Location: US Sector, Gulf of Mexico
Water Depth: 2000m
The objective was to determine the surface geometry and the curvature of the pipeline in three dimensions. The geometry of the 3D model would be used to determine residual strength using Finite Element Analysis, and the curvature would be used to fabricate a clamp.
An 18-inch natural gas pipeline was dented and dragged several hundred feet from its original path when it was hooked by an anchor. The 2m section surrounding the dent was surveyed to construct a 3D model, which was then used to determine the pipeline curvature. The 3D model was provided to the client as a .stp file for use in clamp design and Finite Element Analysis. The damage to the pipeline can be seen in Figure 1.
Figure 1: Damaged 18” natural gas pipeline
The underside of the pipe was not accessible, so approximately 300 degrees of the pipe surface was modeled and the rest was artificially constructed using a 3D model manipulation program. Figures 3 shows the original model as viewed from two angles and Figure 4 shows the model with the underside and thickness artificially constructed.
Figure 2: 300 degree pipeline model, viewed from two angles
Figure 3: 360-degree model, underside and thickness artificially constructed
The model shown in Figure 2 was further analyzed to determine the radius of curvature of the pipeline. Cross-sections were taken at 100mm increments along the length of the model, as indicated by the green lines in the figure below. Then a circle of the pipe’s nominal radius, 230mm, was placed at each cross-section using an alignment of best fit.
Figure 4: Cross-sections at 100mm increments
The center points of the circles were found and aligned with an x-y plane of best fit, as seen in Figure 5. A relative coordinate system was applied, and the x, y, z coordinates of each center point were provided to the client.
Figure 5: Center Points shown on plane, with best fit curve applied
Finally, a circle of best fit was aligned with the center points to determine the pipeline radius of curvature of 10.7m.
The final 3D model was presented to the client (in .stp format) from which FEA was performed and a full analysis of the pipeline curvature in the x,y,z planes.A report detailing the modeling and curvature analysis procedures accompanied the final products sent to the client. This information was used to design and fabricate the clamp. The model exhibited a relative error less than 0.2%, or approximately 0.91mm.
