Tie-in.
A tie-in is the physical connection point where new piping, equipment, or instrumentation is joined to an existing operating system, typically during a revamp, expansion, or turnaround. Each tie-in is identified, listed, and scheduled because it touches live plant and usually needs isolation or a shutdown window.
What Tie-in means.
Every brownfield project reaches the moment where new work has to meet old plant, and each of those junctions is a tie-in. On the P&IDs the boundary between new and existing scope is marked, often with a cloud or a dedicated tie-in symbol carrying a tie-in number, and that number ties back to a tie-in list that records the host line, its size and rating, the isolation method, whether the connection is made live or under shutdown, and the sheet the tie-in appears on. Because a tie-in breaks into operating plant, each one is controlled through management of change and planned around isolation, draining, and purging. A hot tap is made on a line still in service. A shutdown tie-in waits for the system to be isolated and freed of hazard. The tie-in list is, in effect, the delta between the register of the plant that exists and the scope being added, which is why getting the existing register right is the precondition for planning the connections.
Where tie-ins appear
Tie-ins show up on revamp, expansion, and turnaround drawings wherever new scope meets existing plant. The P&ID marks the new-to-existing boundary, commonly with a cloud or a tie-in symbol carrying the tie-in number, so a reviewer can see exactly where the project breaks into the running facility.
The tie-in list
Each tie-in is recorded on a tie-in list. The list carries the tie-in number, the host line and its size and rating, the connection type, the isolation method, whether it is hot or under shutdown, and the source P&ID. It is what planners and the turnaround team schedule and risk-assess the connections against.
Hot tap versus shutdown tie-in
A hot tap connects to a line that stays in service, made under controlled conditions without shutting the system down. A shutdown tie-in waits until the host system is isolated, drained, and purged. The choice drives the schedule, the risk assessment, and whether the work needs a shutdown window at all.
Tie-ins and management of change
Because every tie-in breaks into operating plant, each is controlled through management of change, with its own isolation plan and hazard review. The MOC ties the new connection back to the affected P&IDs so the records stay consistent once the work is built and the drawings are updated.
Common questions
What is a tie-in on a P&ID.
What is a tie-in list.
What is the difference between a hot tap and a shutdown tie-in.
Why are tie-ins managed through MOC.
Pull the tie-in list off the drawings.
Every tie-in point on a revamp set, with the line and equipment it connects to, in one register.