One of the problems with oil and gas pipelines is that they go very deep underwater and this can make them very difficult to discover faults. Currently, the way it's done is by using PIGS which propel through the pipelines cleaning them out and with sensors, discovering leaks.
But now, a new prototype waterproof quadcopter can fly tethered (due to wireless signals not working at the depths) underwater allowing inspection to be carried out from the comfort of the deck of the oil rig or ship. Students at Rutgers University developed the unit in response to a commission from the Office of Naval Research which wanted a flying device that could be used anywhere and for any purpose.
At the moment, it's about the size of a child's toy but there are plans to scale it up so that it can carry heavier payloads including high definition underwater cameras and sensors to be used for whatever mission it's needed for. Since at present it's only being tested in swimming pools, there hasn't been any issues with pressure but for it to be used where gas and oil pipelines are at hundreds of feet, it needs to withstand extreme changes in pressure.
To see how it's working in the university's pool, watch this video.