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Here’s a suggestion to consider for stopping the Deepwater Horizon leak.  If necessary, use a linear shaped charge to cut the leaking pipe more uniformly.  Then, use a high pressure pipe stopper such as a hydrostatic test isolation plug, for example, the Curtis Wright Flow Control Company’s GRIPTIGHT TEST PLUG GT-24P120, to seal the pipe temporarily.  To permanently seal the pipe, explosive coating can be applied to the pipe surface that covers the isolation plug, and explosive welding can fuse the pipe to the plug  ( See http://estgroup.cwfc.com/productsServices/spokes/01a_HTplugs_01-GripTight_HiPressure.htm or http://www.mechanicalresearch.com/hp.html ).