Pacific Flow Control recently completed another large-diameter line stopping project in Western Canada. This work involved 1524mm (60”) and 1372mm (54”) single line stops on carbon steel transmission mains operating under pressure.
Projects of this scale demand far more than simply installing a fitting and inserting a stopping head. They require engineered planning, qualified in-service welding procedures, controlled hot tapping operations, and documented pressure and flow monitoring to ensure system integrity throughout the isolation.
The work was completed safely, under pressure, and without disruption to downstream users.
What Is a Line Stop?
A line stop is a controlled method used to temporarily isolate a section of a live pipeline so maintenance, tie-ins, or modifications can be completed without shutting down the entire system.
The process typically includes:
Installation of a welded or mechanical line stop fitting
Pressure testing of the fitting and valve assembly
Hot tapping through a full-port valve
Insertion of a mechanical stopping head
Confirmation of seal integrity
Completion plug installation and removal of temporary equipment
Unlike a system shutdown, line stopping allows flow to remain active in the pipeline while a specific section is safely isolated.
How We Execute Large Diameter Line Stops
Large diameter transmission mains require a disciplined, procedure-driven approach.
- Engineered Welded Fittings
For carbon steel applications, fittings are installed using qualified in-service weld procedures in accordance with applicable standards such as CSA Z662 and AWWA M11.
Before welding begins, the pipe is:
- Inspected for integrity
- Verified for outside diameter
- Cleaned and prepared
- Evaluated for adequate wall thickness
All welds are completed in accordance with approved procedures, followed by leak testing prior to any cutting operations.
- Pressure Testing Before Hot Tapping
Before the hot tap begins, the fitting and valve assembly are pressure tested using:
- CO₂ leak testing (soap/bubble test) for smaller cavities
- Hydrostatic pressure testing for larger nozzle assemblies
Testing is completed in accordance with recognized guidelines (such as API 2201 recommendations), and held long enough to verify assembly integrity before introducing cutting equipment into the system.
No cutter touches the pipe until the assembly proves tight.
- Calculated Hot Tapping
Hot tapping on 54” and 60” mains is never guesswork.
Prior to mounting the tapping machine, technicians complete a calculation sheet that confirms:
- Internal diameter
- Gate clearance
- Distance to back of pipe
- Required cutter depth
- Machine travel
- Retraction distance after completion
Knowing exactly where the pilot and cutter are positioned relative to the pipe wall is critical to preventing back wall strikes, gate damage, or coupon loss.
Machines are centered, travel indicators calibrated, and cutter assemblies inspected prior to engagement. Upon completion, coupons are retrieved and measured to confirm actual pipe ID for sealing element configuration.
- Line Stop Insertion & Seal Verification
After the hot tap is completed and internal measurements confirmed, the line stop head is assembled to match the true pipe dimensions.
Once inserted, seal performance is verified through purge/equalization procedures. Blow-by is measured and documented to confirm the isolation is within acceptable limits before downstream work begins.
- Pressure & Flow Monitoring Program
For large diameter isolations, Pacific Flow Control implements a formal Pressure and Flow Monitoring Program.
This includes:
- Establishing a controlled pressure zone
- Monitoring upstream operating pressure
- Measuring controlled zone pressure
- Calculating blow-by flow rates in gallons per minute
- Recording readings at defined time intervals
If pressure or flow conditions deviate beyond acceptable thresholds, immediate evaluation procedures are triggered. In the event of a major irregularity, evacuation protocols are in place to protect downstream workers.
This structured monitoring approach provides an added layer of safety for confined space operations and high-consequence transmission systems.
Why Line Stopping Is Important
Line stopping eliminates the need for full system shutdowns, draining, or prolonged service interruptions.
For critical transmission infrastructure, this means:
Reduced operational risk
No widespread service disruption
Controlled isolation zones
Safer working conditions
Maintained system pressure and stability
On pipelines of this size, proper planning and execution are essential. Every step — from weld prep to final blind flange torque — must be deliberate and documented.
Large Diameter Line Stops You Can Trust
Pacific Flow Control specializes in complex and large diameter live pipeline work, including carbon steel transmission systems.
Projects like 54” and 60” line stops require:
Senior-level technicians
Dedicated heavy-duty tapping and stopping equipment
Engineered procedures
Formal quality control documentation
Comprehensive safety management
We routinely execute work where precision, experience, and procedural discipline matter most.
Our Services
Pacific Flow Control provides turnkey live pipeline solutions, including:
Hot tapping
Line stopping
Valve insertion
Pipe freezing
Hydrant services
Emergency pipeline support
We work with engineers, municipalities, contractors, and industrial operators to ensure every project is completed safely, efficiently, and in compliance with applicable standards.
If you are planning a project that requires expert large diameter line stopping or hot tapping services, contact Pacific Flow Control to discuss your requirements.