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

Field 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.

What to check first

• 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.

Why it matters

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

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