According to the Australian Pipelines and Gas Association, Australia has more than 39,000 kilometres of natural gas transmission pipelines that transport gas across Australia. The Dampier to Bunbury Natural Gas Pipeline (DBNGP) is the longest natural gas pipeline in Australia and runs entirely underground. At almost 1600 km, it is longer than the state of California (1,240 km).
The pipeline transports natural gas from the north-west of Western Australia (starting near the township of Dampier) to commercial, industrial and domestic markets in the south-west of the State (finishing near the city of Bunbury). The DBNGP is 660mm in diameter, which makes it one of Australia’s largest in terms of transmission capacity and, at the time of commissioning in 1984, it was one of the longest gas pipelines in the world.
Long-distance pipelines, like the DBNGP, are critical pieces of energy infrastructure and a failure during their service can have serious consequences including the loss of product and time, but more importantly, the potential for loss of flora, fauna and human life. There are many causes and contributors to pipeline failures but one of the leading reasons is corrosion. Pipelines can be corroded both internally and externally. Internal corrosion may be due to a chemical reaction to the pipe’s internal surface or material loss due to microbiological reactions, which is also an electrochemical reaction.
External pipeline corrosion on the other hand, is due to external conditions on the outside of the pipe. This includes the natural interaction between the exterior surface of the pipe and the soil, air, or water surrounding it.
Over the past decade, there has been a lot of academic and industry research focused on corrosion prevention methods (such as protective coatings) as well as methods to detect corrosion in in-service pipelines. One of those methods is long range ultrasonic testing (LRUT), otherwise known as guided wave ultrasonic testing.
WHAT IS LONG RANGE ULTRASONIC TESTING?
LRUT is a fast and efficient non-destructive testing (NDT) technique which can locate defects in pipelines by sending an acoustic wave down the walls of a pipe, and then detecting reflections scattered by a crack or region of corrosion in the pipe walls. The aim of this method is to test long lengths of pipe rapidly with 100 per cent coverage of the pipe wall and to identify areas of corrosion or erosion for further evaluation using other NDT techniques such as radiography or conventional ultrasonic inspection.
Here’s how it works: LRUT employs low frequency guided waves (operating just above audible frequencies), propagated from a ring of equally spaced ultrasound probes which are fixed around the pipe being inspected.
The uniform spacing of the probes around the perimeter of the pipe allows for the guided waves to propagate symmetrically along the pipe axis, providing a complete coverage of the pipe wall (including areas such as clamps and sleeves or buried pipes). The ultrasonic waves are then reflected to the probes whenever they reach a change in wall thickness, which is how the process can detect corrosion, metal loss or other discontinuities. This data is subsequently analysed by a professional using the system’s software.
WHAT ARE SOME ADVANTAGES OF LRUT?
LRUT has many advantages for pipeline owner-operators. It is capable of measuring significant lengths of pipe (typically 60metres, but up to 350 metres) from a single point, detecting and locating areas of corrosion rapidly. This is particularly beneficial when the inspection of pipelines is complex or potentially dangerous.
If, for example the pipeline is positioned at high elevation, it may remove the need to construct extensive scaffolding along the pipe to perform a full inspection, and also reduces risk to personnel of extended periods of working at height. LRUT is an efficient method which is equally sensitive to metal loss on both outside and inside surfaces of pipe. Additionally, as the pipes can remain in-service whilst being inspected, pipeline owner-operators could benefit from reduced inspection costs and reduced production delays.
Pipelines are among the safest method of transportation for oil and gas. However, when failure does occur, it can have significant and far-reaching consequences for companies i.e. by causing injuries and/or fatalities or damage to the environment. Corrosion is one of the most common causes of pipeline failure and LRUT can assist owner-operators to quickly identify corrosion, metal loss or other disparities so that pipes can be repaired or replaced when required.
Sources: Dampier to Bunbury Natural Gas Pipeline Environment plan revision 8.1 Summary document; Statistical analysis of failure consequences for oil and gas pipelines, C. Belvederesi & M. R. Dann, Int. of Safety and Security Eng., Vol. 7, No. 2 (2017) 103–112; Case Study – Energy Pipelines Cooperative Research Centre, NERA; Long-Range Guided-Wave Ultrasonics: A New Age in Pipeline Inspection, Stephen Birch and Floyd Baker; Use of long range ultrasonic testing (LRUT) technique for health assessment of critical piping in LPG service in a petroleum refinery, V.S. Desai et al.; Power to the People – A History of Gas and Electricity in Western Australia, McIllwraith, John; Pipeline Integrity Handbook, Hazards and Threats to a Pipeline System, Ramesh Singh; Pipeline Safety Stakeholder Communications, Pipeline and Hazardous Materials Safety Administration
