Under Pressure Connections
Live pipeline connections and diversions using controlled techniques to maintain continuity across varied pipeline materials, diameters and operating conditions.
Radius Subterra delivers engineered under pressure connections on polyethylene (PE) and metallic pipelines, enabling safe tie-ins, diversions and live network modifications without shutdowns.
Under pressure connections allow new connections, diversions and network modifications to be completed on live pipelines without interrupting supply or depressurising the wider system. These engineered techniques provide controlled access to operational assets, enabling safe and efficient delivery of live network works.
Radius Subterra provides a comprehensive range of under pressure connection services, allowing new outlets to be formed on live pipelines without interrupting supply. Radius Subterra capabilities cover polyethylene (PE) and metallic mains of all materials, diameters and operating pressures, supporting both routine and complex network works. This engineered approach enables live connections for planned upgrades, asset modifications and reactive interventions.
We deliver standard and bespoke electrofusion branch saddles for mechanical or welded metallic pipelines, alongside a range of metallic under pressure tees for steel, ductile iron, cast iron and other metallic mains. Our connection solutions are supported by an extensive range of drilling equipment suited to a varied outlet configurations and site conditions. This ensures each connection is matched accurately to pipeline material, geometry and operating requirements.
Under pressure connections are routinely used to support bypass installations, diversions, flowstopping activities and pipeline repair works. These connections form a key part of live network modification and maintenance strategies across multiple sectors. Their ability to avoid shutdowns reduces operational disruption and supports continuous service to end users.
Where non-standard requirements exist, Radius Subterra’s engineering capability allows connection solutions to be tailored to suit the host pipeline and site constraints. This includes bespoke branch saddles and under pressure tees manufactured to meet specific diameter, outlet or installation requirements, while maintaining compliance with applicable industry standards and network approvals.
All under pressure connection works are planned and executed by experienced teams using approved procedures and equipment. Operations are fully monitored and recorded, with detailed completion reporting provided to support asset records, compliance and future network management. This structured process delivers safe, consistent and fully traceable outcomes for all live connection activities.
Key Benefits
Reduced excavation and site impact
Under pressure connections typically require a smaller excavation than flowstopping and equal tee installations, reducing ground disturbance, reinstatement scope and overall site footprint. This minimised footprint helps accelerate works and limit disruption in constrained or sensitive locations.
Made-to-measure connection solutions
Connections can be engineered to suit non-standard pipe diameters, wall thicknesses and legacy assets, providing flexibility where standard fittings or tees are not suitable. Bespoke options allow connection arrangements to be closely matched to host pipe geometry and operational requirements.
Fast, efficient installation
Under pressure connections are installed quickly and with minimal site setup, supporting shorter programme durations and enabling live network modifications completed within tight operational windows. This efficiency allows teams to progress critical works while maintaining full-service continuity.
Under Pressure Connection technologies
Engineered under pressure connection technologies enabling live tie-ins, diversions and controlled access to polyethylene and metallic pipelines without shutdowns.
PE branch saddle connections
Electrofusion branch saddles are used to form permanent live connections on polyethylene (PE) pipelines without interrupting supply. The process begins with the branch saddle being electro-fused directly onto the outside diameter of the host main, creating a fully integrated, pressure-rated joint. This fused joint creates a stable base for controlled under-pressure drilling on live PE mains.
Once fusion is complete, a valve is installed onto the saddle outlet, followed by connection with an under-pressure drilling unit. The complete assembly is pressure tested in line with network requirements to confirm joint integrity. The valve operation is verified before drilling begins. The drilling unit is advanced through the valve to cut the host pipe wall, after which the cutter is safely retracted. The valve is then closed to isolate the new outlet. The removed pipe coupon is retained within the drilling equipment and safely retrieved once cutting is complete. The outlet can either be blanked or connected directly to downstream pipework, depending on project requirements.
Radius Subterra operates an exclusive range of electrofusion branch saddles in both standard and bespoke configurations. This allows connections on a range of pipe diameters, SDRs and outlet sizes, including non-standard and legacy pipelines. The range includes size-for-size options as an efficient alternative to cut-out and tee installations, and imperial saddles to suit legacy pipelines. Solutions cover mains up to 1000 mm in diameter with outlet sizes up to DN500. Installations are carried out by trained technicians using approved procedures and calibrated equipment.
Each installation is recorded through Radius Subterra’s digital reporting system, capturing saddle specifications, batch numbers, operator details, ambient conditions, GPS location and pressure test results, ensuring full traceability and compliance.
Metallic under pressure connections
Metallic under-pressure tees are used to form permanent live connections on steel, ductile iron and cast-iron pipelines without interrupting supply. The technique provides a controlled and proven method of creating branch outlets on operational metallic mains across a wide range of diameters and pressures.
The process begins with the installation of an under-pressure tee assembly selected and configured to suit the host pipe material, diameter and operating conditions. A valve is installed onto the outlet, followed by connection to an under-pressure drilling unit. The complete assembly is pressure tested in line with network requirements to confirm integrity. Valve operation is verified before drilling commences. The drilling unit is then advanced through the valve to cut the pipe wall, with the removed coupon securely retained within the equipment and retrieved on completion. The drill is retracted and the valve closed, leaving a fully isolated outlet ready for blanking or immediate connection to downstream pipework.
Radius Subterra delivers metallic under-pressure tee solutions using engineered assemblies capable of supporting a wide range of outlet sizes, pipe materials and site conditions. This approach allows connection arrangements to be matched closely to project requirements, including bespoke configurations where standard options are not suitable. All works are delivered by trained and competent teams using approved equipment and procedures, supported by stringent on-site dynamic risk assessment to ensure safe execution under live conditions.
Each installation is fully recorded through Radius Subterra’s digital reporting system, capturing pressure test results, component details, installation data and site information. Comprehensive reporting provides full traceability and assurance that each live connection meets applicable standards and network requirements.
Grouted tee connections
Grouted tees are a specialist live connection technology primarily used on UK gas networks to install branch outlets on metallic pipelines where welded connections are not suitable or permitted. This makes grouted tees well suited to cast iron and ductile iron pipelines, particularly on legacy assets where pipe ovality, dimensional variation or material characteristics that require a controlled, nonwelded connection method.
The system comprises a split tee assembly that is clamped around the host pipeline following surface preparation. An annular cavity between the tee body and the pipe wall is injected with grout, which cures to transfer structural load between the pipeline and the tee. This creates a stable, pressure-capable connection without introducing heat or weld-induced stresses into the host pipe. This construction accommodates higher ovality and geometric variation than many alternative fittings.
Once the grout has cured in accordance with the approved procedure, a valve is installed onto the tee outlet and an under-pressure drilling unit is connected. The complete assembly is pressure tested in line with network requirements before drilling starts. The pipe wall is drilled under pressure, with the removed coupon fully retained within the drilling equipment and safely retrieved on completion.
Grouted tees are recognised within GDN standards as a suitable live-connection solution for iron gas mains, including higher-pressure applications where welding is prohibited or impractical. They support new connections, diversions, bypass installations, flowstopping and permanent modifications. Grouted tee assemblies can be supplied for a wide range of diameters and outlet sizes, with all installations delivered using approved methods and fully documented for compliance, traceability and asset integrity.
Sample and dosing points
Sample and dosing points are dedicated access locations installed on pipeline systems to enable regulated water quality sampling and controlled chemical dosing without disrupting normal flow or network operation. Sampling points provide a secure and representative location where water quality can be assessed for parameters such as microbiological indicators, disinfectant residuals and other compliance measures in line with network and regulatory requirements. Together, these points help maintain water quality, asset protection, system performance and regulatory compliance.
In addition to installation on new pipework, sample and dosing points can be retrospectively installed onto live pipelines using under-pressure drilling techniques. This approach allows access fittings, valves and sample points to be added without draining or shutting down the network, minimising operational disruption and customer impact. The connection is formed by installing an approved fitting onto the host main, followed by under-pressure drilling to create a controlled access point while maintaining system operation.
The location and configuration of sample and dosing points are designed to meet network standards for representativeness, hydraulic performance and safety. Installations are commonly required at treatment works outlets, service reservoir connections, critical distribution points or areas of known water quality concern. Dosing points are engineered to support safe chemical introduction and effective mixing.
All installations are planned and delivered by trained and competent teams using approved procedures and equipment. Each installation is fully documented, with completion records provided to support asset registers, compliance reporting and ongoing water quality management.
Tapping tee connections
Tapping tee drilling is a well-established under-pressure connection method used to form live branch connections on polyethylene pipelines. For smaller diameter and thin-walled PE pipes, electrofusion tapping tees with integrated cutters are commonly installed directly by network operators for routine activities.
As pipe diameters increase and wall thicknesses become greater, the limitations of integral tapping cutters become more pronounced. Increased wall thickness, higher resistance during cutting and reduced control over coupon retention can make standard tapping tees unsuitable for larger mains or non-standard applications. In these situations, a more engineered drilling solution is required to safely and reliably form the connection under pressure.
Radius Subterra has developed a specialist tapping tee solution for larger diameter polyethylene pipelines, supporting mains up to 800 mm in diameter. These tapping tees are designed to be electro-fused onto the host main and paired with a dedicated under-pressure drilling system, allowing the pipe wall to be cut in a controlled manner while the pipeline remains live. A purpose-designed cutter and internal plug carrier enable controlled drilling, secure coupon retention and positive isolation once cutting is complete.
The drilling assembly is installed on to a valve and pressure tested in accordance with network requirements prior to cutting. Following verification of valve operation, the drill is advanced, the pipe wall is cut under pressure, and the tool is safely retracted. This engineered method provides a reliable solution for large-diameter or nonstandard PE connections.
Air valve installation
Air valves are critical components in water pipeline systems, designed to manage the presence of air within pressurised mains. They allow air to be released during filling and normal operation, and admit air during draining or rapid pressure changes, helping to prevent air locking, vacuum conditions and associated structural or hydraulic issues. Correctly installed air valves support efficient pipeline performance, asset protection and long-term network reliability.
Radius Subterra can install air valves on existing pipelines without interrupting supply by utilising under-pressure connection techniques. This approach allows air valve assemblies to be retrofitted onto live mains, avoiding the need for shutdowns, extensive temporary works or network disruption. A suitable connection fitting is installed onto the host pipeline, followed by controlled under-pressure drilling to form a live access point for the valve installation. This enables safe installation while the pipeline remains fully operational.
Air valve installations are designed in accordance with water network design standards and manufacturer guidance, taking into account pipeline material, diameter, operating conditions and system hydraulics. Valves may be installed as air release valves, air/vacuum valves or combination air valves, depending on the operational requirement and location within the network. Typical installation points include pipeline high points, changes in gradient, long rising mains and sections prone to air accumulation.
All installations are carried out by trained and competent teams using approved procedures and equipment. Each installation is pressure tested and verified in line with network requirements prior to commissioning. Comprehensive documentation supports asset records, operational management and compliance requirements, ensuring reliable long-term system performance.
Wash out connections
Wash out connections are installed on pipeline networks to provide a controlled means of flushing, draining and removing sediment or debris from mains during commissioning, maintenance or operational activities. They are commonly used on water and wastewater pipelines where the removal of accumulated solids is required to maintain hydraulic performance and water quality. Wash outs help restore flow conditions and support ongoing asset performance.
Radius Subterra installs wash out connections retrospectively on live pipelines using under-pressure connection techniques. This allows new wash out points to be added without interrupting supply, minimising disruption and avoiding full system shutdowns. Access to the pipeline is achieved via electrofusion branch saddles or metallic under-pressure tees, depending on pipe material and operating conditions. A valve and drilling assembly is installed and pressure tested prior to drilling, enabling the outlet to be formed safely while the main remains in service.
Once installed, wash out connections can be fitted with valves, pipework and discharge arrangements to allow controlled flushing. This supports activities such as initial commissioning, routine flushing, post-repair cleaning and targeted removal of sediment. The location of wash out points is chosen to suit network gradients, flow direction and site constraints, ensuring effective drainage and flushing capability.
All wash out installations are planned and delivered in accordance with applicable network standards and procedures. Works are carried out by trained and competent teams using approved equipment, with full records provided on completion. This ensures safe operation, traceability and reliable long-term maintainability across the network.
Welded under pressure tee
Welded under pressure tees are manufactured and delivered by Radius Subterra for live branch connections on metallic gas and water pipelines where mechanical fittings are unsuitable or where a permanent welded solution is required. These fittings are designed to be welded directly onto the host main, forming a structural branch outlet capable of supporting controlled under pressure drilling operations.
Welded tees are typically selected on steel or other metallic mains where higher operating pressures, asset criticality, or network specifications require a fully welded branch configuration. Each tee is manufactured to suit the confirmed outside diameter and wall thickness of the host pipe, ensuring accurate fit-up and controlled load transfer into the parent main.
Installation involves welding the tee body onto the live main in accordance with approved welding procedures and competent, qualified welders. Following weld completion, appropriate inspection and non-destructive testing is undertaken in line with project or network requirements. Once verified, a full-bore valve is mounted onto the branch outlet, and an under-pressure drilling machine is installed.
The drilling operation is then carried out without depressurising the main, retaining the coupon and maintaining system integrity. This enables new connections, bypasses, or intervention access points to be created while the pipeline remains in service.
Radius Subterra provides the complete scope, tee manufacture, welding coordination, under pressure drilling, and final completion, supported by structured reporting and documentation aligned with UK gas and water network standards.
Our other solutions
Explore other Radius Subterra solutions designed to enhance safety, efficiency and long‑term performance.
Pre-Insulated Pipework
Pressure Testing
Pipework Installation & Mainlaying
Pipe Cutting
Manufacture & Fabrication
Engineering and Project Management
Pipe Lining
Pipeline Repair & Maintenance
Flowstopping
Case Studies
Discover the prowess of Radius Subterra through our latest case studies.
Witness how we excel in tackling intricate pipeline challenges with innovative solutions and state-of-the-art technology. Stay tuned for more videos showcasing our commitment to engineering excellence.
Faced with severe leaks in a critical 1500mm trunk main, Radius Subterra provided an innovative pipeline rehabilitation solution using their close-fit PE liner system. This approach restored the pipeline’s integrity
Discover how Radius Subterra’s precision engineering revitalises a historic London waterway with cutting-edge pipeline solutions, installing a bespoke branch saddle onto a live water main in Finsbury Park. This job
Radius Subterra partnered with Anglian Water to solve leak issues in a hard-to-reach 10” water pipeline in East Anglia. Using their innovative Rolldown & Slipline method, Subterra maximised pipe bore
In February an accidental incident occurred that resulted in a 10” gas main being damaged, and a hole being drilled into the main. The incident was near to the main
Case Studies
Discover how Radius Subterra delivers safe, innovative and technically assured solutions across the UK’s most challenging pipeline environments.
Faced with severe leaks in a critical 1500mm trunk main, Radius Subterra provided an innovative pipeline rehabilitation solution using their close-fit PE liner system. This approach restored the pipeline’s integrity
Discover how Radius Subterra’s precision engineering revitalises a historic London waterway with cutting-edge pipeline solutions, installing a bespoke branch saddle onto a live water main in Finsbury Park. This job
Radius Subterra partnered with Anglian Water to solve leak issues in a hard-to-reach 10” water pipeline in East Anglia. Using their innovative Rolldown & Slipline method, Subterra maximised pipe bore
What our client’s say about us
Why choose Radius Subterra?
Trusted expertise, engineered solutions and a service approach shaped around your challenges.
For decades we’ve supported utility networks in the UK and beyond with safe, reliable and efficient pipeline services. Our teams combine technical knowledge, industry-leading equipment and a problem-solving mindset to deliver high-quality outcomes with minimal disruption. Whether planned works or complex operational challenges, we provide proven capability and dependable support.
Decades of expertise
With deep roots across the wider Radius Group and extensive experience in live gas, water, biogas and pipeline rehabilitation operations, our teams bring exceptional hands-on knowledge to every project. We understand the pressures faced by network operators and contractors and deliver work that is safe, compliant and technically robust from start to finish.
Committed to quality and safety
Safety underpins every service we deliver. Our work follows industry standards, rigorous internal procedures and environmental best practice. From accredited techniques to specialist equipment, we ensure consistent quality while reducing risk, waste and unnecessary disruption across gas, water and biogas networks.
Minimising disruption
Our specialist techniques, including under-pressure connections, flowstopping and trenchless rehabilitation, allow essential works to continue while maintaining customer service, protecting highways and minimising community impact. Reduced excavation and streamlined operations, support faster reinstatement and lower overall disruption.
Innovation and customisation
From bespoke branch saddles to tailored fittings for non-standard assets, innovation is central to our approach. We engineer solutions to suit each site, material and operating condition, enabling safer, faster and more cost-effective outcomes across complex project environments.
Safety and sustainability
We champion safe working and long-term sustainability. Our methods reduce carbon, excavation material, traffic disruption and reinstatement, while modern equipment and ongoing training create a safer environment for teams and the public. Every project is designed and delivered with environmental responsibility and operational resilience in mind.
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