RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ASTM B265 / B348 material traceability, Third-Party Inspection (SGS / BV / DNV / Lloyds), and complete EPC, aerospace, and offshore export documentation packages.
Titanium
Fasteners
A world-class technical reference for EPC contractors, structural and mechanical engineers, procurement heads, TPI inspection agencies, and global project buyers specifying titanium bolts, studs, nuts, screws, and washers for offshore structures, subsea equipment, marine systems, chemical process equipment, desalination plants, aerospace structures, medical implant assemblies, and any application requiring the unique combination of high strength, ultra-low weight, and outstanding corrosion resistance that only titanium delivers.
Grade Classification
& Engineering Advantages
Titanium fasteners are bolts, studs, nuts, screws, and washers manufactured from titanium alloys — offering a unique engineering combination of high specific strength (strength-to-weight ratio superior to both steel and aluminium), outstanding corrosion resistance in marine and chemical environments, excellent cryogenic toughness, and complete biocompatibility that no other engineering metal provides simultaneously.
1.1 — Why Titanium Fasteners — Engineering Rationale
Titanium is element 22 in the periodic table — a transition metal with a density of 4.51 g/cm³ (57% of steel at 7.85 g/cm³; 167% of aluminium at 2.70 g/cm³). The outstanding corrosion resistance of titanium derives from the immediate formation of a tenacious, self-healing titanium dioxide (TiO₂) passive oxide film on any exposed surface — a film that is highly stable in seawater, dilute acids (nitric, sulphuric, hydrochloric), chlorinated solvents, and wet chlorine gas, environments where stainless steel experiences pitting, crevice corrosion, and stress corrosion cracking.
For fastener applications, titanium’s value proposition is most compelling in three scenarios: (1) weight-critical structures where substituting titanium Grade 5 (Ti-6Al-4V, UTS 950 MPa) for SS 316 stud bolts saves 43% of fastener mass — critical on offshore topsides where topsides weight directly drives jacket steel cost and hull displacement; (2) severe corrosion environments where neither carbon steel nor stainless steel provides adequate long-term corrosion resistance — subsea structures in seawater, desalination plant evaporator sections, chemical plant chlorine handling; and (3) galvanic compatibility — titanium is electrically noble, sitting close to platinum on the galvanic series, meaning titanium fasteners in contact with carbon fibre composite, graphite, or noble alloy components create negligible galvanic current vs the significant galvanic attack that SS 316 fasteners create in the same environments.
1.2 — Titanium Grade Classification for Fasteners
Grade 1 — Commercially Pure (CP-Ti), Softest
Unalloyed titanium, lowest strength CP-Ti grade. UTS ≥ 240 MPa; Yield ≥ 170 MPa; Elongation ≥ 24%. Highest formability and ductility of all titanium grades. Used for highly cold-worked fasteners and stampings, medical soft tissue implants, chemical equipment in very aggressive environments (wet chlorine). Rarely used for structural fasteners — strength insufficient for most engineering bolted connections. Per ASTM B265 Grade 1 sheet; ASTM B348 Grade 1 bar for fastener manufacture.
Grade 2 — Commercially Pure (CP-Ti), Standard
Unalloyed titanium — the most widely used CP titanium grade for fasteners. UTS ≥ 345 MPa; Yield ≥ 275 MPa; Elongation ≥ 20%. Excellent corrosion resistance across the full range of chemical environments — equivalent to Grade 5 in corrosion performance but with higher ductility. Per ASTM B348 Grade 2 bar; ASTM F467 Grade 2 (nuts); ASTM F468 Grade 2 (bolts/screws). Standard titanium fastener grade for: desalination plant heat exchangers, marine hardware, chemical plant equipment, offshore deck plating fasteners, and medical device cases. Non-magnetic.
Grade 5 — Ti-6Al-4V (The Workhorse Alloy)
Alpha-beta titanium alloy with 6% aluminium and 4% vanadium. UTS ≥ 950 MPa; Yield ≥ 880 MPa; Elongation ≥ 14%. The most widely used titanium alloy globally — combines high strength with good corrosion resistance, weldability, and wide manufacturing experience. Per ASTM B265 Grade 5 sheet; ASTM B348 Grade 5 bar; AMS 4928 (aerospace specification). Used for: aerospace structural fasteners, offshore structural connections, subsea connector bolts, high-strength lightweight fastener applications. Specific strength (UTS/density) exceeds most structural steels and aluminium alloys. Annealed or solution-treated and aged (STA) condition for fasteners.
Grade 7 — Ti-0.15Pd (Palladium Addition)
Commercially pure titanium with 0.12–0.25% palladium addition. Similar mechanical properties to Grade 2 (UTS ≥ 345 MPa) but with substantially improved corrosion resistance in reducing acid environments (hydrochloric acid, sulphuric acid, phosphoric acid) where Grade 2 would corrode. The palladium addition shifts the corrosion potential in the noble direction, providing corrosion immunity in reducing acid concentrations that attack Grade 2. Per ASTM B265 Grade 7; ASTM B348 Grade 7. Used for: chemical plant fasteners in HCl, H₂SO₄, and mixed acid environments; flue gas desulphurisation (FGD) plant; pharmaceutical acid processing.
Grade 12 — Ti-0.3Mo-0.8Ni
Titanium with molybdenum and nickel additions — higher strength than Grade 2 (UTS ≥ 483 MPa) with improved crevice corrosion resistance in hot chloride environments. Grade 12 is specifically designed to resist crevice corrosion in hot seawater (above 70°C) where Grade 2 and even Grade 7 can experience crevice attack under fastener heads and in threaded connections. Per ASTM B265 Grade 12. Used for: offshore heat exchanger titanium bolt-and-tube-sheet assemblies; seawater lift pump casing fasteners; high-temperature seawater desalination plant bolting.
Grade 23 — Ti-6Al-4V ELI (Extra Low Interstitials)
Ti-6Al-4V with reduced interstitial elements (oxygen ≤ 0.13%; nitrogen ≤ 0.05%; iron ≤ 0.25%) — the medical-grade titanium alloy. UTS ≥ 860 MPa; excellent fracture toughness and fatigue resistance at cryogenic temperatures; superior biocompatibility to standard Grade 5. Per ASTM F136 (implant quality); AMS 4956. Used for: orthopaedic bone screws and trauma fixation bolts, spinal implant screws, dental implant abutment screws, LNG cryogenic structural bolts requiring superior fracture toughness below −150°C, and aerospace fasteners requiring maximum damage tolerance.
1.3 — Titanium vs Competing Fastener Materials
| Property | Ti Grade 2 | Ti Grade 5 | SS 316L | Inconel 625 | A193 B7 Steel |
|---|---|---|---|---|---|
| Density (g/cm³) | 4.51 | 4.43 | 8.00 | 8.44 | 7.85 |
| UTS (MPa) | 345 | 950 | 485 | 827 | 1035 |
| Specific Strength (UTS/ρ) | 76 | 214 | 61 | 98 | 132 |
| Seawater corrosion | Excellent | Excellent | Fair | Excellent | Poor |
| H₂S sour service | Excellent | Excellent | Good | Excellent | Cond. (B7M only) |
| Crevice corrosion (Cl⁻) | Good (Grade 2) | Good | Poor | Very Good | Poor |
| Galvanic effect vs CFRP | Negligible | Negligible | Moderate | Low | Severe |
| Magnetic | Non-magnetic | Non-magnetic | Non-magnetic | Non-magnetic | Magnetic |
| Biocompatible | Yes | Yes | Conditional | No | No |
| Relative cost vs SS 316 | ~5× | ~8× | 1× | ~12× | ~0.4× |
1.4 — Critical Engineering Considerations for Titanium Fasteners
Galling — The Primary Installation Risk
Titanium is highly susceptible to galling (cold welding) when titanium-to-titanium threaded surfaces slide under load — the TiO₂ passive film is disrupted by the sliding contact and the underlying titanium surfaces weld together, shearing the fastener. Galling is the most common cause of titanium fastener failure and it occurs during installation — at final tightening, the nut can seize to the bolt and the bolt shank twists off. Prevention: apply a dry-film lubricant or anti-galling compound (molybdenum disulphide paste, Molykote G-Rapid Plus, Bostik Never-Seez Pure Nickel) to all titanium threads and bearing surfaces before assembly. Never assemble dry titanium-to-titanium threaded connections.
Titanium Thread Galling — Anti-Galling Specification
Anti-galling specification for titanium fasteners on project purchase orders: “All titanium fastener threads and bearing surfaces to be coated with MoS₂ dry film lubricant (Molykote 321R or equivalent) or nickel-based anti-galling compound (Never-Seez NSN-8 or equivalent) prior to dispatch. Site installation procedure to include re-application of anti-galling compound to all titanium threads before nut run-down.” This specification must be on every titanium fastener PO — without it, site assembly teams will default to dry assembly and galling fractures will occur. Galling is irreversible — a galled titanium bolt cannot be salvaged; the fastener set must be replaced.
Torque-Tension Uncertainty with Anti-Galling Lubricants
Anti-galling lubricants reduce the thread friction coefficient from 0.12–0.18 (dry Ti-Ti) to 0.04–0.08 (lubricated) — this creates a significant torque-tension uncertainty: the same torque applied to a lubricated titanium fastener produces approximately 2× the bolt tension vs an unlubricated assembly. If the torque value specified for installation is based on dry-thread assumption and the fastener is lubricated, overtightening will yield the titanium bolt and potentially fracture it. Torque values for titanium fasteners must be calculated specifically for the lubricated friction coefficient — never use standard steel torque tables for titanium without correction.
Galvanic Compatibility — Titanium is Noble
Titanium sits near platinum on the galvanic series (corrosion potential approximately +0.05 V vs SCE for Ti Grade 2 in seawater). When coupled to a less noble metal (carbon steel, aluminium, zinc) in an electrolyte, titanium acts as the cathode and the less noble metal corrodes as the anode. Titanium fasteners in aluminium structures will accelerate aluminium corrosion at the contact zone — insulating sleeves and washers are required. Conversely, titanium fasteners in carbon fibre reinforced polymer (CFRP) structures are the preferred choice because titanium is close in galvanic potential to graphite fibre, minimising galvanic current.
Crevice Corrosion Susceptibility by Grade
Despite excellent general corrosion resistance, CP titanium (Grades 1 and 2) is susceptible to crevice corrosion in hot concentrated chloride solutions above 70°C — a crevice under the bolt head or nut creates an occluded cell where the chemistry becomes more acidic and chloride-concentrated than the bulk environment, eventually breaking down the TiO₂ passive film. Grade 5 (Ti-6Al-4V) is somewhat more resistant to crevice corrosion than Grade 2 in hot chloride, but Grade 12 (Ti-0.3Mo-0.8Ni) provides the best crevice corrosion resistance among standard titanium fastener grades and is specified for hot seawater applications above 70°C.
Hydrogen Embrittlement in Titanium
Titanium can absorb hydrogen from: cathodic protection over-protection (hydrogen generated at the titanium surface); acid pickling during manufacturing without controlled hydrogen bake-out; galvanic coupling with a very active anode; and crevice corrosion environments generating nascent hydrogen. Hydrogen absorption degrades titanium ductility and can cause delayed hydride cracking (DHC) — particularly in Grade 4 and Grade 5 at hydrogen concentrations above 150–200 ppm. DHC manifests as delayed fracture hours or days after installation at stresses below the yield strength. Avoid cathodic over-protection of titanium fasteners: maintain potential above −0.80 V vs Ag/AgCl in seawater cathodic protection systems.
1.5 — Specific Strength and Weight Saving Calculation
ρ_SS 316 = 8.00 g/cm³ ρ_CS (B7) = 7.85 g/cm³
Weight saving — Ti Grade 2 vs SS 316: (1 − 4.51/8.00) × 100 = 43.6%
Weight saving — Ti Grade 5 vs SS 316: (1 − 4.43/8.00) × 100 = 44.6%
Weight saving — Ti Grade 5 vs A193 B7: (1 − 4.43/7.85) × 100 = 43.6%
Specific strength advantage — Ti Grade 5 vs SS 316 (for equal bolt tension):
Required bolt area for equal tension: A_Ti = A_SS × (σ_SS / σ_Ti) = A_SS × (485/950) = 0.51 × A_SS
Ti Grade 5 bolt at 51% of SS 316 bolt cross-section → same clamping force → additional weight saving beyond density difference.
Net weight saving for equal preload: approx. 72–76% lighter than equivalent SS 316 stud bolt
ASME B16.5 6″ Class 300: 12 × ¾” studs × 165 mm long; SS 316 stud weight ≈ 0.43 kg per stud → 5.16 kg per joint
Ti Grade 5 equivalent studs (same preload): ≈ 0.24 kg per stud → 2.88 kg per joint → 44% weight reduction
For offshore platform with 2000 flanged joints: SS 316 bolting ≈ 10.3 tonne → Ti Grade 5 ≈ 5.8 tonne → 4.5 tonne topsides weight saving at significant cost premium per kg but reduced jacket steel, hull steel, and crane capacity.
Submit your grade, thread size, length, head type, quantity, and certification requirements for a documented RFQ within 24 hours.
Mechanical Properties
& Standards Compliance
Titanium fastener grades and mechanical property requirements are governed by ASTM F467 (titanium nuts), ASTM F468 (titanium bolts and screws), ASTM B348 (titanium bar for fastener manufacture), AMS 4928 / 4911 (aerospace), and ISO 4014 / ASME B18 for dimensional compliance. All applicable standards are supported at RR Hydraulic with full certification.
Submit grade, diameter, length, thread, head type, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — ASTM F468 / F467 Titanium Fastener Mechanical Properties
| Grade | Alloy | Condition | UTS (MPa min) | Yield 0.2% (MPa min) | Elongation (% min) | RA (% min) | Hardness Max | Primary Fastener Application |
|---|---|---|---|---|---|---|---|---|
| Grade 1 | CP-Ti (Gr.1) | Annealed | 240 | 170 | 24 | 30 | 80 HRB | Very soft; chemical; medical; non-structural |
| Grade 2 | CP-Ti (Gr.2) | Annealed | 345 | 275 | 20 | 30 | 80 HRB | Standard offshore; marine; chemical; desalination |
| Grade 4 | CP-Ti (Gr.4) | Annealed | 550 | 483 | 15 | 25 | 36 HRC | High-strength CP; marine hardware; chemical plant |
| Grade 5 | Ti-6Al-4V | Annealed | 895 | 828 | 10 | 25 | 36 HRC | Aerospace; offshore structural; subsea; CFRP structures |
| Grade 5 | Ti-6Al-4V | STA | 1000 | 930 | 8 | 20 | 38 HRC | Maximum strength; aerospace primary structure bolts |
| Grade 7 | Ti-0.15Pd | Annealed | 345 | 275 | 20 | 30 | 80 HRB | Chemical plant; FGD; acid process; reducing environments |
| Grade 12 | Ti-0.3Mo-0.8Ni | Annealed | 483 | 345 | 18 | 30 | 28 HRC | Hot seawater; desalination; offshore HX above 70°C |
| Grade 23 | Ti-6Al-4V ELI | Annealed | 860 | 795 | 10 | 25 | 35 HRC | Medical implants; cryogenic; aerospace damage tolerance |
2.2 — Titanium Fastener Standard Size Reference
| Thread Size | Pitch (mm) | Stress Area (mm²) | Proof Load — Gr.2 (kN) | Proof Load — Gr.5 Annealed (kN) | Weight per 100 mm length (g) — Ti Gr.5 |
|---|---|---|---|---|---|
| M6 | 1.0 | 20.1 | 5.5 | 18.0 | 5.6 |
| M8 | 1.25 | 36.6 | 10.1 | 32.9 | 10.1 |
| M10 | 1.5 | 58.0 | 16.0 | 52.2 | 16.0 |
| M12 | 1.75 | 84.3 | 23.2 | 75.8 | 23.2 |
| M16 | 2.0 | 157 | 43.2 | 141 | 43.2 |
| M20 | 2.5 | 245 | 67.4 | 220 | 67.4 |
| M24 | 3.0 | 353 | 97.1 | 317 | 97.1 |
| M30 | 3.5 | 561 | 154 | 505 | 154 |
| M36 | 4.0 | 817 | 225 | 735 | 225 |
| M48 | 5.0 | 1473 | 405 | 1325 | 405 |
2.3 — Applicable Standards and Compliance Framework
ASTM F468 / F467
ASTM F468: Nonferrous Bolts, Hex Cap Screws, and Studs for General Use — covers titanium (and other nonferrous metals) bolt and stud mechanical requirements per grade. ASTM F467: Nonferrous Nuts for General Use — covers titanium nut grades. Both standards are the primary reference for EPC and offshore titanium fastener specification. F468 defines UTS, yield, elongation, and hardness requirements for each titanium grade. Chemical composition requirements are per the base material standard (ASTM B348 for bar stock used to manufacture fasteners).
ASTM B348 / B265
ASTM B348: Titanium and Titanium Alloy Bars and Billets. ASTM B265: Titanium and Titanium Alloy Strip, Sheet, and Plate. B348 is the raw material standard for titanium bar stock from which fasteners are machined — covers chemical composition, mechanical properties, surface condition, and inspection for each grade. EN 10204 3.1 certification on the B348 bar stock is the starting point for complete titanium fastener material traceability. For aerospace titanium fasteners (AMS 4928 Grade 5): additional chemistry controls and mechanical test requirements beyond ASTM B348.
AMS 4928 / AMS 4911
AMS 4928: Titanium Alloy Bars, Billets, and Rings (Ti-6Al-4V Annealed) — the SAE Aerospace Material Specification governing Grade 5 titanium bar for aerospace fastener manufacture. More stringent than ASTM B348 in chemistry control (tighter oxygen, nitrogen, and iron limits), microstructure (alpha grain size verification), and mechanical test sampling frequency. AMS 4911: Ti-6Al-4V sheet and plate (AMS). Mandatory for all aerospace-grade titanium fasteners — EPC projects rarely require AMS specifications but offshore operators specifying highest-quality Ti Grade 5 fasteners for safety-critical subsea connections may require AMS 4928 bar stock.
ASTM F136
Wrought Ti-6Al-4V ELI (Grade 23) Alloy for Surgical Implant Applications. The governing standard for medical-grade titanium Grade 23 fasteners — bone screws, spinal implant fasteners, dental abutment screws. ASTM F136 requires chemistry per Grade 23 ELI composition with maximum oxygen 0.13% (vs 0.20% for standard Grade 5) and nitrogen 0.05% (vs 0.05% standard). The reduced interstitial content improves fracture toughness and fatigue resistance in the cyclic loading environment of human musculoskeletal anatomy. ISO 5832-3 is the equivalent European standard for metallic surgical implants.
NACE MR0175 / ISO 15156
Titanium Grades 2, 5, 7, and 12 are all NACE MR0175-compliant for use in H₂S sour service at temperatures within their allowable service range — with one critical qualification: titanium must NOT be cathodically over-protected in sour service. If the cathodic potential drops below −0.75 V vs Ag/AgCl (the hydrogen evolution potential for titanium in seawater), hydrogen is generated at the titanium surface and absorbed into the titanium lattice, causing hydrogen embrittlement and potential delayed hydride cracking. For sour service with cathodic protection: verify CP potential remains above −0.75 V vs Ag/AgCl at all titanium fastener contact points.
ISO 4014 / ASME B18.2.1
ISO 4014 (Hexagon head bolts — product grades A and B) and ASME B18.2.1 (Square and Hex Bolts and Screws — Inch Series) govern the head geometry dimensions for titanium hex bolts and heavy hex bolts. Titanium fastener head dimensions are the same as steel fastener heads of equivalent nominal size — the material change does not alter the head geometry. Titanium nuts are manufactured to ISO 4032 (hex thin nut) or ISO 4033 (hex nut) dimensions. Thread tolerances per ASME B1.1 (UNC 2A/2B) or ISO 965 (metric 6g/6H) — same as steel fasteners.
DNV-RP-B401
DNV Recommended Practice for Cathodic Protection Design. Governs the cathodic protection design for offshore structures — the protected potential range for titanium fasteners must be specified in the CP design: −0.60 V to −0.75 V vs Ag/AgCl. If titanium fasteners are used in a structure protected to potentials more negative than −0.75 V (as is common for steel-structure CP design with −0.80 V target), the titanium fasteners must be electrically isolated from the CP system by insulating sleeves and washers. This is a critical design consideration for offshore structures using mixed titanium-steel bolted connections.
ISO 3506 Parts 1–4
ISO 3506 covers mechanical properties of corrosion-resistant stainless steel and titanium fasteners. Part 4: Titanium bolts, screws, studs, and nuts — defines property classes for titanium fasteners compatible with the ISO 3506 family. ISO 3506-4 property classes for Ti Grade 2 bolts (Ti-P235 class) and Ti Grade 5 (Ti-P900 class) align with ASTM F468 grade designations. Used on European EPC projects and for equipment destined for European CE-marked pressure systems where ISO standards are required alongside ASTM material certification.
Thread Production
& Surface Treatments
Titanium fasteners require specialised manufacturing techniques — titanium’s low thermal conductivity, high reactivity at elevated temperatures, and tendency to work-harden demand controlled cutting speeds, sharp tooling, and flood coolant throughout all machining operations. RR Hydraulic manufactures titanium fasteners from certified ASTM B348 / AMS 4928 bar stock with full EN 10204 3.1 / 3.2 traceability.
3.1 — Corrosion Resistance vs Environment Matrix
| Environment | Grade 1 / 2 (CP) | Grade 5 (Ti-6Al-4V) | Grade 7 (Ti-Pd) | Grade 12 (Ti-Mo-Ni) | Notes |
|---|---|---|---|---|---|
| Seawater — ambient | Excellent | Excellent | Excellent | Excellent | All grades superior to SS 316 in seawater |
| Seawater — hot (>70°C) | Good (crevice risk) | Good (crevice risk) | Very Good | Excellent | Grade 12 for hot seawater under-fastener-head crevice |
| Dilute HCl (<20%) | Fair | Fair | Excellent | Good | Grade 7 Pd addition prevents reducing acid attack |
| Dilute H₂SO₄ (<10%) | Fair | Fair | Excellent | Good | Grade 7 for acid process fasteners; Grade 2 borderline |
| Wet chlorine / ClO₂ | Excellent | Excellent | Excellent | Excellent | All Ti grades superior to all SS and Ni alloys in wet Cl₂ |
| H₂S sour service | Excellent | Excellent | Excellent | Excellent | NACE-compliant; avoid CP over-protection (see text) |
| NaOH / caustic | Good (≤80°C) | Good (≤80°C) | Good | Good | Concentrated hot NaOH can attack titanium above 80°C |
| Nitric acid (all conc.) | Excellent | Excellent | Excellent | Excellent | Outstanding in nitric acid — far superior to SS 304/316 |
| Dry chlorine gas | Poor — reacts | Poor — reacts | Poor — reacts | Poor — reacts | All titanium ignites/reacts with dry chlorine — wet Cl₂ only |
| Cryogenic (LNG, −165°C) | Excellent | Excellent (Gr.23 preferred) | Excellent | Good | Ti retains ductility at cryogenic temps; Grade 23 for max toughness |
3.2 — Machining Titanium — Process Requirements
3.2.1 — Cutting Parameters for Titanium
- Cutting speed: Grade 2 CP-Ti: 30–80 m/min (vs 200+ m/min for SS 316); Grade 5 Ti-6Al-4V: 15–40 m/min — low speeds are mandatory to prevent heat build-up; titanium’s low thermal conductivity (6.7 W/m·K vs 16 W/m·K for SS 316) means heat concentrates at the cutting edge, rapidly degrading tool life if cutting speed is too high
- Feed rate: Moderate-to-high feed rate — light cuts at low feed rates cause work hardening (rubbing without cutting); use feed rates sufficient to form a proper chip and stay below the work-hardened layer from the previous pass
- Tool geometry: Sharp cutting edges are essential — a worn tool causes rubbing and work hardening rather than cutting; high positive rake angle tools (10–15° rake) reduce cutting forces and heat; replace inserts more frequently than for steel machining
- Coolant: Flood coolant (water-soluble cutting fluid) at maximum flow rate — cools the cutting zone, prevents chip re-welding to the tool, and prevents chip fires (titanium chips can ignite if allowed to accumulate and heat); dry machining of titanium is not permitted
- Chip control: Titanium forms long, stringy chips that can wrap around the tool and workpiece — use chip-breaking inserts and clear chips frequently; chip fires are a fire safety hazard in titanium machining shops
3.2.2 — Thread Manufacture for Titanium Fasteners
- Thread rolling (preferred): Cold thread rolling produces compressive residual stress at the thread root — superior fatigue resistance vs cut threads; also avoids the work hardening and surface damage that thread cutting can produce on titanium; thread rolling preferred for Ti Grade 5 fatigue-critical fasteners (aerospace, high-cycle offshore)
- Thread cutting: Used for large-diameter studs (M36+) where rolling tooling is unavailable; single-point thread turning on CNC lathe with sharp HSS or fine-grain carbide inserts; cutting speed 20–30 m/min; flood coolant mandatory throughout
- Nut threads: Tapping titanium nuts requires: sharp taps with polished flute surfaces; low cutting speed (5–10 m/min); high-pressure cutting oil (not water-based coolant for tapping); frequent tap reversal to break chip; spiral-flute taps preferred for through-hole tapping in Ti
- Anti-galling pre-treatment: After thread manufacture, all titanium thread surfaces and bearing faces are coated with MoS₂ dry-film lubricant or nickel-based anti-galling compound before dispatch — this is a manufacturing process step, not an optional installation instruction
3.2.3 — Surface Treatments for Titanium Fasteners
Anodising (Type II and Type III)
Electrochemical anodising of titanium produces a controlled TiO₂ oxide layer thicker than the natural passive film — Type II (decorative): 2–7 µm producing vivid interference colours (silver, gold, purple, blue, green) used for identification coding of fastener grades and sizes. Type III (hard anodise): 20–30 µm; increases surface hardness (up to 3000 HV at the surface), improves wear resistance, and reduces the tendency for fretting and galling. Type III anodising is specified for titanium fastener threads in aerospace and medical applications to reduce galling — it does not eliminate the need for anti-galling lubricant but reduces the galling risk for repeated assembly/disassembly cycles.
Passivation (Nitric Acid)
Nitric acid passivation per ASTM A967 removes any free iron or steel contamination from the titanium surface that would cause galvanic corrosion pitting at the contamination site. Particularly important for titanium fasteners machined in shops that also machine carbon steel — iron particles deposited on the titanium surface create local galvanic cells. Passivation verifies that the TiO₂ passive film is complete and undamaged. Standard for all offshore and marine titanium fasteners. Passivation does not change dimensions — it is a chemical surface treatment only. Certificate per ASTM A967 included in the documentation package.
MoS₂ Dry-Film Lubrication
Molybdenum disulphide (MoS₂) applied to all titanium thread and bearing surfaces before dispatch — prevents galling during assembly. Applied as: bonded dry film (Molykote 321R, Dow Corning 321 — sprayed or dipped, 5–15 µm thick, cured at 150–200°C); or as paste/grease (Never-Seez NSN-8 — applied at site immediately before nut run-down). Bonded dry-film provides the most reliable and durable anti-galling protection for multiple assembly cycles. Paste/grease provides anti-galling for single-assembly or must be re-applied each time. For critical titanium fastener packages: specify bonded MoS₂ at the manufacturing stage, not site-applied paste.
Electroplating Prohibited on Titanium
Electroplating of titanium is not recommended for structural fasteners — the acid pickling pretreatment required before electroplating introduces hydrogen into the titanium lattice (titanium has a high hydrogen affinity) and can cause hydrogen embrittlement. Cadmium plating, zinc plating, and chrome plating on titanium structural fasteners are not practised in aerospace or offshore engineering. If surface protection is required beyond the natural TiO₂ passive film, specify anodising (Type II or III) — an electrochemical process that does not involve acid pickling or cathodic current that would introduce hydrogen.
PVD / CVD Hard Coatings
Physical vapour deposition (PVD) coatings — TiN (titanium nitride, gold-coloured), TiAlN, CrN — deposited on titanium fasteners as hard, wear-resistant coatings for: reduced galling in repeated-assembly applications (dental implant screws that are tightened and removed multiple times over the implant lifetime); improved wear resistance on Ti Grade 5 structural screws in high-vibration environments; and aesthetic finish. PVD coatings are applied at low temperature (150–300°C) — no risk of hydrogen embrittlement or dimensional change beyond the coating thickness (typically 2–4 µm). High cost — specified for aerospace and medical applications.
Colour Coding for Grade Identification
Titanium fasteners of different grades are visually identical — Grade 2 CP-Ti and Grade 5 Ti-6Al-4V look the same to the naked eye. Grade misidentification in critical applications (using Grade 2 bolts at Grade 5 design strength) causes structural failure. Standard practice: Type II anodising colour coding to identify grades — silver/natural = Grade 2; gold/yellow = Grade 5 (common industry convention in aerospace and offshore); purple = Grade 23 (medical standard). The colour-coding system must be specified in the project fastener specification and consistent across all supply packages. Confirm with the EPC procurement engineer which colour code convention applies to the project.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified ASTM B348 / AMS 4928 bar stock to final lubricated, anodised, and packed titanium fastener shipment. PMI verification on every piece, mechanical testing, thread gauging, anti-galling treatment certification, and complete EN 10204 3.1 / 3.2 documentation are standard on all project-grade titanium fastener supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC / Offshore Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Manufacturer | Not acceptable for structural / pressure service | Never for structural offshore or process titanium fasteners |
| 3.1 | Bar heat-traceable mech + chem | Manufacturer’s authorised QC | Minimum for all EPC titanium fasteners | All titanium fasteners for structural, offshore, chemical service |
| 3.2 | 3.1 + TPI countersign | Manufacturer + SGS / BV / DNV / Lloyds | Subsea; offshore critical; nuclear; aerospace | Subsea connectors; offshore safety-critical; nuclear; AMS |
4.3 — Applications by Industry
Offshore Topside Weight-Saving Flange Bolting
Ti Grade 5 stud bolts replacing SS 316 stud bolts on offshore topside flange connections — 44% weight saving per bolt, structural equivalent bolt tension. The cost premium (Ti Grade 5 ≈ 8× SS 316 by weight) is justified for: floating production platforms (FPSO, semi-submersible, TLP) where topsides weight drives hull steel tonnage; helicopter deck structural connections; crane pedestal bolting; and helipad deck plate fixings. Full EPC cost-benefit analysis per the topside weight-to-jacket-steel cost ratio for the specific platform concept determines the minimum weight saving threshold at which titanium fastener substitution is economically justified.
Subsea Connector and Tree Bolting
Ti Grade 5 stud bolts for subsea tree, manifold, and flowline connector assemblies — Grade 5 provides the required 950 MPa UTS for high-pressure subsea connections with 44% weight saving vs equivalent stainless steel, and outstanding corrosion resistance in seawater at all depths and temperatures without cathodic protection (titanium does not require CP). For subsea applications: verify the CP potential at all titanium-steel interfaces — titanium fasteners in a CP-protected steel structure must be electrically isolated to prevent hydrogen evolution on the titanium surface below −0.75 V. EN 10204 3.2 with DNV/Lloyds TPI mandatory for all subsea titanium fastener supply.
Desalination and Marine Water Treatment
Ti Grade 2 or Grade 12 fasteners for multi-stage flash (MSF) and multi-effect distillation (MED) desalination plant evaporator section bolting — brine concentrations up to 70,000 ppm Cl⁻ at 60–120°C where SS 316 pits and SS 2205 Duplex has limited service life. Grade 12 (Ti-0.3Mo-0.8Ni) is the preferred grade for above-70°C brine service due to its superior resistance to crevice corrosion under fastener heads in hot concentrated brine. Seawater reverse osmosis (SWRO) pressure vessel end cap bolts: Grade 2 or Grade 5 for the 55–70 bar operating pressure of SWRO membranes with long-term seawater wetting of the bolt threads.
Chemical Process — Wet Chlorine and Acid Service
Ti Grade 2 fasteners for wet chlorine handling systems (chlor-alkali plants, water treatment chlorination systems) — titanium is immune to wet chlorine attack; SS 316 rapidly pits and fails. Ti Grade 7 (Ti-0.15Pd) for HCl and H₂SO₄ scrubber and reactor vessel fasteners in chemical process plant — the palladium addition suppresses titanium corrosion in reducing acid concentrations. Ti Grade 7 fasteners for FGD (flue gas desulphurisation) absorber column internals bolting — combined SO₂-laden acid droplet and elevated temperature environment that attacks both SS 316 and Hastelloy C276. EN 10204 3.1 minimum; 3.2 with TPI for nuclear facility chemical process titanium fasteners.
Aerospace and CFRP Structures
Ti Grade 5 (AMS 4928 bar) or Grade 23 (AMS 4956, ELI for fracture-critical locations) bolts and screws for aircraft primary structure, engine mount brackets, landing gear components, and carbon fibre reinforced polymer (CFRP) composite wing and fuselage fasteners. Titanium is the preferred fastener material for CFRP structures because: galvanic compatibility with graphite fibre (negligible galvanic current vs aluminium’s severe galvanic attack in CFRP-aluminium joints); density close to CFRP for balanced stiffness-weight ratio; and oxidation resistance in the mixed wet/dry aircraft service environment. AMS processing from certified AMS 4928 bar; 100% PMI; Type III anodise or PVD-TiN for galling resistance.
Medical Implants and Orthopaedic Fixation
Ti Grade 23 (ASTM F136, ISO 5832-3) cortical bone screws, pedicle screws (spinal fixation), trauma fixation bolts (locking plate screws), and dental implant abutment screws — the global standard for metallic implant fasteners. Biocompatibility: titanium produces no adverse tissue response (no nickel ion release that causes SS sensitivity reactions in some patients); osseointegration (direct bone-to-implant bonding of titanium surface); long-term stability in physiological saline and hydrogen peroxide environments. MRI compatibility: titanium is non-magnetic and non-ferrous — Grade 23 fasteners cause minimal image artefact in MRI imaging. Sterilisation: autoclave (134°C steam), EtO gas, or gamma radiation — all compatible with Grade 23 titanium.
4.4 — Export Packaging Specification
- Titanium fasteners individually or batch-packed in dedicated titanium-only polybags — strictly segregated from carbon steel, stainless steel, and all other metal hardware; iron contamination from other metals depositing on titanium surfaces causes galvanic pitting that destroys the titanium passive film
- VCI poly bags for all titanium fastener packages — prevents moisture condensation on the MoS₂-coated thread surfaces during ocean transit; moisture on MoS₂ dry film coating does not damage the film but prevents visual inspection at receiving and may promote biological contamination on long transit times
- Grade identification: each polybag clearly labelled with titanium grade (Grade 2 / Grade 5 / Grade 7 / Grade 23), diameter, length, thread form, anti-galling treatment type, and lot number — visible without opening the bag; separate polybags for each grade even if the same size
- Anti-galling treatment protection: MoS₂-coated threads wrapped in individual lightweight polyethylene sleeves before bagging — prevents MoS₂ coating transfer to the packaging that could mislead receiving inspection; protects the coating from abrasion damage during transport
- Anodised fasteners (colour-coded): individual cells in foam-lined box separating anodised fasteners to prevent colour scratching — scratch on anodised colour code surface prevents grade identification in the field; foam cell trays are the standard packaging for aerospace and medical titanium fasteners
- Individual serialisation for aerospace (AMS) and medical (ASTM F136) Grade 23 titanium fasteners: each fastener has a unique alphanumeric serial number engraved on a non-thread surface, traceable to the bar heat certificate and CMM inspection record
- ISPM-15 heat-treated timber crates for all international export; inner packaging in moisture-barrier sealed bags with desiccant sachets
- Documentation package: EN 10204 3.1/3.2 MTC, mechanical test certificate, PMI report (individual piece), thread gauge report (100%), dimensional inspection report, anti-galling treatment certificate, passivation certificate, anodising certificate (where applicable), and FAI report in waterproof document pocket
4.5 — Complete Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | Mandatory — all titanium fasteners | Bar heat-traceable; ASTM B348 / AMS 4928 per grade |
| 02 | Chemical Composition Report | Certified lab analysis per ASTM B348 / AMS | Mandatory | All elements per grade — Al, V, Pd, Mo, Ni, O, N, Fe limits |
| 03 | Mechanical Properties Report | UTS, yield, elongation, RA, hardness | Mandatory | Per ASTM F468 / B348 / AMS 4928 for the grade |
| 04 | PMI Report (XRF) — 100% Individual Pieces | XRF per fastener | Mandatory — every single piece, no exceptions | Grade 2 vs Grade 5 differentiation; all grades verified |
| 05 | Thread Gauge Report | ASME B1.1 / ISO 965 Go/No-Go — 100% | Mandatory | Post-anti-galling coating verification; 100% all threads |
| 06 | Dimensional Inspection Report | Per ASME B18.2.1 / ISO 4014 / drawing | Mandatory | All critical dimensions per applicable standard |
| 07 | Anti-Galling Treatment Certificate | MoS₂ compound type + application method | Mandatory — all titanium fasteners | Compound ID, lot; assembly test confirmation; no dry dispatch |
| 08 | Passivation Certificate | ASTM A967 nitric acid | Mandatory — all titanium fasteners | Method confirmed; water immersion or Cu sulphate test |
| 09 | Anodising Inspection Certificate | Type II colour / Type III thickness | Conditional — where anodising specified | Colour code per project convention; film thickness (Type III) |
| 10 | Hardness Test Report | ASTM E18 Rockwell / E92 Vickers | Mandatory — per lot (5% min) | Grade-specific hardness limits per ASTM F468 |
| 11 | Microstructure Report (AMS Grade 5) | AMS 4928 alpha grain size per ASTM E112 | Conditional — AMS 4928 Grade 5 | Alpha grain size; no beta-fleck; per AMS 4928 requirements |
| 12 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project line items | All parameters; released before batch production |
| 13 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — subsea; offshore; nuclear; AMS | Co-witness at manufacturer; PMI + dimensional + test |
| 14 | NACE Compliance Statement | CP potential limitation declaration | Conditional — sour service / CP structures | States CP potential limit −0.75 V vs Ag/AgCl for titanium |
| 15 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers titanium fastener manufacture |
| 16 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code (7108.20 for titanium fasteners) |
| 17 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering ASTM B348 / AMS 4928 bar procurement and chemistry verification, CNC turning process qualification for titanium (cutting speed, coolant, chip control procedures), thread rolling and thread cutting parameter qualification, anti-galling dry-film application and cure cycle qualification, passivation process control, anodising process qualification (Type II colour and Type III film thickness), 100% PMI procedure, and full material traceability from bar heat to finished fastener. Mandatory for all EPC, offshore, and aerospace titanium fastener procurement qualification.
ASTM F468 / F467
The primary fastener mechanical property standards for titanium bolts (F468) and nuts (F467). All titanium fasteners supplied by RR Hydraulic are manufactured and tested per ASTM F468 for the applicable grade — UTS, yield, elongation, and hardness tested on representative lot specimens. ASTM F467 applies to titanium nuts: nut proof load per grade is the critical acceptance criterion — the nut must withstand a proof load of 90% of the bolt minimum tensile strength without permanent elongation, cracking, or thread failure. Lot-based testing with individual bar heat traceability to EN 10204 3.1.
DNV-ST-F101 / DNVGL-RP-B401
DNV ST-F101 (Submarine Pipeline Systems) and DNVGL RP-B401 (Cathodic Protection Design) govern subsea pipeline and structure design including titanium fastener application in CP-protected environments. The ‘CP potential window’ for titanium (−0.60 V to −0.75 V vs Ag/AgCl) is narrower than for steel (−0.80 V to −1.10 V) — the CP system must be designed to maintain this potential range at all titanium connection points, or the titanium fasteners must be electrically isolated from the CP system. DNV-ST-F101 is mandatory for all subsea pipeline titanium connector bolt specification on DNV-classed projects.
AS9100 / EN 9100 (Aerospace)
AS9100 / EN 9100 (Quality Management Systems — Requirements for Aviation, Space, and Defense Organizations) extends ISO 9001 with aerospace-specific requirements: first article inspection (FAI) per AS9102; control of supplier-furnished articles; configuration management; risk management for safety-critical fasteners; traceability to aerospace-lot level. Required for titanium fasteners supplied to aerospace OEM programmes. RR Hydraulic supports AS9100 certification for titanium fastener supply to aerospace customers. All aerospace Grade 5 (AMS 4928) fasteners are manufactured and documented per AS9100 quality system requirements.
Submit your grade, diameter, length, thread form, head type, anti-galling treatment, and quantity to RR Hydraulic for a complete, certified commercial offer.