SWRO High-Pressure Pump Outlet Coil Tube — 2507 / Inconel 625
1. Product Overview
This product is a specialized stainless steel coil tube (盘管) engineered for use in the high-pressure pump outlet piping of Seawater Reverse Osmosis (SWRO) desalination facilities. Operating under extreme conditions of 6–8 MPa differential pressure and chloride ion concentrations exceeding 19,000 ppm, the coil tube is designed to deliver long-term integrity and resistance against crevice corrosion, pitting corrosion, and chloride-induced stress corrosion cracking (Cl-SCC).
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube represents a critical component in marine engineering desalination infrastructure, where material degradation can lead to catastrophic system failures, environmental contamination, and significant operational downtime.
2. Material & Properties
2.1 Available Material Grades
- SAE 2507 (UNS S32750) — Super Duplex Stainless Steel (SDSS), offering a Pitting Resistance Equivalent Number (PREN) exceeding 40, providing superior resistance to localized corrosion in highly chlorinated environments.
- Inconel 625 (UNS N06625) — Nickel-based alloy with exceptional resistance to chloride pitting, crevice corrosion, and stress corrosion cracking, suitable for the most aggressive seawater conditions.
2.2 Key Material Properties
| Property | SAE 2507 (UNS S32750) | Inconel 625 (UNS N06625) |
|---|---|---|
| PREN (Pitting Resistance Equivalent Number) | > 40 | > 50 |
| Tensile Strength (MPa) | ≥ 550 | ≥ 620 |
| Yield Strength (MPa) | ≥ 450 | ≥ 275 | Corrosion Potential (mV vs. SCE) | > 250 | > 300 |
| Maximum Service Temperature (°C) | 300 | 593 |
| Chloride Resistance (ppm) | > 20,000 | > 25,000 |
| Density (g/cm³) | 7.80 | 8.44 |
2.3 Chemical Composition (Typical)
| Element | SAE 2507 (%) | Inconel 625 (%) |
|---|---|---|
| C | ≤ 0.03 | ≤ 0.10 |
| Cr | 24.0–28.0 | 20.0–23.0 |
| Ni | 6.0–8.0 | 52.0–58.0 |
| Mo | 3.0–5.0 | 8.0–10.0 |
| N | 0.24–0.32 | — |
| Fe | Balance | ≤ 5.15 (balance) |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Type | Coil Tube (盘管) — Continuous Coiled Length |
| Applicable Standards | ASTM A790, ASTM A240, ASTM B564, ASTM B444, ASME SB-564 |
| Operating Pressure | 6–8 MPa (870–1,160 psi) |
| Service Medium | Seawater, Cl⁻ > 19,000 ppm |
| Operating Temperature | −20°C to +80°C (typical seawater intake) |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) or electropolished |
| Welding Method | Orbital TIG (Tungsten Inert Gas) welding — fully automated |
| Corrosion Verification | Crevice corrosion testing per ASTM G44 / ASTM G60 |
| PREN Requirement | > 40 (mandatory) |
| Coil Diameter | Customizable per project requirement (typical: 1.2–2.5 m) |
| Tube OD × Wall | Customizable (typical range: 12–108 mm OD × 1.0–6.0 mm WT) |
4. Manufacturing Process
- Raw Material Procurement — Certified super duplex stainless steel (SAE 2507) or Inconel 625 plate/bar stock with full mill test certificates (MTC) and heat traceability.
- Slitting & Forming — Precision slitting of coil strip followed by cold-rolled seamless or welded tube forming to achieve exact dimensional tolerances.
- Coiling — Continuous coiling onto precision-wound coils using tension-controlled winding systems to prevent deformation and surface damage.
- Welding — Orbital TIG welding with internal helium leak detection to ensure full-penetration, gas-tight weld seams suitable for high-pressure service.
- Heat Treatment — Solution annealing (for Inconel 625) or stabilization treatment (for SAE 2507) to restore full corrosion resistance and mechanical properties.
- Surface Finishing — Mechanical polishing followed by electropolishing to achieve a low-roughness surface that minimizes crevice corrosion initiation sites.
- Passivation — Citric acid or nitric acid passivation to remove free iron and restore the protective chromium oxide layer.
- Corrosion Testing — Crevice corrosion verification per ASTM G44 and ASTM G60 standards, including Immersion Test (ASTM G48), to validate PREN > 40 performance in simulated seawater.
- Final Inspection & Packaging — Dimensional verification, hydrostatic pressure testing at 1.5× working pressure, visual and NDT (Non-Destructive Testing) inspection, followed by protective wrapping and corrosion-inhibitive packaging.
5. Applications
5.1 Primary Application
SWRO High-Pressure Pump Outlet Piping — The coil tube is specifically designed for the high-pressure discharge line connecting the multi-stage high-pressure pump to the reverse osmosis membrane skid in seawater desalination plants. This is the most demanding location in the SWRO process due to the combination of:
- High differential pressure (6–8 MPa) creating elevated mechanical stress
- Concentrated chloride ions (> 19,000 ppm) promoting localized corrosion
- Hydrodynamic flow conditions that may accelerate corrosion at welds and crevices
- Continuous immersion in aggressive seawater medium
5.2 Secondary Applications
- Brine recirculation lines in SWRO plants
- High-pressure feedwater distribution piping
- Marine desalination vessels and offshore platforms
- Chemical dosing system piping (anti-scalant, antiscalant injection)
- Seawater intake and pre-treatment system components
6. Quality Certifications & Compliance
6.1 Material Certifications
- EN 10204 3.1 — Material Test Certificate with full chemical and mechanical test data
- EN 10204 3.2 — Third-party inspection certificate available upon request
- ASTM A790 — Standard specification for seamless and welded austenitic stainless steel and super austenitic stainless steel pipe
- ASTM B444 — Standard specification for seamless nickel-iron-chromium-molybdenum alloy pipe (Inconel 625)
- ASME BPV Code — Section II Part D material compliance for pressure vessel applications
6.2 Testing & Verification
- Crevice Corrosion Testing — ASTM G44 (Crevice Corrosion Test of Stainless Steel and Related Alloys in Chloride Solutions)
- Pitting Corrosion Testing — ASTM G48 Practice A (Critical Pitting Temperature / CCT method)
- Hydrostatic Testing — 100% inline hydrostatic pressure test at ≥ 1.5× design pressure
- NDT Inspection — 100% radiographic testing (RT) or ultrasonic testing (UT) of all weld seams
- Helium Leak Detection — Full penetration weld verification for high-pressure integrity
- Surface Roughness Verification — Ra ≤ 0.4 μm confirmation via profilometry
6.3 Industry Compliance
- ISO 9001:2015 — Quality Management System certification
- NACE MR0175 / ISO 15156 — Materials for use in H₂S-containing environments (where applicable)
- NSF/ANSI 61 — Drinking Water System Components (for potable water applications)
- DNV-GL — Marine classification society approval for offshore applications
7. Unique Selling Points
Why Choose Jixing SWRO Coil Tubes?
- PREN > 40 Guaranteed — All materials are verified to exceed the critical pitting resistance threshold for chloride concentrations above 19,000 ppm, ensuring long-term service life in the most aggressive seawater environments.
- Dual Material Option — Customers can select between cost-effective SAE 2507 Super Duplex Stainless Steel or premium Inconel 625 nickel alloy based on project-specific corrosion risk assessment and budget requirements.
- Crevice Corrosion Verified — Every production batch undergoes rigorous crevice corrosion testing per ASTM G44/G60 standards, providing documented proof of performance in high-chloride, high-pressure conditions.
- Continuous Coil Configuration — Eliminates field-weld joints in high-pressure lines, reducing leak points and maintenance requirements compared to straight pipe sections.
- Full Traceability — Complete heat-to-coil traceability from raw material mill certificate through final product delivery, enabling robust quality assurance and lifecycle management.
- Custom Engineering — Coil diameter, tube dimensions, surface finish, and coating options are fully customizable to meet specific project design requirements and installation constraints.
8. Recommended Service Life & Maintenance
| Parameter | SAE 2507 | Inconel 625 |
|---|---|---|
| Expected Service Life | 20–25 years | 30+ years |
| Recommended Inspection Interval | Every 5 years (UT wall thickness) | Every 5 years (UT wall thickness) |
| Minimum Wall Thickness Allowance | 1.0 mm corrosion allowance | 0.5 mm corrosion allowance |
| Passivation Re-treatment | Every 3 years or after repair | Every 3 years or after repair |
9. Ordering Information
To specify this product, the following information is required:
- Material grade selection (SAE 2507 or Inconel 625)
- Tube outer diameter (OD) and wall thickness (WT)
- Coil inner diameter (ID)
- Total coil length
- Surface finish requirement (polished Ra value)
- Weld type (seamless or orbital TIG welded)
- Required certifications and testing protocols
- End treatment (beveled, capped, or raw)
- Special packaging or shipping requirements
Wenzhou Jixing Metal Materials Co., Ltd — Engineering Excellence for Marine Desalination Infrastructure