Hiduron Torque Chart (Cu-Ni-Al Fastener Torque Values)

Target preload F (N) = 0.60 x Rp0.2 x stress area. Torque T (N.m) = K x F x d / 1000, where d is the nominal bolt diameter in mm. K is the nut factor that accounts for the friction at the thread and at the bearing face under the nut or bolt head. Dry K = 0.20 represents the as-machined, oxide-bearing, unlubricated condition; lubricated K = 0.13 represents the standard practice of applying copper-graphite anti-seize compound to both the thread and the bearing face. The values below assume the joint is bolted up with a Hiduron nut against a Hiduron bolt against a Hiduron washer, with a hardened bearing washer protecting the flange face from galling on the under-head rotation.

Standard practice on Hiduron bolting installation is to apply copper-graphite anti-seize compound to both the thread and the bearing face under the nut or under the bolt head before assembly, then to torque to the lubricated value (K = 0.13) using a calibrated torque wrench. The anti-galling response of the Cu-Ni-Al matrix is good but lubrication still benefits the joint by reducing the spread on the preload-against-torque response and by easing disassembly years later when the flange is opened for maintenance. For submerged service the joint is bolted up topside before deployment, with the anti-seize protecting the thread against seawater ingress on the long-term inspection schedule. For sour-service NACE applications the anti-seize must be confirmed sulphur-free; copper-graphite anti-seize meets this requirement.

TorqBolt supplies Hiduron 130 (UNS C72400, DTD 900/4805) and Hiduron 191 (UNS C72420, NES 835, DEF STAN 02-835, DOD-C-24676) in round bar, stud bolts, hex bolts, heavy hex bolts, nuts, washers, forgings and machined components. Standard fastener lead time is 4 to 8 weeks from order, subsea machined components quote project-specific lead time. Send an enquiry through TorqBolt Contact with the controlling specification, the form factor, the size envelope and the certification level (3.1 default, 3.2 on call-out, NACE on call-out).

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Q. Why is the Hiduron torque value lower than the steel torque value?
Because the Cu-Ni-Al modulus of elasticity is 130 to 135 GPa against 207 GPa on carbon steel. The bolt elongates more at the same preload, which means the same target preload develops at lower torque.

Q. What preload target should I use on Hiduron bolting?
60 percent of the 0.2 percent proof stress is the recommended target. This is 290 MPa on Hiduron 130 (proof 480 MPa) and 350 MPa on Hiduron 191 (proof 580 MPa). The target avoids yielding the bolt while developing enough clamp force for joint integrity.

Q. Should I lubricate Hiduron bolts before torquing?
Yes. Standard practice is to apply copper-graphite anti-seize compound to both the thread and the bearing face, then torque to the lubricated value (K = 0.13). The anti-seize reduces preload spread and eases long-term disassembly.

Q. Is the lubricant sulphur-free for NACE service?
Copper-graphite anti-seize compound is sulphur-free and meets NACE MR0175 sour-service requirements. Avoid nickel-graphite and molybdenum-disulphide anti-seize on Hiduron 191 NACE bolting.