Static field route #19108

What do I do when a wide TDC/TDF flange bows open in the middle?

Rectangular Duct Assembly: TDC / Ductmate / Flanges✅ STANDARD FIELD CORRECTIONV191 answer-gap expansion

📖 Verified core answer

Large flat flange spans may need clips or approved intermediate fastening so the gasket stays compressed across the whole joint, not just at the corners.

Open in Field Rescue Open category

Field verification checklist

Look for daylight, whistle, or gasket gap along the center span.
Confirm corner bolts are installed and gasket is continuous.
Check approved TDC/TDF clip/intermediate fastener detail for the duct size/pressure class.
Install clips evenly and recheck seal compression.
Retest during fan or leakage check.

Ask foreman

The wide TDC/TDF joint at [location] is sealed at corners but bowing open in the center. I checked gasket and corners. Do you want flange clips/intermediate fastening added per detail?

Text to foreman

Route options

AMake the field correction only if it is within your assignment and the approved method.

BHold and document the condition if the fix affects airflow, access, life safety, pressure class, rated assemblies, equipment, or another trade.

CBring the foreman/detailer the location, what you checked, and what decision you need before cover, startup, or rework.

Do not do this

Do not rely on corner bolts alone if the middle of a wide flange is visibly bowing open.

Why this matters

Center-span flange leaks waste air, make noise, fail leakage checks, and can get worse under pressure.

Final verification

Use this as field training guidance. Final direction still comes from the foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements.

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