Flat-oval spiral duct starts changing shape under pressure

Flat-oval duct needs shape control across the flat spans. Hold the run and add approved reinforcement or replace with properly rated duct.

Round, Spiral & Oval Duct 2nd Year YELLOW

Watch out

Do not keep pressurizing flat-oval duct that is visibly deforming.

Check

Look for top/bottom bowing, hanger rods pulled out of plumb, or joints opening.
Confirm pressure class and flat-oval reinforcement detail.
Check whether supports are squeezing or failing to cradle the duct.
Hold pressure/startup if deformation is growing.
Get foreman/detailer approval before adding internal supports.

Steps

Look for top/bottom bowing, hanger rods pulled out of plumb, or joints opening.
Confirm pressure class and flat-oval reinforcement detail.
Check whether supports are squeezing or failing to cradle the duct.
Hold pressure/startup if deformation is growing.
Get foreman/detailer approval before adding internal supports.

Say this to your foreman

The flat-oval line at [location] is changing shape under pressure and pulling rods out of plumb. I checked supports and pressure class. Do you want reinforcement added or the section replaced per detail?