Static field route #19593

What do I do when back-to-back 45-degree TDC flanges bind and the bolts will not seat?

Rectangular Duct Assembly: TDC / Ductmate / Flanges✅ LEARN / STANDARD FIXField answer expansion

📖 Verified core answer

Close back-to-back flanged fittings can run out of corner clearance. Align the faces, protect the gasket, and get approval before trimming or using alternate hardware.

Open in Field Rescue Open category

Field verification checklist

Check whether the gasket faces are square or being pulled sideways.
Identify the exact corner lip or bracket that is binding.
Loosen nearby hangers if the run is locked under stress.
Use clamps to align faces before bolting.
Verify any trimming or alternate bolt detail with the foreman/shop standard.

Ask foreman

The back-to-back 45s are so tight that the TDC corners are binding before the gasket faces seat. I can clamp and align it, but the corner lip may need approved cleanup. How do you want it handled?

Text to foreman

Route options

A Correct it only if the fix is within your assignment and approved method.

B Hold and document if it affects pressure class, listed assembly, material spec, support load path, fire barrier, equipment, TAB, or another trade.

C Bring the foreman/detailer the location, what you checked, and what decision you need before sealing, testing, cover, or startup.

Do not do this

Do not force TDC/Ductmate corners together with a drift pin so hard that the flanges twist or the gasket gaps.

Why this matters

Twisted companion flanges leak, whistle, and make the tight offset harder to service or seal.

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, pressure/material schedule, and AHJ/code requirements.

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