Abstract: An erosive fluid jet tool for underwater operation, comprising an erosive fluid jet nozzle connected to a fluid receiver receiving fluid under elevated pressure for providing hydraulic power to the tool, the nozzle providing the working output jet of the tool; and a counterthruster for providing a counterthrusting force for balancing the thrust on the tool produced by the erosive fluid jet, the counterthruster including (a) a counterthrusting fluid jet nozzle connected to the fluid receiver and facing oppositely to the erosive nozzle for providing a counterthrusting jet, and (b) an open ended shroud coaxially surrounding the counterthrusting nozzle, whereby water surrounding the submerged tool is entrained through the shroud for providing additional counterthrusting force during operation of the counterthrusting nozzle, the erosive fluid jet nozzle and the counterthruster being constructed so that in excess of 50% of the hydraulic power provided to the tool is provided to the erosive fluid jet nozzle.

Abstract: Fluid jet apparatus and method for cleaning material from the inside of a tubular conduit utilizing a cleaning head that lies adjacent to one wall of the conduit and includes at least two fluid jet forming means for directing a plurality of high pressure fluid cutting jets in a forward direction and at an acute angle relative to the axis of the head and the conduit so that they are directed toward the opposite wall of the conduit. The cleaning head is rotated around and remains adjacent to the wall of the conduit and is advanced into the conduit as the jets cut away the material whereby the fluid jets create an asymmetric cutting pattern on the surface of the material and the counter thrust of the fluid jets keeps the cleaning head offset relative to the axis of the conduit and against the wall of the conduit to provide passage for removal of the cut material and spent fluid away from the cutting area and out the end of conduit.