Low melting point alloys such as bismuth can be applied easily with little heat input to the substrate and expand on solidification to form a very tight seal. The low viscosity of the molten alloy enables penetration into porous substrates with pore throats as tight as 25 microns, with expansion on solidification for a gas-tight seal. The high density of the alloy displaces water to enable sealing underwater or against large leaks, while being easily removed by re-melting, if required. The bismuth casting process only takes hours, as opposed to days for cement to set - a factor that is even more significant offshore, as a costly rig vessel is not required.
As an example of the capabilities of bismuth, a 3' (0.91m) bismuth plug can readily outperform a conventional cement seal, which - by comparison - may be up to 500' (152m) in length.
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