamless pipe blanks sourced from certified mills (e.g., Outokumpu, Sandvik, Taigang) undergo incoming chemical composition analysis (spectrometric verification) and mechanical property testing (tensile, hardness, impact) per ASTM E415 and ASTM A370.
- Coil Winding & Forming: Precision CNC-controlled cold winding machines form the continuous tube into the specified serpentine geometry. The winding process maintains controlled bending radii (minimum 3× tube OD) to prevent wall thinning and ovality exceeding 1% of nominal OD.
- Welding & Joining: Butt welds and socket-weld connections are executed using Gas Tungsten Arc Welding (GTAW / TIG) with inert gas (argon) shielding. Weld parameters are controlled per AWS D10.9M (Stainless Steel Welding Procedure Specification). Welded joints undergo 100% visual inspection and selective radiographic testing (RT) or dye penetrant inspection (PT) per ASME Section V.
- Heat Treatment & Stress Relief: Solution annealing at 1040–1150°C followed by rapid water quenching eliminates residual stresses from cold forming and welding, restoring full austenitic microstructure and maximum corrosion resistance. Intergranular corrosion resistance is verified per ASTM A262 Practice E (acid solution test).
- Surface Finishing & Passivation: The coil surface undergoes mechanical cleaning, pickling (HNO₃/HF mixture), and chemical passivation (citric acid or nitric acid treatment) to establish a uniform chromium oxide passive film (≥ 10 nm thickness). Final surface roughness is measured per ASTM B463.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the maximum design pressure for a minimum hold time of 30 minutes, with zero leakage permitted. Test records are documented per ASME BPV Code Section VIII Div.1, UG-99(h).
- Non-Destructive Testing (NDT): Eddy current testing (ECT) per ASTM E3097 is performed on the coil body to detect surface and near-surface defects. Ultrasonic testing (UT) per ASTM E164 may be applied to wall thickness verification. All NDT results are archived and traceable to individual coil serial numbers.
- Dimensional Verification & Final Inspection: Coordinate measuring machine (CMM) or laser scanning verifies coil geometry, pitch uniformity, and overall dimensions. Final inspection includes surface quality assessment, marking verification, and packaging preparation per ISO 12944.
Applications
The coiltune is engineered for deployment in demanding industrial heat exchange environments, with primary applications including:
- Thermal Power Station Condensers: Core heat transfer element in evaporative condensing condenser systems, rejecting waste heat from turbine exhaust steam through forced-draft or induced-draft evaporative cooling. Typical capacity: 50 MW to 500 MW per power block.
- Combined Cycle Power Plants (CCPP):strong> Condensing heat recovery units in integrated gas-steam turbine configurations, optimizing Carnot cycle efficiency by maximizing heat rejection at the coldest available sink temperature.
- Industrial Process Cooling: High-temperature process fluid cooling in chemical processing, petrochemical refining, and pulp/paper manufacturing where water conservation is critical.
- Waste Heat Recovery Systems (WHRS):strong> Capturing thermal energy from industrial exhaust streams for district heating or process preheating applications.
- Nuclear Auxiliary Cooling Systems: Emergency cooling loops and containment heat removal systems requiring high reliability and radiation-resistant materials (Grade 316L or TP316LN).
- Marine & Offshore Platforms: Compact heat exchange units for offshore production facilities where space constraints and corrosion resistance (chloride-containing seawater) are critical design drivers.
- Pharmaceutical & Food Processing: Hygienic-grade coiltunes (electropolished, Ra ≤ 0.25 μm) for CIP/SIP-compatible heat exchange in aseptic processing environments.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications and compliance accreditations:
- ISO 9001:2015 — Quality Management Systems (QMS) certification covering all manufacturing and inspection processes
- ISO 14001:2015 — Environmental Management Systems (EMS) certification
- ASME "S" Stamp — Authorization for pressure vessel and pressure component manufacturing per ASME Boiler and Pressure Vessel Code
- EN 10204 Type 3.1 — Third-party inspection and testing certificates for all material batches
- NDT Level II/III Certification — Personnel certified per ISO 9712 / ASNT NDT Level III for all applicable methods (RT, UT, PT, MT, ECT)
- Mill Test Reports (MTR) — Full chemical composition and mechanical property documentation provided with every coil assembly shipment
- Material Traceability System — Complete lot-to-serial-number traceability from raw material mill certification through final product delivery
- TEMA Compliance — Design and manufacturing in accordance with Tubular Exchanger Manufacturers Association Standards (R-Series for refrigeration, C-Series for general process)
- API 5L / API 5CT — For upstream oil and gas applications requiring API monogram compliance
- CE Marking (EU PED 2014/68/EU) — Conformity with European Pressure Equipment Directive for deployment in EU member states
- NB (Notified Body) Inspection — Third-party surveillance inspections by EU Notified Bodies for Category II and above pressure equipment
Unique Selling Points
1. Academic-Validated Design: The coiltune design is informed by published engineering research on evaporative condensing condenser system optimization, ensuring thermal hydraulic performance is validated through computational fluid dynamics (CFD) modeling and experimental heat transfer coefficient correlation (Nusselt number analysis).
2. Continuous Winding Geometry: The seamless serpentine coil design eliminates inter-tube leakage paths inherent in discrete tube bundle configurations, providing superior pressure integrity and long-term reliability in high-cycle power station duty.
3. Modular Scalability: Coiltune assemblies are designed for modular installation and field expansion, enabling capacity augmentation without full system replacement — a critical advantage for power stations undergoing staged capacity upgrades.
4. Corrosion-Durability Advantage: The austenitic stainless steel construction provides a design service life exceeding 25 years in aggressive condensate environments, significantly outperforming carbon steel alternatives requiring frequent replacement and shutdown maintenance.
5. Water Conservation: Evaporative condensing systems utilizing this coiltune technology reduce cooling water consumption by 60–80% compared to conventional once-through or recirculating cooling tower systems — a decisive environmental and economic advantage in water-scarce regions.
6. Full Traceability & Certification: Every coil assembly ships with complete material documentation, NDT records, pressure test certificates, and dimensional verification reports, facilitating seamless integration into owner's quality assurance programs and regulatory compliance filings.
Technical Design Notes
Based on the referenced study "Design of Heat Exchanger Coil Units for Evaporative Condensing Condensate Systems in Power Stations," the following design parameters govern optimal coiltune performance:
- Heat Transfer Coefficient: Target overall heat transfer coefficient (U-value) of 1,200–1,800 W/(m²·K) for steam-to-water condensation duty, achieved through optimized tube diameter, wall thickness, and coil pitch selection.
- Pressure Drop Limitation: Maximum allowable pressure drop across the coil circuit is limited to 0.05 MPa (50 kPa) to minimize pumping power consumption and maintain turbine back-pressure stability.
- Thermal Stress Management: Expansion loops and flexible joint connections are incorporated to accommodate differential thermal expansion between the coil and supporting structure, preventing fatigue failure at weld joints.
- Flow Distribution: Inlet and outlet headers are designed with equal-length branch connections or flow-distributing plates to ensure uniform fluid distribution across all coil turns, maximizing heat transfer effectiveness and minimizing local hot spots.
This product represents the convergence of metallurgical science, thermal engineering, and manufacturing precision — delivering a heat exchange solution engineered for the rigorous demands of modern power generation infrastructure.