Static field route #19339

What do I do when double-wall spiral liner crushes at a fitting?

Spiral, Round & Oval Duct Install⚠️ CHECK BEFORE YOU FIXField answer expansion

📖 Verified core answer

Pull it apart before it gets buried. The inner liner and outer shell need to slide together cleanly, not pack insulation into the airstream.

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Field verification checklist

Look inside the joint for buckled perforated liner or bunched insulation.
Check that inner liner and outer shell are aligned before pushing.
Deburr/correct any sharp collar edges.
Use an alignment sleeve or helper support for large pieces.
Verify no insulation is exposed into the air path before sealing.

Ask foreman

The double-wall spiral at [location] caught the inner liner and packed insulation into the pipe. I pulled it back apart. Do you want this liner straightened or the section replaced before we seal it?

Text to foreman

Route options

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

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

CBring 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 double-wall spiral together if the inner liner is catching.

Why this matters

A crushed liner restricts airflow, ruins acoustic performance, and can shed insulation into the duct system.

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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