There are numerous authorised methods of building a welded joint for grease exhaust ductwork. The choices will depend upon the code for your jurisdiction but must involve flanged, telescoping, Bell kind or overlapping joints. PlenumWrap gives really effective thermal insulation to keep up the pipe or cable coating temperature below https://greasetightextractductwor23445.frewwebs.com/37337362/grease-tight-extract-ductwork-secrets