For most ambient seawater service, Grade 2 (UNS R50400) commercially pure titanium is the default, because titanium forms a stable passive oxide film that does not corrode in chloride water. When the service runs hot (roughly above 70 to 80 C), involves tight crevices, or carries concentrated brine, move up to Grade 7 (UNS R52400) or Grade 12 (UNS R53400), which resist crevice corrosion under those conditions. When the part must carry structural load, use Grade 5 (Ti-6Al-4V, UNS R56400) or, for fracture-critical and implant-class parts, Grade 23 ELI (UNS R56407 to the ASTM B-series, R56401 to ASTM F136).
Beiyu Titanium supplies these grades to ASTM B265, B338 and B348 according to the ordered product form. When EN 10204 3.1 documentation and heat or lot traceability are required, state the requested reporting scope in the RFQ.
Why titanium is used in seawater at all
Titanium resists seawater not because it is noble, but because it builds a thin, self-healing oxide film (mostly TiO2) on its surface. That film re-forms almost instantly if scratched, as long as oxygen is present. In oxygenated seawater the film stays intact across the full pH range and across a wide temperature range, which is why titanium is specified for condensers, heat exchangers, desalination plant, offshore risers, pumps, valves and seawater piping where copper alloys, stainless steels and even some nickel alloys pit or fail.
The film does have a limit: in environments where oxygen cannot reach the surface to repair it, the protection can break down locally. That single fact is what drives almost every grade decision below.
The four variables that actually decide the grade
You do not choose a marine titanium grade by “how corrosive the water is.” You choose it by four service variables:
| Service | What the guide states |
|---|---|
| Temperature | Cold and ambient seawater is easy for any titanium grade. Hot seawater and hot brine are where commercially pure titanium starts to show crevice attack. |
| Crevices | Gasket faces, tube-to-tubesheet joints, lap joints, deposits, biofouling and weld backing rings all create oxygen-starved gaps. Crevice corrosion, not general corrosion, is the usual failure mode for titanium in chloride service. |
| Chloride concentration | Open seawater is roughly 3.5 percent dissolved salts. Evaporators, reject brine and desalination stages concentrate it well beyond that, which lowers the temperature at which crevice attack can start. |
| Mechanical load | Fasteners, shafts, springs and structural hardware need strength that commercially pure grades do not have, which moves you to the alloy grades. |
Match the grade to the worst combination of these four that the part will actually see, not to the average.
Grade by grade for marine service
Grade 2 (UNS R50400): the default
Commercially pure titanium, the workhorse for seawater. Excellent general corrosion resistance in oxygenated chloride water, good weldability and good formability. ASTM minimums are 345 MPa tensile and 275 MPa yield (confirmed on the EN 10204 3.1 mill test certificate per heat). Grade 2 is the right choice for ambient and moderate-temperature seawater heat exchanger tube, condenser tube, sheet and plate for tanks and linings, and general piping. Its limit is hot, crevice-prone, concentrated chloride: in tight crevices, Grade 2 can begin to suffer crevice corrosion as the metal temperature climbs above roughly 70 to 80 C.
Grade 7 (UNS R52400): the crevice-resistant grade
Grade 7 is commercially pure titanium with a small palladium addition (about 0.12 to 0.25 percent). Mechanically it matches Grade 2 (345 MPa tensile, 275 MPa yield minimum), so you specify it purely for corrosion. The palladium shifts the metal into its passive region under reducing, oxygen-starved conditions, which is exactly what a crevice creates. Grade 7 raises the temperature at which crevice corrosion can start in hot chloride and reducing-acid service well above where Grade 2 stops being safe. Use it for hot brine, concentrated chloride, reducing-acid contamination, and gasketed or tube-to-tubesheet joints that run hot. It is the most expensive of the corrosion grades because of the palladium.
Grade 12 (UNS R53400): the cost-balanced crevice grade
Grade 12 is a lean titanium alloy with about 0.3 percent molybdenum and 0.8 percent nickel. ASTM minimums are 483 MPa tensile and 345 MPa yield, so it is both stronger than Grade 2 and more crevice-resistant in hot chloride, at a lower cost than the palladium-bearing Grade 7. It is widely specified for desalination, hot brine handling and chloride process equipment where Grade 2 is marginal but full Grade 7 performance is not required. For many hot-seawater heat exchanger and evaporator duties, Grade 12 is the practical middle choice.
Grade 5 (Ti-6Al-4V, UNS R56400): when the part carries load
Grade 5 is the high-strength alloy, with ASTM minimums of 895 MPa tensile and 828 MPa yield. Its general seawater corrosion resistance is good, though it is not as crevice-tolerant in hot chloride as Grade 7 or Grade 12, so it is chosen for strength, not for the most aggressive corrosion. Typical marine uses are fasteners, shafts, pump and valve internals, springs, and structural hardware that must be both light and corrosion-resistant.
Grade 23 (Ti-6Al-4V ELI, UNS R56407 industrial / R56401 implant): fracture-critical and implant class
Grade 23 is the extra-low-interstitial version of Grade 5, with tighter oxygen, nitrogen, carbon and iron limits that give it higher fracture toughness and better fatigue behaviour. ASTM minimums are 828 MPa tensile and 759 MPa yield. In marine and offshore work it is specified where fracture toughness and fatigue matter, and it is the standard for medical-adjacent and implant-class parts to ASTM F136. Note that the correct UNS for Grade 23 / Ti-6Al-4V ELI depends on the standard ordered: R56407 under ASTM B265, B348, B863 and B381, and R56401 under ASTM F136.
Temperature limits in seawater: the real numbers
Grade choice in seawater is ultimately a temperature decision, so it helps to work from the published numbers rather than from “how corrosive the water feels”:
| What the guide states |
|---|
| Grade 2 resists crevice corrosion in seawater to roughly 80 C (about 175 to 180 F) in tight crevices, and its general corrosion resistance in open seawater is effectively unlimited at temperatures up to around 120 C (250 F) at typical marine pressures. |
| Grade 7 extends crevice resistance much higher and remains viable in hot chloride service approaching 260 C (500 F). |
| Grade 12 delivers much of that high-temperature crevice resistance at a lower cost than the palladium-bearing Grade 7. |
If your part runs cool and has no tight crevices, Grade 2 is genuinely sufficient and the upgrade is wasted money. The move to Grade 7 or Grade 12 buys margin specifically where metal temperature and crevice geometry push commercially pure titanium past its limit.
For the leanest-cost crevice resistance, the wider palladium family is worth knowing. Alongside Grade 7, the lean-palladium Grade 16 (UNS R52402) keeps most of the crevice benefit at a lower palladium content and cost, so it is worth quoting as an alternative to full Grade 7.
Selection logic in one pass
| What the guide states |
|---|
| Ambient or moderate-temperature oxygenated seawater, no strength requirement: Grade 2. |
| Hot seawater or hot brine, crevices present, concentrated chloride: Grade 12 first, Grade 7 when conditions are at the limit or reducing-acid contamination is possible. |
| Structural load, fasteners, shafts, lightweight hardware: Grade 5. |
| Fracture-critical, high-fatigue or implant-class load-bearing parts: Grade 23 ELI (ASTM F136). |
When the part sees more than one of these at once, specify for the worst case.
Comparison table
| Grade | UNS | ASTM min tensile / yield | Seawater behaviour | Specify it for |
|---|---|---|---|---|
| Grade 2 | R50400 | 345 / 275 MPa | Excellent in ambient seawater; crevice risk in hot, tight, concentrated chloride | Default tube, sheet, plate, piping |
| Grade 7 | R52400 | 345 / 275 MPa | Best crevice and reducing-condition resistance | Hot brine, concentrated chloride, hot gasketed joints |
| Grade 12 | R53400 | 483 / 345 MPa | Strong crevice resistance in hot chloride at lower cost than Grade 7 | Desalination, hot-brine heat exchangers |
| Grade 5 | R56400 | 895 / 828 MPa | Good general resistance; chosen for strength | Fasteners, shafts, pump and valve parts |
| Grade 23 | R56407 (B-series); R56401 (F136) | 828 / 759 MPa | Good general resistance, high toughness | Fracture-critical, fatigue, implant-class |
Mechanical values are ASTM minimums and are confirmed on the EN 10204 3.1 mill test certificate for each heat.
Forms and standards you will quote for marine titanium
| Field to state | What the guide states |
|---|---|
| Tube and pipe | ASTM B338 (seamless and welded tube), ASTM B861 / B862 (pipe). Condenser and heat exchanger tube is usually Grade 2, moving to Grade 12 or Grade 7 for hot or concentrated duty. |
| Sheet and plate | ASTM B265, for tanks, vessel linings, tubesheets and fabricated equipment. |
| Bar | ASTM B348, for machined valve and pump parts, shafts and fittings. |
| Fasteners | usually Grade 5 for strength, Grade 2 or Grade 7 where corrosion dominates over load. |
For pressure equipment, the project may reference the ASME adoption (for example ASME SB-265 for plate). State that on the RFQ if the drawing calls it out.
Crevice corrosion, in real engineering terms
The reason this whole decision exists is crevice corrosion. Inside a tight gap, dissolved oxygen is consumed and cannot be replenished, the local chemistry turns acidic and chloride concentrates, and the passive film can break down even though the open surface is untouched. For commercially pure Grade 2 this becomes a real risk as metal temperature rises above roughly 70 to 80 C in seawater and earlier in concentrated brine. Grade 7 and Grade 12 push that onset temperature substantially higher, which is the entire engineering reason to pay for them. If your part has no tight crevices and runs cool, Grade 2 is genuinely sufficient and the upgrade is wasted money. If it has gasketed joints running hot, the upgrade is cheap insurance against a through-wall failure.
If the condenser or cooler will see hot brine and tight tube-to-tubesheet crevices, compare that temperature window with where Grade 12 is used for hot brine and crevice-corrosion service before keeping the order on Grade 2.
Procurement checklist for marine titanium
When you send a marine titanium RFQ, state:
| What the guide states |
|---|
| Grade and UNS number, and the controlling standard (ASTM B338 / B265 / B348, plus any ASME reference). |
| Service temperature and whether crevices are present (gaskets, tube-to-tubesheet, deposits). |
| Chloride concentration if it is above open seawater (evaporator, reject brine, desalination stage). |
| Form and dimensions: OD and wall for tube, thickness for plate, diameter for bar. |
| Whether the part is load-bearing, and any fatigue or fracture-toughness requirement. |
| Inspection and document scope: EN 10204 3.1 mill test certificate, and any UT, eddy-current or hydrostatic test for tube. |
A clear RFQ on these points lets the grade be confirmed before quotation, instead of after a failure in service.
How Beiyu Titanium supplies marine grades
Beiyu Titanium supplies Grade 2, Grade 7, Grade 12, Grade 5 and Grade 23 titanium for seawater and marine service as tube and pipe to ASTM B338, sheet and plate to ASTM B265, and bar to ASTM B348. State any required EN 10204 3.1 document, chemistry, mechanical results and heat or lot traceability in the RFQ so Beiyu can confirm the available document scope before order release. Send the service temperature, crevice condition, chloride level, form and dimensions, and the correct grade can be confirmed before quotation.
For condenser and cooler tubing under the same grade decision, the ASTM B338 titanium tube guide shows the tube route, wall and inspection details that sit behind the RFQ.
Related guides and tools
- Titanium grade for chemical processing
- Titanium vs 316L stainless vs copper-nickel for seawater
- Medical-grade titanium (ASTM F136, Grade 23 ELI)
- Titanium grade selector tool
Specification detail with sources
AWS A5.16 is the specification that carries a marine titanium grade decision through to welded fabrication, because its filler classifications mirror the base-metal grades: ERTi-2 pairs with Grade 2, ERTi-7 with Grade 7, ERTi-9 with Grade 9 and ERTi-12 with Grade 12. Naming the filler classification on the fabrication order keeps the weld chemistry in the same corrosion family as the parent metal, which matters most on the Grade 7 and Grade 12 selections this page reserves for hot chloride: an unmatched commercially pure weld bead in a line bought for crevice resistance hands the corrosion problem straight back to the joint, the one place a piping system is hardest to repair.
Beiyu Titanium supplies the welding side of a marine order from the same enquiry as the tube and plate: titanium weld wire to AWS A5.16 in straight lengths from 0.8 to 6.0 mm diameter up to 6,000 mm long, coiled wire from 0.8 to 12 mm, and spooled wire up to 6.35 mm. The grade-to-classification pairing, Grade 2 as ERTi-2 and Grade 12 as ERTi-12, is stated on Beiyu’s quotation so base metal and filler arrive documented under the same heat-traceable chain.