A strap or hanger that is too narrow, too tight, or improperly placed will deform spiral duct - especially on lighter-gauge pipe. An out-of-round spiral will not connect to the next fitting correctly and will leak at the joint.
Do not let straps or hangers crush the spiral or pull it off line.
Check
Look at the duct cross-section at the strap location. Spiral should be visibly round. If you can see a flat spot, pinch, or oval at the hanger, the duct is being deformed.
Check strap width and bearing area. Narrow straps concentrate load and can cut into the pipe
wider straps or approved saddle supports spread the load.
Check tightness: the strap should support the duct without squeezing it. If you need a tool to tighten a strap around spiral duct, it may already be too tight.
If duct is already deformed at a hanger: the duct section may need to come down and be replaced - a significantly out-of-round section will not seat the next connection correctly.
For larger or heavier spiral, use the support method shown on the approved detail rather than improvising a narrow strap.
Steps
Look at the duct cross-section at the strap location. Spiral should be visibly round. If you can see a flat spot, pinch, or oval at the hanger, the duct is being deformed.
Check strap width and bearing area. Narrow straps concentrate load and can cut into the pipe
wider straps or approved saddle supports spread the load.
Check tightness: the strap should support the duct without squeezing it. If you need a tool to tighten a strap around spiral duct, it may already be too tight.
If duct is already deformed at a hanger: the duct section may need to come down and be replaced - a significantly out-of-round section will not seat the next connection correctly.
For larger or heavier spiral, use the support method shown on the approved detail rather than improvising a narrow strap.
Say this to your foreman
This spiral section looks [flattened / oval / pinched] at the hanger location. Do you want me to loosen the strap and check, or does this section need to come down and be replaced?