GB2029984A - Flow control ferrule - Google Patents

Abstract

The ferrule (10) has a passageway through it in which a part of greater diameter (14b) lies between two parts of smaller diameter (14a and 20). Two successive parts are formed in one steel block (12), the outer part is formed in another steel block (11) and the parts are welded together by a diffusion bonding technique. <IMAGE>

Description

SPECIFICATION Improvements in or relating to ferrules This invention relates to ferrules which are used in controlling the flow of fluid to a plurality of tubes supplied from a common source. Such ferrules, are commonly used in boilers or other heat exchangers having a bank of tubes through which fluid flows in parallel.

In such a boiler, ferrules can be included to control the water flow through the tubes of the boiler. This has an effect in controlling the resultant metal temperature of boiler tubing and, by virtue of the pressure drop induced by the ferrule, helping to stabilize the boiler system. Where the boiler is included in a gas cooled reactor system, the use of ferrules facilitates the matching of the water flow through the tubes to the gas flow over them.

The flow restriction induced by a ferrule is commonly achieved by the reduction of the crosssectional area of the flow path, although the required pressure drop can be achieved by other means, such as a change of direction. Where the tubes of the boiler are themselves of small diameter, the diameter of the passage through a short ferrule may need to be as little as 2mm. By increasing the length of the ferrule, a bore of larger diameter may be used; the diameter will, nevertheless, still be small and difficulties can arise in trying to form such a bore in a ferrule several inches long with an accuracy sufficient to enable the effect of the ferrule to be predicted.

As an alternative to such a ferrule, it has been proposed that the passage through the ferrule should include a portion of a diameter larger than that of either of the portions leading to and from that portion so that pressure loss will result from expansion into the chamber and contraction in flowing out of the chamber. It is desirable that the dimentsions of the passage should be highly accurate and the internal surface smooth. At the same time, there are advantages in forming the ferrule from material that is erosion resistant. An object of the present invention is to facilitate the provision of a ferrule of which the passage includes an expansion chamber without the presence of bead protrusion or screw threads in the passage.

According to the present invention there is provided a ferrule for use in controlling a flow of fluid to one of a plurality of tubes supplied from a common source, the passage through the ferrule containing a part of greater diameter lying between two parts of lesser diameter, the part of greater diameter being in, and terminating at one end of, a steel block, and an a adjacent part of lesser diameter being in another steel block that has been connected to the face of the first block at which the part of greater diameter terminates by a diffusion bonding tech nique.

The present invention also provides a method of forming a ferrule for use in controlling the flow of fluid to one of a plurality of tubes supplied from a common source and having a passage therethrough containing a part of greater diameter lying between two parts of lesser diameter, in which the part of greater diameter is formed in one block of steel with an end of the part of greater diameter lying in an end face of the block, an adjacent part of lesser diameter is formed in, and extends to one end of, another block of steel, and said ends are connected together by a diffusion bonding technique.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings in which Figure 1 shows, in axial cross-section a ferrule leading to an upstanding part of a tube that is connected to a tube plate; and Figure 2 shows, in plan view, part of a bank of ferrules similar to that shown in Figure 1.

In Figure 1, the numeral 1 indicates a tube plate between which and a further tube plate (not shown) extend a bank of parallel tubes on which one is indicated at 2. A cylindrical upstand 3 forms, in effect, a part of the tube 2 but, being of Inconel, is of a material different from that of the rest of the tube.

The upstand is friction welded at its lower end, at 4, to a plane surface formed in part by the end of the tube 2 and in part by the surrounding margin of the tube sheet 1. Thus, the inner annulus of the end of the upstand 3 is connected to the end of the tube 2 and the outer annulus of the end of the upstand 3 is connected to the tube plate 1. The ferrule, indicated generally at 10, is connected to the upper end of the upstand 3.

The ferrule 10 is formed from three generally cylindrical blocks 11, 12 and 13 connected together co-axially end-to-end. The central block 12 is of right-cylindrical external section. A bore 14 extends co-axially through the block, being formed by drilling from each end of the block. The part 14a of the bore that opens into one end face of the block is of a smaller diameter than the part 14b of the bore that opens into the other end face of the block. The surface of the part 14h is partly right cylindrical (at 15), partly flat (at 16) in a plane perpendicular to the axis of that cylinder, and partly (at 17) formed by a curved surface merging from the cylindrical part 15 to the flat part 16.

The upper of the three blocks, 13, is essentially similar to the central block 12, except that its outer surface is recessed, at 18, at the end into which the part of the bore of smaller diameter opens.

The lower block 11 may be referred to as the connecting block, and is provided co-axially with a bore 20 of uniform diameter, the same as that of the parts 14a of smaller diameter in the blocks 12 and 13.

The end of block 11 that is connected to the central block 12 is of the same outer diameter as that of the block 12 and the rest of the outer surface, as will be described later, lies within the cylindrical envelope defined by that end.

Each of the blocks 11, 12 and 13 is formed from erosion resistant steel and in forming the ferrule, the adjacent end surface of the blocks are highly finished and each block is brought into end-to-end contact with the next, with their axes aligned. They are then welded together by a diffusion bonding technique in which they are held together under pressure and heated, under vaccuum or in an inert atmosphere, so that there occurs between the contacting surfaces a molecular interchange that effects a bond. Subsequent machining is nenecessary and the bond is effected virtually without shrinkage or distortion, and without the production of a weld bead, protrusion or rag.

The aligned bores in the blocks 11,12 and 13 form, in effect, a single bore through the ferrule. Both parts of the bore that are of the larger diameter are of the same diameter and the parts that are of the smaller diameter are also of the same diameter. The ends of the parts of smaller diameter that lie at the end face of a block are slightly countersunk, at 21, before the blocks are joined together. In modifications, the parts of smaller diameter may not all be of the same diameter.

The major part 22 of the length of the connecting block 11 is of smaller outer diameter than the end part that is connected to the block 12. The lower surface 23 of the end part provides a shoulder at the upper end of the major part 22 and the major part 22 is externally threaded to engage with a screw th read formed internally of the upstand 3. The distance between the lower end of the upstand 3 and the lower, or outlet end of the ferrule 10 is at least twenty times the diameter of the outlet from the ferrule. Any cavitation resulting from discharge from the ferrule is most likely to occur within this range, so that the range in which cavitation is most likely to occur is defined by material that is apt to resist cavitation.

The threaded connection between the ferrule 10 and the upstand 3 facilitates the replacement of the ferrule by another. To change ferrules easily is an advantage during boiler commissioning if minor corrections to boiler performance and stability are required, or if the ferrule becomes eroded, blocked or damaged in any way during subsequent boiler service.

In connecting the ferrule 10 to the upstand 3, the major part 22 passes through a "banjo" collar 30. At each end of the collar is a metallic O-ring 31 and the collar 30 and O-rings 31 are clamped between the upper end of the upstand 3 and the shoulder 23. A passage 34 through the collar 30 communicates at one end with the interior of the upstand 3 through a recess 35 in the thread of the threaded portion of the upstand 3. The passage 34 is connected at its other end, in a way that is not illustrated, to a pressure responsive device lying outside the wall of the containing feed header in which the ferrules lie, the connection being by a small bore tapping tube 36.At its connection with the passage 34, the tube 36 contains a simple ball check valve 38 so that should the tube 36 become damaged and result in a leak, the valve would operate to close the passage and insulate the tube. By use of the pressure responsive device, the pressure drop through each individual ferrule can be measured. By knowing the pressure drop, the water flow through the ferrule can be deduced so that the performance of the boiler circuit in which the ferrule is included can be predicted.

Since the tube 2 lies close to the other tubes in the tube bank, the associated upstands 3 also lie in closely ganged parallel rows with the result that in providing all the tubes with ferrules it is not easy to hold each collar still whilst the corresponding ferrule is screwed into its tube, yet significant movement of the collar could damage the connection to the tapping tube 36. For this reason, the external surface of the collar 30 is formed to provide five consecutive sides 40 (as is shown in Figure 2) that would constitute part of a regular hexagon. There are two additional longer sides 41 that project from these beyond the limits of the hexagon and have a further, shorter, side 42 between their outer ends. When the collars 30 of any row are in position, the projecting sides 41 of the collars all project to that side of the row. The projecting sides 41 of the collars associated with the next adjacent row all project towards those of the previous row and the sides 41 of any collar in the new row lie between the sides 41 of two adjacent collars in the previous row which will then act to prevent rotation of the collar in the new row whilst the associated ferrule is being screwed into poSition.

Claims (13)

1. A ferrule for use in controlling the flow of fluid to one of a plurality of tubes supplied from a common source, the passage through the ferrule containing a part of greater diameter lying between two parts of lesser diameter, the part of greater diameter being in, and terminating at one end of, a steel block, and an adjacent part of lesser diameter being in another steel block that has been connected to the face of the first block at which the part of greater diamterterminates by a diffusion bonding technique.

2. A ferrule as claimed in claim 1 in which the other adjacent part of lesser diameter is formed in the block that contains the part of greater diameter.

3. A ferrule as claimed in either of the preceding claims in which the bore through the block to which the block containing the part of larger diameter is connected is of constant diameter, and that block is received within, and sealed to, one of the tubes.

4. A ferrule as claimed in claim 3 in which the external surface of the block that is received within the tube provides a shoulder projecting outwardly from a portion that is externally threaded, the externally threaded portion engages with a thread formed internally of the tube so as to hold the ferrule in position, and sealing means lie clamped between the shoulder and the end of the tube.

5. A ferrule as claimed in any of the preceding claims in which the tube to which the ferrule is connected is formed for part of its length from stainless steel connected to one end of a part formed from different material, and fluid discharging from the ferrule flows first through the part of stainless steel and then into the other part.

6. Aferrule as claimed in Claim 5 in which the distance between the end of the ferrule and the junction between the part of stainless steel as the rest of the tube is not less than twenty times the diameter of the outlet from the ferrule.

7. A ferrule as claimed in either of claims 5 and 6 in which the rest of the tube is received within a tube sheet, the end of the rest of the tube is in the same plane as the surrounding part of the surface of the tube sheet, and the part of stainless steel has been connected to the end of the part of the tube and to the surrounding part of the surface of the tube sheet by a friction weld.

8. A ferrule as claimed in claim 2 or any of claims 3 to 7 when appendant to claim 2 in which the passage through the ferrule contains a plurality of parts of greater diameter alternating with parts of lesser diameter, and the ferrule includes a plurality of blocks that have been connected end-to-end by a diffusion technique, each block containing one part of greater diameter and one part of lesser diameter.

9. A bank of ferrules each as claimed in claim 4 or any of claims 5 to 8 when appendant to claim 4 in which there is clamped between each shoulder and the tube by which the ferrule is received a collar, each collar is so shaped that a surface of the collar associated with one ferrule abuts a surface of the collar associated with the next associated ferrule to prevent rotation of that collar as a consequence of rotation of the ferrule in the sense that screws it into clamping co-operation with the tube in which it is received.

10. A method of forming a ferrule for use in controlling the flow of fluid to one of a plurality of tubes supplied from a common source and having a passage therethrough containing a part of greater diameter lying between two parts of lesser diameter, in which the part of greater diameter is formed in one block of steel with an end of the part of greater diameter lying in an end face of the block, an adjacent part of lesser diameter is formed in, and extends to one end of, another block of steel, and said ends are connected together by a diffusion bonding technique.

11. A ferrule as claimed in any of Claims 1,2 and 8 formed by a method as claimed in Claim 10.

12. a bank of tubes, each fitted with a ferrule substantially as described with reference to, and as illustrated by the accompanying drawings.

13. A-method of forming a ferrule substantially as described with reference to, and as illustrated by, the accompanying drawings.