TA2 Titanium Bolt and Nut: Galling and Strength Limits

Опубликовано Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd от 2026-11-12

TA2 titanium bolts and nuts are stocked from M6 to M36 in metric and UNC/UNF threads, but a TA2 bolt is not a corrosion-proof steel bolt — it is a weaker one. Grade 2 commercially pure titanium has a minimum yield around 275 MPa against roughly 828 MPa for Gr5 (Ti-6Al-4V), and a proof load roughly one third of a same-size Gr5 fastener. Substituting TA2 for a steel or B8M stud on a Class 300 flange, then applying the original torque, stretches the bolt and loses the gasket compression. Pair that bolt with a TA2 nut and the first disassembly attempt cold-welds the threads.

This guide is for buyers specifying fasteners for chemical equipment: reactor covers, flanged piping, tank closures, heat exchanger covers and marine hardware. It covers the strength boundary, the galling mechanism, anti-seize selection, bolt-nut grade pairing, the F467/F468 and B348/B18 standard chain, galvanic isolation from carbon steel, the service limits of TA2, the economics of a seized stud, and the eight fields that belong on the RFQ. For the full fastener range see our Titanium Fasteners category and the bolts and screws guide.

Standards	ASTM F468 (bolts) / F467 (nuts); B348 (bar stock); ASME B18.2.1 / B18.2.2 (dimensions); B18.21.1 (washers)
Grades	TA2 / Gr2 / UNS R50400 for general corrosion service; Gr5 / TC4 for high load; Gr7, Gr23 for special duties
Service	Chemical equipment covers, flanged piping, tank and reactor closures, heat exchanger covers, marine hardware
Core distinction	TA2 is chosen for corrosion resistance, not strength. Specify proof load, a dissimilar nut grade and anti-seize, or the joint will stretch and then seize.

The "Corrosion-Proof Steel Bolt" Trap: A Class 300 Flange That Would Not Seal

A chemical plant replaced the B8M stainless studs on a Class 300 TA2 flanged line with TA2 titanium bolts during a 2023 shutdown. The reasoning sounded reasonable: the line was corrosive, the stainless studs showed surface staining, and titanium is more corrosion resistant. The same size, the same thread and the same torque procedure were used. Three bolts yielded during hydrotest, the raised face wept, and two more broke off in the flange holes when the crew tried to remove them after the first heat-up.

Two different errors sat in the same joint. First, the bolts had been treated as a material upgrade rather than a strength downgrade. TA2's proof load is far below that of a B8M or Gr5 fastener of the same diameter; applying the original torque took several of them past yield, so the gasket never held the design seating stress. Second, TA2 bolts were paired with TA2 nuts with no anti-seize. Under thread contact pressure, the thin TiO2 film ruptured and bare titanium cold-welded to bare titanium — classic galling. The crew then applied an impact wrench, which tore the first engaged threads and left broken studs in the flange.

The rule: a fastener substitution is a recalculation, not a material swap. Check proof load and available gasket seating stress first, then specify the nut grade and anti-seize. Corrosion resistance and load capacity are independent properties, and TA2 trades the second for the first.

The eventual fix was a Gr5 bolt set with B8M nuts, MoS2 anti-seize and a revised torque table. Our fastener assembly accident analysis and anti-seize versus threadlocker notes cover both mechanisms in more depth.

What TA2 Fasteners Actually Are, and the Standard Chain

Four standards sit behind a titanium bolt, and buyers who cite only one of them create gaps. ASTM B348 covers the bar stock the bolt is made from — chemistry, mechanical properties, condition and NDT. ASTM F468 covers finished nonferrous bolts, hex cap screws and studs, including mechanical requirements and testing; F467 covers the matching nuts. ASME B18.2.1, B18.2.2 and B18.21.1 define the dimensions, thread forms and washer geometry. A complete PO names the grade and UNS number, the F468/F467 mechanical requirement, the B18 dimensional standard, and the B348 bar origin.

There is a further manufacturing distinction. Small-diameter hex bolts up to roughly 1/2 inch can be cold-headed, which produces grain flow that follows the head-to-shank transition — the highest-stress region of the part. Larger bolts are normally hot-headed from B381-type forgings at roughly 800–950 C with an adequate reduction ratio. A bolt machined entirely from bar stock has grain running along the bar axis and exposes transverse grain under the head; for larger diameters and cyclic duty that is not a code-compliant fastener, however good the surface finish looks. Ask how the head was formed on any bolt above 1/2 inch.

Grade	Approx. min. yield	Correct use
TA2 / Gr2	approx. 275 MPa	Low-load covers, light flanges, marine hardware, non-structural corrosion-resistant fixing
Gr5 / TC4 (Ti-6Al-4V)	approx. 828 MPa	Class 300 and above, high bolt preload, structural and cyclic joints
Gr7 / TA9	similar to Gr2	Crevice corrosion resistance at the bolted joint; strength still low
Gr23 ELI	lower than Gr5	Implant and high-toughness duties with F136 material certification

These are approximate orientation values; use the actual F468 mechanical property table and the certificate for design. See our Gr2 vs Gr5 bolt comparison and the F468 fastener standard page for the detailed numbers.

Strength: The Number That Ends Most Substitutions

On a nominal 1/2 inch fastener, a Gr2 proof load is commonly quoted around 19.5 kN against roughly 58.5 kN for Gr5 — about three times the difference. That ratio is why the substitution in the opening case failed at hydrotest. It also interacts with the flange: titanium's lower elastic modulus means the flange stores less elastic strain energy at a given preload, so any gasket creep eats the sealing stress faster than on a steel joint. A weaker bolt and a low-modulus flange together are an unforgiving combination on a thermally cycled line.

Three rules follow. Never substitute a titanium bolt for a steel or stainless stud without recalculating the bolt load and the gasket seating stress. For Class 300 and above, high preload, or any structural or cyclic joint, use Gr5 — or use B8/B8M stainless studs with proper galvanic isolation. Where TA2 bolts are used, reduce the torque to the TA2 proof load, use a larger diameter if necessary, and document the torque table in the assembly procedure. Our flange, bolt and gasket three-piece analysis covers the joint calculation.

Galling: Why Titanium Threads Cold-Weld

Titanium's passive TiO2 film is only a few nanometres thick and brittle. Thread flanks under assembly contact pressure commonly see a few hundred MPa, well above the stress needed to rupture that film. Once the film is gone, bare titanium presses against bare titanium under relative rotation; the asperities friction-weld, the junctions grow, and the thread locks. This is galling, and it is not a lubrication inconvenience — it destroys the fastener on the first disassembly attempt.

Three controls work together. Use dissimilar grades or materials for the bolt and nut so the surface hardnesses differ by roughly 100 HV or more — a Gr2 bolt with a Gr5 nut, or a titanium bolt with a B8M stainless nut. A Gr2 bolt with a Gr7 nut does not help, because both sit near the same hardness. Apply an anti-seize compound to the threads and under the nut bearing face. And control assembly: use a calibrated torque wrench, slow steady rotation, no impact tools, and stop if torque rises abnormally. Our anti-seize guidance explains why threadlocker is not a substitute.

Anti-Seize: Three Families and One to Ban

Molybdenum disulfide (MoS2) anti-seize is the general-purpose default for titanium, usable to roughly 400 C in non-oxidising conditions and effective at preventing metal-to-metal contact. Copper-based anti-seize handles higher temperatures, up to around 800 C, but copper is a bad choice in many chemical environments and can contribute to galvanic effects — do not use it on acid-exposed joints. PTFE-based compounds are clean and suitable for lightly loaded, low-cycle assemblies where contamination must be minimised, but they are weaker under repeated disassembly. Nickel-based anti-seize should be avoided on titanium: nickel can interact with titanium at temperature and is a poor galvanic partner in chloride service.

Specify the compound by name on the assembly procedure, state the coverage (threads plus nut bearing face), and require that it be applied at assembly rather than at the supplier's factory, where it can attract dirt in transit. Also state the retorque and disassembly procedure: after a thermal cycle, break the joint in a controlled way rather than with an impact wrench. A seized stud that has to be drilled out costs hours per hole and risks damaging the flange.

Bolt, Nut, Washer and Galvanic Isolation

Buying a bolt is buying a set. The washer is not decorative: it spreads the bearing load, protects the flange face from galling under the nut, and provides a place to put an insulating layer. On a titanium flange bolted with B8M studs, or a titanium bolt on a carbon steel flange, use isolation washers and sleeves to break the galvanic path. Titanium is the cathode in most couples, so the active metal corrodes and the titanium may absorb hydrogen — a slow embrittlement mechanism that shows up months later at the hub fillet or under the bolt head.

Kit the parts. A bolt, nut and washer set from one controlled lot, with the same heat numbers documented together, avoids the classic storeroom problem of a Gr2 nut being fitted to a Gr5 bolt because they looked the same. Our bolt, nut and washer set page shows how we package these kits, and the hex bolt dimensional guide covers thread and length selection. Check the bar versus finished fastener boundary if your PO mixes raw bar and finished bolts.

Where TA2 Fasteners DO Fail: Read This Before You Approve the Set

Overload from torque calculated for steel

The opening-case failure. TA2 proof load is roughly one third of Gr5 at the same size. Recalculate bolt load and gasket seating stress, reduce torque, and use Gr5 or stainless studs for Class 300 and above.

Galling on same-grade titanium threads

TiO2 film rupture plus rotation produces cold welding. Pair dissimilar grades with a hardness difference of roughly 100 HV or more, apply MoS2 anti-seize, and assemble slowly with a calibrated wrench. Impact tools turn a difficult nut into a broken stud.

Hot chloride crevices under the head and in the thread root

The bolt head bearing face, the thread root and any washer gap are stagnant crevices. Above roughly 60–70 C in chloride service they acidify and attack the film. Smooth bearing surfaces, correct washers and a crevice-free joint design matter more than a grade upgrade; see the Gr2 vs Gr7 guide.

Hydrogen embrittlement from galvanic couples and pickling

Carbon steel contact, cathodic protection and over-long HF/HNO3 pickling can charge hydrogen into the surface. Above a few hundred ppm, hydride platelets precipitate and ductility falls; delayed cracking under load can occur well after hydrotest. Control the couple, control the pickling time, and inspect at shutdowns.

Reducing acids, fluoride and dry chlorine

TA2 has no useful resistance to HF or fluoride contamination, degrades in hot concentrated HCl and H2SO4, and needs trace water to repassivate in dry chlorine and water-free organics. Check cleaning chemicals and upset cases. These are absolute exclusions, not grade-selection questions.

Do not replace a steel or B8M stud with a same-size TA2 bolt without a bolt-load recalculation, do not pair a TA2 bolt with a TA2 nut, do not assemble titanium threads dry, and do not use an impact wrench to remove a stiff titanium nut.

Cost Economics: What a Seized Stud Costs

Fasteners are the cheapest line on an equipment bill and one of the most expensive to get wrong. A Gr2-to-Gr5 upgrade, a matched nut set and a tin of MoS2 anti-seize add very little to a flange joint. Drilling out a broken stud, chasing the thread, replacing the gasket and re-hydrotesting a reactor cover consumes hours of skilled labour and holds the vessel out of service. A bolt that yielded at hydrotest also means the gasket must be replaced and the seating face inspected for damage.

Where TA2 is genuinely the right and economical choice: low-load covers, light flanges, marine hardware and non-structural corrosion-resistant fixing where the bolt load is small and the joint is assembled with correct anti-seize. Where the extra cost is justified: Class 300 and above, cyclic or structural joints (Gr5), hot chloride crevices (Gr7 or a redesigned joint), and any assembly that will be disassembled repeatedly (a well-kitted dissimilar-grade set with a documented procedure). Our small-order bolt service covers repair quantities, and the price index plus the latest daily report give base material context. All multiples here are approximate planning figures.

Seven Procurement Mistakes That Show Up at Disassembly

1. Treating TA2 as a strength-equivalent substitute. Recalculate proof load and gasket seating stress.
2. Pairing the same grade for bolt and nut. Use Gr2 bolt with Gr5 nut, or titanium bolt with B8M nut.
3. Assembling dry. Specify the anti-seize compound, coverage and application point.
4. Citing only a dimensional standard. Name F468/F467, B348 bar origin and B18 dimensions.
5. Accepting bar-machined heads on large bolts. Require cold or hot heading with correct grain flow.
6. No galvanic isolation from carbon steel. Use insulating washers and sleeves and control CP potentials.
7. Using impact tools on a stiff joint. Put the controlled removal procedure in the assembly instruction.

Stock, Small Order and Lead Time

We stock TA2 / Gr2 and Gr5 / TC4 bolts, nuts and washers in M6 to M36, metric and UNC/UNF threads, in hex, socket and countersunk head forms, kitted as matched sets with heat-number documentation. Exact sizes and quantities are on our inventory page and the bolt size chart; confirm live availability when you enquire. Non-standard lengths, special threads and fasteners made to drawing are supplied through our non-standard fastener route.

Small orders are normal. A handful of replacement bolts for one shutdown repair is as valid as a full equipment bill of materials, and same-day dispatch on stocked sizes is where a stockholder beats a mill minimum. We can also supply the matching flanges, gaskets and anti-seize as one compatible joint package, so the three-piece system is consistent rather than assembled from three suppliers' assumptions.

Lead time depends on whether the size, grade and thread are in stock and whether F468 certification, third-party witnessing or custom heading is required. We quote a firm date with the offer. Send the size, thread, length, grade, head form, nut grade, washer and anti-seize requirements, bolt load and document set to our quotation desk; our enquiry response procedure lists what we need to reply within 24 hours. For export orders, state the certificate language and packing — threaded parts need protection against handling damage.

Supplier Verification: What to Ask Before the PO

Ask which heat the bar came from and request the B348 chemistry and mechanical results. Ask for the F468/F467 mechanical test report for the finished fastener, including proof load. Ask how the head was formed — cold-headed, hot-headed or machined from bar — and what reduction ratio was achieved on larger sizes. Ask how threads are produced and checked, and what gauge class is used. Ask whether the bolt and nut are kitted from controlled lots with matching documentation, and whether PMI is performed on the finished parts.

Then ask the assembly question: given this flange class and gasket, do you recommend TA2 or Gr5, and what torque and anti-seize would you specify? A supplier who asks for the bolt load before quoting has understood the failure mode. Our certifications page, the materials overview and the fastener guide give the document set and grade range.

Frequently Asked Questions

Q1: What causes titanium bolt galling?

The thin brittle TiO2 film ruptures under thread contact pressure of a few hundred MPa. Bare titanium then contacts bare titanium under rotation, asperities friction-weld, and the thread locks. Prevent it with a dissimilar bolt/nut grade pairing (roughly 100 HV hardness difference or more), MoS2 anti-seize on threads and bearing faces, and slow controlled assembly with a calibrated torque wrench.

Q2: Should the nut be a different grade?

Yes. A Gr2 bolt with a Gr5 nut, or a titanium bolt with a B8M stainless nut, is the usual solution. A Gr2 bolt with a Gr2 or Gr7 nut does not help because the hardnesses are too similar. Kit the pair from documented lots so the storeroom cannot mix them.

Q3: Is TA2 strong enough for Class 300 flanges?

Generally no. TA2 has a minimum yield around 275 MPa and a proof load roughly one third of a same-size Gr5 fastener. Class 300 and above, high preload, structural and cyclic joints should use Gr5 / TC4 or properly isolated B8/B8M stainless studs, with the bolt load and gasket seating stress recalculated. Use the actual F468 table for design, not the approximate figures in this article.

Q4: Which anti-seize compound should be used?

MoS2 is the general-purpose default for titanium, usable to roughly 400 C in suitable conditions. Copper-based compounds handle higher temperatures but are a poor choice in acid service. PTFE compounds suit clean, low-cycle, lightly loaded assemblies. Avoid nickel-based anti-seize on titanium. State the compound by name in the assembly procedure and apply it at assembly, not in transit.

Q5: Can titanium bolts contact carbon steel?

Not directly in wet or chloride service. Titanium is the cathode in most couples, so the steel corrodes and the titanium can absorb hydrogen and embrittle over time. Use insulating washers and sleeves, control cathodic protection potentials, and inspect for hydrogen pickup at shutdowns.

Q6: What do F467 and F468 cover?

F468 covers finished nonferrous bolts, hex cap screws and studs — mechanical requirements and testing. F467 covers the matching nuts. B348 covers the bar stock, and ASME B18.2.1 / B18.2.2 / B18.21.1 define dimensions and washers. A complete PO names all of them plus the grade and UNS number.

Q7: Do you supply small bolt quantities from stock?

Yes, including matched bolt, nut and washer kits for repair work. Check the inventory page and send the size, thread, grade, nut grade and bolt load to the quotation desk for a firm date. Stocked sizes can often be dispatched the same day.

Choose TA2 Fasteners if / Choose Something Else if

Choose TA2 / Gr2 bolt and nut sets if the joint is low-load, non-structural and low-pressure; the driver is corrosion resistance on a chemical cover, light flange or marine fitting; you can recalculate the bolt load and torque for TA2's proof load; and you specify a dissimilar nut grade, MoS2 anti-seize and galvanic isolation. It is also the right choice for small repair quantities from stock.

Choose something else if the flange is Class 300 or above, or the joint is structural, cyclic or highly preloaded (use Gr5 / TC4 or isolated B8M studs); if hot chloride crevices cannot be designed out (consider Gr7 or a redesigned joint); if the medium contains fluoride, hot concentrated reducing acid or dry chlorine (re-specify the material system); or if the part is an implant, which requires F136 material with the appropriate certification and traceability.

Summary: The Eight Fields That Belong on the RFQ

1. Standards and grade: ASTM F468 bolts / F467 nuts, B348 bar origin, ASME B18 dimensions, TA2 / Gr2 / UNS R50400.
2. Dimensions: diameter, thread (metric / UNC / UNF) and class, length, head form, and washer type.
3. Mechanical requirement: proof load and yield to the F468 table, with the design bolt load and gasket seating stress stated.
4. Manufacturing route: cold-headed, hot-headed with reduction ratio, or machined from bar — with the head-forming method named for sizes above 1/2 inch.
5. Nut pairing and lubrication: dissimilar grade with a stated hardness difference, MoS2 or other named anti-seize, assembly torque and controlled removal procedure.
6. Galvanic isolation: insulating washers and sleeves, bolt material review against flange material, cathodic protection limits.
7. Documentation: B348 MTR with heat number, F468/F467 mechanical report, dimensional and thread gauge report, PMI, certificate of origin, third-party witnessing if required.
8. Commercial terms: kitted sets (small orders accepted), export packing with thread protection, certificate language, target date, incoterms.

Send those eight items with your flange class, gasket type, bolt load and process conditions to our quotation desk, or use the contact page to check the grade first. Related reading: the Titanium Fasteners category, the bolts and screws guide, and the full product range.