Weld Bead behaviour in SOLIDWORKS when selecting different entities

Say you have two pipes (as pictured below) that you want to weld together. SOLIDWORKS allows you to model a weld bead at the part or assembly level. In this case, we will add the weld bead in the assembly, by selecting Insert >  Assembly Feature > Weld Bead.

Pipe ends to be welded

You can set the options for the weld in the Weld Bead PropertyManager. In our case, if we select the closest edges of each pipe for the “Weld From” and “Weld To” fields, we get the result below.

Selecting closest edges

As shown, the weld bead extends into the pipe interior.

Resulting weld bead when selecting edges

If, instead, we select the inside faces (shown below) the weld bead does not extend into the pipe interior.

Selecting closest faces

Resulting weld bead when selecting faces