Composite pipeline prestressed construction

Claim 2

A composite construction for use in a high pressure pipeline, comprising at least one tubular pipe portion adapted to contain and transmit fluid under pressure, and at least one layer of high tensile strength strap wrapped around the outer surface of said pipe portion and longitudinally unrestrained relative thereto whereby said strap does not longitudinally reinforce said pipe portion, said pipe portion and said strap both being of elastically deformable material and having substantially the same modulus of elasticity, said strap having a yield strength greater than the yield strength of said pipe portion and being operable to carry a substantial portion of the pressure load in said composite construction when the latter is operating at a normal pressure, said strap being of Martensitic steel having a tensile strength of at least about 130,000 psi and said composite construction being prestressed prior to being operated at a normal pressure by increasing the internal pressure therein to a value sufficient to exceed the yield strength of said pipe portion but insufficient to exceed the yield strength of said strap.

Claim 3

The composite construction of claim 1, further characterized in that the turns of said strap are spaced from each other to provide gaps therebetween, said gaps facilitating bending of said composite construction.

Claim 4

The composite construction of claim 2, further characterized in that a plurality of layers of said strap are wrapped around said pipe portion, and said layers are staggered so that the gaps in one layer are covered by the strap of the next overlying layer.

Claim 5

The composite construction of claim 2, further characterized in that said gaps have a width of from about 0.021 to about 1.25 inches dependent upon the strap width.

Claim 6

The composite construction of claim 4, further characterized in that the width of said strap is from about one-half to about 30 inches.

Claim 7

The composite construction of claim 1, further characterized in that said pipe portion comprises high strength steel pipe.

Claim 8

A composite pressure tensioned pipeline construction for transmitting fluid under high pressure, comprising a plurality of connected, elastically and plastically deformable metal pipe portions, and at least one layer of high tensile strength, elastically deformable metal strap wrapped around each of said pipe portions, said strap being of steel having a tensile strength of at least 100,000 psi and being longitudinally unrestrained relative to said pipe portions whereby said strap does not longitudinally reinforce said pipe portions and said strap being operable to carry a portion of the pressure load in the respective pipe portions, said pipe portions having an actual yield strength that is equal to or greater than a specified minimum except for a few pipe portions having an actual yield strength less than said specified minimum, substantially all of said strap having an actual yield strength that is equal to or greater than a specified minimum, the specified minimum yield strength of said strap being greater than the actual yield strength of all of said pipe portions, and said pipeline being prestressed by the strap and pressure tensioned to a predetermined internal pressure, prior to being operated at a normal operating pressure less than said predetermined internal pressure, by increasing the internal pressure therein to a value sufficient to exceed the actual yield strength of all of said pipe portions but insufficient to exceed the specified minimum yield strength of said strap, whereby the prestressed pipeline during operation is self-compensating for variations in the actual yield strength of said pipe portions.

Claim 9

A composite pressure tensioned pipeline construction for transmitting fluid under high pressure, comprising a plurality of connected, elastically and plastically deformable metal pipe portions, and at least one layer of high tensile strength, elastically deformable metal strap wrapped around each of said pipe portions, said strap being of steel having a tensile strength of at least 100,000 psi and being longitudinally unrestrained relative to said pipe portions whereby said strap does not longitudinally reinforce said pipe portions and said strap being operable to carry a portion of the pressure load in the respective pipe portions, said pipe portions having an actual yield strength that is equal to or greater than a specified minimum except for a few pipe portions having an actual yield strength less than said specified minimum, substantially all of said strap having an actual yield strength that is equal to or greater than a specified minimum, the specified minimum yield strength of said strap being greater than the actual yield strength of all of said pipe portions, and said pipeline being prestressed by the strap and pressure tensioned to a predetermined internal pressure, prior to being operated at a normal operating pressure less than said predetermined internal pressure, by increasing the internal pressure therein to a value sufficient to exceed the actual yield strength of all of said pipe portions but insufficient to exceed the specified minimum yield strength of said strap, whereby the prestressed pipeline during operation is self-compensating for variations in the actual yield strength of said pipe portions.

Claim 10

The composite pipe construction of claim 7, further characterized in that said strap is of plain carbon steel haVing a carbon content of from about 0.03 wt. % to about 0.25 wt. % and a microstructure consisting essentially of tempered martensite.

Claim 11

The composite construction of claim 1 further characterized in that said martensitic steel comprises a plain carbon steel having a carbon content of from about 0.03 wt% to about 0.25 wt% and a microstructure consisting essentially of tempered martensite.

Claim 12

The composite pipeline construction of claim 7, further characterized in that said pipeline has a classification factor, and said normal operating pressure is equal to or less than said classification factor multiplied by said predetermined internal pressure.

Claim 13

The composite pipeline constructed of claim 10, further characterized in that the stress in any pipe portion when said pipeline is operating at said normal operating pressure is equal to or less than said classification factor multiplied by the actual yield strength of that pipe portion.

Claim 14

The composite pipeline construction of claim 11, further characterized in that the stress in the strap around the pipe portions having actual yield strengths equal to their specified minimum when said pipeline is operating at normal pressure is equal to or less than said classification factor multiplied by the specified minimum yield strength of said strap. strap.