Structural Steel Bolting and Connection Inspection
Bolted connection inspection verifies that the correct bolt, hole, joint preparation, and pretensioning method were used. High-strength bolts are typically ASTM F3125, which consolidated A325 and A490; grade markings, lubricant, washers, and coating must match the specification. The inspector checks hole type and alignment, faying-surface condition, snugging, pretensioning, and final condition.
Pretensioning methods
- Turn-of-nut: snug the joint, match-mark, then apply the code-required rotation.
- Calibrated wrench: verify daily with a tension calibrator.
- DTI: compress the washer gaps to the specified feeler-gauge limit.
- Twist-off: tighten until the splined end shears.
Worked example
A turn-of-nut joint uses bolts shorter than four diameters. After snugging and match-marking, the crew applies the required one-third turn. The inspector verifies that all match marks show the full rotation and that the joint was snugged first. Reasoning: rotation applied before snugging is not pretension; the match marks document the actual rotation.
Traps
- Counting impact-wrench “tightening” as pretension without a qualified method.
- Inspecting rotation without verifying snugging.
- Using damaged or mismatched DTI washers.
- Painting faying surfaces with a coating not qualified for slip-critical service.
- Ignoring oversized or slotted holes and cover plates.