Torque & Tension Specifications Flashcards

In a flanged joint, why is a cross-pattern (star pattern) bolt tightening sequence specified?

Answer: To distribute clamp load evenly and avoid flange distortion

Tightening in a star pattern distributes load progressively across the flange, preventing uneven seating and gasket compression.

An M12 class 10.9 bolt has a tensile stress area of 84.3 mm². If proof strength is 830 MPa, what is the approximate proof load?

Answer: 70 kN

Proof load = 830 MPa × 84.3 mm² ≈ 69,969 N ≈ 70 kN.

What is the purpose of the 'snug tight' condition in structural steel connections?

Answer: The condition where plies are in firm contact and the wrench begins to turn with full effort

Snug tight is achieved when the full effort of an ironworker with a spud wrench brings plies into firm contact; it is the starting point for further pretensioning.

Which lubricant reduces the nut factor (K) the most, enabling lower torque for the same preload?

Answer: Molybdenum disulfide (MoS₂) paste

MoS₂ has an extremely low coefficient of friction (≈0.04–0.08) and reduces K to approximately 0.10–0.12, lower than most other lubricants.

If a torque specification was developed for a zinc-plated bolt and a waxed nut, but the actual bolt is plain (uncoated) and dry, what is the most likely outcome?

Answer: Lower clamp load than specified due to higher friction consuming more torque

Higher friction on dry threads means more torque energy is absorbed by friction and less converts to bolt tension, resulting in lower preload.

A torque specification states '50 N·m ± 10%'. What is the acceptable torque range?

Answer: 45–55 N·m

10% of 50 N·m is 5 N·m, so the acceptable range is 50 − 5 = 45 N·m to 50 + 5 = 55 N·m.

What is the effect of a hardened washer placed under a nut on the effective nut factor?

Answer: Decreases K by providing a smoother, harder bearing surface

A hardened, smooth washer reduces bearing-surface friction, lowering K and allowing more torque to convert into bolt tension.