Structural Fabrication, Welding, and Mechanical Joining

Verify replacement material identity, thickness, section shape, and orientation against the approved repair design before fabrication. Lay out cuts and holes from controlled datums, preserve specified edge distances, and prepare smooth transitions without unauthorized notches in flanges or webs. Trial-fit components and check joint gaps and access before permanent attachment; forcing a poorly fitted member into place can introduce residual stress.

Structural welding requires an applicable welding procedure specification and a welder qualified for the process and work involved. The procedure must address the base material, filler, joint preparation, position, shielding, preheat and interpass controls where applicable, and required inspection. Remove coatings, moisture, oil, and contaminants from the joint area using appropriate controls, and do not improvise filler selection or temperature limits for unidentified material.

Use an authorized welding sequence, suitable restraint, and repeated dimensional checks to control shrinkage and distortion. Tack welds incorporated into the joint must meet the applicable procedure, and defective tacks must be removed or corrected as required. Do not conceal cracks with a weld overlay or grind a finished weld flush unless the approved detail permits it and the required weld section remains.

For aluminum work, verify the alloy and temper and use dedicated clean tools to avoid introducing contamination. Account for the heat-affected zone and any design allowance for reduced strength; an attractive weld bead does not demonstrate that the original properties have been restored. For bonded or composite repairs, follow the approved system's limits for substrate preparation, moisture, adhesive selection, bond-line control, curing conditions, and inspection rather than substituting welding or generic adhesive.

For bolted or riveted joints, use the specified fastener type, grade, diameter, grip, washers, locking method, and installation process. Do not replace an engineered rivet or lockbolt joint with ordinary bolts without approval, and correct damaged holes using an approved repair rather than simply installing larger fasteners. Tightening requirements depend on the fastener system, coatings, lubrication, and joint design, so a generic torque chart cannot establish every structural joint's requirement.

Protect brake hoses, wiring, bearings, and electronic equipment from heat, sparks, and welding current, and place the welding return connection close to the work on a suitable clean part of the same assembly so current does not pass through vulnerable components. Follow equipment-specific isolation requirements, control hazardous coating fumes, provide ventilation and fire protection, and inspect concealed spaces for ignition hazards under the shop's hot-work procedure. After inspection, restore compatible coatings, sealants, drainage, and specified isolation between dissimilar metals to limit crevice and galvanic corrosion.