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Apprentice answer

Why is flat-oval spiral duct bowing or pancaking under static pressure

3rd YearRound, Spiral & Flat Oval DuctCheck first

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

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Plain-English answer

Flat-oval spiral can deform across the flat top and bottom when pressure, gauge, support, or reinforcement is not right for the job. Once the shape changes, hanger rods, joints, and airflow all start fighting each other.

Check the pressure class, duct size, support spacing, and manufacturer/SMACNA reinforcement requirement. The recovery is usually internal tie-rods, external reinforcement ribs, corrected supports, or replacement with a properly rated section.

Ask 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?

Verify before acting

Use this as training guidance. Foreman direction, approved drawings, project specs, manufacturer instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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