One Alloy, Three Designations
Grade 2 commercially pure titanium is identified by three widely used systems. ASTM B265 and related product standards call it Grade 2; the Unified Numbering System designates it UNS R50400; and the European material numbering system lists it as 3.7034 with the DIN material name Ti 99.2. All three refer to the same nominal composition: at least 99.2 percent titanium with controlled oxygen up to 0.25 percent and iron up to 0.30 percent.
The multiple designations matter in international trade, because a tube order may be written to any of the systems. A responsible supplier cross-references the designations on the certificate so the buyer can verify that the material meets the local code requirement, whether that is ASTM, EN or an internal standard.
Properties of Grade 2 Tube
Annealed Grade 2 tube has a minimum tensile strength of 345 MPa, minimum yield strength of 275 MPa and minimum elongation of 20 percent in a 50 mm gauge length. This strength is sufficient for condenser and heat exchanger service at typical shell-side and tube-side pressures, and it allows thin walls that keep the bundle light and thermally efficient.
The corrosion resistance is the defining feature: Grade 2 resists seawater, brackish water, chlorides, oxidising acids and most organic media through its stable oxide film. It is immune to chloride stress corrosion cracking and shows excellent resistance to pitting and erosion, which is why it replaces copper-nickel and stainless steel tubes in plants with corrosive cooling water.
Why Condensers and Heat Exchangers Use It
Power plant condensers, refinery coolers, desalination units, chemical exchangers and shipboard coolers all specify Grade 2 tube. The operating experience is measured in decades: titanium tubes do not pit, do not need corrosion allowance, and do not require chemical treatment of the cooling water for corrosion control. The low fouling tendency of the smooth oxide surface keeps heat transfer high and cleaning intervals long.
The economic case is strongest where cooling water is seawater or industrial chloride-laden water. A titanium-tubed condenser costs more initially than a copper-nickel unit but outlasts several replacements, and it eliminates the copper discharge and biocide dosing that environmental regulation now restricts. Life-cycle cost analysis consistently favours titanium in these duties.
Seamless and Welded Forms
ASTM B338 covers both seamless and welded Grade 2 tube. Seamless tube is pierced and drawn from billet, giving a uniform wall with no weld, and is preferred for high-pressure and critical bundles. Welded tube is formed from strip and welded under inert gas, then annealed and examined; with proper weld quality it matches seamless corrosion performance at lower cost, which makes it the standard for large condenser retubing projects.
Both forms are supplied in straight lengths or U-bends, with diameters from about 6 mm upward and walls from 0.4 mm. The finished tube is eddy-current or ultrasonically tested over its full length, and hydrostatic testing is applied where the design specifies it.
Fabrication and Retubing Practice
Fabrication follows established titanium practice: clean handling to avoid iron contamination, controlled rolling of tubes into tube sheets, and argon-shielded seal welding where leak tightness is critical. For retubing an existing condenser, the old tubes are pulled, the tube sheet holes are cleaned and measured, and the new titanium tubes are rolled and optionally seal-welded with the same expansion control.
Tube sheet materials are usually carbon steel with a titanium clad face, or solid titanium where seawater corrosion of the sheet is a concern. The bundle is then tested hydrostatically and, for code-registered exchangers, the tube-to-tubesheet joints are examined and documented. This disciplined practice delivers the long service life for which titanium condensers are known.
Frequently Asked Questions
Q: What do UNS R50400 and 3.7034 mean?
A: R50400 is the UNS designation and 3.7034 the European material number for the same Grade 2 commercially pure titanium alloy.
Q: What is the strength of Grade 2 titanium tube?
A: Minimum tensile strength is 345 MPa, yield strength 275 MPa, and elongation at least 20 percent in the annealed condition.
Q: Why is Grade 2 used in condensers?
A: It resists seawater and chloride attack without corrosion allowance, fouling or chemical treatment, giving decades of service at low life-cycle cost.
Q: Is welded Grade 2 tube acceptable for heat exchangers?
A: Yes, when the weld is made under inert gas and the tube is annealed and full-length examined, welded tube matches seamless corrosion performance at lower cost.
Q: Can Grade 2 titanium tubes be U-bent?
A: Yes, U-bending is standard with mandrel tooling, and the bend radius follows the tube diameter and wall thickness according to the fabricator's practice.
