When you need to add a new branch to an existing pipe, you have a decision to make. You can keep the line running and drill into it live, or you can take the section out of service, drain it down, and work on an empty pipe. That second option is called cold tapping, and while it is often seen as the slower route, there are real situations where it is the better engineering choice.
What is a cold tap?
A cold tap is a branch connection made on a pipe that has been isolated, drained, and fully depressurised. Once the line is empty and confirmed safe, an engineer cuts into the wall to fit a new branch, valve, or fitting. Because there is no internal pressure or flow pushing back, the work can be carried out with simpler equipment and tighter control over the cut.
This is the key difference from live methods. With under pressure drilling, the pipe stays in service while the connection is made, so the contents never stop moving. A cold tap reverses that order. You stop everything first, then work in a static, empty system where the only variable is the pipe itself.
The steps involved in a cold tap
A cold tap follows a strict sequence, and each stage protects the next.
- Plan the shutdown. Agree a window when the line can be taken offline with the least disruption to operations.
- Isolate the section. Close valves so the work area is positively cut off from the live system.
- Drain and depressurise. Remove the contents and bring the pressure down to zero. This is the part that makes a cold tap “cold.”
- Prove the line is empty. Verify there is no residual fluid, gas, or trapped pressure before any cutting begins.
- Cut and fit the branch. Add the new connection, valve, or fitting to the open pipe.
- Test and recommission. Pressure test the work, bring the section back up, and return the line to service.
When a shutdown is worth it
A cold tap is not always the slow, costly option people assume. In the right conditions it is the cleaner and lower-risk choice.
| Situation | Why a cold tap suits it |
|---|---|
| The line is already due to be offline | If a planned shutdown is happening anyway, draining for a cold tap adds little extra cost. |
| There is no pressure or flow to control | An empty pipe is simpler and safer to cut into, with no live contents to manage. |
| The pipe wall or condition is uncertain | Working empty removes the risk of an uncontrolled release if the wall is thinner or weaker than expected. |
| The contents are hazardous or hard to contain | Some fluids and gases are far safer to handle once fully drained and purged. |
| The branch is large or geometrically complex | Bigger or more detailed connections are often easier to align and weld on a static pipe. |
The deciding factor is usually whether the line can be taken offline without serious disruption. If it can, a cold tap removes a great deal of risk in a single move.
When a shutdown is not worth it
Draining a line is never free. A shutdown halts production, interrupts supply, and can be expensive when the system feeds a process that cannot pause. In those cases, keeping the line live is the stronger answer. This is where techniques such as line stopping earn their place, isolating a section without draining the whole system, or where a live tap avoids any downtime at all.
It ultimately comes down to the cost of downtime against the cost of complexity. For a fuller side-by-side breakdown, see our guide on the difference between hot tapping and cold tapping.
Safety always comes first
Whichever method you choose, pressure systems can be hazardous, and a line that has not been properly proven empty is a genuine danger. The Health and Safety Executive explains why pressure equipment safety matters and what can go wrong when a system is not handled correctly.
Talk to the team
Not sure whether a cold tap, a live tap, or another approach suits your pipeline? Get in touch with RDS Pipeline on 01277 500510, or visit our contact page and we will help you weigh up the best option for your line.
