Tie-in

Tie-ins are where brownfield projects touch the plant that is already running, and they are managed with corresponding formality: a tie-in list enumerating every connection, each with its location, the existing line or system it enters, the method — a shutdown connection made with the system down and cleared, or a hot tap performed on the live line — and the isolation, draining and permitting the method requires. The list is a contract between the project and operations: these intrusions, at these points, in these windows.

Each tie-in also carries a small discovery risk from the existing side: the line whose actual routing, wall thickness or condition differs from the documents — verified by walkdown, scan or UT before the window, or discovered during it, at window prices. Shutdown-dependent tie-ins concentrate the schedule risk further, queueing the project's connections into turnaround windows that will not wait.

The classic failures: the tie-in discovered late, after the shutdown scope froze; the existing side not as documented; and the register treated as an engineering list rather than the operations negotiation it actually is.