Gr.1 vs Gr.2 vs Gr.7 – Which One for Seawater?
May 22, 2026
Choose Based on Your Application
| If your application involves... | Choose this grade | Reason |
|---|---|---|
| U-bent tubes / tight bending / deep drawing | Gr.1 | Highest ductility (24% elongation), will not crack during bending |
| Straight tubes / general seawater cooling / higher pressure | Gr.2 | Higher strength (275 MPa yield), good corrosion resistance |
| Stagnant seawater / crevice risk / tube-to-tubesheet joints | Gr.7 | Palladium addition provides superior crevice corrosion resistance |
Solve Your Material Selection Problem
Gr.1 Gr.2 Gr.7 Differences
| Comparison | Gr.1 | Gr.2 | Gr.7 |
|---|---|---|---|
| UNS Number | R50250 | R50400 | R52400 |
| Oxygen (max) | 0.18% | 0.25% | 0.25% |
| Iron (max) | 0.20% | 0.30% | 0.30% |
| Palladium (Pd) | None | None | 0.12-0.25% |
| Tensile Strength (min) | 240 MPa | 345 MPa | 345 MPa |
| Yield Strength (min) | 170 MPa | 275 MPa | 275 MPa |
| Elongation (min) | 24% | 20% | 20% |
| Corrosion resistance (seawater) | Excellent | Excellent | Superior (crevice) |
| Relative price | $$ | $$ | $$$ (50-80% higher) |
Gr.1 is the most formable (24% elongation). Gr.2 offers higher strength. Gr.7 adds palladium for crevice corrosion protection in stagnant seawater.
When Should You Choose Gr.1 ?
Choose Gr.1 when your application requires bending, forming, or deep drawing.
| Application | Why Gr.1 is the best choice |
|---|---|
| U-bent heat exchanger tubes | 24% elongation means no cracking during tight radius bending |
| Deep drawn components | Softest titanium grade, easiest to form |
| Thin wall heat exchanger tubes (0.5-1.5mm) | High ductility allows thin wall without failure |
| Seawater cooling – any velocity | No velocity limit, excellent corrosion resistance |
| Desalination brine heaters | Resists high temperature brine |
U-bent tubes, thin wall heat exchangers, deep drawing, and applications requiring complex shapes.
When Should You Choose Gr.2?
Choose Gr.2 when you need higher strength but still want commercially pure titanium.
| Application | Why Gr.2 is a good choice |
|---|---|
| Straight tube heat exchangers | No bending required, higher strength is beneficial |
| Higher pressure seawater cooling | 275 MPa yield vs 170 MPa for Gr.1 |
| Industrial piping systems | General purpose, most widely available |
| Marine applications (straight tubes) | Good balance of strength and corrosion resistance |
Straight tubes, higher pressure systems, and general industrial seawater cooling.
When Should You Choose Gr.7?
Choose Gr.7 when your application involves stagnant seawater or crevice risk.
| Application | Why Gr.7 is required |
|---|---|
| Stagnant seawater conditions | Palladium prevents crevice corrosion when flow stops |
| Tube-to-tubesheet joints | Crevice between tube and tubesheet is protected |
| Under gaskets / deposits | Areas where biofouling or debris can create crevices |
| Low flow or intermittent service | Gr.1 and Gr.2 may crevice corrode; Gr.7 will not |
| Aggressive chemical environments | Reducing acids (HCl, H2SO4) – Gr.7 outperforms Gr.1/Gr.2 |
Stagnant seawater, tube-to-tubesheet joints, gasketed connections, and reducing acid environments.
Real Project Cases
Middle East Desalination Plant (U-bent Tubes)
Customer needed U-bent tubes for seawater brine heater. Tight bending radius. Risk of cracking during forming.
GNEE Recommendation: Gr.1 titanium tube (24% elongation, best formability)
Specification: 25.4mm OD x 0.9mm wall, U-bent to drawing
Quantity: 25 tons
Result: Delivered in 2023. No cracking during bending. 3 years in service – no corrosion issues.
Southeast Asia Power Plant (Straight Tubes, High Pressure)
Condenser tube replacement. Seawater cooling. Operating pressure 4.5 MPa.
GNEE Recommendation: Gr.2 titanium tube (275 MPa yield strength, higher than Gr.1)
Specification: 19.0mm OD x 0.7mm wall, straight tubes, 6m length
Quantity: 18 tons
Result: Delivered in 2024. Stable operation for 2 years. No pitting or leakage.
China Chemical Plant (Chloride Environment)
Cooling system handling chlorides at 80°C. Crevice risk at tube sheet.
GNEE Recommendation: Gr.1 titanium tube (excellent chloride resistance)
Specification: 19.0mm OD x 1.0mm wall seamless, straight tubes
Quantity: 12 tons
Result: Delivered in 2022. 4 years in service. No corrosion detected.
Common Mistakes
| Mistake | Consequence | Correct choice |
|---|---|---|
| Using Gr.2 for U-bent tubes | Cracking during bending due to lower ductility (20% vs 24%) | Use Gr.1 |
| Using Gr.1 for high pressure | Tube burst or deformation under pressure | Use Gr.2 |
| Using Gr.1 or Gr.2 in stagnant seawater | Crevice corrosion at tube sheet or under deposits | Use Gr.7 |
| Using Gr.7 for everything | Wasted money (50-80% higher cost) | Use Gr.1 or Gr.2 where sufficient |
What GNEE Can Provide
| Grade | Form | Stock Sizes | U-Bending | Certification |
|---|---|---|---|---|
| Gr.1 | Seamless / Welded | ✅ In stock | ✅ Yes | EN 10204 3.1 |
| Gr.2 | Seamless / Welded | ✅ In stock | ✅ Yes | EN 10204 3.1 |
| Gr.7 | Seamless | 🟡 Make to order | ✅ Yes | EN 10204 3.1 |
Mill Test Certificate included. SGS inspection available upon request.
FAQ
1. Why is titanium preferred over copper-nickel for seawater heat exchangers?
Titanium has no velocity limit, no pitting risk, and lasts 20-30 years. Cu-Ni suffers erosion-corrosion at high velocities and requires replacement every 5-10 years.
2. Can Gr.1 titanium be used for U-bent heat exchanger tubes?
Yes. Gr.1 has 24% elongation – the highest among CP grades – making it ideal for tight radius U-bending without cracking.
3. What is the difference between Gr.1 and Gr.2 for seawater service?
Both have excellent corrosion resistance. Gr.1 is softer and more ductile (24% vs 20% elongation). Gr.2 has higher strength (275 MPa vs 170 MPa yield). Choose Gr.1 for bending; Gr.2 for higher pressure.
4. When do I need Gr.7 instead of Gr.1 or Gr.2?
Use Gr.7 when the tube will be in stagnant seawater or has crevice risk (tube-to-tubesheet joints, under gaskets, or biofouling). The palladium addition prevents crevice corrosion.
5. How much more expensive is Gr.7 than Gr.1?
Gr.7 is typically 50-80% more expensive than Gr.1 or Gr.2 due to the palladium content. Only use it when crevice corrosion is a real risk.
6. Can welded titanium tube be used in seawater heat exchangers?
Yes. ASTM B338 welded tube is fully accepted. The weld must be cold worked and annealed, with 100% eddy current testing required.
7. What is the typical wall thickness for seawater heat exchanger tubes?
Thin wall from 0.5mm to 1.5mm is sufficient. Thinner wall means better heat transfer and lower material cost.
8. How long will titanium tube last in seawater service?
20-30+ years. Titanium's self-repairing oxide film prevents pitting and crevice corrosion (except in stagnant conditions where Gr.7 is required).
9. Does GNEE supply U-bent Gr.7 titanium tubes?
Yes. GNEE can supply U-bent tubes in Gr.1, Gr.2, and Gr.7 to your drawing. Lead time: 20-25 days.
10. How do I get a recommendation for my project?
Email us with your working conditions: seawater flow rate (or stagnant), operating temperature, tube OD/wall thickness, straight or U-bent, and pressure. GNEE will recommend the right grade and provide a quote.
Packaging
Each Gr.1, Gr.2, or Gr.7 titanium tube is individually wrapped in plastic film or VCI paper to prevent moisture and scratches. Both ends are sealed with plastic caps to keep out debris. Tubes are bundled with steel straps and protective padding, then packed in export-standard plywood wooden boxes for seaworthy delivery. Labels with grade, heat number, size, and quantity are attached to each bundle and box. Custom packaging is available upon request.
Inspection & Testing
| Test | Coverage | Purpose |
|---|---|---|
| Chemical Analysis | Per heat | Verify O ≤0.18% (Gr.1) / ≤0.25% (Gr.2/Gr.7), Fe, C, N, H |
| Tensile Test | Per heat | Confirm yield strength and elongation (Gr.1 ≥24%) |
| Flattening Test | Per ASTM B338 | Verify ductility |
| Flaring Test | Per ASTM B338 | Verify expansion capability |
| Ultrasonic Test (UT) | 100% (seamless) | Detect internal flaws |
| Eddy Current Test (ECT) | 100% (welded) | Detect surface flaws on weld |
| Hydrostatic Test | 100% | Pressure integrity |
| PMI Test | 100% | Confirm grade (UNS R50250 / R50400 / R52400) |
EN 10204 3.1 Mill Test Certificate included. SGS / BV third-party inspection available at buyer's cost.
