Location: Norwegian Sector, North Sea
Water Depth: 360m
The project was performed to determine the relative orientation of mating components in the diverless remote tie-in system for four subsea structures. Leakage had been observed and, although considered unlikely, misalignment of the connection system could not be ruled out.
The connections were located on four subsea templates and are depicted generically below in Figure 1.
Figure 1: Exploded view of pipe connection
Any misalignment resulting in improper mating of the diverless connection could result in the observed leakage. As the connection system is machined to close tolerances two reference planes parallel to the actual connection mating faces could be agreed upon to represent the Fixed Side (plane 1) and Flying Side (plane 2) of the connection. Any out of plane deviation found between the two reference planes would therefore represent a misalignment of the connection system. Superimposition of the two reference planes allows quantification of the misalignment.
Figure 2, below, represents the camera locations when taking photos (shown with the purple icons) and the matching pixels (shown by the yellow dots) generated to produce the 3D model. A clear visualization of the connection system is apparent simply from the matching pixels.
Figure 2: Interim model showing matched pixels (yellow)
The final model of the connection system is shown in Figure 3. For this project it was not necessary to model the complete arrangement between both reference planes. By utilizing the information defining the reference planes and photgrammametrically linking them, any misalignment at the actual interconnection point could be determined. It should be noted that the actual interconnection point is not visible in the figure, as it is located under a substantial clamping arrangement.
Figure 3: Finished model with superimposed planes on flanges to test alignment
The client was provided with a detailed report describing the angular alignment of the reference planes to a tenth of a degree.
At all of the modeled locations, alignment between the fixed and flying side of the diverless connection system was confirmed to be within acceptable limits, ruling out misalignment as the cause of the leakage.
