Why are loop hangers buckling round spiral duct?

Field answer

A loose strap loop can support dead weight but still let the pipe kick, dimple, or twist when fan pressure changes.

Inspect the barrel where the strap bears. If the wall is dimpling, unload the run and change the support method so the load spreads around the pipe instead of cutting or squeezing one strip.

What to check first

• Look for strap dimples, sidewall buckles, or rub marks.
• Check whether the run moves on startup.
• Identify fan/damper pressure changes nearby.
• Use approved rigid support/cradle where needed.
• Repair or replace dented pipe if the airflow path is affected.

Why it matters

Dimpling can damage the barrel, create leaks, cause noise, and move the run out of alignment.

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Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.