National Gas Services offers a wide range of inspection services to assess the condition of gas pipelines and assets across the UK. We use a variety of inspection techniques, from aerial and drone surveys to line walking and remote monitoring. 

Our services include corrosion measurement and rectification, non-destructive testing, hydrostatic, radiography and ultrasonic phased-array testing. We use 3D handheld laser scanners to improve the efficiency and accuracy of pipeline damage measurements, while improving safety for technicians. 

Aerial surveys

We operate a fleet of helicopters to conduct aerial surveys, looking for activity on the ground that may threaten the gas pipeline. We work with our pilots to plan and deliver a schedule of surveys, carried out at 500 feet and 185km/h. 

Drone surveys

National Gas Services is fully authorised by the Civil Aviation Authority to pilot unmanned aerial vehicles (drones). These offer an easy way to survey pipes in difficult-to-reach areas. These inspections enable us to capture photographs and videos simultaneously. The use of drones minimises shutdown costs and reduces the need for working at height.

Line walking

Line walking complements our aerial surveys. Our surveyors use bespoke applications to provide real-time status updates and images from the field. If faults are detected, we record the pipeline depth, fault description and location. Minor repairs can be completed during line walks, while remedial works are planned and carried out later.

Cathodic protection monitoring 

We monitor cathodic protection on steel gas pipes using advanced remote monitoring systems and AC collision management.

Our highly experienced in-line inspection team works with our preferred partner to provide full inspection services to detect corrosion, damage and defects inside pipelines of all diameters.

We use a range of Pipeline Inspection Gauges (PIGs), ranging from 8” to 48”, to conduct in-line inspections within gas pipelines. These are used along with launch-and-receive trolleys, flanged portable PIG traps (from 8” to 36”) and – where required – associated bridle pipework. We can also provide transmitter and receiver equipment to locate PIGs or confirm their passage at a specific location.

Our specialists provide expert interpretations of the inspection reports, as well as offering consultancy advice based on the inspection findings.

Magnetic flux inspections 

Magnetic flux leakage PIG inspections are a non-destructive testing method used to identify corrosion and pitting in pipelines. The technique involves magnetising ferrous metal objects to a saturation level with a powerful magnetic field. If the object has no flaws, the magnetic flux remains undisturbed. Where there is internal or external metal loss, the magnetic flux will leak from the object – enabling us to identify the defect.

Geometric pipeline inspection

We use intelligent pipeline inspections to carry out precise geometrical mapping and dent sizing within gas pipes. These high-resolution inspections enable us to conduct detailed stress analysis, ensuring faults are accurately identified. We can combine geometric inspections with magnetic flux testing. 

National Gas Services has the expertise to safely carry out a range of services on pressurised gas pipelines, including complete flow stopping for planned and emergency works.

Our engineers carry out under-pressure operations for the full range of gas pipeline diameters and materials, across all pressure ranges. This includes working on steel, cast-iron and ductile iron pipes, as well as polyethylene (PE) pipes up to 60” in diameter – at all pressure ranges up to 100 bar. We can also carry out under-pressure drilling for all pipe diameters and material limits.

To ensure safe working on under-pressure pipelines, we use a range of connection and stopple techniques, including:

• Flow stopping
• Hot tapping
• Plug setting
• Sealant/event plug adaption.

As leading gas pipeline maintenance and repair specialists, we are constantly exploring innovative new flow-stopping techniques. 

National Gas Services operates a fleet of mobile gas compressors. These are used to de-pressurise sections of pipeline to enable remedial works, and then recompress the gas to pressurise and commission the system.

Our engineers transport gas compressors to site, where they are connected to isolated pressure systems to transfer gas into live sections of pipeline. Using mobile gas compressors helps to minimise the environmental and commercial impacts associated with vented gas.

The transfer of gas from the isolated section to another location is done by reducing the pressure from anywhere up to 100 bar, down to as low as 7 bar. To minimise disruption, this technique can be carried out when the live section is operating at full pressure. 

The skilled engineers at National Gas Services conduct a full range of mechanical maintenance work on gas pipelines, ensuring the network continues to operate efficiently and cost effectively.

Maintaining the national and local gas pipeline network requires specialist expertise. Our experienced team has developed robust repair and maintenance techniques that can eliminate the need for expensive valve replacements. To minimise costs and disruption, we can often repair valves without decommissioning the pipeline.

Our range of mechanical maintenance expertise includes:

• Flushing and sealing techniques using existing valve connections.
• Sealant-vent plug adaption carried out where bling plugs are fitted.
• Vent-sealant line replacement.
• Actuator and extension tube repair and replacement.
• Stem seal leak repairs.
• Re-validation and pressure testing on site. 

National Gas Services carries out pipeline repairs on gas pipes of all diameters and materials, across all pressure ranges. We have the expertise to provide generic and bespoke repairs to both leaking and non-leaking defects on gas pipework.

When a suspected pipeline defect is identified, our trained technicians carry out an on-site assessment and provide details to our mechanical damage assessor. Our assessor calculates the severity of the defect and recommends appropriate repairs.

Our team offers permanent epoxy sleeve repairs, which are suitable for non-leaking pipeline defects such as dents, gouges, cracks and corrosion. We can manufacture epoxy sleeves to individual specifications, within short timescales. No welding is required for epoxy sleeves, minimising risks and enabling repairs to be completed without interrupting gas supplies. Our team has also developed a technique to repair leaking end seals on nitrogen sleeves. 

Gas pipeline repair and maintenance work often requires skilled welding and intricate pipework fabrication. National Gas Services has the highly skilled welders and fabricators required to carry out this work across our depots.

Our team of coded welders operates to internationally recognised standards, including BS 4515-1:2009, API 1104 and ASME 9. This means we can carry out high-quality welding on steel pipelines of varying diameters, wall thicknesses and pressure ranges.

Where complex fabrication work is required, we can construct intricate steel pipe fabrications off-site in our depots. Completing fabrication work in this controlled environment enables us to achieve the highest quality and safety standards.

As well as working in our depots, our welders and welding inspectors conduct on-site repairs and planned works to existing pipelines and plant. Our off-site fabrication works are supported by in-house radiography inspection services. 

At our Ambergate depot, we have a state-of-the-art paint and blast facility, which provides painting, coating and blasting services for the full array of gas pipeline assets – from the smallest valves to the largest PIG traps.

Our paint and blast facility covers all painting and blasting requirements across the gas pipeline network. All work is completed efficiently and to the highest standards. Our paint and blast booths can accommodate pipe lengths of up to 12m, and items as tall as 3.6m. That means we can blast, paint and coat assets ranging from 1” valves up to 54” closure PIG traps.

To maintain the highest safety standards and eliminate manual handling operations, we provide a 25-tonne overhead crane capable of lifting items into place directly from the bed of a lorry. This ensures the safe movement of pipes and other items to and from site. 

National Gas Services has more than 20 years’ experience of operating and carrying out construction works on gas pipeline projects, acting as contractor or principal contractor.

We specialise in carrying out mechanical works for gas transmission and distribution projects, ensuring we provide reliability and value for money, alongside exceptional standards of work.

Our teams have the necessary skills, knowledge and experience of the construction design management (CDM) regulations to ensure we adopt best practices and comply with all statutory duties.

We have developed and refined our processes, approaches and documentation so that we can provide the services of any of the required appointed roles of principal designer, principal contractor or contractor on multi-disciplinary projects. As well as taking on these roles ourselves, we can advise clients on managing projects under CDM.