Join Breps failed in grasshopper

I followed the tutorial here to create a pipe

but it always failed at the last step while combining all the surfaces together with the brep join battery.
seems the battery doesn’t want to be connected with more than one surface…

Does anyone know how can i figure this out?
Thanks so much… (20.9 KB)

hey you’re missing geometry in the file you attached,

anyway did you try ‘flatten’ on the inputs for the BrepJoin component?