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Apprentice answer

Why did the inner liner buckle when installing double-wall spiral duct

3rd YearRound, Spiral & Flat Oval DuctCheck first

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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Plain-English answer

Double-wall spiral has more going on than single-wall pipe. If the perforated liner catches the collar, it can buckle backward and shove insulation into the airflow path.

Separate the joint, straighten or replace the damaged liner, clean up the collar, and use a guide sleeve/alignment method so the inner and outer walls seat together. If the liner is torn or the insulation is packed, replace the damaged section.

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?

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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