Grade 12

Grade 12 was developed as the economic answer to the crevice corrosion problem that limits commercially pure titanium in hot chloride service. Its 0.3% molybdenum and 0.8% nickel deliver a substantial part of the crevice and elevated-temperature resistance that palladium gives Grade 7, without the cost of a precious metal addition, and it is widely used in hot brine and geothermal duty where Grade 2 would be at risk and Grade 7 would be uneconomic for the quantity involved.

The second benefit is strength. At a specified minimum 483 MPa tensile and 345 MPa yield, Grade 12 is 40% stronger than Grade 2 and Grade 7 on minimum tensile while remaining a lean, weldable, formable alloy — so for a bolted joint it offers both better crevice performance and a higher allowable preload. Where absolute crevice resistance in the most aggressive hot acid chloride service is required, Grade 7 remains the better choice.

Three absolute exclusions. Titanium must not be used in dry chlorine, with which it reacts violently; it must not be used with red fuming nitric acid; and it is rapidly attacked by hydrofluoric acid at any concentration. Fine titanium swarf and grinding dust are also a genuine fire hazard and must be handled wet and stored separately. These limits apply to every grade on this page, including the palladium and molybdenum-nickel modified grades — the alloying additions improve crevice and reducing-acid performance, they do not change these exclusions.

Titanium galls, and for a threaded fastener this is the single most important practical fact about the material. Titanium’s protective oxide is thin and the metal beneath it is adhesive, so a titanium thread run against another titanium thread will cold-weld and seize — often badly enough that the fastener has to be cut off. Every titanium bolted joint needs one of three mitigations: an anti-seize compound or dry-film lubricant such as molybdenum disulphide on the thread; a plated or coated thread, commonly silver or a solid-film lubricant; or a nut in a dissimilar material rather than titanium. Exotic Alloy supplies titanium fasteners with a lubricant or coating specified at order stage, and will advise on the combination if you tell us the mating material.

Titanium is galvanically noble, which makes it a hazard to what it is bolted into. It sits close to the passive stainless steels and the nickel alloys on the galvanic series and well above carbon steel, aluminium, zinc and magnesium. A titanium fastener in an aluminium or carbon steel structure will not itself corrode, but it will drive accelerated corrosion of the structure around it, and the small-anode-large-cathode geometry of a bolted joint is the worst case. Where titanium fasteners are used in a less noble assembly, an insulating washer and sleeve or a barrier coating on the mating faces should be specified.

Note on section size: the ASTM B348 tensile requirements apply to longitudinal sections up to 76 mm (3 in.) thick with a maximum area of 64.5 cm² (10 in.²). Mechanical properties for larger sections are negotiated between manufacturer and purchaser, so for large-diameter bolting the acceptance values must be agreed on the order rather than assumed from the table.