Protection of piles

A pile or riser wrapping comprising a water-impermeable, reinforced, flexible and elastic plastic sheet with substantially rigid outwardly extending flanges along substantially the entire length of the opposed edges which are adjacent when the wrapping is positioned around a pile, the flanges affording counter-abutments for the application of a tool by which hoop stresses to make said wrapping resistant to wave suction forces can be imposed on the wrapping and having detents at intervals along their length to accept fastening elements securable while the hoop stresses are maintained, and wherein the sheet comprises an outer skin of water-impermeable and flexible material, and an inner layer of liquid-permeable plastic material bonded to the skin and impregnated with a water resistant sealant.