I've done work for Subsea 7 but had never heard of this. They're present in oil and gas fields as well as offshore wind farm* areas worldwide, so it's possible they have something similar elsewhere.
*My guess for the longest object to travel on a railway would have been a wind turbine blade. So wrong!
216m lengths of long welded rail on a delivery train would trump wind turbine blades, and probably be much more frequent?
Paul
That looks a good bet for the longest thing to travel on a railway in the accepted sense of "travel on a railway". Many large machines include wheels running on rails as part of their load-bearing structure, but would you describe such as a dockside or factory crane, boat lift, or radio telescope as "travelling on a railway"?