Titanium and most titanium alloys are readily weldable, using several welding processes. Properly made welds in the as-welded condition are ductile and, in most environments, are as corrosion resistant as base metal. Improper welds, on the other hand, might be embrittled and less corrosion-resistant compared to base metal.
The techniques and equipment used in welding titanium are similar to those required for other high-performance materials, such as stainless steels or nickel-base alloys. Titanium, however, demands greater attention to cleanliness and to the use of auxiliary inert gas shielding than these materials. Molten titanium weld metal must be totally protected from contamination by air. Also, hot heat-affected zones and root side of titanium welds must be shielded until temperatures drop below 800°F (427°C).
Titanium reacts readily with air, moisture, grease, dirt, refractories, and most other metals to form brittle compounds. Reaction of titanium with gases and fluxes makes common welding processes such as gas welding, shielded metal arc, flux cored arc, and submerged arc welding unsuitable.
This specification covers the requirements for 33 grades of titanium and titanium alloy welded pipe intended for general corrosion resisting and elevated temperature service. Welded pipe shall be made from annealed flat-rolled products by a welding process. Welded pipe may be further reduced by cold working or hot working. Grades 1, 2, 2 H, 7, 7H, 11,13, 14, 16, 16H, 17, 26H, 33, and 37 shall be furnished as welded or annealed. Grades 3, 12, 15, and 34 shall be furnished as annealed. Grade 5, 23, 24, 25, 35 shall be furnished as annealed, or aged. Grade 9, 18, 38 shall be furnished as annealed. Grade 19, 20, 21 shall be furnished as solution treated, or solution treated and aged. The materials shall conform to the required chemical composition for nitrogen, carbon, hydrogen, iron, oxygen, aluminum, vanadium, tin, ruthenium, palladium, cobalt, molybdenum, chromium, nickel, niobium, zirconium, silicon, and titanium. They shall also conform to the required mechanical propetries such as tensile strength, yield strength, and elongation.
Titanium and its alloys are most often welded with the gas tungsten-arc (GTA or TIG) and gas metal-arc (GMA or MIG) welding processes. Resistance, plasma arc, electron beam and friction welding are also used on titanium to a limited extent. All of these processes offer advantages for specific situations.
The GTA process can be used to make butt joints without filler metal in titanium base sheet of up to about 1/8-inch thickness. Heavier sections generally require the use of filler metal and grooved joints. Either the GTA or GMA welding process can be used, although GMA welding is more economical for sections heavier than about one-half inch. If the GTA process is used, care should be exercised to prevent contact of the tungsten electrode with the molten puddle, thereby preventing tungsten pickup.