Patent ID: 7712487

Claim:
A spirally wound tube formed to have enhanced ID stiffness under radially inward compressive loads on the tube, the tube comprising: an inner zone extending radially from an inner surface of the tube outwardly, the inner surface defining an inner diameter of the tube, the inner zone includes at least one inner layer of at least one inner ply; an outer zone extending radially from an outer surface of the tube inwardly, the outer zone includes at least one outer layer of at least one outer ply; and an intermediate zone extending from the inner zone to the outer zone for insulating the inner diameter from the radially inward compressive loads, the intermediate zone comprising a plurality of intermediate layers and each intermediate layer having at least one intermediate ply, each intermediate ply being spirally wound such that a gap exists between consecutive turns of each intermediate ply; wherein a plurality of the gaps of radially adjacent intermediate plies have overlapping portions that together define at least one void in the intermediate zone that extends radially for a distance greater than a thickness of any of the intermediate plies whose gaps define the void.