EP0234200B1 - Process and device for the heat treatment of longitudinally welded pipes - Google Patents

Process and device for the heat treatment of longitudinally welded pipes Download PDF

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Publication number
EP0234200B1
EP0234200B1 EP87100199A EP87100199A EP0234200B1 EP 0234200 B1 EP0234200 B1 EP 0234200B1 EP 87100199 A EP87100199 A EP 87100199A EP 87100199 A EP87100199 A EP 87100199A EP 0234200 B1 EP0234200 B1 EP 0234200B1
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Prior art keywords
annealing
heat treatment
weld seam
pipe
heat
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EP87100199A
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German (de)
French (fr)
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EP0234200A1 (en
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Friedhelm Schmitz
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Siemens AG
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Siemens AG
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Priority claimed from DE19863639403 external-priority patent/DE3639403A1/en
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces

Definitions

  • the present invention relates to a method for increasing the corrosion resistance of longitudinally welded pipes and an apparatus for performing the method.
  • Stainless steel tubes e.g. for steam condensers, are subjected to heat treatment after longitudinal seam welding to reduce stresses and to reduce segregations that occur as a result of the welding process. This results e.g. from an article by K. Schleithoff, F, Schmitz: "Condenser tubes made of stainless steels - operating experience and material development" in "VGB Kraftmaschinestechnik 61", Issue 9, p. 730, Sept. 1981.
  • the heat treatment is usually carried out in continuous annealing furnaces under protective gas at temperatures of 950 ° C to 1100 ° C depending on the material and a holding time of a few minutes. Other annealing processes are also used.
  • This object is achieved by a method for increasing the corrosion resistance by compensating for chrome and / or molybdenum segregation of a longitudinally welded tube made of austenitic or austenitic-ferritic stainless steel, the tube being heat-treated after welding the longitudinal seam in a pass under an annealing section and partial solution annealing in the area of the entire weld seam and the heat affected zone at a temperature greater than 1100 ° C. for more than 5 seconds, while the rest of the area is heat treated at a lower temperature.
  • the essential idea of the invention is to carry out only a partial solution annealing of the weld seam and the heat affected zone.
  • This annealing can be carried out inside or outside the welding section.
  • temperatures can even be set above 1200 ° C or even 1300 ° C in the weld seam area and the heat affected zone, which leads to an optimized solution annealing and a better balance of the chromium - or lead to molybdenum segregation.
  • the remaining pipe wall temperature of the rest can be carried out only a partial solution annealing of the weld seam and the heat affected zone.
  • the ranges are set so low that problem-free processing in the welding, processing and annealing and deformation sections is possible, but a reduction in the stresses introduced by the manufacturing process is achieved. Because the majority of the tube does not have to be brought to the maximum annealing temperature, the stability of the tube is maintained and undesirable deformations under the influence of gravity or of the transport devices cannot occur.
  • the proposed annealing treatment basically offers the possibility of both the temperature and the holding time compared to conventional ones process significantly. It is also possible to manufacture testable thin-walled tubes.
  • the desired selective annealing can be achieved by partial heating and partial cooling. Depending on the desired holding time, partial heating may be sufficient, but it can be supplemented at any time by cooling the areas of the pipe that are not to be annealed, as long as the remaining pipe would be heated too much by heat conduction or radiation.
  • Various methods can be used for the partial heating, for example using infrared radiators, lasers or correspondingly guided electrical currents which are induced in the tube.
  • the cross section shown in FIG. 1 through a longitudinally welded tube 1 illustrates the areas of the tube which are essential for the invention.
  • the individual zones are not shown to scale.
  • the weld seam 2 is generally located on the top of the tube 1 during manufacture. It is surrounded by a heat-affected zone 3, in which the welding process has left changes and inhomogeneities.
  • the rest of the tube consists of unchanged base material, but it makes sense to include an area 4 outside of the heat affected zone 3 during a heat treatment for safety reasons, since the exact extent of the heat affected zone 3 is not always known.
  • the tube 1 to be annealed should preferably be kept under protective gas during the annealing in order to avoid subsequent pickling.
  • the tube 1 to be annealed is located inside a quartz glass tube 5, the space 9 between the two being filled with protective gas.
  • One or more infrared emitters 6 are arranged above the quartz glass tube 5 and provided with focusing reflectors 8 in a housing 7.
  • the focusing reflectors can, for example, have a parabolic cross section, in the focal point or focal line of which there are infrared radiators.
  • there are also other focusing elements e.g. infrared transparent lens systems u. Like., applicable.
  • the infrared rays are focused in such a way that they irradiate and heat up the desired area 4 of the tube 1 to be partially annealed.
  • the desired partial annealing can be carried out over almost any holding times, although annealing in a continuous process under a corresponding annealing section is preferable.
  • the present invention enables the use of steels with, for example, a lower molybdenum content for longitudinally welded corrosion-resistant pipes and also enables the production of thin-walled pipes with a wall thickness of e.g. 0.3 to 0.5 mm.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Heat Treatment Of Articles (AREA)

Description

Die vorliegende Erfindung betrifft ein Verfahren zur Erhöhung der korrosionsbeständigkeit von längsnahtgeschweißten Rohren sowie eine Vorrichtung zur Durchführung des Verfahrens. Rohre aus nichtrostenden Stählen, z.B. für Wasserdampf-Kondensatoren, werden nach dem Längsnahtschweißen zur Reduzierung von Spannungen und zur Minderung von Seigerungen, die durch den Schweißprozeß auftreten, einer Wärmebehandlung unterzogen. Dies ergibt sich z.B. aus einem Artikel von K. Schleithoff, F, Schmitz: "Kondensatorrohre aus nichtrostenden Stählen - Betriebserfahrungen und Werkstoffentwicklung" in "VGB Kraftwerkstechnik 61", Heft 9, S. 730, Sept. 1981. Die Wärmebehandlung erfolgt in der Regel in Durchlauf-Glühöfen unter Schutzgas bei Temperaturen je nach Werkstoff von 950°C bis 1100°C und einer Haltezeit von einigen Minuten. Auch andere Glühverfahren werden angewendet.The present invention relates to a method for increasing the corrosion resistance of longitudinally welded pipes and an apparatus for performing the method. Stainless steel tubes, e.g. for steam condensers, are subjected to heat treatment after longitudinal seam welding to reduce stresses and to reduce segregations that occur as a result of the welding process. This results e.g. from an article by K. Schleithoff, F, Schmitz: "Condenser tubes made of stainless steels - operating experience and material development" in "VGB Kraftwerkstechnik 61", Issue 9, p. 730, Sept. 1981. The heat treatment is usually carried out in continuous annealing furnaces under protective gas at temperatures of 950 ° C to 1100 ° C depending on the material and a holding time of a few minutes. Other annealing processes are also used.

Ein prinzipielles Problem tritt jedoch dadurch auf, daß die optimalen Werte von Temperatur und Haltezeit nicht erreicht werden können. Werden nämlich Rohre auf die gewünschte hohe Temperatur gebracht, so sind sie nicht formstabil, so daß sie sich bei größeren Haltezeiten verformen und unter dem Einfluß der Schwerkraft "zusammenfallen". Eine optimale Lösungsglühung und Verminderung von Seigerungen, z.B. der korrosionsbeständigkeit-bestimmenden Elemente Chrom oder Molybdän im Schweißnahtbereich, kann daher mit herkömmlichen Methoden nicht erreicht werden. Somit kann die Schweißnaht trotz der Verbesserung durch Wärmebehandlung etwas schlechtere Korrosionseigenschaften aufweisen als der Grundwerkstoff. Daher wird z.B. der Molybdängehalt des Grundwerkstoffes höher als eigentlich nötig gewählt, um auch in der Schweißnaht noch die jeweils gewünschten Korrosionseigenschaften sicherzustellen. Vom wirtschaftlichen Standpunkt jedoch ist eine Verminderung des Gehaltes an teuerem Molybdän wünschenswert.A fundamental problem arises, however, in that the optimal values of temperature and holding time cannot be achieved. If pipes are brought to the desired high temperature, they are not dimensionally stable, so that they deform during longer holding times and "collapse" under the influence of gravity. Optimal solution annealing and reduction of segregation, e.g. The elements that determine corrosion resistance, chromium or molybdenum in the area of the weld seam, can therefore not be achieved with conventional methods. Thus, despite the improvement due to heat treatment, the weld seam can have somewhat poorer corrosion properties than the base material. Therefore e.g. the molybdenum content of the base material is chosen higher than is actually necessary in order to ensure the desired corrosion properties in the weld. From the economic point of view, however, a reduction in the expensive molybdenum content is desirable.

Ein weiteres Problem entsteht, insbesondere bei dünnwandigen Rohren, durch die Handhabungs- bzw. Transportvorgänge bei hoher Temperatur. Hierbei entstehen Verformungen, insbesondere Beulen, die eine spätere Qualitätsprüfung, z.B. durch Wirbelstrommessungen, erschweren oder verhindern.Another problem arises, particularly in the case of thin-walled pipes, from the handling or transport processes at high temperature. This creates deformations, in particular dents, which can later be checked for quality, e.g. by eddy current measurements, complicate or prevent.

Aus der US-PS-2 673 276 ist schon die partielle Wärmebehandlung einer Schweßnaht bei durchlaufenden längsnahtgeschweißten Rohren bekannt. Diese Wärmebehandlung dient jedoch nur dem Normalisieren der Schweißnaht zur Verbesserung ihrer mechanischen Eigenschaften. Ein Ausgleich von Chrom- oder Molybdän-Seigerungen, wie sie bei nichtrostenden Stählen auftreten können, wird nicht in Betracht gezogen.From US Pat. No. 2,673,276, the partial heat treatment of a weld seam in the case of continuous longitudinally welded tubes is already known. However, this heat treatment only serves to normalize the weld seam to improve its mechanical properties. A balance of chromium or molybdenum segregation, as can occur with stainless steels, is not considered.

Aus der US-PS-4 168 190 ist weiter ein Verfahren zur Wärmebehandlung der Umgebung von Schweißnähten in rostfreien Stählen bekannt. Mit dieser Wärmebehandlung soll die Sensibilisierung einer durch den Schweißvorgang beeinflußten Umgebungszonge der Schweißnaht, die zu einer verstärkten Anfälligkeit für Spannungsrißkorrosion führt, rückgängig gemacht werden. Die zu diesem Zwecke angewandten Temperaturen und Haltezeiten eignen sich nicht für eine Lösungsglühung zum Ausgleich von Seigerungen. Auch ist die Anwendung des Verfahrens auf längsnahtgeschweißte Rohre nicht ohne Schwierigkeiten möglich. Ein ähnliches Verfahren zur Wärmebehandlung ist auch in der JP-A-55 54 524 beschrieben, wobei der Bereich der Rundschweißnaht eines Rohres von innen mit einem Laserstsrahl aufgeheizt wird. Auch bei dieser Wärmebehandlung reichen die Temperatur und die Haltezeit nicht aus, um Seigerungen in der Schweißnaht zu beheben.From US-PS-4 168 190 a method for heat treatment of the vicinity of welds in stainless steels is further known. This heat treatment is intended to undo the sensitization of a surrounding zone of the weld seam which is influenced by the welding process and which leads to an increased susceptibility to stress corrosion cracking. The temperatures and holding times used for this purpose are not suitable for solution annealing to compensate for segregation. It is also not possible to apply the method to longitudinally welded pipes without difficulty. A similar method for heat treatment is also described in JP-A-55 54 524, the area of the circular weld seam of a tube being heated from the inside with a laser steel beam. With this heat treatment, too, the temperature and the holding time are not sufficient to eliminate segregations in the weld seam.

Aufgabe der vorliegenden Erfindung ist es, unter Vermeidung der oben genannten Nachteile die Schweißnähte von längsnahtgeschweißten Rohren aus austenitischem oder austenitisch-ferritischem nichtrostendem Stahl so zu behandeln, daß diese sich den Korrosionseigenschaften des Grundwerkstoffes annähern.It is the object of the present invention, while avoiding the disadvantages mentioned above, to treat the weld seams of longitudinally welded tubes made of austenitic or austenitic-ferritic stainless steel in such a way that they approximate the corrosion properties of the base material.

Diese Aufgabe wird durch ein Verfahren zur Erhöhung der Korrosionsbeständigkeit durch Ausgleich von Chrom- und/oder Molybdän-Seigerungen eines längsnahtgeschweißten Rohres aus austenitischem oder austenitisch-ferritischem nichtrostendem Stahl gelöst, wobei das Rohr nach dem Schweißen der Längsnaht im Durchlauf unter einer Glühstrecke wärmebehandelt wird und dabei partiell im Bereich des gesamten Schweißnaht und der Wärmeeinflußzone bei einer Temperatur größer 1100°C länger als 5 sec lösungsglüht wird, während der übrige Bereich bei niedrigerer Temperatur wärmebehandelt wird.This object is achieved by a method for increasing the corrosion resistance by compensating for chrome and / or molybdenum segregation of a longitudinally welded tube made of austenitic or austenitic-ferritic stainless steel, the tube being heat-treated after welding the longitudinal seam in a pass under an annealing section and partial solution annealing in the area of the entire weld seam and the heat affected zone at a temperature greater than 1100 ° C. for more than 5 seconds, while the rest of the area is heat treated at a lower temperature.

Wie anhand der Zeichnung noch näher erläutert wird, besteht der wesentliche Gedanke der Erfindung darin, nur eine partielle Lösungs-Glühung von Schweißnaht und Wärmeeinflußzone durchzuführen. Diese Glühung kann innerhalb oder außerhalb der Schweißstrecke vorgenommen werden, Dabei können z.B. bei hochlegierten, molybdänhaltigen Stählen Temperaturen sogar oberhalb von 1200°C oder sogar 1300°C im Schweißnahtbereich und der Wärmeeinflußzone eingestellt werden, die zu einer optimierten Lösungsglühung und einem besseren Ausgleich der Chrom- oder Molybdän-Seigerungen führen. Die restliche Rohrwandtemperatur der übrigen. Bereiche wirdso niedrig eingestellt, daß eine problemlose Verarbeitung in der Schweiß-, Bearbeitungssowie Glüh- und Verformungsstrecke möglich ist, jedoch ein Abbau der Spannungen, die durch den Herstellungsprozeß eingebracht wurden, erreicht wird. Dadurch, daß der größte Teil des Rohres nicht auf die maximale Glühtemperatur gebracht werden muß, bleibt die Stabilität des Rohres erhalten und unerwünschte Verformungen unter dem Einfluß der Schwerkraft oder der Transportvorrichtungen können nicht auftreten. Die vorgeschlagene Glühbehandlung bietet grundsätzlich die Möglichkeit, sowohl die Temperatur wie auch die Haltezeit gegenüber herkömmlichen Verfahren deutlich zu erhöhen. Eine Herstellung prüfbarer dünnwandiger Rohre wird ebenfalls möglich.As will be explained in more detail with reference to the drawing, the essential idea of the invention is to carry out only a partial solution annealing of the weld seam and the heat affected zone. This annealing can be carried out inside or outside the welding section.For example, in the case of high-alloy steels containing molybdenum, temperatures can even be set above 1200 ° C or even 1300 ° C in the weld seam area and the heat affected zone, which leads to an optimized solution annealing and a better balance of the chromium - or lead to molybdenum segregation. The remaining pipe wall temperature of the rest. The ranges are set so low that problem-free processing in the welding, processing and annealing and deformation sections is possible, but a reduction in the stresses introduced by the manufacturing process is achieved. Because the majority of the tube does not have to be brought to the maximum annealing temperature, the stability of the tube is maintained and undesirable deformations under the influence of gravity or of the transport devices cannot occur. The proposed annealing treatment basically offers the possibility of both the temperature and the holding time compared to conventional ones process significantly. It is also possible to manufacture testable thin-walled tubes.

Fakultative Merkmale des erfindungsgemäßen Verfahrens sind in den Ansprüchen 2-8 angeführt.Optional features of the inventive method are set out in claims 2-8.

Die gewünschte selektive Glühung kann durch partielle Aufheizung und partielle Kühlung erreicht werden. Je nach der gewünschten Haltezeit kann eine partielle Aufheizung ausreichen, jedoch ist die Ergänzung durch eine Kühlung der nicht zu glühenden Rohrbereiche jederzeit möglich, sofern bei längerer Haltezeit durch Wärmeleitung oder Strahlung das restliche Rohr zu sehr aufgeheizt werden würde.The desired selective annealing can be achieved by partial heating and partial cooling. Depending on the desired holding time, partial heating may be sufficient, but it can be supplemented at any time by cooling the areas of the pipe that are not to be annealed, as long as the remaining pipe would be heated too much by heat conduction or radiation.

Für die partielle Aufheizung lassen sich verschiedene Verfahren anwenden, beispielsweise unter Verwendung von Infrarotstrahlern, Lasern oder entsprechend geführten elektrischen Strömen, die in dem Rohr induziert werden.Various methods can be used for the partial heating, for example using infrared radiators, lasers or correspondingly guided electrical currents which are induced in the tube.

Ein erhöhter Stickstoffanteil, der die Schweißbarkeit des Werkstoffes beeinträchtigen würde, kann nach derSchweißung durch Glühung in einer Atmosphäre mit geeignetem Partialdruck von Stickstoff oder einer Stickstoffverbindung erzielt werden. Dies verbessert die Korrosionseigenschaften des Rohres bzw. der Schweißnaht erheblich.An increased proportion of nitrogen, which would impair the weldability of the material, can be achieved after welding by annealing in an atmosphere with a suitable partial pressure of nitrogen or a nitrogen compound. This considerably improves the corrosion properties of the pipe or the weld seam.

Geeignete Vorrichtungen zur Durchführung der genannten Verfahren sind in den Ansprüchen 9, 10 und 11 angegeben.Suitable devices for carrying out the methods mentioned are specified in claims 9, 10 and 11.

Das Prinzip der Erfindung und eine nur als Ausführungsbeispiel augeführte Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens sind in der Zeichnung dargestellt, und zwar zeigen.

  • Fig. 1 einen Querschnitt durch ein längsnahtgeschweißtes Rohr zur Veranschaulichung der verschiedenen Zonen und
  • Fig. 2 schematisch einen Querschnitt durch eine erfindungsgemäße Vorrichtung zur partiellen Glühung eines solchen Rohres.
The principle of the invention and a device for carrying out the method according to the invention, which is only shown as an exemplary embodiment, are shown in the drawing and show.
  • Fig. 1 shows a cross section through a longitudinally welded tube to illustrate the different zones and
  • Fig. 2 shows schematically a cross section through an inventive device for the partial annealing of such a tube.

Der in Fig. 1 dargestellte Querschnitt durch ein längsnahtgeschweißtes Rohr 1 veranschaulicht die für die Erfindung wesentlichen Bereiche des Rohres. Dabei sind die einzelnen Zonen nicht maßstabgerecht dargestellt. Die Schweißnaht 2 liegt im allgemeinen bei der Herstellung an der Oberseite des Rohres 1. Sie ist umgeben von einer Wärmeeinflußzone 3, in welcher der Schweißvorgang Veränderungen und Inhomogenitäten hinterlassen hat. Der Rest des Rohres besteht aus unverändertem Grundwerkstoff, wobei es jedoch sinnvoll erscheint, aus Sicherheitsgründen einen Bereich 4 außerhalb der Wärmeeinflußzone 3 bei einer Wärmebehandlung einzubeziehen, da die genaue Ausdehnung der Wärmeeinflußzone 3 nicht immer bekannt ist.The cross section shown in FIG. 1 through a longitudinally welded tube 1 illustrates the areas of the tube which are essential for the invention. The individual zones are not shown to scale. The weld seam 2 is generally located on the top of the tube 1 during manufacture. It is surrounded by a heat-affected zone 3, in which the welding process has left changes and inhomogeneities. The rest of the tube consists of unchanged base material, but it makes sense to include an area 4 outside of the heat affected zone 3 during a heat treatment for safety reasons, since the exact extent of the heat affected zone 3 is not always known.

In Fig. 2 ist eine Vorrichtung zur partiellen Glühung eines längsnahtgeschweißten Rohres 1 dargestellt. Die Schweißnaht 2 mit der sie umgebenden Wärmeeinflußzone 3 wird wiederum im allgemeinen an der Oberseite des Rohres liegen. Die maximale Wärmebehandlung soll sich auf die Schweißnaht 2, die Wärmeeinflußzone 3 und einen zusätzlichen Sicherheitsbereich 4 erstrekken, während der Rest des Rohres bei niedriger Temperatur spannungsarm geglüht wird. Wegen der hohen Glühtemperaturen soll das zu glühende Rohr 1 während der Glühung vorzugsweise unter Schutzgas gehalten werden, um anschließendes Beizen zu vermeiden. Im vorliegenden Ausführungsbeispiel befindet sich das zu glühende Rohr 1 im Inneren eines Quarzglasrohres 5, wobei der Zwischenraum 9 zwischen beiden mit Schutzgas gefüllt ist. Ein oder mehrere Infrarotstrahler 6 sind oberhalb des Quarzglasrohres 5 angeordnet und mit fokussierenden Reflektoren 8 in einem Gehäuse 7 versehen. Die fokussierenden Reflektoren können beispielsweise einen parabolischen Querschnitt haben, in deren Brennpunkt bzw. Brennlinie sich Infrarotstrahler befinden. Es sind jedoch auch andere fokussierende Elemente, so z.B. infrarot-durchlässige Linsensysteme u. dgl., anwendbar. Die Infrarotstrahlen werden so fokussiert, daß sie den gewünschten Bereich 4 des partiell zu glühenden Rohres 1 bestrahlen und aufheizen. Durch Anwendung von Blenden oder durch zusätzliche Kühlung der restlichen Wände des Rohres 1 kann die gewünschte partielle Glühung über beinahe beliebige Haltezeiten durchgeführt werden, wobei jedoch eine Glühung im Durchlaufverfahren unter einer entsprechenden Glühstrecke vorzuziehen ist.2 shows a device for partial annealing of a longitudinally welded tube 1. The weld seam 2 with the heat-affected zone 3 surrounding it will again generally lie on the top of the tube. The maximum heat treatment should extend to the weld 2, the heat affected zone 3 and an additional safety area 4, while the rest of the tube is stress relieved at low temperature. Because of the high annealing temperatures, the tube 1 to be annealed should preferably be kept under protective gas during the annealing in order to avoid subsequent pickling. In the present exemplary embodiment, the tube 1 to be annealed is located inside a quartz glass tube 5, the space 9 between the two being filled with protective gas. One or more infrared emitters 6 are arranged above the quartz glass tube 5 and provided with focusing reflectors 8 in a housing 7. The focusing reflectors can, for example, have a parabolic cross section, in the focal point or focal line of which there are infrared radiators. However, there are also other focusing elements, e.g. infrared transparent lens systems u. Like., applicable. The infrared rays are focused in such a way that they irradiate and heat up the desired area 4 of the tube 1 to be partially annealed. By using screens or by additional cooling of the remaining walls of the tube 1, the desired partial annealing can be carried out over almost any holding times, although annealing in a continuous process under a corresponding annealing section is preferable.

Die vorliegende Erfindung ermöglicht die Verwendung von Stählen mit beispielsweise niedrigerem Molybdängehalt für längsnahtgeschweißte korrosionsbeständige Rohre und ermöglicht auch die Herstellung dünnwandiger Rohre mit einer Wanddicke von z.B. 0,3 bis 0,5 mm.The present invention enables the use of steels with, for example, a lower molybdenum content for longitudinally welded corrosion-resistant pipes and also enables the production of thin-walled pipes with a wall thickness of e.g. 0.3 to 0.5 mm.

Claims (11)

1. Method for increasing the corrosion resistance by compensation of chromium and/or molybdenum segregations of a longitudinally seam-welded pipe (1) made of austenitic or austenitic-ferritic stainless steel, wherein after the longitudinal seam (2) has been welded the pipe (1) is subjected to heat treatment in passage below an annealing stage during which it is partially solution-annealed in the region of the whole weld seam (2) and the heat-affected zone (3) at a temperature which is greater than 1100°C for longer than 5 seconds, whilst the remaining region is subjected to heat treatment at a lower temperature.
2. Method according to claim 1, characterised in that annealing is carried out at a temperature which is greater than 1250°C.
3. Method according to claim 1 or 2, characterised in that the annealing temperature is maintained for approximately 25 seconds.
4. Method according to claim 1, 2 or 3, characterised in that the pipe (1), for the purpose of selective annealing, is partly heated and partly cooled.
5. Method according to claim 1, 2, 3 or 4, characterised in that the pipe (1) is partly heated by infrared radiators (6) or lasers.
6. Method according to claim 1, 2, 3 or 4, characterised in that the pipe (1) is partly heated by correspondingly conducted electric currents by means, for example, of saddle-shaped induction coils, if applicable with additional cooling of partial areas.
7. Method for the heat treatment of longitudinally seam-welded pipes according to one of the preceding claims, characterised in that the heat treatment is carried out in an atmosphere which contains nitrogen or a compound which liberates nitrogen at a partial pressure such that at the maximum annealing temperature the content of dissolved nitrogen in the region of the weld seam (2) rises above 0.2% without, however, crossing the limit of solubility of the material.
8. Method according to claim 7, characterised in that at the maximum annealing temperature the content of dissolved nitrogen in the region of the weld seam (2) rises to between 0.3 and 0.4%.
9. Apparatus for carrying out the method according to one of the claims 1 to 5, characterised in that the apparatus has one of several infrared radiators (6), the radiation of which can be concentrated by suitable focussing means, more particularly reflector surfaces with parabolic cross section (8), onto the weld seam (2) and the heat-affected zone (3) of the pipes (1) and which effect only partial solution-annealing of the pipes (1) in the region of the weld seam (2) and the heat-affected zone (3), and with the pipes (1) to be annealed being guided or supported in a protective covering (5), upon the interior of which protective gas can act and which, at least in partial regions, is highly permeable to infrared radiation.
10. Apparatus according to claim 9, characterised in that a cooling apparatus is provided, which apparatus cools the pipes (1) apart from in the region of the weld seam (2) and the heat-affected zone (3).
11. Apparatus according to claims 9 or 10, characterised in that the apparatus has means for adjusting a defined partial pressure of nitrogen or a compound which liberates nitrogen in the vicinity of the pipe during the heat treatment.
EP87100199A 1986-01-21 1987-01-09 Process and device for the heat treatment of longitudinally welded pipes Expired - Lifetime EP0234200B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT87100199T ATE58919T1 (en) 1986-01-21 1987-01-09 METHODS AND DEVICES FOR THE HEAT TREATMENT OF LONG SEAM WELDED PIPES.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE3601670 1986-01-21
DE3601670 1986-01-21
DE3639403 1986-11-18
DE19863639403 DE3639403A1 (en) 1986-11-18 1986-11-18 Process for improving the corrosion resistance of welded workpieces of stainless steel, and correspondingly produced workpiece

Publications (2)

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EP0234200A1 EP0234200A1 (en) 1987-09-02
EP0234200B1 true EP0234200B1 (en) 1990-12-05

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EP87100199A Expired - Lifetime EP0234200B1 (en) 1986-01-21 1987-01-09 Process and device for the heat treatment of longitudinally welded pipes

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US (1) US4975128A (en)
EP (1) EP0234200B1 (en)
JP (1) JP2668870B2 (en)
BR (1) BR8700234A (en)
DE (1) DE3766507D1 (en)

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US5217158A (en) * 1992-07-14 1993-06-08 Brush Wellman, Inc. Process for thermodynamically treating a region joining two members
EP1204772B1 (en) * 1999-05-10 2007-07-25 EUROPIPE GmbH Method for producing welded steel pipes with a high degree of strength, ductility and deformability
CA2391052C (en) * 2000-09-11 2006-12-19 Baker Hughes Incorporated Multi-layer screen and downhole completion method
US7540402B2 (en) * 2001-06-29 2009-06-02 Kva, Inc. Method for controlling weld metal microstructure using localized controlled cooling of seam-welded joints
US7618503B2 (en) * 2001-06-29 2009-11-17 Mccrink Edward J Method for improving the performance of seam-welded joints using post-weld heat treatment
CA2390054C (en) * 2002-06-28 2013-03-19 Weatherford Canada Partnership Method for manufacturing continuous sucker rod
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US9840752B2 (en) * 2014-05-27 2017-12-12 Keystone Engineering Company Method and apparatus for performing a localized post-weld heat treatment on a thin wall metallic cylinder
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Also Published As

Publication number Publication date
BR8700234A (en) 1987-12-01
JP2668870B2 (en) 1997-10-27
DE3766507D1 (en) 1991-01-17
JPS62180016A (en) 1987-08-07
EP0234200A1 (en) 1987-09-02
US4975128A (en) 1990-12-04

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