Technology from Europe:
United Kingdom

New digital level gauge used for subsea work

It's crucial to control position during pile driving operations. This is especially true with subsea installations. Normally a “bulls eye” type instrument would be used for this application. However, the accuracy and especially the undersea readability (via an ROV) of such an instrument is far from optimal. During pile driving breaks, the potential alternative of reinstalling a gyro was expensive, especially since a specialist survey technician was required. In addition, such a route would have delayed the installation process. 

The new digital level gauge (DLG) allows measurement of pitch and roll during and after pile driving operations. The compactness, accuracy, simplicity and re-usability of the new DLG benefited the recent installation of the drilling templates for Nini and Cecilie fields in the North Sea. DONG is operator of the fields, and has partners DENERCO Oil A/S and RWE Dea AG. The DLG was incorporated into the installation program primarily for cost savings, according to the maker of the DLG, Norwich, UK, firm UWG Group. 

During pre-mobilization calibration, the DLG was calibrated to the subsea gyro module for pitch and roll, while allowing the gyroscope to be demobilized before pile driving began. According to UWG, pile driving vibrations tested the DLG far beyond the operational limits of other electronic devices, but the client was able to obtain the critical data necessary to confirm successful conclusion to operations. 

ROV pilots noted that the digital readout was much more visible than other devices, and they were able to fire up and read the DLG from a greater distance (about 3 m) than any other devices with which they had previously worked. This capability permits the DLG to be placed along the main axis of any subsea structure without concerns regarding the ROV's ability to activate and read the gauge. The instrument is housed in a casing suitable for subsea deployment and is mounted on an adjustable table to facilitate calibration (see picture). The unit is operated via a light-sensitive switch. After awhile, the display is terminated, and the unit reverts to sleep mode to conserve battery power and prolong its operational life. In its standard form, the DLG can provide in excess of 2,000 sets of readings and can remain in sleep mode for about three years. Thus, it can be used for both temporary and permanent installations.