Bolted, Riveted and Dissimilar-Metal Structural Joints
- Identify joint movement and unacceptable hole damage.
- Select and install the approved structural fastener system.
- Restore corrosion protection, bonding and drainage.
- Supports and clamps — Restrain joined parts against movement before releasing structural fasteners; use equipment suitable for the supported load.
- Inspection light and mirror — Inspect fastener heads, mating surfaces and concealed areas for movement marks, cracks and corrosion.
- Caliper — Measure accessible holes and fastener dimensions for comparison with applicable acceptance limits.
- Torque wrench and suitable sockets — Apply the specified tightening method where torque-controlled installation is approved, using calibrated equipment where required.
- Approved rivet or lockbolt installation tool — Install the specified fastener system with the correct tooling rather than substituting an ordinary bolt.
- Scraper and cleaning brushes — Remove loose contamination and failed sealant for inspection without damaging sound surfaces or spreading incompatible metal debris.
Structural bolts, rivets and lockbolts transfer loads through a designed combination of clamping friction and bearing at the joint. Fretting debris, polished movement marks, loose heads and elongated holes indicate possible joint movement, so replacing a visibly loose fastener without assessing the joint may leave the failure mechanism in place.
Before disassembly, restrain the joined parts and determine whether fastener removal will release a structural load or allow movement. Inspect the full fastener group, mating surfaces and holes; cracked or elongated holes require an approved repair disposition rather than an arbitrary larger bolt.
Match the specified fastener system, including diameter, grade or strength class, grip length, washers, locking method and coating. Do not substitute an ordinary bolt for a structural rivet or lockbolt without approval, and do not reuse fasteners designated as single-use.
Install with the specified tools, sequence and tightening method, using calibrated equipment where required. Torque values depend on the fastener and joint condition, including lubrication and coating, so applying a dry torque value to lubricated threads can produce excessive preload; a paint witness mark indicates relative movement, not verified clamping force.
At dissimilar-metal joints, retain the approved insulating barriers, sealants and compatible coatings while preserving required electrical bonding and drainage. Exclude moisture without sealing over existing corrosion or blocking drain paths, and perform any specified settling inspection or retightening rather than applying a blanket retorque rule to every joint.
How It Works
Load transfer and evidence of movement
Structural fasteners transfer loads through a designed combination of clamping friction and bearing against the joint holes. When mating surfaces slip, repeated rubbing can produce fretting debris and polished marks, while bearing movement can elongate holes. A replacement fastener alone cannot restore damaged holes or correct an unresolved joint movement mechanism.
Fastener systems and controlled clamping
Diameter, strength, grip length, washers, locking method and coating work together as an approved fastener system rather than interchangeable hardware choices. Tightening torque is affected by friction, so lubricated threads subjected to a dry torque requirement can develop excessive preload. A paint witness mark can reveal relative movement, but it does not verify clamping force.
Dissimilar metals and moisture control
Dissimilar metals connected through a conductive moisture film can experience galvanic corrosion, making approved isolation and compatible coatings important. Restore barriers and sealants without defeating required electrical bonding or drainage, and never seal over existing corrosion. Follow the specified settling inspection or retightening requirements rather than assuming every joint needs routine retorque.
Step-by-Step Procedure
0/7 doneMechanical Joint Specification Controls
| Fastener selection | Match the approved diameter, strength, grip, locking system and corrosion protection. |
| Tightening | Use the specified torque or tension method for the stated thread, lubrication and coating condition. |
| Hole acceptance | Use applicable dimensional and damage limits; do not assume an oversize fastener is an acceptable repair. |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Loose heads, fretting debris or polished movement marks | Restrain the joined parts before removal, then inspect the full fastener group, mating surfaces and holes rather than only the visibly loose fastener. | Inspect the fastener group, mating surfaces and hole condition. | Possible joint movement; replacing the loose fastener without assessing the joint may leave the failure mechanism in place. Basis: General shop practice (not from a downloaded manual) |
| Cracked or elongated fastener holes | Assess damage and hole dimensions against applicable limits, and obtain an approved repair disposition before selecting replacement hardware. | Use applicable dimensional and damage limits; do not assume an oversize fastener is an acceptable repair. | Joint movement may have damaged the holes; an arbitrary larger bolt does not establish an acceptable structural repair. Basis: General shop practice (not from a downloaded manual) |
| Installation records show lubricated threads tightened using a dry torque requirement | Verify the fastener system, thread condition, lubrication, coating and specified tightening method; obtain the applicable disposition for the installation. | Use the specified torque or tension method for the stated thread, lubrication and coating condition. | Applying a dry torque value to lubricated threads can produce excessive preload. Basis: General shop practice (not from a downloaded manual) |
| Corrosion or trapped moisture at a dissimilar-metal joint | Inspect insulating barriers, compatible coatings, sealants, required bonding provisions and drain paths before restoring protection. | Retain the approved insulating barriers, sealants and compatible coatings while preserving required electrical bonding and drainage. | Damaged isolation or moisture retention can promote corrosion; sealing over corrosion leaves deterioration hidden beneath the repair. Basis: General shop practice (not from a downloaded manual) |
At the Bay: Diagnose the Case
CASE 1 / 4
Loose heads, fretting debris or polished movement marks
- Test
- Compare
- Correct
Select the next check
Basis: General shop practice (not from a downloaded manual). A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Removing structural fasteners before restraining the joined parts.
- ✕ Treating a larger bolt as an automatic repair for damaged holes.
- ✕ Substituting ordinary bolts or reusing designated single-use fasteners.
- ✕ Treating witness marks as proof of clamping or applying blanket retorque.
Quick Check
Practice only — not scored.
Plan the Service Sequence
Planning practice only. Follow the applicable manufacturer's instructions, employer safety program and qualified supervision on real equipment.
Plan the first action. Compare the service steps with the bay mistakes.
Source: General shop practice (not from a downloaded manual)