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A flexible pipe body and method of producing a flexible pipe body, the flexible pipe body including a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions e

A flexible pipe body and method of producing a flexible pipe body, the flexible pipe body including a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions extending in a direction perpendicular to a tangent of the radially inner surface, for breaking up a boundary layer of fluid flowing along the flexible pipe body in use.

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1. Flexible pipe body for transporting fluids from a sub-sea location, comprising: a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions extending in at le

1. Flexible pipe body for transporting fluids from a sub-sea location, comprising: a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions extending in at least one direction perpendicular to a tangent of the radially inner surface, arranged to break up a boundary layer of fluid flowing along the flexible pipe body in use,wherein the collapse resistant layer comprises a helically wound elongate tape element having at least one cavity between adjacent windings of the tape element or wherein the collapse resistant layer comprises interlocked discrete annular elements, and wherein the collapse resistant layer comprises a plurality of cavities, each cavity between an annular element and an adjacent annular element;wherein the height of the protrusions or the depth of the depressions is between 1/70th and 1/10th the depth of each cavity. 2. Flexible pipe body as claimed in claim 1, wherein the plurality of protrusions and/or depressions extend at least partly along a longitudinal axis of the flexible pipe body. 3. Flexible pipe body as claimed in claim 2, wherein the plurality of protrusions and/or depressions extend at least partly around a circumference of the flexible pipe body. 4. Flexible pipe body as claimed in claim 1, wherein the plurality of protrusions and/or depressions have a shape comprising a polygon, a stripe, a zigzag, a square, a diamond, a rectangle, a triangle, a circle, an oval, or any combination thereof when viewed radially from a centre of the pipe body. 5. Flexible pipe body as claimed in claim 1, wherein, in a cross section taken along a central longitudinal axis or a cross section taken in a direction orthogonal to the central longitudinal axis, the collapse resistant layer has a profile with the plurality of protrusions and/or depressions having a shape comprising a convex protrusion, a concave depression, a polygon, a square, a rectangle, a triangle, or any combination thereof. 6. Flexible pipe body as claimed in claim 1, wherein the plurality of protrusions and/or depressions extend along a portion of the collapse resistant layer and the portion is at an end of the pipe body. 7. A method of providing a flexible pipe body, comprising: providing a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions extending in at least one direction perpendicular to a tangent of the radially inner surface, arranged to break up a boundary layer of fluid flowing along the flexible pipe body in use,wherein the collapse resistant layer comprises a helically wound elongate tape element having at least one cavity between adjacent windings of the tape element or wherein the collapse resistant layer comprises interlocked discrete annular elements, and wherein the collapse resistant layer comprises a plurality of cavities, each cavity between an annular element and an adjacent annular element;wherein the height of the protrusions or the depth of the depressions is between 1/70th and 1/10th the depth of each cavity. 8. A method as claimed in claim 7, further comprising providing an elongate sheet element having the plurality of protrusions and/or depressions extending from a surface of the sheet element, andforming the sheet element into a substantially cylindrical configuration to form the collapse resistant layer. 9. A method as claimed in claim 7, further comprising providing an elongate sheet element;forming the plurality of protrusions and/or depressions on a surface of the sheet element; andforming the sheet element into a substantially cylindrical configuration to form the collapse resistant layer. 10. A method as claimed in claim 9, wherein forming the plurality of protrusions and/or depressions is performed at the same time as forming the sheet element into a substantially cylindrical configuration. 11. A method as claimed in claim 7, further comprising the steps of: providing an elongate sheet element; andforming the sheet element onto a mandrel having a plurality of substantially regular protrusions and/or depressions to thereby form the collapse resistant layer having the protrusions and/or depressions. 12. A method as claimed in claim 7, further comprising the steps of: providing a substantially cylindrical tubular element; and thenforming the plurality of protrusions and/or depressions on a radially inner surface of the tubular element to thereby form the collapse resistant layer. 13. A method as claimed in claim 12, wherein the step of forming the plurality of protrusions and/or depressions comprises forming depressions in the collapse resistant layer by pigging the flexible pipe body with a suitably configured pig, or blasting the radially inner surface of the collapse resistant layer with a material at a force sufficient to form depressions.