They are calling the “top hat” operation a success. Take a look at the video feed and tell me how bad failure must have looked like.
I was dubious of this contraption from the start. You can’t just set a flat rubber seal on a set of unevenly cut pipe ends and expect to create a good enough seal contain a very high pressure (9000psi? 10,000psi?) flow. You couldn’t even contain a low pressure flow with that.
I don’t understand why they didn’t fabricate a fishing tool to force thread over the riser. It could also have had gates to relieve the pressure during the installation process.