Detailed design (detail engineering)

Where FEED decides what the project is, detailed design works out every remaining fact of it: piping engineered isometric by isometric, structures down to connections and rebar, cable by cable, instrument by instrument, with the 3D model coordinated across disciplines and the final material take-offs extracted from the result. It is the volume stage of engineering — most of the documents, most of the hours — performed by the EPC contractor's engineering organisation or a design institute, and consumed directly by procurement and the site.

Its productivity depends almost entirely on what it inherits. Detail engineering on a frozen, consistent FEED basis is production; on an unfrozen basis it is rework at production headcount, with every upstream change rippling through hundreds of issued documents. The stage also runs concurrently with procurement and early construction, so its sequencing is dictated by the site's needs — and a detail-design effort that falls behind the construction sequence turns the entire project into a queue behind engineering.