MXPA96004943A - Method for mitigating the soldied metal complete residual efforts using high sopl travel specimens - Google Patents

Abstract

The present invention relates to a method of heat treating first and second metallic components joined in a depth direction by a weld joint formed, at least in part, by a root pass in a nearby surface and a plurality of steps successively constructed in the upper part of said root passage in a direction from the near surface to a far surface, comprising the step of heating the far surface of the solder joint during a passage by discharge of an electric current arc from a tip of an electrode that travels along the far surface at a torch travel speed so that a temperature distribution is created across the material between the near and far surfaces, so the state of stress in said near surface undergoes an inversion of the compression stress substantially without external cooling to the surface. icie close

Description

METHOD FOR MITIGATING RESIDUAL EFFORTS IN SOLDED METAL COMPONENTS USING HIGH SPEEDS OF TORCH TRAVEL 5 Field of the Invention The present invention relates to the welding of pipe and other components sensitive to residual stress. In particular, the invention relates to the welding of pipe and other components used in nuclear reactors, the components of which are susceptible to stress corrosion fracture in the areas affected by heat adjacent to a weld. 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 The reactor cooler, ie, water, 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. Operating pressures and temperatures for the pressure reservoir of the reactor are approximately 7 MPa and 288 ° C for a boiling water reactor (BWR), and of 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 more, 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, pressure relief valve gluing, and isotope increase of gamma-emitting Co-60 isotope. 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 thermal sensitization which can lead to 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 a welding electrode. cylindrical circular (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 these welded joints has led to the need to repair or replace a lot of pipe in light 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 makes the residual stress on the side of the joint exposed to the water environment of the potentially aggressive reactor significantly decreases the tension or makes it more preferably compressive. These previous methods, including "heat-sunken welding" and "heat-sunken welding 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 utilizes a broad 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 radiation, where the impurities in the alloy of the Stainless steel diffuses to 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 precipitate 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 eliminates chromium, creating an area that will not be more resistant to corrosion and therefore is susceptible to stress corrosion fracture. 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. Another contribution to stress corrosion fracture in stainless steels to stabilized corrosion stenitic steels is the dissolution of stabilizing carbides near the melting line of the welds, which in turn can result in grain growth and Thermal sensitization when the welding heat input is excessively high. This particular variation of stress corrosion fracture generally refers to "knife line attack" because it often occurs in localized regions of the area affected by the welding heat. A type of reduced striae amplitude welding process used commercially in power plant piping welds, it is called "narrow groove" welding, of which an illustration is given in FIGURE IB. This technique produces a weld 6 'between the tubes 2' and 4 'which 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 angle of stria of the V-groove welding process. The "narrow groove" welding process uses a standard circular cylindrical electrode geometry. These standard electrodes come in several 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 previous welds, including the "narrow groove" welds have been made with the cylindrical electrode shape - * circular, which has become the industry standard. The minimum diameter of a circular cylindrical electrode in turn is limited by the current transmission capacity and of 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. The Patent of the United States of North America No. 4,588,869 and French Patent Publication No. 2,448,574 describe welding methods or sections of heat treatment tubes to alleviate residual stresses. However, refrigerants are used to cool the surface of pipe sections away from the electrode. These sources are silent according to the travel speed of the electrode. United States Patent No. 4,302,658 describes a method of improving the mechanical properties of silicon steel welded by the passage of the welding electrode over the weld at speeds greater than 25.4 centimeters per minute while fixing the restricted movements of the welded electrodes. accessories of the welded pieces during welding and the subsequent heat treatment.

SUMMARY OF THE INVENTION The present invention is a process for providing a significant improvement in the residual stress state of damaging stress on the root side of the welds, especially on the inner wall of the tube welds. The process uses a new combination of welding parameters, in particular, an extremely fast welding torch travel speed, especially in the last or more steps, commonly referred to as the "cover" steps. In order to obtain the maximum benefits of effort improvement, the process of the invention further improves the low residual stress welding process described in the United States of America patent application with serial number 08 / 237,732, whose technique of welding employs a tungsten electrode blade that has a non-circular cross section. That patent application describes welding torch travel speeds in the range of 5.1 to 25.4 centimeters per minute (2 to 10 inches per minute). The process of the present invention can be performed using the same flat electrode blade, but higher welding torch travel speeds, that is, greater than 25.4 centimeters / minute (10 inches / minute), particularly during the so-called "steps" cover". The aforementioned low residual stress welding process has been shown to mitigate the normally high levels of residual stress (approximately the resistance to permanent deformation or more) at a low stress value substantially less than the resistance to permanent deformation or, preferably, , to a state of compressive effort. This result has been achieved without the use of any complementary cooling on any of the surfaces of the component that is being coupled, as is sometimes used in water cooling processes such as in heat sinking welding and sinking welding heat of last step. The process according to the present invention is primarily intended for, but is not limited to, welding or heat treatment of relatively thin materials (e.g. in the range of 9.5 millimeters (3/8 of an inch thick). The process is considered to be soldering if the underlying material of the solder joint melts during the step or the cover steps., the process is considered to be a heat treatment if the underlying material of the welded joint is heated, but does not melt during one or more steps of the tip of the welding electrode on the distal surface (remote from the root) of the joint welded The present invention encompasses both welding and heat treatment. The term "deck step", as used herein, includes the step or conventional steps in the welding process as well as the step or steps of heat treatment. The essence of the invention is, using a moving welding torch, to introduce heat into the remote surface (away from the pitch of the welded root) at a speed such that the remote surface is heated and the nearby surface is cooled (without use of external heat sinking, for example, cooling with water) to a degree such that reduced stress stress or preferably compressive stress occurs on the near surface. Specifically, the process of the invention uses very high welding torch travel speeds during the cover steps, that is, 25.4 centimeters / minute (10 inches / minute), to obtain the maximum stress mitigation benefits. This process, either used as a welding process or as a heat treatment, as mentioned hereinafter as a "passive heat sink" to distinguish it clearly from existing techniques requiring fluid cooling (including cooling) With gas) . The process of the invention relies on the capacity of subsidence by limited thermal heat of the tube wall and the welded joint itself almost complete to generate a temperature gradient across the significant wall, and therefore a gradient of stress through of sufficient wall during welding. This stress gradient, and therefore a reduction in the magnitude of the final residual stress or, preferably, as conditions permit, an inversion in the direction of compressive tension stresses. A suitable temperature gradient is achieved when the high torch travel speeds of the present invention, allowing the outer layer of the component wall to become sufficiently hot before excessive conduction through the wall to the inner layer can occur. . This effect was previously demonstrated in thicker wall material (high heat sinking) at a slower torch travel speed (ie, 5.1-25.4 centimeters / minute (2-10 inches / minute)) in the welding process of low residual effort. According to the invention, this effect can also be obtained for a thin wall material (low heat sinking) at faster torch travel speeds (ie, >25.4 centimeters / minute (10 inches / minute)). A key difference between these two conditions is that for the thin material, the inversion of the increased stress is achieved first during the step or steps of the roof, while for the coarse material the inversion of the effort is achieved progressively as it is completed. For welding without supplementary cooling on thin material, the heat input from the step or cover steps can easily dominate the temperatures through the pairs, while the thick materials, the heat input from the step or cover steps have an effect reduced on the distribution of the temperature through the wall. For welding with complementary cooling, such as in the conventional processes of heat sinking and heat sinking welding in the last step, the heat of the last step must be even greater to compensate for the effect of losses due to fluid cooling .

According to a further aspect of the invention, the welding torch is oscillated laterally during the passage or cover steps. The purpose of the lateral oscillation of the torch is to diffuse the heat on the distal surface of the tube in a manner that produces a reduced stress stress substantially less than the resistance to permanent deformation or, preferably, a compressive stress over a longer axial length. wide in the near surface, thereby reducing the concentration of the bending moment applied through the root of the weld and mitigating the thin circumference fracture along the melt line on both sides of the weld.

Brief Description of the Drawings FIGURE A 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 groove 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.

FIGURES 2A-2C are sectional views of the geometries of the alternative grooves of the tube to be joined according to the welding technique of the present invention. FIGURE 4 is a perspective view showing the structure of a second electrode geometry that can be used for welding in accordance with the present invention. FIGURE 5 is a schematic perspective view showing a set of joint and welding equipment that can be used for welding in accordance with the present invention. FIGURES 6A and 6B are graphs showing the axial and tangential residual stresses, respectively, as measured on the inner diameter of Type 347 stainless steel diameter tube of 10.2 centimeters (4 inches) welded to butt circumference in accordance with the present invention.

Detailed description of the preferred embodiments. The welding equipment that is preferably used to carry out the process of the present invention comprises a gas tungsten arc welding system with mechanized torch movement. The sheet of the tungsten welding electrode has a non-circular cross section. However, it is believed that the use of a flat tungsten electrode is not necessary to practice the present invention. According to a welded joint geometry (see FIGURE 1C) which is useful for practicing the present invention, the groove between the tubes 2 and 4 preferably have an acute angle of < 6o and is filled with welding material 6 having a reduced width that requires less heat to achieve fusion. The result is an area affected by heat that is narrower than that produced by "narrow groove" welding, as seen in FIGURE Ib. Preferably, the process of the present invention employs a tungsten electrode having a non-circular cross-cut blade. 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 shortened dimension that is oriented perpendicular to the length of the joint, for example, a cylinder having a generally transverse cut. rectangular. Preferably, the sheet is cut or stamped from a flat sheet material, for example tungsten alloy sheet material. The sheet can be cut into the shape of a triangle (preferably isosceles) or a strip having straight parallel sides and a point pointed at one end. The geometry of the thin electrode provides an electrode having a dimension (ie, the width) that is smaller than the diameter of a circular cylindrical electrode of equal area in cross section. This thinner dimension and its orientation allows the electrode to enter thin ridges for which a cylindrical electrode is too wide to enter. In consecuense, the width of the joint to be welded can be made significantly smaller than in the case where a circular cylindrical electrode is to be used. In addition, the use of a thin, non-cylindrical electrode allows the heat input of the weld to be significantly reduced for each step, and therefore, the size and the sensitization of the affected area by heat is correspondingly reduced. The elongated cross-section electrode used in the welding process of the invention is basically not limited in how thin it may be, and therefore how thin can be the joint, as long as there is space towards the walls of the board for travel towards •* -* ahead. One embodiment of a flat tungsten alloy electrode that can be used to practice the invention has the geometry shown in FIGS. 2A-2C. He 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 pronounced corners are rounded to avoid arching. The cross section of the sheet 10b preferably has the shape of a rectangle with rounded corners. Preferably, the ratio of the length to the width of the rectangle is at least 1.5: 1. Another embodiment of a flat tungsten alloy electrode that can be used to practice the invention has the geometry shown in FIGURE 4. The electrode comprises a generally triangular sheet 18 stamped or cut from a sheet of tungsten alloy. An exemplary thickness of a tungsten alloy sheet is .762 millimeters (30 mils). Optionally, the triangular shape of the sheet can be moved away from being strictly isosceles by tapering the tip 18c at an increased rate. As shown in FIGURE 4, the blade comprises a base 18a, a body 18b and a tip 18c. The base 18a is pressed or otherwise supported by an electrode holder 20. The electrode holder 20 is preferably made of a conductive, oxidation-resistant material, such as copper alloy (e.g., beryllium copper alloy) , optionally electroplated with silver or nickel. The electrode holder is preferably in the form of a T-shaped metal body, comprising a stem 20a and a crosspiece 20b. The trunk 20a is connected to a conventional welding torch 14. The crosspiece 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 of the sheet 18a is securely held in the slot of the cross piece by fitting a pair of sets of screws 22 in a corresponding pair of holes with rope formed in the cross piece. The blade can be easily removed from the support after the screws are loosened. This allows easy replacement of the 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 can be secured in the holder by tying it down to create a monolithic sheet assembly, ie, the sheet would not be easily replaceable. The body of the preferential sheet 18b is covered with an insulating coating, for example, A1203 or Y203, to prevent arching against the side walls of the groove. Also, all the rough edges of the stamped or cut sheet are rebagged to avoid arching. According to the preferred embodiment, the triangular flat sheet incorporates one or more spacers 24. Each insulating spacer protrudes on both flat sides of the electrode sheet beyond the plane of the surface of the sheet. 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 wear of the ceramic coating during the path of the electrode in the weld groove. . 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. 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 3A. The tube has the 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 <6th. A rounded extension surface 2c connects the outer periphery of the earth 2a with the inner periphery or beveled surface 2b. The extension surface 2c has a radius R. The height of the earth 2a is designated with h1; the height of extension 2c is designated with h2. The process of the present invention was successfully applied in 4 inch diameter tubes made of Type 304, 316 and 347 stainless steel in the horizontal position. The tube 10.2 centimeters (4 inches) in diameter had a wall thickness t = 6.35 millimeters (0.250 inches). For the purpose of only testing the weld, the bevel angle? was selected to be equal to one of the following: 0o, 2o, 3o, 4o, and 5o. The height of the earth hl was varied from 0.635 to 1.27 millimeters (0.025 to 0.050 inches); the radius of extension R was varied from 0.81 to 1.57 millimeters (0.032 to 0.062 inches). According to a preferred alternative embodiment of the stria geometry, the rounded land extension was replaced with a 2d transition of 45 ° angle, as shown in FIGURE 3b. During welding, two tubes 2 and 4 are placed, end to end, in a horizontal position with a groove 8 therebetween, as shown in FIGURE 5. A consumable ring-shaped insert 16 was placed between the lands of the opposite ends of the tubes and at the root of groove 8 to compensate for any poor radial correspondence of the lands. During the first step (root), the groove between the tubes to be joined must be bridged. The earth and the material supplied consumable insert (optional) that is melted to form the root will be welded. After the step of the root, a second hot step is made, followed by a series of filling steps and one or more cover steps. The optional insert can, but does not need to have the same composition as the filler wire. During the development of the welding, inserts made of Type 308L or Type 347 stainless steel were used. Inserts having different cross sections were tested, including the following cross sections that proved to be satisfactory: 0.81 x 1.4 millimeters (0.032 x 0.055 inches) ), 1.78 x 3.05 millimeters (0.070 x 0.120 inches) 2.3 x 3.18 millimeters (0.090 x 0.125 inches), 0.94 x 3.05 millimeters (0.037 x 0.120 inches), and 1.27 x 3.18 millimeters (0.050 x 0.125 inches). 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 length of the arc (between the electrode and the bottom of the welded joint) is reduced, ensuring that the arc does not transfer to the joint walls that are closer to the electrode than in the case of other welding processes. Preferred gas mixtures are hotter (ionize at a higher temperature 35a), and allow the specific heat input rate to be maximized to make the greatest benefit from the speed of the fast cover step. The typical prior use of these hot gas mixtures is to improve the welding production without defects, and not to improve the residual stress state as described herein. An alternative method specified in the welding process to prevent the arc from transferring 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 mixture of welding gases. This condition helps to ensure that the edges (geometric discontinuities) of the electrode along its length are not arc transfer zones which are more favorable than the tip of the electrode. This method also eliminates the need to insert an electrically insulating gas cover extension into the joint, as practiced in some other welding processes of wider joints. In accordance with the low residual stress welding process, the solder pellets are deposited inside the flute using the thin elongate tungsten alloy electrode to melt the fill wire fed into the flute. The electrode fits inside the groove 8 with space between the electrode and the side walls as shown in FIGURE 5. The blade of the electrode 18 is electrically coupled to a welding torch 14. The flat electrode together with the small bevel angle and the selected welding parameters produce a very thin welded joint as shown in FIGURE 1C. The very thin welded joint allows the two surfaces that are being joined to be closer together. As a result of this closeness, both surfaces are wetted simultaneously with a small weld pool fused with a significantly lower heat input rate (i.e., improved thermal efficiency) than is 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 area affected by the heat adjacent to the melted zone to be significantly reduced. With the benefit of a corresponding reduction in susceptibility to stress corrosion fracture 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 low temperature of the far surface of the component (also known as the "root" or first step of welding). This pronounced temperature gradient across the component that is achieved with the very thin welded joint also leads 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 leads to a reduction in susceptibility to fracture stress corrosion cracking. The combined effects of reduced thermal sensitization (ie precipitation of carbides) in the areas affected by heat and the improved stress state at the root of the weld provide a significant increase in resistance to stress corrosion fracture 5 of a welded joint exposed to an aggressive environment. Another related benefit of reduced heat input, size and temperature of the affected area - heat according to the stress welding process Low residual is a reduction in, or removal of grain growth during welding. A significant grain growth in the area affected by heat and the corresponding thermal sensitization in this area results in the formation of the "knife line attack" of the fracture by stress corrosion on materials that are otherwise resistant to stress fracture corrosion, ~ such as the stabilized grades of austenitic stainless steel. The residual stress state improved at the root of a joint made by the low residual stress welding process, in relation to the conventional welded joint with a wider flute and a circular cylindrical electrode, is generated by an inversion of the stress during the welding process. During welding, the affected area By the weakened, hot heat, and the newly solidified welded metal, they are plastically compressed due to their thermal expansion relative to the colder and more resistant surrounding material. During cooling, this compressed zone contracts against the surrounding material and is placed in a state of residual stress stress. The contraction and the corresponding stresses are balanced with the surrounding material, in particular the welded root, by going to the desired state of less stress or a more convenient compressive stress. The degree of improvement of the effort depends on the parameters of the particular welding process used. In the process of welding residual stress, a key factor to make effective a welding process to generate a sensitization of the affected area by reduced heat and residual stresses of -voltage of the root without cooling with water (subsidence of external heat) of the component being welded is the very low heat input capacity of the process (and the corresponding internal heat sink), made possible by very thin gasket geometry and in turn by the shape of the very thin welding electrode, not circular. Another benefit of the reduction of residual stresses at the root of a joint made with the low residual stress welding process is a decrease in the susceptibility of materials exposed in a radiation environment to the corrosion fracture mechanism with radiation aided effort (IASCC). This beneficial effect arises due to the delay of the diffusion of the harmful elements up to the internal interfaces, which is aided by the influence of higher residual stresses. The passive heat sinking welding process of the present invention further improves the low residual stress welding process. The process of the invention has application in all pipes and other types of components to be welded. According to this process, the effects of conductive self-cooling of the base metal alone, when combined with a very high velocity of the welding torch, are able to significantly improve the residual stress of the welded joints of the components without need for water or other coolant that complements the component during welding. Due to the exclusively high torch travel speeds (< 25.4 centimeters / minute (10 inches / minute)) used, the process of the invention becomes effective even for thin-walled material (eg, 6.35 and 9.53 millimeters (0.25 and 0.375 inches) thick) with a capacity of sinking by inherently small heat. High torch travel speeds in turn become possible due to the use of welding gases having high dissociation / ionization temperatures, including mixtures of inert gases comprising hydrogen and / or helium. The temperature gradient across the significant wall produced by the high torch travel speeds is achieved due to the high heating efficiency, at high heating and cooling rates, the design of the thin joint used and the corresponding small size of each welding step, combined. The required temperature gradient and thermal stress, and the improved distribution of the resulting residual stress, are subsequently established by the thickness of the material being welded. The final levels of the residual stresses are established as the exterior steps are completed, especially the joint cover steps. The level of the welding current is adjusted so that for a limited range of torch travel speed, the desired temperature distribution is established through the thickness of the wall. The requirement is to have a portion of the wall thickness sufficiently hot so that its thermal expansion will cause it to deform into compression (while hot and weakened) by the equilibrium forces of the coldest part of the wall, and subsequently, to go under tension after cooling to room temperature. In order to maintain the balance of forces through the wall after cooling, the part of the wall that was in tension as the torch passed, then goes towards compression, which is the desired result. In order for the passive heat sinking welding process of the invention to be more efficient, it is desirable that the welding parameters used to fill the joint before the very fast covering steps which are of a type of low heat input / low distortion, so that the level of residual stresses at the root of the joint is initially as low as practical. In this regard, the use of the low residual stress welding process before the passive heat sinking welding process would be very beneficial as the base method for new welding applications. Existing standard type welds, which need mitigation of residual stress, are expected to benefit from the subsequent application of the heat sinking welding process as well as, especially for welds that join thin materials. By applying a heat treatment during the cover steps, that is, without the fusion of the underlying material, the residual stress state can be mitigated up to a reduced stress stress substantially less than the resistance to permanent deformation or, preferably, to a compressive state. The degree of stress mitigation depends on the thermal and mechanical properties of the material as a function of the temperature, as well as the thickness of the material and the general welding parameters. The exclusive feature of the passive heat sinking welding process according to the invention is that the residual stresses are significantly reduced or eliminated by intentionally controlling the specific heat input rate of the final weld (for unit area of the outer surface of the welded joint) against a relatively high value, applied for a relatively short time, and in turn generating the typical magnitude of the temperature gradient across the wall (from above the melting temperature of the metal on the final surface until temperatures close to the ambient on the initial surface) normally reached only with complementary cooling, which is generally water flowing. The specific heat input regime is maximized as convenient using a heat-welding gas, and especially by moving the torch at exclusively high forward travel speeds during the final step or deck steps. The secondary adjustments to the heat input rate are controlled with the welding current and / or the voltage. At higher torch run speed according to the demonstration of the invention (in other words, <25.4 centimeters / minute (10 inches / minute)) is faster than the speeds conventionally used for electric arc welding in general and gas tungsten arc welding in particular, by a factor of at least three, and that It has previously been considered unacceptable to practice deep welding. The invention uses the effect of extremely high torch travel speeds to redistribute and significantly optimize residual stresses. However, tests have shown that the passive heat sinking welding process is both effective for stress mitigation and suitable for various types of mechanized applications without sacrifice in the structural integrity of the weld. Some of the parameters of the welding process. which control the thermal efficiency of the process include the gas composition of the arc, the torch travel speed, and the values of the arc current and the current impulse. These and other parameters were selected for the purpose of further minimizing the area affected by the heat and the residual stress of the root tension. Measurements of tube diameter and axial length revealed that the leaks were reduced, resulting in less stress stress, if not a compressive stress on the near surface of the welded joint.

Different mixtures of inert gases were tested as the protective gas. Mixing argon with either hydrogen or helium increases the temperature of the arc, making the kneaded filler welded wet the substrate faster. Due to the high energy density, the surface of the substrate heats up quickly, leaving less time for heat conduction below the surface. This produces a zone affected by heat thinner than is conventionally known. The addition of hydrogen or helium also shortens the arc, so that less space is needed with respect to the side walls. Different torch travel speeds were tested during the test weld. The root step was made at speeds of 12.7-25.4 cenfemetros / minute (5.0-10.0 inches / minute). The torch travel speed for the hot passage varied between 14 and 42 centimeters / minute (5.5 and 16.5 inches per minute). The deck steps were made at speeds of 25.4 centimeters / minute (10 inches / minute) or more. Satisfactory welds, that is welds with a reduced tensile stress substantially less than the resistance to permanent deformation or with a compressive stress on the near surface, were obtained using blow torch travel speeds of 42, 50.8 and 63.5 centimeters per minute (16.5, 20 and 25 inches / minute) for the step or the deck steps.

X-ray diffraction measurements on the inner surface of the welds made in accordance with the present invention showed that a substantial improvement of the stress was achieved, the entire region of interest being close to, and at the root of the weld in a state of compressive effort. This can be seen in FIGURES 6A and 6B and in FIGS. 7A and 7B, which respectively show the axial and tangential residual stresses measured on the inner diameter of the Type 347 and Type 304 stainless steel 4-inch diameter with joint. of circumference to weld stop in accordance with the present invention. X-ray diffraction results were confirmed by tests performed in accordance with ASTM G36-73, the Standard Recommended Practice for performing stress corrosion fracture tests on a boiling magnesium chloride solution. According to a further aspect of the invention, the welding torch is oscillated laterally during the passage or the cover steps. The purpose of the lateral oscillation of the torch is to spread the heat on the far surface of the tube in a manner that produces a state of compressive stress over a wider axial length on the nearby surface, thus reducing the concentration of the applied bending moment. through the welded root and mitigating the thin circumferential fracture along the fusion line on each side of the weld. The lateral oscillation can be carried out mechanically or by moving the head back and forth driven by motor or electromagnetically by applying an electromagnetic oscillation field that causes the arc to flex from side to side. According to an additional alternative, two or more granules can be left side by side in separate deck steps. This condition of multiple deck steps laterally distributes the heat on both sides of the middle line of the weld, again in order to reduce the concentration of the bending moment applied through the root of the weld.

Claims (7)

1. A method for welding and / or heat treating a first and a second metal component (2, 4) joined in a direction of depth by a welded joint (6) formed, at least in part, by a root passage in a near surface and a plurality of steps successively constructed on top of the root passage in a direction from the near surface to a far surface, wherein before that joint welded by welding and / or heat treatment is heated during a deck step unloading an electric current arc from one electrode tip (10 or 18) running along the far surface at a torch travel speed greater than 25.4 centimeters / minute (10 inches per minute) creating this mode a temperature distribution through the material between those near and far surfaces, and then allowing the far surface to cool, by which a compressive or compressive stress is formed a tensile stress less than the residual stress stress, on the near surface, and where the heating and cooling steps are performed without cooling with a fluid complementary to the near surface. The method as defined in claim 1, characterized in that said far surface is heated without the fusion of the material constituting the far surface. 3. The method as defined in claim 1, further characterized by the step of adding filler material during the heating step. 4. The method as defined in the claim 1, characterized in that each of the first or second metal components has a bevel angle that is less than 6o. The method as defined in claim 1, characterized in that the heating step is carried out in an inert gas atmosphere comprising hydrogen and / or helium. The method as defined in claim 1, characterized in that the arc oscillates laterally during the travel of the tip of the electrode < 10c or 18c). 7. The method as defined in the claim 1, characterized in that the heating step comprises a first and a second parallel passage of the electrode to a first and a second axial position, respectively. PTC.qTTMÍOJ A process to provide a significant improvement in the state of the detrimental residual stress by stress on the root side of the welds, especially on the inner wall of the pipe welds. The method uses a high torch run speed for welding (> 10 inches / minute), especially at the last or the last two deck steps. The process relies on the limited capacity of deformation by the thermal heat of the tube wall and the almost complete weld joint itself to generate a temperature gradient across the significant wall, and therefore a stress gradient across the wall. enough wall during welding. This stress gradient results in the plasticity of the metal and permanent deformations, and therefore a reduction in the magnitude of the final residual stress or, preferably, as conditions permit, an inversion in the direction of tensile to compressive stresses. . The method can be used as a welding process or as a heat treatment. In the case of heat treatment, the surface remote from the weld joint is heated without melting the material forming the remote surface. * * * * *