CA2286956A1 - Steel-composite pipe apparatus and method of manufacturing same - Google Patents
Steel-composite pipe apparatus and method of manufacturing same Download PDFInfo
- Publication number
- CA2286956A1 CA2286956A1 CA002286956A CA2286956A CA2286956A1 CA 2286956 A1 CA2286956 A1 CA 2286956A1 CA 002286956 A CA002286956 A CA 002286956A CA 2286956 A CA2286956 A CA 2286956A CA 2286956 A1 CA2286956 A1 CA 2286956A1
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- Prior art keywords
- steel
- composite
- layer
- pipe
- stress
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B1/00—Layered products having a general shape other than plane
- B32B1/08—Tubular products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/18—Layered products comprising a layer of metal comprising iron or steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/20—Layered products comprising a layer of metal comprising aluminium or copper
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
- F16L58/02—Protection of pipes or pipe fittings against corrosion or incrustation by means of internal or external coatings
- F16L58/04—Coatings characterised by the materials used
- F16L58/10—Coatings characterised by the materials used by rubber or plastics
- F16L58/1054—Coatings characterised by the materials used by rubber or plastics the coating being placed outside the pipe
- F16L58/1063—Coatings characterised by the materials used by rubber or plastics the coating being placed outside the pipe the coating being a sheet wrapped around the pipe
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L9/00—Rigid pipes
- F16L9/14—Compound tubes, i.e. made of materials not wholly covered by any one of the preceding groups
- F16L9/147—Compound tubes, i.e. made of materials not wholly covered by any one of the preceding groups comprising only layers of metal and plastics with or without reinforcement
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/18—Titanium
Abstract
A pipe for high pressure pipelines and method of manufacturing same are provided in accordance with the invention.
The pipe comprises an inner steel layer and a composite outer layer wrapped in continuous contact around the steel layer. The parameters of the steel and composite layers are optimally selected so that the respective strengths of the steel and composite are fully utilized. The selected parameters include at least the thickness and yield strengths of the respective layers, wherein the thicknesses of the respective layers are selected so that at a maximum internal operating pressure, the circumferential stresses in the pipe are desirably distributed such that the composite layer is at or below a composite design operating stress and the steel layer is at or below a steel design operating circumferential stress. The circumferential stresses are desirably distributed by first determining the appropriate amount of plastic deformation of the steel layer that will produce the desired stress distribution, then autofrettaging the steel layer to obtain the desired plastic deformation.
The pipe comprises an inner steel layer and a composite outer layer wrapped in continuous contact around the steel layer. The parameters of the steel and composite layers are optimally selected so that the respective strengths of the steel and composite are fully utilized. The selected parameters include at least the thickness and yield strengths of the respective layers, wherein the thicknesses of the respective layers are selected so that at a maximum internal operating pressure, the circumferential stresses in the pipe are desirably distributed such that the composite layer is at or below a composite design operating stress and the steel layer is at or below a steel design operating circumferential stress. The circumferential stresses are desirably distributed by first determining the appropriate amount of plastic deformation of the steel layer that will produce the desired stress distribution, then autofrettaging the steel layer to obtain the desired plastic deformation.
Description
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llBm vanlSYSICLIENTS11P00110075 calspec final 990603.wpd STEEL-COMPOSITE PIPE AND METHOD OF MANUFACTURING SAME
s Field of the Invention The present patent application relates generally to pipelines and specifically to a pipe for a high pressure gas pipeline and a method of manufacturing the pipe, the materials io and dimensions of which are optimally selected.
Background Of The Invention~
Pipelines for transmitting natural gas and other fluids i5 typically span many hundreds of kilometres of terrain. These pipelines tend to be pressurized at high pressures; some known pipelines are designed to operate around 1750 psi. Pipes that are connected together to form such pipelines are typically made from a high-strength steel so that the pipeline can 2o withstand stresses caused by high internal pressures and resist adverse external environmental conditions.
To protect the exterior of the pipeline and to provide additional circumferential strength, high-pressure pipelines 2s have been known to be wrapped with a covering such as a wire winding or a flexible non-metallic sheet. Such coverings also serve to arrest propagation of cracks that originate from ..
failures in the pipe wall. For example, U.S. patent no.
4,559,974 (Fawley) discloses a plurality of circumferential bands of unidirectional non-metallic fibres that wrap around a conventional steel pipe. The patent states that the plurality of bands are intended in part to equalize the circumferential strength of the pipe with its longitudinal strength so that the pipe can bear an increased stress before failing. However, the patent does not appear to disclose any particulars about the amount of increased stress that can be io safely borne for a particular amount of band material and for a particular selection of pipe parameters; without such particulars, increasing the stress level beyond specified maximum operating levels would be hazardous. Further, covering-wrapped pipes such as those disclosed in Fawley tend i5 to be costlier to manufacture than non-wrapped pipes having a comparable steel layer thickness and operating at a comparable pressure. Further, the covering adds undesirable weight to the underlying pipe, making pipeline construction more difficult and more costly.
It is apparent that a covering that provides some circumferential strength to the pipe structure will permit a covering-wrapped pipeline to withstand some increase in its internal operating pressure. Increasing the internal 2s operating pressure will increase the rate of gas transmittable by the pipeline, thereby increasing the revenue that can be generated. Therefore, it is a desirable objective to ..
construct a covering-wrapped pipeline that enjoys the benefits of a covering and whose increased construction costs are sufficiently offset by an increased rate of fluid transmission so that the covering-wrapped pipeline is as or more profitable than a comparable non-covered pipeline.
Alternatively, the cost of construction of the covering-wrapped pipeline may be offset by utilizing the circumferential strength of the covering in place of some of io the circumferential strength provided by the steel, so that the amount of steel used in the covering-wrapped pipeline can be reduced relative to an all-steel pipeline operating at a comparable pressure. This reduction can in some cases reduce the weight and material cost of the covering-wrapped pipe.
No known method has been devised to accomplish optimally the above objectives. That is, there is no known method to select the materials, dimensions, and operating parameters of the covering and pipe portions of the covering-wrapped pipe so 2o that the strength and other properties of the materials are fully utilized, thereby optimizing the fluid transmission capacity of the covered pipeline relative to its cost of construction and operation.
2s The present invention overcomes some of the shortcomings of the prior technology and achieves further advantages that will be apparent after reviewing the following summary and detailed description of the invention.
Summary Of The Invention:
s The present invention in one aspect is a pipe for use in high pressure fluid-bearing pipelines, wherein the pipe has a wall with an inner steel layer and an outer composite layer continuously wrapped around the steel layer. The outer composite layer provides exterior protection for the pipe and io provides circumferential strength to the pipe. The dimensions and other significant parameters of the layers are selected in accordance with criteria to be discussed further below.
In another aspect, the invention is a method of i5 manufacturing a pipe with optimal selection of materials, dimensions, and other significant parameters of the pipe.
The parameters to be selected for the layers forming the pipe of the invention depend upon the internal cross-sectional 2o area and maximum operating pressure of the pipe. These selected area and pressure values relate to the transmission capability of the pipeline and are usually specified by the customer.
2s Then, a suitable grade of steel is selected for the steel layer and a suitable composite is selected for the composite layer, in accordance with steps of the invention to be discussed below. High-strength steels typically used in conventional all-steel pipelines are suitable choices for the steel layer. A composite outer layer that provides circumferential strength, protection from impacts, and some s ability to arrest crack propagation in the steel layer is a suitable choice for the composite layer.
Then, suitable steel and composite design operating stresses are selected for the steel and composite layers, io respectively. Preferably, the steel design operating stress should not exceed a value that would cause fatigue failure of the steel layer under normal pressure fluctuations.
Preferably, the composite design operating stress is selected to be a safe operating percentage of the composite's ultimate i5 tensile strength that is consistent with industry practice.
While it is possible to choose design operating stress values that are greater than the foregoing preferred values, there is an obvious risk of failure if such values are chosen. While it is possible to choose design operating stress values that 2o are significantly lower than the preferred values, such choice will not optimally use the strength of the materials, thus entailing higher manufacturing cost than may be acceptable to the customer.
2s Then, a preferred range of steel and composite layer thickness combinations are determined as those thickness combinations wherein the steel and composite layers are stressed at their respective design operating stresses when the steel-composite pipe is at the maximum operating pressure.
The minimum preferred thickness of the steel layer in this range is determined to be the minimum thickness at which the s steel layer only is able to withstand pressurization at the maximum operating pressure. However, in certain circumstances, a thinner minimum thickness is suitable, for example, in situations where there is little or no risk that the composite layer will suffer complete failure. The minimum to preferred thickness of the composite layer in this range is the minimum thickness that is able to provide suitable circumferential strength, toughness against impacts, and resistance against crack propagation in the steel layer.
i5 Other acceptable layer thickness combinations other than the preferred combinations may be selected in accordance with the invention that will provide some advantages of the invention; however, these other acceptable layer thickness combinations do not optimally utilize the strength and other 2o properties of the steel and composite and are therefore not preferred. The acceptable-but-not-preferred thickness combinations may be any combination that has steel and composite layers that are above the respective minimum thickness values, above the respective thicknesses in each of 2s the preferred thickness combinations, and whose combined per unit length mass is less than the per unit length mass of a comparable all-steel pipe, i.e. a steel pipe made of the same grade of steel, having the same internal diameter and operating at the same maximum operating pressure.
Because the composite layer is continuously wrapped s around the steel layer, the two layers will behave as one from a strain standpoint; the layers will strain together at the same rate and degree . As the steel has an elastic modulus that is substantially higher than the composite, the steel will bear a substantially higher stress than the composite at io a particular strain. In order for the steel and composite layers having a selected thickness combination to be at their respective design operating stresses when the pipe is at the maximum operating pressure, the stress distribution must be appropriately distributed between the steel and composite.
15 The stress distribution between the steel and composite layers may be selectively changed by plastically deforming the steel by a selected amount.
The steel layer is plastically deformed by autofrettaging 2o the steel-composite pipe at a selected autofrettage pressure.
Autofrettage testing is the application of hydrostatic pressure wherein the steel layer is stressed beyond its specified minimum yield stress. An autofrettage pressure is selected that will effect the appropriate amount of plastic 2s deformation; this selected autofrettage pressure is determined by mathematically modelling the stress-strain curves of the steel and composite layers respectively, and the pressure-strain curve of the steel-composite pipe.
Then, the pipe is manufactured for the most part in accordance with conventional composite/steel pipe s manufacturing practice by manufacturing a circular tubular steel inner layer whose strength and dimensions are as determined by the applicable constraints, and then applying to that steel layer an outer composite layer whose strength and dimensions are as determined by the applicable constraints.
io The general nature of the constraints has been discussed above and will be elaborated below. Then, the composite/steel pipe is autofrettaged at the selected autofrettage pressure so that an appropriate amount of plastic strain is effected to distribute the stresses between the steel and composite layers i5 so that the steel layer and the composite layer are at their respective design operating stresses when the pipe is at the selected operating pressure.
Summary of the Drawings:
A detailed description of the preferred embodiments is provided herein below with reference to the accompanying drawings, in which:
2s Figure 1 is a schematic three-dimensional view of a pipe according to an embodiment of the invention;
Figure 2 is a stress/strain graph for E-Glass type composite;
Figure 3 is a stress/strain graph for X-80 steel;
Figure 4 is a graph of acceptable composite and steel layer thickness combinations for a 48~~ inner diameter pipe having an X-80 steel layer and an E-glass composite layer and operating at a pressure of 2200 psi.
io Figure 5 is a stress/strain curve of X-80 steel and E-glass composite, superimposed with a pressure-strain curve of the same, the three curves being for a 48 inch diameter pipe operating at 2200 psi, 0.80 steel design stress percentage, 0.661 inch thick steel layer, and 0.160 inch thick composite i5 layer;
Figure 6 is a stress/strain curve of X-80 steel and E-glass composite, superimposed with a pressure-strain curve, the three curves being for a 48 inch diameter pipe operating at 20 2200 psi, 0.80 steel design stress percentage, 0.723 inch thick steel layer, and 0.100 inch thick composite layer.
Detailed Description 25 A pipe 10 in accordance with the invention is shown generally in Figure 1. The pipe 10 is a circular cylindrical pipe section of a pipeline used for transmitting gas or other fluids under high pressures. The following discussion relates to gas pipelines, but it is understood that the invention also applies to pipelines bearing other fluids, such as oil. The wall of the pipe 10 comprises an inner steel layer 12 and an s outer composite layer 14 that is attached to and covers the steel layer 12. The steel layer 12 primarily provides circumferential, radial and axial strength to the pipe 10; the composite layer 14 primarily provides circumferential and radial strength, fracture propagation arrest capability, and io protection against external environmental conditions. The materials and dimensions of the wall layers of the pipe 10 are selected in accordance with a method of the invention, described in detail below, so that the steel and composite portions are optimally utilized to achieve the above described i5 purposes and the steel-composite pipe is more cost effective and lighter than a comparable all-steel pipe. Optimal utilization means that for given operating conditions and selected materials, the dimensions of the pipe, including the steel and composite layer thicknesses, are selected so that 2o the strength of the steel and composite are fully utilized, i.e. at maximum operating conditions, the steel and composite layers are at their respective maximum design operating stresses.
2s According to the preferred method of the invention, the materials and dimensions of the pipe 10 are optimally selected in accordance with a given internal cross-sectional area and a maximum internal operating pressure of the pipe 10. These values are usually customer-specified, as they relate to the transmission capacity of the pipeline. Typical pipeline diameters in conventional mainline transmission high pressure s steel pipelines vary, the most common diameters being less than or equal to 48 inches. A typical operating pressure of such pipelines is 1400 psi, although some high-strength pipelines have been known to transmit gas at operating pressures in excess of 1700 psi. To illustrate the method of io the invention, the pipe materials and dimensions selected below are based on a maximum operating pressure of 2200 psi and an inner diameter of 48". However, the method of the invention may be applied to optimally select the materials and dimensions of a pipe 10 having any pipe diameter and operating i5 pressure typically selected for conventional high pressure pipes and still achieve the advantages of the invention.
Further, operating pressures beyond typical operating pressures in conventional all-steel pipelines can be achieved by the pipe 10, as will be described in further detail below.
A number of grades of steel are typically used for conventional high pressure steel pipelines, including X-70 and X-80 steel. The next step of the preferred method of the invention is to select an appropriate grade of steel for the 2s steel layer 12 of the pipe 10. For illustration, X-80 grade steel having a specified minimum yield strength (SMYS) of 80 ksi and a specified minimum ultimate tensile strength (SMUTS) of 90 ksi is selected, it being understood that any grade of steel typically used for high pressure pipelines is a suitable selection for the steel layer of the pipe.
s Grades of steel with higher yield strengths than X-80 are typically not used in conventional all steel high-pressure pipelines because the increased yield strength provided by these steels aver X-80, is not accompanied by a proportionate increase in fracture toughness. However, as the composite io layer of the pipe 10 provides some fracture toughness in conjunction with that provided by the steel layer, it is possible to use such higher grades of steel in addition to grades conventionally used in high-pressure pipelines for the pipe 10, provided that the dimensions of the composite and i5 steel wall layers are appropriately selected to provided adequate strength and fracture toughness.
The maximum desired stress in the pipe wall when the pipe is pressurized at the maximum operating pressure is known 2o as the design operating stress. For conventional all-steel pipes, the pipe is typically designed so that the circumferential and axial stresses in the pipe wall when the pipe 10 is pressurized at the maximum operating pressure are at a level that is less than or equal to a specified design 2s stress percentage (SDSP) of the yield strength of the steel.
The SDSP provides a °safety factor" for the safe operation of the pipe at the design operating conditions. For high pressure pipelines, the Canadian Standards Association (CSA) requires that steel pipes be designed with a SDSP that typically does not exceed 80% of the steel's SMYS. However, this value depends on a number of factors including the s proximity of the pipeline to inhabited areas.
As there does not appear to be any applicable regulation for composite wrapped steel pipes, the steel design operating stress (circumferential) of pipe 10 is selected to be 80% of io the steel's SMYS in accordance with current CSA standards for all-steel pipes, so that for X-80 steel having a SMYS of 80,000 psi, the steel design operating (circumferential) stress is 64,000 psi. However, the current North American pipe standards do not take into consideration the additional i5 strength provided by the composite layer, and therefore, such a safety factor is probably overly conservative. Preferably, the steel design operating stress should be defined as the maximum stress that would not cause a fatigue induced failure when the pipe is pressurized at the maximum operating pressure 2o and subjected to typical pressure fluctuations in gas transmission lines.
In accordance with typical industry standards, the pipe should not be pressurized beyond its maximum operating 2s pressure for a prolonged period of time, and should not at any time exceed a pressure that would stress the steel layer beyond 110% of its specified minimum yield stress ("maximum allowable overpressure").
Preferably, E-glass fibre composite is selected as the material for the composite layer 14 of the pipe 10 wall. The s composite comprises a plurality of lightweight high-strength unidirectional E-glass fibres encased in a polyester or epoxy resin matrix. The composite is wrapped around the steel layer 12 so that the unidirectional fibres are aligned circumferentially around the pipe 10. Depending on the l.o selection of the type of resin, the composite may provide the pipe 10 with some corrosion resistance. Alternatively, corrosion resistance may be provided by applying a conventional layer of fusion-bond epoxy onto the pipe 10.
Although E-glass is selected as the preferred material for the i5 composite layer 14 of the pipe 10, other materials may be suitably substituted if they are cost-effective, can bear substantial circumferential stress, and can provide some protection against crack formation and propagation. Such alternative materials includes a composite manufactured by 2o Owens Corning and sold under the commercial trade-name Advantex, which offers superior resistance to environmental degradation than standard E-glass.
As shown in Figure 2, the E-Glass composite is a brittle 2s material that has an elastic modulus of 6x106psi. It has an ultimate strength of 164 ksi. The ultimate strength represents the highest short term stress that the composite can withstand before failing. Typical industry standards recommend that the maximum design operating stress of a composite should not exceed 40% of the composite's ultimate strength. It has been found that the composite maximum design operating stress also represents the highest repeated cyclic stresses that the composite can withstand without suffering fatigue failure. In this connection, to fully utilize the strength of the composite, the magnitude of circumferential stress in the composite wall layer of the pipe 10 should be to close to the composite design operating stress when the pipe is at the maximum operating pressure, and should be at a stress below the composite's ultimate tensile strength when the pipe 10 is temporarily pressurized beyond the maximum operating pressure.
The composite is able to provide some protection against propagation of fractures occurring in the steel layer in a longitudinal direction of the pipe 10. In both long-seam weld and spiral weld pipes subjected to high circumferential 2o stresses, failure is typically observed in the form of a small longitudinal fracture that if left unchecked, quickly propagates into long ductile longitudinal fractures. The ability of the composite to impede propagation of a fracture in the steel layer is related to the amount of energy that can be absorbed by the composite layer before failing. This energy can be estimated by determining the amount of energy required to cause fracture of a given cross-sectional area of the composite fibres.
The E-glass composite does not offer much strength in the axial direction of the pipe 10. The unidirectional fibres provide only tensile strength around the circumference of the pipe wall, and the resin matrix does not offer significant strength in any direction. Therefore, the steel layer 12 must be thick enough to withstand axial stresses caused by prolonged pressurization at the maximum operating pressure, l.o and temporary pressurization at the maximum allowable overpresssure. In this connection, the axial stress in the steel layer of the pipe 10 should not exceed the maximum limits as set by the Canadian Standards Association (or some other appropriate regulatory authority) for a steel pipe 15 pressurized at the maximum design operating conditions; for the purposes of illustrating the method of the invention, a steel design operating axial stress is selected to be 80°s of the steel s SMYS, which is 64,000 psi for X-80 steel.
2o One of the objectives of pipeline design is to minimize the mass of a unit length of a pipe with respect to its other properties. This will tend to reduce the cost of manufacturing and make the pipe easier to handle. In this connection, the mass of a unit length of the composite-steel pipe 10 should 25 not exceed the mass of a unit length of a comparable all-steel pipe designed to operate under the same conditions.
The above discussed design parameters constrain the suitable selection of materials and dimensions of the invention and are summarized below:
(1) the internal pressure does not exceed a level that would cause the circumferential and axial stresses in the steel layer 12 to exceed 110% of the steel's SMYS, i.e.
the internal pressure does not exceed the maximum allowable overpressure during autofrettage;
to (2) the internal pressure does not exceed a level that would cause the circumferential stress in the composite layer 14 to exceed the composite's ultimate tensile strength during autofrettage;
(3) the circumferential stress in the steel layer 12 does not exceed the steel design operating (circumferential) stress when the pipe 10 transmits gas at the maximum operating pressure; and (4) the axial stress in the steel layer 12 does not exceed the steel design operating (axial) stress when the pipe 10 transmits gas at the maximum operating pressure; and (5) the circumferential stress in the composite layer 14 is at or below a selected composite design operating stress when the pipe 10 transmits gas at the maximum operating pressure.
llBm vanlSYSICLIENTS11P00110075 calspec final 990603.wpd STEEL-COMPOSITE PIPE AND METHOD OF MANUFACTURING SAME
s Field of the Invention The present patent application relates generally to pipelines and specifically to a pipe for a high pressure gas pipeline and a method of manufacturing the pipe, the materials io and dimensions of which are optimally selected.
Background Of The Invention~
Pipelines for transmitting natural gas and other fluids i5 typically span many hundreds of kilometres of terrain. These pipelines tend to be pressurized at high pressures; some known pipelines are designed to operate around 1750 psi. Pipes that are connected together to form such pipelines are typically made from a high-strength steel so that the pipeline can 2o withstand stresses caused by high internal pressures and resist adverse external environmental conditions.
To protect the exterior of the pipeline and to provide additional circumferential strength, high-pressure pipelines 2s have been known to be wrapped with a covering such as a wire winding or a flexible non-metallic sheet. Such coverings also serve to arrest propagation of cracks that originate from ..
failures in the pipe wall. For example, U.S. patent no.
4,559,974 (Fawley) discloses a plurality of circumferential bands of unidirectional non-metallic fibres that wrap around a conventional steel pipe. The patent states that the plurality of bands are intended in part to equalize the circumferential strength of the pipe with its longitudinal strength so that the pipe can bear an increased stress before failing. However, the patent does not appear to disclose any particulars about the amount of increased stress that can be io safely borne for a particular amount of band material and for a particular selection of pipe parameters; without such particulars, increasing the stress level beyond specified maximum operating levels would be hazardous. Further, covering-wrapped pipes such as those disclosed in Fawley tend i5 to be costlier to manufacture than non-wrapped pipes having a comparable steel layer thickness and operating at a comparable pressure. Further, the covering adds undesirable weight to the underlying pipe, making pipeline construction more difficult and more costly.
It is apparent that a covering that provides some circumferential strength to the pipe structure will permit a covering-wrapped pipeline to withstand some increase in its internal operating pressure. Increasing the internal 2s operating pressure will increase the rate of gas transmittable by the pipeline, thereby increasing the revenue that can be generated. Therefore, it is a desirable objective to ..
construct a covering-wrapped pipeline that enjoys the benefits of a covering and whose increased construction costs are sufficiently offset by an increased rate of fluid transmission so that the covering-wrapped pipeline is as or more profitable than a comparable non-covered pipeline.
Alternatively, the cost of construction of the covering-wrapped pipeline may be offset by utilizing the circumferential strength of the covering in place of some of io the circumferential strength provided by the steel, so that the amount of steel used in the covering-wrapped pipeline can be reduced relative to an all-steel pipeline operating at a comparable pressure. This reduction can in some cases reduce the weight and material cost of the covering-wrapped pipe.
No known method has been devised to accomplish optimally the above objectives. That is, there is no known method to select the materials, dimensions, and operating parameters of the covering and pipe portions of the covering-wrapped pipe so 2o that the strength and other properties of the materials are fully utilized, thereby optimizing the fluid transmission capacity of the covered pipeline relative to its cost of construction and operation.
2s The present invention overcomes some of the shortcomings of the prior technology and achieves further advantages that will be apparent after reviewing the following summary and detailed description of the invention.
Summary Of The Invention:
s The present invention in one aspect is a pipe for use in high pressure fluid-bearing pipelines, wherein the pipe has a wall with an inner steel layer and an outer composite layer continuously wrapped around the steel layer. The outer composite layer provides exterior protection for the pipe and io provides circumferential strength to the pipe. The dimensions and other significant parameters of the layers are selected in accordance with criteria to be discussed further below.
In another aspect, the invention is a method of i5 manufacturing a pipe with optimal selection of materials, dimensions, and other significant parameters of the pipe.
The parameters to be selected for the layers forming the pipe of the invention depend upon the internal cross-sectional 2o area and maximum operating pressure of the pipe. These selected area and pressure values relate to the transmission capability of the pipeline and are usually specified by the customer.
2s Then, a suitable grade of steel is selected for the steel layer and a suitable composite is selected for the composite layer, in accordance with steps of the invention to be discussed below. High-strength steels typically used in conventional all-steel pipelines are suitable choices for the steel layer. A composite outer layer that provides circumferential strength, protection from impacts, and some s ability to arrest crack propagation in the steel layer is a suitable choice for the composite layer.
Then, suitable steel and composite design operating stresses are selected for the steel and composite layers, io respectively. Preferably, the steel design operating stress should not exceed a value that would cause fatigue failure of the steel layer under normal pressure fluctuations.
Preferably, the composite design operating stress is selected to be a safe operating percentage of the composite's ultimate i5 tensile strength that is consistent with industry practice.
While it is possible to choose design operating stress values that are greater than the foregoing preferred values, there is an obvious risk of failure if such values are chosen. While it is possible to choose design operating stress values that 2o are significantly lower than the preferred values, such choice will not optimally use the strength of the materials, thus entailing higher manufacturing cost than may be acceptable to the customer.
2s Then, a preferred range of steel and composite layer thickness combinations are determined as those thickness combinations wherein the steel and composite layers are stressed at their respective design operating stresses when the steel-composite pipe is at the maximum operating pressure.
The minimum preferred thickness of the steel layer in this range is determined to be the minimum thickness at which the s steel layer only is able to withstand pressurization at the maximum operating pressure. However, in certain circumstances, a thinner minimum thickness is suitable, for example, in situations where there is little or no risk that the composite layer will suffer complete failure. The minimum to preferred thickness of the composite layer in this range is the minimum thickness that is able to provide suitable circumferential strength, toughness against impacts, and resistance against crack propagation in the steel layer.
i5 Other acceptable layer thickness combinations other than the preferred combinations may be selected in accordance with the invention that will provide some advantages of the invention; however, these other acceptable layer thickness combinations do not optimally utilize the strength and other 2o properties of the steel and composite and are therefore not preferred. The acceptable-but-not-preferred thickness combinations may be any combination that has steel and composite layers that are above the respective minimum thickness values, above the respective thicknesses in each of 2s the preferred thickness combinations, and whose combined per unit length mass is less than the per unit length mass of a comparable all-steel pipe, i.e. a steel pipe made of the same grade of steel, having the same internal diameter and operating at the same maximum operating pressure.
Because the composite layer is continuously wrapped s around the steel layer, the two layers will behave as one from a strain standpoint; the layers will strain together at the same rate and degree . As the steel has an elastic modulus that is substantially higher than the composite, the steel will bear a substantially higher stress than the composite at io a particular strain. In order for the steel and composite layers having a selected thickness combination to be at their respective design operating stresses when the pipe is at the maximum operating pressure, the stress distribution must be appropriately distributed between the steel and composite.
15 The stress distribution between the steel and composite layers may be selectively changed by plastically deforming the steel by a selected amount.
The steel layer is plastically deformed by autofrettaging 2o the steel-composite pipe at a selected autofrettage pressure.
Autofrettage testing is the application of hydrostatic pressure wherein the steel layer is stressed beyond its specified minimum yield stress. An autofrettage pressure is selected that will effect the appropriate amount of plastic 2s deformation; this selected autofrettage pressure is determined by mathematically modelling the stress-strain curves of the steel and composite layers respectively, and the pressure-strain curve of the steel-composite pipe.
Then, the pipe is manufactured for the most part in accordance with conventional composite/steel pipe s manufacturing practice by manufacturing a circular tubular steel inner layer whose strength and dimensions are as determined by the applicable constraints, and then applying to that steel layer an outer composite layer whose strength and dimensions are as determined by the applicable constraints.
io The general nature of the constraints has been discussed above and will be elaborated below. Then, the composite/steel pipe is autofrettaged at the selected autofrettage pressure so that an appropriate amount of plastic strain is effected to distribute the stresses between the steel and composite layers i5 so that the steel layer and the composite layer are at their respective design operating stresses when the pipe is at the selected operating pressure.
Summary of the Drawings:
A detailed description of the preferred embodiments is provided herein below with reference to the accompanying drawings, in which:
2s Figure 1 is a schematic three-dimensional view of a pipe according to an embodiment of the invention;
Figure 2 is a stress/strain graph for E-Glass type composite;
Figure 3 is a stress/strain graph for X-80 steel;
Figure 4 is a graph of acceptable composite and steel layer thickness combinations for a 48~~ inner diameter pipe having an X-80 steel layer and an E-glass composite layer and operating at a pressure of 2200 psi.
io Figure 5 is a stress/strain curve of X-80 steel and E-glass composite, superimposed with a pressure-strain curve of the same, the three curves being for a 48 inch diameter pipe operating at 2200 psi, 0.80 steel design stress percentage, 0.661 inch thick steel layer, and 0.160 inch thick composite i5 layer;
Figure 6 is a stress/strain curve of X-80 steel and E-glass composite, superimposed with a pressure-strain curve, the three curves being for a 48 inch diameter pipe operating at 20 2200 psi, 0.80 steel design stress percentage, 0.723 inch thick steel layer, and 0.100 inch thick composite layer.
Detailed Description 25 A pipe 10 in accordance with the invention is shown generally in Figure 1. The pipe 10 is a circular cylindrical pipe section of a pipeline used for transmitting gas or other fluids under high pressures. The following discussion relates to gas pipelines, but it is understood that the invention also applies to pipelines bearing other fluids, such as oil. The wall of the pipe 10 comprises an inner steel layer 12 and an s outer composite layer 14 that is attached to and covers the steel layer 12. The steel layer 12 primarily provides circumferential, radial and axial strength to the pipe 10; the composite layer 14 primarily provides circumferential and radial strength, fracture propagation arrest capability, and io protection against external environmental conditions. The materials and dimensions of the wall layers of the pipe 10 are selected in accordance with a method of the invention, described in detail below, so that the steel and composite portions are optimally utilized to achieve the above described i5 purposes and the steel-composite pipe is more cost effective and lighter than a comparable all-steel pipe. Optimal utilization means that for given operating conditions and selected materials, the dimensions of the pipe, including the steel and composite layer thicknesses, are selected so that 2o the strength of the steel and composite are fully utilized, i.e. at maximum operating conditions, the steel and composite layers are at their respective maximum design operating stresses.
2s According to the preferred method of the invention, the materials and dimensions of the pipe 10 are optimally selected in accordance with a given internal cross-sectional area and a maximum internal operating pressure of the pipe 10. These values are usually customer-specified, as they relate to the transmission capacity of the pipeline. Typical pipeline diameters in conventional mainline transmission high pressure s steel pipelines vary, the most common diameters being less than or equal to 48 inches. A typical operating pressure of such pipelines is 1400 psi, although some high-strength pipelines have been known to transmit gas at operating pressures in excess of 1700 psi. To illustrate the method of io the invention, the pipe materials and dimensions selected below are based on a maximum operating pressure of 2200 psi and an inner diameter of 48". However, the method of the invention may be applied to optimally select the materials and dimensions of a pipe 10 having any pipe diameter and operating i5 pressure typically selected for conventional high pressure pipes and still achieve the advantages of the invention.
Further, operating pressures beyond typical operating pressures in conventional all-steel pipelines can be achieved by the pipe 10, as will be described in further detail below.
A number of grades of steel are typically used for conventional high pressure steel pipelines, including X-70 and X-80 steel. The next step of the preferred method of the invention is to select an appropriate grade of steel for the 2s steel layer 12 of the pipe 10. For illustration, X-80 grade steel having a specified minimum yield strength (SMYS) of 80 ksi and a specified minimum ultimate tensile strength (SMUTS) of 90 ksi is selected, it being understood that any grade of steel typically used for high pressure pipelines is a suitable selection for the steel layer of the pipe.
s Grades of steel with higher yield strengths than X-80 are typically not used in conventional all steel high-pressure pipelines because the increased yield strength provided by these steels aver X-80, is not accompanied by a proportionate increase in fracture toughness. However, as the composite io layer of the pipe 10 provides some fracture toughness in conjunction with that provided by the steel layer, it is possible to use such higher grades of steel in addition to grades conventionally used in high-pressure pipelines for the pipe 10, provided that the dimensions of the composite and i5 steel wall layers are appropriately selected to provided adequate strength and fracture toughness.
The maximum desired stress in the pipe wall when the pipe is pressurized at the maximum operating pressure is known 2o as the design operating stress. For conventional all-steel pipes, the pipe is typically designed so that the circumferential and axial stresses in the pipe wall when the pipe 10 is pressurized at the maximum operating pressure are at a level that is less than or equal to a specified design 2s stress percentage (SDSP) of the yield strength of the steel.
The SDSP provides a °safety factor" for the safe operation of the pipe at the design operating conditions. For high pressure pipelines, the Canadian Standards Association (CSA) requires that steel pipes be designed with a SDSP that typically does not exceed 80% of the steel's SMYS. However, this value depends on a number of factors including the s proximity of the pipeline to inhabited areas.
As there does not appear to be any applicable regulation for composite wrapped steel pipes, the steel design operating stress (circumferential) of pipe 10 is selected to be 80% of io the steel's SMYS in accordance with current CSA standards for all-steel pipes, so that for X-80 steel having a SMYS of 80,000 psi, the steel design operating (circumferential) stress is 64,000 psi. However, the current North American pipe standards do not take into consideration the additional i5 strength provided by the composite layer, and therefore, such a safety factor is probably overly conservative. Preferably, the steel design operating stress should be defined as the maximum stress that would not cause a fatigue induced failure when the pipe is pressurized at the maximum operating pressure 2o and subjected to typical pressure fluctuations in gas transmission lines.
In accordance with typical industry standards, the pipe should not be pressurized beyond its maximum operating 2s pressure for a prolonged period of time, and should not at any time exceed a pressure that would stress the steel layer beyond 110% of its specified minimum yield stress ("maximum allowable overpressure").
Preferably, E-glass fibre composite is selected as the material for the composite layer 14 of the pipe 10 wall. The s composite comprises a plurality of lightweight high-strength unidirectional E-glass fibres encased in a polyester or epoxy resin matrix. The composite is wrapped around the steel layer 12 so that the unidirectional fibres are aligned circumferentially around the pipe 10. Depending on the l.o selection of the type of resin, the composite may provide the pipe 10 with some corrosion resistance. Alternatively, corrosion resistance may be provided by applying a conventional layer of fusion-bond epoxy onto the pipe 10.
Although E-glass is selected as the preferred material for the i5 composite layer 14 of the pipe 10, other materials may be suitably substituted if they are cost-effective, can bear substantial circumferential stress, and can provide some protection against crack formation and propagation. Such alternative materials includes a composite manufactured by 2o Owens Corning and sold under the commercial trade-name Advantex, which offers superior resistance to environmental degradation than standard E-glass.
As shown in Figure 2, the E-Glass composite is a brittle 2s material that has an elastic modulus of 6x106psi. It has an ultimate strength of 164 ksi. The ultimate strength represents the highest short term stress that the composite can withstand before failing. Typical industry standards recommend that the maximum design operating stress of a composite should not exceed 40% of the composite's ultimate strength. It has been found that the composite maximum design operating stress also represents the highest repeated cyclic stresses that the composite can withstand without suffering fatigue failure. In this connection, to fully utilize the strength of the composite, the magnitude of circumferential stress in the composite wall layer of the pipe 10 should be to close to the composite design operating stress when the pipe is at the maximum operating pressure, and should be at a stress below the composite's ultimate tensile strength when the pipe 10 is temporarily pressurized beyond the maximum operating pressure.
The composite is able to provide some protection against propagation of fractures occurring in the steel layer in a longitudinal direction of the pipe 10. In both long-seam weld and spiral weld pipes subjected to high circumferential 2o stresses, failure is typically observed in the form of a small longitudinal fracture that if left unchecked, quickly propagates into long ductile longitudinal fractures. The ability of the composite to impede propagation of a fracture in the steel layer is related to the amount of energy that can be absorbed by the composite layer before failing. This energy can be estimated by determining the amount of energy required to cause fracture of a given cross-sectional area of the composite fibres.
The E-glass composite does not offer much strength in the axial direction of the pipe 10. The unidirectional fibres provide only tensile strength around the circumference of the pipe wall, and the resin matrix does not offer significant strength in any direction. Therefore, the steel layer 12 must be thick enough to withstand axial stresses caused by prolonged pressurization at the maximum operating pressure, l.o and temporary pressurization at the maximum allowable overpresssure. In this connection, the axial stress in the steel layer of the pipe 10 should not exceed the maximum limits as set by the Canadian Standards Association (or some other appropriate regulatory authority) for a steel pipe 15 pressurized at the maximum design operating conditions; for the purposes of illustrating the method of the invention, a steel design operating axial stress is selected to be 80°s of the steel s SMYS, which is 64,000 psi for X-80 steel.
2o One of the objectives of pipeline design is to minimize the mass of a unit length of a pipe with respect to its other properties. This will tend to reduce the cost of manufacturing and make the pipe easier to handle. In this connection, the mass of a unit length of the composite-steel pipe 10 should 25 not exceed the mass of a unit length of a comparable all-steel pipe designed to operate under the same conditions.
The above discussed design parameters constrain the suitable selection of materials and dimensions of the invention and are summarized below:
(1) the internal pressure does not exceed a level that would cause the circumferential and axial stresses in the steel layer 12 to exceed 110% of the steel's SMYS, i.e.
the internal pressure does not exceed the maximum allowable overpressure during autofrettage;
to (2) the internal pressure does not exceed a level that would cause the circumferential stress in the composite layer 14 to exceed the composite's ultimate tensile strength during autofrettage;
(3) the circumferential stress in the steel layer 12 does not exceed the steel design operating (circumferential) stress when the pipe 10 transmits gas at the maximum operating pressure; and (4) the axial stress in the steel layer 12 does not exceed the steel design operating (axial) stress when the pipe 10 transmits gas at the maximum operating pressure; and (5) the circumferential stress in the composite layer 14 is at or below a selected composite design operating stress when the pipe 10 transmits gas at the maximum operating pressure.
(6) the mass of a unit length of the composite-steel pipe 10 does not exceed the mass of a unit length of a comparable all-steel pipe operating under comparable conditions.
Having defined these design parameters, the next step of io the method of the invention is to select suitable steel and composite layer thickness combinations. This step is described in the following paragraphs:
Let an internal pressure p be exerted on the wall of pipe i5 10, the pipe 10 having an inside diameter di, a composite layer of thickness tromp and a steel layer 12 of thickness tateel ~ The force tending to separate two halves of a unit length of the pipe 10 is p~di . This force is resisted by the circumferential stress, acting uniformly over the stressed 2o area. Assuming that, under pressure, the radial stress in the pipe 10 is relatively small compared to the circumferential stress, the relationship between the circumferential stresses in the wall layers and the internal pressure is:
25 p ~ di/ 2 - ~eteel ~ tateel + comp ~ tromp (equation 1) wherein 68tee1 is the circumferential stress in the steel layer 12 and 6°°mp is the circumferential stress in the composite layer 14 at pressure p. At the maximum operating pressure p°p, 6steel 1S eCjual t0 the steel design operating StreSS 6gteel°p and s a°°mp is equal to the composite design operating stress a°°mp°p:
p°p ~ dil 2 - ~eteel°p ~ tsteel + comp p tcomp (equation 2) io As discussed above, the values for p°p, di, 6eteel°pi comp°p have been selected. Therefore equation 2 provides an optimal range of steel and composite layer thickness combinations that fully utilize the strength of the steel and composite; that is, layer thickness combinations in accordance with equation 2 15 will provide a pipe having steel and composite layers that are at their respective maximum design operating stresses when the pipe is pressurized at the maximum operating pressure.
There is a preferred minimum steel layer thickness for 2o the optimal range of selectable thicknesses; this minimum thickness and the corresponding composite thickness (calculated from equation 2) define one boundary of the above range. Preferably, the minimum steel layer thickness is the minimum thickness of steel that the steel layer of the pipe 10 2s can by itself withstand the maximum internal operating pressure without yielding. Thus, where the composite layer cannot provide any circumferential strength, e.g. if it is damaged, the steel layer of the pipe 10 will bear the pressurized gas long enough to effect the necessary repairs.
This steel layer thickness is determined by solving for teteel in the following equation:
~]~P ' [~y~2 = SMYS ' tHteel (equation 3) A composite thickness corresponding to the minimum steel layer io thickness is determined by solving for t~omP in equation 2 to obtain a steel and composite layer thickness combination (°first boundary combination~~).
A thinner minimum steel layer thickness may be acceptably i5 selected in certain circumstances. For example, the conditions may be such that there is a low risk that the composite layer will suffer damage. Or, a user may not desire the added safety feature provided by a thicker steel layer.
In this case, the minimum steel layer thickness is the minimum 2o thickness that will provide sufficient strength to withstand axial stresses when the pipe 10 is pressurized at prolonged periods at the maximum operating pressure, and temporary periods at the maximum allowable overpressure. To determine this thickness, assume again that the radial stresses are 25 minor relative to the circumferential and axial stresses;
then, the axial stress in the steel layer 12 of the pipe 10 is approximately one-half of the circumferential stress in both the steel and composite layers. Making the appropriate substitutions, the following equation may be derived:
pip ~ dil 4 - ~eteel, axial P ~ tateel (equation 4) wherein 6eteel, axial~p 1S the steel axial stress and is equal to the SDSP multiplied by the steel SMYS. This equation may then be solved for tHteel io The other boundary of the above optimal range is defined by the minimum composite layer thickness t~omp'"ln that is able to provide suitable circumferential strength, crack arrest capability, and toughness against impacts; this composite layer thickness will depend on the external environment and i5 other circumstances, but for the sake of illustration in this example has been selected to be 0.100". The corresponding steel layer thickness can be determined by solving for t9teel in equation 2 to obtain a composite and steel layer thickness combination ("second boundary combination").
The following table illustrates the optimal range of steel and composite layer thickness combinations for a 48"
inner diameter pipe having X-80 steel and E-glass composite layers and operating at a pressure of 2200 psi, based on the 2s above calculations. The bolded combinations represent the preferred thickness layer combinations wherein the steel layer can bear by itself the stress associated with pressurization at the maximum operating pressure.
Table 1: optimal steel and composite layer thickness combinations for 48"
diameter X-80 and E-glass composite pipe operating at 2200 psi.
Wall Thickness Axial Autofrettage inches Stress Pressure psi psi Composite Steel Steel 11.100 (1.723 365411 2879 (1.115 (1.711737334 2868 (1.1311 11.692 38164 2856 11.145 (1.676 39032 2845 (1.1611 (1.661 39939 2834 0.175 0.646 40891 2822 0.190 0.63() 41888 2811 0.205 0.615 42936 2800 0.220 0.60() 44037 2788 0.235 0.584 45196 2777 0.250 0.569 46418 2766 0.265 0.553 47707 2754 0.28(1 (1.538 49071 2743 ().295 0.523 50514 2732 0.311) 0.507 52045 2720 0.325 0.492 53672 2709 0.340 0.477 55404 2698 0.355 0.461 57251 2686 0.370 0.446 59226 2675 ().385 0.43() 61342 2664 ().40(1 0.415 63614 2653 Other layer thickness combinations other than the above optimal combinations may be acceptably selected in accordance with the invention that will provide some advantages of the invention, including a steel-composite pipe that is lighter than a comparable all-steel pipe, having a composite layer that provides some circumferential strength, fracture arrest s capability, and protection from the external environment.
However, these other layer thickness combinations do not optimally utilize the strength and other properties of the steel and composite and are therefore not preferred. The acceptable non-preferred thickness combinations may be any io combination that falls within an area on a steel and composite thickness graph illustrated in Figure 4, that is, within the area defined by the following lines: (1) the minimum preferred steel layer thickness (line A), (2) the minimum preferred composite layer thickness (line B), (3) the range of optimal i5 thickness combinations (line C), and (4) the range of thickness combinations of a unit length of steel-composite pipe that equals the mass of a unit length of a comparable all-steel pipe (Line D). Line D may be readily plotted given the respective densities and dimensions of the steel and 2o composite layers; for the exemplary pipe illustrated in Figure 6, the steel and composite densities are 0.2829 lb/in3 and 0.0779 lb/in3, respectively.
Once the foregoing parameters are determined for the 2s steel and composite layers and acceptable dimensions for the pipe 10 have been selected, the pipe 10 is manufactured for the most part in accordance with conventional composite/steel pipe manufacturing practice by manufacturing a circular tubular steel inner layer, and then applying to that steel layer an outer composite layer by known means. In an exemplary known means, the fibres of the composite are drawn s from a plurality of spools contained in a creel, are fed through gathering and aligning devices, through a bath of polyester resin, and onto the outside surface of the metal layer. While the above is a suitable means of attaching the composite to the steel layer, any suitable known means for to attaching the composite may be alternatively used, so long as continuous contact is maintained between the composite and steel layers when the pipe 10 is subjected to axial, compressive and radial stresses, and so long as that under such stresses, the steel and composite layers 12, 14 will i5 strain at the same rate and by the same amount.
Referring to Figure 5, it can be seen that when the manufactured pipe is first pressurized to the maximum operating pressure of 2200 psi, the stress in the composite 20 layer is well below the composite design operating stress of 64 ksi, and the stress in the steel layer exceeds the steel design operating stress of 64 ksi. This is because the steel and composite layers are in continuous contact and will have the same strain for a given internal pressure. As the elastic 2s modulus of the steel is significantly higher than that of the composite, the steel will bear a higher amount of stress than the composite for a given strain. For the steel and composite layers to be at their respective design operating stresses when the pipe is at the maximum operating pressure, the stress distribution between the steel and composite layers at the maximum operating pressure must be changed. This is achieved s by stressing the steel beyond its yield stress so that the steel is plastically deformed. This overstressing of the steel may be effected by autofrettaging the pipe during a field hydrostatic pressure test, i.e. by pressurizing the pipe beyond the maximum operating pressure to a selected io autofrettage pressure.
In a conventional field hydrostatic pressure test, a portion of a field-installed pipeline is pressurized with water to a selected pressure. Evidence of leakage is then is monitored; leakage is particularly prevalent around the weld seams between pipe sections but may occur anywhere on the pipe wall that experiences a failure. If no leakage occurs, then the pipeline portion has passed the pressure test.
2o Autofrettage is the application of hydrostatic pressure wherein the steel layer is stressed beyond its specified minimum yield stress. Generally accepted industry practice recommends that the autofrettage pressure not exceed a level that would cause the wall of the pipe to be stressed beyond 2s 110% of the steel's SMYS. An effect of pressure testing conventional all-steel pipes between 100-110% of the steel's yield stress is that the steel wall will experience some plastic deformation. As illustrated in Figure 3, when plastically deformed, the elastic range of the steel is increased. Referring to Figures 5 and 6, plastically deforming the steel in the steel-composite pipe will impart a s compressive stress in the steel layer and a tensile stress in the composite layer, thereby changing the stress distribution between the respective layers when the pipe is re-pressurized.
It can be seen that when the pipe is re-pressurized to to the maximum operating pressure, the stress distribution between the steel and composite layers is different than that before autofrettaging. To achieve the desired stress distribution, namely, that distribution wherein the steel layer and composite layers are at their respective design 15 operating stresses, the steel is plastically deformed by an amount that will locate line II-III in Figure 6 so that it passes through a point corresponding to the steel design operating circumferential stress at the operating strain.
2o Once the appropriate amount of plastic deformation has been determined, an appropriate autofrettage pressure that will effect the appropriate plastic deformation must be determined. This is determined by mathematically modelling the stress-strain curves of steel and composite, and the 2s pressure-strain curve of the pipe 10. Using Figure 6 to illustrate, the stress-strain curves of the steel and composite may be modelled using a combination of the Ramberg-Osgood equation and linear equations:
For line I-II:
(equation 5) steel f~ ( steel' n steel L.' pY F
steel Y
Where Eateei is the steel' strain s ~ateel 1.S the steel' stress s EHceei is the steel' Elastic Modulus s F
a =0.05-- y py E
steel to FY is the steel's effective specified minimum yield strength according to CAN/CSA 2662-96.
18.5 for X-80 - X-100 grade steel and 17.5 for X-70 grade steel for line II-III
+b (equation 6) steel steel steel At line B, the steel is at its operating stress and strain.
cs =c3°p =F ~s (elation 7) steel steel y steel 2o Where SHteel 1S the steel design stress percentage. The strain of the steel layer and composite layer at the operating strain are the same:
s UTS (equation 8) fop -fop comp comp steel comp $
comp Where S~omp UTScomp and Eoomp are the composite design stress s percentage, ultimate tensile strength and Elastic Modulus, respectively.
Then, at operating conditions, (equation 9) b=S F - steel ~ S . UTS ) steel y F comp comp comp to At the autofrettage strain (Line A) (equation 10) 1 c c~'' -b >
steel E steel steel and (equation 11) 1 ( ~5p __b' - «steel +~ ( (3steel' n steel E' PY F
steel steel y i5 Solving for 'SHteei at line A provides the maximum allowable stress of the steel, i.e. the steel autofrettage stress:
(equation 12) -b c5A =F ~ ) 1 / n steel y g $
py steel 2a With the steel autofrettage stress, the autofrettage strain may be readily determined. Then, the appropriate autotrettage pressure can be readily determined from equation 1. Figures and 6 illustrate the steel and composite stress-strain s curves and pressure-strain for the first and second boundary thickness combinations having an appropriate degree of plastic strain.
The last step of the method of the invention is to io autofrettage the pipe 10 at the above determined autof rettage pressure. The resultant steel-composite pipe 10 will be able to operate at a higher internal pressure than a conventional all-steel pipe having a wall thickness equal to the thickness of the steel layer of the steel-composite pipe. The composite layer bears a proportion of the load caused by the internal pressure; in the all-steel pipe, this load must be borne entirely by the steel wall. Therefore, maximum operating pressures of a steel-composite pipeline can be increased beyond those presently specified for conventional all-steel 2o pipelines, thereby increasing the flow rate of gas and profitability of the steel-composite pipeline.
Other alternatives and variants of the above described methods and apparatus suitable for practising the methods will 2s occur to those skilled in the technology. For example, aluminum may be substituted for the material for the inner layer if a lighter overall weight is desired. Other alternative materials for the inner layer include stainless steel or titanimum. Carbon fibre or other materials may be substituted for the E-glass fibres to enhance the modulus of the composite, increase the composite's operating stress, or s provide enhanced corrosion resistance. The scope of the invention is as defined in the following claims.
Having defined these design parameters, the next step of io the method of the invention is to select suitable steel and composite layer thickness combinations. This step is described in the following paragraphs:
Let an internal pressure p be exerted on the wall of pipe i5 10, the pipe 10 having an inside diameter di, a composite layer of thickness tromp and a steel layer 12 of thickness tateel ~ The force tending to separate two halves of a unit length of the pipe 10 is p~di . This force is resisted by the circumferential stress, acting uniformly over the stressed 2o area. Assuming that, under pressure, the radial stress in the pipe 10 is relatively small compared to the circumferential stress, the relationship between the circumferential stresses in the wall layers and the internal pressure is:
25 p ~ di/ 2 - ~eteel ~ tateel + comp ~ tromp (equation 1) wherein 68tee1 is the circumferential stress in the steel layer 12 and 6°°mp is the circumferential stress in the composite layer 14 at pressure p. At the maximum operating pressure p°p, 6steel 1S eCjual t0 the steel design operating StreSS 6gteel°p and s a°°mp is equal to the composite design operating stress a°°mp°p:
p°p ~ dil 2 - ~eteel°p ~ tsteel + comp p tcomp (equation 2) io As discussed above, the values for p°p, di, 6eteel°pi comp°p have been selected. Therefore equation 2 provides an optimal range of steel and composite layer thickness combinations that fully utilize the strength of the steel and composite; that is, layer thickness combinations in accordance with equation 2 15 will provide a pipe having steel and composite layers that are at their respective maximum design operating stresses when the pipe is pressurized at the maximum operating pressure.
There is a preferred minimum steel layer thickness for 2o the optimal range of selectable thicknesses; this minimum thickness and the corresponding composite thickness (calculated from equation 2) define one boundary of the above range. Preferably, the minimum steel layer thickness is the minimum thickness of steel that the steel layer of the pipe 10 2s can by itself withstand the maximum internal operating pressure without yielding. Thus, where the composite layer cannot provide any circumferential strength, e.g. if it is damaged, the steel layer of the pipe 10 will bear the pressurized gas long enough to effect the necessary repairs.
This steel layer thickness is determined by solving for teteel in the following equation:
~]~P ' [~y~2 = SMYS ' tHteel (equation 3) A composite thickness corresponding to the minimum steel layer io thickness is determined by solving for t~omP in equation 2 to obtain a steel and composite layer thickness combination (°first boundary combination~~).
A thinner minimum steel layer thickness may be acceptably i5 selected in certain circumstances. For example, the conditions may be such that there is a low risk that the composite layer will suffer damage. Or, a user may not desire the added safety feature provided by a thicker steel layer.
In this case, the minimum steel layer thickness is the minimum 2o thickness that will provide sufficient strength to withstand axial stresses when the pipe 10 is pressurized at prolonged periods at the maximum operating pressure, and temporary periods at the maximum allowable overpressure. To determine this thickness, assume again that the radial stresses are 25 minor relative to the circumferential and axial stresses;
then, the axial stress in the steel layer 12 of the pipe 10 is approximately one-half of the circumferential stress in both the steel and composite layers. Making the appropriate substitutions, the following equation may be derived:
pip ~ dil 4 - ~eteel, axial P ~ tateel (equation 4) wherein 6eteel, axial~p 1S the steel axial stress and is equal to the SDSP multiplied by the steel SMYS. This equation may then be solved for tHteel io The other boundary of the above optimal range is defined by the minimum composite layer thickness t~omp'"ln that is able to provide suitable circumferential strength, crack arrest capability, and toughness against impacts; this composite layer thickness will depend on the external environment and i5 other circumstances, but for the sake of illustration in this example has been selected to be 0.100". The corresponding steel layer thickness can be determined by solving for t9teel in equation 2 to obtain a composite and steel layer thickness combination ("second boundary combination").
The following table illustrates the optimal range of steel and composite layer thickness combinations for a 48"
inner diameter pipe having X-80 steel and E-glass composite layers and operating at a pressure of 2200 psi, based on the 2s above calculations. The bolded combinations represent the preferred thickness layer combinations wherein the steel layer can bear by itself the stress associated with pressurization at the maximum operating pressure.
Table 1: optimal steel and composite layer thickness combinations for 48"
diameter X-80 and E-glass composite pipe operating at 2200 psi.
Wall Thickness Axial Autofrettage inches Stress Pressure psi psi Composite Steel Steel 11.100 (1.723 365411 2879 (1.115 (1.711737334 2868 (1.1311 11.692 38164 2856 11.145 (1.676 39032 2845 (1.1611 (1.661 39939 2834 0.175 0.646 40891 2822 0.190 0.63() 41888 2811 0.205 0.615 42936 2800 0.220 0.60() 44037 2788 0.235 0.584 45196 2777 0.250 0.569 46418 2766 0.265 0.553 47707 2754 0.28(1 (1.538 49071 2743 ().295 0.523 50514 2732 0.311) 0.507 52045 2720 0.325 0.492 53672 2709 0.340 0.477 55404 2698 0.355 0.461 57251 2686 0.370 0.446 59226 2675 ().385 0.43() 61342 2664 ().40(1 0.415 63614 2653 Other layer thickness combinations other than the above optimal combinations may be acceptably selected in accordance with the invention that will provide some advantages of the invention, including a steel-composite pipe that is lighter than a comparable all-steel pipe, having a composite layer that provides some circumferential strength, fracture arrest s capability, and protection from the external environment.
However, these other layer thickness combinations do not optimally utilize the strength and other properties of the steel and composite and are therefore not preferred. The acceptable non-preferred thickness combinations may be any io combination that falls within an area on a steel and composite thickness graph illustrated in Figure 4, that is, within the area defined by the following lines: (1) the minimum preferred steel layer thickness (line A), (2) the minimum preferred composite layer thickness (line B), (3) the range of optimal i5 thickness combinations (line C), and (4) the range of thickness combinations of a unit length of steel-composite pipe that equals the mass of a unit length of a comparable all-steel pipe (Line D). Line D may be readily plotted given the respective densities and dimensions of the steel and 2o composite layers; for the exemplary pipe illustrated in Figure 6, the steel and composite densities are 0.2829 lb/in3 and 0.0779 lb/in3, respectively.
Once the foregoing parameters are determined for the 2s steel and composite layers and acceptable dimensions for the pipe 10 have been selected, the pipe 10 is manufactured for the most part in accordance with conventional composite/steel pipe manufacturing practice by manufacturing a circular tubular steel inner layer, and then applying to that steel layer an outer composite layer by known means. In an exemplary known means, the fibres of the composite are drawn s from a plurality of spools contained in a creel, are fed through gathering and aligning devices, through a bath of polyester resin, and onto the outside surface of the metal layer. While the above is a suitable means of attaching the composite to the steel layer, any suitable known means for to attaching the composite may be alternatively used, so long as continuous contact is maintained between the composite and steel layers when the pipe 10 is subjected to axial, compressive and radial stresses, and so long as that under such stresses, the steel and composite layers 12, 14 will i5 strain at the same rate and by the same amount.
Referring to Figure 5, it can be seen that when the manufactured pipe is first pressurized to the maximum operating pressure of 2200 psi, the stress in the composite 20 layer is well below the composite design operating stress of 64 ksi, and the stress in the steel layer exceeds the steel design operating stress of 64 ksi. This is because the steel and composite layers are in continuous contact and will have the same strain for a given internal pressure. As the elastic 2s modulus of the steel is significantly higher than that of the composite, the steel will bear a higher amount of stress than the composite for a given strain. For the steel and composite layers to be at their respective design operating stresses when the pipe is at the maximum operating pressure, the stress distribution between the steel and composite layers at the maximum operating pressure must be changed. This is achieved s by stressing the steel beyond its yield stress so that the steel is plastically deformed. This overstressing of the steel may be effected by autofrettaging the pipe during a field hydrostatic pressure test, i.e. by pressurizing the pipe beyond the maximum operating pressure to a selected io autofrettage pressure.
In a conventional field hydrostatic pressure test, a portion of a field-installed pipeline is pressurized with water to a selected pressure. Evidence of leakage is then is monitored; leakage is particularly prevalent around the weld seams between pipe sections but may occur anywhere on the pipe wall that experiences a failure. If no leakage occurs, then the pipeline portion has passed the pressure test.
2o Autofrettage is the application of hydrostatic pressure wherein the steel layer is stressed beyond its specified minimum yield stress. Generally accepted industry practice recommends that the autofrettage pressure not exceed a level that would cause the wall of the pipe to be stressed beyond 2s 110% of the steel's SMYS. An effect of pressure testing conventional all-steel pipes between 100-110% of the steel's yield stress is that the steel wall will experience some plastic deformation. As illustrated in Figure 3, when plastically deformed, the elastic range of the steel is increased. Referring to Figures 5 and 6, plastically deforming the steel in the steel-composite pipe will impart a s compressive stress in the steel layer and a tensile stress in the composite layer, thereby changing the stress distribution between the respective layers when the pipe is re-pressurized.
It can be seen that when the pipe is re-pressurized to to the maximum operating pressure, the stress distribution between the steel and composite layers is different than that before autofrettaging. To achieve the desired stress distribution, namely, that distribution wherein the steel layer and composite layers are at their respective design 15 operating stresses, the steel is plastically deformed by an amount that will locate line II-III in Figure 6 so that it passes through a point corresponding to the steel design operating circumferential stress at the operating strain.
2o Once the appropriate amount of plastic deformation has been determined, an appropriate autofrettage pressure that will effect the appropriate plastic deformation must be determined. This is determined by mathematically modelling the stress-strain curves of steel and composite, and the 2s pressure-strain curve of the pipe 10. Using Figure 6 to illustrate, the stress-strain curves of the steel and composite may be modelled using a combination of the Ramberg-Osgood equation and linear equations:
For line I-II:
(equation 5) steel f~ ( steel' n steel L.' pY F
steel Y
Where Eateei is the steel' strain s ~ateel 1.S the steel' stress s EHceei is the steel' Elastic Modulus s F
a =0.05-- y py E
steel to FY is the steel's effective specified minimum yield strength according to CAN/CSA 2662-96.
18.5 for X-80 - X-100 grade steel and 17.5 for X-70 grade steel for line II-III
+b (equation 6) steel steel steel At line B, the steel is at its operating stress and strain.
cs =c3°p =F ~s (elation 7) steel steel y steel 2o Where SHteel 1S the steel design stress percentage. The strain of the steel layer and composite layer at the operating strain are the same:
s UTS (equation 8) fop -fop comp comp steel comp $
comp Where S~omp UTScomp and Eoomp are the composite design stress s percentage, ultimate tensile strength and Elastic Modulus, respectively.
Then, at operating conditions, (equation 9) b=S F - steel ~ S . UTS ) steel y F comp comp comp to At the autofrettage strain (Line A) (equation 10) 1 c c~'' -b >
steel E steel steel and (equation 11) 1 ( ~5p __b' - «steel +~ ( (3steel' n steel E' PY F
steel steel y i5 Solving for 'SHteei at line A provides the maximum allowable stress of the steel, i.e. the steel autofrettage stress:
(equation 12) -b c5A =F ~ ) 1 / n steel y g $
py steel 2a With the steel autofrettage stress, the autofrettage strain may be readily determined. Then, the appropriate autotrettage pressure can be readily determined from equation 1. Figures and 6 illustrate the steel and composite stress-strain s curves and pressure-strain for the first and second boundary thickness combinations having an appropriate degree of plastic strain.
The last step of the method of the invention is to io autofrettage the pipe 10 at the above determined autof rettage pressure. The resultant steel-composite pipe 10 will be able to operate at a higher internal pressure than a conventional all-steel pipe having a wall thickness equal to the thickness of the steel layer of the steel-composite pipe. The composite layer bears a proportion of the load caused by the internal pressure; in the all-steel pipe, this load must be borne entirely by the steel wall. Therefore, maximum operating pressures of a steel-composite pipeline can be increased beyond those presently specified for conventional all-steel 2o pipelines, thereby increasing the flow rate of gas and profitability of the steel-composite pipeline.
Other alternatives and variants of the above described methods and apparatus suitable for practising the methods will 2s occur to those skilled in the technology. For example, aluminum may be substituted for the material for the inner layer if a lighter overall weight is desired. Other alternative materials for the inner layer include stainless steel or titanimum. Carbon fibre or other materials may be substituted for the E-glass fibres to enhance the modulus of the composite, increase the composite's operating stress, or s provide enhanced corrosion resistance. The scope of the invention is as defined in the following claims.
Claims (30)
1. A method of manufacturing a circular cylindrical metal-composite pipe of selected inner diameter for operation at a selected maximum internal operating pressure; said steel-composite pipe having an inner steel layer and an outer composite layer wrapped in continuous contact around the steel layer, the method comprising (a) manufacturing an inner metal layer from suitable selected metal material and conforming to selected metal layer parameters;
(b) manufacturing and applying to the metal layer an outer composite layer of suitable selected composite material and conforming to selected composite layer parameters;
the selected parameters including at least the thickness and strength of the respective layers, the thicknesses and strengths of the respective layers being selected so that at a maximum internal operating pressure after a selected plastic deformation of the metal layer, the circumferential stresses in the metal-composite pipe are desirably distributed such that the composite layer is around or below a composite design operating stress and the metal layer is around or below a steel design operating circumferential stress, and (c) plastically deforming the metal layer at a selected autofrettage pressure to obtain the desired stress distribution between the metal and composite layers when the pipe is at the maximum internal operating pressure.
(b) manufacturing and applying to the metal layer an outer composite layer of suitable selected composite material and conforming to selected composite layer parameters;
the selected parameters including at least the thickness and strength of the respective layers, the thicknesses and strengths of the respective layers being selected so that at a maximum internal operating pressure after a selected plastic deformation of the metal layer, the circumferential stresses in the metal-composite pipe are desirably distributed such that the composite layer is around or below a composite design operating stress and the metal layer is around or below a steel design operating circumferential stress, and (c) plastically deforming the metal layer at a selected autofrettage pressure to obtain the desired stress distribution between the metal and composite layers when the pipe is at the maximum internal operating pressure.
2. The method as claimed in claim 1 wherein the metal is steel having a steel design operating circumferential stress that is a specified steel design stress percentage of the steel's specified minimum yield strength.
3. The method as claimed in claim 2 wherein the composite design operating stress is a specified composite design stress percentage of the composite's ultimate tensile strength.
4. The method as claimed in claim 3 wherein the mass of a unit length of the steel-composite pipe is less than or equal to the mass of a unit length of an all-steel pipe having the same steel grade, inner diameter, and the maximum operating pressure as the steel-composite pipe.
5. The method as claimed in claim 4 wherein the autofrettage pressure stresses the steel layer of the steel-composite pipe between 100% and 110% of the steel's specified minimum yield strength.
6. The method as claimed in claim 5 wherein the thickness of the steel layer is selected so that the axial stress in the steel layer is at or below a selected steel design operating axial stress when the pipe is pressurized at the maximum internal operating pressure.
7. The method as claimed in claim 5 wherein the thickness of the steel layer is selected so that the steel layer will not yield when an internal pressure equal to the maximum operating pressure is fully borne by the steel layer.
8. The method as claimed in claim 5 wherein the material of the steel layer is selected from one of X-70, X-80, X-90, X-100 grade steel.
9. The method as claimed in claim 1 wherein the metal is one of aluminum or titanium.
10. The method as claimed in claim 5 wherein the composite layer is comprised of a plurality of circumferential unidirectional non-metallic fibres encased in a resin.
11. The method as claimed in claim 10 wherein the composite layer comprises E-glass.
12. A circular cylindrical metal-composite pipe of selected inner diameter for operation at a selected maximum internal operating pressure; the metal-composite pipe comprising an inner metal layer made of a selected metal material and conforming to selected metal layer parameters; and an outer composite layer wrapped in continuous contact around the metal layer and made of a selected composite material and conforming to selected composite layer parameters;
the selected parameters including at least the thickness and strength of the respective layers, the thicknesses and strengths of the respective layers being selected so that at a maximum internal operating pressure and after plastically deforming the metal layer at a selected autofrettage pressure, the circumferential stresses in the metal-composite pipe are distributed such that the composite layer is around or below a composite design operating stress and the metal layer is around or below a metal design operating circumferential stress.
the selected parameters including at least the thickness and strength of the respective layers, the thicknesses and strengths of the respective layers being selected so that at a maximum internal operating pressure and after plastically deforming the metal layer at a selected autofrettage pressure, the circumferential stresses in the metal-composite pipe are distributed such that the composite layer is around or below a composite design operating stress and the metal layer is around or below a metal design operating circumferential stress.
13. The metal-composite pipe as claimed in claim 12 wherein the metal is steel having a steel design operating circumferential stress that is a specified steel design stress percentage of the steel's specified minimum yield strength.
14. The steel-composite pipe as claimed in claim 13 wherein the composite design operating stress is a specified composite design stress percentage of the composite's ultimate tensile strength.
15. The steel-composite pipe as claimed in claim 14 wherein the mass of a unit length of the steel-composite pipe is less than or equal to the mass of a unit length of an all-steel pipe having the same steel grade, inner diameter, and maximum operating pressure as the steel-composite pipe.
16. The steel-composite pipe as claimed in claim 15 wherein the autofrettage pressure stresses the steel layer of the steel-composite pipe between 100 and 110% of the steel's specified minimum yield strength.
17. The steel-composite pipe as claimed in claim 16 wherein the thickness of the steel layer is selected so that the axial stress in the steel layer is at or below a selected steel design operating axial stress when the pipe is pressurized at the maximum internal operating pressure.
18. The steel-composite pipe as claimed in claim 16 wherein the thickness of the steel layer is selected so that the steel layer will not yield when an internal pressure equal to the maximum operating pressure is fully borne by the steel layer.
19. The steel-composite pipe as claimed in claim 13 wherein the material of the steel layer is one of X-70, X-80, X-90 or X-100 grade steel.
20. The metal-composite pipe as claimed in claim 12 wherein the metal is one of aluminum or titanium.
21. The steel-composite pipe as claimed in claim 12 wherein the composite wall layer comprises a plurality of circumferential, unidirectional non-metallic fibres encased in a resin.
22. The pipe as claimed in claim 21 wherein the material of the composite wall layer comprises E-glass.
23. A method of manufacturing a circular cylindrical steel-composite pipe of selected inner diameter for operation at a selected maximum internal operating pressure; said steel-composite pipe having an inner steel layer and an outer composite layer wrapped in continuous contact around the steel layer, the method comprising (a) manufacturing an inner steel layer from suitable selected steel material and conforming to selected steel layer parameters;
(b) manufacturing and applying to the steel layer an outer composite layer of suitable selected composition and conforming to selected composite layer parameters;
the selected parameters including at least the thickness and strength of the respective layers, wherein the thickness and strength of the steel layer are selected so that when a maximum operating pressure is fully borne by the steel layer, the steel layer does not yield, and the thickness and strength of the composite layer are selected so that when the maximum operating pressure is borne by both the steel and composite layers after the steel layer has been selectively plastically deformed, the steel and composite layers are in the vicinity of their respective design operating stresses, (c) plastically deforming the steel layer at a selected autofrettage pressure to obtain the desired stress distribution between the steel and composite layers.
(b) manufacturing and applying to the steel layer an outer composite layer of suitable selected composition and conforming to selected composite layer parameters;
the selected parameters including at least the thickness and strength of the respective layers, wherein the thickness and strength of the steel layer are selected so that when a maximum operating pressure is fully borne by the steel layer, the steel layer does not yield, and the thickness and strength of the composite layer are selected so that when the maximum operating pressure is borne by both the steel and composite layers after the steel layer has been selectively plastically deformed, the steel and composite layers are in the vicinity of their respective design operating stresses, (c) plastically deforming the steel layer at a selected autofrettage pressure to obtain the desired stress distribution between the steel and composite layers.
24. The method as claimed in claim 23 wherein the steel design operating circumferential stress is a specified steel design stress percentage of the steel's specified minimum yield strength.
25. The method as claimed in claim 24 wherein the composite design operating stress is a specified composite design stress percentage of the composite's ultimate tensile strength.
26. The method as claimed in claim 25 wherein the mass of a unit of length of the steel-composite pipe is less than or equal to the mass of a unit of length of an all-steel pipe having the same inner diameter, and maximum operating pressure as the steel-composite pipe.
27. The method as claimed in claim 26 wherein the autofrettage pressure stresses the steel layer of the steel-composite pipe between 100% and 110% of the steel's specified minimum yield strength.
28. The method as claimed in claim 27 wherein the material of the steel layer is selected from one of X-70, X-80, X-90, X-100 grade steel.
29. The method as claimed in claim 27 wherein the composite layer is comprised of a plurality of circumferential unidirectional non-metallic fibres encased in a resin.
30. The method as claimed in claim 29 wherein the composite layer comprises E-glass.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002286956A CA2286956A1 (en) | 1999-10-18 | 1999-10-18 | Steel-composite pipe apparatus and method of manufacturing same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002286956A CA2286956A1 (en) | 1999-10-18 | 1999-10-18 | Steel-composite pipe apparatus and method of manufacturing same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2286956A1 true CA2286956A1 (en) | 2001-04-18 |
Family
ID=4164434
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002286956A Abandoned CA2286956A1 (en) | 1999-10-18 | 1999-10-18 | Steel-composite pipe apparatus and method of manufacturing same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2286956A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110173598A (en) * | 2019-05-14 | 2019-08-27 | 西南交通大学 | A kind of structure of high bearing composite material pipeline |
| CN112066099A (en) * | 2020-09-25 | 2020-12-11 | 朱永德 | Steel band reinforcing PVC pipe |
| CN113007461A (en) * | 2021-03-10 | 2021-06-22 | 北京玻钢院复合材料有限公司 | High-sealing composite material high-pressure pipeline and processing method thereof |
-
1999
- 1999-10-18 CA CA002286956A patent/CA2286956A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110173598A (en) * | 2019-05-14 | 2019-08-27 | 西南交通大学 | A kind of structure of high bearing composite material pipeline |
| CN112066099A (en) * | 2020-09-25 | 2020-12-11 | 朱永德 | Steel band reinforcing PVC pipe |
| CN113007461A (en) * | 2021-03-10 | 2021-06-22 | 北京玻钢院复合材料有限公司 | High-sealing composite material high-pressure pipeline and processing method thereof |
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