ASTM B862 Ti2 Welded Titanium Pipe: Properties, Applications and Selection

What Is ASTM B862 Ti2 Welded Titanium Pipe?

ASTM B862 is the international standard that covers welded titanium and titanium alloy pipe for general corrosion service. A Ti2 designation refers to Grade 2 commercially pure titanium, identified as UNS R50400, with chemical limits defined in ASTM B265. Grade 2 is the most widely specified commercially pure titanium grade because it balances useful strength, excellent weldability, and outstanding corrosion resistance at a moderate cost.

Unlike seamless pipe produced under ASTM B338 or ASTM B861, welded pipe is formed from strip or plate and joined with a full-penetration longitudinal weld made by automated gas tungsten arc welding (GTAW) under inert gas shielding. When the weld is verified by nondestructive testing, the finished pipe delivers mechanical performance close to that of the base metal while remaining significantly more economical than seamless equivalents.

Chemical Composition and Mechanical Properties

Grade 2 titanium contains a minimum of 99.2 percent titanium. Impurity limits, which directly control strength and corrosion behavior, are summarized below per ASTM B265.

Minimum mechanical properties for Grade 2 pipe per ASTM B861 and ASTM B862 are a tensile strength of 345 MPa, a yield strength (0.2 percent offset) of 275 MPa, and an elongation of 20 percent in 50 mm. These values allow process piping to be designed with familiar ASME B31.3 allowable stress rules.

Why Grade 2 Welded Pipe Fits the Chemical Processing Industry

Grade 2 titanium forms a stable, self-healing oxide film that makes it immune to pitting, crevice corrosion, and chloride-induced stress corrosion cracking under conditions where 316 stainless steel fails rapidly. It performs well in oxidizing, neutral, and mildly reducing media, including chlorates such as sodium chlorate, hypochlorites such as bleach, wet chlorine gas, oxidizing acids such as nitric and chromic acid, and a wide range of organic chlorides.

The material has limits: it should not be used in non-aerated, strongly reducing acids such as hot concentrated hydrochloric or sulfuric acid. For those services, palladium-stabilized Grade 7 (Ti-0.15Pd) or Grade 12 (Ti-0.3Mo-0.8Ni) is the appropriate upgrade.

Application Areas in Process Plants

Chlor-alkali plants: wet chlorine gas transfer (hot or cold), sodium hypochlorite storage and transfer, chlorate solution lines for chlorine dioxide generation in pulp bleaching.

Organic chemical production: streams containing chlorobenzene, vinyl chloride, and other organic chlorides in pesticide, dye, pigment, and PVC manufacturing; acetic and formic acid service with chloride contamination.

Inorganic chemicals: nitric acid concentration and recovery units, urea plant high-pressure decomposition sections.

Oil refining and petrochemicals: crude distillation overhead systems handling HCl, H2S, and water vapor; hydrotreating unit condensates containing ammonium chloride and ammonium bisulfide.

Environmental engineering: industrial wastewater piping with chlorides and sulfides, flue gas desulfurization condensate lines downstream of scrubbers.

Design and Fabrication Considerations

Welding: use GTAW with high-purity argon shielding on both the root and face; filler metal ERTi-2 is standard. Contamination above 250 ppm oxygen pickup embrittles the weld.

Crevice corrosion: avoid stagnant zones, gasketed dead spaces, and flanges exposed above 120 degrees Celsius in high-chloride, oxygen-deficient service.

Erosion and cavitation: limit fluid velocity when solids are present, typically below 6 to 9 m/s depending on particle loading.

Galvanic coupling: isolate titanium from carbon steel and copper alloys to prevent accelerated attack of the less noble metal.

Welded Pipe versus Seamless Pipe: How to Choose

Welded pipe per ASTM B862 is the preferred economic solution for most CPI process lines, heat exchanger connections, and utility systems because it offers equivalent corrosion resistance at a lower cost. Seamless pipe per ASTM B338 or ASTM B861 should be specified when the service demands maximum pressure integrity without a weld seam, such as high-pressure hydrogen service, severe cyclic loading, or thin-wall instrumentation lines where weld inspection is impractical.

FAQ

Is ASTM B862 Ti2 pipe suitable for seawater service?

Yes. Grade 2 titanium is widely used in seawater cooling systems, desalination plants, and offshore piping because its oxide film is immune to chloride pitting and stress corrosion cracking.

What filler metal is used to weld Grade 2 titanium pipe?

ERTi-2 filler wire is standard for Grade 2 joints. Both sides of the weld must be shielded with high-purity argon, and the weld zone must stay below 250 ppm oxygen pickup.

How does Grade 2 welded pipe compare with 316L stainless steel in chlorides?

Grade 2 titanium is immune to chloride pitting, crevice attack, and chloride stress corrosion cracking, while 316L stainless steel is susceptible to pitting and crevice corrosion above roughly 60 degrees Celsius in chloride media.

What wall thickness and diameter ranges are typical for welded titanium pipe?

Welded pipe is commonly supplied in diameters from about 15 mm to 600 mm with wall thicknesses from 0.9 mm to 12 mm; larger and thicker sections are available on a project basis.

Is post-weld heat treatment required for Grade 2 titanium pipe?

No. Commercially pure titanium does not require post-weld heat treatment. A clean weld with proper argon shielding provides full-strength, ductile joints in the as-welded condition.

Can ASTM B862 welded pipe be used for high-pressure service?

Yes, within the allowable stress limits of the applicable design code. The weld seam is 100 percent inspected, and the pipe is hydrostatically tested, but seamless pipe remains the first choice for the most severe pressure and fatigue conditions.