WO1994010492A1

WO1994010492A1 - Improved offshore umbilical and method of forming an offshore umbilical

Info

Publication number: WO1994010492A1
Application number: PCT/US1993/010003
Authority: WO
Inventors: Kevin Gendron
Original assignee: Kevin Gendron
Priority date: 1992-10-26
Filing date: 1993-10-26
Publication date: 1994-05-11
Also published as: AU5364594A

Abstract

An improved offshore umbilical (15) is provided which includes one or more continuously longitudinally welded, alloyed or unalloyed titanium flow conduits (35-51) which provide a low density, high strength-to-weight ratio material which is substantially inert in sea water as well as common performance enhancing chemicals.

Description

Improved Offshore Umbilical And Method Of Forming An Offshore Umbilical

Technical Field

The present invention relates generally to control umbilicals and specifically to offshore control umbilicals for transporting fluid and communicating control signals between first and second offshore sites.

Background Art

The use of an umbilical is a convenient way of bundling multiple lines, rather than simply installing a multitude of individual parallel conduits. Umbilicals comprised of multiple lines in a bundled configuration are currently used offshore in oil and gas drilling and production systems to transport hydraulic fluids and electrical signals over long distances for control systems, to transport injection fluids used to facilitate drilling, production, and workover operations, and for well monitoring activities. Conventional umbilicals consist of an array of thermoplastic hoses cabled together and protected by an outer plastic jacket and/or metal armoring.

Umbilical applications can be divided into two primary categories: drilling and production. In subsea drilling systems, umbilicals are used to control blow- out prevention equipment located on the seabed. Since these blow-out prevention stacks only see short term continuous usage (typically about 3 months) drilling umbilicals do not have to be designed for long periods of continuous service. Most subsea drilling is performed in water of depths less than 5,000 feet, which limits required umbilical length since the umbilical is typically strapped to the outside of the drilling riser connecting the surface vessel to the seabed. Depending on water depth, drilling umbilicals may be subjected to significant dynamic loading. This loading is created by current and wave loads on the umbilical and by movement of the drilling vessel caused by current, wind, and wave forces. Control systems used in drilling applications typically include hydraulic signals at an operating pressure of 10 or 20 MPa (1,500 or 3,000 psi) .

Umbilicals used in production applications often are subject to more demanding design requirements. Offshore production systems typically require a design life of at least 20 years, with little opportunity for significant maintenance. The umbilicals often connect a subsea installation to a remote production and control center located many miles away, thus creating the need for very long umbilical lengths. Production system umbilicals transport hydraulic fluid for direct control systems or piloted hydraulic control systems and hydraulic fluid and electrical signals for multiplex control systems. In each case, other lines may provide conduits for chemical injection and/or pressure monitoring.

Production system umbilicals are used in both static loading and dynamic loading applications. Umbilicals between subsea installations and floating vessels are dynamic, subjected to many load cycles. Umbilicals laid with pipelines or tying flowlines to fixed platforms are relatively static, with less significant cyclic loading. Conventional umbilicals are limited by problems inherent to their thermoplastic conduits. The most significant of these problems are:

(1) permeation of contaminants through thermoplastic conduits and contamination of the fluid contained therein;

(2) chemical incompatibility with fluids and/or gasses either internal or external of thermoplastic conduits which are in contact with the thermoplastic and eventual erosion of thermoplastic conduits;

(3) an undesirably lengthy amount of the time required to transmit hydraulic control signals in thermoplastic conduits;

(4) size limitations on thermoplastic conduits which results from strength limitations of thermoplastic material;

(5) the limited collapse resistance of thermoplastic conduits; and

(6) the limited temperature range of thermoplastic conduits.

Fluids injected through flowlines in umbilicals (such as methanol) frequently degrade the thermoplastic lines over a period of time, eventually migrating through their wall section and potentially contaminating other lines. This phenomenon is usually caused by a combination of chemical attack on the thermoplastic hose and diffusion of the fluid through the porous thermoplastic material.

The lack of stiffness and strength of thermoplastic hose results in significant expansion of the hose when subjected to fluid pressure. This hose expansion combined with intrinsic thermoplastic material properties causes long response times for traveling hydraulic signals. The long response time frequently causes designers of control systems to specify a piloted hydraulic system or multiplex system (that is, a combination hydraulic and electrical control system) in lieu of a less expensive direct hydraulic control system when the umbilical length exceeds several thousand feet. Lags in response time due to characteristic changes in hoses cause slow response of well control equipment, which in turn can damage the well control equipment and cause serious safety issues. The lack of strength and stiffness of thermoplastic lines also results in a lack of significant resistance to hydrostatic collapse when subjected to external pressure.

Strength limitations of thermoplastic hoses limit the sizes of hoses available for use at certain pressures. For example, thermoplastic hoses rated to 52 MPa (7,500 psi) to control surface-controlled subsurface safety valves are typically limited in interior diameter size to about 6.35 mm (.25 inches). In such high- pressure applications these size limitations restrict obtainable flowrate, further effecting response time. The problems with thermoplastic umbilicals have been consistently cited for years in the offshore industry, creating the need for alternative umbilical designs. Several companies are currently developing umbilicals with steel and stainless steel conduits as an alternative to thermoplastic hoses. The greater strength and stiffness of metal lines significantly decreases response time and increases collapse resistance.

But the use of steel and stainless steel lines creates potential corrosion and contamination problems due to the effects of long-term exposures to seawater, water-based control fluids, and chemical injection fluids. Their greater stiffness and weight, compared to thermoplastic lines, also create handling, shipping, and installation difficulties. Disclosure of the Invention

It is one objective of the present invention to provide an offshore umbilical which includes fluid flow conduits which provide a low density, high strength-to- weight ratio fluid flow path which does not interfere with the transmission of hydraulic control signals through fluid contained therein, which is not subject to deterioration due to exposure to seawater or performance-enhancing chemicals, but which is sufficiently elastic to allow transportation and storage of the offshore umbilical in a spool.

It is a specific objective of the present invention to provide an offshore umbilical which includes one or more fluid flow conduits which are formed of alloyed or unalloyed titanium which define a single uninterrupted conduit which allows the communication of fluid between first and second offshore sites.

It is yet another objective of the present invention to provide an offshore umbilical which includes a plurality of fluid flow conduits which are formed of alloyed or unalloyed titanium which are sufficiently inert to seawater to allow for long-term communication of fluid between first and second offshore sites even though the outermost surfaces of the fluid flow conduits are exposed to seawater.

These and other objectives are achieved as is now described. An offshore umbilical is provided for extending between first and second offshore sites, which allows for the selective communication of fluid and/or hydraulic control signals between the first and second offshore sites. In the preferred embodiment, the offshore umbilical includes a plurality of fluid flow conduits, at least one of which is formed from alloyed or unalloyed titanium, and a bundling member for maintaining the plurality of fluid flow conduits in substantially fixed positions relative to a central axis. The bundling member may extend continuously over the plurality of fluid flow conduits between the first and second offshore sites, or may be provided at selected locations between the first and second sites. For example, the bundling member may comprise a jacket which extends continuously between the first and second sites, or jacket segments which surround selected portions of the plurality of fluid flow conduits between the first and second sites, at selected locations. The bundling member may also comprise a spreader bar which holds the plurality of fluid flow conduits in relative parallel fixed positions. Of course, the offshore umbilical may be provided in a variety of shapes, including circular and rectangular shapes.

In an alternative embodiment, an offshore umbilical is provided which extends between first and second offshore sites. The offshore umbilical includes a plurality of alloyed or unalloyed titanium fluid flow conduits which are formed in a helical pattern about a foundation member, and which are self-sustained in a fixed position relative thereto, thus not requiring the use of a bundling member to hold the array of fluid flow conduits in a fixed position. The present invention may also be characterized as a method of communicating fluids between first and second offshore sites, which includes a number of method steps. At least one continuous tubular member is provided which is formed for alloyed or unalloyed titanium. This continuous tubular member is extended between first and second offshore sites. Fluid is passed through the continuous tubular member between the first and second offshore sites. The offshore umbilical may be formed by a method which includes a number of steps. At least one continuous strip of alloyed or unalloyed titanium is provided. The at least one continuous strip of alloyed or unalloyed titanium is bent into at least one tubular shape. The continuous strip of alloyed or unalloyed titanium is longitudinally welded to define at least one uninterrupted tubular member. The tubular member may be jacketed and combined with other tubular members, and spooled for storage and transportation.

Additional objectives, features and advantages will be apparent in the written description which follows.

Description of the Drawings

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

Figure 1 is a perspective view of an offshore umbilical extended between offshore sites;

Figure 2 is a perspective view of an array of fluid flow conduits connecting an offshore site to other offshore sites;

Figures 3a and 3b depict one embodiment of the preferred offshore umbilical of the present invention;

Figures 4a and 4b depict another embodiment of the preferred offshore umbilical of the present invention; Figures 5a and 5b depict yet another embodiment of the preferred offshore umbilical of the present invention;

Figures 6a and 6b depict still another embodiment of the preferred offshore umbilical of the present invention; Figures 7a and 7b depict yet another embodiment of the preferred offshore umbilical of the present invention;

Figures 8a and 8b depict still another embodiment of the preferred offshore umbilical of the present invention;

Figure 9 depicts one technique for forming titanium fluid flow conduits; and

Figure 10 depicts in plan view, a manufacturing assembly for producing offshore umbilicals according to the present invention.

Description of the Invention

Titanium alloys provide a unique combination of properties and attributes that are very attractive for offshore flowline and umbilical applications. These characteristics include:

(1) density of about half that of steels;

(2) modulus of elasticity of about half that of steels; (3) strengths equal to or greater than steels;

(4) corrosion and erosion resistance superior to steels; and

(5) seawater fatigue resistance greater than steels. Titanium is commercially available in a variety of ASTM grades. Four of these grades are considered "commercially pure". The remaining grades are considered to be alloyed titanium. In the present invention, it is contemplated that ASTM Grades 2, 9, and 12 are most likely to be used, although the invention contemplates the use of any type of alloyed or unalloyed titanium to form a fluid flow conduit in an offshore control umbilical.

Generally speaking titanium and its alloys have a density which is approximately 55% that of steel, resulting in a weight of approximately one-half that of steel. More specifically, titanium and its alloys have a density of about 4.4 g/mL (0.16 pounds per cubic inch) , as compared to oil field grade steels which generally have a density of about 7.8 g/mL (0.283 pounds per cubic inch) . Titanium and its alloys generally have a low modulus of elasticity as compared to steel. Specifically, titanium and its alloys have a modulus of elasticity of about 103 GPa (15,000,000 pounds per square inch) , as compared to the modulus of elasticity for oil field grade steels which is approximately 207 GPa (30,000,000 pounds per square inch). The result is that fluid flow conduits which are formed from titanium and its alloys are very flexible as compared to steel.

While titanium and its alloys are less dense than steel, and more flexible than steel, titanium and its alloys have a strength which at least partially overlaps the range of strengths found in standard oil field grade steels. More specifically, titanium and its alloys have a yield strength in the range of 27.6 MPa to 1,379 MPa

(40,0000 pounds per square inch to 200,000 pounds per square inch) . In contrast, standard oil field grade steels have strengths in the range of 27.6 MPa to 1,241

MPa (40,000 pounds per square inch to 180,000 pounds per square inch) . Thus, the use of titanium to provide fluid flow conduits in an offshore umbilical results in flow conduits which have strengths which are comparable to those found in standard oil field grade steels.

Titanium and its alloys are also quite corrosion and erosion resistant. Specifically, titanium and its alloys are substantially inert in seawater. In contrast, standard oil field grade steels are very easily degraded in seawater. Titanium and its alloys is also substantially inert to water-based or oil-based hydraulic fluids which are commonly used in the industry to communicate control signals between the first and second offshore sites. Furthermore, titanium and its alloys are substantially inert to most common performance-enhancing chemicals which may be injected during the drilling and/or production of subsea wells. The common chemicals include hydrated methanol, and many fracturing fluids, acids, corrosion inhibitors, paraffin modifiers, and emulsifiers. Certain titanium alloys are somewhat reactive with anhydrous methanol, but this does not present a problem since hydrated methanol is commonly used as a performance enhancing chemical. Therefore, fluid flow conduits formed from titanium and its alloys are substantially inert to most fluids which are likely to come into contact with an offshore umbilical during drilling, production, and workover operations.

Titanium conduits provide an offshore umbilical with the significant advantages inherent with the use of metal in lieu of thermoplastic materials, such as greater strength, increased stiffness, greatly improved response times, increased collapse resistance, reduced susceptibility to damage, and elimination of fluid permeation problems. In addition, the superior corrosion resistance of titanium lines compared to steel, stainless steel, and thermoplastic lines in a marine environment increases reliability and service life. Using titanium also eliminates the need to rely on expensive coatings on the exterior surface of steel lines to protect against corrosion and surface treatments on the interior surface of steel lines to minimize fluid contamination due to scaling. Titanium lines eliminate thermoplastic hose contamination problems caused by leeching of thermoplastic particles into the transported fluid. The greater flexibility and lighter weight of titanium flowlines compared to steel and stainless steel lines, due to titanium's lower modulus of elasticity and density, will provide significant advantages during installation, storage, and shipping. The weight of a titanium flowline could be less than one-third the weight of an equivalent steel line, due to lower density, elimination of wall thickness corrosion allowances, and potential increases in strength. Although the greater flexibility of titanium flowlines for umbilicals compared to steel lines may increase response time, the reduction in response time with titanium lines compared to thermoplastic hoses will be far greater than the difference in the response times of the metal lines. The greater flexibility, combined with a greater fatigue strength, will also enable the titanium lines to withstand dynamic loading with less detrimental fatigue damage.

In summary, the advantages of titanium flowlines over existing thermoplastic lines are:

(1) faster response times for hydraulic control signals;

(2) high-pressure capabilities at larger diameters;

(3) no fluid permeation and contamination; (4) superior chemical injection fluid compatibility;

(5) higher cleanliness level on the interior surface;

(6) greater collapse resistance;

(7) less susceptibility to damage;

(8) greater reliability; (9) longer service life; and

(10) wider temperature range capabilities.

The advantages of titanium flowlines over steel and stainless steel flowlines currently being developed are: (1) superior corrosion resistance on the interior and exterior surfaces without coatings; (2) higher cleanliness level on the interior surface;

(3) lighter weight and greater flexibility;

(4) easier to reel, transport, and install;

(5) lower dynamic stress; (6) greater reliability; and (7) longer service life.

The purpose of offshore umbilicals is to allow for the communication of hydraulic control signals and/or performance enhancing chemicals and/or electrical power and control signals between a plurality of offshore sites. For purposes of this patent application, "offshore sites" is intended to comprehend all types of above-surface and below-surface marine equipment, as well as shoreline equipment, including but not limited to: platforms, wellheads, pipelines, valve assemblies (such as Christmas trees) , drilling templates, production templates, manifolds, blow-out prevention equipment, shoreline valving, shoreline oil and gas storage and processing facilities, and shoreline safety equipment.

As is shown in Figure 1, offshore umbilical 15 may extend between first offshore site 11 and second offshore site 13 to allow for the communication of hydraulic control signals through a hydraulic data communication medium, electrical control signals through electrical conductors, and performance-enhancing fluids through fluid flowlines. Figure 1 depicts the extension of offshore umbilical 15 between platform 11 and production template 13. In the view of Figure 1, offshore umbilical 15 comprises a bundled offshore umbilical which includes a plurality of fluid flow conduits and electrical conductors, which are jacketed continuously between first offshore site 11 and second offshore site 13. In contrast, in Figure 2, conduit array 19 is depicted as extending from offshore site 17 to a remote (but undepicted) offshore site. As is shown, conduit array 19 is composed of a plurality of fluid flow conduits which are disposed in substantially parallel alignment, and which are not "bundled" as is offshore umbilical 15 of Figure l. A spreader bar, such as that depicted in Figures 8a and 8b, or other means, is provided to hold the conduit array 19 in alignment to prevent the lines from becoming damaged by repeated contact with one another as wave and current forces act upon conduit array 19.

A typical nine-line umbilical with electrical lines is shown in Figures 3a and 3b. This umbilical has a central titanium conduit around which the other lines are cabled. As shown in Figures 4a and 4b, all titanium lines could be cabled around a central member (of another material) which may encapsulate electrical lines. In either case, the resulting array of titanium tubes could be surrounded by a plastic jacket to assist in holding the titanium lines in a tight bundle. In all embodiments, the individual titanium flowlines would be sized to meet pressure and flowrate requirements. In the embodiments shown, all titanium lines are 12.7 mm (0.5 inch) outer diameter tubing with a wall thickness of .889 mm (.035 inches), rated to 34 MPa (5,000 psi) working pressure. In the preferred embodiment, the tubes are fabricated from ASTM Grade 12 titanium, having a minimum yield strength of 379 MPa (55 ksi) in the annealed condition, with a typical cold- worked strength of 483 MPa (70 ksi) . Other titanium grades such as Grade 2 and Grade 9 could be used, depending on strength and corrosion requirements.

Figures 3a and 3b depict one embodiment of the preferred offshore umbilical of the present invention, with Figure 3a providing a perspective view, and Figure 3b providing a cross-section view. As is shown, offshore umbilical 21 includes central conduit 23, which is preferably formed of alloyed or unalloyed titanium, and which includes interior surface 25 which defines a fluid flow conduit which may be used either for communicating performance enhancing chemicals to a remote location, or transmitting hydraulic control signals through a fluid contained therein. As is shown in Figure 3a, central axis 27 is defined with regard to central conduit 23. A plurality of insulated electrical conductors, such as insulated electrical conductors 31, 33, may be provided about central conduit 23. Spacers 29 may be employed to fill in the space between insulated electrical conductors. Interior jacket 35, which is preferably formed of a plastic or thermoplastic material, surrounds insulated electrical conductors 31, 33, spacers 29, and central conduit 23. Interior jacket 35 may be formed of plastic or metal. As is also shown in Figures 3a and 3b, a plurality of fluid flow conduits, such as fluid flow conduits 37, 39, 41, 43, 45, 47, 49, and 51 surround interior jacket 35, and are disposed in a helical pattern relative to central axis 27 and interior jacket 35. One or more of these fluid flow conduits may be formed from alloyed or unalloyed titanium. Finally, outer jacket 53, which is preferably composed of a plastic such as thermoplastic, is disposed over the helical array of fluid flow conduits. In the preferred embodiment, as is conventional, outer jacket 53 is extruded in molten form over the helical array of fluid flow conduits. Outer jacket 53 serves to maintain the helical pattern of fluid flow conduits in a fixed position relative to central axis 27. The molten plastic or thermoplastic of outer jacket 53 also serves as a filler which eliminates voids between the plurality of fluid flow conduits. Considered broadly, inner jacket 35 and outer jacket 53 comprise a bundling member which maintains the plurality of fluid flow conduits and insulated electrical conductors in fixed relative positions, and which eliminates voids between the plurality of fluid flow conduits and insulated electrical conductors.

Figures 4a and 4b provide a view of an alternative embodiment of the preferred offshore umbilical of the present invention, with Figure 4a providing a perspective view, and Figure 4b providing a cross- section view. As is shown, offshore umbilical 55 includes insulated electrical conductors 57, 59, and spacer 61 which are centrally disposed within offshore umbilical 55. Strapping 63 is provided about insulated electrical conductors 57, 59 and spacer 61 to hold them together. Inner jacket 65 is disposed over strapping 63, and is preferably formed from extruded molten plastic, and in particular extruded molten thermoplastic which hardens about strapping 63, insulated electrical conductors 57, 59 and spacer 61, and defines a cylindrical central body, about which helical array of fluid flow conduits 67 is disposed. As is shown in Figure 4b, helical array of fluid flow conduit 67 includes fluid flow conduits 71, 73, 75, 77, 79, 81, 83, 85, and 87, with one or more of the fluid flow conduits being formed from alloyed or unalloyed titanium. Finally, outer jacket 69 is disposed about helical array of fluid flow conduits 67. Preferably, molten plastic or thermoplastic material is extruded about the outer surface of helical array of fluid flow conduit 67, and hardens to define a cylindrical outer surface. As is shown, the plastic or thermoplastic material fills voids in the helical array of fluid flow conduit 67, and overall serves to maintain all the components of the offshore umbilical 55 in relative fixed positions. The embodiments of Figures 3a, 3b, 4a, and 4b contemplate having an outer jacket which extends continuously between the first and second offshore sites. The embodiment which is shown in Figures 5a and 5b contemplates the use of a bundling member which is disposed at selected portions of the array of fluid flow conduits, but which allows exposure of the exterior surface of the helical array of fluid flow conduits to seawater. Figure 5a is a perspective view of this embodiment, while Figure 5b is a cross-section view of this embodiment.

With reference first to Figure 5a, offshore umbilical 89 includes insulated electrical conductors 91, 93 and spacer 95 which are surrounded by strapping 97. As is shown, inner jacket 99 surrounds insulated electrical conductors 91, 93, spacer 95, and strapping 97 and provides a cylindrical outer surface about which helical array of fluid flow conduits 101 is disposed. Preferably, inner jacket 99 is composed of a plastic or thermoplastic material which is extruded in molten form over strapping 97, and which hardens into a cylindrical shape which holds insulated electrical conductors 91, 93, and spacer 95 in a fixed position with respect to central axis 127. Preferably, one or more of the fluid flow conduits in helical array of fluid flow conduits 101 is formed of alloyed or unalloyed titanium. A plurality of bundling members, such as bundling members 103, 105 surround selected portions of the helical array of fluid flow conduits 101 at selected locations, and holds them together in a fixed position relative to central axis 127. In this embodiment, each of fluid flow conduits 107, 109, 111, 113, 115, 117, 119, 121, and 123 of helical array of fluid conduits 101 are exposed to seawater. Bundling members 103, 105 are disposed at selected positions between the first and second offshore sites and may be hundreds of feet apart. Bundling member 103, 105 may be formed of metal, plastic, or rubberized fabric, which is wrapped around a selected portion of the helical array of fluid flow conduits 101. Fasteners, such as fastener 125 which is depicted in Figure 5b, are used to secure the ends of the bundling members together.

Figures 6a and 6b depict still another embodiment of the preferred offshore umbilical of the present invention, with Figure 6a providing a perspective view, and with Figure 6b providing a cross-section view. As is shown in Figure 6a, offshore umbilical 129 includes insulated electrical conductor 131, insulated electrical conductor 133, and spacer 135 which are surrounded by strapping 137. As is shown, inner jacket 139 is disposed over strapping 137, insulated electrical conductors 131, 133, and spacer 135. Preferably, an inner jacket is formed from extruded molten plastic or thermoplastic which hardens in a cylindrical shape, and which holds insulated electrical conductors 131, 133, and spacer 135 in a fixed position relative to central axis 159. The outer cylindrical surface of inner jacket 139 provides a surface for receiving helical array of fluid flow conduits 141, which includes fluid flow conduit members 143, 145, 147, 149, 151, 153, 155, 157, and 159. Inner jacket 139 provides a foundation member about which the fluid flow conduits are wrapped. Preferably, each of the fluid flow conduits is formed from alloyed or unalloyed titanium, and is thus substantially insusceptible to corrosion from long exposure to salt water. It has been discovered that the helical array of fluid flow conduits which are formed from alloyed or unalloyed titanium does not need a bundling mechanism to maintain them in a tight helical arrangement about inner jacket 139. Therefore, no bundling mechanism, or plastic jacket is provided in this embodiment, and the helical array sustains itself in this configuration during normal use.

Still another embodiment of the preferred offshore umbilical of the present invention is depicted in Figures 7a and 7b, with Figure 7a providing a perspective view, and Figure 7b providing a cross- section view. As is shown, offshore umbilical 163 includes fluid flow conduits 165, 167, 169, and 171, one or more of which are formed from alloyed or unalloyed titanium. The fluid flow conduits are disposed in a single plane, and are encapsulated by rectangular plastic jacket 173 which is extruded over the fluid flow conduits in molten form, and which hardens into the rectangular shape shown in Figures 7a and 7b. This embodiment depicts an alternative geometry to the circular offshore umbilicals of the other embodiments.

Figures 8a and 8b depict yet another embodiment of the preferred offshore umbilical of the present invention. This embodiment corresponds to the system depicted in Figure 2, and is especially useful to provide a plurality of alloyed or unalloyed titanium fluid flow conduits which are held together with a selected spacing by a spreader bar. Figure 8a provides a perspective view, while Figure 8b provides a cross- section view. As is shown, alloyed or unalloyed titanium fluid flow conduits 175, 177, 179, and 181 are provided, and secured together in a desired spacing pattern by a plurality of spacers, such as first and second spacers 183, 185. The spacers may be provided at selected distances between the first and second offshore sites to maintain the array of alloyed or unalloyed titanium fluid flow conduits close together, but to prevent them from coming into repeated contact which may damage one or more of the fluid flow conduits. First spacer 183 is best depicted in the cross- section view of Figure 8b. As is shown, first spacer 183 includes rear plate 187 which includes a plurality of arcuate segments 189, 191, 193, 195, each of which is adapted to surround a selected portion of the alloyed or unalloyed titanium fluid flow conduits. A plurality of hinged arcuate segments 197, 199, 201, 203 are provided for surrounding another selected portion of the alloyed or unalloyed titanium fluid flow conduits. Hinges 205, 207, 209, and 211 are provided to allow arcuate segments 197, 199, 201, and 203 to be moved outward relative to rear plate 187. Pins 213, 215, 217, and 219 are provided to selectively secure arcuate segments 197, 199, 201, 203 in a fixed position relative to rear plate 187.

As is shown, first spacer 183, and the other spacers, operate to grip and hold each of the plurality of fluid flow conduits in a fixed position relative to every other one of the plurality of fluid flow conduits. Since the alloyed or unalloyed titanium fluid flow conduits are substantially inert in seawater, they will not degrade over extended periods of use. The spacers operate to maintain the fluid flow conduits in a tight configuration, while preventing undesirable physical contact between the fluid flow conduits which could damage or degrade the conduits over time as a result of wave or current forces.

The titanium flowlines may be manufactured using a continuous welding and spooling process, as shown in Figure 9. A power reel would be added to a conventional continuous welding tube mill, enabling long continuous lengths of titanium tubing (without circumferential seams) to be produced.

Prior art tube mills form titanium strip into a cylindrical configuration using a series of rollers, and then seam weld the tubing using arc welding methods. In the prior art, individual tubing lengths are typically produced, with the tubing automatically cut-off in 40 to 80 foot lengths as it comes off the mill. Also, in the prior art, stainless steel flowlines for umbilicals have been produced in long lengths by welding short sections of tubing together. These welds introduce potential weak spots in tubing, increasing risk. In the present invention a continuous welding and spooling process, like that currently used to fabricate steel coiled tubing for oilfield applications, eliminates a need for circumferential welds in the titanium tubing, decreasing overall costs and increasing reliability. The spooled titanium flowlines are fed individually, along with any electrical lines, into a conventional type of cabling machine, like those used to cable thermoplastic umbilicals or heavy wire rope (like that used in mooring lines) . Slight changes may need to be made to existing cabling equipment due to the greater forces required to helically form titanium flowlines than thermoplastic lines or steel wire. The cabled titanium flowline assembly is then fed into an extruder where a plastic jacket is formed around the tube bundle. This jacket can be made from different conventional jacket materials, depending on desired abrasion and corrosion properties.

Long lengths of umbilicals with titanium flowlines can be produced, with length limitations defined by shipping requirements. The lighter weight of titanium flowlines compared to steel lines facilitates shipment of longer umbilical lengths. The fabrication of the titanium tubing and the cabling could all be performed in a single manufacturing setup, potentially allowing for economic mass-production. Individual tubing mills could be setup in parallel, all feeding into a central cabling machine.

Figure 9 depicts one technique for forming titanium fluid flow conduits for use in the present invention. Figure 10 depicts, in plan view, a manufacturing assembly for producing offshore umbilicals with titanium flow lines according to the present invention. With reference first to Figure 9, there is depicted a continuous tube mill 251 which receives continuous titanium strip 253 from feed reel 255. Feed roller array 257 aligns the continuous titanium strip 253 before it is fed into bending arrays 259, 261, which include a plurality of rollers which serve to bend the continuous flat titanium strip 253 into a tubular shape. The tubular-shape titanium is fed into arch welding housing 263 which longitudinally welds the tubular- shaped titanium strip to form a continuous tubular member which is fed through output rollers 265 onto power reel 267. Power reel 267 is actuated by prime mover 269.

Titanium is a reactive metal, and thus must be welded in an inert environment. Preferably, arch welding housing 263 is filled with an inert gas, such as either argon gas or nitrogen gas, which displaces the oxygen within arc welding housing 263.

The continuously welded and spooled titanium tubing may be stored on power reel 267, which may be removed from prime mover 269. An empty reel may be placed on prime mover 269, for receipt of additional sections of continuously welded titanium tubing. Each reel may contain hundreds or thousands of feet of continuously longitudinally welded titanium tubing. When a sufficient amount of titanium tubing is obtained, they may be combined in an offshore umbilical according to the process which is depicted in plan view in Figure 10. As is shown in Figure ιo, feed reels 271, 273, 275 contain continuously longitudinally welded titanium tubing of preselected lengths. Feed reels 277, 279 contain insulated electrical conductors of preselected lengths. Insulated electrical conductors 301, 303 are combined and encapsulated in plastic at extruder 281. As is shown, the encapsulated insulated electrical conductors 301, 303, and continuously longitudinally welded titanium tubing members 305, 307, 309 are all routed to cabling apparatus 285 which helically winds the continuously longitudinally welded titanium tubing members 305, 307, 309 about encapsulated insulated electrical conductors 301, 303. The output 287 of cabling apparatus 285 is an array of alloyed or unalloyed continuously longitudinally welded and spooled titanium fluid flow conduits arranged in a helical pattern about encapsulated insulated electrical conductors 301, 303. This product may be used as an offshore umbilical (see the embodiment of Figure 6a and 6b) . Output 287 is spooled onto storage/feeder reel 289 for subsequent storage and/or transportation, or for subsequent encapsulation in a plastic or thermoplastic jacket.

If encapsulation is desired, output 287 is directed to jacket extruder 291 which receives molten thermoplastic material from reservoir 293 and extrudes it about the helical array of alloyed or unalloyed, continuously longitudinally welded titanium flow conduits jacket. Output 295 is directed to cooling bath 297 which cools the outer thermoplastic jacket before storage of the umbilical on storage reel 299.

In alternative embodiments, a plurality of binding members may be placed at selected locations along the length of the helical array of continuously longitudinally welded alloyed or unalloyed titanium flow conduits (such as depicted in Figures 5a and 5b) . In still another embodiment, a plurality of continuously longitudinally welded alloyed or unalloyed titanium tubing flow conduits may be fed into an assembly line where spreader bars, such as first and second spacers 183, 185 of Figure 8, are placed about the array to set the array in a predetermined spacing pattern. It is most probable that the placement of spacers is going to be performed on location at an offshore platform as the lines are fed into the sea.

While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.

Claims

1. An offshore umbilical (15) extending between first (11) and second (13) offshore sites, characterized in that: a plurality of fluid flow conduits (35-51) , at least one of which is formed from alloyed or unalloyed titanium; and a bundling member (53) for maintaining said plurality of fluid flow conduits in substantially fixed positions relative to a central axis (27) of the umbilical.

2. An offshore umbilical (15) extending between first (11) and second (13) offshore sites, characterized in that: a plurality of fluid flow conduits(37-51) , at least one of which is formed of a material:

(a) having a modulus of elasticity intermediate that of thermoplastic and steel;

(b) having a density of approximately half that of steel;

(c) having a yield strength range which at least partially overlaps that of steel; and (d) which is substantially inert in seawater; and thus provides a low density, high strength-to- weight ratio fluid flow conduit; and a bundling member maintains said plurality of fluid flow conduits in substantially fixed positions relative to a central axis (27) of the umbilical.

3. An offshore umbilical (15) extending between first (11) and second (13) offshore sites, comprising: a foundation member (23) for defining a central axis; a plurality of fluid flow conduits (37-51) , at least one of which is formed from alloyed or unalloyed titanium; and a bundling member (53) for maintaining said plurality of fluid flow conduits in substantially fixed positions about said central axis.

4. An offshore umbilical (15) extending between first (11) and second (15) offshore sites, comprising: a foundation member (23) for at least temporarily defining a central axis; a plurality of fluid flow conduits (37-51) , at least one of which is formed of a material:

(b) having a density of approximately half that of steel;

(c) having a yield strength range which at least partially overlaps that of steel; and (d) which is substantially inert in seawater; each thus providing a low density, high strength- to-weight ratio fluid flow conduit; and a bundling member (53) for maintaining said plurality of fluid flow conduits in substantially fixed positions relative to said central axis.

5. An offshore umbilical according to Claims 1, 2, 3, or 4, wherein said bundling member is further characterized as a jacket (53) which surrounds said plurality of fluid flow conduits.

6. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that said bundling member is a jacket (53) which extends continuously between said first and second offshore sites.

7. An offshore umbilical according to Claims 1, 2, 3, or 4 further characterized in that said bundling member is a jacket (103, 105) which surrounds only selected portions of said plurality of fluid flow conduits.

8. An offshore umbilical according to Claims 1, 2, 3, or 4 further characterized in that said bundling member is a jacket which surrounds only selected portions of said plurality of fluid flow conduits at selected locations.

9. An offshore umbilical according to Claims 1, 2, 3, or 4 further characterized in that said bundling member is a plastic jacket.

10. An offshore umbilical according to Claims 1, 2, 3, or 4 further characterized in that said bundling member is a thermoplastic jacket.

11. An offshore umbilical according to Claims 1, 2, 3, or 4 further characterized in that said bundling member substantially maintains said plurality of fluid flow conduits in a single plane.

12. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that a filler material (65) eliminates voids between said plurality of fluid flow conduits and said bundling member.

13. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that at least one insulated electrical conductor (43, 91) is carried in a fixed position relative to said plurality of fluid flow conduits for delivering electrical power between said first and second offshore sites.

14. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that at least one insulated electrical conductor (31) is secured by said bundling member to said plurality of fluid flow conduits for transmission of electrical control and data signals between said first and second offshore sites.

15. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that at least one of said plurality of fluid flow conduits defines a hydraulic control line for transmission of hydraulic control signals between said first and second offshore sites.

16. An offshore umbilical according to Claim 1, further characterized in that at least one of said plurality of fluid flow conduits defines a fluid injection line for delivery of performance enhancing fluids to a remote subsea site.

17. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that all of said plurality of fluid flow conduits are formed from alloyed or unalloyed titanium.

18. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that said plurality of fluid flow conduits are disposed in a helical arrangement about said central axis.

19. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that said at least one fluid flow conduit which is formed of alloyed or unalloyed titanium defines a low density, high strength- to-weight ratio fluid flow path.

20. An offshore umbilical according to Claim 1 or 3, further characterized in that said at least one fluid flow conduit which is formed of alloyed or unalloyed titanium: (a) has a modulus of elasticity intermediate of that of thermoplastic and steel;

(b) has a density of approximately half that of steel; and

(c) has a yield strength which at least partially overlaps that of steel.

21. An offshore umbilical according to Claims 1 or 3 further characterized in that said at least one of said fluid flow conduits which is formed of alloyed or unalloyed titanium includes at least one longitudinal weld.

22. An offshore umbilical according to Claims 1, 2, 3, or 4, which is operable in a plurality of modes including a storage mode of operation with said offshore umbilical being coiled about a spool.

23. An offshore umbilical according to Claims 1 or 3 further characterized in that said at least one of said fluid flow conduits which is formed of alloyed or unalloyed titanium defines a substantially continuous tubular conduit member which has a length sufficient to extend from said first offshore site to said second offshore site.

24. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that all of said plurality of fluid flow conduits are formed from a material: (a) having a modulus of elasticity intermediate that of thermoplastic and steel;

(b) having a density of approximately half that of steel;

(c) having a yield strength range which at least partially overlaps that of steel; and

(d) which is substantially inert in seawater; each thus providing a low density, high strength- to-weight ratio fluid flow conduit.

25. An offshore umbilical according to Claims 1, 2, 3, or 4, further characterized in that said plurality of fluid flow conduits each define a substantially continuous tubular conduit member which has a length sufficient to extend from said first offshore site to said second offshore site.

26. An offshore umbilical according to Claims 3 or 4, further characterized in that said foundation member comprises a tubular fluid flow conduit which is concentric to said bundling member.

27. An offshore umbilical according to Claims 3 or 4, further characterized in that said foundation member comprises a tubular fluid flow conduit which is formed of metal.

28. An offshore umbilical according to Claims 3 or 4, further comprising a filler material which eliminates voids between said foundation member, said plurality of fluid flow conduits, and said bundling member.

29. An offshore umbilical according to Claims 3 or 4, further characterized in that at least one insulated electrical conductor is disposed between said foundation member and said bundling member for delivering electrical power between said first and second offshore sites.

30. An offshore umbilical according to Claims 3 or 4, further characterized in that at least one insulated electrical conductor disposed between said foundation member and said bundling member for transmission of electrical control and data signals between said first and second offshore sites.

31. An offshore umbilical (15) between first (11) and second (13) offshore sites, characterized in that: a foundation member (23) ; a first fluid flow conduit (35) , which is formed from alloyed or unalloyed titanium; at least one additional fluid flow conduit (37) which is formed from alloyed or unalloyed titanium; and said first fluid flow conduit and said at least one additional fluid flow conduit being formed in a helical pattern about said foundation member and being self- sustained in a fixed position relative thereto.

32. A method of forming an offshore umbilical, characterized by the steps of: providing at least one continuous strip (253) of alloyed or unalloyed titanium; bending said at least one continuous strip of alloyed or unalloyed titanium into at least one tubular shape; longitudinally welding said at least one continuous strip of alloyed or unalloyed titanium to define at least one uninterrupted tubular member; and spooling, for storage and transportation, said offshore umbilical including said at least one uninterrupted tubular member.

33. A method of forming an offshore umbilical according to Claim 32, further characterized by the steps of: placing a jacket over at least selected portions of said at least one uninterrupted tubular member.

34. A method of forming an offshore umbilical according to Claim 32, further characterized by the method steps of: providing additional tubular members; and coupling, with a bundling member, said additional tubular member within a jacket with said at least one uninterrupted tubular member to define an offshore umbilical with a plurality of fluid flow paths.

35. A method of forming an offshore umbilical according to Claim 32, further characterized by the method step of positioning said at least one uninterrupted tubular member in a helical pattern about a central axis.

36. A method of forming an offshore umbilical according to Claim 32, further characterized by the method steps of: providing at least one insulated electrical conductor; and bundling said at least one insulated electrical conductor with said at least one uninterrupted tubular member.

37. A method of communicating fluids between first and second offshore sites, characterized by the method steps of: providing at least one continuous tubular member formed of alloyed or unalloyed titanium; extending said at least one continuous tubular member between said first and second offshore sites; and passing fluid through said at least one continuous tubular member between said first and second offshore sites.