Patent Number: 
Section: claims

1. A method of inspecting an underwater pipeline to determine wall thickness or information about contents of the underwater pipeline, the method comprising:interposing the underwater pipeline between a gamma radiation source and an array of detector units, the gamma radiation source and the array of detector units being mounted in a fixed relationship with each other on a support so that radiation emitted by the gamma radiation source passes along a plurality of paths through a portion of the underwater pipeline and impinges upon the array of detector units;rotating the support, the gamma radiation source, and the array of detector units around a circumference of the underwater pipeline and acquiring data at a plurality of radially offset positions around the underwater pipeline to acquire density data at a variety of angles through the underwater pipeline; andpresenting a representation of the underwater pipeline or contents of the underwater pipeline using the density data;wherein the support, the gamma radiation source, and the array of detector units are provided on an apparatus that comprises a buoyancy material. 2. The method according to claim 1, wherein the apparatus is hinged so that the apparatus is configured to be opened and closed around the underwater pipeline. 3. The method according to claim 1, wherein the representation is a representation of a composition of the underwater pipeline or its contents. 4. The method according to claim 1, wherein presenting a representation comprises building the representation using tomography algorithms. 5. The method according to claim 1, further comprising detecting a void in the underwater pipeline. 6. The method according to claim 1, further comprising detecting a crack in the underwater pipeline. 7. The method according to claim 1, further comprising detecting wall thinning in the underwater pipeline. 8. The method according to claim 1, further comprising detecting a gas hydrate within the underwater pipeline. 9. The method according to claim 1, further comprising detecting scale within the underwater pipeline. 10. The method according to claim 1, further comprising detecting a change in density relative to a reference value. 11. The method according to claim 10, wherein the reference value is a calculated value. 12. The method according to claim 10, wherein the reference value is a value from an adjacent portion of the underwater pipeline.