When the Basic Design is finished, the Detailed Design phase can start. It covers the German Ausführungsplanung. All engineering work will be completed to an extent, that the manufacturer has all information to setup the execution works including purchasing and fabrication.
The consideration of fabrication issues is mandatory for steel design especially in offshore purposes. Handling, transportation, assembly, welding, non-destructive testing and coating is addressed in this phase avoiding deficits in these aspects. They will pop up during the execution phase, when they are much more difficult to correct.