Cooling method and apparatus

Abstract

A cooling apparatus (1) and method are disclosed for cooling a weld line (110) of a product (100). The apparatus comprises a cooling zone (10) having an entry (14) and an exit (15) and the product (100) is arranged to pass along the cooling zone (10) from the entry (14) to exit (15). The apparatus further comprises delivery means for delivering liquid to an outer surface of the product, the delivery means comprising a first set of nozzles (11) arranged to deliver liquid at a first flow rate to the outer surface of the product (100) at a first region (111) comprising the weld line area and a second set of nozzles (12a, 12b) arranged to deliver liquid at a second flow rate to a second region (112a, 112b) adjacent to the first region (111).

Description

[0001] Cooling Method and Apparatus

[0002] Technical field

[0003] The invention relates to a cooling method and apparatus for cooling a weld line of a product, in particular but not exclusively of welded tubes, in particular but not exclusively for high frequency induction (HFI) welded tubes, such as electrical resistance welded (ERW) tubes. In particular, but not exclusively, the method and apparatus are for cooling the welded zone of an ERW tube following annealing.

[0004] Background

[0005] ERW tubes are manufactured by cold forming a sheet of steel into a cylindrical shape.

[0006] Once the substantially cylindrical shape has been formed, the two edges of the steel sheet that then face each other are welded together to form the tube. In ERW, a current is passed between the two edges to heat the steel to a temperature that causes the edges to be welded together.

[0007] Welding of steels can result in an undesirable loss of toughness in the weld region due to the presence of brittle phases, e.g., upper bainite and martensite. Such phases are often a result of uncontrolled high cooling rates during the welding process. The solidification and subsequent cooling in the weld and surrounding region results in grain sizes that are not well controlled, leading to increased hardness and reduced ductility.

[0008] For this reason, once the edges have been welded together, the weld may be subjected to an annealing process. Post weld annealing provides the opportunity to re-set the material around the weld, with the aim of improving toughness and restoring ductility to allow the product to be worked more easily.

[0009] In such an annealing process, brittle phases such as upper bainite are removed by austenisation, i.e. by heating the steel to a high temperature in the austenite stability range such that austenite is formed. Then, by controlled cooling, austenite transforms back into ferrite, while hard phases are prevented from forming and the grain size is minimised. There is a small range of cooling rates at which both of these conditions are met; the rate must be fast enough that grain size is minimized, and slow enough that undesirable phases are avoided. Conventional cooling strategies spray water on the outer surface of the steel in order to achieve a desired cooling rate as austenite transforms back into ferrite. Austenite has a face-centred cubic (FCC) structure, while ferrite has a body-centered cubic (BCC) structure, and the rate of cooling as the steel transforms from the FCC structure to the BCC strongly influences the resulting phases and grain structure. Typically, transformation from austenite starts in the region of 800°C and is completed by 600°C.

[0010] However, conventional water spray cooling utilises a uniform spray pattern. This can lead to the outer surface of the steel having a high cooling rate, which increases the likelihood of the formation of undesirable brittle phases at the outer surface of the tube and relatively large grain sizes at the inner surface of the tube. As this compromises the resulting properties of the tube, it may be necessary to apply a further heat treatment process if the structural application requires greater weld line toughness.

[0011] The present invention aims to ameliorate the disadvantages of the prior art by providing a method and apparatus for controlled cooling of ERW tubes following post weld annealing. The present invention may address corresponding problems in the cooling of a weld line of any type of product and is not limited to use with welded tubes, or to use with a particular material.

[0012] The method and apparatus of the invention are particularly useful for a tube produced in a continuous process where cooling on the inside of the tube is not generally possible. In such scenarios, due to the conductive properties of steel, there is a higher cooling rate at the outer surface compared the inner surface. It is an aim of the invention to use specific and modifiable cooling rates through the phase transformation temperature range, while also minimising the cooling rate difference between the inner and outer surfaces of the tube. This optimizes the crystal structure of the surrounding area.

[0013] The method and apparatus of the invention provide improved and consistent properties of the weld following post weld annealing and cooling. This avoids the need for a subsequent process in which the whole tube is heated to improve the properties of the welded region and therefore the tube. This offers significant energy savings, while producing a product with comparable properties to a tube that has been treated by a subsequent heating process. Summary of invention

[0014] In accordance with a first aspect of the invention, there is provided a cooling apparatus for cooling a weld line of a product, the apparatus comprises a cooling zone having an entry and an exit, the product being arranged to pass along the cooling zone from the entry to exit, the apparatus further comprising delivery means for delivering liquid to an outer surface of the product, the delivery means comprising a first set of nozzles arranged to deliver liquid at a first flow rate to the outer surface of the product at a first region comprising the weld line area, and a second set of nozzles arranged to deliver liquid at a second flow rate to a second region adjacent to the first region.

[0015] In an embodiment, the second flow rate is greater than the first flow rate, and the first and second regions are coaxial with the weld line.

[0016] In an embodiment, the delivery means is configured to deliver liquid simultaneously to the first and second regions.

[0017] In an embodiment, the first set of nozzles are arranged in a substantially linear array substantially parallel with the weld line in use, and the second set of nozzles comprises a first subset of nozzles arranged in a substantially linear array, substantially parallel with the first set of nozzles at a first side thereof, and a second subset of nozzles arranged in a substantially linear array, substantially parallel with the first set of nozzles at a second side thereof.

[0018] In an alternative embodiment, the first set of nozzles are arranged in a substantially linear array parallel with the weld line in use, and the second set of nozzles are arranged in a substantially linear array, which is substantially collinear with the first set of nozzles.

[0019] In an embodiment, the first flow rate increases along the first set of nozzles in a direction which is from the entry to the exit of the cooling zone, and the second flow rate increases along the second set of nozzles in a direction which is from the entry to the exit of the cooling zone. Optionally, at each respective location along said direction from the entry to the exit of the cooling zone, the second flow rate is greater than the first flow rate.

[0020] In an embodiment, the cooling zone is a first cooling zone and the apparatus comprises a second cooling zone arranged downstream of the first cooling zone, the second cooling zone having an entry and an exit, the product being arranged to pass along the second cooling zone from the entry to the exit of the second cooling zone, and the second cooling zone comprises a further delivery means for delivering liquid to the outer surface of the product, the further delivery means comprising a third set of nozzles arranged to deliver liquid at a third flow rate to the outer surface of the product at a third region of the outer surface of the product.

[0021] In an embodiment, the third flow rate is greater than the first flow rate. Optionally the third flow rate is greater than the maximum value of the first flow rate.

[0022] In an embodiment, the third set of nozzles is arranged in a substantially linear array substantially parallel with the weld line in use, and the third flow rate increases along the third set of nozzles in a direction which is from the entry to the exit of the second cooling zone.

[0023] In an embodiment, the third region is coaxial with the weld line and includes the weld line. The first region has a width that is substantially perpendicular to the weld line and the third region has a width that is substantially perpendicular to the weld line, the width of the third region being greater than the width of the first region.

[0024] In an embodiment, the first set of nozzles extend along an axis which is parallel with a longitudinal axis of the apparatus and the third set of nozzles extend along an axis which is parallel with the longitudinal axis of the apparatus, the axes of the first and third set of nozzles being colinear.

[0025] In an embodiment, the apparatus comprises a third cooling zone arranged downstream of the second cooling zone, wherein the third cooling zone comprises a fourth set of nozzles arranged to deliver liquid at a fourth flow rate to the outer surface of the product. The fourth flow rate can be greater than the third flow rate.

[0026] In an embodiment, the or each cooling zone is arranged between an entry and an exit of the apparatus, the apparatus further comprising conveying means for conveying the product from the entry to the exit of the apparatus.

[0027] In an embodiment, the apparatus further comprises a tracking system for detecting and tracking the position of the weld line. In an embodiment, the apparatus further comprises an adjustment system for adjusting the position of the nozzles relative to the product, and / or an orientation of the nozzles relative to the product.

[0028] In accordance with a second aspect of the present invention, there is provided a method for cooling a weld line of a product, the method comprising: introducing the product to a cooling zone of an apparatus for cooling the weld line and passing the product along the cooling zone from an entry to an exit of the cooling zone; and delivering liquid to the outer surface of the product via a delivery means of the apparatus, the delivery means comprising a first set of nozzles and a second set of nozzles, wherein the step of delivering liquid to the outer surface comprises delivering liquid at a first flow rate via the first set of nozzles to a first region comprisingthe weld line and delivering liquid at a second flow rate via the second set of nozzles to a second region adjacent to the first region.

[0029] In an embodiment, the second flow rate is greater than first flow rate, and the first and second regions are coaxial with the weld line.

[0030] In an embodiment, the method comprises delivering the liquid simultaneously to the first and second regions.

[0031] In an embodiment, the cooling zone is a first cooling zone and the method further comprises introducing the product to a second cooling zone of the apparatus the second cooling zone comprising an entry and an exit, wherein the second cooling zone is downstream of the first cooling zone and comprises a further delivery means for delivering liquid to the outer surface of the product, the further delivery means comprising a third set of nozzles, the method further comprising: introducing the product to the second cooling zone such that the product passes along the second cooling zone from the entry to the exit thereof; and delivering liquid at a third flow rate via the third set of nozzles to a third region of the surface. In an embodiment, the third flow rate is greater than the first flow rate, and the third region is coaxial with and includes the weld line.

[0032] In an embodiment, the first region has a width that is substantially perpendicular to the weld line and the third region has a width that is substantially perpendicular to the weld line, the width of the third region being greater than the width of the first region.

[0033] In an embodiment, the method further comprises the step of introducing the product to a third cooling zone of the apparatus, wherein the third cooling zone is downstream of the second cooling zone, and the method further comprises delivering liquid at a fourth flow rate via a fourth set of nozzles to the outer surface of the product.

[0034] The fourth flow rate can be greater than the third flow rate. The method can further comprise conveying the product from an entry to an exit of the apparatus using a conveying means, wherein the or each cooling zone is arranged between the entry and the exit of the apparatus.

[0035] In an embodiment, the method comprises using a tracking system for detecting and tracking the position of the weld line, and using an adjustment system to adjust the position of the nozzles relative to the product and / or or an orientation of the nozzles relative to the product.

[0036] Brief description of drawings

[0037] Figure 1 shows a section of a cooling apparatus according to an embodiment of the invention.

[0038] Figure 2 shows a plan view of the cooling zones of the cooling apparatus shown in Figure 1.

[0039] Figure 3a shows a cross-section of the nozzle arrangement of the first cooling zone of the cooling apparatus, taken along line Ill-Ill in Figure 2, within which an ERW tube is arranged. Figure 3b shows a cross-section of the nozzle arrangement of the second cooling zone of the cooling apparatus, taken along line IV-IV in Figure 2, within which an ERW tube is arranged.

[0040] Figure 3c shows a cross-section of the nozzle arrangement of the second cooling zone of the cooling apparatus, taken along line V-V in Figure 2, within which an ERW tube is arranged; and,

[0041] Figure 4 is a schematic illustration of the steps associated with a method accordingto an embodiment of the present invention.

[0042] Detailed description

[0043] The apparatus and method will now be described with reference to the drawings.

[0044] Figure 1 illustrates a section of a cooling apparatus 1 accordingto an embodiment of the invention. The apparatus 1 comprises a first cooling zone 10 arranged at a first end 1 a of the apparatus (i.e. the entry of the apparatus), and a second cooling zone 20 arranged adjacent and downstream of the first cooling zone 10. The apparatus 1 of the embodiment illustrated in Figure 1 is for cooling the outer surface of a product such as an ERW tube (100, shown in Figures 2 and 3).

[0045] The first cooling zone 10 comprises liquid delivery means for delivering a liquid to the outersurface 100a ofthe tube 100. The delivery means ofthefirst coolingzone comprises a first set of nozzles 11 which is indicated generally by reference numeral 11 . The nozzles 11 are shown in a linear arrangement which is parallel with the longitudinal axis of the apparatus. Liquid, preferably water, is delivered to the nozzles 11 via a pump and conduit system (shown schematically in Figure 3a as ‘61 ’), which may form part of the delivery means. The liquid can be delivered at any appropriate temperature. In some embodiments, the liquid can be delivered at 20-50°C, preferably 35-45°C.

[0046] The delivery means of the illustrated embodiment also comprises a second or outer set of nozzles 12a, 12b arranged linearly in two rows either side of the first set of nozzles 11 . Liquid, preferably water, is delivered to the nozzles 12a, 12b via a pump and conduit system (shown schematically in Figure 3a as ‘62a, 62b’), which may form part of the delivery means. Each of the rows of nozzles extends substantially parallel to the first set of nozzles 11 in a longitudinal direction of the apparatus 1. However, in alternative embodiments, other arrangements of the first and second sets of nozzles may be used.

[0047] In the illustrated embodiment, each of the first and second sets of nozzles 11 , 12a, 12b is arranged in a linear array which extends longitudinally from a first end 14 to a second end 15 of the first cooling zone 10. The second end 15 of the first cooling zone 10 corresponds to a first end of the second cooling zone 20.

[0048] In the illustrated embodiment, thefirstset of nozzles 11 comprises a range of nozzles that are configured to deliver liquid at a first flow rate which increases from the first end 14 to the second end 15 of the first cooling zone 10. Any appropriate number of different types of nozzles can be used to achieve this. In some embodiments, the first set of nozzles 11 can comprise 2-10 different nozzle types, preferably 4-8 different nozzle types, and more preferably 5 different nozzle types. The pressure of the liquid supplied to the nozzles 11 , the type of the nozzles and / or the size of the nozzles 11 , for example, may be varied so as to provide said increase in the first flow rate from the first end 14 to the second end 15 of the first cooling zone 10.

[0049] Similarly, the second set of nozzles 12a, 12b comprise a range of nozzles that are configured to deliver liquid at a second flow rate. In some embodiments, the second flow rate is constant from the first end 14 to the second end 15 of the first cooling zone 10. In other embodiments, the second flow rate can increase from the first end 14 to the second end 15 of the first cooling zone 10. The flow rate is selected to ensure the required cooling rate of the tube 100 in the first cooling zone 10. Again, any appropriate number of different types of nozzles can be used. The pressure of the liquid supplied to the nozzles 12a, 12b, the type of the nozzles and / or size of the nozzles 12a, 12b, for example, may be varied so as to provide said increase in the second flow rate from the first end 14 to the second end 15 of the first cooling zone 10.

[0050] The second cooling zone 20 comprises further delivery means for delivering liquid to the outer surface 100a of the tube 100. The further delivery means comprises a third set of nozzles 21 , a pump and conduit system (shown schematically in Figure 3b as ‘63a, 63b’)). The third set of nozzles 21 is for delivering a liquid to the outer surface 110a of the tube 100. In the illustrated embodiment, the third set of nozzles 21 comprises two adjacent rows of nozzles 21 a, 21 b in a parallel arrangement. The two rows of nozzles 21 a, 21 b extend longitudinally from point 15 to point 16 (as shown in Figure 2), which is the second end of the second cooling zone 20.

[0051] In the illustrated embodiment, the third set of nozzles 21 comprises a range of nozzles that are configured to deliver liquid at a third flow rate which in some embodiments can increase from the first end 15 to the second end 16 of the second zone 20 to ensure the required rate of cooling of the tube 100. The pressure supplied to the nozzles 21 , the type of the nozzles and / or size of the nozzles, for example, may be varied so as to provide said increase in the third flow rate from the first end 15 to the second end 16 of the second cooling zone 20. In other embodiments, the third flow rate remains constant from the first end 15 to the second end 16 of the second cooling zone 20.

[0052] Figure 2 is a schematic plan view illustrating the first and second cooling zones 10, 20, and a third cooling zone 30 (not shown in Figure 1 ), wherein each of the cooling zones is arranged between the first end (or entry) 1 a and the second end (or exit) 1 b of the apparatus. Figure 3 illustrates a cross-section of the first cooling zone 10 within which an ERW tube 100, which has been subjected to a post weld annealing process, is arranged.

[0053] The first set of nozzles 11 deliver liquid to a first region 111 of the outer surface of the tube 100 comprising the weld line 110 and an adjacent region. Liquid is delivered by the first set of nozzles 11 at a first flow rate, which increases from the first end 14 to the second end 15 of the first cooling zone 10, as described above.

[0054] At the same time, the second set of nozzles 12a, 12b deliver liquid to the second region 112 of the outer surface of the tube, which comprises a first subregion 112a on a first side of the first 111 region and second subregion 112b on a second side of the first region 111 , at a second flow rate, which can be greater than the first flow rate, and which can remain constant or increase from the first end 14 to the second end 15 of the first cooling zone 10, as described above. As shown in Figure 3a, the first set of nozzles 11 is arranged generally vertically above the weld line 110 and the first region 111 of the tube 100. The second set of nozzles 12a and 12b are arranged adjacent to the first set of nozzles 11 , the first row of nozzles 12a being located above the first subregion 112a and the second row of nozzles 12b being located above the second subregion 112b.

[0055] While, as described above, the second set of nozzles 12a, 12b of the illustrated embodiment is arranged either side of the first set of nozzles 11 , in alternative embodiments, other arrangements of the first and second sets of nozzles can be used; for example, the first and second sets of nozzles 11 , 12a, 12b can be arranged colinearly, with the second set of nozzles 12a, 12b being angled to deliverwaterto the second region 112, provided that liquid is delivered to the first region 111 at a first flow rate and to a second region 112 at a second flow rate. In some embodiments, this may negate the need for a separate spray system (i.e. a separate, first set of nozzles) between the second set of nozzles.

[0056] It will be appreciated that, in relation to each respective set of nozzles, the number of the nozzles in the set, the size of the nozzles, the type of the nozzles and / or the pressure(s) of the liquid supplied to the nozzles by the respective pump and conduit arrangement(s), may be arranged such that the respective flow rate(s) is / are provided. In the described embodiments, the first 11 and second 12a, 12b sets of nozzles are connected to different pumps, i.e. respective first and second pumps, to provide said delivery of liquid at the respective flow rates. Alternatively, the first and second sets of nozzles may be connected to the same pump.

[0057] The first flow rate is such that liquid is delivered to the first region 111 at a lower flow rate than the second flow rate, which causes a reduced rate of cooling of the first region 111 compared to the second region 112 when these regions are in the first cooling zone 10.

[0058] The second flow rate is higher than the first flow rate such that the liquid is concentrated in the second region 112 of the tube when the tube is in the first cooling zone 10. As the second region 112 is a region of lower temperature than the first region 111 , heat is conducted from the first region 111 to the second region 112, as shown by arrows C. Effective cooling of the second region 112 by the apparatus and method of the invention therefore aids the cooling of the first region 111 at a desired rate. A further benefit of the increased flow rate in the second region 112 is that it promotes cooling rates at the inner surface 100b of the tube 100 while keeping the outer cooling rates of the first region 111 at an acceptable level, thereby improving the properties of the cooled regions.

[0059] The liquid is delivered to the first region 111 at a flow rate which provides controlled cooling at the desired rate when the product has an outer surface temperature in the first region 111 of between 800°C and 600°C and will depend on the grade of the steel being processed. For example, some steels (such as API X60-X70 grade line pipe steel) can tolerate a cooling rate of approximately 30°C per second (or a range of 26-34°C, preferably 28-32°C per second), while other steels (such as API X52 grade line pipe steel) should generally have a cooling rate of 15°C per second or less (or a range of 11 -19°C per second, preferably 13-17°C per second).

[0060] The apparatus 1 can be of any appropriate length that delivers the required rate of cooling. However, in preferred embodiments, the distance between the first end 14 and the second end 15 of the first cooling zone can be approximately 2-5 metres, preferably 3-4 metres and more preferably 3.5 metres.

[0061] If the first region is to be cooled at a rate of approximately 15°C per second in the first cooling zone 10, the first flow rate can begin at approximately 8 Litre / Min. metre at the first end 14 and increase to approximately 31 Litre / Min. metre at the second end 15. If the first region is to be cooled at a rate of approximately 30°C per second in the first cooling zone 10, the first flow rate can begin at approximately 25 Litre / Min. metre and increase to approximate 125 Litre / Min. metre at the second end 15.

[0062] If liquid is to be delivered to the outer surface of a tube to provide a cooling rate of the first region 111 (specifically, the outer surface of the tube at the first region) of approximately 15-30°C per second, then the second flow rate may begin at approximately 110 Litre / Min. metre at the first end 14 and increase gradually to approximately 220 Litre / Min. metre at the second end 15 of the first cooling zone 10. In some embodiments, the second flow rate can be constant throughout the first cooling zone.

[0063] Once the outer surface of the first region 111 is cooled to below 600°C and the transformation from austenite is complete, a higher flow rate can be applied to the outer surface area of the tube 100 comprising weld line 110 to increase the cooling rate without the risk of forming undesirable brittle phases. In the illustrated embodiment, to increase or control the rate of cooling of the first region once the first region 111 of the tube 100 has been cooled to below 600°C in the first cooling zone 10, the tube 100 enters the second cooling zone 20. In the second cooling zone 20, the third set of nozzles 21 delivers liquid at a third flow rate (which can be constant or can increase from the first end 15 to the second end 16 of the second cooling zone 20) to a third region 121 of the tube. As shown in Figure 2 and 3b, the width of the third region 121 (the width being substantially perpendicular to the longitudinal axis of the apparatus 1 ) is wider than that of the first region 111. Both the first region 111 and the third region 121 comprise the weld line 110.

[0064] When the first region 111 has been cooled at a rate of approximately 30°C per second in the first cooling zone 10, the third flow rate can be greater than the first flow rate and can remain the same throughout the second cooling zone 20. When the first region 111 has been cooled at a rate of approximately 15°C in the first cooling zone 10, the third flow rate can be an extension of the increasing rate of cooling in the first cooling zone 10 so that the cooling rate increases in a gradual or stepped manner from the first end 14 of the first cooling zone 10 to the second end 16 of the second cooling zone 20. It will be appreciated that the flow rate in the first and second zones 10, 20 can be adapted to achieve the desired rate of cooling, and that the flow rate can be consistent or varied from a first end of a cooling zone to a second end of a cooling zone.

[0065] The distance between the first end 15 and the second end 16 of the second cooling zone 20 can be of any appropriate length that delivers the required rate of cooling. In a preferred embodiment, the distance between the first end 15 and the second end 16 can be 1 -4 metres, preferably 2-3 metres. As with the nozzles of the first cooling zone 10, the third set of nozzles 21 can include any appropriate number of nozzles to provide the desired rate of cooling. Once liquid has been delivered in the first cooling zone to provide a cooling rate of 15°C per second, the third flow rate can be an average of approximately 42 Litre / Min. metre at the first end 15 of the second cooling zone 20, increasing to an average of approximately 56 Litre / Min. metre at the second end 16 of the second cooling zone 20. If liquid has instead been delivered in the first cooling zone to provide a cooling rate of 30°C per second, the third flow rate can be an average of approximately 165 Litre / Min. metre throughout the second cooling zone 20, and in some embodiments, liquid will not be delivered along the full length of the second cooling zone.

[0066] When a cooling rate of 15°C per second is used, it may be necessary to provide additional cooling at the end of the second cooling zone. In such embodiments, a third cooling zone

[0067] 30 can be provided. The distance between the first end 16 of the third cooling zone 30 (which corresponds to the second end of the second cooling zone 20) and the second end 17 of the third cooling zone 30 can be any appropriate length that delivers the required level of cooling. The third cooling zone 30 comprises a fourth set of nozzles 31 arranged in substantially two linear, parallel arrays of nozzles 31 a, 31 b, orientated substantially parallel with the weld line 110 in use (as shown in figure 3c), which are arranged to deliver liquid at a fourth flow rate to a fourth region 131 of the outer surface of the product. The two rows of nozzles 31 a, 31 b extend longitudinally from point 16 to point 17 (as shown in Figure 2), which is the second end of the third cooling zone 30. The fourth region 131 may be equivalent in width to the third region 121. In a preferred embodiment, the distance between the first end 16 and the second end 17 can be 0.25- 2 metres, preferably 0.5 metres. The fourth flow rate can be 120 Litre / Min. metre between the first and second ends 16, 17 of the third cooling zone 30.

[0068] Liquid, preferably water, is delivered to the nozzles 31 a, 31 b via a pump and conduit system (shown schematically in Figure 3c as ‘64a, 64b’) which may, with the nozzles 31 a,

[0069] 31 b, form part of a further delivery means.

[0070] While the cooling of the product is described in the context of different regions, it will be appreciated that these are described in relation to the regions that are cooled by the nozzles at a particular point in time. Referring to figure 4 of the drawings, as a particular point along the length of the tube 100 enters the first cooling zone 10 (at step 201) 10, the outer surface of that point corresponding to the first and second regions 111 , 112 will be cooled, as the tube 100 moves along the first cooling zone (step 202) by the liquid delivered (at step 203) by first set of nozzles 11 at a first flow rate (step 204), and by liquid delivered by the second set of nozzles 12a, 12b at the second flow rate (at step 205). As the same point enters the second cooling zone 20 (at step 206), the outer surface of that point correspondingto the third region 121 will be cooled by liquid delivered by the third set of nozzles 21 at the third flow rate (at step 207). If required, the tube 100 can then be introduced (at step 208) to a third cooling zone 30 for cooling with liquid delivered by a fourth set of nozzles 31 at a fourth flow rate (at step 209).

[0071] The apparatus 1 can comprise means for moving the tube 100 relative to the apparatus 1 . For example, the apparatus 1 can comprise conveying means such as rollers, bearings or belts for conveying the tube 100 through the apparatus, for example from the first end 1 a to the second end 1 b of the cooling apparatus, and this can be at any appropriate speed to perform the desired cooling. In a preferred embodiment, the tube 100 can move from the first end 1 a to the second end 1 b of the cooling apparatus 1 at a speed of between 0.24m / s to 0.4m / s (i.e. between 50 feet per minute and 75 feet per minute).

[0072] In some embodiments, for example embodiments comprising means for conveying the tube 100 through the apparatus 1 , the tube may rotate slightly as it moves through the apparatus, causing poor alignment of the nozzles 11 , 21 , 31with the weld line 110 and preventing liquid from being directed at the correct regions of the tube. For this reason, in some embodiments, the apparatus 1 comprises a tracking system 40 for tracking the position of the weld line 110 (at step 210) in the apparatus and an adjustment system 50 for adjusting the position of the nozzles relative to the tube 100 and / or or an orientation of the nozzles 11 , 21 , 31 relative to the tube 100 (at step 211 ). If the tracking system 40 detects that the nozzles 11 , 21 , 31 are not correctly aligned with and / or directed to the weld line 110, the position and / or orientation of the nozzles 11 , 21 , 31 relative to the tube 100 can be adjusted using the adjustment system 50, for example by alteringthe position of the nozzles 11 , 21 , 31. This ensures that the nozzles remain in the correct position and orientation relative to the weld line for optimum cooling.

[0073] This arrangement allows the cooling rate at the outer tube surface 110a to be tuned to the desired values, whilst the tube inner cooling rate is maximised. This prevents the formation of brittle phases whilst promoting the formation of smaller grain, especially at the inner surface 110b. Toughness performance of the weld line 110 is also maximised, without the need for further manufacturing processes.

[0074] During ERW tube manufacturing, only a small portion of the tube (i.e. the weld and surrounding area) is raised to a temperature over 800°C, so a uniform spray over a large area is not a necessary, and does not lead to optimal results. Compared to conventional water spray cooling which use a uniform spray pattern to deliver water to the tube outer surface 110a, the present invention uses a focused application of water spray to a small portion of the weld and the surrounding area for controlled cooling. By concentrating the liquid spray on a peripheral region of the outer surface to achieve the desired cooling rates without subjecting the weld line 110 to the same high rate of cooling, it is possible to achieve an optimised crystal structure and the required weld toughness.

[0075] It will be appreciated that the method and apparatus of the invention can be used to mitigate or address corresponding problems with different types of products and / or different materials and is not limited to where the liquid is water. The method and apparatus of the invention can utilise water spray under pressure through conventional, commercially available nozzles.

Claims

CLAIMS1 . A cooling apparatus for cooling a weld line of a product, the apparatus comprises a cooling zone having an entry and an exit, the product being arranged to pass along the cooling zone from the entry to exit, the apparatus further comprising delivery means for delivering liquid to an outer surface of the product, the delivery means comprising a first set of nozzles arranged to deliver liquid at a first flow rate to the outer surface of the product at a first region comprising the weld line area, and a second set of nozzles arranged to deliver liquid at a second flow rate to a second region adjacent to the first region.

2. An apparatus according to claim 1 , wherein the second flow rate is greater than the first flow rate.

3. An apparatus according to any preceding claim, wherein the first and second regions are coaxial with the weld line.

4. An apparatus according to any preceding claim, wherein the delivery means is configured to deliver liquid simultaneously to the first and second regions.

5. An apparatus according to any preceding claim, wherein the first set of nozzles are arranged in a substantially linear array substantially parallel with the weld line in use, and the second set of nozzles comprises a first subset of nozzles arranged in a substantially linear array, substantially parallel with the first set of nozzles at a first side thereof and a second subset of nozzles arranged in a substantially linear array, substantially parallel with the first set of nozzles at a second side thereof.

6. Apparatus according to any of claims 1 to 4, wherein the first set of nozzles are arranged in a substantially linear array parallel with the weld line in use, and the secondset of nozzles are arranged in a substantially linear array, which is substantially collinear with the first set of nozzles.

7. An apparatus according to claim 5 or 6 wherein the first flow rate increases along the first set of nozzles in a direction which is from the entry to the exit of the cooling zone.

8. An apparatus according to any of claims 5 to 7 wherein the second flow rate increases along the second set of nozzles in a direction which is from the entry to the exit of the cooling zone.

9. An apparatus according to any preceding claim, wherein the cooling zone is a first cooling zone and the apparatus comprises a second cooling zone arranged downstream of the first cooling zone, the second cooling zone having an entry and an exit, the product being arranged to pass along the second cooling zone from the entry to the exit of the second cooling zone, wherein the second cooling zone comprises a further delivery means for delivering liquid to the outer surface of the product, the further delivery means comprising a third set of nozzles arranged to deliver liquid at a third flow rate to the outer surface of the product at a third region of the outer surface of the product.

10. An apparatus according to claim 9, wherein the third flow rate is greater than the first flow rate.

11. An apparatus according to claim 9 or 10 wherein the third set of nozzles is arranged in a substantially linear array substantially parallel with the weld line in use, and wherein the third flow rate increases along the third set of nozzles in a direction which is from the entry to the exit of the second cooling zone.

12. An apparatus according to any of claims 9-11 , wherein the third region is coaxial with and includes the weld line.

13. An apparatus according to any of claims 9-12, wherein the first region has a width that is substantially perpendicular to the weld line and the third region has a width that is substantially perpendicular to the weld line, the width of the third region being greater than the width of the first region.

14. An apparatus according to any of claims 9-13, wherein the first set of nozzles extend along an axis which is parallel with a longitudinal axis of the apparatus and the third set of nozzles extend along an axis which is parallel with the longitudinal axis of the apparatus, the axes of the first and third set of nozzles being colinear.

15. An apparatus according to any of claims 9-14 comprising a third cooling zone arranged downstream of the second cooling zone, wherein the third cooling zone comprises a fourth set of nozzles arranged to deliver liquid at a fourth flow rate to the outer surface of the product.

16. An apparatus according to claim 15, wherein the fourth flow rate is greater than the third flow rate.

17. An apparatus according to any preceding claim, wherein the or each cooling zone is arranged between an entry and an exit of the apparatus, the apparatus further comprising a conveying means for conveying the product from the entry to the exit of the apparatus.

18. An apparatus according to any preceding claim comprising a tracking system for detecting and tracking the position of the weld line.

19. An apparatus accordingto any preceding claim comprising an adjustment system for adjusting the position of the nozzles relative to the product.

20. A method for cooling a weld line of a product, wherein the method comprises: introducing the product to a cooling zone of an apparatus for cooling the weld line and passing the product along the cooling zone from an entry to an exit of the cooling zone; and delivering liquid to the outer surface of the product via a delivery means of the apparatus, the delivery means comprising a first set of nozzles and a second set of nozzles, wherein the step of delivering liquid to the outer surface comprises delivering liquid at a first flow rate via the first set of nozzles to a first region comprising the weld line and delivering liquid at a second flow rate via the second set of nozzles to a second region adjacent to the first region.21 . A method according to claim 20, wherein the second flow rate is greater than the first flow rate.

22. A method according to claim 20 or 21 , wherein the first and second regions are coaxial with the weld line.

23. A method according to any of claims 20-22, wherein the liquid is delivered simultaneously to the first and second regions.

24. A method according to any of claim 20-23, wherein the cooling zone is a first cooling zone and the method further comprises introducing the product to a second cooling zone of the apparatus the second cooling zone comprising an entry and an exit, wherein the second cooling zone is downstream of the first cooling zone and comprises a further delivery means for delivering liquid to the outer surface of the product, the further delivery means comprising a third set of nozzles, the method further comprising: introducing the product to the second cooling zone such that the product passes along the second cooling zone from the entry to the exit thereof; and delivering liquid at a third flow rate via the third set of nozzles to a third region of the surface.

25. A method according to claim 24, wherein the third flow rate is greater than the first flow rate.

26. A method according to claim 24 or 25, wherein the third region is coaxial with and includes the weld line. l. A method according to any of claims 24-26, wherein the first region has a width that is substantially perpendicular to the weld line and the third region has a width that is substantially perpendicular to the weld line, the width of the third region being greater than the width of the first region.

28. A method accordingto any of claims 24-27 comprising the step of introducingthe product to a third cooling zone of the apparatus, wherein the third cooling zone is downstream of the second cooling zone, and the method further comprises delivering liquid at a fourth flow rate via a fourth set of nozzles to the outer surface of the product.

29. A method according to claim 28, wherein the fourth flow rate is greater than the third flow rate.

30. A method according to any of claims 20-29, wherein the method comprises conveying the product from an entry to an exit of the apparatus using a conveying means, wherein the or each cooling zone is arranged between the entry and the exit of the apparatus.

31. An method according to any of claims 20-30, further comprising using tracking system for detecting and tracking the position of the weld line.

32. An method accordingto any of claims 20-31 , further comprising using adjustment system to adjust the position of the nozzles relative to the product or an orientation of the nozzles relative to the product.

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