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Apprentice answer

Why can an adjustable round elbow split open on a high-velocity duct run

3rd YearRound, Spiral & Flat Oval DuctCheck first

A light adjustable elbow may not belong on a high-velocity or pressure-critical run. Replace failed fittings with the approved round elbow type/radius/gauge for that system.

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Plain-English answer

If a pleated or adjustable round elbow pops at the heel seam, the fitting is likely not strong enough for the pressure/velocity or it was used in the wrong place.

Stop treating it as a sealant-only leak. Check the drawing, pressure class, duct size, and approved fitting type. The likely recovery is replacing the failed elbow with a factory-rated smooth elbow, heavier-gauge fitting, or approved long-radius sweep per project detail.

Ask Foreman

The round elbow at [location] split at the heel seam under startup pressure. I checked the fitting type and system. Do you want it replaced with the approved heavier/smoother elbow detail?

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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