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.
Three drawings included on a new account.
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.
Tie-in list columns
The tie-in list is the bridge between the new design and the operating plant, and it is read by construction, operations and the isolation planner at the same time.
| Column | What it records |
|---|---|
| Tie-in number | The unique identifier for this connection point |
| P&ID number | The drawing that shows the tie-in, new and existing |
| Existing line or equipment number | What is being connected into |
| New line number | What is being connected |
| Size and rating | Nominal bore, and the flange rating or piping class of the connection |
| Existing material and class | What the existing pipe is made of, and to which class it was built |
| Tie-in type | Flanged spool, welded branch, hot tap, an existing spare nozzle, or an existing valved connection |
| Method | Shutdown, hot tap, or an online isolation technique |
| Isolation required | The valves, spades, blinds or freeze plugs that must be in place before work starts |
| Operating condition at the tie-in | Pressure, temperature, fluid, and whether the system can be drained and purged |
| Decontamination requirement | Purge, flush, steam out, and any gas free certificate needed |
| Execution window | Which shutdown or turnaround the work is scheduled into |
| Management of change reference | The change record that authorises the connection |
| Status | Not started, isolated, cut, welded, tested, reinstated |
Hot tap against a shutdown tie-in
Both are routine. They trade a production outage against an engineering assessment, and the choice is usually made by whether a window exists at all.
| Aspect | Hot tap | Shutdown tie-in |
|---|---|---|
| Plant state | The line stays in service and under pressure | The line is drained, depressurised, purged and isolated |
| When it is chosen | A large header that cannot be taken out of service, or no window within the project schedule | Almost every other case, where a window exists |
| Governing constraints | Pressure, temperature, wall thickness, flow velocity, fluid flammability and the weld procedure | Isolation integrity, purging, and the duration of the window |
| Welding | Welding onto a live line, with a burn through and hydrogen cracking assessment | Normal fabrication welding on dead pipe |
| Main cost driver | Specialist contractor, equipment and the engineering assessment | Lost production for the duration of the window |
| Record produced | A hot tap procedure and a specific engineering assessment for that connection | An isolation certificate and a normal work pack |
| Where it shows on the drawing | Marked as a hot tap on the tie-in list and annotated on the P&ID | Marked as a tie-in point, with the isolation shown |
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.