Heat treating hardenable carbon steel pipe

Description

[0001] The present invention relates to an apparatus for hardening steel pipe by heating and then quenching and also to a process therefore.

[0002] The usual method of heat treating eutectoid steel is to first convert the ferrite phase to austenite by heating the steel to temperatures of the order of 1000°C. The steel is then cooled sufficiently rapidly for the austenite phase to convert to martensite rather than to ferrite and carbide. Cooling times of more than the order of one second can result in significant formation of the softer ferrite-carbide phase. Achieving controlled quenching within such a time constraint for large objects such as long pipes has proven to be difficult. Methods such as immersing the heated pipe into a water bath are subject to splashing onto the upper areas of the pipe or rapid steam formation contacting the upper areas of the pipe both of which result in localized ferrite-carbide formation and resultant nonuniform hardening of the pipe.

[0003] Another problem with conventional methods is that they generally necessitate heating long sections of pipe and thus encounter difficulties in transporting the pipe, in deformation due to sag in the heated area and cooling during transport to the quenching bath.

[0004] It is desirable to cool the heated pipe close to the heat source in order to avoid cooling through radiation, heat conduction along the pipe and local heat transfer to rollers in other parts contacting the pipe in its travel from the heater to the quenching spray. Such heat loss not only represents a lower efficiency of operation but exposes the pipe to development of nonuniformity of hardness due to the aforesaid localized cooling. Cooling the pipe close to the heater also reduces the length of heated pipe and thus avoids problems associated with sag.

[0005] However, cooling the interior surface of long sections of pipe sufficiently rapidly and within a well defined area close to the area being heated poses many problems. One method disclosed in U.S. Patent No. 4,110,092 issued to Kunioka on August 24,1978 and directed only to cooling pipe as opposed to quenching it uses an annular cooling nozzle having a plurality of equispaced nozzle openings whose spray direction is at a dip angle of between 30° and 70° and at a transversal angle of between 30° and 90° with respect to the radial direction of the nozzle. The method disclosed in Kunioka although suitable for cooling pipe is not suitable for quench hardening pipe as the helical flow up one side of the pipe would not be the same as that down the other. In addition, the areas of intersection of water on the pipe surface from adjacent nozzle openings would create turbulence.

[0006] DE-752084 discloses a process for heat treating steel pipes comprising heating an annular zone to an austenizing temperature, which zone moves at a preselected speed in the direction along the pipe towards an end thereof and simultaneously quenching the heated pipe proximate said annular zone thereof with the spray of an even conical sheet of cooling liquid travelling at a preselected angle to the internal surface of the pipe. The purpose of this process is surface hardening at the internal surface and the frequency of the alternating current supplied to the induction coil is selected to concentrate the heat at this surface. The present invention on the other hand is arranged to heat the total thickness of the annular zone of the pipe. Furthermore, in order to produce an extremely hard martensitic structure on the surface quenched, the spray is generated at great force and from a head spaced from the surface so that air is educted from the upstream end of the pipe by the spray causing an airflow in the direction of the longitudinal component of the velocity of the spray, thus assisting in preventing backflow or the development of a vapour barrier along the pipe surface. In DE-752084 the spray head is virtually in contact with the surface quenched, thus leaving virtually no passage for air between the spray head and the pipe and liquid will thus creep around the edges of the nozzles and travel along the outer surface of the spray head and the inner surface of the pipe to the heated region. This creeping or "lipping" action will be increased by the broad walls of the nozzle in the spray head in DE-752084. The passage of cooling liquid to the heating region will reduce the heating effect at the induction heater and smooth out the temperature gradients in the pipe as it passes from the heating zone to the quenching zone, so that the high temperature gradients required for production of martensite will not be achieved. GB-1347445 suffers from the same disadvantages in that the spraying head includes a hood which extends almost to the internal surface of the pipe being quenched so that air flow is similarly prevented. Furthermore, the spray generated near the axis of the pipe impinges on the hood and so a similar lipping action will occur around the edge of the hood and cause cooling fluid to travel back around the outer edge of the hood towards the upstream end of the pipe, creating the same disadvantages as outlined above. ,

[0007] In the apparatus forming the subject of the present application the spray or quench head is not only spaced from the inner surface of the pipe but also is positioned upstream in terms of pipe movement, of the induction heater. The jet or spray of liquid which is produced by the spray head passes through the plane of the induction heater before it strikes the inner surface of the pipe.

[0008] According to one aspect of the invention a process for heat treating hardenable carbon steel pipe to provide differential hardening of the pipe the hardness and ductility decreasing radially outwardly comprises heating an annular zone of the pipe to an austenizing temperature using an annular induction heater through which the, pipe is passed at a preselected speed, simultaneously quenching the internal surface of the heated pipe proximate said annular zone with a spray of an even conical sheet of cooling liquid which is directed at a preselected angle of less than 40° to the internal surface of the pipe from a quench head located within the pipe, characterised in that the conical sheet of cooling liquid passes through the plane containing the induction heater before it strikes the internal surface of the pipe.

[0009] Advantageously, the cooling liquid is water and the temperature of the water in the spray is maintained at a level less than 80°C.

[0010] By moving an end of the pipe adjacent to which induction heating and quenching is commenced in a circular arc of a selected radius away from the induction heating zone and associated quenching area, a quench hardened bend is produced. In establishing such a bend an annular zone of a width lying in the range of 2.5 to 5 cm (1 to 2 inches) is produced by utilizing a narrow induction coil.

[0011] In another aspect of the invention there is provided apparatus for heat treating hardenable carbon steel pipe comprising an annular induction heater, means for supporting and moving said pipe through said induction heater so that an annular zone of the pipe is heated and a quench head surrounded by the pipe said quench head being adapted to produce an even conical sheet spray of coolant liquid which is directed at an angle of less than 40° onto the interior surface of the pipe after the pipe has passed through the induction heater to effect rapid cooling of the pipe, said coolant remaining in contact with the surface of the pipe after impact, said spray of coolant liquid educting air flow from the upstream end of the pipe characterised in that the quench head is positioned upstream of the plane containing the induction heater so that the coolant liquid spray passes through said plane before it contacts the surface of the pipe.

[0012] Preferably the quench head has an adjustable annular orifice for directing cooling liquid onto the pipe surface so that adjustment of the angle of impact of the conical sheet of spray is possible in order to optimize the flow of cooling liquid along the pipe surface after impact.

[0013] Advantageously, the quench head includes an adjustable lance for support and adjustment of the position of the quench head relative to the induction heater so that the spray impinges on the heated pipe adjacent the annular zone of pipe being heated. A bending machine may also be provided for bending an end of the pipe as it passes over the quench head and through the induction heater.

[0014] In the accompanying drawings:

Figure 1 is an elevation view of the apparatus for heat treating hardenable carbon steel,

Figure 2 is a sectional view of a portion of the apparatus showing a portion of the induction heater, the quench head and a section of pipe undergoing treatment,

Figure 3 is a plan view of apparatus for induction bending and simultaneously hardening the bend of a pipe according to the invention, and

Figure 4 is a sectional view of a portion of the apparatus of Figure 3 showing the quench head, induction heating coil and a portion of the pipe undergoing bending.

Figures 1 and 2 show apparatus for heat treating a straight elongated pipe 10 supported on a plurality of rollers 12 in a position in which it is enclosed by an induction heater 14 and passes over a quench head 16 axially aligned with the pipe axis. The quench head 16 is supported by an elongated lance 18 which also provides cooled water to the quench head 60. The lance 18 is supported at one end by an adjustable lance support tower mechanism 20 which positions the quench head at a selected position along the longitudinal axis of the pipe.

Figure 2 illustrates the relationship between the quench head 16, the pipe 10 and the induction heater 14. The quench head consists of a front cup-shaped plate 26 supported from an extension 28 of the lance 18 and an opposed back plate 24 also supported by the lance 18. The peripheries 25 and 27 of the back plate 24 and the front plate 26, respectively, define an annular orifice which directs water under pressure within a chamber 32 in an even conical sheet spray 22 toward the interior surface of the pipe 10 at an angle thereto of less than 40°. Water reaches chamber 32 by a plurality of apertures 30 in pipe extension 28. Adjustment of the angle of spray is achieved by adjusting the size of the annular orifice. It will be noted that the quench head 16 is positioned upstream in terms of movement of the pipe, of the induction heater 14. The spray 22 issuing from the quench head passes through a plane normal to the direction of pipe movement and containing the induction heater, before it strikes the inner surface of the pipe.

[0015] The process of hardening pipe involves delivering a section of pipe 10 to be hardened onto rollers 12 at one end of the feeding and quenching apparatus. The pipe is then advanced longitudinally into the induction heater 14 which heats a small annular zone of the pipe as it is moved through the heater 14 and over the quench head 16. For a given size of pipe diameter an initial adjustment is made of the quench head annular orifice by moving the pipe over the quench head and adjusting the orifice so that the angle of spray results in the water in the spray maintaining contact with the interior surface of the pipe after impact. The position of the quench head 16 is also adjusted for a given diameter of pipe 10 so that it impacts on the interior of the pipe surface a short distance past the induction heater 14. After the pipe has been moved through the induction heater and quenched it is positioned over lance 18 and must therefore be reversed back to its initial position, taken off the rollers 12, a new section of pipe delivered to the rollers 12, and the process repeated.

[0016] The width of the zone heated is in the range of 15 to 20 cm (6 to 8 inches) which is less than the width of the induction heater.

[0017] Shown in Figures 3 and 4 is an apparatus for producing a quench hardened bend in a section of pipe. The apparatus consists of the quench head 34 supported on a lance 36 in a manner similar to the apparatus illustrated in Figures 1 and 2. However, in Figure 3 the quench head 34 is reversed from its position as shown in Figures 1 and 2. In addition, the induction heating coil 38 is narrower lying in the range of 2.5 to 5 cm (1 to 2 inches). An adjustable rotatable bending arm 32 clamps an end of the pipe and is movable from a position adjacent the induction heater 38 in a circular path away from the latter. A ram 31 compresses the pipe against the bending arm 32. Illustrated in Figure 4 is the quench head 34 and associated lance 36 in combination with the inductor coil 38 and a section of pipe 30. The quench head is identical to that shown in Figures 1 and 2 except that the annular orifice is directed forwardly of the lance 36 through the induction coil 38 and onto the pipe surface a short distance beyond the induction coil 38.

[0018] The process of producing a quench hardened bend according to the apparatus shown in Figures 3 and 4 is initiated by positioning the pipe 30 so that it projects through the induction coil a short distance and is clamped by the bending arm 32. The pipe is moved forward against the force of the bending arm 32 by ram 31. The bending arm 32 rotates and the induction heater heats a small annular zone of the pipe thereby providing the flexibility for the pipe to be bent. A small heated zone is desirable in such a case in order to produce an accurate, well-defined bend. The spray 40 is adjusted in angle of direction in a way similar to that shown in Figures 1 and 2 in order that the water after impact on the pipe surface flows evenly along the surface to maximize cooling and minimize any tendency toward splash back in the upstream condition. In a way similar to the process for hardening straight sections of pipe, air is educted from the upstream end of the pipe by the spray causing an airflow in a direction of the longitudinal component of velocity of the spray. The latter airflow assists in preventing back flow or the development of a vapour barrier along the pipe surface.

[0019] By quenching only the interior surface of the pipe the interior surface is hardened while the exterior surface is tough and ductile.

[0020] Alternatively, both the interior and exterior surfaces of the pipe could be quenched and the exterior surface subsequently tempered at temperatures up to approximately 700°C.

[0021] A single machine, which provides an alternative reduced capital equipment option, may comprise one set of mechanical pipe handling equipment, rams, and drive control systems, one lance for internal quenching, various quench heads as required, two alternative induction heating ring systems (one for bending the other for straight pipe hardening since the latter can be processed faster), and one electrical/water and other service supply system This single combined machine can manufacture hardened straight pipe and hardened bends by having the body of the bending machine tracked out of line and beyond the bending arm and into line with the larger induction coil, that is the coil used for straight pipe. There are speed controls, enabling straight hardened pipe to be manufactured many times faster than the bends. The machine is thus a combination of the embodiments of Figures 1 and 3. The direction of straight hardening over the quench lance may be reversed, i.e. the pipe travels off the lance rather than on to it as it is being hardened.

[0022] Other variations include means to rotate the pipe while heating and quenching are taking place; means to allow rotation of the quench head while heating and guenching straight or, especially, bent pipe and means to rotate the pipe and the guench head in opposite directions during heating and quenching.

[0023] Relative rotation between the pipe and the quench head provides a margin of safety for ensuring that the pipe is quenched uniformly. This is critical if irregular bending of the pipe is to be avoided.

[0024] Typically, in straight hardening, the heater draws 1000W and quenching is effected by a flow of 37.9 litres per second (500 gallons per minute) of cooling water.

Claims

1. An apparatus for heat treating hardenable carbon steel pipe (10, 30) comprising an annular induction heater (14, 38), means (12, 31) for supporting and moving said pipe (10,'30) through said induction heater (14, 38) so that an annular zone of the pipe is heated, a quench head (16, 34) surrounded by said pipe (10, 30) said quench head (16, 34) being adapted to produce an even conical sheet spray (22, 40) of coolant liquid which is directed at an angle of less than 40° onto the interior surface of the pipe (10, 30) after the pipe has passed through the induction heater (14, 38) to effect rapid cooling of the pipe said coolant remaining in contact with the surface of the pipe after impact, said spray of coolant liquid educting air flow from the upstream end of the pipe, characterised in that the quench head (16, 34) is positioned upstream of the plane containing the induction heater (14,38), so that the coolant liquid spray (22, 40) passing through said plane before it contacts the surface of the pipe.

2. Apparatus, as defined by Claim 1, wherein said quench head (16 or 34) is adapted to emit water.

3. Apparatus, as defined by Claim 2, wherein said quench head (16 or 34) includes an adjustable lance (18, or 36) for supporting said quench head (16 or 34) and adjusting its position relative to said induction heater (14 or 38) so that the spray (22) impinges on the heated pipe (10 or 30) adjacent the annular zone of pipe (10 or 30) being heated.

4. Apparatus, according to any one of Claims 1-3, for heat treating pipe (10) wherein both ends of the pipe (10) remain in coaxial alignment, in which means are provided for effecting relative rotation between the pipe (10) and the quench head (16).

5. Apparatus, as defined by any one of Claims 1-3, further including a bending machine (32) for bending an end of said pipe (30) as said pipe (30) passes over said quench head (34) and through said induction heater (38) for simultaneously heating a zone of said pipe proximate said induction heater (38) and quenching the interior surface of said pipe (30) to form a martensitic phase.

6. An apparatus according to Claims 1-3 including means for quenching the exterior surface of the pipe.

7. A process for heat treating hardenable carbon steel pipe to provide differential hardening of the pipe the hardness and ductility decreasing radially outwardly comprising heating an annular zone of the pipe to an austenizing temperature using an annular induction heater through which the pipe is passed at a preselected speed, simultaneously quenching the internal surface of the heated pipe proximate said annular zone with a spray of an even conical sheet of cooling liquid which is directed at a preselected angle of less than 40° to the internal surface of the pipe from a quench head located within the pipe, characterised in that the conical sheet of cooling liquid passes through the plane containing the induction heater before it strikes the internal surface of the pipe.

8. A process according to Claim 7 wherein said sheet (22 or 40) of cooling liquid impacts said pipe (10 or 30) at a position where the pipe is in the austenitic phase, the rapid quenching resulting in the formation of a martensitic structure.

9. A process as claimed in Claim 7 or Claim 8 wherein the interior and exterior surfaces of the pipe are heated and quenched to form a martensitic structure and the exterior surface only is tempered by heating.

10. A process as claimed in any one of Claims 7 to 9 wherein both ends of the pipe (10) remain in co-axial alignment and the width of the heated zone is in the range of 15 to 20 cm.

11. A process as claimed in any one of Claims 7 to 10 wherein relative rotation is imparted to the pipe (10) and the quench head (22).

12. A process as claimed in Claim 7 or Claim 8 including moving an end of the pipe (30) adjacent to which the induction heating and quenching takes place in a circular arc of a selected radius away from the zones of heating and quenching, by a ram (31) which compresses the pipe (30) against a bending arm (32) whereby a quench hardened bend is produced.

13. A process as claimed in Claim 7 wherein the width of the heated zone is in the range of 2.5 to 5cm.

Ansprüche

1. Gerät zur Wärmebehandlung eines härtbaren Kohlenstoffstahlrohres (10, 30), wobei das Gerät eine ringförmige Induktionsheizeinrichtung (14, 38), eine Einrichtung (12,31), um das Rohr (10, 30) zu halten und so durch die Induktionsheizeinrichtung (14, 38) zu bewegen, daß ein Ringbereich des Rohres erwärmt wird, sowie einen Abschreckkopf (16, 34) enthält, der vom Rohr (10, 30) umgeben ist, wobei der Abschreckkopf (16, 34) so eingerichtet ist, daß er eine regelmäßige Kegelfläche eines Kühlflüssigkeits-Sprühnebels (22, 40) erzeugt, der unter einem Winkel kleiner als 40° auf die Innenfläche des Rohres (10, 30) gerichtet ist, nachdem das Rohr die Induktionsheizeinrichtung (14,38) durchlaufen hat, um ein rasches Abkühlen des Rohres zu erreichen, wobei das Kühlmittel nach dem Auftreffen mit der Rohrfläche in Berührung bleibt, wobei der Kühlflüssigkeits-Sprühnebel vom stromaufwärts liegenden Rohrende einen Luftstrom abzieht, dadurch gekennzeichnet, daß der Abschreckkopf (16, 34) stromaufwärts jener Ebene angeordnet ist, in der die Induktionsheizeinrichtung (14, 38) liegt, so daß der Kühlflüssigkeits-Sprühnebel (22, 40) diese Ebene durchläuft, bevor er die Rohroberfläche berührt.

2. Gerät gemäß Anspruch 1, wobei der Abschreckkopf (16 oder 34) so aufgebaut ist, daß er Wasser abgibt.

3. Gerät gemäß Anspruch 2, wobei der Abschreckkopf (16 oder 34) eine einstellbare Lanze (18 oder 36) aufweist, um den Abschreckkopf (16 oder 34) zu halten und seine Lage relativ zur Induktionsheizeinrichtung (14 oder 38) einzustellen, so daß der Sprühnebel (22) auf dem erwärmten Rohr (10 oder 30) neben dem Ringbereich des Rohres (10 oder 30) auftrifft, der erwärmt werden soll.

4. Gerät gemäß jedem der Ansprüche 1 bis 3 zur Wärmebehandlung eines Rohres (10), wobei beide Enden des Rohres (10) koaxial ausgerichtet bleiben, wobei eine Einrichtung vorgesehen ist, um eine relative Drehung zwischen dem Rohr (10) und dem Abschreckkopf (16) hervorzurufen.

5. Gerät gemäß jedem der Ansprüche 1 bis 3,- wobei das Gerät weiters eine Biegemaschine (32) aufweist, um ein Ende des Rohres (30) zu biegen, wenn das Rohr (30) über den Abschreckkopf (34) und durch die Induktionsheizeinrichtung (38) läuft, um gleichzeitig einen Bereich des Rohres nahe der Induktionsheizeinrichtung (38) zu erwärmen und die Innenfläche des Rohres (30) abzuschrecken, um eine martensitische Phase auszubilden.

6. Gerät gemäß Anspruch 1 bis 3, wobei das Gerät eine Einrichtung aufweist, um die Außenfläche des Rohres abzuschrecken.

7. Verfahren zur Wärmebehandlung eines härtbaren Kohlenstoffstahlrohres, um eine unterschiedliche Härtung des Rohres zu liefern, wobei die Härte und die Verformbarkeit radial nach außen abnehmen, wobei das Verfahren das Erwärmen eines Ringbereichs des Rohres auf eine austenitbildende Temperatur unter Verwendung einer ringförmigen Induktionsheizeinrichtung, die das Rohr mit einer vorgewählten Geschwindigkeit durchläuft, sowie das gleichzeitige Abschrecken der Innenfläche des erwärmten Rohres in der Nähe des Ringbereichs mit einem Kühlflüssigkeits-Sprühnebel in Form einer regelmäßigen Kegelfläche enthält, der unter einem vorgewählten Winkel kleiner als 40° auf die Rohrinnenfläche von einem Abschreckkopf gerichtet wird, der innerhalb des Rohres angeordnet ist, dadurch gekennzeichnet, da8 die Kegelfläche der Kühlflüssigkeit jene Ebene durchläuft, in der die Induktionsheizeinrichtung liegt, bevor sie auf die Rohrinnenfläche fällt.

8. Verfahren gemäß Anspruch 7, wobei die Fläche (22 oder 40) der Kühlflüssigkeit auf das Rohr (10 oder 30) an einer Stelle auftrifft, an der sich das Rohr in der austenitischen Phase befindet wobei die rasche Abschrekkung zur Ausbildung eines martensitischen Gefüges führt.

9. Verfahren gemäß Anspruch 7 oder 8, wobei die Innen- und Außenfläche des Rohres erwärmt und abgeschrecktwerden, um ein martensitisches Gefüge auszubilden, wobei nur die Außenfläche warm angelassen wird.

10. Verfahren gemäß jedem der Ansprüche 7 bis 9, wobei beide Enden des Rohres (10) koaxial ausgerichtet bleiben und die Breite des erwärmten Bereichs im Bereich von 15 bis 20 cm liegt.

11. Verfahren gemäß jedem der Ansprüche 7 bis 10, wobei dem Rohr (10) und dem Abschreckkopf (22) eine relative Drehung aufgeprägt wird.

12. Verfahren gemäß Anspruch 7 oder 8, wobei das Verfahren das Bewegen eines Endes des Rohres (30), das neben der Stelle liegt, wo die Induktionsheizung und die Abschreckung erfolgen, in einer Kreisbahn mit einem ausgewählten Radius vom Heizbereich und Abschreckbereich weg durch einen Stempel (31) aufweist, der das Rohr (30) gegen einen Biegearm (32) drückt, wodurch ein abschreckgehärtetes Kniestück erzeugt wird.

13. Verfahren gemäß Anspruch 7, wobei die Breite des erwärmten Bereichs in der Größenordnung von Z,5 bis 5 cm liegt.

Revendications

1. Dispositif de traitement thermique de tubes (10, 30) en acier au carbone durcissable, compre- nantun moyen de chauffage inductif annulaire (14, 38), des moyens (12, 31) pour supporter et déplacer le tube (10,30) à travers le moyen de chauffage inductif (14,38) de façon qu'une zone annulaire du tube soit chauffée, une tête de trempe (16, 34) entourée par le tube (10,30), la tête de trempe (16, 34) étant conçue pour produire un jet étalé conique et uniforme (22, 40) de liquide réfrigérant qui est dirigé à un angle inférieur à 40° sur la surface intérieure du tube (10, 30) après que le tube ait traversé le moyen de chauffage inductif (14, 38), afin de réaliser un refroidissement rapide du tube, le réfrigérant restant en contact avec la surface du tube après l'impact, le jet de liquide réfrigérant évacuant un flux d'air par l'extrémité amont du tube, caractérisé en ce que la tête de trempe (16, 34) est positionnée en amont du plan contenant le moyen de chauffage inductif (14, 38), de sorte que le jet de liquide réfrigérant (22, 40) traverse ce plan avant d'entrer en contact avec la surface du tube. 2. Dispositif selon la revendication 1, dans lequel la tête de trempe (16 ou 34) est conçue pour émettre de l'eau.

3. Dispositif selon la revendication 2, dans lequel la tête de trempe (16 ou 34) comprend une lance réglable (18 ou 36) pour supporter la tête de trempe (16 ou 34) et régler sa position par rapport au moyen de chauffage inductif (14 ou 38), de sorte que le jet (22) agit sur le tube chauffé (10 ou 30) au voisinage de la zone annulaire du tube (10 ou 30) qui est chauffée.

4. Dispositif selon l'une quelconque des revendications 1 à 3, pour le traitement thermique d'un tube (10) dont les deux extrémités restent en alignement coaxial, dans lequel des moyens sont prévus pour réaliser une rotation relative entre le tube (10) et la tête de trempe (16).

5. Dispositif selon l'une quelconque des revendications 1 à 3, comprenant en outre une machine de cintrage (32) pour cintrer une extrémité du tube (30) tandis que le tube (30) passe au-dessus de la tête de trempe (34) et à travers le moyen de chauffage inductif (38), afin de, simultanément, chauffer une zone du tube voisine du moyen de chauffage inductif (38), et tremper la surface intérieure du tube (30) pour former une phase martensitique.

6. Dispositif selon les revendication 1 à 3, comprenant des moyens pour tremper la surface extérieure du tube.

7. Procédé de traitement thermique de tubes en acier au carbone durcissable, pour fournir un durcissement différentiel du tube, la dureté et la ductilité diminuant radialement vers l'extérieur, comprenant le chauffage d'une zone annulaire du tube à une température d'austénisation en utilisant un moyen de chauffage inductif annulaire à travers lequel on fait passer le tube à une vitesse présélectionnée, et, dans le même temps, la trempe de la surface intérieure du tube chauffé voisine de la zone annulaire, à l'aide d'ur jet étalé conique et uniforme de liquide réfrigérant qui est dirigé à un angle présélectionné inférieur à 40° sur la surface intérieure du tube à partir d'une tête de trempe située à l'intérieur du tube, caractérisé en ce que le jet étalé conique de liquide réfrigérant traverse le plan contenant le moyen de chauffage inductif avant de venirtoucher la surface intérieure du tube.

8. Procédé selon la revendication 7, dans lequel le jet étalé (22 ou 40) de liquide réfrigérant heurte le tube (10 ou 30) à une position où le tube est dans la phase austénitique, la trempe rapide se traduisant par la formation d'une structure martensitique.

9. Procédé selon la revendication 7 ou 8, dans lequel les surfaces intérieur et extérieure du tube sont chauffées et trempées pour former une structure martensitique, et seule la surface extérieure est soumise à un traitement de revenu par chauffage.

10. Procédé selon l'une quelconque des revendications 7 à 9, dans lequel les deux extrémités du tube (10) restent en alignement coaxial, et la largeur de la zone chauffée se situe dans la plage allant de 15 à 20 cm.

11. Procédé selon l'une quelconque des revendications 7 à 10, dans lequel une rotation relative est imprimée au tube (10) et à la tête de trempe (22).

12. Procédé selon la revendication 7 ou 8, comprenant le déplacement d'une extrémité du tube (30) au voisinage de laquelle ont lieu le chauffage inductif et la trempe, selon un arc circulaire de rayon sélectionné, en éloignement des zones de chauffage et de trempe, à l'aide d'un piston-plongeur (31) qui comprime le tube (30) contre un bras de cintrage (32), de sorte qu'un coude durci et trempé est produit.

13. Procédé selon la revendication 7, dans lequel la largeur de la zone chauffée se situe dans la plage allant de 2,5 à 5 cm.

Drawing