I had to come up with a hinge for a six inch pipe and came up with the enclosed.  This is for a rope guard which sits on the tops of fender piles alongside a wharf.  The purpose of the rope guard is to keep ship's ropes from entangling in the fender piles below.  The hinge had to be reasonably smooth so the rope would easily slide over it.  The hinges were needed to allow movement of the piles supporting it.  There was also a sliding joint for movement parallel to the pipe axis.

Hope this is useful somehow.

Bob G.