RU2571294C2 - Method of submerged arc welding of joints resistant to electrochemical corrosion - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: butt joint gap is filled with metal chemical additive. The additive contains mixture of chopped metal grits 1.0-2.0 mm, made from edges cutting of welded blanks in ratio 1:1 with its cleaning of the oxides, and connection of the negative active elements 0.5-0.8 wt % and aluminium 0.2-0.34 wt %. The gap width is set as 0.6-0.8 of thickness of welded parts. One-side or double-side welding is performed by several passes at straight polarity DC ensuring minimum mixing of the welding pool. The gap filling with grits is performed by its preliminary backfilling or feeding to the arc zone by the dosing unit.

EFFECT: method reduces potential gradient across the weld and ensures increased steelwork resistance to electrochemical corrosion.

3 cl, 1 dwg, 3 tbl, 1 ex

Description

The invention relates to submerged arc welding and can be used in the manufacture of sheet metal structures, tanks and pipelines for various purposes, resistant to electrochemical corrosion.

A known method of corrosion protection of a welded metal structure located in an electrically conductive liquid medium, comprising applying an anticorrosion coating of a highly conductive material from the back of the weld, including sputtering and copper [1]. The method allows shunting, and thereby reduce electric currents flowing between local zones of the surface of the metal structure through an electrically conductive medium. The causes of such currents are thermoelectromotive forces (TEMFs) arising near the boundaries of welds of a metal structure under the influence of the Seebeck effect, primarily due to the difference in the physicochemical properties of the welded workpieces. As a result of current shunting between local volumes of the surface of the metal structure through an electrically conductive medium, the corrosion destruction of the metal structure is reduced.

The method has the following disadvantages:

- he does not fight with the cause of TEDS, but only with the consequence, that is, with the TEDs themselves. Since at the same temperature difference between the working and free ends of the thermocouples of the weld seam of the workpieces and a fixed difference in their physicochemical properties, the thermopower in the weld zone of the workpieces is distributed fairly evenly, the layers of material that are farthest from the anti-corrosion coating are the least protected when using this method. That is, those that are in direct contact with sea water and for the protection of which the method is directed. Moreover, the higher the thickness of the vessel skin, the less the effect of the protection used;

- in the presence of a large differentiation of the physicochemical properties of the workpieces, large TEDs actually created in their contacts with the same anticorrosive protection can lead to significant damage to welds and heat-affected zones;

Из-за встречного включения термопар по правой и левой границам сварного шва, казалось бы, не важно, каковы будут свойства материала самого сварного шва: важно рассогласование свойств основных металлов заготовок. Однако при наличии больших ТЭДС термопар в области сварного соединения по двум границам сварного шва в электропроводящей жидкой среде проявляются две локальные зоны повышенной коррозии.- a sharp transition of the potential is observed along the weld boundary, i.e. high gradient potential grad $$(u)=\frac{du}{dx}.$$

Due to the onset of thermocouples along the right and left boundaries of the weld, it would seem that it does not matter what the material properties of the weld itself will be: it is important to mismatch the properties of the base metals of the workpieces. However, in the presence of large thermoelectric coefficient of thermocouples in the weld area along two boundaries of the weld in an electrically conductive liquid medium, two local zones of increased corrosion appear.

The closest in technical essence to the proposed device is a method of one-sided arc welding No. 791482, according to which the welding is carried out on a copper lining with a recess, which is covered with fiberglass with the formation of a closed air space between the recess and the space. Butt joint is assembled without cutting edges with a gap. The optimal value of the welding gap was established experimentally from the conditions for obtaining a high-quality, durable-dense and defect-free welded joint. After assembling the joint, the welding gap to the entire height is filled with a metal-chemical additive, which is a mixture of chopped welding wire (grit) with a diameter of 1.0-2.0 mm and compounds of negative elements in an amount of 0.5-0.8 wt.% (Oxygen-free alkali metal salt for example, sodium fluoride NaF and other chemical additive) [2].

The disadvantages of the method:

возникающего под действием термоэлектродвижущих сил. При условии контакта с электропроводящей жидкой средой именно в этом месте проявляется максимальная скорость коррозии;- due to a sharp transition of the chemical composition and structure of the metal along the boundary of the weld, a sharp transition of the potential is observed, i.e. high gradient potential grad $$(u)=\frac{du}{dx},$$

arising under the influence of thermoelectromotive forces. When exposed to an electrically conductive liquid medium, it is in this place that the maximum corrosion rate is manifested;

поперек сварного шва повышен и на всей ширине шва в контакте с электропроводящей жидкой средой в ней создаются электрические линии токов, соединяющие рядом расположенные локальные объемы сварного шва. Это приводит к повышенной коррозии всей поверхности шва, контактирующей с электропроводящей жидкой средой;- since the width of the weld is small, the potential gradient $$(u)=\frac{du}{dx}$$

across the weld is increased and along the entire width of the seam in contact with the electrically conductive liquid medium, electric current lines are created in it, connecting adjacent local volumes of the weld. This leads to increased corrosion of the entire surface of the seam in contact with the electrically conductive liquid medium;

- a sharp transition in the chemical composition and structure of the metal along the boundary of the weld is facilitated by the fact that the filler material mainly consists of electrode material.

Essentially, when welding sheet metal structures, tanks and pipelines for various purposes, the method does not provide their resistance to electrochemical corrosion.

The technical result of the invention of a method of submerged arc welding of joints resistant to electrochemical corrosion provides resistance of welded joints of metal structures to electrochemical corrosion by reducing the potential gradient across the weld due to: expanding the width of the cutting edges of the workpieces for welding, and hence the width of the weld, using chemical additives with grit made from the trimmings of the edges of the welded workpieces in a ratio of 1: 1, equalizing the share of the main metals of the workpieces in the whole the volume of the weld, the use of multi-pass welding, which does not allow mixing of the weld metal in the entire cross-section of the cutting edges, the use of other measures to reduce arbitrary mixing of the metal bath.

The essence of the invention lies in the fact that the method of submerged arc welding of compounds resistant to electrochemical corrosion, including feeding a metal chemical additive into the arc zone, assembling the butt joint with a gap, and after assembling the joint, filling the welding gap with a metal chemical additive, which is a mixture of chopped grains fraction 1.0-2.0 mm, compounds of negative elements in an amount of 0.5-0.8 wt.% And aluminum in an amount of 0.2-0.34 wt.%, Additionally includes an increase in the width of the gap to 0.6-0 , 8 thickness weld x parts, the manufacture of grains from the trimmings of the edges of the welded workpieces in a ratio of 1: 1, as well as welding in several passes using a single or double sided method with direct current of direct polarity and using other known measures to reduce mixing of the metal bath, and in another embodiment, the method further includes feeding grains with a dispenser with a discrete increase in the content of material in the grains as the passage in the weld approaches the border with this material.

The main idea of the invention is to smooth the gradient of the potential across the weld at its boundary with electrically conductive fluids. This allows us to reduce the values of thermoelectromotive forces of neighboring local areas of the weld in contact with electrically conductive liquid media. The result is to reduce the electric currents flowing between these local sections of the weld through the fluid. In this regard, to reduce the electrochemical corrosion of welded metal structures, thereby increasing the resistance of welded metal structures to electrochemical corrosion.

The invention is primarily aimed at eliminating the sharp transition of physico-chemical properties that occur in the prototype invention along the boundaries of the weld. It is in these places that a surge of thermoelectromotive forces arising under the influence of the Seebeck effect is observed.

The use of cutting edges allows to differentially dilute the material of metal grains, increasing the proportion of the base metal of this workpiece as it approaches the border of the seam with this workpiece. This measure helps to reduce the gradient of the chemical composition along the boundaries of the weld.

The expansion of the width of the cutting edges of the workpieces for welding allows you to increase the width of the seam, which, first of all, reduces the gradient of the chemical composition across the seam.

The use of a metal chemical additive with grit made from the trimmed edges of the welded billets in a ratio of 1: 1 makes it possible to bring together the chemical compositions of local volumes along the weld, reducing the gradient of the chemical composition across the weld. In addition, the use of filler grains reduces the heating of the metal bath. This, in turn, reduces the mixing of the metal weld pool and provides a gradual transition of the physicochemical properties of the weld metal from one workpiece to another.

Compounds of negatively active elements introduced into the filler material are, for example, an oxygen-free alkali metal salt, NaF. They protect the weld metal from oxidation, reduce metal spatter and help increase process productivity. The content of compounds of negatively active elements is limited to 0.5-0.8 wt.%. A lower content of compounds of negatively active elements in welds is detected by lack of fusion. An increase in the content of compounds of negatively active elements in excess of 0.8 wt.% Leads to the formation of pores in the welds.

Aluminum is introduced into the filler material for additional deoxidation of the weld pool metal. The aluminum content is limited to 0.2-0.3 wt.%. The lower aluminum content does not significantly affect the properties of the welded joint. An increase in the aluminum content of more than 0.3 wt.% In the deposited metal leads to the appearance of a large number of non-metallic inclusions, and this, in turn, leads to a decrease in toughness.

The use of multi-pass welding does not allow mixing of the weld metal in the entire section of the cutting edges. The passages form, first of all, the outer side of the seam. This allows you to discretely change from one passage to another the share of the base metals of both billets, increasing the share of the first base metal in the border passage with the first billet and, accordingly, increasing the share of the second base metal in the border passage with the second billet. In the intermediate layers, taking into account the mutual penetration of passages, a gradual transition from one border pass to another is observed. This ensures a smoother transition of the physicochemical properties of the weld material from one base metal to another, from one weld border to another.

The use of direct polarity of the supply voltage refers to known measures to reduce the mixing of a metal bath. As well as reducing the heating of the metal bath, the direct polarity reduces the mixing of the metal weld pool and provides a gradual transition of the physicochemical properties of the weld metal from one workpiece to another.

Other known measures to reduce the mixing of a metal bath include:

- increase in welding speed;

- longitudinal vibrations of the electrode;

- increased overhang of the electrode.

A discrete increase in the content of material in the grains, as the passage in the weld approaches the border with this material, makes it possible to purposefully and more effectively change the physicochemical properties of the weld material from one base metal to another, from one border of the weld to another.

Thus, a comparison of the claimed solution with other technical solutions shows that the newly introduced operations are known. However, their introduction in this connection with other operations of the method, as well as their mutual correspondence, leads to the appearance of the new properties mentioned above, which ensure the resistance of welded joints of metal structures to electrochemical corrosion.

The drawing shows the butt joint, (a) - assembled for unilateral automatic welding on a copper lining and (b) - welded to it. The blank 1 is made of base metal 1 (OM1). It does not have a groove and forms a welded edge 3. The workpiece 2 is made of base metal 2 (OM2). It also has no cutting and forms a welded edge 4. Edges 3 and 4 form a gap. The copper lining 6 has a recess 7. It, together with both edges, forms a cavity 5 into which a metal chemical additive is filled. 8, 9 - passages.

When welding with a metal-chemical additive, at each pass, the volume of the liquid metal bath increases, and the width of the penetration of the edges decreases.

The method is implemented as follows

Welding is carried out in accordance with the instructions for automatic submerged arc welding and electroslag welding with powder filler metal (PPM) VSN 375-77 of the USSR Ministry of Assembly and Special Construction Work [3], as well as taking into account the recommendations [4].

As a metal base of a metal-chemical additive, grains of a fraction of 1.0–2.0 mm prepared on a machine tool [3, 4] are used from the trimmings of the edges of the welded workpieces in a ratio of 1: 1.

Before assembling the welded workpieces, edges are prepared, for example, on an edge-cutting machine. Workpieces that are welded without cutting edges, face.

Types of welded joints, structural elements for preparing welded edges (cutting angles, blunting, etc.) should correspond to the data in Table 1.

Table 1 Butt joints of bevel joints without bevel edges, double-sided on a copper lining or flux pad Seam type according to GOST 8713-70 Edge preparation Seam C2   Parameters, mm: S = s ₁ 10 twenty thirty 40 fifty b four 6 7 8 9 l = l ₁ 20 ± 4.0 22 ± 4.0 35 ± 5.0 34 ± 5.0 35 ± 5.0 q = q ₁ 2.5 ± 2.0

The resulting trim of the workpieces, the chips from each workpiece (separately) are passed through the machine for the manufacture of grits. The grits of two welded billets are mixed in a ratio of 1: 1 to obtain metal grits ready for welding.

Krupka is cleaned of technological and anticorrosive lubricants, oils, dirt and rust, primarily by chemical means. In case of large rust, etching is used. The rusty surface of the grain is etched in weak acid solutions or their reagents. If the grain is contaminated, it is first washed in hot water, and coated with lubricating oils or fats, it is degreased. Then the grains are poisoned, neutralized and passivated. Grains contaminated with fats are degreased with alkali solutions of 5-10% concentration or with organic solvents.

Grains should not have an oxidized surface. Oxides are etched in acid solutions with an admixture of inhibitors, etching additives or etching regulators, due to which the pure metal is almost not destroyed, and only rust is corroded. Grains are kept in solutions until rust disappears, and then washed in water (temperature 60 ° C), in which 1.5-5.5 g of soda ash and 0.5-5 g of potassium or sodium chromic are dissolved. Passivation grains of ferrous metals must be used after etching them in acidic solutions, otherwise they are again covered with rust. During this treatment, a protective film forms on the surface of the grits, which partially prevents rusting.

Fat-free and rust-free nibs are stored in metal closed vessels in a dry room. On its basis, a metal chemical additive is made for welding these two workpieces, loading the obtained metal grains in the required ratio into the mixer along with the other components of the metal chemical additive (charge). The mixture is stirred.

Welding flux AN-348A, AN-60, AN-22, AN-8 before welding is calcined at a temperature of 200-250 ° C for 1.0-1.5 hours, if the humidity of the flux exceeds 0.1%, in accordance with technical conditions for these materials.

When assembling structural parts for welding and surface preparation, it is recommended to be guided by the instructions of SNiP III-18-75 “Metal structures. Rules for the manufacture, installation and acceptance. "

The optimal value of the welding gap was established experimentally from the conditions for obtaining a high-quality, durable-dense and defect-free welded joint (table 2).

The welding method with preliminary filling of the metal-chemical additive is intended for two-sided welding without cutting edges, as well as for making joints with cutting edges. To prevent spillage of the metal filler material, the welding of the first pass of the joints is performed on a metal sheet. For these purposes, it is also possible to use a flux pad or a chopped-up pillow.

A metal-chemical additive is introduced into the welding zone in two possible ways:

- by pre-filling the metal chemical additive into the gap or groove before welding;

- by supplying a metal chemical additive and to the electrode stick-out during the welding process. Dosage and feeding of the grains for the electrode take-off is carried out by a dispenser, which is installed on the welding tractor [3].

Since the temperature in the zone of welding with an additive is slightly lower than in conventional submerged arc welding, the formation of pore formation of weld metal is possible. Therefore, the additive is made immediately before welding by thoroughly mixing the components and stored in a closed vessel. The prepared metal-chemical additive is used during the day. In this case, the filler material is poured into the gap immediately before welding. Krupka has an increased integral surface area. Therefore, the presence of an oxide film on the surface of the grains can lead not only to the appearance of pores in the weld, but also to the burnout of carbon and alloying components from the metal. To eliminate these phenomena when welding steels, manganese and silicon, which are good deoxidizers, are traditionally added to the welding wire. Their introduction reduces the oxidation of carbon and the burning out of other elements from the metal, which prevents the formation of pores and provides welds with high mechanical properties.

However, many additives in the welding wire, such as silicon, increase the thermoelectromotive force (TEMF) along the boundary of the weld. Therefore, to limit the values of TEDS, the introduction of a large number of additives into the welding zone is undesirable. Qualitatively carried out pre-welding preparation of grits allows to reduce operational deoxidizing additives in the welding zone.

table 2 Modes of automatic two-sided welding of butt joints without beveling of edges under the submerged arc with preliminary filling of metal-chemical additive Metal thickness mm Optimum clearance mm Diameter of electrode wire, mm Wire feed speed, m / h Welding current strength, A Voltage Welding speed, m / h Chopped grits consumption, g / cm twenty 7 5 103 1000-1100 40-44 35 5,0 thirty 8 5 103 1000-1100 42-45 19.5 8.0 40 9 5 128 1200-1300 43-48 16 12.0 fifty 10 5 140 1300-1400 44-48 12 16,0 60 12 5 163 1350-1450 45-50 12 18.0 twenty 7 four 154 900-950 42-45 35 5,0 thirty 8 four 163 950-1000 42-46 19 8.0 40 9 four 163 950-1000 43-48 fourteen 12.0 fifty 10 four 210 1100-1200 44-49 fourteen 16,0 60 12 four 240 1300-1400 46-50 12 18.0

Table 3 Modes of automatic submerged arc welding of angular joints “in a boat” of low-carbon steels with preliminary filling of a metal-chemical additive Seam leg, mm Wire diameter, mm Welding current, A Voltage Wire feed speed, m / h Welding speed, m / h Additive consumption
g / cm Number of passes 8 5 750-800 36-38 68.5 54.5 2 2 10 5 800-850 38-40 74.5 47.0 3 2 12 5 850-900 40-42 81.0 37.5 four 3 fourteen 5 900-950 40-42 87.5 32,0 5 3

When welding sheets up to 36 mm thick on one side, the gap in the joint is filled with a metal chemical additive flush with the surface of the sheets; for thicknesses of 36-60 mm, the gap is filled by 2/3 of the thickness of the metal being welded. Carry out welding in several passes. After welding the lower layers during multi-pass welding of the upper layers, the remaining cuts are refilled with the prepared additive flush with the surface of the sheets (blanks).

Увеличение зазора более 0,8 толщины свариваемых деталей приводит к нестабильному проплавлению металлохимической присадки.When implementing the method, the gap width is increased to 0.6-0.8 thickness of the welded parts. Reducing the gap less than 0.6 of the thickness of the welded parts significantly reduces the effect of lowering the gradient of the potential grad $$(u)=\frac{du}{dx}.$$

An increase in the gap of more than 0.8 thickness of the welded parts leads to unstable penetration of the metal chemical additive.

на границе шва по всей его ширине. Отклонение от этого соотношения в ту или другую сторону ведет к возрастанию градиента потенциала grad $$(u)=\frac{du}{dx}$$

на одной из границ шва.The production of grains from the trimmings of the edges of the welded workpieces in a ratio of 1: 1 is optimal and is determined by the requirement of lowering the gradient of potential grad $$(u)=\frac{du}{dx}$$

on the border of the seam over its entire width. Deviation from this relation in one direction or another leads to an increase in the potential gradient grad $$(u)=\frac{du}{dx}$$

on one of the borders of the seam.

Example.

Two workpieces 10 mm thick, 100 mm wide and 250 mm long, cut from two different sheets of industrial-grade steel of the same grade - 09Г2С, were butt-welded with a longitudinal seam without cutting edges and transverse vibrations of the electrode by unilateral automatic welding with direct current on a copper lining with an Sv- electrode 08GA with a diameter of 4 mm under the AN-17M flux. Welding was carried out by the welding tractor ADS-1002 complete with a welding rectifier VKSM-1001 in the traditional way. In this case, a metal-chemical additive was not used, welding was carried out at a direct current of reverse polarity in one pass with a gap of 1.5 mm. The wire feed speed of 2.5 m / min. Welding current 850 A. Welding speed 32 m / h.

Then, by analogy, the experiments were repeated for welding of the other two workpieces with direct current of direct polarity using the proposed method using a pre-prepared and filled in the gap metal-chemical additive with a grain from the materials of both workpieces in two passes with a gap of 6 mm. The electrode wire feed speed is 1.3 m / min. Welding current 750 A. Welding speed 42 m / h.

After welding, for each brewed sample using an external heat source, a temperature difference was created between the outer surface of the weld and its reverse side Δt≈20 ° С. The temperature difference was regulated and fixed. The potential difference of the thermocouple formed between pairs of points on the outside of the seam located on both sides of the weld boundary at a distance of 3 mm was measured. Voltages were measured in three ways: M-64 millivoltmeters and MSChR and S1-65A oscilloscope. Measurements were repeated on each of the two boundaries of the seam through 10 mm. At the end of the measurements, poor-quality and doubtful results were rejected by Student's criterion. The remaining data were averaged modulo.

As the research results showed, on average, the voltage generated at the weld boundary for the traditional welding method was 0.012 mV with a standard deviation of 0.004, for the proposed 0.006 mV with a standard deviation of 0.003. According to Ohm's law, for a section of the circuit, a decrease in voltage, ceteris paribus, leads to a proportional decrease in the current flowing through the conductive fluid between the local sections located on both sides of the weld boundary. Since thermoelectromotive forces arising at the weld boundary during welding by the proposed method are reduced by about half compared with traditional welding methods, as a result, the resistance of welded joints to electrochemical corrosion increases by almost the same amount.

The proposed method allows the welding of sheet metal structures, tanks and pipelines for various purposes, resistant to electrochemical corrosion.

INFORMATION SOURCES

[1] - Method of corrosion protection of welded metal structures [Text]: US Pat. 2476621 ROS. Federation: IPC C23F 13/00, C23C 4/08 / Verevkin V.I .; Lisevich V.I .; Astrauh O.V .; Teryusheva S.A .; Zebrova E.M .; Applicant and patent holder of the Baltic State Academy of the Fishing Fleet. - No. 20111100923/02; declared 01/12/2011; publ. 07.20.11, Bull. No. 6. - 7 p.: Ill.

[2] - Method of one-sided arc welding [Text]: US Pat. 791482 Ros. Federation: IPC B23K 9/02, B23K 37/06 / Bolshakov K.P., Peredereev B.M., Grebenchuk V.G .; applicant and patent holder of the All-Union Scientific Research Institute of Transport Construction - No. 2619814 / 25-27; declared 05/22/1978; publ. 12/30/80, Bull. No. 48. - 7 p.: Ill. 1.

[3]. - Instructions for automatic submerged arc welding and electroslag welding with powder filler metal (PPM) [Text]: VSN 375-77 // MSS USSR. Central Bureau of Scientific and Technical Information. - M., 1978.

[4] - Ivochkin I.I. Submerged arc welding with an additional additive [Text]: monograph / II. Ivochkin, B.D. Malyshev. - M.: Stroyizdat, 1981. - 175 p., Ill.

Claims (3)

1. The method of submerged arc welding of billets of low carbon steels in the manufacture of metal structures resistant to electrochemical corrosion, including assembly with a gap of the butt joint, filling the gap with a metal chemical additive containing a mixture of chopped metal grains with a fraction of 1.0-2.0 mm and compounds of negatively active elements in an amount of 0.5-0.8 wt.%, characterized in that they use an additive additionally containing aluminum in an amount of 0.2-0.34 wt.%, while the grains are preliminarily made from trimmings Mok of both welded workpieces in a ratio of 1: 1 with its cleaning of oxides, and the width of the gap of the butt joint set 0.6-0.8 thickness of the welded parts, and carry out one-sided or two-sided welding in several passes with direct current of direct polarity from the condition of ensuring the minimum mixing the weld pool. 2. The method according to p. 1, characterized in that the filling of the gap with the grains is carried out by preliminary filling it. 3. The method according to p. 1, characterized in that the filling of the gap with a grain is carried out by feeding it into the arc zone using a dispenser.