Pipeline heating

Abstract

A flow line section 21, 22, 23, for use in a thermally controlled gaseous flow line 20, the flow line comprises a first tubular wall portion (2, fig 1) defining a gaseous flow conduit 24, 25, 26, a se

Description

Field The present invention relates to a gaseous flow line for use in a thermally controlled gaseous flow line. The present invention also relates to a modular thermally controlled gaseous flow line, a seal for sealing adjacent gaseous flow line sections, an abatement system comprising thermally controlled gaseous flow line(s), and a method of assembling a gaseous flow line section. Background For some applications, gaseous flow lines (i.e. pipes) carrying a gaseous flow from process equipment are heated to reduce the likelihood of blockages. Often, the gaseous flow may be an exhaust flow. Typically, the gaseous flow may be at elevated temperatures. Such blockages may be caused by condensation of by-products and / or residual process materials present in the gaseous flow. Condensation may be more likely if there is a region of the gaseous flow line where the temperature is lower in comparison to the rest of the gaseous flow line, i.e. a cold spot, as this will cause the temperature of the gaseous flow to reduce. By way of example, the exhaust line of process equipment used in the production of semiconductor wafers or microprocessors (patterned wafers) for semiconductor products, memory, sensors, solar panels, and / or LEDs, may comprise chemical vapours which, if condensed, may deposit within the exhaust line and cause various issues. It is therefore desirable to avoid such accumulation of condensates within the exhaust line. Problems associated with condensates include blocked lines, fire risk due to highly reactive condensates, risk to the operator during maintenance due to acidic condensates, and / or violent reactions when certain condensates are exposed to process gases, oxygen, or water. To reduce the likelihood of condensation of the constituents of the gaseous flow within the exhaust line, the temperature of the gaseous flow should be maintained at or above a threshold temperature. The threshold temperature will vary with application and according to the composition of the gaseous flow. To maintain the gaseous flow at or above the threshold temperature, the gaseous flow line may be heated. Typically, gaseous flow lines of the prior art are enclosed in heated insulation jackets and / or silicone rubber heating mats. However, the inventors have found these options exhibit a number of problems. The heated insulation jackets are relatively energy inefficient, making them expensive to run. Furthermore, there is a desire to increase the upper limits of the operating temperatures of the heated insulation jackets and silicone rubber heating mats. A typical maximum operating temperature for silicone rubber heating mat is around 250 °C. Accordingly, there is a desire to provide improved gaseous flow line heating solutions to improve energy efficiency and increase operating temperatures. The present invention aims to solve, at least in part, these and other problems associated with the prior art. Summary In an aspect, the present invention provides a gaseous flow line section for use in a thermally controlled gaseous flow line. The gaseous flow line section comprises a first generally tubular wall portion defining a gaseous flow conduit configured to convey a substantially gaseous flow. The gaseous flow line section further comprises a second generally tubular wall portion substantially surrounding the first generally tubular wall portion to define therebetween a liquid conduit configured to contain a thermally controlled liquid. The gaseous flow line section further comprises a third generally tubular wall portion substantially surrounding the second generally tubular wall portion to define therebetween a vacuum conduit configured to be evacuated. A gaseous flow line section may, in use, define either a portion or the entirety of a thermally controlled gaseous flow line. A thermally controlled gaseous flow line is a gaseous flow line wherein, in use, the temperature is maintained within a temperature range. The thermal control may be active and / or passive, preferably active. The gaseous flow line section may be an exhaust line section for a thermally controlled exhaust line. The gaseous flow line section may be a fore line section for a thermally controlled fore line. Thus, a gaseous flow line or gaseous flow line section according to the present invention may be an exhaust line or exhaust line section and / or a fore line or fore line section, respectively. References to a fore line or section thereof may usually be solely a reference to a fore line or section thereof. Additionally, or alternatively, a reference to an exhaust line or section thereof may be solely to an exhaust line. It will be appreciated that the present invention may be used for applications where it is advantageous for the likelihood of condensation of the gaseous flow through the gaseous flow conduit to be reduced. For example, the present invention may be used for chemical precursor delivery lines, where reducing the likelihood condensation of the chemical precursors within the gaseous flow conduit may be advantageous. The gaseous flow conduit is configured to convey a substantially gaseous flow. The skilled person will appreciate that substantially gaseous flow may comprise other constituents, such as a solid component (e.g. particulate) and / or a liquid component. When in use, the gaseous flow conveyed through the gaseous flow conduit may be above, at or below substantially atmospheric pressure. For example, the gaseous flow may be at a pressure from substantially atmospheric pressure to ultra-high vacuum pressure (i.e. pressures below about 10’7 mbar). Typically, the gaseous flow conduit defined by the first generally tubular wall portion may have a circular cross-section. The skilled person will appreciate that the first generally tubular wall portions may have a non-circular cross-section, although a circular cross-section is typically preferred to provide more uniform heat transfer between the liquid in the liquid conduit and the gaseous flow in the gaseous flow conduit. Preferably the gaseous flow conduit may be substantially cylindrical. The cross-sectional area of the of the gaseous flow conduit may be substantially uniform along its length, or alternatively the cross-sectional area of the gaseous flow conduit may increase and / or decrease along its length. By way of example, the gaseous flow conduit may have a diameter of from about 30 mm to about 60 mm, preferably from about 38.1 mm (i.e. 1.5 inches) to about 50.8 mm (i.e. 2 inches). The skilled person will understand that the invention may be used for applications wherein the cross-sectional area of the gaseous flow conduit falls outside of these ranges. Typically, the liquid conduit defined by the first and second generally tubular wall portions may have an annular cross-section. Preferably, the liquid conduit may be substantially toroidal. Preferably, the cross-sectional area of the liquid conduit may be substantially uniform along its length. Typically, the vacuum conduit defined by the second and third generally tubular wall portions may have an annular cross-section. Preferably, the vacuum conduit may be substantially toroidal. Preferably, the cross-sectional area of the vacuum conduit may be substantially uniform along its length. The first and / or second and / or third generally tubular wall portions may each comprise a polymeric and / or a metallic and / or a ceramic material. Preferably, the first and / or second and / or third generally tubular wall portions may each comprise a metallic material. By way of example, the first and / or second and / or third generally tubular wall portions may comprise stainless steel, or aluminium or an alloy thereof. Specifically, the first and / or second and / or third generally tubular wall portions may comprise 316L stainless steel. In some embodiments, the first, and / or second, and / or third generally tubular wall portions may each comprise the same material. In alternative embodiments, the first and / or second and / or third generally tubular wall portions may each comprise a different material. Typically, the first, second, and third generally tubular wall portions have a length of from about 0.1 m to about 10 m. It is typically preferred to have relatively long first, second and third generally tubular wall portions, as this may allow a thermally controlled gaseous flow line having fewer gaseous flow line sections. The first, second and third generally tubular wall portions may have substantially the same length. The first, and / or second, and / or third generally tubular wall portions may each have a different length to each other. For example, the first generally tubular portion may have a greater length than the second generally tubular wall portion. Additionally, or alternatively, the second generally tubular wall portion may have a greater length than the third generally tubular wall portion. The dimensions (i.e. length, diameter, cross-sectional shape) of the first, and / or second, and / or third generally tubular wall portions may differ according to the geometric requirements of the coupling portion(s). The composition of the gaseous flow conveyed through the gaseous flow conduit when in use may depend on the process apparatus to which the gaseous flow line is connected. Typically, the gaseous flow may be at a temperature greater than about 150 °C, preferably greater than about 200 °C, for example greater than about 250 °C. The liquid conduit may be configured to contain a liquid. In use, the liquid conduit may contain a liquid. Preferably the liquid may be contained within a closed-loop system. When in use, the liquid may be circulated through the liquid conduit and / or closed-loop system. The liquid may be configured to transfer heat to the gaseous flow via the first generally tubular wall portion. This may reduce the likelihood of condensation of the gaseous flow within the gaseous flow conduit. Preferably, the liquid within the gaseous flow conduit may be a perfluoropolyether. For example, the liquid within the gaseous flow conduit may be, for example, perfluorinated polyether (PFPE) oils, silicone oils, a poly(siloxane), or Galden™ HT270. Preferably, the direction liquid flow through the liquid conduit may be substantially opposite to the direction of conveyance of the gaseous flow through the gaseous flow conduit. This may be because, in the absence of trace heating, the temperature of the gaseous flow may decrease as it travels through the gaseous flow conduit. Similarly, the temperature of the liquid may decrease as the liquid is conveyed through the liquid conduit. Accordingly, it may be preferable to configure the direction of flow of the liquid through the liquid conduit to be contrary to the direction of conveyance of the gaseous flow through the gaseous flow conduit so that the relatively hotter liquid transfers heat to the relatively lower temperature sections of the gaseous flow. The liquid within the liquid conduit may flow from a first end of the liquid conduit to a second end of the liquid conduit substantially continuously. Alternatively, the flow of liquid within the liquid conduit may be separated into two or more circulating zones. The or each circulating zone(s) may be shorter than the total length between the first and second ends of the liquid conduit. Typically, there may be from about 2 to about 10 circulating zones along the length of the liquid conduit. Each circulating zone may be substantially equal in length. For the avoidance of doubt, the first end and second end of the liquid conduit, respectively, may be either end of the gaseous flow line section depending on the direction of fluid flow within the liquid conduit. For the purposes of the present invention, a vacuum may be defined as a pressure less than about 1 mbar. The vacuum conduit may provide an insulating jacket around the liquid conduit. Advantageously, when in use, heat transfer from the liquid within the liquid conduit may maintain the temperature of the gaseous flow within the gaseous flow conduit along the length of the gaseous flow line section. Furthermore, the vacuum conduit surrounding the liquid conduit may reduce the radially outward heat transfer, thereby increasing the heat transfer radially inwards to heat the gaseous flow. Typically, the gaseous flow line section may further comprise a first coupling linkage arranged at a first end of the gaseous flow line section and a second coupling linkage arranged at a second end of the gaseous flow line section. Each coupling linkage may be configured to enable the gaseous flow line section to be coupled to further gaseous flow line sections and / or other components. The first coupling linkage may be arranged at an outermost part of the first end of the gaseous flow line section. The second coupling linkage may be arranged at an outermost part of the second end of the gaseous flow line section. Preferably, the first coupling linkage and / or second coupling linkage may each comprise a flange. The flange may be a bolted flange. Preferably, the flange may be a substantially annular flange. The annulus of the flange may be configured to permit the gaseous flow to pass therethrough during use. The flange may be generally radially extending flange. Preferably, the flange may be a generally radially outwardly extending flange. The flange may comprise the same material as the first, second, or third generally tubular portion. The first and / or second coupling linkage may conform to a coupling configuration as set out in PNEUROP 6601 / 1981. Preferably, the first and / or second coupling linkage may resemble standard KF or ISO rotatable fittings. The skilled person will appreciate that other flange systems appropriate for use as first and / or second coupling linkage are known. Preferably, the first coupling linkage and second coupling linkage are substantially identical. Each flange may comprise a sealing face configured to interact with one or more sealing system as defined elsewhere herein. Preferably, the flange may be an ISO rotatable flange. The flange may be a bolted flange. The first coupling linkage and / or the second coupling linkage may be a vacuum coupling radiation (VCR) style fitting. Preferably, each (i.e. first and second) coupling linkage may be couplable to a coupling linkage of a further gaseous flow line section via demountable, bolted flanges and / or a snap ring. Advantageously, the first and second coupling linkage may provide reliable fixing of the gaseous flow line section to further components. Typically, the gaseous flow line section may further comprise sealing system configured to substantially prevent fluid transfer between the gaseous flow conduit, the liquid conduit, the vacuum conduit, and a region outside the gaseous flow line section, respectively. Advantageously, the sealing system may enable the respective gaseous flow conduits and / or liquid conduits and / or vacuum conduits of adjacent gaseous flow line sections to be in communication. Typically, the sealing system may comprise a first sealing portion configured to substantially prevent fluid transfer between a region outside the gaseous flow line section and the vacuum conduit. The sealing system may further comprise a second sealing portion configured to substantially prevent fluid transfer between the gaseous flow conduit and the vacuum conduit. The sealing system may further comprise at least one aperture arranged between the first sealing portion and the second sealing portion. The or each aperture may be configured to permit fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections arranged about the seal. The sealing system may substantially prevent fluid transfer by the deformation of a relatively deformable gasket by a relatively hard flange. Preferably, the relatively deformable gasket is substantially flat and the relatively hard flange is profiled, or vice versa. For example, a gasket may be deformed by compression against a substantially flat surface of a flange to provide a seal. In another example, a flange may comprise a relatively hard profiled surface (e.g. a knife-edge) that is configured to deform a relatively soft, flat surface of a gasket when compressed together to provide a seal. The skilled person will appreciate that the sealing system are not limited to the specific examples provided and may select appropriate sealing system according to the operating conditions of the system in use. The first sealing portion may comprise a first gasket. The first gasket may be annular. Preferably, the flange of the coupling linkage may comprise a recess configured to receive at least a portion of the first gasket. The first gasket may be configured to substantially prevent fluid transfer between the vacuum conduit and a region outside the gaseous flow line section. The first gasket may be arranged towards a radially outermost edge of the flange. The material(s) of the first gasket may be selected according to the operating conditions of the system in use (e.g. operating temperature), and the composition of the gaseous flow. In some embodiments, the first gasket may be an elastomer O-ring. In alternative embodiments, the first gasket may be a metallic gasket. The second sealing portion may comprise a second gasket. The second gasket may be annular. Preferably, the flange may comprise a recess configured to receive at least a portion of the second gasket. The second gasket may be configured to substantially prevent fluid transfer between the gaseous flow conduit and the vacuum conduit. The second gasket may be arranged radially inwardly of the first gasket. The material(s) of the second gasket may be selected according to the operating conditions of the system in use (e.g. operating temperature), and the composition of the gaseous flow. In some embodiments, the first gasket may be an elastomer O-ring. In alternative embodiments, the first gasket may be a metallic gasket. In an example, the first sealing portion may comprise an elastomer O-ring and the second sealing portion may comprise a metallic gasket. The at least one aperture may be positioned radially inwardly of the first sealing portion, and radially outwardly of the second sealing portion. The at least one aperture may be defined in a region of the flange. Preferably the sealing system may comprise a plurality of apertures, preferably from about 1 to about 30 apertures. The apertures may be substantially evenly spaced in a circle ring. Each aperture may extend generally parallel to the direction of the gaseous flow in use. The first gasket and the second gasket may each be made from the same material or different materials. Preferably, the first gasket and / or the second gasket may each comprise an elastomeric or a metallic material. When the temperature of the liquid within the liquid conduit is less than about 250 °C, the first gasket and / or the second gasket may comprise an elastomeric material. When the temperature of the liquid within the liquid conduit is greater than about 250 °C, the first gasket and / or the second gasket may comprise a metallic material. Typically, where two gaseous flow line sections are coupled, the first gasket and second gasket may each be compressed between the respective flanges of the coupling linkage of the gaseous flow line sections. The gaseous flow conduit of the first gaseous flow line section may be coupled to the gaseous flow conduit of the second gaseous flow line section through the annulus of the second gasket. In such embodiments, the gaseous flow is also conveyed through the annulus of the first gasket. The vacuum conduit of the first gaseous flow line section may be coupled to the vacuum conduit of the second gaseous flow line section through the at least one aperture of the sealing system. The first gasket and second gasket may be configured to prevent fluid ingress into the respective vacuum conduits. Typically, the gaseous flow line section may further comprise at least one duct configured to enable the liquid to enter or exit the liquid conduit. Preferably, the or each duct may be fluidly connected to a pump configured to circulate fluid through the liquid conduit. In some embodiments, the liquid conduit of the first gaseous flow line section may be coupled to the liquid conduit of the second gaseous flow line section by passing around the sealing system. The liquid may be conveyed through an egress duct of the first gaseous flow line section to an ingress duct of the second gaseous flow line section, passing around the sealing system, i.e. radially outward of the first gasket. The liquid may be conveyed via a pump and / or a thermal regulator between the first and gaseous flow line sections. In some embodiments, the liquid conduit of the first gaseous flow line section may be coupled to the liquid conduit of the second gaseous flow line section by passing through a port of the sealing system. The port may be through the flange. The skilled person will appreciate that in embodiments wherein liquid is configured to transfer between the respective liquid conduits of the adjacent gaseous flow line sections, the second sealing portion may be configured to substantially prevent fluid transfer between the gaseous flow conduit and the liquid conduit. The sealing system may further comprise a third sealing portion configured to substantially prevent fluid transfer between the liquid conduit and the gaseous flow conduit. Further features of the sealing system in such embodiments may be as defined hereinbefore. Preferably the gaseous flow line section may comprise a plurality of ducts configured to enable the liquid to enter or exit the liquid conduit. More preferably, the gaseous flow line section may comprise at least one ingress duct configured to enable the liquid to enter the liquid conduit. The at least one ingress duct may be arranged at or towards a first or second end of the gaseous flow line section. The gaseous flow line section may further comprise at least one egress duct configured to enable the liquid to exit the liquid conduit. The at least one egress duct may be arranged at or towards a first or second end of the gaseous flow line section, preferably distal to the ingress duct(s). Preferably, at least one ingress duct may be configured to be coupled to either pump or an egress duct of an adjacent gaseous flow line section. Preferably, at least one outlet duct may be configured to be coupled to either a pump or an ingress duct of an adjacent gaseous flow line section. Typically, the ingress duct is positioned relative to the egress duct such that the liquid conduit may be substantially entirely filled. The pump may be configured to provide a substantially continuous flow of liquid through the liquid conduit. The pump may be configured to regulate the temperature of the liquid entering the liquid conduit. Advantageously, this may allow the liquid to flow in a closed loop. Preferably, the or each duct may extend substantially radially outwardly through the vacuum conduit. In some embodiments, this may enable the duetto pass outside of the sealing system. In alternative embodiments, a duct may pass through the sealing system. Typically, during operation, the liquid in the liquid conduit may have a temperature at or above a threshold temperature sufficient to substantially prevent condensation of gases of the gaseous flow within the gaseous flow conduit. The threshold temperature may depend on the composition of the gaseous flow through the gaseous flow conduit. The threshold temperature may be greater than about 100 °C, preferably greater than about 200 °C, more preferably greater than about 250 °C. For the purposes of the present invention, the temperature of the liquid may be defined as the temperature of the liquid exiting the liquid conduit. Typically, during operation, the vacuum conduit may be evacuated to a pressure from about 1 mbar to about 1 x 10’7 mbar. For the purposes of the invention the vacuum conduit may be considered evacuated when within this range. The vacuum conduit may be operably connected to a vacuum pump. Typically, the gaseous flow line section may be substantially linear. Alternatively, the gaseous flow line section comprises an elbow joint. Preferably, the elbow joint may be angled between about 20° and about 120°, more preferably between about 30° and about 90°. For the purposes of the present invention, the angle of the elbow joint may be defined as the angle between the central axis of the gaseous flow line section at a first end and the central angle of the gaseous flow line section at a second end, distal the first end. The angle of the elbow joint is typically an obtuse, right, or acute angle. Most commonly, the angle of the elbow joint is an obtuse angle. Providing gaseous flow line sections having different angles and lengths may enable a bespoke modular thermally controlled gaseous flow line to be assembled to fit the components and arrangement of any abatement system. Typically, each gaseous flow line section may have compatible coupling linkage. This may enable any pair of gaseous flow line sections to be coupled. Typically, the gaseous flow line section may further comprise thermal regulator for controlling the temperature of the liquid within the liquid conduit. Preferably, the gaseous flow line section further comprises a pump configured to convey liquid through the liquid conduit. Preferably, the thermal regulator and / or pump may be coupled to a controller. The controller may be configured to increase and / or decrease and / or maintain the temperature of the liquid within the liquid conduit by controlling the pump and / or thermal regulator. The skilled person will appreciate that multiple gaseous flow line sections may be coupled to the same thermal regulator and / or pump and / or controller. Additionally, or alternatively, the or a controller may be coupled to a vacuum pump and may be configured to regulate the pressure within the vacuum conduit. The controller(s) may be configured to operate automatically. In an aspect, the present invention provides a modular thermally controlled gaseous flow line (i.e. gaseous flow line). The thermally controlled gaseous flow line comprises a plurality of interconnectable gaseous flow line sections according to any embodiment of the preceding aspect. During operation, the gaseous flow conduits of the respective gaseous flow line sections may be fluidly connected. Preferably, the vacuum conduits of the respective gaseous flow line sections may be fluidly connected. Additionally, or alternatively, the liquid conduits of the respective gaseous flow line sections may be fluidly connected. Preferably, when assembled, the gaseous flow line comprises from about 2 to about 50 interconnected gaseous flow line sections. Preferably, during operation, the gaseous flow conduits of the respective gaseous flow line sections are fluidly connected, and the vacuum conduits of the respective gaseous flow line sections are fluidly connected, and the liquid conduits of the respective gaseous flow line sections may be fluidly connected. Preferably, the gaseous flow line may comprise a vacuum pump configured to evacuate the gaseous flow conduits of the respective gaseous flow line sections. The vacuum pump may be, for example, a rotary vane pump, a diaphragm pump, a scroll pump, or a multi-stage roots pump, such as produced by Edwards Limited. The vacuum pump may also be used as part of one or more additional processes elsewhere in the system to which the gaseous flow line is coupled in use. Preferably, the gaseous flow line may comprise one or more thermal regulator for controlling the temperature of the liquid within the liquid conduits of the gaseous flow line sections. Preferably, the thermal regulator may comprise a pump configured to convey liquid through the liquid conduits of the respective gaseous flow line sections. Preferably, the gaseous flow line may comprise a controller. The controller may be connected to the vacuum pump and configured to regulate the pressure within the respective vacuum conduits of the gaseous flow line sections. Additionally, or alternatively, the controller may be connected to the thermal regulator and may be configured to regulate the temperature of the liquid within the respective liquid conduits of the gaseous flow line sections. Advantageously, the thermally controlled gaseous flow line of the present invention may reduce the likelihood of condensation of one or more component(s) of the gaseous flow within the gaseous flow conduit. Furthermore, the arrangement and dimensions of the thermally controlled gaseous flow line may be tailored to the specific operating conditions required when in use. The present invention encompasses the modular thermally controlled gaseous flow line both when disassembled and when assembled. In a further aspect, the present invention provides a seal for sealing adjacent gaseous flow line sections of a thermally controlled gaseous flow line according to the preceding aspect. The seal comprises a first sealing portion configured to substantially prevent fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections and a region outside the gaseous flow line section. The seal further comprises a second sealing portion configured to substantially prevent fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections and the respective gaseous flow conduits of the adjacent gaseous flow line sections. The seal further comprises an apertured portion configured to permit fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections. The seal may be an integrated part of a gaseous flow line section. Alternatively, the seal may be a separate component that is coupled to the gaseous flow line section in use. Preferably, the seal may comprise a first flange and a second flange. The flanges may function as connecting linkages for connecting the gaseous flow line sections. Each flange may be substantially annular. Preferably, in use, the gaseous flow may pass through the annuli of the first and second flanges. Each flange may have a sealing surface. In use, the flanges may be arranged such that their sealing surfaces are in a face-to-face relationship. The first sealing portion may comprise a first gasket. The first gasket may be annular. Preferably, the first gasket may be arranged between the pair of flanges. Preferably, the first gasket may be in contact with the respective sealing surfaces of the flanges. Preferably, the sealing surface(s) of one or both flanges may comprise a recess configured to receive at least a portion of the first gasket. The first gasket may be configured to substantially prevent fluid transfer between the vacuum conduit and a region outside the gaseous flow line section. The first gasket may be arranged towards a radially outermost edge of the flanges. The materials of the first gasket may be selected according to the operating conditions of the system in use (e.g. operating temperature and pressure differential across the flange), and the composition of the gaseous flow. In some embodiments, the first gasket may be an elastomer O-ring. In alternative embodiments, the first gasket may be a metallic gasket. Preferably, the metallic gasket may be deformable for use in a knife-edge seal. In such embodiments, preferably, the first sealing system may be a knife-edge seal. More preferably, the first sealing system may be a double knife-edge seal. The first gasket may comprise aluminium or an alloy thereof. Preferably, the first gasket may comprise a nickel-plated aluminium or alloy thereof. For example, the first gasket may comprise an aluminium electro-plated base layer with electroless nickel outer layer. Preferably, the nickel plating will have a thickness of about 25 pm. The first flange may comprise a sealing ridge (i.e. knife edge) at least partially defining the sealing surface. The sealing ridge may be configured to engage and deform the first gasket in use. The sealing ridge may be a substantially circular protrusion from the sealing surface of the first flange. The second flange may comprise a sealing ridge (i.e. knife edge) at least partially defining the sealing surface. The sealing ridge of the second flange may be substantially identical to the sealing ridge of the first flange. The sealing ridge may be configured to engage and deform the first gasket in use. The sealing ridge may be a substantially circular protrusion from the sealing surface of the first flange. The first and / or second flanges may comprise materials with a relatively higher hardness than that of the first gasket. Accordingly, when the first gasket is compressed between the first flange and the second flange, the first gasket may be deformed by the sealing ridge of the first flange and / or the sealing ridge of the second flange to provide a substantially fluid-tight seal. The sealing ridges of the first and / or second flange may be a knife-edge protrusion or a radiused protrusion. Alternatively, the first sealing portion may comprise one or more ISO rotatable flange. For example, the first sealing may comprise a first gasket compressed between a pair of ISO rotatable flanges. The ISO rotatable flanges may be bolted together. The second sealing portion may comprise a second gasket. The second sealing portion may have the features of any embodiment as defined in relation to the first sealing portion. The diameter of the outermost portion of the second gasket may be less than the diameter of the innermost portion of the first gasket. The apertured portion may be positioned radially inwardly of the first sealing portion, and radially outwardly of the second sealing portion. The apertured portion may be defined by a region of the flange. The apertured portion may comprise one or more aperture. Preferably, the apertured ring may comprise from about 1 to about 30 apertures. The apertures may be evenly spaced about the ring. Each aperture may extend longitudinally through the ring, i.e. parallel to the direction of the gaseous flow in use. In embodiments wherein the first sealing portion and / or second sealing portion comprise a knife-edge seal, the apertured portion may be defined in a portion of the flange radially inward of the sealing ridge of the first sealing portion and / or radially outward of the sealing ridge of the second sealing portion. The first gasket and second gasket may have the same material or different materials. Preferably, the first gasket and second gasket comprise an elastomeric or metallic material. When configured for applications where the liquid temperature is less than about 250 °C, the first gasket and / or the second gasket may comprise an elastomeric material. When configured for applications where the liquid temperature is greater than about 250 °C, the first gasket and / or the second gasket may comprise a metallic material. In some embodiments, the liquid conduit of the first gaseous flow line section may be coupled to the liquid conduit of the second gaseous flow line section by passing through a port of the sealing system. The port may be through the flange. In some embodiments, the sealing system may comprise a sensor configured to monitor for failure (i.e. leakage) of the sealing system. Said sealing system may be as defined in the European patent EP 3058251 B1, which is incorporated by reference herein. In a further aspect, the present invention provides an abatement system (i.e. a system) comprising process apparatus having an exhaust outlet through which an exhaust flow (i.e. a gaseous flow) may exit the process apparatus. The system further comprises exhaust abatement apparatus having an inlet through which the exhaust flow may enter the exhaust abatement apparatus. The system further comprises a modular thermally controlled gaseous flow line according to any embodiment of the earlier aspect described herein. The thermally controlled gaseous flow line is connected at a first end to the exhaust outlet of the process apparatus, and at a second end to the inlet of the exhaust abatement apparatus. During operation, the exhaust flow is conveyed through the or each gaseous flow conduit of the or each gaseous flow line section, thermally controlled liquid is present in the liquid conduits of the gaseous flow line sections, and the vacuum conduits of the gaseous flow line sections are evacuated to a pressure less than about 1 mbar. For the avoidance of doubt, further details of the thermally controlled gaseous flow line may be as defined elsewhere herein. The process apparatus may be a process apparatus for production of semiconductor wafers. For example, the process apparatus may comprise a process chamber coupled to a vacuum pump, wherein the vacuum pump is configured to evacuate the process chamber. In such an embodiment, the exhaust outlet may be that of the vacuum pump. The exhaust abatement apparatus may be configured to treat the exhaust gas flow. Said treatment may include, for example, abatement of the exhaust flow in a gas burner (e.g. natural gas or methane) or an electric arc burner. Preferably, the exhaust abatement apparatus may be an abatement furnace. For example, the exhaust abatement apparatus may comprise an inward-fired combustor, a plasma chamber, and / or electric arc discharge chamber. By way of example, the exhaust gas abatement apparatus may be an Atlas™ as produced by Edwards Limited. In a further aspect, the present invention provides a method of assembling a modular thermally controlled gaseous flow line according to any embodiment as described elsewhere herein. The method comprises the steps of: a) Providing a plurality of gaseous flow line sections. b) Arranging adjacent gaseous flow line sections such that their respective coupling linkages are aligned. c) Coupling the adjacent gaseous flow line sections such that the sealing system are compressed between the coupled flanges of the gaseous flow line sections. d) Repeating for additional gaseous flow line sections. e) Coupling the gaseous flow conduit of a gaseous flow line section to a gaseous flow outlet of a process equipment. The gaseous flow line sections may be as defined elsewhere herein. Preferably the step of coupling the adjacent gaseous flow line sections may comprise coupling via one or more bolts, collars, and / or claw clamps. Preferably, the method may further comprise the step of coupling the gaseous flow line section distal the process equipment to an exhaust abatement apparatus. Preferably, the method may comprise the step of connecting the vacuum conduit of the modular thermally controlled gaseous flow line to a vacuum pump. The vacuum pump may be configured to evacuate the vacuum conduit to a pressure of from about 1 mbar to about 1 x 10’7 mbar during operation. Preferably, the method may comprise the step of connecting the liquid conduit of the modular thermally controlled gaseous flow line to a pump. The pump may be configured to regulate the temperature of the liquid within the liquid conduit during operation. The pump may be configured to circulate liquid through the liquid conduit during operation. In a further aspect, the present invention provides a method of assembling a gaseous flow line section as defined hereinbefore. The method comprises the steps of a) providing a first annular flange, a second annular flange, a first generally tubular wall portion, a second generally tubular wall portion, and a third generally tubular wall portion; b) connecting the third generally tubular wall portion to the first annular flange; c) connecting the second generally tubular wall portion to the first annular flange, such that the second generally tubular wall portion is arranged radially inwardly of the third generally tubular wall portion; d) connecting the second annular flange to the third generally tubular wall portion and second generally tubular wall portion; e) inserting the first generally tubular wall portion through the annulus of the first annular flange and the second annular flange, such that the first generally tubular wall portion is arranged radially inwardly of the second generally tubular wall portion; and f) connecting the first generally tubular wall portion to the first annular flange and the second annular flange. Preferably, the steps of connecting a generally tubular wall portion to an annular flange may comprise welding said generally tubular wall portion to the flange. Alternatively, the method of assembling a gaseous flow line section may comprise additive manufacture of a gaseous flow line section as defined elsewhere herein. Preferably, the additive manufacture may comprise laser metal powder bed fusion. In a further aspect, the present invention provides a method of conveying a gaseous flow along a modular thermally controlled gaseous flow line of any previous embodiment The method comprises the steps of: a. providing a modular thermally controlled gaseous flow line as described elsewhere herein, the gaseous flow conduit of said gaseous flow line being coupled to a gaseous flow outlet of a process apparatus; b. evacuating the vacuum conduit to a pressure less than about 1 mbar; c. circulating liquid through the liquid conduit via a pump, such that the liquid is maintained at or above a threshold temperature; and d. conveying the gaseous flow from the gaseous flow outlet through the modular thermally controlled gaseous flow line. Preferably, the vacuum conduit is maintained in an evacuated state by throughout operation, i.e. whenever the gaseous flow is being conveyed through the gaseous flow line. The vacuum conduit may be connected to a vacuum pump for this purpose. Preferably the vacuum conduit is evacuated to a pressure less than about 1 mbar. For the avoidance of doubt, the threshold temperature may be as defined hereinbefore. The threshold temperature may be greater than about 100 °C, preferably greater than about 200 °C, more preferably greater than about 250 °C. Preferably, liquid may be substantially continuously circulated through the liquid conduit throughout operation. The pump may be configured to regulate the temperature of the liquid entering the liquid conduit. Preferably, the liquid may be circulated between the pump and the liquid conduit in a closed loop. Preferably, the direction of flow of the liquid through the liquid conduit may be substantially opposite to the direction of conveyance of the gaseous flow through the gaseous flow conduit. In some embodiments, the liquid may be circulated along substantially the entire length of the liquid conduit before passing through the pump. Alternatively, the flow of liquid within the liquid conduit may be separated into a plurality of circulating zones wherein the liquid circulates back to the pump after exiting each circulating zone. Each circulating zone may have a length that is shorter than the total length of the liquid conduit, preferably wherein the combined length of the circulating zones is substantially equal to the entire length of the liquid conduit. For the avoidance of doubt, all aspects and embodiments described herein may be combined mutatis mutandis. Brief Description of Figures Preferred features of the present invention will now be described, by way of example, with reference to the accompanying figures, in which: Figure 1 shows a cutaway view of a gaseous flow line section in accordance with an embodiment of the present invention; Figure 2 shows a metallic gasket suitable for use with the gaseous flow line section of Figure 1; Figure 3 shows a thermally controlled gaseous flow line in accordance with an embodiment of the present invention; Figure 4 shows a view of a coupling portion of a gaseous flow line section; Figure 5A-C show various embodiments of sealing systems in accordance with the present invention. Detailed Description of Figures Figure 1 illustrates a cutaway view of a gaseous flow line section (1) in accordance with an embodiment of the present invention. The cutaway is a vertical cutaway along a centre axis of the gaseous flow line section (1). The gaseous flow line section (1) may be for use in a thermally controlled gaseous flow line. The gaseous flow line section (1) comprises a first generally tubular wall portion (2). The first generally tubular wall portion (2) defines a gaseous flow conduit (3) configured, in use, to convey a gaseous flow. The gaseous flow line section (1) further comprises a second generally tubular wall portion (4). The second generally tubular wall portion (4) substantially surrounds the first generally tubular wall portion (2) to define therebetween a liquid conduit (5) configured to contain a thermally controlled liquid. The gaseous flow line section (1) further comprises a third generally tubular wall portion (6) substantially surrounding the second generally tubular wall portion (4) to define therebetween a vacuum conduit (7) configured to be evacuated. The gaseous flow line section (1) further comprises a coupling linkage (8) arranged at a first end of the gaseous flow line section (1). The first coupling linkage (8) may be configured to enable the gaseous flow line section (1) to be coupled to further gaseous flow line sections and / or other components. For the avoidance of doubt, typically the gaseous flow line section (1) would comprise a further coupling linkage at the second end, but this is not fully shown in Figure 1. The coupling linkage (8) comprises a flange (9). The flange (9) is a substantially annular flange. The flange (9) is a generally radially extending flange. In this embodiment, the flange (9) is of two-part construction, with an inner flange (10) and an outer flange (11). The inner flange (10) and outer flange (11) are coupled. The inner flange (10) comprises sealing surfaces (12) configured to interact with a gasket (as shown in Figure 2). The inner flange (10) further comprises an apertured portion (13) between the sealing surfaces (12). The apertured portion (13) is coupled to the vacuum conduit (7) and is configured to enable the fluid coupling of vacuum conduits of adjacent gaseous flow line sections when in use. The outer flange (11) comprises bore holes (14) configured to receive bolts to attach the outer flange (11) to a further component (e.g. corresponding flange) when in use. The inner flange (10) further comprises a pair of ducts (15) configured to enable liquid to enter and / or exit the liquid conduit (5). The ducts (15) extend radially outwardly. The ducts (15) allow connection of liquid conduits of adjacent gaseous flow line sections outwards of the outer flange (11). Figure 2 illustrates a metallic gasket suitable for use with the gaseous flow line section (1) of Figure 1. The gasket comprises an inner ring (16), an outer ring (17), and connecting portions (18). The gasket has a one-piece construction. The gasket further comprises alignment tabs (19) configured to maintain alignment of the gasket between the flanges of adjacent gaseous flow line sections. The metallic gasket comprises nickel plated aluminium. In use, the inner ring (16) and outer ring (17) are configured to be compressed between the sealing surfaces (12) of adjacent gaseous flow line sections. As the material of the sealing surfaces (12) has a relatively higher hardness than the material of the gasket, the inner ring (16) and outer ring (17) are configured to deform when compressed to provide a seal. Figure 3 illustrates a sectional view of a modular thermally controlled gaseous flow line (20) in accordance with an embodiment of the present invention. The modular thermally controlled gaseous flow line comprises three gaseous flow line sections (21,22,23). The gaseous flow line sections (21,22,23) are coupled together to define the gaseous flow line (20). The first (21) and third (23) gaseous flow line sections are 90-degree elbow sections. The second gaseous flow line section (22) is a straight section as shown in Figure 1. The gaseous flow line sections (21,22,23) comprise further features as set out in relation to Figure 1. Each pair of adjacent gaseous flow line sections (21,22,23) comprises coupling linkages (30) and a sealing system (31) at their interface. The coupling linkages (30) are configured to allow the gaseous flow line sections (21,22,23) to be connected during use. The coupling linkages (30) comprises a pair of flanges configured to be connected via bolts and / or a snap ring (not shown). The sealing system (31) comprise an annular gasket compressed between the flanges of the coupling linkages (30). The annular gasket may be the same or similar to that illustrated in Figure 2 and described previously herein. Each gaseous flow line section (21,22,23) comprises a gaseous flow conduit (24,25,26). The gaseous flow conduits (24, 25, 26) of the gaseous flow line (20) are connected to allow a gaseous flow to be conveyed during operation. Each gaseous flow line section (21,22,23) further comprises a liquid conduit (27,28,29). The liquid conduits (27,28,29) substantially surround the gaseous flow conduits (24,25,26) of the respective gaseous flow line sections (21,22,23). The liquid conduits (27,28,29) are configured to contain liquid during operation. The temperature of the liquid may be controlled. The liquid may be configured to transfer thermal energy to the gaseous flow to maintain the temperature thereof. This may reduce the likelihood of condensation of the gaseous flow within the gaseous flow line (20). Each gaseous flow line section (21,22,23) comprises at least one liquid ingress duct (32) through which liquid may enter the liquid conduit (27,28,29) during operation. Each gaseous flow line section (21,22,23) further comprises at least one liquid egress duct (33) through which liquid may exit the liquid conduit (27,28,29) during operation. In use, liquid may be conveyed through a liquid ingress duct (32) of a first gaseous flow line section (21), through the liquid conduit (27) and out of the liquid egress duct (33) of a first gaseous flow line section (21). The liquid may then be conveyed through the liquid ingress duct (32) of a second gaseous flow line section (22) into the liquid conduit (28) thereof. This may occur between each pair of adjacent gaseous flow line sections. Each gaseous flow line section (21,22,23) further comprises a vacuum conduit (34,35,36). The vacuum conduits (34,35,36) are configured to be evacuated in use. This may reduce the dissipation of heat from the liquid conduits (27,28,29) in a direction away from the gaseous flow conduits (24,25,26). In use, the vacuum conduits (34,35,36) may be evacuated to a pressure of from about 1 x 10~7 mbar to about 1 mbar. Preferably, the vacuum conduits may be evacuated to a pressure less than about 1 mbar. The vacuum conduits (34,35,36) of adjacent gaseous flow line sections (21,22,23) are connected. The sealing system (31) are configured to provide a pathway to connect the vacuum conduits (34,35,36) of adjacent gaseous flow line sections (21,22,23). The sealing systems (31) are configured to substantially prevent fluid transfer between the gaseous flow conduits (24,25,26), the liquid conduits (27,28,29), the vacuum conduits (34,35,36), and a region outside of the gaseous flow line (20), respectively. Figure 4 illustrates a view of a coupling linkage (37) of a gaseous flow line section. The coupling linkage (37) may define an end of a gaseous flow line section (not shown). The coupling linkage (37) comprises a flange (38). The flange (38) has defined therein an annulus (39) configured to permit the gaseous flow to pass from one gaseous flow line section to an adjacent gaseous flow line section. The flange (38) further comprises a plurality of channels (40). The channels (40) are arranged radially outward of the annulus (39). The channels (40) are configured to permit fluid transfer between the respective vacuum conduits of adjacent gaseous flow line sections during use. The coupling linkage (37) further comprises a duct (41). The duct (41) is configured to allow ingress and / or egress of liquid from the liquid conduit of the gaseous flow line section. Figures 5A-C illustrate various embodiments of sealing systems (i.e. seals) (42,43,44) in accordance with the present invention. The seals (42,43,44) comprise a number of corresponding features, for which the same reference numerals will be used. The seals (42,43,44) are configured to substantially prevent fluid transfer between the gaseous flow conduit, the liquid conduit, the vacuum conduit, and a region outside the gaseous flow line section, respectively, when in use. The seals (42,43,44) are each configured to be arranged between a pair of flanges of the coupling linkages of adjacent gaseous flow line sections. For example, the seals (42,43,44) may be compressed between a pair of coupling linkages (37) as shown in Figure 4. The seals (42,43,44) each comprise an annulus (45). Each seal (42,43,44) further comprises a first sealing portion (46) configured to substantially prevent fluid transfer between a region outside of the gaseous flow line section and the vacuum conduit. Each seal (42,43,44) further comprises a second sealing portion (47) configured to substantially prevent fluid transfer between the gaseous flow conduit and the vacuum conduit. Each seal (42,43,44) further comprises an apertured portion (48) arranged between the first (46) and second (47) sealing portions. The apertured portion (48) is configured to permit fluid transfer between the vacuum conduits of adjacent gaseous flow line sections arranged about the seal (42,43,44). The apertured portion (48) may comprise a plurality of apertures. The first sealing portion (46) of the seal (42) depicted in Figure 5A comprises an elastomer O-ring. The second sealing portion (47) of the seal (42) also comprises an elastomer O-ring. Such a seal (42) may be appropriate for operation at temperatures less than about 250 °C. The first sealing portion (46) of the seal (43) depicted in Figure 5B comprises a metallic gasket. The second sealing portion (47) of the seal (43) also comprises a metallic gasket. Such a seal (42) may be appropriate for operation at temperatures greater than about 250 °C. The metallic gaskets may be for use in knife-edge seals. The metallic gaskets may comprise nickel-plated aluminium gaskets. The first sealing portion (46) of the seal (44) depicted in Figure 5C comprises an elastomer O-ring. The second sealing portion (47) of the seal (44) comprises a metallic gasket. The first sealing portion (46) and second sealing portion (47) of the seals (42,43,44) may be modified according to the requirements of the system in operation. For the avoidance of doubt, features of any aspects or embodiments recited herein may be combined mutatis mutandis. Reference Kev 1. Gaseous flow line section 2. First generally tubular wall portion 3. Gaseous flow conduit 4. Second generally tubular wall portion 5. Liquid conduit 6. Third generally tubular wall portion 7. Vacuum conduit 8. Coupling linkage 9. Flange 10. Inner flange 11. Outer flange 12. Sealing surfaces 13.Apertured portion 14. Bore holes 15. Duct 16. Inner ring 17. Outer ring 18. Connecting portions 19. Alignment tabs 20. Thermally controlled exhaust line 21. Gaseous flow line section 22. Gaseous flow line section 23. Gaseous flow line section 24. Gaseous flow conduit 25. Gaseous flow conduit 26. Gaseous flow conduit 27. Liquid conduit 28. Liquid conduit 29. Liquid conduit 30. Coupling means 31. Sealing means 32. Liquid ingress duct 33. Liquid egress duct 34. Vacuum conduit 35. Vacuum conduit 36. Vacuum conduit 37. Coupling linkage 38. Flange 39. Annulus 40. Channel 41. Duct 42. Seal 43. Seal 44. Seal 45. Annulus 46. First sealing portion 47. Second sealing portion 48.Apertured portion

Claims

1. A gaseous flow line section (1) for use in a thermally controlled gaseous flow line, comprising:a first generally tubular wall portion (2) defining a gaseous flow conduit (3) configured to convey a substantially gaseous flow;a second generally tubular wall portion (4) substantially surrounding the first generally tubular wall portion to define therebetween a liquid conduit (5) configured to contain a thermally controlled liquid; anda third generally tubular wall portion (6) substantially surrounding the second generally tubular wall portion to define therebetween a vacuum conduit (7) configured to be evacuated.

2. The gaseous flow line section of claim 1, further comprising a first coupling linkage (8) arranged at a first end of the gaseous flow line section and a second coupling linkage arranged at a second end of the gaseous flow line section, each coupling linkage being configured to enable the gaseous flow line section to be coupled to further gaseous flow line sections and / or other components, preferably wherein the first coupling linkage and / or second coupling linkage comprises a flange (9).

3. The gaseous flow line section of claim 1 or 2, further comprising sealing system configured to prevent fluid transfer between the gaseous flow conduit, the liquid conduit, the vacuum conduit, and a region outside the gaseous flow line section, respectively.

4. The gaseous flow line section of claim 3, wherein the sealing system comprises:a first sealing portion configured to substantially prevent fluid transfer between a region outside the gaseous flow line section and the vacuum conduit;a second sealing portion configured to substantially prevent fluid transfer between the gaseous flow conduit and the vacuum conduit; andat least one aperture (13) arranged between the first sealing portion and the second sealing portion, the or each aperture being configured to permit fluid transfer betweenthe respective vacuum conduits of the adjacent gaseous flow line sections arranged about the seal.

5. The gaseous flow line section of any preceding claim, further comprising at least one duct (15) configured to enable the liquid to enter or exit the liquid conduit, preferably wherein the or each duct is fluidly connected to a pump configured to circulate fluid through the liquid conduit.

6. The gaseous flow line section of any preceding claim, wherein during operation, the liquid in the liquid conduit has a temperature at or above a threshold temperature sufficient to substantially prevent condensation of gases of the gaseous flow within the gaseous flow conduit.

7. The gaseous flow line section of any preceding claim, wherein during operation, the vacuum conduit is evacuated to a pressure less than about 1 mbar.

8. The gaseous flow line section of any preceding claim, wherein the gaseous flow line section is substantially linear or wherein the gaseous flow line section comprises an elbow joint, preferably wherein the elbow joint is angled between about 30° and about 90°.

9. The gaseous flow line section of any preceding claim, further comprising thermal regulator for controlling the temperature of the liquid within the liquid conduit, preferably further comprising a pump configured to convey liquid through the liquid conduit.

10. A modular thermally controlled gaseous flow line (20), comprising a plurality of interconnected gaseous flow line sections (21,22,23) according to any preceding claim, wherein, during operation, the gaseous flow conduits (24,25,26) of the respective gaseous flow line sections are fluidly connected; preferably wherein the vacuum conduits (34,35,36) of the respective gaseous flow line sections are fluidly connected, and / or wherein the liquid conduits (27,28,29) of the respective gaseous flow line sections are fluidly connected.

11. A seal (42,43,44) for sealing adjacent gaseous flow line sections of a thermally controlled gaseous flow line according to claim 10, the seal comprising:a first sealing portion (46) configured to substantially prevent fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections and a region outside the gaseous flow line section;a second sealing portion (47) configured to substantially prevent fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections and the respective gaseous flow conduits of the adjacent gaseous flow line sections; anda apertured portion (48) configured to permit fluid transfer between the respective vacuum conduits of the adjacent gaseous flow line sections.

12. The seal of claim 11, wherein the first sealing portion and / or the second sealing portion comprises an elastomeric gasket, preferably wherein the first sealing portion and / or the second sealing portion comprises an elastomeric O-ring.

13. The seal of claim 11 or 12, wherein the first sealing portion and / or the second sealing portion comprises a metallic gasket, preferably a deformable metallic gasket for use in a knife-edge seal.

14. An abatement system comprising:process apparatus having an exhaust outlet through which an exhaust flow may exit the process apparatus;exhaust abatement apparatus having an inlet through which the exhaust flow may enter the exhaust abatement apparatus; anda modular thermally controlled gaseous flow line according to claim 10 connected at a first end to the exhaust outlet of the process apparatus, and at a second end to the inlet of the exhaust abatement apparatus;wherein during operation, the exhaust flow is conveyed through the or each gaseous flow conduit of the or each gaseous flow line section, thermally controlled liquid is present in the or each liquid conduit of the or each gaseous flow line section, and theor each vacuum conduit of the or each gaseous flow line sections are evacuated to a pressure less than about 1 mbar.

15. A method of assembling a gaseous flow line section as defined in any of claims 1 to 9, comprising the steps of:a) providing a first annular flange, a second annular flange, a first generally tubular wall portion, a second generally tubular wall portion, and a third generally tubular wall portion;b) connecting the third generally tubular wall portion to the first annular flange;c) connecting the second generally tubular wall portion to the first annular flange, such that the second generally tubular wall portion is arranged radially inwardly of the third generally tubular wall portion;d) connecting the second annular flange to the third generally tubular wall portion and second generally tubular wall portion;e) inserting the first generally tubular wall portion through the annulus of the first annular flange and the second annular flange, such that the first generally tubular wall portion is arranged radially inwardly of the second generally tubular wall portion; andf) connecting the first generally tubular wall portion to the first annular flange and the second annular flange.

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