External inspection of a subsea riser was required to verify indications identified by in-line inspection.
Subsea Export Riser Inspection using DRS
A 12 mm thick neoprene coating was present on the subsea riser, which prevented external inspection using conventional ultrasonic techniques.
To complete an external inspection of the subsea riser through the neoprene coating, Sonomatic used its dynamic response spectroscopy (DRS) technique. DRS uses low-frequency ultrasound to penetrate coatings which are attenuative to conventional ultrasonic inspection techniques. The low-frequency excitation causes a natural frequency response from the steel. Using advanced signal processing methods, the steel thickness can be derived from the natural frequency response.
Using the DRS technique, Sonomatic were able to build a thickness map of the area of interest on the subsea riser. The results identified regions of degradation which were below the nominal wall thickness.
The inspection was a success. The results obtained by Sonomatic contributed to demonstrate the integrity of the riser at the maximum operating pressure.