A strap hanger crushing a duct corner is a support problem, not something to tighten harder. Loosen, spread the load, or change the support method before the corner gets permanently damaged.
Do not re-tighten a strap that is already creasing the duct corner. Tighter does not fix the problem - it makes the crush worse.
Check
Look at the duct corner at the strap location. A crushed corner shows a visible crease, dent, or collapse where the strap edge is digging in.
Check whether the strap is too narrow or bearing on a sharp edge. Narrow bearing concentrates load at the weakest part of the duct corner.
Check strap position. A strap riding up the corner instead of sitting flat under the duct face will crease the metal.
If the strap is already crushing the corner, loosen it and use an approved wider bearing surface, corner protector, saddle, or trapeze detail instead of re-tightening the same bad point load.
On insulated duct, check under the insulation if allowed. The wrap can hide a crushed corner that is already leaking or deforming.
Steps
Look at the duct corner at the strap location. A crushed corner shows a visible crease, dent, or collapse where the strap edge is digging in.
Check whether the strap is too narrow or bearing on a sharp edge. Narrow bearing concentrates load at the weakest part of the duct corner.
Check strap position. A strap riding up the corner instead of sitting flat under the duct face will crease the metal.
If the strap is already crushing the corner, loosen it and use an approved wider bearing surface, corner protector, saddle, or trapeze detail instead of re-tightening the same bad point load.
On insulated duct, check under the insulation if allowed. The wrap can hide a crushed corner that is already leaking or deforming.
Say this to your foreman
The strap hanger at [location] is crushing the duct corner - there is a visible crease/collapse in the metal. Do you want me to switch to a wider bearing surface, add a corner protector, or change to a trapeze at this location?