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Guided Wave Testing on pipelines in the Algerian Desert

A team from TWI subsidiary Plant Integrity Ltd  (Pi) used guided wave testing (GWT) followed by a fitness for service (FFS) assessment to inspect over 5,300m of pipeline in the Algerian desert. The project resulted in detection of corrosion at two different locations and data which informed the client about their assets remaining life.


Pi were invited by a long-term client to develop and implement an inspection plan for their extensive pipeline network in Algeria, North Africa. Pi had previously worked with this client before, on a variety of projects dating back to 2010, where Pi inspected 100% of their trunk and flow lines.



The client had identified specific areas of the pipeline which were at high risk of corrosion. Therefore, the objective of the project was to inspect and calculate the corrosion level in these areas.

Pi decided to use ultrasonic guided wave testing which uses controlled excitation of transducers for the transmission of one or more guided wave modes. The modes travel along the length of the pipe and reflect its features. The reflected guided wave modes are received back at the transducer and the data is analysed to determine the location of features, such as corrosion, on the pipe wall. GWT is typically used to detect corrosion, erosion and other defects in pipework. Subsequently, a FFS assessment was applied to determine the integrity of the pipeline and judge its suitability for continued use.

Figure 1. Typical overview of corrosion product at a test location.
Figure 1. Typical overview of corrosion product at a test location.
Figure 2. An example of an 18 inch trunk line which was inspected using guided wave testing.
Figure 2. An example of an 18 inch trunk line which was inspected using guided wave testing.


Pi inspected the specified areas of the pipeline over a 30 day time period; 25 different pipelines were inspected spanning a distance of over 5,300m. The pipeline was challenging to work with due to having a variety of diameters (between 6 and 18 inches) and being in problematic locations, such as buried within shifting sand dunes or under road crossings. Two test locations were identified as having substantial pipe wall reduction; these were subjected to phased array ultrasonic testing (PAUT) and visual examination to gain further insights.


The project successfully detected corrosion at two different locations. The GWT identified changes in wall thicknesses, allowing the results to be categorised into different risk levels and assessed both visually and with data analysis software. Pi concluded the project with a comprehensive report for the client.

Plant Integrity Ltd is a technical services company that supports industrial plants and structures. We are specialists in guided wave testing technology and inspecting pipelines in inaccessible locations such as road and river crossings. In addition to guided wave testing inspections, we can also: utilise the full range of other standard, advanced and specialist NDT techniques, implement structural health and condition monitoring services and provide 3rd party oversight. All of which are supported by risk and reliability engineering services.


Avatar David Welsh NDT inspector

David Welsh joined TWI in April 2003, in the fatigue integrity management department. His work involved many activities, including strain gauging, resonance fatigue testing, and residual stress measurement, in both the lab and off-site. After working off-site on many occasions, his interests moved to the non-destructive testing (NDT) field. He gained an array of NDT qualifications, including his CSWIP NDT certification, which eventually led to him transferring to work as an NDT inspector. His work now involves performing demonstrations and field services worldwide.