This fan outlet duct has a fabric expansion joint (flex connector) belt attached to angle flanges. Originally designed as a molded-corner “U-Belt” it’s now a flat-belt with 90 degree corners. The aftermarket flanges use 1/4” welded studs which have broken off inside the duct, causing leakage. The backup bars which clamp the belt down are also undersized for this application. We’re going to pull the whole assembly out and replace it with a high-temperature Viton rubber U-Belt expansion joint.