What Is Titanium Grade 7
Titanium Grade 7, UNS R52400, is Grade 2 base composition with a palladium addition of 0.12 to 0.25 percent. The palladium raises the corrosion potential and blocks the initiation of crevice corrosion in hot chlorides and reducing acids, where standard CP titanium can fail under deposits and gaskets. Grade 7 is regarded as one of the most corrosion-resistant titanium materials available.
How Cold-Drawn Seamless Tubing Is Made
Seamless tubing begins as an extruded hollow shell that is reduced in stages by cold drawing through dies over mandrels. Cold drawing refines the dimensional accuracy, produces a smooth bore and surface, and develops the fine-grained structure needed for thin-wall exchanger tubes. Intermediate annealing restores ductility between passes, and the final pass is followed by a controlled anneal to meet the ASTM property requirements.
Mechanical Properties
Because Grade 7 builds on the Grade 2 base, its strength minimums match Grade 2: 345 MPa tensile and 275 MPa yield with 20 percent elongation in tube form. The cold-drawn product typically delivers these values with excellent consistency from tube to tube, which simplifies the design of the tube bundle. Density is 4.51 g per cubic centimetre.
Corrosion Resistance in Exchanger Service
Heat exchanger tubes face the harshest conditions at tube-to-tubesheet joints, under fouling deposits and beneath gaskets, exactly where crevice corrosion develops. Grade 7 resists attack in these locations across a wide range of chloride concentration and temperature. It also handles dilute sulfuric and hydrochloric acids better than CP grades, making it a first choice for aggressive chemical service.
Standards and Supply
Grade 7 tubing is supplied to ASTM B338 and ASME SB338, with each tube hydrostatically or pneumatically tested and dimensionally verified. Tubes are furnished in straight lengths or coils with a clean, pickled or polished surface. Mill certificates report composition, mechanical results and the test pressure applied to the lot.
Applications
Chemical process heat exchangers handling hot chlorides.
Seawater and brine coolers with crevice risk.
Pollution control and acid recovery equipment.
High-reliability condensers in process plants.
Frequently Asked Questions
Q: What is UNS R52400?
A: UNS R52400 is the designation for titanium Grade 7, the palladium-stabilized version of Grade 2.
Q: Why is palladium added?
A: Palladium raises the corrosion potential and suppresses crevice corrosion in hot chlorides and reducing acids.
Q: What are the strength minimums of Grade 7 tube?
A: 345 MPa tensile and 275 MPa yield with 20 percent elongation, matching the Grade 2 base.
Q: Why cold-drawn seamless tubing?
A: Cold drawing gives tight dimensional tolerances, a smooth bore and a consistent fine-grained structure for exchanger tubes.
Q: Which standard covers Grade 7 tubing?
A: ASTM B338 and ASME SB338 cover Grade 7 seamless and welded heat exchanger tubing.
Q: Where does Grade 7 outperform CP titanium?
A: Under crevice conditions, fouling deposits and in dilute reducing acids where standard CP grades can corrode.
