Low-permeability hollow spheres and pipe filled with the spheres for temporary weight reduction

Claim 1

Reduced-density pipe which absorbs water at a rate that remains substantially unchanged even after storage under moist or wet conditions and which improves the laying of underwater pipeline at great depths by minimizing forces that tend to buckle a pipeline and by permitting retrieval of recently laid pipeline, said pipe comprising a porous cement-based cylindrical shell surrounding a core pipe and filled with hollow spheres that (a) average between 0.05 and 2 centimeters in diameter, (b) have a density of no more than about 0.35 gram per cubic centimeter, and (c) individually comprise (i) a porous hollow core sphere comprising a polymeric binder material and a plurality of solid particles held by the binder material, at least a portion of the thickness of the sphere wall being filled by the particles and the particle-filled sphere wall being permeable such that said core spheres fill instantly with air at a pressure of about 2 pounds per square inch; and (ii) a coating on the exterior surface of the porous hollow core sphere that partially seals the core sphere; said coated spheres exhibiting a stable slow permeability to water such that between about one and ten weeks is required for the spheres to fill with water under an ocean-depth pressure of 10 or more kilograms per square centimeter, whereby the cement shell gradually increases in density when immersed in a body of water at depths that apply such a pressure.