Grade 2 titanium handles most oxidizing and neutral media, but it loses ground in hot reducing acids such as hydrochloric and sulfuric acid, where the protective oxide film is harder to keep stable. Grade 7 titanium is the answer the chemical industry reaches for when the medium is reducing, hot, or chloride-rich and a plain commercially pure grade would corrode too fast. This guide explains what Grade 7 is, why the palladium addition matters, where it belongs, and how to specify it on an RFQ.
What Grade 7 titanium actually is
Grade 7 is commercially pure titanium with a small palladium addition, nominally 0.12 to 0.25% Pd, covered by UNS R52400. Mechanically it behaves almost exactly like Grade 2: the same modest strength, the same good formability and weldability, the same density. The palladium does not change the mechanics. What it changes is electrochemistry.
In reducing acids, titanium's passive oxide film becomes harder to maintain, and unalloyed grades can move into an active corrosion state. The palladium raises the alloy's corrosion potential into a more noble range, which keeps the film passive at acid concentrations and temperatures where Grade 2 would already be corroding. The result is the same titanium you already know how to fabricate, with a much wider window of chemical service.
Because the mechanical properties track Grade 2, Grade 7 is specified by corrosion need, not by strength. If the environment does not attack Grade 2, paying for palladium adds cost without benefit. The engineering question is always the medium, not the grade in isolation. The full chemistry and mechanical class sit on our Grade 7 titanium (Ti-0.15Pd, UNS R52400) spec page.
Why palladium helps in reducing acids
Titanium resists corrosion because it carries a thin, self-healing oxide film. In oxidizing conditions that film reforms instantly, which is why Grade 2 shines in seawater, wet chlorine, and nitric acid. In reducing acids there is less oxygen available to rebuild the film, so a scratch or a crevice can stay active and dissolve.
The palladium in Grade 7 acts as a catalyst for the cathodic reaction, shifting the metal's potential far enough to keep the oxide film stable even in these oxygen-starved conditions. That single change extends useful resistance to higher acid concentrations, higher temperatures, and the tight chloride-rich crevices where plain titanium is most vulnerable to pitting and crevice attack.
How far the resistance actually extends
Published titanium iso-corrosion data give a useful sense of the gap between grades. The figures below are approximate room-temperature limits for low corrosion rates and should be read as an orientation, not a design guarantee, because real service depends on temperature, aeration, chloride content, and impurities.
| Medium (room temperature, approximate) | Grade 2 | Grade 12 | Grade 7 |
|---|---|---|---|
| Hydrochloric acid, useful resistance to about | 7% | 9% | 27% |
| Sulfuric acid, useful resistance to about | low single digits | intermediate | about 45% |
| Crevice and pitting resistance in hot chlorides | limited | improved | best of the three |
Two points matter for specification. First, Grade 7 does not make titanium immune to acid; it widens the window, and boiling or concentrated conditions still need testing against the actual stream. Second, the ranking is consistent: for reducing-acid duty the order is Grade 7 first, then Grade 12, then unalloyed grades. Where a stream is borderline for Grade 2, Grade 7 usually converts it into safe titanium service.
Where Grade 7 belongs
Grade 7 is a chemical-processing grade first. It is specified for reactors, heat exchangers and acid coolers, columns, piping, and vessel linings in duties involving hydrochloric or sulfuric acid, chloride-bearing process streams, and fertilizer and pigment production. It also appears in metal-finishing and pickling lines, and anywhere hot brine or acidic chlorides would drive crevice corrosion in a leaner grade.
It is not the grade for structural or high-strength parts; that is where Ti-6Al-4V lives. And in strongly oxidizing service such as seawater, wet chlorine, or nitric acid, Grade 2 is already fully passive, so Grade 7 adds cost without adding life. The way to choose between commercially pure grades for a given medium is covered in our Leitfaden zur Auswahl von Reintitan-Graden, and the seawater and chloride side is covered in our titanium seawater corrosion resistance guide.
Standards, forms, and equivalents
Grade 7 is a mill-product grade available across the common wrought forms. Specify the form standard that matches the part.
| Property | Detail |
|---|---|
| UNS number | R52400 |
| Nominal palladium | 0,12 bis 0,25 % Pd |
| Stangen und Knüppel | ASTM B348 |
| Blech, Band und Platte | ASTM B265 |
| Seamless and welded tube and pipe | ASTM B338 (tube); ASTM B861 (seamless pipe) and B862 (welded pipe), which replaced the legacy ASTM B337 |
| Mechanical class | Comparable to Grade 2 (CP) |
| Zertifikat | EN 10204 3.1 with heat number and chemistry, including palladium |
When you order, make sure the mill test certificate reports the actual palladium content against the 0.12 to 0.25% range, not just a grade name, because palladium is the reason the grade costs more and it is the one element the certificate must confirm.
How to read the Grade 7 certificate when it arrives
Grade 7 costs more than Grade 2 for exactly one reason, and that reason has to be visible on the certificate:
- Palladium content. Confirm the certificate reports actual palladium in the 0.12 to 0.25% range by heat, not just the words Grade 7. Palladium is the element you are paying for and the only one that distinguishes Grade 7 from Grade 2, so a certificate that omits it does not confirm what you bought.
- Balance chemistry and mechanicals. The rest of the chemistry and the strength values track Grade 2, so read them against the same commercially pure limits and against the ordered form’s standard.
- Form and standard match. Check the certificate is written against the standard for the form you ordered, ASTM B348 for bar, B265 for plate, B338 for tube, since limits and test bases differ by form.
Close with the heat number matching the material marking. The trap in Grade 7 procurement is a certificate that names the grade but never prints the palladium result, which leaves you unable to prove you received a palladium-bearing heat rather than Grade 2 relabelled.
Grade 7 versus the leaner alternatives
Palladium is expensive, so the industry created leaner corrosion grades that aim for most of the benefit at lower alloy cost. Grade 16 uses a smaller palladium addition (nominally 0.04 to 0.08% Pd) and Grade 26 uses ruthenium instead of palladium; both target similar reducing-acid and crevice duties at a lower precious-metal loading. Grade 12, which adds molybdenum and nickel rather than a precious metal, is a further economical option for moderately aggressive hot brines and chlorides.
The practical decision comes down to how aggressive the stream is and how the palladium price sits when you buy. For the most demanding reducing-acid duty, Grade 7 remains the reference. For borderline streams, a leaner grade can carry the load at lower cost. Beiyu supplies Grade 7, Grade 12, and the leaner corrosion grades Grade 16 and Grade 26, so the grade can be matched to the actual stream rather than defaulting to the most expensive option. When even Grade 7 is not enough because the medium attacks titanium itself, the conversation moves to nickel alloys such as Legierung 625, which is why we keep both material families in scope for Chemieanlagen.
How to specify Grade 7 on an RFQ
Because Grade 7 is chosen by corrosion duty, the most useful RFQ describes the service, not just the part. State the medium and concentration, the operating temperature, the form and dimensions, the governing standard, the quantity, and the certificate requirement. Naming the actual acid stream lets the supplier confirm that Grade 7 is the right call rather than a leaner or heavier grade. The full field list is in our Checkliste für Titanstab-Anfragen. Beiyu supplies Grade 7 bar, sheet and plate, and tube on an RFQ basis with EN 10204 3.1 documentation that reports palladium against the specified range.
Fabrication and welding: palladium changes the chemistry, not the workshop
Grade 7 forms, machines and welds like Grade 2, because mechanically it is Grade 2; the palladium addition works in the corrosion cell, not in the press brake. Welding follows standard titanium practice with full inert gas shielding, and the filler question matters here more than anywhere: a Grade 7 vessel welded with plain Grade 2 filler has Grade 2 weld seams facing the acid, which defeats the point of paying for palladium. Specify matching Ti-Pd filler on fabrication-bound orders and keep weld colour acceptance in the fabrication file.
Verifying palladium: the certificate and the PMI check
Palladium is invisible: Grade 7 Stab looks exactly like Grade 2, and the price difference makes misidentification expensive in both directions. Two controls close the gap. The certificate must report palladium in the chemistry table, in the 0.12 to 0.25 percent band the standards define. Positive material identification by X-ray fluorescence can confirm palladium in the delivered metal at receiving, which is why Ti-Pd grades are a textbook case for adding a PMI line to the RFQ on safety-critical acid service. A buyer who orders Grade 7 and never verifies palladium is trusting the label on the most label-dependent grade in the family.
Handling and segregation: two invisible grades, one rack
The plant-side risk with Grade 7 is mix-up, not corrosion of the stock itself. Because Grade 2 and Grade 7 are visually identical, segregate them physically, keep heat-number marking legible through cutting and fabrication, and re-mark offcuts before they return to stores. An unmarked Ti-Pd offcut is economically stranded, and an unmarked CP offcut in the Grade 7 rack is a latent acid-service failure. The general titanium rules also apply: keep the material clear of carbon steel contact so embedded iron does not stain the surface or seed local attack.
Einkaufshinweise vom Export-Team
Palladium makes Grade 7 the most price-volatile grade in the CP family, so quotes carry shorter validity than Grade 2 and comparing offers weeks apart misleads. Three habits keep orders clean: state the acid, concentration and temperature on the RFQ so the mill’s review confirms the grade fits the duty; ask whether Grade 12 or Grade 16 covers the condition at lower cost, because the honest answer is sometimes yes and the existing section on leaner alternatives sets out when; and put the PMI requirement on the order rather than negotiating it after delivery. Beiyu reviews each Ti-Pd enquiry line against mill capability before quoting, with EN 10204 3.1 documentation and heat-number traceability by order scope.
FAQ
What is the difference between Grade 2 and Grade 7 titanium?
Grade 7 is Grade 2 titanium with 0.12 to 0.25% palladium added. The mechanical properties are essentially the same; the palladium greatly improves resistance to reducing acids such as hydrochloric and sulfuric acid and to crevice corrosion in hot chlorides. Use Grade 2 when the medium is oxidizing or neutral and Grade 7 when it is reducing, hot, or chloride-rich.
What is the UNS number for Grade 7 titanium?
Grade 7 titanium is UNS R52400. It is supplied as bar and billet to ASTM B348, as sheet and plate to ASTM B265, as tube to ASTM B338, and as pipe to ASTM B861 or B862.
Is Grade 7 titanium resistant to hydrochloric acid?
Yes, within limits. Grade 7 offers useful resistance to substantially higher hydrochloric acid concentrations than Grade 2 at room temperature, but boiling or concentrated acid still needs testing against the actual stream, including its temperature and chloride content.
When should I choose a leaner grade instead of Grade 7?
If the stream is only moderately aggressive, a lower-palladium grade such as Grade 16, a ruthenium grade such as Grade 26, or the molybdenum-nickel Grade 12 can carry the duty at lower precious-metal cost. Grade 7 remains the reference for the most demanding reducing-acid service. Share the medium and temperature and the supplier can confirm the leanest grade that still meets the duty.