MXPA00004810A - Method of cooling coated pipe - Google Patents

Abstract

Pipe coated with a hot plastic coating is cooled by applying a liquid cooling medium to the interior of the pipe. The cooling medium may be applied from a lance or pressurised cart that is stationary relative to the surroundings and moves internally relative to sections of pipe that pass successively through coating and cooling stations.

Description

COOLING METHOD OF A COATED PIPE In the manufacture of pipe coverings, the pipe is heated to a high temperature and a polymeric material is applied in the form of a powder or extruded there. The material is in the melted state or melts and adapts to the surfaces of the pipe. Usually, the pipe is rotated around its axis. After the passage of a sufficient time for flow and / or curing, the material is cooled to solidify and prevent damage during subsequent handling. Damage may occur if the still-melted coating comes into contact with equipment used to transport it, such as support tires on a transport line. In known processes, cooling has been carried out by flooding the external surface with cold water using many open pipes or spray nozzles. The process lasts until the material has reached the predetermined temperature. With the known cooling processes, it has always been a problem to obtain a coating without defect, especially with pipes having high welding profiles. It has been found that the difficulty arises in part due to the shrinkage when the coating solidifies as well as in the order in which different regions solidify.

The solidification of the outer surface first produces a layer of film which has a high tension and is not yet bonded to the surface of the pipe. If the layer has a defect such as, for example, a pin hole or a bubble, this may become the weakest point and the coating may break in this position. In places where there is a concave curve in the surface such as, for example, the neck area of a weld, the tension in the film layer causes its detachment from the surface of the pipe. The material on the surface of the pipe remains in fusion and deforms but at the same time creates pin holes and cavities to replace the displaced material. The cavities in the lining on the weld neck that are known as openings can extend over considerable distances along the weld. In a convex surface such as, for example, in the upper part of a weld, the material still fused under the cooled film can be squeezed to produce a coating thickness less than that specified when the coating solidifies completely. The present invention provides a method of cooling a pipe lined with hot plastic, comprising the application of a liquid cooling medium on the inner surface of the pipe. The transformation of the coating from a fluid or melting state to a solid state using the cooling of the internal part of the pipe has numerous advantages compared to external cooling. For example, the material on the surface of the pipe solidifies first. This promotes a better adhesion on the surface, minimizes the tensions of solidifications in the interface that can affect the adhesion of the coating later. The internal cooling eliminates damage to defects and, in the case where the pipe is a welded pipe, ie metal, usually steel, a pipe having an externally elevated longitudinal welded profile, the openings in the welded areas are eliminated. The solidification front travels from the coating interface to the outer surface of the coating exposed to air (the coating-air interface) which is the last area to be solidified. The coating material that shrinks with solidification can flow and shrink inward on the surface exposed to air. This process is not impeded and this results in a low coating stress. The external melting surface of the coating does not come into contact with the cooling medium that can deform it and affect it to produce an uneven surface. With an internal cooling, the external surface solidifies without any physical interference, leaving a uniform and aesthetically satisfactory surface. A uniform coating thickness can be achieved even in highly marked welded profiles. This means that a smaller amount of coating material is required to maintain a minimum coating thickness. Internal cooling is also considered more efficient than external cooling. The overall rate of heat transfer to the pipe surface is much higher. In addition, the water or other cooling medium remains in the pipeline and continues to remove heat while in the case of external cooling, the water disappears after its initial contact. Accordingly, this invention allows the use of a smaller amount of water as well as a shorter cooling time for the pipe to reach the required temperature. The preferred process for carrying out the process of the present invention, a water assortment device is placed in the inner part of the pipe at the location where the coating must be cooled. Cooling is applied after the coating has had enough time to melt, flow and soften. Water or other means can be applied using nozzles. A self-driven cart can be supported on the pipeline by wheels and is not fixed on the outside of the pipe. The car may contain a reserve under water pressure that is filled after the cooling of each pipe. The alignment of the wheels can be controlled in such a way that the relative position of the carriage is maintained. While the pipe is rotating and while the pipe is moving forward, the carriage can remain stationary relative to a fixed external point. The pipe is cooled as it moves forward. Some cooling procedures are described in greater detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows in a relatively schematic manner a side view of a coating and cooling process. Figure 2 shows in a relatively schematic manner on an enlarged scale a coupling and cooling medium feeding unit that is employed in the apparatus of Figure 1. Figure 3 shows in a relatively schematic view a plan view of an additional embodiment of the process of application and coating. Figure 1 shows a coated and cooled section 11 of pipe and a subsequent section of pipe 12 subjected to coating and cooling. The pipes are supported on respective spiral conveyors 13 and 14 which comprise rubber-driven tires or similar rollers inclined relative to the axis of the pipe such that the pipe is rotated about its axis while being transported forward in the direction of the pipeline. arrow 16. The pipe 12 is preheated before entering a coating application station 17, for example, a powder application booth where polymer powder is applied to the pipe and melts and fuses on the surface of the pipe . A carriage 18 is supported within the pipe 12 on roller members such as for example machined wheels 19 for free rotation on shafts adjusted at an angle inclined relative to the axis of the pipe such that the pipe rotates and moves forward. , the carriage 18 maintains a stationary position with respect to the neighboring parts such as for example the powder booth 17 and the conveyor 14. Extending backwards relative to the carriage 18 is a rigid spray lance 21 supported in an intermediate position by its connection to a frame 22 connected to wheels that move freely on the inside of the pipe surface. In an area 23, the end of the spray lance 21 has spray nozzles. The carriage 18 carries one or more pressurizable tanks 24, equipped, for example, with diaphragms, bags, or the like containing a compressed gas. Normally, the spray lance 21 and the nozzles in the zone 23 are continuously fed with a cooling medium under pressure such as cold water coming from the tanks 24. Typically, successive sections of pipe such as, for example, the sections 11 and 12 move through station 17 with their ends in close proximity. Figure 1 shows a step in which a front pipe section 11 has been accelerated to open a space between its rear end and the forward end of the next pipe 12, allowing a refill coupling device 26 observed in Figure 2 can be actuated to raise its engaging portion 27 from a lower position illustrated in broken lines in Figure 2 to an upper position illustrated in solid lines where it is aligned with a forwardly projecting charging lance 28 connected to the carriage 18. The device 26 is then urged backwards in such a way that its coupling device 27 receives a complementary attachment 29 at the front end of the refill lance 28, allowing water or other cooling medium to pass under pressure of a supply line 31 through lance 28 to reload tanks 24. During this operation, the attachment 29 can be retained by holding devices 32. The tanks 24 are fully charged at the moment in which the front end of the pipe 12 approaches the device 26. At this point, the holding devices 32 are opened, the device 26 is displaced forward in its wheels 33 and the coupling portion 27 is lowered forward, the position of the dotted line as can be seen in figure 2, in such a way that the section of pipe 12 can be passed forward to be received by the rims or similar transport members 13a of the conveyor 13 which has meanwhile been unoccupied by the pipe section 11. The following pipe section subsequent to the pipe section 12 continues to advance through the spray booth 17 and is cooled by application of the spray through the nozzles in the region 23. After the wheels of the carriage 18 have moved in the inner part of this following The pipe section, when it reaches approximately the position illustrated for the pipe 12 in Figure 1, the pipe 12 is accelerated forward towards the position illustrated for the pipe section 11 in Figure 1 and the operation cycle described above is repeated . It can be seen that, in the illustrated procedure, the cooled zone 23 is located between the coating application station 17 and the point at which the cooled and coated pipe comes into contact with the rearmost part of the tires 14a or else transport devices constituting the spiral conveyor 14. Figure 3 illustrates an additional form of process wherein a pipe 41 is subjected to coating and cooling while the pipes 42, 43 and 44 are stopped in a side conveyor and support 46, while that an additional pipe 47 placed in an inlet station awaits its loading in the support 46. The pipe 41 is transported in the rims or in other roll members of spiral conveyors 48 through an acid and rinsing cabinet 49 and through of coils 51 that preheat the pipe for receiving dust in a powder application booth 52 to form a plastic coating fluent The cooling is applied to the inner part of the pipe 41 in a region 53 from the spray nozzles provided at one end of a rigid spray lance 54 which travels on angular track wheels within the pipe 41 in such a manner that the spear 54 actually moves backward relative to the pipe 41 as it proceeds. The lance 54 is receiving water or other cooling medium through a detachable coupling 56 at its rear end which connects with an auxiliary lance 57 that travels through the next pipe 42. A rear end of the auxiliary lance 57 is it is connected to a water supply through a detachable coupling 58. The next pipe section 43 contains a section of the auxiliary lance material 57a pre-installed there. In operation, the pipe section 42 is accelerated forward by spiral conveyors 59 placed below it and forming part of the support 46 in such a way that its leading edge reaches the trailing edge of the pipe section 41 and the wheels supporting the rigid lance 54 penetrate into the pipe section 42. Once the pipe 42 has left the support 46 and reached approximately the position illustrated for the pipe 41 in Figure 3, a temporary water supply 61 indicated in interrupted lines in the figure is connected. 3 to the coupling 56 for supplying water to the lance 54, the auxiliary lance 57 is detached from the couplings 56 and 58 and is relocated within the pipe section 44 as shown through an interrupted line and with the reference number 57 The pipe section 43 containing the auxiliary lance 57a is then moved forward towards the position illustrated for the pipe 42 in figure 3 and the lance 57 a is connected to the supply 58 and the connection 56, to reestablish the water supply to the lance 54 from the water supply at 58, and the temporary supply 61 is switched off. A new section of pipe, such as for example the section 47 is then rolled into the holder, the pipe section 54 which now contains the auxiliary lance 57 is rolled forward towards the position illustrated for the pipe section 43 in figure 3, a new pipe section is supplied to the input station to replace the pipe section 47 and the previous operation cycle is repeated. In the preferred form, the auxiliary lance 57 is a flexible pipe such that it can be fed in a partially circular path 62 through a track drive 63 through a guide 64 so that it penetrates the pipe section 44.

Claims (15)

1. CLAIMS A method for cooling a pipe lined with hot plastic, comprising the application of a liquid cooling medium on the internal surface of the pipe.
2. A method according to claim 1 wherein, when the cooling medium is applied, the coating is substantially entirely in the fluid state.
3. A method according to claim 1 or claim 2 wherein, when the cooling medium is applied, the coating is substantially at the temperature at which it was formed.
4. A method according to any one of the preceding claims wherein the application of a cooling medium to a pipe section begins while the coating is being applied to a rear portion of the same pipe section.
5. A method according to any one of the preceding claims wherein the cooling is applied to the internal part of a pipe that is longitudinally moving in a region between a coating application station and a point at which the coated pipe comes in contact with a transport device.
6. A method according to any of the preceding claims wherein the pipe is rotated about its axis and the cooling means is applied from a device that travels within the pipeline on members of rollers inclined relative to the axis of the pipeline in such a way that the device maintains a stationary position in relation to the surrounding parts.
7. A method according to claim 6 wherein the device comprises a carriage carrying a tank under pressure for the cooling medium that is intermittently recharged through a line passing through a front end of the pipe.
8. A method according to claim 6 wherein the device comprises a lance that travels through a portion of the pipe adjacent to the coating station and that receives cooling medium from a supply back of the rear end of the pipeline. .
9. A method according to any of the preceding claims wherein the cooling medium is water.
10. A method according to any of the preceding claims wherein the cooling means is applied uniformly on the inner surface continuously along a longitudinally extending zone of the pipe.
11. 11. A method according to any one of the preceding claims wherein the coating is an applied coating of melt powder or an extruded coating.
12. 12. A method according to any of the preceding claims wherein the pipe is a metal pipe.
13. 13. A method according to any of the preceding claims wherein the pipe is a steel pipe.
14. A method according to any of the preceding claims wherein the pipe is a metal pipe having a weld profile raised externally longitudinally.
15. 15. A method according to any of the preceding claims wherein the welding profile has a convex curve in its upper part and a concave curve in the neck of the weld.