{"id":4615,"date":"2026-07-12T13:33:03","date_gmt":"2026-07-12T13:33:03","guid":{"rendered":"https:\/\/beiyutitanium.com\/grade-7-titanium-reducing-acids\/"},"modified":"2026-07-18T11:53:28","modified_gmt":"2026-07-18T11:53:28","slug":"grade-7-titanium-reducing-acids","status":"publish","type":"post","link":"https:\/\/beiyutitanium.com\/de\/grade-7-titanium-reducing-acids\/","title":{"rendered":"Grade 7 Titanium for Reducing Acid Service: Where the Palladium Earns Its Cost"},"content":{"rendered":"

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.<\/p>\n

What Grade 7 titanium actually is<\/h2>\n

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.<\/p>\n

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.<\/p>\n

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<\/a>.<\/p>\n

Why palladium helps in reducing acids<\/h2>\n

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.<\/p>\n

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.<\/p>\n

How far the resistance actually extends<\/h2>\n

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.<\/p>\n\n\n\n\n\n\n\n
Medium (room temperature, approximate)<\/th>\nGrade 2<\/th>\nGrade 12<\/th>\nGrade 7<\/th>\n<\/tr>\n<\/thead>\n
Hydrochloric acid, useful resistance to about<\/td>\n7%<\/td>\n9%<\/td>\n27%<\/td>\n<\/tr>\n
Sulfuric acid, useful resistance to about<\/td>\nlow single digits<\/td>\nintermediate<\/td>\nabout 45%<\/td>\n<\/tr>\n
Crevice and pitting resistance in hot chlorides<\/td>\nlimited<\/td>\nimproved<\/td>\nbest of the three<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

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.<\/p>\n

Where Grade 7 belongs<\/h2>\n

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.<\/p>\n

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<\/a>, and the seawater and chloride side is covered in our titanium seawater corrosion resistance guide<\/a>.<\/p>\n

Standards, forms, and equivalents<\/h2>\n

Grade 7 is a mill-product grade available across the common wrought forms. Specify the form standard that matches the part.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\nDetail<\/th>\n<\/tr>\n<\/thead>\n
UNS number<\/td>\nR52400<\/td>\n<\/tr>\n
Nominal palladium<\/td>\n0,12 bis 0,25 % Pd<\/td>\n<\/tr>\n
Stangen und Kn\u00fcppel<\/td>\nASTM B348<\/td>\n<\/tr>\n
Blech, Band und Platte<\/td>\nASTM B265<\/td>\n<\/tr>\n
Seamless and welded tube and pipe<\/td>\nASTM B338 (tube); ASTM B861 (seamless pipe) and B862 (welded pipe), which replaced the legacy ASTM B337<\/td>\n<\/tr>\n
Mechanical class<\/td>\nComparable to Grade 2 (CP)<\/td>\n<\/tr>\n
Zertifikat<\/td>\nEN 10204 3.1 with heat number and chemistry, including palladium<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

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.<\/p>\n

<\/p>\n

How to read the Grade 7 certificate when it arrives<\/span><\/h2>\n

Grade 7 costs more than Grade 2 for exactly one reason, and that reason has to be visible on the certificate:<\/p>\n