I don't think the spherical tanks in the petrochemical kit come with wind girders, however the standard Plastruct spherical tank kit does include this. I think the wind girder adds a lot to the tank structure.
The supplied wind girder is a very thin plastic ring. It is too late for your spheres but for future builds to add a wind girder instead of trying to cut out a ring simply cut a circle and glue the two hemispheres to it. This way you can make the girder as thick as you want. This way the girder can be used as extra glue surface for the leg assembly.
Joe
