If someone had asked me a few years ago what the highest risk offshore system was, I certainly would not have said a fully cased well in the process of being suspended. Yet that was the scenario for both of the recent mega-incidents, Montara and Macondo.
I would have instead suggested that dynamic production risers were the highest risk offshore system. The combination of relatively new technology, movement, fatigue potential, exposure in the splash zone, and continuous hydrocarbon flow poses risks that must be carefully managed. That is why investigations of incidents like the Visund gas leak are so important. In that regard, PSA does an excellent job and prominently posts all of their reports so that we all may benefit. I recommend that you take a look at this one.
In connection with the planned shutdown on Visund on 9 April 2011, a hydrocarbon leak occurred from well A21’s 6” flexible riser UK-18-0009. The Petroleum Safety Authority Norway (PSA) has carried out an investigation of certain aspects of the incident.
We have identified three nonconformities within the areas of establishment and follow-up of preconditions for safe operation of dynamic risers, training and expertise and governing documentation.
Bud's Offshore Energy (BOE) 
” dynamic flexible risers” the hose liner is glued to the end fitting and therefor does not qualify as a “metal to metal” system , only the end fitting which can be an API / ANSI flange or other sort of proprietary connection made be of steel or alloy.
I remember while in Norway we found that flexible risers became suspicious with a “foamy/plastic” substance coming out “extruded” ot the hose fitting between the elastomer braided hose and the riser connection.