High-Salt Wastewater Evaporator Heat Exchange Coil Tubes — 2507 / Titanium Grade
Product Overview
The High-Salt Wastewater Evaporator Heat Exchange Coil Tube is a specialized stainless steel coil tube engineered for the most aggressive wastewater treatment environments, specifically designed for multi-effect evaporators (MEE) and mechanical vapor recompression (MVR) systems handling extremely high-chloride industrial effluent. Developed by Wenzhou Jixing Metal Materials Co., Ltd., this product addresses the unique challenges posed by chloride concentrations exceeding 50,000 ppm, where conventional austenitic stainless steels suffer catastrophic pitting and crevice corrosion.
Unlike standard heat exchanger tubes, this coil tube is purpose-built to withstand simultaneous thermal stress, boiling point elevation (BPE), and severe mineral scaling — three phenomena that compound to accelerate degradation in high-salinity evaporation cycles. The product integrates a forced circulation anti-clogging design and online cleaning (CIP) interface ports to maximize uptime and minimize maintenance downtime in continuous-duty operations.
Material & Properties
Two primary material grades are offered to match varying severity levels of chloride exposure and operating temperature:
- UNS S32750 / 2507 Super Duplex Stainless Steel (SDSS): The primary recommended grade for chloride environments up to approximately 55,000 ppm. 2507 offers a PREN (Pitting Resistance Equivalent Number) of 40–42, combining the high yield strength of duplex microstructures (minimum yield strength 550 MPa) with exceptional resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking (SCC). The elevated chromium (22–25%), molybdenum (3–5.7%), and nitrogen (0.24–0.32%) content provides a synergistic corrosion barrier that far exceeds 316L or 904L grades in aggressive chloride media.
- Grade 2 Titanium (Ti-99.2% minimum): Specified for the most extreme conditions where chloride concentrations persistently exceed 55,000 ppm or where temperatures approach the titanium passivation limit. Titanium provides virtually unmatched resistance to chloride-induced SCC across a broad temperature range (up to ~90°C in chloride solutions), though it requires careful avoidance of dry oxidation and fluoride-containing environments.
Key Material Properties Comparison
| Property | 2507 Super Duplex (UNS S32750) | Grade 2 Titanium (ASTM B348) |
|---|---|---|
| Chloride Resistance (Cl⁻ tolerance) | >50,000 ppm (with PREN 40–42) | >100,000 ppm (passive film stable to ~90°C) |
| Yield Strength (minimum) | 550 MPa | 275 MPa |
| Tensile Strength (minimum) | 795 MPa | 450 MPa |
| Maximum Operating Temperature | 300°C (continuous) | 300°C (in air); limited in chloride solutions |
| Thermal Conductivity (W/m·K) | ~16.3 | ~21.9 |
| Density (g/cm³) | 7.8 | 4.51 |
| SCC Resistance | Excellent (up to ~60°C in Cl⁻) | Exceptional (up to ~90°C in Cl⁻) |
| Boiling Point Elevation Tolerance | Up to 30°C BPE | Up to 30°C BPE |
Specifications
| Parameter | Specification / Range |
|---|---|
| Tube Outer Diameter (OD) | 19.05 mm (3/4"), 25.4 mm (1"), 31.75 mm (1-1/4") |
| Tube Wall Thickness | 1.5 mm – 4.0 mm (customizable based on pressure rating) |
| Coil Inner Diameter (ID) | 200 mm – 1,200 mm (custom-coiled to vessel geometry) |
| Coil Length (per unit) | 15 m – 120 m (configurable) |
| Maximum Design Pressure | Up to 2.5 MPa (gauge), depending on wall thickness |
| Maximum Operating Temperature | Up to 150°C (process side); steam side up to 180°C |
| Chloride Concentration Handling | Cl⁻ > 50,000 ppm (design envelope) |
| Boiling Point Elevation (BPE) | Designed for up to 30°C BPE |
| Circulation Mode | Forced circulation (pump-driven), flow velocity ≥ 1.5 m/s |
| Online Cleaning (CIP) Interface | Dedicated CIP ports with quick-disconnect couplings (DN25 – DN50) |
| Surface Finish | Pickled & passivated; Ra ≤ 0.4 μm (inner surface) |
| Standard References | ASTM A790 / ASME SA-790 (2507); ASTM B348 / B370 (Ti) |
| Welding Standard | ASME Section IX; ISO 15614 |
| Coating / Passivation | HNO₃/HF mixed acid passivation; optional TiCl₄ passivation for Ti tubes |
Manufacturing Process
The production of these high-performance coil tubes follows a rigorously controlled multi-stage process to ensure metallurgical integrity and dimensional precision:
- Material Selection & Mill Certification: Raw plate or bar stock is sourced from certified mills (e.g., Outokumpu, Sandvik, Timet) with full traceability documentation, including heat-number-linked chemical composition and mechanical property certificates.
- Cold Rolling / Forging: 2507 plate is cold-rolled to precise thickness tolerances (±0.05 mm). Titanium plate is annealed and rolled under controlled strain conditions to prevent work-hardening brittleness.
- Tubular Forming: Tubes are formed via cold-rolled and welded (CWR) or seamless (SMS) processes. For 2507, CWR tubes are welded using orbital GTAW (Gas Tungsten Arc Welding) with helium back-purging to maintain internal oxidation-free welds. Seamless tubes are produced via Mannesmann piercing or capillary extrusion for critical applications.
- Heat Treatment: 2507 tubes undergo solution annealing at 1050–1100°C followed by rapid water quench to dissolve precipitates and restore full corrosion resistance. Titanium tubes are annealed at 650–750°C in vacuum or argon atmosphere.
- Precision Coiling: Tubes are cold-coiled on CNC-controlled mandrels to exact inner-diameter specifications, with minimum bend radius of 5D (5 times tube OD) to prevent cross-sectional ovality exceeding 5%. Post-coiling stress relief is applied at 300–400°C for 2507 to eliminate residual bending stresses.
- Pickling & Passivation: All finished coil assemblies undergo acid pickling (HNO₃/HF for stainless; HCl/HNO₃ for titanium) to remove scale and contaminants, followed by passivation treatment to establish a stable chromium oxide (or titanium dioxide) protective film.
- Non-Destructive Testing (NDT): 100% volumetric inspection via eddy current (for 2507) or ultrasonic testing (UT) for titanium. Radiographic testing (RT) is performed on all welded joints. Hydrostatic pressure testing at 1.5× design pressure with zero-leak acceptance criteria.
Applications
This product is specifically engineered for the following high-severity wastewater treatment scenarios:
- Petrochemical & Refinery Wastewater Evaporation: Treatment of high-chloride effluent from crude oil desalting units, hydrochlorination processes, and chlorinated solvent recovery streams where Cl⁻ concentrations routinely exceed 50,000 ppm.
- Pharmaceutical & Fine Chemical Wastewater: Evaporative concentration of chlorinated reaction mother liquors, solvent wash streams, and halogenated byproduct solutions requiring high-purity material contact surfaces.
- Mine & Mining Acid Mine Drainage (AMD): Treatment of acidic, chloride-laden mine water containing dissolved salts, heavy metals, and high total dissolved solids (TDS) exceeding 80,000 ppm.
- Textile & Dyeing Industry Effluent: Evaporative recovery of salt-laden dyeing wastewater containing sodium chloride, sodium sulfate, and organic chlorinated compounds.
- Zero Liquid Discharge (ZLD) Systems: Integration into multi-effect evaporator trains where progressive concentration drives chloride levels beyond conventional material limits, requiring the ultimate corrosion resistance envelope of 2507 or titanium.
Unique Selling Points
- Forced Circulation Anti-Clogging Design: The coil geometry, combined with a dedicated circulation pump loop, maintains process-side flow velocities above 1.5 m/s, effectively preventing scaling deposition and ensuring uniform heat transfer across the entire tube surface. This design eliminates the stagnant zones that typically accelerate fouling in natural-circulation evaporators.
- Integrated Online Cleaning (CIP) Interface: Dedicated CIP ports allow operators to flush, chemically clean, or acid-pickle the coil tubes without system shutdown, enabling continuous production while maintaining heat transfer efficiency. This feature reduces unplanned maintenance by an estimated 60–70% compared to conventional evaporator tube designs.
- Boiling Point Elevation (BPE) Optimized Geometry: Coil dimensions and surface area are calculated to account for BPE-induced temperature differentials (up to 30°C), ensuring that wall temperatures remain within the corrosion-safe zone of the selected material grade throughout the concentration cycle.
- Full Material Traceability: Every coil tube assembly ships with a complete material passport including mill certificates, NDT reports, hydrostatic test records, and passivation verification — meeting the documentation requirements of international environmental compliance frameworks (ISO 14001, ISO 9001).
Quality Certifications & Standards Compliance
All products manufactured by Wenzhou Jixing Metal Materials Co., Ltd. conform to the following international quality and material standards:
| Standard / Certification | Scope of Compliance |
|---|---|
| ASTM A790 / ASME SA-790 | Welded and seamless tubes of austenitic-ferritic (duplex) stainless steel |
| ASTM B348 / B370 | Welded titanium and titanium alloy tube |
| EN 10216-5 / EN 10217-7 | European standard for seamless and welded stainless steel tubes |
| ISO 9001:2015 | Quality management system certification |
| ISO 14001:2015 | Environmental management system certification |
| ASME Section IX | Welding qualification procedures |
| ISO 15614 | Welding procedure qualification |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for evaporator assemblies |
| Third-Party Inspection (TPI) | Available via SGS, BV, or Lloyd's upon request |
Note: For chloride concentrations persistently exceeding 55,000 ppm or operating temperatures above 80°C in chloride solution, Grade 2 Titanium is the recommended material selection. For chloride levels between 30,000–55,000 ppm with temperatures below 70°C, 2507 Super Duplex provides optimal cost-performance balance. Material selection should be validated through a corrosion engineering assessment specific to the full chemical composition of the target wastewater stream, including pH, temperature profile, and presence of oxidizing agents (e.g., Fe³⁺, Cu²⁺) or reducing species.