Flange corners after assembly not sealed

A TDC/Ductmate corner leak is fixed by checking the gasket path, corner seating, flange contact, and approved corner seal-not by hiding bad alignment under extra sealant.

Rectangular Duct & Fittings 2nd Year YELLOW

Stop if

Ask when connector type, gasket, cleat/bolt schedule, pressure class, or manufacturer detail is unclear.

Watch out

Do not mastic over a twisted joint or use the corner bolts to drag crooked duct together.

Check

Support and align the duct level and square before tightening.
Confirm gasket is continuous on one flange face and not folded, stretched, or displaced at the corner.
Seat the joining-duct corners and start hardware evenly.
Use drift pins only on close holes and clamps only to hold aligned flange faces, protecting the gasket/flange.
Seal the corner by the approved project or manufacturer method, then recheck the backside corners.

Steps

Support and align the duct level and square before tightening.
Confirm gasket is continuous on one flange face and not folded, stretched, or displaced at the corner.
Seat the joining-duct corners and start hardware evenly.
Use drift pins only on close holes and clamps only to hold aligned flange faces, protecting the gasket/flange.
Seal the corner by the approved project or manufacturer method, then recheck the backside corners.

Say this to your foreman

In Rectangular Duct Assembly: TDC / Ductmate / Flanges, I'm looking at: Flange corners after assembly not sealed. What should I verify before I cut, drill, seal, cover, move, or install?