Does the Horizontal tube go through the vertical tube? If so SolidWorks might be confused on what surface to creat the weld bead. I've done some engine exhaust manifolds which had compound bends without any problems. Just a thought
they are weldments. it gives me an error that there is more than one resultant edge after selecting the tubes and it gets confused is there any way around that?
Probably not. You will have to make 2 separate sketches for each side of the pipe. Both pipes must be trimmed and intersecting each other before a Weldbead can be added.