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Apprentice answer

Why is the wide side of a 45-degree duct elbow buckling

3rd YearField Mods, Fittings, Offsets & TransitionsCheck first

Wide, shallow angled fittings need enough stiffness to hold shape. If the panel oil-cans, stop and add approved reinforcement or get the fitting remade heavier.

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Plain-English answer

A wide flat panel on a 45° fitting takes a lot of air impact and mechanical stress. If the throat or heel plate is too flat and unsupported, it can buckle, boom, or oil-can under airflow.

Recovery is usually approved external stiffeners, internal tie support, heavier-gauge replacement, or a revised fitting detail. The fix must preserve the duct shape without creating an internal obstruction.

Ask Foreman

The wide panel on this 45 elbow is oil-canning under airflow at [location]. I checked the hangers and the panel needs stiffening or a revised fitting. Do you want external reinforcement or a remake?

Verify before acting

Use this as training guidance. Foreman direction, approved drawings, project specs, manufacturer instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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