AU785507B2

AU785507B2 - Encased piping system

Info

Publication number: AU785507B2
Application number: AU1999010126A
Authority: AU
Inventors: Jan Dubbelman
Original assignee: SPIRAL TUBE MAKERS Pty Ltd
Current assignee: PIHA Pty Ltd
Priority date: 1997-11-07
Filing date: 1998-11-05
Publication date: 2009-10-22
Anticipated expiration: 2018-11-05
Also published as: AU1012699A; AUPP023697A0; WO1999024748A1

Description

WO 99/24748 PCT/AU98/00917 ENCASED PIPING SYSTEM WO 99/24748 PCT/AU98/0091 7 2 ENCASED PIPING SYSTEM This invention relates to improvements in piping 5 systemsand, specifically, topiping systems inwhich a durable inner pipe of relatively low strength or rigidity is reinforced by being encased in an outer casing of higher strength or rigidity. In the operation of pipelines, where it is 10 necessary to convey liquids, slurries or the like of a corrosive or abrasive nature, it is common to employ a piping system comprising a durable inner pipe resistant to the deleterious effects of the particular flow agent to be conveyed, encased or 15 enclosed within a stronger and stiffer outer part, usuallyof ametallic material, capable of sustaining the internal pressures to which said pipeline is to be subjected. While such durable inner pipe may simply take the form of a coating applied to the 20 inner wall of said metallic outer part, more demanding applications require the use of a composite piping system. Typical of such composite piping systems are those described in patents DE 2 923 544, EP 0 024 220 and AU 40019/85. The first of these 25 patents teaches a process for the manufacturing of a multi-layer pipe in which an intermediate layer of plastics material is co-extruded onto an inner tube, also of plastics material, the combination WO 99/24748 PCT/AU98/00917 3 then being covered with a tube of metallic material and subjected to an elongation operation. The second patent teaches a process in which two layers of plastics material are extruded inside a metallic 5 tube. The third patent teaches a process in which an inner plastic tube is prepared by extrusion and a tube of metallic material is formed around it and sealed by butt welding, the diameter of the metallic tube then being reduced without elongation. A 10 reinforcing mesh and adhesive are optionally inserted between layers and an outer coating of plastic material is formed on the external surface of the metallic tube. The disadvantages of the three processes when 15 applied to the manufacturing of pipes of larger diameter, which may be defined as pipes having an internal diameter greater than 100 millimetres, is that they require the use of very large plastics extrusion plant and very large metal forming plant, 20 both of which are expensive, require skilled operation and are relatively immovable. The object of the present invention is to provide a process for the manufacturing of a jacketed piping system of larger diameter in which standard, 25 readily available components are employed, which can be performed in the field without the use of heavy and expensive plant, and which can be performed without the use of higher level skills, the result WO 99/24748 PCT/AU98/00917 4 being a product of flexible arrangement, lower cost and manufactured in a shorter lead time. Further objects of the present invention are the manufactur ing of a jacketed piping system which is readily 5 assembled and installed in the field and which incorporates provisions which may be employed to regularly assess, whilst a pipeline is in operation, the condition of its durable inner pipe. According to the present invention, a composite 10 piping system is provided comprising an outer casing into which is introduced a durable inner pipe resistant to the deleterious effects of the particular flow agent to be conveyed. Conveniently, said outer casing is fabricated into tubular form 15 by spirally winding strip material of some suitable metal alloy which is then joined at the edge by welding or lockseam jointing, or by rolling of a sheet of some suitable metal alloy into tubular form, the edges then being welded or joined by mechanical 20 means. In alternative embodiments, said outer casing is fabricated or formed from other suitable, non metallic materials. Said inner pipe is preferably formed by extrusion of a suitable polymer material, branches and sealing flanges being welded to it as 25 appropriate. In alternative embodiments, said inner pipe is fabricated or formed from other suitable materials. In the manufacturing of a length of said WO 99/24748 PCT/AU98/00917 5 composite pipe, a length of said inner pipe is reduced in diameter using one of several methods well known in the art and winched into position into a suitable length of said outer casing, to the ends 5 of which attachment flanges have been welded. Said inner pipe is then expanded into interference with said outer casing and cut to length. Sealing flanges are then welded to its ends, the cut length of said inner pipe being such that said sealing flanges 10 extend beyond said attachment flanges by a length sufficient to accommodate the maximum thermal contraction which might be experienced in service. In an alternative embodiment in which said inner pipe is made from a polymer material with some degree 15 of elasticity, where a full interference fit is not required between said inner pipe and said outer casing, said inner pipe is made of a diameter such that minimal clearance exists between it and the internal surface of said outer casing and is winched 20 into position in said outer casing. During employment of this method, where movement of said inner pipe is impeded during its installation by frictional contact with the internal surface of said outer casing, elongation of said inner pipe occurs 25 with an attendant reduction in diameter which restores movement. Following its installation in this way, said inner pipe must be permitted to relax before being cut to its required length.

WO 99/24748 PCT/AU98/00917 6 Bends for a said composite piping system are manufactured in the same way as straight lengths, said outer casing being fabricated in 'lobsterback' form from a plurality of short, straight lengths 5 joined together, or bent from a single straight length. Connections to said composite piping system, such as tributary connections, instrumentation tappings, washouts, pig launchers and the like are 10 provided by the insertion of a connection piece between lengths of said composite piping system. A said connection piece is made by welding to a suitable length of said inner pipe a projecting piece of pipe of similar material and suitable length and 15 diameter, sealing flanges then being welded to the three resultant ends. An outer casing is then fabricated in two halves from a suitable material, flanges being provided along all longitudinal abutting edges to allow said halves to be bolted 20 together to closely enclose said inner pipe and projecting piece. Halved attachment flanges are welded to the ends of said halves of said outer casing prior to the assembly of said halves over said inner pipe and projecting piece, each pair of 25 half flanges making a complete flange when their edges are assembled into abutment. To permit measurement of the thickness of said inner pipe whilst a said composite pipeline is in WO 99/24748 PCT/AU98/00917 7 service, prior to its assembly together with said inner pipe, holes of a suitable diameter are drilled in said outer casing in appropriate locations and internally threaded bushes arewelded to theexternal 5 surface of said outer casing over said holes. Said bushes are preferably sealingly closed with suitable plugs which are removed as required to permit the sensing head of a thickness measurement device to be inserted through a said bush and into contact 10 with the outer surface of said inner pipe. In an alternative application, when such procedure is acceptable, said bushes are left open in appropriate positions to permit telltale leakage to be observed when attrition of said inner pipe has progressed 15 to the point of failure. Should the use of thickness testing equipment disclose unacceptable localised thinning of said inner pipe, a length of said composite piping system is withdrawn from service for repair or replacement. 20 Where it is desirable to minimise the possibili ty of leakage of flow agent from a said composite piping system following localised failure of said inner pipe, a shroud is welded to the external surface of said outer casing enclosing appropriate 25 locations and acts to capture any leakage caused by perforation of said outer casing. A hole of suitable diameter is drilled in each said shroud in its lowest installed location and an internally WO 99/24748 PCT/AU98/00917 8 threaded bush is welded to the external surface of said shroud over said hole. Said bush is preferably sealingly closed with a plug which is removed as required to permit a test for evidence of leakage 5 to be made. The various aspects of the present invention will be more readily understood by reference to the following description of preferred embodiments given in relation to the accompanying drawings in which: 10 Figure 1 depicts transverse cross-sectional views through a composite pipe showing two stages of the installation of the inner pipe; Figure 2 is a longitudinal cross-sectional view of a composite pipe immediately following 15 installation of the inner pipe; Figure 3 is a longitudinal cross-sectional view of lengths of pipe in a composite piping system in a partially assembled state; Figure 4 is a longitudinal cross-sectional 20 view of a connection piece for a composite piping system; Figure 5 is a transverse cross-sectional view of the connection piece depicted at Figure 4 through the centreline of its tributary 25 connection; Figure 6 is a longitudinal cross-sectional view of a shrouded connection piece; Figure 7 is a transverse cross-sectional WO 99/24748 PCT/AU98/00917 9 view of the shrouded connection piece depicted at Figure 6 through the centreline of its tributary connection; Figure 8 is a longitudinal cross-sectional 5 view through an alternative form of connection piece; Figure 9 is a longitudinal cross-sectional view of the connection of two lengths of pipe in a composite piping system; 10 Figure 10 is a view of a shrouded 90 degree pipe bend; Figure 11 is a longitudinal cross-sectional view of the end of a length of pipe showing the arrangement of a floating attachment flange. 15 With reference to Figure 1, a composite piping system is provided comprising outer casing 1 into which is introduced durable inner pipe 2. Conveni ently, said outer casing is fabricated into tubular form by spirally winding strip material of some 20 suitable metal alloy which is then joined at the edge by welding or lockseam jointing, or by the rolling up of a sheet of some suitable metal alloy into tubular form, the edges then being welded or joined by mechanical means. Said inner pipe is 25 preferably formed by extrusion of a suitable polymer material. In alternative embodiments, both said outer casing and said inner pipe are fabricated or formed from other suitable materials.

WO 99/24748 PCT/AU98/00917 10 In the manufacturing of a length of said composite pipe, a length of said inner pipe is made by extrusion, a method well known in the art. The material from which said inner pipe is manufactured 5 is preferably a polymer material resistant to the deleterious effects of the particular flow agent to be conveyed through said piping system. Where said flow agent is abrasive in nature, said inner pipe is preferably manufactured from high molecular 10 weight polyethylene. Where said flow agent is corrosive in nature, said inner pipe is manufactured from a material suitably resistant to its attack. Preferably, but not necessarily, said material is also a polymer material. Following its extrusion, 15 said inner pipe is reduced in diameter using one of several methods well known in the art. Such methods, for example, include those disclosed in patents AU 69585/94 and AU 34547/89. The first of these teaches a method of partially collapsing a 20 tube to reduce its diameter. In this method, as depicted in Figure 1, inner pipe 2 is preferably heated to soften it and is then passed through rollers (not shown), one or more of which act to collapse a substantial part of its circumference 25 inwardly to form channel 3, the pressure of further rollers being used, if required, to deflect lobes 4 inwardly towards each other. Said collapsed tube is then winched into place in outer casing 1 and WO 99/24748 PCT/AU98/00917 11 pressurised to restore it to its round form and original diameter, providing an interference fit with said jacket or casing. The second said patent teaches a method in which said inner pipe is passed 5 between pairs of shaped rollers which apply to it a radially inwardly directed crushing force equally distributed around its circumference, causing it to adopt a set at reduced diameter whilst maintaining its round shape. Said inner pipe is then similarly 10 winched into position in outer casing 1 and pressurised to restore it to its original diameter, providing an interference fit with said jacket or casing. In a third method, employed where said inner 15 pipe is made f rom a polymer material with some degree of elasticity and where a full interference fit is not required between said inner pipe and said outer casing, said inner pipe is made of a diameter such that minimal clearance exists between it and the 20 internal surface of said outer casing and is winched into position in said outer casing. In this this method, a draw bar is inserted through apertures (depicted as 5 in Figure 2) provided in the end of said inner pipe and tension is applied to a cable 25 attached to said drawbar to draw said inner pipe into position within said outer casing. During this process, the leading edge of said inner pipe is optionally chamfered to facilitate its entry into WO 99/24748 PCT/AU98/00917 12 said outer casing and, also optionally, a suitable lubricant is applied to the exterior of said inner pipe to reduce friction between it and the inner surface of said outer casing. Where, during its 5 installation, movement of said inner pipe is impeded by frictional contact with the internal surface of said outer casing, elongation of said inner pipe occurs with an attendant reduction in diameter which restores its movement. Regardless of the method 10 of installation of said inner pipe and particularly following its installation through use of the third method detailed, said inner pipe is permitted to relax for a minimum of 24 hours before being cut to its required length. 15 With reference to Figures 2 and 3, prior to installation into it of inner pipe 2, attachment flanges 6, 7 are welded to the ends of outer casing 1, a plurality of equally-spaced attachment bolt holes 9, 10 being provided in each. When relaxation 20 of said inner pipe has ceased, it is cut to length. Conveniently, one end of said inner pipe is cut square a suitable distance outside the outer face of attachment flange 7 and sealing flange 8 is welded to it using welding methods well known in the art. 25 Said inner pipe is then jacked into said outer casing such that the inner face of said sealing flange abuts the outer face of attachment flange 7. In suitable circumstances, sealing flange 8 is welded to the WO 99/24748 PCT/AU98/00917 13 end of said inner pipe prior to its installation in said outer casing. The other end of said inner pipe is then cut square, extending by additional length 13 beyond the outer face of attachment flange 5 6, and sealing flange 14 is welded to its end. Said additional length is calculated as the minimum required to accommodate the maximum thermal contraction of said inner pipe which might be experienced in service. Due to the low tensile 10 strength of the welds used to attach sealing flanges 8, 14 to the ends of said inner pipe, tensile forces due to thermal contraction are preferably avoided by pre-loading said inner pipe in compression during the assembly of abutting lengths of said composite 15 piping system. During assembly of abutting lengths of said composite piping system, sealing flanges 8, 12 are crushed together in sealing co-operation by pressure of attachment flanges 7, 11 urged together by their attachment bolts (not shown). 20 When a further length of said composite piping system is assembled to attachment flange 6, extended bolts are temporarily employed as required to draw the abutting flanges together, said bolts being drawn up slowly and evenly to compress additional length 25 13 of said inner pipe into said outer casing. With reference to Figures 4 and 5, connections to said composite piping system, such as tributary connections, instrumentation tappings, washouts, WO 99/24748 PCT/AU98/00917 14 pig launchers and the like are provided by the insertion of a connection piece between lengths of said composite piping system. A said connection piece is made by welding to a suitable length of 5 said inner pipe 27 a lateral inner pipe 16 of similar material and suitable length and diameter, sealing flanges 19, 20 then being welded to the ends of inner pipe 27. An outer casing is fabricated in two halves 25, 26 from a suitable material, attachment flanges 10 30, 31 being provided along all longitudinal abutting edges to allow said halves to be bolted together with a plurality of attachment bolts (not shown) passing through a plurality of attachment bolt holes (not shown) provided in said attachment flanges. 15 Halved attachment flanges 17, 18, 28, 29 are welded to the ends of said said outer casing halves, each pair of half flanges making up a complete, circular flange when their edges are assembled into abutment. A plurality of equally-spaced attachment bolt holes 20 (not shown) are provided in each said attachment flange halves. Lateral outer casing 15 of sufficient length to accommodate lateral inner pipe 16 is welded to outer casing half 26 in the appropriate location and attachment flange 21 is welded to its end. A 25 plurality of equally-spaced attachment bolt holes is provided in attachment flange 21. Said outer casing halves with said lateral outer casing attached to half 26 are assembled over said inner pipe and WO 99/24748 PCT/AU98/00917 15 said lateral inner pipe, force being applied as required to urge said lateral inner pipe out through said lateral outer casing, a form or mandrel being temporarily installed within the bore of said inner 5 pipe to prevent its collapse during the assembly process. When attachment flanges 30, 31 are abutting, said form or mandrel is withdrawn from the bore of said inner pipe and said attachment bolts are installed and tightened to retain said outer 10 casing halves in position closely enclosing said inner pipe and said lateral inner pipe. The outer end of said lateral inner pipe is then cut square to length and sealing flange 22 welded to it. With said outer casing halves and said lateral outer 15 casing assembled over said inner pipe and said lateral inner pipe, the inner faces of sealing flanges 19, 20, 22 abut, respectively, the outer faces of attachment flange halves 17, 18 and 28, 29 and attachment flange 21. 20 Because of the difficulty of precisely matching the external shapes of said inner pipe and said lateral inner pipe in the area in which they are joined to the internal shapes of outer casing half 26 and said lateral outer casing in the area in which 25 they are joined (depicted as 23 in Figure 4), it has been found desirable, following assembly of said outer casing halves and said lateral outer casing over said inner pipe and said lateral inner pipe, WO 99/24748 PCT/AU98/00917 16 to inject a suitable settable resin material between the said inner and outer components in the same area to fill any voids which may have been created. The filling of said voids eliminates flexing of said 5 inner components as a result of pressure fluctu ations, thereby eliminating the possibility of cracking failure due to fatigue. For the purpose of injecting said settable resin material, injection nipples (not shown) are provided in suitable 10 locations in said outer components to provide entry and flow paths through them, together with complemen tary bleed holes (not shown) in said outer components to permit egress of excess said settable resin material. 15 With reference to Figures 6 and 7, it has been found in practice that flow impingement and turbulent flow may lead to the localised corrosion, erosion or ablation of said inner pipe, with leakage eventually occurring if the deterioration is not 20 detected and arrested. Localised flow impingement may occur from a tributary line where it enters a main line and broader and more general flow impingement may occur on bends. Turbulent flow may result from any disturbance of flow and is particu 25 larly pronounced in the region of the opening of a lateral connection into a main line or where an object, such as a sensing device or the like, protrudes into the flow. Obviously, the rate of WO 99/24748 PCT/AU98/00917 17 removal of material from said inner pipe depends upon resistance of the particularmaterial fromwhich said inner pipe is made, velocity of the impinging flow and the abrasive or corrosive nature of the 5 particular flow agent. Depicted in Figures 6 and 7 are a connection piece similar in form to that depicted in Figures 4 and 5 and with similar features numbered similarly. Also depicted in Figure 7 is an instrumentation probe 10 35 supported by plug support 34 secured in place by closure plate 36. Tightening of attachment bolts (not shown) passing through closure plate 36 and attachment flange 21 of lateral outer casing 15 seals said closure plate and said attachment flange to 15 each other by the crushing of sealing flange 22. Said instrumentation probe extends along the length of lateral inner pipe 16 to project into the flow in inner pipe 27. The connection piece depicted in Figures 6 and 7 incorporates provisions to allow 20 the detection of deterioration of inner pipe 27 and to restrict leakage should attrition of said inner pipe occur to the point of perforation of outer casing halves 25, 26. To permit measurements to be made of the 25 thickness of inner pipe 27 whilst a said composite pipeline is in service, holes of a suitable diameter are drilled in appropriate locations in said outer casing halves prior to their assembly and internally WO 99/24748 PCT/AU98/00917 18 threaded bushes 39, 40 are welded to the external surface of said outer casing halves over said holes. Preferably, said bushes are located in appropriate positions in groups of four, on the upper and lower 5 surfaces and at each side where a closed cylindrical outer casing is employed, and in opposed pairs where a split casing arrangement is employed as depicted in Figures 4, 5, 6 and 7. Said bushes are preferably sealingly closed with suitable plugs (not shown) 10 which are removed as required to permit the sensing head of a thickness measurement device (not shown) to be inserted through a said bush and brought into contact with the outer surface of said inner pipe. In an alternative application, when such procedure 15 is acceptable, said bushes are left open in appropriate locations to permit telltale leakage to be observed when attrition of said inner pipe has progressed to the point of perforation. Should the use of thickness testing equipment disclose 20 unacceptable localised thinning of said inner pipe in a length of said composite piping system or in a connection piece, that component may be withdrawn from service for repair or replacement in a timely way. 25 Where it is desirable to minimise the possibili ty of leakage of flow agent from a said composite piping system following perforation of said outer casing following localised failure of said inner WO 99/24748 PCT/AU98/00917 19 pipe, shrouds 37, 38 are welded to the external surface of said outer casing halves enclosing appropriate locations and act to capture any leakage. A hole of suitable diameter is drilled in said shroud 5 in its lowest installed location and an internally threaded bush 41 is welded to the external surface of said shroud over said hole. Said bush is preferably sealingly closed with a plug (not shown) which is removed as required to test for evidence 10 of leakage. Provision is made in this arrangement, in a manner similar to that described in relation to Figures 4 and 5, to inject a settable resin to fill any voids existing between the area of joining of said inner pipe and said lateral inner pipe and 15 said outer casing halves and said lateral outer casing halves. With reference to Figure 8, a connection piece is depicted, adapted for use as a pipeline washout fitting or pig launcher. In this arrangement, 20 lateral inner pipe 55 is welded to inner pipe 42 and sealing flanges 50, 51, 57 are welded to their three ends. A split outer casing (part of half of which is visible in Figure 8) is fabricated from a suitable material and comprises outer casing half 25 43 and lateral outer casing half 54, along all abutting edges of which are provided attachment flanges 44, 47, 48, having, in suitable positions, a plurality of attachment bolt holes 45, 46, 49.

WO 99/24748 PCT/AU98/00917 20 Attachment flange halves 52, 53, 56 are welded to the ends of said outer casing and lateral outer casing halves. Said split outer casing halves are assembled over said inner pipe and said lateral inner 5 pipe and their said abutting attachment flanges are secured together by tightening of a plurality of attachment bolts (not shown). With said split outer casing halves assembled together, attachment flange halves 52, 53, 56 and their complementary halves 10 (not shown) are brought into abutment to create complete flanges of circular form. Said attachment flange halves are provided with a plurality of equally-spaced attachment bolt holes (not shown) for the attachment of said connection piece to other 15 members of said composite piping system. With said split outer casing halves assembled together, the inner faces of sealing flanges 50, 51, 57 abut the outer faces of attachment flange halves 52, 53, 56 and their complementary halves. When said connection 20 piece is not in use for its intended application, lateral inner pipe 55 is preferably filled by filler plug 58, secured in place by attachment bolt 60 passing through closure plate 59. Said closure plate is provided with a plurality of equally-spaced 25 attachment bolt holes complementary to those in attachment flange 56. Tightening of a plurality of attachment bolts (not shown) passing through closure plate 59 and attachment f lange 56 seals said WO 99/24748 PCT/AU98/00917 21 closure plate and said attachment flange to each other by the crushing of sealing flange 57. The length of said filler plug is made such that, in its installed position, its inner end 61 is 5 coincident with the inner surface of inner pipe 42 and said inner end is shaped to conform as closely as possible to the generality of the inner surface of said inner pipe. In this way, disturbance of flow and resultant flow impingement is minimised. 10 Provision is made in this arrangement, in a manner similar to that described in relation to Figures 4 and 5, to inject a settable resin to fill any voids existing between the area of joining of said inner pipe and said lateral inner pipe and said outer 15 casing halves and said lateral outer casing halves. Obviously, where there is the possibility of erosion or corrosion of said inner pipe as a result of flow impingement, localised shrouding may be provided as described in relation to Figures 6 and 7. 20 Obviously, also, the connection pieces depicted at Figures 4, 5, 6 and 7 may be made in a similar manner to that depicted at and described in relation to Figure 8. With reference to Figure 9, a connection of 25 two length of pipe in said composite piping system is depicted. Two pipeline lengths comprising, respectively, inner pipe 62, 72, sealing flanges 67, 68, outer casing 63, 64 and attachment flanges WO 99/24748 PCT/AU98/00917 22 66, 65 are connected together by a plurality of attachment bolts 70, 71, the tightening of which urges said attachment flanges against said sealing flanges, crushing their abutting faces into sealing 5 co-operation. Retaining ring 69 is optionally provided, positioned around the peripheries of sealing flanges 67, 68 to prevent the extrusion of said sealing flanges when said pipeline is highly pressurised. Said retaining ring is made with an 10 axial width slightly lessthan the combined thickness of said sealing flanges in their crushed form and with an inner diameter slightly greater than that of said sealing flanges in their relaxed form. Where a said composite piping system is not highly 15 pressurised but may be subjected to high compressive forces which might similarly act to extrude sealing flanges 67, 68, a compression spacing ring (not shown) is positioned between the outer faces of attachment flanges 65, 66 around the outside of 20 attachment bolts 70, 71. Said compression spacing ring is made sufficiently thick to sustain the compressive forces to which it may be subjected and its axial width is made such that, with said sealing flanges properly crushed, the outer faces of said 25 attachment flanges just abut its edges. With reference to Figures 10 and 11, bends for said composite piping system are manufactured in the same way as that described for straight lengths WO 99/24748 PCT/AU98/00917 23 as depicted and described in relation to Figures 1, 2 and 3, excepting that outer casing 73 is optionally fabricated in 'lobsterback' form, by welding together a plurality of short straight 5 lengths of pipe, instead of being bent from a single straight length of pipe. Attachment flanges 76, 77 are welded to the end of said outer casing and sealing flanges 78, 79 are welded to the ends of said inner pipe (depicted as 2 in Figure 2 and not 10 visible in Figure 10). Although not shown in this Figure, said inner pipe is extended in a similar way to that depicted in and described in relation to Figure 3 to accommodate the maximum degree of thermal contraction that it is likely to experience 15 in service. Where, due to thermal distortion, manufacturing inaccuracies and the like, difficulty is likelyto beexperienced in aligning complementary attachment bolt holes in the attachment flange at the end of a bend and those in the attachment flange 20 of another member of said composite piping system, f loating attachment f langes are optional ly provided. In this arrangement (depicted in greater detail for a straight length of pipe in Figure 11), floating attachment flanges 74, 75 are positioned over said 25 outer casing prior to the welding to its ends of attachment flanges of reduced diameter 76, 77. The inner diameters of said floating attachment flanges are made such as to just allow said flanges to slide WO 99/24748 PCT/AU98/00917 24 over the outer surface of said outer casing with freedom to rotate. A plurality of equally-spaced attachment bolt holes 87 are provided in each said floating attachment flange. When assembling a said 5 bend together with other members of said composite piping system, said floating attachment flanges are rotated to bring their attachment bolt holes into coincidence with those of the attachment flanges of an adjacent member. Tightening of attachment 10 bolts urges ajacent said f loating attachment flanges against said attachment flanges, urging them, in turn, against said sealing flanges and thereby crushing their abutting faces together in sealing co-operation. 15 Where there is a possibility of said inner pipe being eroded or corroded away by localised flow impingement in a bend, holes are drilled in said outer casing in appropriate locations and internally threaded bushes 82, 83, 84, 85 are welded over them 20 as described in relation to Figures 6 and 7. Preferably, said bushes are arranged in groups of four, on the upper and lower surfaces and at each side of said outer casing in each location. Said bushes are optionally sealingly closed with suitable 25 plugs or left open to provide telltale leakage in the event of attrition of said inner pipe to the point of perforation. By removing said plugs, the sensing head of a thickness measurement device may WO 99/24748 PCT/AU98/00917 25 be inserted through said bushes and brought into contact with the outer surface of said inner pipe. Where it is desired to minimise the possibility of leakage of a flow agent as a result of perforation 5 of said outer casing following localised erosion or corrosion of said inner pipe, one or more shrouds 80 or a single continuous shroud as depicted, are provided welded to the outer surface of said outer casing. Said shrouds are optionally fabricated in 10 'lobsterback' form or bent from a single pipe of pipe. Similarly, a hole is drilled in said shrouds at their lowest installed points and threaded bushes 81 are welded over them. Said bushes are preferably closed with suitable plugs, which are removed as 15 required to check for evidence of leakage. The type of composite piping system described herein is frequently used in situations in remote locations. Typical of these are gas treatment plants, mineral treatment plants, oil wells and the 20 like. As far as possible, stock components, such as pipe sections, flanges and the like, are used in fabricating component members of said composite piping system and the relatively simple equipment required for their fabrication and assembly, as 25 described herein, is readily transported to and operated in remote locations. The advantages of the said system are that it provides a high degree of flexibility in the arrangement of component WO 99/24748 PCT/AU98/00917 26 members and the use of stock components and relatively simple equipment equipment for their fabrication and assembly acts to reduce the manufacturing lead time and cost of the completed 5 product.

Claims

1. An encased piping system comprising an inner pipe of specified durability characteristics installed in and supported by an outer casing of 5 greater strength or stiffness; lateral extensions of said inner pipe to provide tributary connections or access, said lateral extensions being similarly enclosed and supported by complementary lateral extensions of said outer casing; attachment flanges 10 welded to the ends of said outer casing and to the ends of its said lateral extensions; sealing flanges welded to the ends of said inner pipe and to the ends of its said lateral extensions; access provisions provided in said outer casing in critical 15 positions to permit measurement of the thickness of said inner pipe; and shrouds provided in critical positions, sealingly enclosing the exterior of said outer casing to prevent leakage where perforation of said inner pipe occurs. 20

2. An encased piping system according to Claim 1 in which said outer casing is made by spirally winding a suitable strip material into tubular form, abutting edges being joined by welding, lockseam 25 jointing or other method.

3. An encased piping system according to Claim 1 in which said outer casing is made by simply rolling Received 17 December 1999 28 suitable sheet material into tubular form, abutting edges being joined in one or more axially arranged seams formed by welding, lockseam jointing or other method. 5

4. An encased piping system according to Claim 1 in which said attachment flanges are welded to the ends of said outer casing or its lateral extensions to permit mechanical connection of successive lengths 10 of said piping system or mechanical connection of said lateral extensions to tributary connections and the like, said attachment flanges preferably being welded to the ends of said outer casing prior to the installation of said inner pipe. 15

5. An encased piping system according to Claim 1 in which said inner pipe is made by extrusion of a suitable polyethylene material. 20

6. Deleted

7. An encased piping system according to Claim 1 in which said inner pipe has an outside diameter more or less equal to the inside diameter of said 25 outer casing and is temporarily reduced in diameter by rolling down or Partial collapse. of its cross sectional shape prior to its installation in said outer casing, whereupon it is internally pressurised Received 17 December 1999 29 to restore it to its original diameter, thereby bringing its outer surface into intimate contact with the inner surface of said outer casing. 5

8. An encased piping system according to Claim 1 in which, where lateral extensions of said inner pipe are provided to permit connection to tributary connections or the like, said inner pipe has an outside diameter more or less equal to the inside 10 diameter of said outer casing, and said outer casing is made in two complementary halves and assembled over said inner pipe and its said lateral extensions.

9. An encased piping system according to Claim 1 15 in which said inner pipe is made with an outside diameter slightly less than the inside diameter of said outer casing and is installed in said outer casing without prior reduction in diameter by being forcefully drawn into said outer casing, its leading 20 edge being chamfered as required, a draw bar being inserted into apertures at its leading end, its outer surfaces being lubricated as required and said outer casing being suitably restrained during the installation process. 25

10. An encased piping system according to Claim 1 in which said inner pipe, after its installation in said outer casing, is permitted to elastically 30 relax for a minimum of 24 hours.

11. An encased piping system according to Claim 1 in which said inner pipe, after installation in said 5 outer casing, is cut to length with a calculated excess protruding beyond the ends of said outer casing such that, when successive lengths of said piping system are connected together, compression forces are generated in said inner pipe of sufficient 10 magnitude to compensate for the maximum degree of thermal contraction to be experienced in service by said inner pipe. 11A. An encased piping system according to Claim 1 in 15 which sealing flanges are welded to the ends of said inner pipe to seal successive lengths of said piping system one to another or said lateral extensions to tributary connections or the like, said sealing * flanges preferably being welded to the ends of said 20 inner pipe following its installation in said outer casing.

12. An encased piping system according to Claim 1 in which successive lengths are mechanically connected 25 together by attachment bolts inserted through a plurality of more or less equally-spaced bolt holes in said attachment flanges, said sealing flanges being sandwiched between adjacent faces of Received 17 December 1999 31 said attachment flanges and urged into sealing abutment by the tension of said attachment bolts.

13. An encased piping system according to Claim 5 1 in which successive lengths are mechanically connected by means of clamps or other means acting upon said attachment flanges.

14. An encased piping system according to Claim 10 1 in which one or more lateral extensions of required length are welded to said inner pipe normal to its axis and a fabricated outer casing, the complementary halves of which divide along a plane normal to the axis of said lateral extensions, is assembled over 15 said inner pipe assembly, said lateral extensions passing out through complementary tubular lateral extensions attached to one or other complementary halves of said outer casing, said inner pipe being supported against collapse during the assembly 20 process by the temporary insertion of a suitable mandrel into its bore.

15. An encased piping system according to Claim 14 in which said complementary halves of said 25 fabricated outer casing are mechanically connected by means of a plurality of attachment bolts passing through aplurality of holes in complementary flanges provided along all abutting edges. Received 17 December 1999 32

16. An encased piping system according to Claim 14 in which the complementary halves of said fabricated outer casing are mechanically connected by clamps or other means acting upon complementary 5 flanges provided along all abutting edges or by clamping bands or rings passing completely around said complementary halves.

17. An encased piping system according to Claim 10 1 in which one or more lateral extensions of required length are welded to said inner pipe at an angle to its axis anda fabricated outer casing, comprising two complementary halves and semi-tubular lateral extensions attached to them to enclose said lateral 15 extensions, is assembled over said inner pipe assembly, the complementary halves of said fabricated outer casing and their said semi-tubular lateral extensions dividing along a common plane coincident with the common axis of said inner pipe lateral 20 extensions.

18. An encased piping system according to Claim 17 in which the complementary halves of said fabricated outer casing and their said semi-tubular 25 lateral extensions are mechanically connected by a plurality of attachment bolts passing through a plurality of holes in complementary flanges provided along all abutting edges. A LA L , IUr*r--f Received 17 December 1999 33

19. An encased piping system according to Claim 17 in which the complementary halves of said fabricated outer casing and their said semi-tubular lateral extensions are mechanically connected by 5 clamps or other means acting upon complementary flanges provided along all abutting edges or by clamping bands or rings passing completely around said complementary halves. 10

20. An encased piping system according to Claims 14 and 17 in which halved attachment flanges are welded to the ends of said fabricated outer casing complementary halves, said flanges dividing along a plane coincident with the plane of division of 15 said outer casing complementary halves.

21. An encased piping system according to Claim 20 in which successive lengths of said piping system are mechanically connected by attachment bolts 20 inserted through a plurality of more or less equally spaced bolt boles in said halved attachment flanges, sealing flanges on the ends of said inner pipe and its said lateral extensions being sandwiched between the faces of adjacent said attachment flanges and 25 urged into sealing abutment by tension applied by said attachment bolts.

22. An encased piping system according to Claim Received 17 December 1999 34 20 in which successive lengths of said piping system are mechanically connected by clamps acting upon said halved attachment flanges, sealing flanges on the ends of said inner pipe and its said lateral 5 extensions being sandwiched between the faces of adjacent said halved attachment flanges and urged into sealing abutment by force applied by said clamps. 10

23. An encased piping system according to Claim 1 in which provision is made to allow the injection of a settable resin into the region between said inner pipe and said fabricated outer casing in the areas of attachment of said lateral extensions for 15 the purpose of filling any residual voids.

24. Deleted

25. An encased piping system according to Claim 20 24 in which said access provisions comprise suitable apertures in said fabricated outer casing over which are sealingly welded threaded bushes, said bushes being sealingly closed as required by threaded plugs when access to said inner pipe is not required. 25

26. An encased piping system according to Claim 1 in which, to prevent leakage when said inner pipe is locally eroded, corroded or ablated to the point Received 17 December 1999 35 of perforation, said fabricated outer casing is provided with shrouds sealingly welded to its external surface and completely enclosing zones in which such attrition of said inner pipe is expected 5 to occur, said shrouds being provided with suitably positioned drain points fromwhichtests forevidence of leakage may be made.

27. An encased piping system according to Claims 10 14 and 17 in which shrouds are sealingly welded to the external surfaces of the complementary halves of said fabricated outer casing for the purpose of confining leakage resulting from the perforation of said inner pipe as a result of localised erosion, 15 corrosion or ablation, each said shroud fully enclosing half of a zone in which such attrition is expected to occur and having suitably positioned drain points from which tests for evidence of leakage may be made. 20

28. An encased piping system according to Claim 1 in which, when a said lateral extension of said inner pipe is not in use, a filler plug completely filling it is inserted into said lateral extension, 25 the inner end of said filler plug conforming to the generality of the inner surface of said inner pipe to thereby minimise disturbance of flow. AMENDuEF -HEE: Received 17 December 1999 36

29. An encased piping system according to Claim 1 in which, when successive lengths are connected, retaining rings are provided fitting neatly around the peripheries of abutting pairs of said sealing 5 flanges, thereby confining said sealing flanges and preventing their extrusion as a result of overtight ening of the means by which said attachment flanges are fastened together. 10

30. An encased piping system according to Claim 1 in which, when successive lengths are connected, a spacer ring is provided between the outer parts of adjacent said attachment flanges of successive lengths of said piping system to carry excessive 15 compression loads applied to said attachment flanges by thermal expansion of said fabricated outer casing, thereby preventing extrusion of or interference with the sealing abutment of adjacent said sealing flanges. 20

31. An encased piping system according to Claim 1 in which said attachment flanges, preferably of reduced diameter, are fixed by welding to each end of a length of said fabricated outer casing and 25 floating attachment flanges of larger diameter are provided positioned inwardly of said fixed attachment flanges, said floating attachment flanges having inside diameters such that they can just move freely AMME cSHET rI/ /tU /U9I / Received 17 December 1999 37 on said outer casing and being provided with a plurality of more or less equally-spaced attachment bolt holes, said floating attachment flanges being rotatable as required to align their said attachment 5 bolt holes with those of adjacent fixed or floating attachment flanges for the purpose of mechanically connecting successive lengths.

32. An encased piping system according to Claim 10 1 in which bends are optionally made in lobster-back form.

33. An encased piping system according to Claim 1 in which said shrouds enclosing curved zones of 15 said fabricated outer casing are optionally made in lobster-back form.