When engineers need to repair or change part of a pipe, they usually don’t want to switch the whole system off. Doing that can be slow, costly, and cause a lot of disruption. Instead, they use special methods to block off just the section they need to work on, while the rest of the system keeps running.
Two of the most common methods used for this are pipe freezing and line stopping. Both do a similar job, but they work in very different ways and suit different situations. This guide explains how each one works, what they’re good for, and how to tell which one fits a job.
What Is Pipe Freezing?
Pipe freezing uses cold temperatures to block a pipe from the outside. A special freezing machine is clamped around the pipe. It cools the pipe down so quickly that the liquid inside turns to ice, forming a solid plug. This ice plug stops the flow just like a valve would, so engineers can safely work on the pipe further along without draining the whole system.
Pipe freezing is often used on:
- Water systems
- Heating pipes
- Chilled water systems
- Pipes carrying low to medium pressure
Because nothing is cut or drilled into the pipe, pipe freezing is quick to set up and causes very little mess or disruption.
Why people choose pipe freezing:
- No need to drain the whole system
- Very little disruption to day to day operations
- Good value for smaller isolation jobs
- Useful for repairs near valves and other tight spots
- Works well in small or hard to reach spaces
What Is Line Stopping?
Line stopping works in a completely different way. Instead of using cold temperatures, it uses a mechanical part called a stopping head. This is fitted into the pipe through a small connection, often made using hot tapping. Once in place, the stopping head physically blocks the flow of liquid or gas, sealing off that section of pipe so work can be carried out safely.
Line stopping is commonly used for:
- Water mains
- Gas and utility pipelines
- Industrial pipe networks
- Large pipes carrying high pressure
Because it’s a mechanical method rather than a cooling one, line stopping can handle much higher pressures and bigger pipes than pipe freezing can.
Why people choose line stopping:
- Works well on large pipes
- Handles high pressure systems
- Allows for bigger or more complex jobs
- Can isolate sections of important infrastructure
- Cuts down the need to shut off the full system
The Main Differences
Both methods stop flow through a pipe, but they get there in very different ways.
Pipe freezing:
- Uses cold to form an ice plug
- Best suited to smaller pipes
- Common in water and heating systems
- Doesn’t involve cutting into the pipe
- Best for shorter jobs
- Uses a mechanical part fitted inside the pipe
- Suited to large or high pressure pipes
- Needs an access point to fit the stopping head
- Better for bigger or longer jobs
- Common in utility and industrial pipelines
Which One Should You Use?
There isn’t one method that’s better than the other. It really comes down to the pipe itself and the size of the job.
Pipe freezing tends to work best when:
- The pipe is on the smaller side
- You need a quick, short-term fix
- The pipe carries water or another low pressure liquid
- You want to avoid cutting into the pipe
Line stopping tends to work best when:
- The pipe is large
- The system is under high pressure
- The job involves major repairs or new connections
- The isolation needs to stay in place for longer
Sometimes, both methods are used together on the same project, depending on what different sections of pipework need.
Safety Comes First
Both pipe freezing and line stopping need to be planned carefully and carried out by people who know what they’re doing. Things like the type of pipe, its size, the pressure inside it, and what’s flowing through it all affect which method is safe to use.
Getting this wrong can lead to leaks, damage, or even danger to the people working on site. That’s why the Health and Safety Executive sets out rules for working safely on pressurised pipes and systems, and why this kind of work should only be done by trained specialists, such as our team at RDS Pipeline, who carry out both pipe freezing and line stopping across a wide range of industries, including utilities, manufacturing, and petrochemical sites.
