A wide 45-degree rectangular elbow buckles or oil-cans
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.
Do not ignore oil-canning on a wide angled fitting and bury it above a finished ceiling.
Check
Look for flat panels moving when the fan starts.
Check whether the fitting is cross-broken, stiffened, or reinforced.
Verify hangers are not pulling the fitting out of shape.
Confirm reinforcement type with project/shop standard.
Document the location before startup or pressure testing continues.
Steps
Look for flat panels moving when the fan starts.
Check whether the fitting is cross-broken, stiffened, or reinforced.
Verify hangers are not pulling the fitting out of shape.
Confirm reinforcement type with project/shop standard.
Document the location before startup or pressure testing continues.
Say this to your 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?