Patent Abstract:
A method produces a welded connection between first and second components each having inner and outer sides interconnected by an end face. The first component has a ferritic basic body carrying a plating at the inside and having an end face with a buffer layer of Ni-based alloy. The second component is of austenitic material. The end faces of the components enclose a weld groove. An austenitic root, connecting the plating to the end face of the second component, is welded in the weld groove. An intermediate layer of a nickel alloy having at least 90% nickel is welded onto the root. The intermediate layer is connected to the end faces of the plating and the second component. A weld seam is then produced in the remaining weld groove using a nickel-based welding additive. A method for repairing a welded connection between first and second components is also provided.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuing application, under 35 U.S.C. §120, of copending International Application No. PCT/EP2006/004701, filed May 18, 2006, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2005 035 585.4, filed Jul. 29, 2005; the prior applications are herewith incorporated by reference in their entirety.  
       BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]     The invention relates to a method for producing a welded connection between first and second components each having an inside, an outside and an end face interconnecting the inside and the outside. The first component is formed from a ferritic basic body that carries an inside plating and has an end face which is provided with a buffer layer formed of a nickel-based alloy. The second component is formed from an austenitic material. The invention furthermore relates to a method for repairing such a welded connection.  
         [0003]     The components in question are, in particular, pipes or pipe connection pieces, the insides of which come into contact with a corrosive medium. In particular, the primary circuit of a nuclear power station is to be mentioned in this case, in which water that is under pressure and has high temperatures circulates as the primary coolant. In order to avoid corrosion phenomena in the reactor pressure vessel which is formed of a ferritic material for reasons of strength, it is provided on the inside with a plating formed of an austenitic material. A pipeline connected to the connection piece of a reactor pressure vessel, by contrast, may be formed entirely of more corrosion-resistant austenitic material. Two components of the type initially mentioned, or a ferritic pipe section with an austenitic inner plating and a fully austenitic pipe section, are connected to one another in a customary procedure through the use of a weld seam formed of a nickel-based alloy. The disadvantage thereof is that specific nickel-based alloys have lower corrosion resistance (intercrystalline stress cracking corrosion) than austenitic materials so that, in the event of lengthy contact with a corrosive medium, for example with water, while a nuclear reactor is in operation, there is the risk of the weld seam corroding from the inside.  
       SUMMARY OF THE INVENTION  
       [0004]     It is accordingly an object of the invention to provide a method for producing a more corrosion-resistant welded connection and a method for repairing a corrosion-damaged welded connection, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type.  
         [0005]     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a welded connection between first and second components each having a respective inside, outside and end face interconnecting the inside and the outside. The first component is formed of a ferritic basic body carrying an inside plating and having an end face provided with a buffer layer formed of a nickel-based alloy. The second component is formed of an austenitic material. The method comprises enclosing a weld groove between the end faces of the two components. The plating is connected to the end face of the second component with a root formed of an austenitic material welded in the weld groove. An intermediate layer formed of a nickel alloy with at least  90 % nickel is welded onto the root and the intermediate layer is connected to an end face of the plating and to the end face of the second component. A weld seam is subsequently generated with a nickel-based welding additive in the weld groove still remaining.  
         [0006]     With the objects of the invention in view, there is concomitantly provided a method for repairing a welded connection between first and second components each having a respective inside, outside and end face interconnecting the inside and the outside. The first component is formed of a ferritic basic body with an inside plating formed of an austenitic material and an end face carrying a buffer layer formed of a nickel-based alloy. A weld seam formed of a nickel-based welding additive interconnects the end faces of the first and second components. The method comprises stripping off a weld region between the two components on a side of the plating to form a recess having a bottom. An intermediate layer, formed of an alloy weldable both to the nickel-based alloy of the buffer layer and to an austenitic material, is welded into the recess to partially fill the recess and completely cover the bottom of the recess. A closing layer formed of austenitic material is welded onto the intermediate layer to cover an entire area of the intermediate layer. The closing layer is smoothed by cutting machining.  
         [0007]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0008]     Although the invention is illustrated and described herein as embodied in a method for producing a welded connection and a method for repairing a welded connection, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0009]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0010]      FIG. 1  is a diagrammatic, longitudinal-sectional view of a reactor pressure vessel with a connection piece and with a pipe connected thereto;  
         [0011]      FIG. 2  is an enlarged, fragmentary, longitudinal-sectional view of a portion II of  FIG. 1 , showing a conventional welded connection between the connection piece and the pipe;  
         [0012]      FIGS. 3 . 1 - 3 . 6  are fragmentary, longitudinal-sectional views illustrating a sequence of a first method variant for producing a welded connection;  
         [0013]      FIGS. 4 . 1 - 4 . 5  are fragmentary, longitudinal-sectional views illustrating a sequence of a second method variant;  
         [0014]      FIGS. 5 . 1 - 5 . 6  are fragmentary, longitudinal-sectional views illustrating a sequence of a third method variant; and  
         [0015]      FIGS. 6 . 1 - 6 . 4  are fragmentary, longitudinal-sectional views illustrating a sequence of a method for repairing a conventional welded connection. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring now to the figures of the drawings in detail and first, particularly, to  FIGS. 1 and 2  thereof, it is seen that  FIG. 2  shows a conventional welded connection between a first component  1  and a second component  2 , in which the first component  1  is, in particular, a pipe section, for example a connection piece  3  of a reactor pressure vessel  4 , and the component  2  is a pipe  5  attached butt to butt thereto, as is seen in  FIG. 1 . The components  1 ,  2  each have a respective outside  6 ,  7 , a respective inside  8 ,  9  and a respective end face  10 , 12  connecting the outside and inside to one another. The first component  1  is composed of a basic body  13  and of a plating  14  attached to the latter on the inside. The basic body  13  is formed of a ferritic material, for example of 22 NiMoCr 37 (material number 1.6751) or SA 508 CI 2 (ASME code). The plating  14  is formed of an austenitic material, for example material number 1.4551 or AISI 347. An end face  15  of the basic body  13  carries a buffer layer  16  formed of a nickel-based alloy, for example Inconel 182, with a nickel content higher than 67%, containing alloying constituents being, inter alia, 16% chromium, 6.5% manganese and 6% iron (the percentages in this case and elsewhere herein are percentages by weight). The buffer layer  16  covers the entire end face  15  of the basic body  13 . An inward-facing narrow side  17  of the buffer layer  16  is connected to the plating  14  in a materially integral manner. The second component  2  is formed of an austenitic material, for example of X 10 CrNiMoTi 1810 (1.4571) or AISI 316 L. The two components  1 ,  2  are oriented in alignment with one another with an axial clearance, and between them they enclose a weld groove  18  and a weld seam  19 . The weld seam  19  is generated with a nickel-based alloy as a welding additive, for example I  82 . It extends as far as the inside  8 ,  9  of the first and second components  1 ,  2  and is exposed there to the corrosive influences of the medium in contact therewith, in particular of a primary coolant which is under high pressure and has high temperatures of more than 280° C. Nickel-based alloys have a comparatively low corrosion resistance, so that corrosion may occur from the inside in the region of the weld seam  19 . The aim of the invention, then, as already mentioned initially, is to remedy such corrosion.  
         [0017]     A first method variant is shown diagrammatically in  FIG. 3 . 1  to  FIG. 3 . 6 . In a first part of the method ( FIG. 3 . 1  to  FIG. 3 . 3 ), the component  1  is first provided with a buffer layer  16  formed of Inconel 182. For this purpose, first ( FIG. 3 . 1 ), the basic body  13  is stripped off on the end face to such an extent that its end face  15  is set back with respect to the plating  14  or that the plating  14  projects with a projecting length  20  beyond the end face  15  in an axial direction  22 . In this case, part of the plating  14  is also stripped off, so that the projecting length  20  has a thickness which is slightly smaller than a thickness  31  of the original plating. In the next step ( FIG. 3 . 2 ), the buffer layer  16  is applied to the end face  15  in the form of non-illustrated multilayered weld beads, starting at the projecting length  20 . The buffer layer thus obtained has a non-uniform end face  23  and on the top side protrudes with a material excess  21  beyond the outside  6  of the component  1 . In the next method step, the buffer layer  16  is machined by cutting and its end face  23  is thereby smoothed and stripped off from the outside to such an extent that it is in alignment with the outside  6  of the component  1  ( FIG. 3 . 3 ). The component  2  is then applied on its end face to the component  1  prepared in this way, so as to leave a weld groove  18  free. A root  25  formed of austenitic material, for example material number 1.4551 or ER 347Si, is welded on between the end face  12  of the component  2  and an end face  24  of the plating  14  ( FIG. 3 . 4 ). A connection point formed between the two components  1  and  2  by the root  25  is formed of the same material as the plating  14  and the component  2  or of a material comparable thereto, so that, in terms of corrosion, it has the same or similar behavior to the plating  16  and the component  2 . Since the welding of an austenitic material to Inconel tends toward cracks, the root  25  can extend only as far as a separating line  26  between the plating  14  and the buffer layer  16 .  
         [0018]     In the next method step, an intermediate layer  28  formed of a nickel alloy with 96% nickel, 3% titanium and customary accompanying elements, such as iron, silicon and manganese, as the remainder, is welded onto the outside of the root  25  ( FIG. 3 . 5 ).  
         [0019]     In the last operation ( FIG. 3 . 6 ), then, a weld seam  19  is applied to the outside of the intermediate layer  28 , with Inconel  82  being used as a welding additive. In this, as in all of the other welding operations mentioned herein, welding is carried out under protective gas. This method is largely automated. In this case, a welding wire formed of the welding additive, that is to say, for example, of Inconel  82 , is not delivered to the welding point by hand, but automatically through a corresponding device. In this case, it is critical that delivery takes place at a constantly uniform speed, in such a way that there is always sufficient molten additive present in the region of the welding arc and the molten pool occurring there. If the nickel-based alloy of the weld seam  19  is welded directly onto the austenitic root, that may lead to the formation of cracks. Since welding takes place from the inside outward, a renewal of a cracked root region is possible only at a high outlay, mostly only by separating the connection between the two components  1 ,  2  again and by beginning the welding of a root  25  once more after complicated preparatory work. It has been shown that, with an intermediate layer  28  of the type mentioned being present, crack formation in the root  25  does not occur. Due to the intermediate layer, the tendency toward crack formation is suppressed because of the more favorable mix ratios with the various materials.  
         [0020]     A second method variant is shown in  FIG. 4 . 1  to  4 . 5 . It differs from that described above in a different preparation of the component  1 . In contrast to the variant described above, the end face  15  of the basic body  13  is not stripped off first, but instead, the plating  14 , although part of the basic body, is also stripped off ( FIG. 4 . 1 ). The plating  14  is thus set back somewhat with respect to the end face  15 , so that a recess  29  is present on the inside  8  of the component  1 . The bottom  30  of the recess  29 , which is formed by the basic body  13 , has a clearance  32  relative to a plane  33  spanned by the inside  8  (the surface of a cylinder in the case of a pipe) which, because of the partial stripping off of the basic body  13  during the removal of the plating  14 , is somewhat greater than the thickness  31  of the plating  14 . In the next step ( FIG. 4 . 2 ), an austenitic layer  34  replacing the stripped-off plating  14  is welded into the recess  29  in such a way that this layer protrudes with a material excess  35  beyond the plane  33  spanned by the inside  8 . The end face  15  of the basic body  13  is subsequently stripped off to such an extent that a projecting length  36  of the austenitic layer  34  projects beyond it in the axial direction  22  ( FIG. 4 . 3 ). In this case, part of the region  41  contiguous to the basic body  13  is also stripped off.  
         [0021]     In the next processing step ( FIG. 4 . 4 ), a buffer layer  16  is welded onto the end face  15  of the basic body  13 , in a similar way to the method step illustrated in  FIG. 3 . 2  in the method described above. This commences at the projecting length  36 . The buffer layer  16  covers the end face  15  completely and is connected in a materially integral manner to the projecting length  36  of the austenitic layer  34 . The buffer layer protrudes with a material excess  21  beyond the outside  6  or beyond the plane  39  spanned by the latter. In the next processing step ( FIG. 4 . 5 ), the material excess  21  of the buffer layer and the material excess  35  of the austenitic layer  34  are stripped off. The end face  23  of the buffer layer  16  and the end face  37  of the austenitic layer  34  are machined by cutting and are shaped correspondingly to the later weld groove. The component  2  is then welded, in the manner described further above and made clear in  FIG. 3 . 4  to  FIG. 3 . 6 , to the component  1  ( FIG. 4 . 5 ) which is prepared in the manner outlined.  
         [0022]     A further method variant ( FIG. 5 . 1  to  5 . 6 ) differs from the variants described further above, mainly in the preparation of the component  1 . In this case, in a first step, a buffer layer  16  is welded onto the end face  15  of the basic body  13  and is subsequently stripped off and smoothed by cutting machining to such an extent that the buffer layer is in alignment with the outside  6  of the basic body and approximately with a separating line  38  between the basic body  13  and plating  14  ( FIG. 5 . 1 ). Before the buffer layer  16  is welded on, an end face  24   a  of the plating  14  is chamfered, so that it forms an angle α&lt;180° pointing away from the buffer layer  16 , with the end face  15  of the basic body  13 .  
         [0023]     In the next method step, another intermediate layer  40  is welded onto the narrow side  17  of the buffer layer  16  ( FIG. 5 . 2 ). This intermediate layer is formed of a material which is weldable both to the nickel-based alloy of the buffer layer  16  and to an austenitic material. By virtue of this measure, then, it is possible to fill a region  42  circumscribed by the narrow side  17  and the end face  24   a  , so as to form an austenitic layer  43 , by welding the material onto the intermediate layer  40  and in this case also connecting the material to the end face  24   a  in a materially integral manner. After a cutting machining of the layer  43  for smoothing and shaping, the component  1  is prepared for connection to the component  2  ( FIG. 5 . 3 ). A material which is suitable for the intermediate layer  40  is, in the first place, a material which may also be used for the intermediate layer  28  (between the root  25  and the weld seam  19 ) described further above, to be precise an alloy with at least 90% nickel, in particular one which contains 96% nickel, 3% titanium and, as the remainder, accompanying elements, such as iron, silicon and manganese. Such an alloy is known under the ASTM designation ERNI  1 . The welding of the component  2  onto the component  1  prepared according to  FIG. 5 . 3  takes place basically in the manner already described further above. In the first step ( FIG. 5 . 4 ), a root  25  is welded into the weld groove  18 , with this root being connected in a materially integral manner to the austenitic layer  43  on the side of the component  1 . In this case, as much austenitic material is introduced into the weld groove  18  as is necessary to ensure that, as far as possible, an entire end face  37   a  of the layer  43  is covered by the root  25  and is thus utilized for the materially integral connection. The root in this case extends at most as far as a separating line  48  between the intermediate layer  40  and the austenitic layer  43 . In the next step ( FIG. 5 . 5 ), the intermediate layer  28  already mentioned is welded onto the outside  27  of the root  25 . The intermediate layer  28  is connected on the side of the component  1  to the intermediate layer  40  and has about the same thickness as the latter. In the last method step ( FIG. 5 . 6 ), finally, the weld seam  18  is generated with Inconel  82 .  
         [0024]     As already mentioned, a conventional welded connection with I  182  between two components  1 ,  2  tends, particularly after lengthy use, toward corrosion upon contact with corresponding media. In the case of advanced corrosion, such a welded connection has heretofore had to be produced completely anew. With the aid of the repair method described below, the welded connection can be renovated at a comparatively low outlay. In the case of pipeline systems, for example the primary circuit of a nuclear power station, manipulator access must, of course, be present in the vicinity of the welded connection, so as not to have to separate the entire welded connection. Manipulator tools and welding robots can then be introduced through this access into the interior of the pipe. Damage  44  ( FIG. 6 . 1 ) caused by corrosion at a weld seam  19  formed of a nickel-based alloy may, as is seen in the circumferential direction, be limited locally or extend even over the entire inner circumference of the weld seam  19 . First, a region containing the damage  44  is copiously stripped off, with the result that a recess  45  is formed ( FIG. 6 . 2 ). The recess  45  extends in the axial direction  22  into regions  46  of the plating  14  and of the component  2  which are laterally contiguous to the weld seam  19 . An intermediate layer  40   a  , which is formed of the same materials as the intermediate layer  40  mentioned further above, is then applied to the bottom  49  of the recess  45  ( FIG. 6 . 3 ). The intermediate layer  40   a  covers the bottom  49  of the recess  45  completely. Finally, a closing layer  50  formed of austenitic material, for example AISI 347, is welded onto the intermediate layer  40   a  so as to cover the entire area. Non-illustrated material protruding beyond the insides  8 ,  9  after the welding operation is subsequently stripped off in such a way that an inside  47  of the closing layer  50  is in alignment with the insides  8  and  9  of the respective components  1  and  2 .

Technology Classification (CPC): 1