Titanium Grade 2 (UNS R50400): Where It Beats Stainless and How to Buy It

Quick answer: Titanium Grade 2 (UNS R50400, commercially pure titanium) is the workhorse titanium: outstanding seawater and chloride resistance, about 60% the density of steel, and excellent formability. Buy it for marine, chlor-alkali, desalination and chemical-plant service where stainless pits and nickel alloys cost more than the duty requires. The watch-outs are hydrogen pickup at high temperature, galling on threads, and welding that must stay shielded from air.

What is Grade 2 titanium?

Grade 2 is commercially pure titanium — ~99% Ti with small oxygen, iron and nitrogen — the balance of strength, ductility and corrosion resistance. Higher-oxygen grades (Gr 3, Gr 4) are stronger; Gr 1 is softer; Gr 5 (Ti-6Al-4V) adds aluminum and vanadium for ~2× the strength of Gr 2. For corrosion service, Gr 2 is the default.

Where Grade 2 wins — and where it does not

Wins: seawater heat exchangers and condensers, chlor-alkali and chlorine dioxide equipment, wet chlorine, desalination brine, and anywhere chloride pitting kills stainless. Its passive film is one of the most stable in the periodic table — the same chemistry that makes it "space-age" makes it nearly immune to coastal atmospheres.

Does not win: strong reducing acids (hot hydrochloric except at very low concentration), fluorides, and dry chlorine gas; and above ~300 °C in air, hydrogen pickup embrittles it. It also galls badly against itself — threads and sliding fits need coatings or dissimilar contacts.

Forms and standards

• Bar and billet: ASTM B348 (Gr 2), round bar up to large diameters, machined shafts and fasteners.
• Plate and sheet: ASTM B265, from 0.5 mm sheet to heavy plate for vessels and cladding.
• Tube and pipe: B338 seamless tube for condensers and heat exchangers; B861/B862 pipe.
• Weld wire: ERTi-2 per AWS A5.16.

Machining and welding cautions

• Machining: low speeds, high feeds, flood coolant, sharp tools, never let the tool dwell — titanium work-hardens and fires when chips accumulate. Rigid setups are non-negotiable.
• Welding: GTA or GMA with matching ERTi-2 filler under trailing shield or full argon atmosphere; titanium absorbs oxygen and nitrogen from air above ~400 °C and the weld becomes brittle. Bright silver weld color means clean; blue/purple straw means contamination.
• Forming: Gr 2 forms well at room temperature; hot forming needs temperature control to avoid grain growth.

What should a Gr 2 RFQ include?

1. Form and standard: bar per B348, plate per B265, tube per B338, Gr 2.
2. Dimensions and tolerance; for shafts, whether straightness matters more than diameter tolerance.
3. Certificates: MTR per melt, and for critical service, UT and oxygen-content verification.
4. Surface: pickled/annealed standard; machined finish where mating matters.
5. End use — "condenser tubing, seawater 40 °C" or "fastener, coastal" tells the supplier exactly what properties to prioritize.

FAQ

Q: Why choose Gr 2 over Gr 5? A: Gr 2 is for corrosion; Gr 5 is for strength. Gr 5 costs more, machines harder, and its corrosion performance is not better — for seawater and chemical service Gr 2 is the engineering answer.

Q: Is titanium worth 3–6× the price of stainless? A: When stainless lasts 2 years and titanium lasts 20, yes. Life-cycle math in seawater, wet chlorine and hot brine overwhelmingly favors Gr 2; in mild service it does not, and 316L stays the right call.

Q: Can titanium be welded to steel? A: Not directly — it forms brittle intermetallics. Transition joints (explosion-bonded or brazed) exist exactly for this; design the system around them.

Q: How do I check the weld was done properly? A: Weld bead color is the quick field check: shiny silver is clean; straw, blue or white powdery deposits indicate oxygen/nitrogen pickup and a rejectable joint.