Today, the in-line inspection of pipelines is a routine procedure. Specialised automated tools are inserted and pumped through the oil, product or gas line to be inspected. Depending on the types of anomalies and flaws to be detected, a variety of non-destructive testing methods can be applied. One such method is ultrasound (UT), a technology widely used for the inspection of liquid lines.
Advantages of UT as compared to other non-destructive testing principles applied in in-line inspection tools are: inspection of thick walls; inspection of ferritic and austenitic steels; highest level of accuracy; enhanced depth resolution; data quality suited for integrity assessment and fitness-for-purpose studies; capable of detecting and sizing metal loss, crack features and mid wall anomalies.
A major advantage of ultrasound technology regarding integrity assessment is its capability to perform true quantitative wall thickness measurements, achieving resolutions of better than 0.1 mm and accuracies of ± 0.4 mm. Ultrasound tools can thus be used to verify and record the actual wall thickness for any location within the pipe. Such an inspection records data which is of particular use in case of a pipeline uprating process.
The accuracy incorporated in ultrasound also provides advantages regarding run comparisons and corrosion growth studies and the use of advanced integrity assessment codes such as DNV RP-F101.
The ultrasonic tools used for metal loss inspection and wall thickness measurement up to now make use of piezo-electric transducers which require a liquid environment within the pipe as a coupling. This coupling is not available in a gas environment and therefore so far UT inspection of gas pipelines was not possible unless the operator accepted a liquid batch during inspection.
Now the challenge was to investigate whether it is possible to make the advantages of ultrasound technology available for the inspection of gas pipelines without the operational limitation of having to run a batch.
NDT developed a new multi-technology tool in cooperation with the Institute of Non-Destructive Testing IZFP of the Fraunhofer Gesellschaft in Germany that utilises a special sensor design incorporating three non-destructive testing technologies, electro acoustic emission (EMAT), magnetic flux leakage (MFL) and eddy current (EC).
Enter X at www.engineerlive.com/iog
NDT Systems & Services AG is based in Stutensee, Germany. www.ndt-ag.de
