MXPA96004944A - Method and apparatus to join components of me - Google Patents

Abstract

A welding process and an apparatus used therein to provide a significant improvement in the stress stof damaging residual stress on the root side of the welds, especially on the interior wall of the welds, especially on the interior wall of the welds. pipe welds. The method combines an extremely thin weld joint design with a non-cylindrical or circular fine welding electrode (10), which has an elong cross-sectional shape. During welding the elong dimension is aligned parallel with the length of the weld joint. This combination allows the joining of the pipe and other components sensitive to residual stress both in the preparation of the initial weld joint and in the complete weld (6) having an exclusive thin width and with a high aspect portion of depth against width. The electrode can also have a tungsten alloy sheet (18). The sheet is made of sheets of tungsten alloy by cutting or stamping. The preferred form of the sheet is an isosceles triangle. the base of the triangular sheet is secured in a groove formed in its electrode holder (20). The electrode holder in preference has a T shape, with the leather (20a) of the support connected to a conventional welding torch (1).

Description

METHOD AND APPARATUS FOR JOINING METAL COMPONENTS Field of the Invention The present invention relates to the welding of pipe and other stress-sensitive components, in particular, the invention relates to the welding of pipe and other components used in nuclear reactors, whose components are susceptible to stress corrosion fracture. the areas affected by heat adjacent to a weld.

Background of the Invention A nuclear reactor comprises a fission fuel core that generates heat during fission. The heat is removed from the fuel core by the reactor cooler, ie, water, which is contained in a pressurized reactor tank. The respective piping circuits carry the hot water or steam to steam generators or turbines and carry the circulated water or feed the water back into the tank. The pressures and operating temperatures for the reactor pressure tank are approximately 7 MPa and 288 ° C for a boiling water reactor (BWR), and approximately 15 MPa and 320 ° C for a pressurized water reactor (PWR) ). The materials used in both the boiling water reactors and the pressurized water reactors must withstand various load, environmental and radiation conditions. As used herein, the term "high temperature water" means water having a temperature of about 150 ° C or higher, steam, or condensate thereof. Some of the materials exposed to high temperature water include carbon steel, steel alloy, stainless steel, and alloys based on nickel, cobalt, and zirconium. Despite the careful selection and treatment of these materials for use in water reactors, corrosion occurs on materials exposed to water at high temperature. Such corrosion contributes to a variety of problems, for example, stress corrosion fractures, crevice corrosion, erosion corrosion, gluing of pressure relief valves and isotope accumulation of gamma-emitting Co-60. Stress corrosion fracture (SCC) is a known phenomenon that occurs in the components of a reactor, such as structural members, pipes, fasteners, and welds, exposed to high temperature water. As used herein, stress corrosion fracture refers to fracture propagated by static or dynamic stress stress in combination with corrosion at the tip of the fracture. The reactor components are subjected to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure necessary for the containment of the reactor cooling water, and other sources such as residual stress from the welding, cold working and other asymmetric metal treatments. In addition, water chemistry, welding, heat treatment, and radiation can increase the susceptibility of the metal in a component to stress corrosion fracture. The present invention relates to the mitigation of residual stresses induced by welding and the thermal sensitization that can result in stress corrosion fracture in susceptible metals. FIGURE A illustrates a conventional V-groove weld 6 for joining two tubes 2 and 4. The weld is formed by filling the V-groove with granules of molten material from a filler wire placed at the tip of an electrode. cylindrical circular welding (not shown). This welding process produces a zone affected by very large heat (HAZ) in the vicinity of the welded joint. The occurrence of stress corrosion fracture in the vicinity of such welded joints has led to the need to repair or replace a lot of pipe in clear water reactor power plants around the world. Numerous methods have been used for more than a decade to improve the state of residual stress in the vicinity of welded joints, including magnetic induction, electrical resistance and electric arc heating methods. All these methods are based on generating a substantial temperature difference through the thickness of the welded material by applying the heat source on one side of the material and maintaining cooling with water on the other side of the material. This temperature difference produces thermal deformations and the plasticity of the subsequent material, and a corresponding inversion of the stress through the thickness of the material. The net result causes the residual stress on the side of the joint exposed to the potentially aggressive reactor water environment to significantly decrease the stress or more preferably, make it compressive. These previous methods, including "sunken heat sink" and "heat sink sunken as last step", all remain on the convective cooling of continuous water on the environmentally exposed side of the welded joint in order to effect the required temperature difference and the investment of effort. This requirement for water cooling is a severe punishment for the manufacturer each time the pipe is being installed or replaced again, since the entire pipe system must be intact in order to contain the water. The arc welding process typically used that requires cooling with water to effect the temperature gradient across the thickness of the material and a corresponding residual stress investment has relatively low thermal and time efficiencies and uses a wide weld joint design with a low aspect ratio of the depth of the joint with respect to the thickness. The reduction of the tensile forces that reside in the lattice structure of the metal by the cooling of internal water during the welding serves to mitigate the occurrence of the corrosion fracture with effort aided by the irradiation, where the impurities in the alloy of the Stainless steel diffuses to the grain boundaries in response to neutron shock. A second important contributor to stress corrosion fracture in chromium alloy stainless steel is the corrosion resistance in the size and degree of sensitization of the heat affected area adjacent to the weld. Thermal sensitization refers to the process by which chromium carbides are precipitated at the grain boundaries of the material. The precipitation of the chromium carbides bind the chromium that would otherwise be in solution. Thus, a thin layer along the grain boundary removes the chromium, creating an area that will not be more resistant to corrosion and therefore is susceptible to fracture by corrosion with stress. These stainless steels corrode the grain boundaries mainly.

One consideration in the design of welds for resistance to fracture by stress corrosion is the minimization of the heat input through the process to the component being assembled. This heat input is typically maintained at a level sufficient to provide reliable fusion by the weld filler metal with the side walls of the joint, which in other welding processes are separated by an amount necessary to move a circular cylindrical electrode on the board. A type of reduced striae width welding process used commercially in power plant pipe welds is called "narrow groove" welding, an illustration of which is given in FIGURE IB. This technique produces a 6 * weld between the 2 'and 4' tubes that have a zone affected by heat that is narrower than, and at a groove angle that is less than the area affected by the heat and that the groove angle of the V-groove welding process. The "narrow groove" welding process uses a standard circular cylindrical electrode geometry. These standard electrodes come in various lengths and diameters, typically with a tapered or pointed end. However, in "narrow groove" welding, the reduction in the amplitude of the groove is limited by the minimum diameter of the electrode required to reliably carry the required welding current. All of the above welds, including the "narrow groove" welds, have been made in the form of a circular cylindrical electrode, which has become the industry standard. The minimum diameter of a circular cylindrical electrode in turn is limited by the capacity of current transmission and heat dissipation of a given size. No considerations have been made for the manufacture or installation of a non-cylindrical electrode or in a V-groove or "narrow groove" welding application. U.S. Patent No. 3,715,561 discloses a non-consumable bar-shaped electrode having at least one longitudinal edge with an acute edge angle. Welding International, Vol. 3, No. 2 (1989) GB-Abington, pages 102-104, V.V. Asimov, and collaborators "Evaluation of the efficiency of electrodes made of tungsten doped with lanthanum" is suggested as an optimal form of the tip of the electrode a triangular or quadrangular shape. Welding International, Vol. 31, No. 9 (1984), GB-Abington, pages 30-32, V.A. Bukov, et al., "Methods for increasing the durability of tungsten electrodes in are welding" describes experiments with symmetric conical, conical asymmetric, and flat wedge shapes of electrode tips.

Compendium of the Invention In one aspect, the present invention is a process and apparatus that significantly improve the residual stress state of damaging stress on the root side of the welds, especially on the inner wall of the pipe welds. The process combines an extremely thin weld joint design with a thin, non-cylindrical circular welding electrode, having an elongated cross-sectional shape. During welding the elongated dimension is aligned parallel with the length of the welded joint. This combination allows the union of pipe and other components sensitive to residual stress both in the preparation of the initial weld and in the finished weld, which has a thin amplitude and with a high aspect ratio of depth to width. The use of this high aspect ratio welding process substantially mitigates the residual stresses induced by welding without the internally required water cooling normally required. The process is effective to mitigate residual stresses and weld deformations (distortion) in the joints that have some form of trajectory, either welded from one or more sides of the material. The welding process of the invention also reduces the entry of heat into the heat-affected areas, thereby mitigating the thermal sensitization of the welded joint. The present invention is also a highly thermal and time-efficient welding process to be applied to all pipes and other types of components where the conductive effects with self-cooling of the base metal alone, when combined with a very weld joint design thin, they are able to significantly improve the residual stress of welded joints of components without the need for water or other component coolant during welding. Due to the high heating efficiency, the high heating and cooling rates, the thin joint design of the described process, and the corresponding small size of each welding step, combined, the required temperature gradient and thermal stress, and The resulting improved residual stress distribution is established by the thickness of the material being welded. The final levels of the residual stresses are established as the external steps of the board are completed. In another aspect, the present invention is a welding electrode that provides a significant improvement in the residual stress state of the damaging stress on the root side of the welds, especially on the inner wall of the pipe welds. The electrode has a replaceable tungsten alloy blade. The blade is made from sheets of tungsten alloys by cutting or stamping. The preferred form of the sheet is an isosceles triangle. Alternatively other shapes may be used, such as a strip having a pointed end. The base of the flat sheet is secured in a groove formed in an electrode holder. The electrode holder is preferably T-shaped, with the trunk of the support connected to a conventional welding torch. The support is made of electrically conductive material, by which the sheet is coupled to the torch to produce an electric arc at the tip of the sheet for welding. The electrode sheet is optionally covered with a ceramic coating to prevent arching against the side walls of the groove formed between the parts being welded. In addition, insulating spacers, which protrude from both flat sides of the electrode sheet, can optionally be provided. These separators serve to maintain a minimum separation between the side walls of the weld groove and the flat sides of the electrode sheet, thus preventing the ceramic coating from detaching during the path of the electrode in relation to the groove. During welding, the sheet plane of the flat electrode is aligned in parallel with the length of the welded joint. This combination allows joining the pipe and other components sensitive to residual stress with both the preparation of the initial weld joint and the full weld having only a thin amplitude and with a high aspect ratio of depth to width. The use of this high aspect ratio solder joint process substantially mitigates the residual stresses induced by welding, without water cooling lv. interior normally required. The process is effective to mitigate the residual stresses and deformations associated with welding (distortion) in joints that have some form of trajectory, either welded from one or more sides of the material. The welding process of the invention also reduces the entry of heat into the areas affected by heat, thus mitigating the thermal sensitization of the welded joint.

Brief Description of the Drawings FIGURE IA is a sectional view of a welded V-groove joint according to a conventional welding technique. FIGURE IB is a sectional view of a narrow flute seal welded according to a conventional welding technique. FIGURE 1C is a sectional view of a welded joint according to the technique of the present invention. FIGURES 2A-2C are front, side and bottom views, respectively, of the geometry of the electrode according to the preferred embodiment of the present invention. FIGURE 3 is a schematic showing the details of the sheet geometry shown in FIGURE 2C. FIGURE 4 is a sectional view of the stria geometry of a portion of a tube to be joined according to the welding technique of the present invention. FIGURES 5A and 5B are side and top views, respectively, of a joint assembly and weld assembly according to the present invention FIGURE 6 is a schematic perspective view showing an assembly of joint and weld equipment in accordance with the present invention. FIGURE 7 is a perspective view showing the structure of an electrode having a triangular blade according to a preferred embodiment of the invention. FIGURE 8 is a sectional view of a portion of the flat triangular electrode sheet of FIGURE 7 showing the technique for mounting ceramic spacers according to the invention. FIGURE 9 is a schematic perspective view showing an assembly of the joint and welding equipment according to the preferred embodiment of the present invention.

Detailed Description of the Preferred Modalities The welding equipment according to the preferred embodiment of the invention comprises a gas tungsten arc welding (GTAW) system with mechanized torch movement that is used in conjunction with an exclusive tungsten electrode geometry. The welding process according to the invention comprises the step of creating an exclusive welded joint geometry, the welding of which is made possible by a novel form of the electrode and is made practical by other special characteristics of this welding process. According to the welded joint geometry of the invention, the groove between the tubes 2 and 4 preferably has an acute angle less than 5o which is filled with welding material having a reduced width requiring less heat to achieve fusion. The result is a zone affected by heat that is narrower than that produced by "narrow groove" welding, as seen in a comparison between FIGS IB and 1C. In contrast to conventional electrodes, the exclusive electrode of one embodiment of the present invention has an elongated, non-circular cut shape with the elongated dimension oriented in parallel with the length of the welded joint and the shortened dimension being oriented perpendicular to the length of the board. For a cross-sectional area, the thin geometry of the electrode of the present invention provides an electrode having a dimension (for example the width) that is smaller than the diameter of a circular cylindrical electrode of an equal cross-sectional area. This thinner dimension and its orientation allows the electrode of the present invention to enter into thin grooves for which a conventional cylindrical circular electrode is too wide to enter. Accordingly, the width of the joint to be welded can be made significantly smaller than in the case in which a cylindrical circular electrode was to be used, while keeping the cutting area of the electrode approximately constant. The maintenance of the area in cross section is very important in order to control the density of the current, Joule heating, and conductive cooling on the electrode during welding. The required mechanical force of the electrode with a constant area in cross section is also maintained. In addition, the use of a thin, non-cylindrical electrode according to the present invention allows the welding heat input to be significantly reduced for each step, and therefore the size and sensitization of the heat-affected area is reduces correspondingly. In contrast to conventional electrodes, an electrode according to another embodiment of the present invention has a sheet geometry wherein the cross section of the sheet is non-circular. In particular, the cross section of the sheet has an elongated dimension that is oriented parallel to the length of the welded joint and a short dimension that is oriented perpendicular to the length of the joint, for example, a cylinder having a cross section generally rectangular. According to the preferred embodiment of the present invention, the sheet is cut or stamped from a flat sheet material, for example tungsten alloy laminate material. The sheet can be cut into the shape of a triangle (preferably isosceles) or a strip having straight parallel sides and a pointed tip at one end. The thin geometry of the electrode of the invention provides an electrode having a dimension (ie, the width) that is smaller than the diameter of a cylindrical circular electrode of equal cross-sectional area. This dimension and its orientation allows the electrode of the present invention to be introduced into thin grooves for which a conventional cylindrical circular electrode is too wide to enter. Accordingly, the width of the joint to be welded can be significantly smaller than in the case where a circular cylindrical electrode is to be used. Furthermore, the use of a thin, non-cylindrical electrode according to the present invention allows the heat input of the weld to be significantly reduced for each step, and therefore the size and sensitization of the affected area by the heat It is correspondingly reduced. From the point of view of providing adequate mechanical strength of the welding electrode, the flat triangular sheet is preferable because the base of the triangle, which is pressed or otherwise supported by means of the sheet holder, provides additional resistance to bending. The flat sheet of the invention can be manufactured economically by cutting or stamping laminated material to form sheets of any desired shape, for example, triangles or strips. This flat construction also facilitates easy replacement of the electrode blade in the event that it is damaged. The elongated cross-section electrode used in the welding process of the invention is basically unlimited in how thin it can be, and therefore how thin the weld joint can be, insofar as the cross-sectional area of the Welding electrode is approximately constant and there is space towards the walls of the board for forward travel. The preferred embodiment according to the invention is a tungsten alloy electrode having the geometry shown in FIGURES 2A-2C. The electrode 10 comprises a circular cylindrical trunk 10a, a non-circular cylindrical sheet 10b and a tip 10c. The sheet 10b is optionally covered with an insulating coating. All sharp corners are rounded to avoid arching. The cross section of the sheet 10b preferably has the shape of a rectangle with rounded corners. Details of the dimensions of the sheet are shown in FIGURE 3. The sheet 10b J has a width a, a thickness B and a medium thickness C, while the trunk 10a has a diameter D. The dotted lines visible in the FIGURE 2A denote an alternative leaf shape when A = D. The following table provides dimensions from A to D for five exemplary electrodes: according to the concept of the present invention, dimensions A-D can be varied over wide ranges and are not restricted to the values set forth above in the table. Preferably, the ratio of A to B is at least 1.5: 1. A preferred embodiment of a stria geometry of a tube 2 to be joined using the welding technique of the present invention is shown in FIGURE 4. The tube has a wall thickness t. The end face of the tube comprises a ground 2a, which is an annular radial surface extending outwardly from the inner circumference of the tube, and a beveled surface 2b, which is a conical surface extending radially outwardly at an angle? in relation to the radial plane. According to the present invention,? it is preferably less than 5 ° and can be as small as 0 °. An extension surface connects the outer periphery of the earth 2a with the inner periphery of the beveled surface 2b. The extension surface 2c can be either a circular cylindrical surface (not shown) or a conical surface, for example, having an angle of 45 ° as shown in FIGURE 4. The height of the ground 2a is designated by h?; the height of the extension is designated with h2. The welding technique of the present invention was successfully applied in 152 and 356 mm (6 and 14 in) diameter tubes made of Type 304 stainless steel in the horizontal position. The tube 152 millimeters (6 inches) in diameter had a wall thickness t = 11 5 millimeters (0.432 inches); the tube of 356 millimeters (14 inches) in diameter had a wall thickness t = 31.75 millimeters (1.25 inches). In order to test only the weld, the bevel angle? it was selected to be equal to one of the following lü ': 0 °, 2 °, 3 °, 3.5 °, and 4 °. The height of the earth hx was varied from 0.762 to 1.778 millimeters (0.030 to 0.70 inches); the height of the extension h2 was varied from 2,286 to 3,962 millimeters (0.90 to 0.156 millimeters). During welding, the two tubes 2 and 4 are placed end to end in a horizontal position with a groove 8 between them, as shown in FIGS. 5A, 5B and 6. In this case, groove 8 has parallel side walls, that is, the bevel angle is? = 0 °. A consumable insert in the form of a ring 16, which has, for example, a cross section of 1588 millimeters x 3.175 millimeters (1/16 inch x 1/8 inch) and having the same composition as the filler wire, was placed between the ends of the pipes opposite the root of groove 8 to compensate for any radial defect of the lands.

During the first step (root, the groove between the tubes to be joined together must be bypassed) The earth and the consumable insert provide the material that melts with each other to form the root of the weld. , a (second) hot step is made, followed by a series of 5 filling steps and one (last) deck step.The weld grains are deposited within the flute using a thin elongated tungsten alloy electrode 10 for melting The filler wire fed into the flute The electrode 10 has the geometry shown in FIGS. 2A-2C and fits within the groove 8 with space between the electrode and the side walls as best seen in FIGURE 5B. The sheet 10b of the electrode 10 is covered with a ceramic coating 12 (see FIGURE 5A) to avoid arching with the side walls., Of the groove 8.

Suitable exemplary ceramic coatings include A1203 or Y203. The electrode is electrically coupled to a conventional welding torch 14. The flat electrode together with the small bevel angle and selected welding parameters produces a very thin weld joint, as is shown in FIGURE 1C. The preferred embodiment according to one aspect of the invention is a flat tungsten alloy electrode having the geometry shown in FIGURE 7. The electrode comprises a generally triangular flat sheet 18 stamped or cut to "from a tungsten alloy sheet, an exemplary thickness of the tungsten alloy sheet is .0254 millimeters (30 mils) .The triangular shape allows a plurality of interleaved sheets to be stamped or cut from A single sheet of tungsten alloy with very little waste Optionally, the triangular shape of the sheet can be moved away from being strictly isosceles by narrowing the point 18c at an increased rate As shown in FIGURE 7, the sheet 18 comprises a base 18a, a stem 18b and a tip 18c the base 18a is pressed or otherwise supported by an electrode holder 20. The electrode holder is preferably made of a conductive material, resistant to oxidation such as alloy copper (for example beryllium copper alloy), optionally electropalatized with silver or nickel.The electrode holder preferably has the shape of a T-shaped metal body, comprising a tr onco 20a and a cross piece 20b. The trunk 20a is connected to a conventional welding torch 14. The cross piece 20b has a longitudinal groove configured to receive the base of the sheet 18a with sufficient clearance to allow easy insertion and removal. The base is securely held in the groove of the cross piece by tightening a pair of set screws 22 in a corresponding pair of rope holes formed in the cross piece. The blade can be easily removed from the support after the screws are loosened. This allows the rapid replacement of a damaged electrode sheet. Interchangeable electrode sheets that have different dimensions depending on the specific application can also be selectively installed. Alternatively, instead of using screws, the sheet could be secured in the holder by tying it together to create a monolithic sheet assembly, that is, the sheet would not be easily replaced. The body of the sheet 18b is preferably covered with an insulating coating, for example A1203 or ^ 2 ° i < to avoid arching against the side walls of the weld groove. Also, all the rough edges on the stamped or cut sheet are rebagged to avoid arching. In accordance with the preferred embodiment, the triangular planar sheet incorporates one or more spacers 24. Each insulating spacer protrudes on both flat sides of the electrode sheet beyond the plane of the sheet surface. These spacers serve to maintain a minimum space between the side walls of the weld groove and the flat sides of the electrode sheet, thus avoiding scraping or excessive or qapt of the ceramic coating during the travel of the electrode in the groove of welding. A sufficiently deep scrape on the coated surface of the sheet will remove the ceramic coating 12, leaving the sheet susceptible to arching along the uncovered site. The construction of an exemplary electrode sheet having a plurality of insulating spacers is shown in detail in FIGURE 8. After the triangular-shaped sheet was cut or stamped from a sheet of tungsten alloy, they are cut or stamped a plurality of circular holes in the sheet. Each separator 24 consists of a medium-roast ore mass of insulating material, for example A1203 or 22 ° 3 'having a cylindrical peripheral wall and a pair of slightly convex opposing surfaces. The diameter of the peripheral wall is slightly smaller than the diameter of the circular holes in the sheet. Each spacer 24 is secured in a corresponding hole by the cement 26. An electrically insulating coating 12a is then applied to the exposed surfaces of the body of the sheet 18b, leaving the base 18a and the tip 18c uncovered. Naturally, the height of the triangle must be greater than the depth of the weld groove by an amount that ensures that the bare base 18a is not close enough to a side wall of the groove to cause arcing. The triangular flat electrode 18 of FIGURE 7 is shown in FIGURE 9 inserted into a weld groove 8. The very thin weld joint becomes practical with the welding process using the elongated cross section electrodes of the invention allows that the two surfaces come together to be closer to each other, so that both are wetted simultaneously by a smaller molten solder pit with a significantly lower heat input index (improved thermal efficiency) than otherwise possible. This reduction in the heat input per weld pass to the deposited fill material and to the base materials being welded allows the size and temperature of the affected area to be significantly reduced by the heat adjacent to the melted zone, with the benefit of a corresponding reduction in the sensitivity of susceptible materials. As a result, the temperature gradient across the thickness of the component being welded is much more pronounced, since the gradient is controlled by the relatively constant high temperature of the molten metal, and the reduced low temperature of the component's distant surface ( also known as the "root" or first step of welding). The pronounced temperature gradient across the component that is achieved with the very thin weld joint also gives rise to the benefit of generating a lower stress or, preferably, a state of compressive residual stress at the root of the weld. This improved stress state also results in a reduction in susceptibility to fracture stress corrosion cracking. The combined effects of reduced thermal sensitization (ie, carbide precipitation) in the heat-affected areas and the improved stress state at the root of the weld provide a significant increase in resistance to stress corrosion fracture of a welded joint exposed to an aggressive environment. The use of a welding gas with a lower electrical resistance in the ionized state in the welding process, such as a mixture of argon and hydrogen and / or helium, instead of pure argon, allows the arc length to be reduced ( between the end of the electrode and the bottom of the joint of the weld), ensuring that the arc does not transfer to the walls of the joint that are closer to the electrode as is the case in other welding processes. An alternative method specified in the welding process to prevent transfer from the arc to the joint walls is to cover the surface of the electrode, except for the tip where the arc is intended to be transferred, with a material such as a ceramic that has a greater resistance to ionize the welding gas mixture. This consideration helps to ensure that the edges (geometric discontinuities) of the electrode along its length are not arc transfer sites that are more favorable than the tip of the electrode. This method also eliminates the need to insert an insulating gas vessel extension into the joint, as is practiced in some other larger joint welding processes. Another benefit related to the reduced heat input with the present invention is a reduction in, or elimination, of grain growth during welding. Significant grain growth in the area affected by heat and corresponding thermal sensitization in this area results in "knife line attack" from stress corrosion fracture in materials that are otherwise resistant to stress corrosion fracture, such as austenitic stainless steel grades. The state of residual stress improved at the root of a joint made by the welding process of the present invention, in relation to the conventional welding of a joint with a wider groove and a circular cylindrical electrode, is generated by an inversion of the effort during the welding process. During welding, the hot, weakened, heat-affected area and newly solidified welded metal are compressed plastically due to their thermal expansion relative to the stronger and colder surrounding material. During cooling, this compressed area contracts against the surrounding material and is put in a state of residual stress of tension. The contraction and the corresponding stresses are balanced by means of the surrounding material, in particular the root of the weld, endo to the desired state of less stress or to a more adequate compressive stress. The degree of improvement of the effort depends on the particular welding processes used. A key factor in making the welding process effective to generate a sensitization of the area affected by the significantly reduced heat and residual stresses of the root tension without cooling with water (subsidence of external heat) of the component being welded is the capacity Very low heat input of the process (and the corresponding collapse of internal heat), are made possible with the very thin geometry of the joint and in turn, by the shape of the thin, non-circular welding electrode. Another benefit of the reduction of the residual stresses of the stress at the root of a joint made with the welding process according to this invention is a decrease in the susceptibility of the materials exposed in a radiation environment to the corrosion fracture mechanism. with effort aided by radiation (IASCC). This beneficial effect grows due to the delay in the diffusion of the elements harmful to the internal interfaces which is helped by the influence of residual stresses with higher tension. Some of the parameters of the welding process that control the thermal efficiency of the process include the composition of the arc gas, the torch travel speed, and the values of the arc current and the current impulse. These and other parameters were modified for the welding process of the invention beyond their normal ranges for V-groove welds or "narrow groove" also in order to minimize the area affected by heat and residual stress of root tension. Measurements of the diameter and length of the tube diameter revealed that the shrinkage was reduced, resulting in a lower strain stress. Different mixtures of inert gas were tested as the protective gas, including (1) 50% argon- 50% helium; (2) 98% argon - 2% hydrogen; and (3) 95% argon - 5% hydrogen. The mixture of argon and hydrogen increases the temperature of the arc, causing the solder to fill to wet the substrate faster. Due to the high energy density, the surface of the substrate heats up quickly, leaving no time for driving below the surface. This produces a zone affected by the thinner heat than is conventionally known. The addition of hydrogen also shortens the arc, so that less space is needed towards the side walls. In addition, the torch travel speed during the test weld was varied between 2 and 10 inches / minute. The higher torch travel speeds allow the solder filling to cool quickly. During the development of the welding process, for the root (first) step the arc current was 90 to 5 115 amps for the first pulse and 60 to 70 amps for the second pulse; for the hot pass (second) the arc current was 115 to 170 amps for the first pulse and 50 to 70 amps for the second pulse; and for the filling steps the step current was 170 to 220 amps for the first impulse lu and 70 to 110 amps for the second impulse. Several pulse schemes were tested. The above process and apparatus were described for purposes of illustration. For those skilled in the welding art, variations and changes will be immediately apparent. process and device modifications described. All those variations and modifications that do not depart from the concept of the present invention are intended to be encompassed by the claims set forth hereinafter.

Claims (12)

1. CLAIMS 1. A welding electrode comprising a blade having an axis and a tip, the tip being attached and electrically connected to one end of the blade, the blade being a cylinder having a generally rectangular cross section and having a dimension of thickness in a thickness direction perpendicular to the axis and a width dimension in a width direction perpendicular to the axis. The ratio of the width dimension against the thickness dimension being at least 1.5: 1, and the tip being a solid body comprising a first, a second and a third faces, the first face being perpendicular to the axis of the sheet, the second face being disposed obliquely with respect to the first face and, the third face being obliquely disposed with respect to the first face and not being parallel with the second face, the second and third faces being of trapezoidal shape, the first face being joined and the second face in a first linear joint, the first and third faces being joined in a second linear joint, the sheet and the second face being joined in a third linear joint, the sheet and the third face being joined in a fourth joint linear, being from the first to the fourth mutually parallel linear joints.
2. 2. The welding electrode as defined in claim 1, characterized in that the tip has the shape of a truncated pyramid.
3. 3. The welding electrode as defined in claim 1, characterized in that the sheet is covered with electrically insulating material.
4. 4. A method for joining a first and a second metal component in a direction of gradual depth, the first and second components in a non-union state have a first and a second parallel side, respectively, that are separated by a groove. or having at least one predetermined width, comprising the steps of: continuously feeding welding material in the vicinity of the tip of an electrode traveling at a selected speed of travel during a particular welding step of material welding that 15 melts continuously within the flute by the electric discharge current from the tip of the electrode according to selected welding parameters while the electrode is displaced at the selected speed and solidifying the molten solder material to form 20 molten granules, the electrode comprising a blade having one end attached and electronically connected to the tip, the blade having a non-circular cross-section with a first dimension in a first direction and a second dimension in a second direction, the first being the 25 second mutually perpendicular directions, the first dimension being smaller than, and the second dimension being greater than, the width of the groove previously determined, a predetermined number of welding steps that collectively create a residual end state of stress, which It is compressive through the solder joint and the areas affected by the heat thereof, achieving the state of compressive residual stress without the use of any external means of subsidence by heat to extract the heat introduced during any of the welding steps .
5. 5. The method as defined in the claim 4, characterized in that a first and a second metal component are tubes and the flute is an annular flute separating the tubes, and the tip of the electrode is displaced circumferentially within the annular flute during the melting of the welding material at a speed greater than 5 inches per minute.
6. 6. A welding electrode characterized by a flat blade (18) made of a sheet of electrically conductive material, and having a base 18a at one end, and a tip 18c at the opposite end, a blade holder (20) made of a rigid electricity conductive material; and an element (22) for securing the base of the blade to the blade holder.
7. The eoldering electrode as defined in claim 6, characterized in that the flat blade has a generally triangular shape.
8. The eoldering electrode as defined in claim 6, characterized in that the flat blade has a strip shape, having parallel sides, an extremity 5 pointed, which forms the tip.
9. 9. The winding electrode as defined in claim 6, characterized in that a portion of the blade is covered by an electrically insulating material (12). ' C
10. 10. The welding electrode as defined in claim 6, further characterized by separating elements (24) made of electrically heated material, forming the elementary and convex elements to be convex on both sides of the blade.
11. 11. The welding electrode as defined in claim 6, characterized in that the blade comprises a through hole and the separating elements comprise a mass of electrically insulating material having opposite convex surfaces which are separated by 20 a distance greater than the groeor of the blade and having an outer periphery that forms the shape of the hole that crosses it.
12. 12. The eolder electrode as defined in claim 6, characterized in that the e-bearing of the The blade comprises a trunk (20a) and a crosspiece (20b) connected in the shape of a T, the crosspiece having a longitudinal slot for receiving the base of the blade.