Together with out key-partner, we have experience with this market for more than 30 years, we do have experience from all materials, and we also have equipment and techniques developed for the different applications – and materials. The latest development in this respect is sensors and accessories for inspection of twisted tubes. Inspection of such tubes was recently successfully performed with a Norwegian client.
On larger projects, we have been able with key-partner to mobilise up to 28 inspectors and assistants.
The system allows for more than one frequency to be used when exciting the ET coils, thus support plates and similar may be mixed out from the sensor signal. When ferritic tubes are to be inspected, a RFET extension may be added so that a combination of ‘conventional’ and RFET inspection may be carried out. A ‘conventional’ inspection of ferritic tubes will in any case include the use of magnetic biased sensors in order to improve depth estimation capability of any defects.
We would also like to emphasize that inspection of ferritic tubes may probably be the most challenging task within tube inspections. Whereas the eddy current field may penetrate several millimetres into a non ferritic steel, will a conventional field only penetrate a few tenths of a millimetre into carbon steel. The main difference here is the magnetic permeability of ferritic steel versus the permeability of austenitic materials – i.e. the higher permeability, the lower penetration by means of a conventional field.
The Remote Field Eddy Current Testing technique does utilise a phenomena that occur when inserting a RFET sensor into a tube, as a low frequency field applied will appear a distance away from the exiting coil. The field has then penetrated the tube wall twice, as it is being detected by coils at the inside of the tube. The signal has a phase shift that equals 2 times wall penetration.
When corrosion occur, the phase shift will be reduced, and subsequently may the corrosion be detected. However, the technique is not as accurate and sensitive as conventional tube inspection. Subsequently one usually wants to optimise inspection results – especially when a defect has been located. However, as this is difficult to do with a conventional ET sensor due to the permeability of the tube, one has to try manipulating the material to simulate an austenitic material. This is done by pre magnetisation of the tube, as a magnetically saturated feritic steel does have similar characteristics as an austenitic steel when deploying a conventional ET sensor.
The equipment package includes the following items:
+ Basic EddyMax system
+ RFET extension
+ Power supply for mag biased sensors
+ RFET and mag biased sensors for all kinds of material
+ Calibration tubes