ASTM B338 Grade 2 Titanium Tubing

The ASTM B338 grade 2 titanium tubing refers to seamless and welded tubes made from grade 2 unalloyed titanium (commercially pure titanium). Standard specification ASTM B338 is identical with ASME SB-338. These grade 2 titanium tubes are primarily used for the fabrication of surface condensers, evaporators, and heat exchangers in seawater desalination, power plant, petrochemical and chemical industries.

Titanium Gr.2: Properties & Microstructure

Grade 2 titanium is the “workhorse” for industrial applications due to its high specific strength and excellent corrosion resistance. It has a guaranteed minimum yield strength of 275 MPa [40 ksi], which is comparable to those of austenitic stainless steel, but a very low density which is only about 55% that of steel. Titanium has an extremely high affinity for oxygen and thus forms a very stable and highly adherent protective oxide film on its surface. This oxide film, which forms spontaneously and instantly when fresh metal surfaces are exposed to air and/or moisture, provides the excellent corrosion resistance of titanium. Besides, Grade 2 titanium has good ductility and formability which facilitate the forming operations in heat exchanging applications. Although lower than carbon steels, the thermal conductivity and thermal diffusivity of Grade 2 titanium are higher than most austenitic stainless steels and nickel alloys. Combined with its high specific strength, this makes it an ideal material for condenser, evaporator and heat exchanger tubing.

The hot-piercing & extrusion production line for seamless titanium tubes.

Generally, grade 2 unalloyed titanium has an all-alpha (hexagonal close-packed, HCP) crystal structure below the typical α transus temperature of 890°C [1635°F]. It has an all-beta (body-centered cubic, BCC) crystal structure above the typical β transus temperature of 913°C [1675°F]. Between these two temperatures, both alpha and beta are present. Annealed grade 2 unalloyed titanium may have an equiaxed or acicular alpha microstructure. Acicular alpha occurs during beta-to-alpha transformation on cooling through the transformation
temperature range. Platelet width decreases with cooling rate. Equiaxed alpha can only be produced by recrystallization of material that has been extensively worked in the alpha phase.

Chemical Composition Requirements

Mechanical Properties

Manufacture & Heat Treatment

Seamless tubes of ASTM B338 grade 2 titanium shall be made from hollow billet by any cold reducing or cold drawing process that will yield a product meeting all technical requirements. Seamless tubes shall be produced with a continuous periphery in all stages of manufacturing operations. The manufacture of titanium seamless tubing from scratch mainly includes: titanium sponge vacuum arc melting for ingot ➡ blooming to get the hollow billet ➡ cleaning ➡ cutting & feeding ➡ hot extrusion, or cross rolling + piercing ➡ degreasing ➡ drying ➡ cutting ➡ on-line annealing & straightening ➡ pickling ➡ multi-pass cold rolling ➡ degreasing ➡ drying ➡ vacuum annealing ➡ straightening ➡ cutting ➡ pickling ➡ final inspection ➡ marking & packaging. All tubes shall be solution annealed.

Autonomous TIG welding production line for the manufacture of ASTM B338 welded titanium tubes.

ASTM B338 Grade 2 titanium welded tubes shall be made from annealed, flat-rolled sheets or strips by an automatic arc welding (TIG) process. The main production procedures include: titanium sheet de-coiling ➡ shear butt welding ➡ cleaning ➡ tubular forming ➡ TIG welding ➡ eddy current testing ➡ pre-sizing ➡ annealing ➡ precise reducing sizing & straightening ➡ eddy current test ➡ diameter gauging ➡ marking ➡ cutting ➡ ultrasonic testing ➡ hydraulic testing ➡ final inspection ➡ packaging. Welded tubing shall be heat treated by at least a stress relief after forming and welding. Use of filler material is not permitted. All tubes shall be solution annealed.

Inspection & Tests

The hydrostatic tests for ASTM B338 Gr.2 seamless tubing.

PMI product analysis, tensile test, flattening test, flaring test, eddy current test, hydrostatic test, ultrasonic test, X-ray inspection, visual examination, dimension inspection.

Sizes & Dimensions

ASTM B338 grade 2 titanium tubing, either seamless or welded, is usually specified with outside diameter and minimum wall thickness. Sometimes the wall thickness may be specified by Birmingham Wire Gauge (B.W.G) numbers. The conventional diameters include: 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, 1″, 1.25″, 1.375″, 1.5″, and 2″. The commonly applied wall thicknesses include: 0.014″(BWG No.28), 0.020″(BWG No.25), 0.025″(BWG No.23), 0.028″(BWG No.22), 0.035″(BWG No.20), 0.049″(BWG No.18), 0.065″(BWG No.16) and 0.083″(BWG No.14). Custom-sizes-and-dimensions are available upon request.