December 2017, Vol. 244, No. 12
Features
National Grid Rolls Out Pipeline Innovations
Britain’s National Grid, operator of the country’s 4,722 miles of high-pressure gas pipeline network, is testing the use of a miniature gas robotic agile inspection device.
This important innovation is the product of an $8.27 million (£6.3 million) research project and is designed for inspection of the oldest and “bendy” parts of the network, unable to be reached by traditional inline inspection devices such as pigs that travel through pipelines checking for anomalies. This meant that significant sections of pipeline could only be checked by expensive, aboveground surveys and asset life-modeling to ensure the integrity of the network.
While the aged and complex geometry of pipelines are a peculiar feature of Britain’s gas pipeline network, a universal problem of pipeline operations worldwide is the risk of pig trapdoor failures. With 208 pig traps at the risk of seal failure and nine failures occurring over a five-year period, National Grid inaugurated a new training and inspection regime that has reduced failure rates of pipeline inspection trap doors to zero.
Inspection Device
Traditional pipeline inspection systems, in which a device is inserted at one end of the pipeline to collect data as the flow of gas pushes it through to the other end, are unsuitable for the UK’s high-pressure installations, some of which are over 50 years old. Project GRAID, National Grid’s miniature robot project, designed to inspect buried high-pressure pipelines with variable gas flows and complex pipework geometry, won initial funding from Britain’s energy regulator Ofgem’s 2014 Gas Network Innovation Competition.
In development since January 2015, the robot is the product of the combined effort of National Grid’s transmission subsidiary and three small British-based engineering and design consultancy enterprises, Synthotech Limited, Premtech Limited and Pipeline Integrity Engineers (PIE). Synthotech is responsible for the physical robotic platform. Premtech is developing a navigation system for the robot while underground and has also designed a launch-and-retrieval device and testing facility. PIE is responsible for developing a technical strategy for the project and interpreting the inspection data.
This miniature robot is designed to work inside a high-pressure gas pipeline with up to 440 pounds (200 kg) of force at peak flow. It is both agile and strong and is said, “to be able to withstand the full force of a rugby tackle.”
In its first design stage, the robot was a single unit. Now in its second design stage (Figure 1), the robot consists of two linked, but separate modules for ease of improved steering and increasing the space available for mounting essential electronics such as sensors and cameras. The robot is designed to be highly maneuverable.
Figure 1: Project Graid Robot
The innovative magnetic system enables the robot to be driven up the sides of the pipeline rather than just along the bottom, allowing it to measure the actual thickness of the entire wall and transmit the information to an operator. The area between the two modules houses a rotating non-destructive training (NDT) package, which can move around the pipe in a circular motion to detect defects and transmit information back to the engineer who, from aboveground, controls and operates the robot’s movements including reverse, stop, turnaround and zoom in on areas requiring further inspection.
In addition, reports the GRAID Project website, “A dual-module approach rather than a single module, enables an engineer to take advantage of active, passive and disruptive flow-control through the use of specially designed skins based on the pipeline’s flow rates determined by network modeling.” The latest modifications provides greater magnetic track contact with the wall of the pipe, improving agility, adaptability and capability.
With this 529-pound (240-kg) new robot, (which just happens to be the weight of a typical adult farm pig), it is possible to assess the actual condition of pipeline along its entire length. The data provided by the robot allows National Grid to determine where investment is needed to manage, maintain and replace sections of the pipeline as required.
Darren Elsom, head of Network Engineering for National Grid Gas Transmission Asset Management, maintains that “Project GRAID helps us to really understand where best to invest our money while keeping our networks safe.”
Project GRAID is expected to save the National Gas Grid Transmission system $78.8 million (£60 million) over the next 20 years and reduce annual carbon emissions by 2,000 tons.
Project Graid
The robot is well into its offline testing phase at RAF Spadeadam in Cumbria and National Grid expects to start commercial trials on its mainline gas pipelines in late 2018.
This innovation has attracted worldwide interest. The project won an award in the land-based onshore pipeline category from the recent Pipeline Industries Guild (PIG) Awards and was chosen for the Innovation Project Award at the 2017 IGEM Gas Industry Awards.
“Developing a device that can withstand the intense pressures of gas flowing through the National Transmission Infrastructure is no mean feat,” said David Salisbury, head of Network Engineering & Gas Transmission at National Grid. “Once the robot is in use, it will help us ensure ourselves, and show to others, that our installations are safe.”
Pig Trap Failures
An important issue facing pipeline operators is the problem of seal failure at the points used for loading and unloading pigs into and out of the pipeline. A new project by National Grid is underway that not only pinpoints the root cause of door seal failures but also reduces the failure rate to zero, and in the process, eliminates carbon emissions.
The National Grid Transmission (NTS) contains 208 pig traps, all holding a volume of gas at line pressure, typically of 70 barg (gauge pressure). In all, National Grid engineers investigated nine pig trapdoor failures between 2008 and 2013 (Figure 2).
Figure 2: Pig trapdoor seal failure.
Source: National Grid
The solution is a new pig trap maintenance-training package produced by National Grid’s training Academy near Sheffield in the English Midlands. There, engineers including apprentices, can obtain practical hands-on training in the latest methods of maintaining pig trapdoor seals and recording their condition.
Before the introduction of this new pig trap maintenance-training package, National Grid was experiencing at least three pig trap failures a year, each costing some $13,130 (£10,000) to repair, and releasing the equivalent of 8.5 tons of CO-2 emissions. With no further trapdoor failures, the new training and maintenance package has proved a success.
Both of these innovations have resulted in significant improvements in National Grid’s ability to manage, inspect and determine requisite investment in an environmentally beneficial manner that is cost-effective, not only for the operator, but for millions of customers.
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