Grade 11: Ductile Titanium with Palladium Protection
Grade 11 titanium adds 0.12 to 0.25 percent palladium to Grade 1 chemistry, which is the softest commercially pure grade, with minimum tensile strength of 240 MPa, yield strength of 170 MPa and elongation of at least 24 percent. The palladium addition promotes passivity in reducing and crevice environments, so the alloy resists attack where plain pure titanium would corrode, while retaining the outstanding formability of Grade 1.
Designated UNS R52250, Grade 11 is the low-strength member of the palladium-bearing family that also includes Grade 7. It is selected where maximum ductility and corrosion margin matter more than strength, such as thin-wall condenser tubes that must be rolled and flared repeatedly, and where process chemistry can shift toward reducing conditions.
Why Palladium Improves Corrosion Resistance
Palladium acts as a cathodic modifier: it lowers the potential needed for titanium to repassivate, so the protective oxide film reforms quickly even when the oxidant level in the process fluid is low. In hot chloride solutions, reducing acids such as dilute sulphuric and hydrochloric acid, and in crevices under deposits and gaskets, Grade 11 keeps its passive film where Grade 1 would pit or slowly dissolve.
The benefit is most visible in crevice situations: tube-to-tubesheet joints, ferrule seals and fouled surfaces create the oxygen-depleted zones where titanium normally becomes vulnerable. The palladium addition extends the safe operating window in temperature and chloride concentration, giving designers confidence in services with upset chemistry.
Round Tube Forms in ASME SB-338
ASME SB-338 covers seamless and welded round tube, and Grade 11 is supplied in both forms. Seamless tube is drawn from pierced billet, while welded tube is formed from strip and welded under inert gas, then annealed and examined. Both forms meet the same chemistry and mechanical requirements, and the standard defines the dimensional tolerances, straightness and surface condition for condenser and heat exchanger use.
Tube is offered in diameters from small bore up to about 80 mm and walls from 0.4 mm upward, in straight lengths typically 3 to 12 metres, with cut tolerances for bundle fabrication. Each lot is hydrostatically or non-destructively tested and certified, and the certification is the basis for code-registered exchanger construction.
Applications of Grade 11 Tube
Grade 11 round tube is specified for heat exchangers and condensers in chlor-alkali plants, pulp bleaching, chemical dosing systems, seawater intakes and geothermal brines, particularly where crevice corrosion has been a problem with other materials. The alloy also serves instrument and sampling lines where small-bore tube must survive aggressive media with maximum formability.
In desalination plants, Grade 11 tubes in the brine heater and recovery stages resist the hot, concentrated seawater that can push plain titanium to its limits. Because the tube is so ductile, bundle fabrication is forgiving: tubes roll into the tube sheet without cracking, and U-bends can be made with tighter radii than higher-strength grades allow.
Fabrication and Service Experience
Grade 11 tube is formed, welded and inspected with the same practice as other titanium grades, with clean handling to prevent iron contamination. Its softness means cutting and deburring must use sharp tooling to avoid smearing, and expansion into tube sheets is carefully controlled. Once in service, the alloy needs no coatings or cathodic protection, and its oxide film self-heals after minor damage.
Service history in aggressive exchangers shows Grade 11 outliving Grade 2 and even stainless alternatives in the same duty, with inspection intervals measured in years rather than months. The higher alloy cost is recovered through longer bundle life and fewer shutdowns, which is why operators with crevice-corrosion experience specify the palladium grades for their critical exchangers.
Frequently Asked Questions
Q: What is Grade 11 titanium?
A: Grade 11 is Grade 1 titanium with 0.12 to 0.25 percent palladium added, designated UNS R52250, combining maximum ductility with enhanced corrosion resistance.
Q: How does Grade 11 differ from Grade 1 titanium?
A: The palladium addition gives Grade 11 immunity to crevice corrosion and reducing media, while its mechanical properties match the soft, ductile Grade 1.
Q: Is Grade 11 tube available as welded product?
A: Yes, ASME SB-338 covers both seamless and welded round tube in Grade 11, with the same chemistry and mechanical requirements for both forms.
Q: Where is Grade 11 titanium tube used?
A: In heat exchangers and condensers for chlor-alkali, pulp bleaching, desalination and geothermal brine service, especially where crevice corrosion defeated other materials.
Q: What is the strength of Grade 11 titanium tube?
A: Minimum tensile strength is 240 MPa and yield strength is 170 MPa, matching Grade 1, which gives the alloy its excellent formability.
