FR2528876A1 - Internally coated metal pipe production - applies coating after welding of strip edges to form pipe - Google Patents

Abstract

The method produces a metal pipe (20) with an internal coating (18), a strip (1) being shaped into a pipe blank (8) and welded along the edges. The pipe (12) so produced is shaped to the desired size. The coating is applied to the inner surface of the pipe after the edges have been welded. This can be done at the same time as the pipe is heated and shaped, and a layer of supporting material can be applied to the strip before this is shaped to take the coating.

Description

 The present invention relates to the production of tubes and in particular relates to a method of producing metal tubes having an inner surface coating.

 The present invention can be successfully applied to the production of metal tubes, the inner surface of which is protected by a wear-resistant anticorrosive coating, for example by a coating of vitreous enamel, for the transport of aggressive fluids.

 This method of producing metal tubes, the inner surface of which is protected by a coating, can be used for the production of tubes constituting water or gas pipes for general purposes, or of tubes used in thermotechnics, in energy nuclear, in the chemical industry as well as in petroleum production, in pumping, compression systems etc.

 A method of producing metallic metal tubes is known, the inner surface of which is protected by a coating which is used in a train.

 During this process, a working tape is freed from an oxide film and impurities, and is then brought to a temperature of 600 to 700 OC. This done, we deposit a powder of vitreous enamel. The heating of the tape to the temperature of 600 to 700 OC is necessary for the leveling of its surface under the effect of its tension by the cylinders of the train and to obtain adhesion of the coating on the surface of the ribbon during the melting of this coating which begins immediately after the powder on the ribbon has gone.

 After that, the ribbon is again heated to a temperature of 8000 to 1000 ° C. at which the final formation of the coating takes place, which involves the melting of the coating and its secure adhesion to the surface of the ribbon during its melting. Then, the ribbon thus coated is formed into a tubular blank after passing through the cylinders of the train. Then, the edges of the ribbon are welded end-to-end in a welding cage by forming a tube by heating the ribbon by high frequency currents.

 After that, the internally coated tube is brought to the temperature of 9000 to 1100 OC at which it is subjected to a strong deformation together with its coating to obtain a tube of a determined diameter and an imposed wall thickness. The tube is cut into parts of a prescribed length (cf. for example, Soviet author's certificate No. 590034, C.I.B. B 21 C; C 23 C).

 The known method does not always ensure a fairly high quality of the imposed thickness of the coating in the weld zone. This drawback is due to the fact that, during the welding of the edges, the temperature blues for a short time in the weld zone and causes partial combustion of certain components of the coating.

 In the case of the production of metal tubes with internal coating, according to the known method, during the formation of a coating of a prescribed thickness, large losses of powder occur which must be collected and recycled. The losses of the powder are due to the limited time during which the powder is in contact with the surface of the heated ribbon and melts during the movement of this ribbon. Although a significant part of the unmelted powder is sucked from the surface of the ribbon and returns to the technological cycle, the losses of the powder are quite significant.

 In addition, the known method requires, for its implementation, a complicated material due to the fact that several induction furnaces have to be used for heating the ribbon and for heating the tube, which results in a considerable consumption of energy.

 It has therefore been proposed to develop a process for producing metal tubes, having an interior surface covered with a coating, which would ensure a fairly high quality of coating over the entire interior surface of the tube including the area of the welded joint. .

 To solve this problem, the subject of the invention is a method of producing metal tubes having a coating on their inner surface, according to which a ribbon is formed into a tubular blank, the edges of the tubular blank are welded to form a tube , then the tube is heated and subjected to deformation and the coating is deposited on the inner surface of the tube after the edges of the tubular blank have been welded.

 It is advantageous for the coating to be deposited on the inner surface of the tube when it is heated and deformed.

 By operating in this way, a uniform distribution of the coating is ensured over the entire interior surface of the tube v including the region of the welded joint and the adhesion of the coating to the interior surface of the metal tube is increased during the simultaneous deformation of a system: metal - coating.

 It is advantageous that a support is deposited on the ribbon before the ribbon is shaped and that the coating is deposited on this support.

 This ensures a regular coating over the entire inner surface of the tube including the welded joint area and increases the adhesion of the coating to the inner surface of the tube through the formation of a relief on the inner face of the metal tube , during the simultaneous deformation of a system: metal-coating.

 In addition, the claimed process makes it possible to supply the powder for the coating by means of air under a lower pressure and thus to ensure the more complete use of the coating powder during the manufacture of tubes coated internally, which reduces to a minimum the losses of coating powder which must be collected and returned again in the technological cycle.

 This advantage is obtained thanks to the fact that the process of depositing the coating powder on the inner surface of the tube begins immediately after the welding of the tubular blank formed into a tube and that no more care is required. to transport the powder with discharged air at a determined size and to overcome the resistance to friction over the length of tube towards which the non-deposited powder can be drawn from the tube after cutting the tube into pieces of a length desired.

 It follows that the process for producing metallic tubes coated internally according to the present invention makes it possible to manufacture a tube with a coating resistant to high temperatures, regular in thickness and of identical quality over the entire perimeter of the interior surface, including the area of the welded joint.

 This is achieved by depositing the coating inside the welded tube after it has been regularly heated over its entire perimeter, when the temperature of the welded joint area and the inner surface of the tube is almost identical. .

 In this case, by applying the embodiment of the present invention, it is possible to manufacture from a ribbon of a certain single dimension by means of a simultaneous hot deformation of the metal tube and of the coating deposited, tubes of different required diameters, with different wall thicknesses, provided with a regular interior coating in thickness and of an identical high quality over the entire perimeter of the tube.

The invention will be better understood and the aims, details and advantages thereof will appear more clearly in the light of the explanatory description which follows, of various embodiments given solely by way of nonlimiting examples, and represented in the non-limiting drawings. annexed limitatives, in which
- Fig. 1 represents a technological diagram of implementation of the method for producing internally coated metal tubes, according to a variant of the present invention in which the coating is deposited simultaneously with the heating and the deformation of the tube;
- Fig. 2 shows a technological diagram of implementation of the process for producing internally coated metal tubes, according to a variant of the invention in which a support is provided before the tube is formed.

 The method according to the invention for producing metal tubes, the inner surface of which is provided with a coating, takes place in the following manner in a tube train.

A ribbon 1 (FIG. 1) of a roll (not designated) is fed into a continuous tube production train by means of tractor cylinders 2, produced according to any design provided that it is suitable for this purpose. The traction cylinders 2 are arranged in pairs on two sides of the
in other words, above and below the ribbon 1, in FIG. 1 in two pairs. A device 3, intended for welding the ends of the ribbons 1 arriving from different rollers used successively, is disposed between these pairs of tractor cylinders 2. Next, the ribbon 1 arrives in an accumulator 4 of the drum type intended to accumulate a certain reserve of ribbon 1. wound for this purpose on the drum (not designated) of the accumulator 4. If the supply of ribbon 1 stops, which can take place when the ends of the ribbons l coming from different rollers in the device are welded 3, the accumulator 4 supplies the ribbon 1 from its reserve and then ensures the continuous production of the metal tube.

 After that, the ribbon 1 arrives in a next pair of tractor cylinders 5 which are mounted on vertical axes. The traction cylinders 5 are arranged on the two edges of the ribbon 1 so that this ribbon passes through a groove formed in the middle part of each pair of cylinders 5.

 Between each pair of towing cylinders 5 is arranged a blasting device 6 intended for descaling the surface of the ribbon 1 (this scale is composed of several oxides). The aforementioned shot blasting device 6 can be produced according to any known design provided that it is suitable for this purpose and ensures a continuous supply of solid particles, here called shot, sent by nozzles (not shown) of compressed air to a speed detexminated towards the surface of the metallic strip 1 to be descaled, by compressed air.

Then, the ribbon 1 arrives at forming rollers 7 mounted on vertical axes. These forming cylinders 7 are arranged in two pairs according to the movement of the ribbon
The cylinders 7 transform the ribbon 1 into a tubular blank 8, the cross section of which is a U.

 The tubular blank 8 passes through a pair of forming cylinders 9, mounted on horizontal axes. These forming cylinders 9 are intended to effect a subsequent compression of the tubular blank 8 and, consequently, to bring the U-shape of the section of the tubular blank 8 closer to the shape of a circle.

 The tubular blank 8 thus formed arrives in the cylinders 10 of a welding cage (not designated). In the middle part of the cylinders 10 is provided a groove, the profile of which corresponds to the round cross section of the tubular blank 8. These cylinders 10 constitute a pair, are located on both sides of the tubular blank 8 and are mounted on vertical axes. The cylinders 10 are intended to more tightly tighten the tubular blank 8 in order to bring its edges together under the pressure necessary for carrying out their welding.

 The welding cage is provided with a welding head 11 intended for the prior heating of the edges of the tubular blank 8 and for the welding of these edges under pressure while the tubular blank 8 passes through the cylinders 10 of the cage. welding, The soldering strip ll is connected by an electrical circuit to a current source (not shown), in the form of a known high frequency generator. After the edges have been welded, the tube 12 is subjected to burr removal operations, by which is understood the metallic and non-metallic inclusions driven from the welded joint and having the form of a ridge on the interior and exterior surfaces of the tube. 12. From the outer surface, the burr is removed by a cutting tool 13. From the inner surface of the tube 12, the burr is removed by its combustion using an oxygen-air mixture supplied by a pipe 14, penetrating into the hollow of the tube 12 through a slot between the edges of the tubular blank 8 upstream of the welding head 11. The jet of oxygen-air mixture is oriented relative to the surface of the tube 12 at a certain angle in the area of the welded joint and in the direction opposite to the movement of this tube 12. A suitable device (not shown) is provided for the suction of unburned particles of motalAiq7zes and non-metallic inclusions contained in the burr.

 After the edges have been welded, a coating is deposited on the inner surface of the tube 12.

 As can be seen in FIG. I, the coating is deposited on the interior surface of the tube 12 simultaneously with its heating and with its deformation. To this end, a pipe 15 is engaged, provided with a nozzle 16 inside the tube 12 through a slot in the tubular blank 8 upstream of the forming cylinders 9. By the tube 15 from a source (not shown) , a powder of a coating suspended in compressed air with a determined concentration is introduced into the interior of the tube. Compressed air from a compressed air line is used. The flow rate and the compressed air pressure depend on the thickness of the covering, the size of the tube 12 and the speed of movement of this tube 12 through the train.

 In the body of the nozzle 16 are formed channels (not shown) through which the powder-air mixture arrives. These channels are oriented so that the powder suspended in the air arrives under pressure along a tangent to the generatrix of the tube 12 at the prescribed angle in the direction of movement of this tube.

 The coating supply tube delivers when the tube 12 is heated in an induction furnace 17 surrounding the tube 12 along its entire perimeter. The induction furnace 17 can be executed according to any known design suitable for these purposes and is composed of three sections.

 During the passage of the tube 12 through the induction furnace 1i, the tube having the temperature of the ambient air is brought to 1100 C. This heating is necessary for the subsequent deformation of the tube 12, for the adhesion and the melting of the coating powder.

 The process of depositing the powder on the inner surface of the tube 12 begins when the tube is heated in the oven 17 to the temperature of 70C to 800 OC and continues with the increase of the heat of the tube to a temperature from 1 1000 to 1 200 OC. At this time, the coating 18 begins to form on the interior surface of the tube 12.

 By continuously supplying coating powder, the thickness of the coating layer 18 is gradually increased on the internal surface of the tube 12 while the latter is moving through the induction furnace 17. The thickness of the coating 18 continues to also increase during the passage of the tube 12 through reduction cylinders 19 arranged in pairs with vertical and horizontal axes.

Figure 1 shows, conventionally, only the cylinders having horizontal axes. In practice, the pairs of cylinders 19 having vertical axes and the pairs 19 having horizontal axes are alternately mounted successively. The profile of the groove of the last pair of cylinders 19 following the movement of the tube 12 corresponds to the round cross section of the finished tube 20 having the desired diameter.

During the passage through the reduction cylinders 19, the tube 12 is subjected to a hot deformation simultaneously with the coating 18 which continuously grows and melts on the inner surface of the tube 12 being deformed
Downstream of the reduction cylinders 19, the finished tube is cut into pieces of the desired length. Is then used for this purpose, a saw 21 disposed downstream of the reduction cylinders 19 according to the progression of the tube 20. The saw 21 is suitable for cutting the tube 20 during its movement.

During the cutting of the tube 20, the saw moves towards the tube 20 in a reciprocating motion and stops therefrom at a speed which is a function of the speed of movement of the tube 20.

 After the tube 20 has been cut off by the saw 21, the coating formation process 18 is practically finished.

 The fact that the coating process 18 on the inner surface of the welded tube 12 takes place simultaneously with its heating and with the deformation ensures a coating of uniform thickness and identical quality over the entire interior surface of the tube 20 including the welded joint area. In this case, the adhesion of the coating 18 to the interior surface of the tube 20 is improved as a result of the formation of a micro-relief on the interior surface of the metal tube 20 during its deformation, thanks to the simultaneous deformation of the system: metal-coating.

 Since the operations of depositing the coating 18, heating the tube 12 in the induction furnace 17 and deforming the tube in the reduction cylinders 19, are carried out simultaneously, the duration of the deposit and the formation of the coating 18 to high temperature believes. The above facts prove that it is possible to manufacture a tube 20 with a coating 18 of a desired thickness at the high speeds of movement of the tube 12 in the train.

 After cutting, the finished tube 20 is brought to a conveyor-cooler (not shown). On the refrigerating conveyor, the tube 20 is moved by rotating around its axis and is simultaneously cooled by the water-air mixture from the outside. The rotation of the tube 20 around its axis during its movement on the conveyor-coolant is necessary for its straightening. The process of final formation of the coating on the inner surface of the tube 20 ends after the progressive cooling of the tube 20 to the temperature of the ambient air.

 The process for producing metal tubes 20 having a coating 18 on their inner surface is preferably to be applied, by forming a coating characterized by immediate satisfactory adhesion with the surface of the metal tube.

 The coating can Between composed of a vitreous enamel with primer or without apprentice, having determined qualities necessary for the use of pipelines of various uses.

 In the case where it is necessary to manufacture a tube 20 with a coating which is characterized by insufficient immediate adhesion with the metal of the tube, it is preferable to apply the other variant of the method for producing metallic tube, coated internally, which allows the coating to be deposited on an intermediate layer characterized by good adhesion both to the metal and to the coating.

 According to the variant embodiment shown in FIG. 2, a support (not shown) is deposited using a device 22 on the tape 1 before training. The coating 18 is deposited on the support before the tube 12 is heated.

 The support acts as an intermediate layer ensuring better adhesion of the dry resale powder to the cold surface of the tube. The support is a soluble glass of a composition compatible with the composition of the coating which is then deposited on this support. In other cases, it is possible to use a silicate or monoethanolamine adhesive of 5 So to 10 S. The device 22 is produced according to any known design suitable for these purposes and ensures a regular layer of support on the ribbon surface.

 In the embodiment shown in FIG. 2 as well as in the embodiment described above, the ribbon 1 is driven from the roller to the train using the traction cylinders 2 produced according to any known design suitable for these Goals. The cylinders 2 are arranged in sections on both sides of the ribbon 1, in other words, seen below and above the ribbon 1, in FIG. 2, in the form of two pairs. Between these cylinders 2 is disposed a device 3, intended for welding the ends of the ribbons 1 arriving from the rollers used successively.

 Then, the ribbon 1 arrives in a drum type accumulator 4, arranged in the direction of movement of the ribbon 1 and intended to accumulate a certain reserve of ribbon 1 wound, for this purpose, on its drum.

 After that, the ribbon 1 arrives in another pair of tractor cylinders 5.

 A shot blasting device 6 intended for descaling the surface of the ribbon 1 is mounted between the pairs of towing cylinders 5.

 Then, a support is regularly deposited over the entire surface prepared and cleaned beforehand of the tape 1.

The ribbon 1 thus prepared arrives in the forming cylinders 7 which transform it into a tubular blank 8, the cross section of which is U-shaped. The tubular blank 8 passes through a pair of forming cylinders 9 which serve to further reduce the tubular blank 8 and to bring the U-shaped cross section closer to tubular blank 8 with a circle-shaped section.

 The tubular blank-8 thus formed reaches the cylinders 10 of a welding cage. In the middle part of these cylinders 10 is formed a groove, the profile of which corresponds to the round cross section of the tubular blank 8. These cylinders 10 are intended to tighten more tightly tubular blank 8 and to join its edges under the necessary pressure to the realization of their welding. Upstream of the cylinders 10 is disposed a welding head 11, intended for the prior heating of the edges of the tubular blank 8 and for the welding of these edges under pressure during the passage of this tubular blank 8 through the cylinders 10 of the cage. The welding head 11 is connected by an electrical circuit to a source of electric current which is produced in a similar manner to the previous case, in the form of a high frequency current generator.

 The welding being completed, the tube 12 thus formed is subjected to a burr removal operation. On the outer surface of the tube 12 the burr is removed by a cutting tool 13 and on its inner surface it is removed by its cc: ibustion by means of a n, oxygen-air lange brought from the pipe 14 introduced into the hollow uu tube 12 through the slot made between the edges of the tubular blank 8 in front of the welding rod 11. The jet of oxygen-air mixture is oriented at an angle relative to the surface of the tube 12 in the region of the welded joint and is oriented in the opposite direction to the movement of the tube 12.A suitable device is provided for the suction of metal particles and unburned non-metallic inclusions.

 The welding of the edges finished, a resale 18 is deposited on the support before the heating of the tube 12. For this purpose, a pipe 15 provided with a nozzle head 23 is introduced into the hollow of the tube 12 through the slot of the tubular blank 8, upstream of the forming cylinders 9.

 Via the pipe 16 from a source (not shown), the powder forming the coating is brought into suspension in compressed air, with a determined concentration. Similarly to the previous case, compressed air from a compressed air line is used. The flow rate and the pressure of the compressed air depend on the thickness required for the coating and on the size of the tube 12 as well as on the speed of movement of this tube through the train.

 In the body of the nozzle cap 23, channels are formed along its length and the perimeter through which the air included transports the coating powder and deposits it on the support covering the inner surface of the tube 12. The support provides the adhesion of a dry coating powder on the inner surface of a cold tube 12 along the entire perimeter. Then, the tube 12 is heated in an induction furnace 17 surrounding the tube 12 along its entire perimeter. The induction furnace is made according to any design suitable for this purpose and is composed of three sections.

 During the passage of the tube 12 through the induction furnace 17, the tube 12 having the temperature of the ambient air is brought to the temperature of 1100 OC at which the coating is melted. Then, the tube 12 with the coating deposited on its inner surface passes through the reduction cylinders 19 which are arranged in pairs: cylinders 19 with horizontal axes and cylinders 19 with vertical axes.

 In Figure 2, the reduction cylinders 19 are shown in a conventional manner with horizontal axes. The profile of the groove of the last pair (according to the movement of the tube 12) of cylinders 19 corresponds to the round cross section of a finished tube 20 of a determined diameter. As the tube 12 passes through the reduction cylinders 19, the tube 12 undergoes hot deformation together with the coating deposited on its inner surface.

 At the outlet of the reduction cylinders 19, the finished tube 20 is cut into pieces of the desired length. For this purpose, use is made of a saw 21 arranged downstream of the reduction cylinders 19 according to the movement of the tube 20. The saw 21 is suitable for cutting the tube 20 into pieces during its movement. During cutting the saw 21 moves at the speed of its reciprocating movement towards the tube 20 and away from it, which is coordinated with the speed of movement of the tube 20.

 After cutting the tube 20 into pieces of the desired length, the definitively cut tubes with their internal coating arrive at a conveyor-cooler.

On the conveyor-refrigerant, the tube 20 moves by turning around its axis and is simultaneously cooled by the water-air mixture of the interior. The rotation of the tube 20 around its axis during its movement on the managing referee is necessary to its straightening and the removal of its possible curvature along its length.

 The process of forming the coating on the inner surface of the tube 20 ends during the gradual cooling of the tube 20 until the temperature of the ambient air.

 Using the present invention, it has been successful in manufacturing tubes with a regular interior coating of thickness and of equal quality over the entire perimeter of the interior surface of the metal tube including the area of the welded joint. In this case, by carrying out the deformation of the internally coated metal tube, it is possible to manufacture, from a ribbon of a single determined size, tubes internally coated with the different desired diameters, with different wall thicknesses and of varying length.

 The use of the claimed process allows the production of internally coated tubes of small diameter, less than 20 mm - 30 mm, and of the desired length.

 After the hot deformation of the metal tube and of the coating deposited thereon, the adhesion of the coating to the surface of the tube increases as a result of the formation of a microrelief on the interior surface of the metal tube during this deformation. Consequently, the resistance of the coating to impact, before its destruction, increases from 3 to 5 times.

 The manufacture of tubes with internal coating according to the claimed process has made it possible to significantly reduce the energy consumption for this production since there is no longer any need to use the additional special heating of the metal tube for adhesion, fusion and coating formation.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only 1 by way of nonlimiting examples. In particular, it includes all the means constituting technical equivalents of the means described, as well as their combinations, if these are carried out according to the spirit and implemented in the context of the claims which follow.

Claims (3)

R E V E N D I C A T I O N S  1 - Method for producing a metal tube (20) with a coating (18) on their inner surface according to which a ribbon (1) is transformed into a tubular blank (8), the edges of the tubular blank are welded ( 8) to form a tube (12), then the tube (12) is heated and deformed when hot to the desired dimension, characterized in that the coating (18) is deposited on the inner surface of the tube (12 ) after welding the edges of the tubular blank (18).  2 - Method according to claim 1, characterized in that the coating (18) is deposited on the inner surface of the tube (12) simultaneously with its heating and its deformation.  3 - Method according to claim 1, characterized in that quton deposits, on the tape (1), a support before its forming into a tubular blank then the coating (18) is deposited on the support previously deposited.