Teletest® guided wave inspection of riser bundles
| Neptune takes to the seas (Courtesy of Barmac) |
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The risers for offshore platforms are often assembled in bundles before insertion into caissons. The caisson tops are sealed with lids, each riser having an anchor flange which sits in a recess in the lid. Once sealed in the caissons, direct access to the risers is no longer possible. Inspection of the risers whilst under construction was an ideal application for Teletest so that a fingerprint could be obtained, against which condition in service could be compared and any degradation due to corrosion detected.
The opportunity was taken to carry out some exploratory tests whilst the riser assemblies were still in the yard. It was found that transmission of ultrasound past the anchor flanges was possible and that the sprayed aluminium coating had no adverse effect on propagation. The pipe ends, 63m away, were readily detected and the possibility of detecting 9% metal loss flaws in the splash zone, 18-20m from the transducers was demonstrated.
The platforms using these risers are now installed in the southern North Sea and in-situ Teletest inspection will continue.