R50400: The Workhorse Titanium Grade
UNS R50400 is the designation of Grade 2 commercially pure titanium, containing at least 99.2 percent titanium with controlled oxygen up to 0.25 percent. Annealed Grade 2 tube shows a minimum tensile strength of 345 MPa, yield strength of 275 MPa and elongation of 20 percent. It is the default titanium grade for heat exchangers, condensers and seawater piping because it combines adequate strength with maximum corrosion resistance and moderate cost.
ASME SB-338 is the code specification for seamless and welded titanium tube in condensers and heat exchangers. The seamless product is pierced and drawn from a solid billet, eliminating the longitudinal weld, which is preferred where the full tube wall must carry pressure without reliance on weld integrity.
What Bright Finish Means
Bright titanium tube is produced by cold drawing with a smooth die and mandrel, followed by bright annealing in a vacuum or inert atmosphere furnace, or by pickling and finishing that leaves a clean, scale-free surface. Unlike hot-finished tube, bright tube has no oxide scale and shows a light, uniform metallic appearance. The surface roughness is low, which improves heat transfer and reduces fouling in service.
The bright surface also simplifies inspection: surface defects are visible, and the clean finish prevents the initial corrosion that can start under residual scale. For marine and hygienic applications, the smooth surface discourages biofouling and makes cleaning easier, both of which keep the tube performing at design heat transfer rates.
Heat Exchanger Performance
In shell-and-tube exchangers, Grade 2 titanium tubes resist the chloride pitting and stress corrosion that attack stainless steel in cooling water. The low surface roughness of bright tube reduces the fouling factor used in design, allowing a smaller exchanger for the same duty. Titanium's good thermal conductivity, about 16 to 17 W per metre kelvin, combined with thin walls, gives heat transfer competitive with copper-nickel at lower maintenance cost.
Erosion by suspended solids is minimal because the hard oxide surface resists impingement, and the tube's flexibility absorbs thermal expansion without the stress concentrations seen in stiffer alloys. These properties make R50400 bright tube the standard retrofit material for condensers previously tubed with copper-nickel or admiralty brass.
Marine Engineering Applications
Seawater systems are the second home of this tube: main and auxiliary condensers, seawater coolers for engines and hydraulics, desalination plant heat recovery units, and fish farm and ballast water systems. Titanium's immunity to seawater attack at ambient and moderate temperatures means tubes can be designed without corrosion allowance, reducing wall thickness and weight compared with copper-nickel.
In naval and offshore construction, the combination of light weight, corrosion resistance and long life offsets the higher first cost. Designers also value the fact that titanium does not require cathodic protection in seawater, eliminating the anodes and monitoring that steel systems need, and it causes no galvanic problems when properly insulated from dissimilar metals.
Fabrication and Quality Assurance
Seamless bright tube is U-bent, flared and roller-expanded with the same equipment used for other titanium grades, and the bright surface requires clean handling to avoid iron contamination. Tube-to-tubesheet joints are made by rolling and, where leak tightness is critical, by seal welding under argon. The finished bundle is hydrostatically tested, and each tube lot carries the SB-338 certification with chemistry, tensile and forming test results.
Non-destructive examination with eddy current or ultrasonic methods checks the full length of every tube, and dimensional verification confirms the tight tolerances that bright drawing provides. The documentation chain from melt to tube enables full traceability, which is a requirement for naval, nuclear and code-registered exchangers.
Frequently Asked Questions
Q: What is R50400 titanium?
A: R50400 is the UNS designation of Grade 2 commercially pure titanium, with at least 99.2 percent titanium, a minimum tensile strength of 345 MPa and yield strength of 275 MPa.
Q: What does bright finish mean for titanium tube?
A: Bright tube is cold drawn and bright annealed or pickled to give a smooth, scale-free surface that improves heat transfer, reduces fouling and simplifies inspection.
Q: Why is seamless tube preferred for heat exchangers?
A: Seamless tube has no longitudinal weld, so the full wall carries pressure uniformly, which is preferred for high-pressure and code-registered exchanger service.
Q: Does titanium tube need cathodic protection in seawater?
A: No, the stable oxide film protects titanium in seawater, so anodes and corrosion monitoring required for steel systems are unnecessary.
Q: What heat exchanger applications use R50400 bright tube?
A: Condensers, seawater coolers, desalination heat recovery units and chemical process exchangers, often as a retrofit replacing copper-nickel or brass tubes.
