What is the difference between titanium Grade 2 and Grade 5?

Grade 2 (UNS R50400) — commercially pure, about 345 MPa tensile, 275 MPa yield. Total immunity to seawater corrosion at ambient temperature makes it the standard for desalination plate heat exchangers, seawater cooling, chlor-alkali plant and hypochlorite service. It is readily cold formed and welded with standard inert gas shielding.

Grade 5 / Ti-6Al-4V (UNS R56400) — 6% aluminium, 4% vanadium, about 950 MPa tensile and 830 MPa yield. The strength-to-weight ratio is why it dominates aerospace, high pressure subsea components, downhole tools and rotating parts. It is far less ductile than Grade 2, needs hot forming, and welding requires tight control and full shielding to avoid embrittlement.

Both grades absolutely require clean, oxygen-free welding — titanium picks up oxygen, nitrogen and hydrogen above about 400 C and becomes brittle. Trailing shields, purge chambers and strict cleanliness are not optional, and weld colour is the field acceptance check (straw is acceptable; blue, grey or white is not).

Select Grade 2 when corrosion drives the choice, Grade 5 when stress drives it. If both drive it, Grade 5 with a corrosion allowance or a Grade 2 liner is usually the practical compromise.