RU2734884C1 - Method and device for protection against electrochemical corrosion of welded metal structure - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention can be used in production and repair of sheet, shell, tank, tube, as well as housing, grate and other metal structures, resistant to electrochemical corrosion and made from interchangeable blanks with close thicknesses and physical and chemical properties. Independently one measures own potential of each workpiece by means of portable electric measuring device and portable reference electrode. Each billet is heated to preset temperature at measurement point. Potential difference is measured in contact of each billet with reference electrode. To the measured potential difference, the known potential of the reference electrode is added at ambient temperature T₀, thereby determining the intrinsic potential of each i-th billet at the specified temperature of workpiece heating T_sp(i). Then workpieces are ranked by value of own potential in decreasing row, by which during assembly of metal structure as difference of own potentials of contacting workpieces, maximum values of thermoelectromotive force in this contact of workpieces are found. On their basis during assembly, billets are arranged on object so that on average throughout metal structure to minimize differences of measured potentials between all pairs of adjacent billets.

EFFECT: disclosed is a method of protection against electrochemical corrosion of a welded metal structure.

2 cl, 2 dwg, 3 ex

Description

The invention relates to methods for increasing the resistance to electrochemical corrosion of a welded metal structure made from interchangeable workpieces, and can be used at the stage of assembling sheathing panels of ships, tanks and pipelines for various purposes, resistant to electrochemical corrosion.

There is a method of monitoring the operating mode of protective systems for steel hulls of ships and vessels [1], including periodic measurement of the potential of the hull of the protected object at control points along the length of the hull using a portable electrical measuring device and a portable reference electrode. At the same time, at the control points, the amperage is measured in the electrical measuring circuit formed by the hull of the ship, an electrical measuring device connected to the hull, a portable electrode connected to the electrical measuring device, and water. Further, the results of measuring the potentials and currents at the control points are compared with their permissible values, assessing the condition of the protectors, paintwork and water resistance of the ship's hull.

Disadvantages:

- the method relates to the means of operational control of systems for the actual protection of steel hulls of ships and vessels from corrosion, and can be used on an operating vessel when it is put into operation, as well as for operational control of the operating mode of the vessel's corrosion protection systems during their operation. At the stage of assembling steel hulls and other metal structures, when the main welds, tread and insulating protection are not yet available, the indicated protection controls are not applicable;

- measurement of the current strength at the control points in the electrical measuring circuit formed by the hull of the ship, an electrical measuring device connected to the hull, a portable reference electrode connected to the electrical measuring device, and water at the stage of assembling the metal structure is impossible. This is due to the absence at the time of assembly of the metal structure of the vessel's one-piece hull and the absence of its contact with water.

A known method of monitoring the operating mode of the protective systems of steel hulls of ships and vessels [2, p. 8], which includes periodic (1 time per month) measurement of the potential of the protected object's body at control points along the length of the body using a portable electrical measuring device (millivoltmeter) and a portable reference electrode (silver chloride reference electrode), comparing the potential measurement results with their permissible values, and also periodic (once a month) visual inspection of the protectors and assessment of the degree of their wear.

Disadvantages:

- the method can be used for operational control of the mode of operation of the vessel's corrosion protection systems on an operating vessel when it is put into operation, as well as during the operation itself. At the stage of assembling steel hulls and other metal structures, when the main welds, tread and insulating protection are not yet available, the indicated protection controls are not applicable;

- the method is a means of control of the mode of operation of the protector protection systems of steel hulls of ships and ships, it does not eliminate the causes of increased electrochemical corrosion in the welded seams of metal structures - a large potential difference caused by the increased heterogeneity of blanks welded to each other in the sheets of steel hulls of ships and ships ... In conditions of temperature differences outside and inside the ship's hull, these welded joints create thermocouples. According to the Seebeck effect, thermoelectromotive forces (TEMF) arise between the welded workpieces. As a result, the rate of electrochemical corrosion of welded seams of ship skin is extremely high - it reaches 1.0-3.0 mm / year [4, p. 211], while the corrosion rate of the outer skin blanks themselves in the underwater part of the ship's hull is much lower, and does not exceed 0.19 mm / year [4, tab. 13 on page 211];

- in an operating vessel, the workpieces are welded to each other, and independent measurement of the potential of each workpiece separately to assess the options for their assembly and subsequent welding in order to reduce the tendency of all joints to electrochemical corrosion is impossible.

The closest in technical essence to the proposed one is a method and device for protection against electrochemical corrosion of welded metal structures [3], in which thermoelectromotive forces (TEMF) are measured at the contacts of all permissible combinations of metal structures blanks and the optimal distribution of blanks in welded metal structures is determined to comply with the conditions for minimizing the maximum to the modulus of the thermodynamic force values generated across all contacts of the pairs of workpieces. If the TEMF is exceeded in at least one pair of blanks of permissible values, the blanks are replaced until the established requirements are reached. Then, the rest of the technological operations for the manufacture of the welded metal structure are carried out.

Disadvantages:

- in this method, the sign of the tendency of the metal structure to electrochemical corrosion (ECC) is of a differential nature. Its implementation requires a large amount of labor-consuming measurements of the thermal electromotive force of all permissible combinations of blanks;

- the transition from measuring the TEMF of one pair of blanks to another is associated with significant labor costs;

- the use of automatic ordering procedures for finding the optimal distribution of workpieces does not lead to a significant reduction in the complexity of the implementation of the method, since the search requires a measurement in each case.

The technical result of the invention of a method for manufacturing a corrosion-resistant welded metal structure from interchangeable workpieces provides a significant reduction in the labor intensity of performing protection against electrochemical corrosion of a welded metal structure from interchangeable workpieces, expanding technological capabilities and significantly reduces the time and volume of operations performed. To do this, before assembling the metal structure, voltage measurements are carried out using a microvoltmeter paired with a reference electrode separately in contact with each workpiece. Thus, each workpiece is only involved in the voltage measurement once. Knowing the potential of the reference electrode used at the measured ambient temperature, according to the measurements of the indicated voltages, the intrinsic potentials of all workpieces are found, the workpieces are ranked by their own potential in a decreasing row, on the basis of which, when assembling, the workpieces are laid out over the object so that, on average, over the entire metal structure to minimize the moduli of the measured potential differences between all pairs of adjacent blanks, after which other operations for the production of metal structures are performed.

A method of manufacturing a welded metal structure made of interchangeable workpieces with similar thicknesses and physicochemical properties, subject to electrochemical corrosion, including cleaning the surfaces of the workpieces, their location in close proximity to each other, sequential finding using measurements of the maximum values of thermoelectromotive forces created in thermocouples formed at the contacts of all the blanks of the metal structure, while at each measurement the temperature of the blank is equalized by presetting the tongs for double-sided spot resistance welding used to heat the said blanks, determining the optimal distribution of blanks in the welded metal structure to comply with the conditions for minimizing the maximum modulus values of thermoelectric forces, created on all contacts, and the absence of excess in contact of at least one pair of blanks of the maximum permissible values of thermoelectromotive forces , amounting to 5-8 mV, while replacing the workpieces until all the selected workpieces meet the above conditions, then carrying out assembly and welding operations and applying an anti-corrosion coating. Additionally, the duration (time) of heating is experimentally specified, the radii of the shell (ring) of heating are determined - inner R ₁ and outer R ₂ , in the center of the wall of the shell (ring) of heating, coordinate axes are applied with a scribe on the outer surface of each workpiece, the intersection of which sets the control point, crocodile hook (set) in the middle of the wall of the shell (ring) of heating the workpiece, set the heating time on the control panel of the tongs, set the compressed air pressure in the system of compression of the electrodes of the tongs, measure the ambient temperature T ₀ and the potential difference at the contact of each workpiece, in the local area of measurement of the workpiece heated to a temperature T _ass (i), with a reference electrode, the measurement in each contact is duplicated to increase the statistical reliability of the measurement, according to the known dependence of the potential of the reference electrode used on the measurement temperature, the potential of the reference electrode is found at the found ambient temperature T ₀ , the known potential of the reference electrode is added to the measured potential difference of each contact, thus determining the intrinsic potential of each i-th workpiece at a given heating temperature of the workpieces T _ass (i), then the workpieces are ranked by their own potential in a decreasing series, according to which when assembling a metal structure, the maximum values of thermoelectromotive forces in a given contact of the workpieces are found as the difference between the intrinsic potentials of the contacting workpieces. In this case, a device for the manufacture of a welded metal structure, made of interchangeable workpieces with similar thicknesses and physicochemical properties, subject to electrochemical corrosion, including assembly and welding devices, a control unit, an AC power source and means for measuring in contact between workpieces, including a heater made in in the form of pincers with high-conductive electrodes for double-sided spot contact welding, designed for clamping each workpiece, passing current and heating, a crocodile-type clamp with the possibility of engaging on each of the workpieces at a given distance from the electrodes of the above-mentioned pincers, connected by a commutating wire placed in the housing a device for measuring in the contact of the workpiece, additionally measuring tools are designed to measure the ambient temperature and the potential difference between the own potential of the workpiece and the potential of the reference electrode at ambient temperature food, they additionally contain a thermometer and a reference electrode, through a switch with a commutating wire connected to the second terminal of the device, and only pliers are used to heat the workpiece.

Taking into account the low internal resistance of the TEMF sources in the welded joints of the blanks in the panel, the power sources created in the welded seams are the current sources. Since the electrical resistance of sea water is many times higher than the resistance of steel, then, as our studies have shown, the currents generated by the current sources through the water noticeably decrease already at a distance of 10-15 mm from the boundary of the weld. Therefore, the main damage from electrochemical corrosion of ship skin is observed along the boundaries of the welded seam and the heat-affected zone.

So when welding in CO ₂ on reverse polarity of the widespread low-carbon structural steel Vst3sp, according to GOST 380-71, containing: C - 0.14-0.22%, Si - 0.12-0.3%, Mn - 0, 4-0.65%, Ni <0.3%, Cr <0.3%, the silicon content in the weld will be in the range from 0.57 to 0.80%. In this case, the potential of the weld is less positive than the potential of the base metal. In other words, stress will be applied at the “welded seam - near-weld zone” boundary: minus - to the seam, plus - to the weld zone. Experimentally proved [5, p. 71], that in this case, near this boundary, the weld under negative potential is significantly destroyed. Since the weld seam connects the workpieces to each other, there will be at least two such boundaries with the OSS.

On the other hand, if the weld potential is less doped with silicon than the materials of the parts, then it turns out to be more positive with respect to the SNR. In this case, the minus is applied to the details, plus to the seam. And the materials of the parts are subject to intensive destruction.

It has been noted that under certain conditions, increased wear of the OSHZ metal during corrosion of welded joints of the hulls of sea vessels began to be observed since the time when their hulls were made of steel 09G2 [5, p. 71]. According to GOST 19282-73, this steel contains: C - 0.12%, Mn - 1.4-1.8% and Si - 0.17-0.37%. In automatic submerged arc welding of these steels, Sv-08GA welding wire and low-silicon weakly oxidizing fused flux AN-22 are usually used. The welding wire contains: C - up to 0.1%, Si - up to 0.06%, Mn - 0.8-1.1%, Ni - up to 0.25%, Cr - up to 0.1%. Flux AN-22 in accordance with GOST 9087-81 contains: MnO - 7-9%, CaF ₂ - 20-24%, Al ₂ O ₃ - 19-23%, SiO ₂ - 18-22%, CaO - 12-15% , MgO - 12-17%.

According to our measurements [5, p. 71] with an average temperature difference between the inner and outer sides of the ship's skin of 20 ° C, the potential of the material of the Sv-08GA welding wire is: 200 μV with a silicon content of 0.02% and 175 μV with a silicon content of 0.06%, respectively. At the same time, the potential of 09G2 steel at the same temperature difference of 20 ° C and a silicon content of 0.17% turned out to be 107 μV, at 0.25% - 40 μV, and at 0.37% - 24 μV. Thus, for any acceptable according to GOST ratio of silicon content in the welding wire and the base metal, the positive potential of the wire significantly exceeds the positive potential of the material of the parts. In other words, a potential difference is applied to the “welded seam - OSSZ” boundary: plus - to the seam, minus - to the OSSZ, which is destroyed.

FIG. 1 shows a diagram of the implementation of a method for manufacturing a welded metal structure.

FIG. 2 shows the measuring device of the electrochemical corrosion protection device of the welded metal structure.

FIG. 1 indicates: 1 - one of the blanks of the metal structure; 2 - the local area of measurement of the workpiece 1, in which a microvoltmeter complete with a reference electrode 19 measures the potential difference between the own potential of the workpiece 1 and the potential of the reference electrode; 3 - the location of one of the welds performed after the completion of assembly operations; 4 - coordinate axis of the workpieces' own potentials, measured in their local measurement areas; 5 - potential of one of the blanks, ranked in a decreasing series according to the values of their own potentials; 6 - a line showing the correspondence of the own potential of the workpiece and the location on the metal structure of the local measurement area of the workpiece, in which the measurement was made.

FIG. 2 indicates: 1 - blank; 2 - the local area of measurement of the workpiece, covered by the crocodile 12 and located under the upper contact of the crocodile 12 with this workpiece 1; 7 - a control point located on the workpiece 1 along the axis of symmetry of both electrodes of the tongs (10 and 11) at the intersection of the coordinate axes 8 applied to the workpiece; 9 - pliers for double-sided spot contact welding; 10 - upper, and 11 - lower electrodes of the tongs; 12 - crocodile covering the local area of measurement 2 of the workpiece 1 in thickness and in the middle of the wall of the shell (ring) of heating 13 formed inside the workpiece; 13 - shell (ring) of heating the workpiece to the average set temperature T _back with an inner radius R ₁ and an outer radius R ₂ ; 14 - case; 15 - recorder (millivoltmeter), 16 and 17 - commutation wires, 18 - switch; 19 - reference electrode; 20 - thermometer.

To implement the known protection method and device, it is necessary to measure thermoelectromotive forces in all variants of contacts of metalwork blanks in two. The number of combinations of n blanks in k requires a comparison of the number of options:

where n is the number of blanks in the metal structure, k is the number of blanks in one combination.

For k = 2, the number of workpiece combinations is:

Thus, with the number of blanks in the metal structure n = 5, the number of combinations (equal to the number of measurements) will be 10. With 10 minutes of time spent on preparing and carrying out one measurement, the total duration of measurements will be 1.7 hours. With 10 blanks - 45 options, 7.5 hours. With 100 blanks - 4950 variants, 825 hours. Etc.

For the proposed method and device for protection against electrochemical corrosion of a welded metal structure, such a combination of blanks of 2 is not required. It is enough, instead of the indicated options for measuring thermoelectromotive forces in all possible contacts of the workpieces, two to carry out measurements in any sequence in n workpieces. As a result, the number of measurements is reduced by the value

where n is the number of blanks in a metal structure (for example, in a panel).

With 10 workpieces in a metal structure, the time savings will be 45 minutes, with 100 workpieces - 8 hours. With two repetitions of measurements, the savings increase by 2 times. At the same time, significant labor costs for finding and bringing together the required pairs of workpieces are completely reduced.

To find the best arrangement of blanks in the panel, methods of directed or random search are used.

In general, various well-known ordering procedures are used as a method for arranging workpieces over an object, which makes it possible to achieve, on average, throughout the entire metal structure, in absolute value differences in measured potentials between all pairs of adjacent workpieces (included in future welded joints), various well-known ordering procedures are used: linear, nonlinear, dynamic programming, branches and boundaries, dominance, logical procedures, search algorithms: iterative Gauss-Seidel method, Galerkin method, random search, etc.

Shown in FIG. 1 blanks 1 are laid out isolated from each other in the order corresponding to the best arrangement in the panel. To the right of the layout of the blanks, the results of measuring the potentials in the local measurement areas of 2 blanks are shown, each of which is located on the blank. The gaps between the workpieces 3 are the workpiece joints, along which welding will be performed after the assembly of the metal structure. The results of measuring the potentials in the local measurement areas of the workpieces are shown on the vertically located coordinate axis 4. The potential of each workpiece is measured in the local measurement area with respect to the portable reference electrode. The ambient temperature, and hence the temperature of the reference electrode, is monitored at the time of measurement. The potential of the latter becomes known. The sum of the potential difference between the local area of measurement and the reference electrode and the potential of the reference electrode is equal to the intrinsic potential of the workpiece. Accordingly, the result of measuring the potential of the workpiece is conveniently displayed in microvolts. For each welded joint of a metal structure, the potential difference of two assembled and then welded workpieces will drop. It is the averaged set of these stress differences over the entire plurality of welds that is minimized using sequencing procedures. It should be noted that one side of the workpiece can contact not with one, but with several other workpieces, which is also taken into account in the optimization criterion. 5 - potential of one of the blanks, ranked in a decreasing series according to the values of the own potentials of the blanks; 6 - a line showing the correspondence of the potential and location on the metal structure of the local area of the workpiece in which the measurement was made.

In fact, after welding of joints (formation of a closed system of workpieces), the potential difference between joining workpieces (open system of workpieces) decreases by an average of 5-7%. Here, a lower value corresponds to a more electrically conductive material of the welding electrodes and a smaller cross-section of the weld. The pairs of workpieces form thermocouples. The main reason for the voltage drop along the weld boundary is the high electrical conductivity of the weld material and the heat-affected zone. Shunting by the welded seam of the current source - TEMF of the formed thermocouple is observed. In general, the level of voltage reduction at the welded joint depends on a large number of factors: the value of the initial TEMF, the materials of the blanks and the weld itself, the geometric dimensions of the blanks and the seam, the type of welded joint, etc. This phenomenon reduces the tendency of metal structures to electrochemical corrosion.

The main idea of the invention: to significantly reduce the experimental part of the method for protecting a welded metal structure from electrochemical corrosion, thus expanding the technological capabilities of protecting a welded metal structure from interchangeable workpieces from electrochemical corrosion. To do this, before assembling the metal structure, a microvoltmeter paired with a reference electrode is used to measure its own electric potentials separately for each workpiece at a temperature T _back corresponding to the operating temperature of the welded metal structure. When assembling, the workpieces are laid out over the object so that, on average, over the entire metal structure to be manufactured, the modules of the measured potential differences between all pairs of adjacent workpieces are minimized. Thus, the reason for the appearance of an increased potential difference in welded joints is eliminated by ensuring that only those homogeneous workpieces that are close to each other in chemical composition and structure are welded to each other.

Taking these changes into account when arranging blanks during assembly of a metal structure, it was proposed to change the criterion for assessing the optimal arrangement of blanks in panels - from the average integral minimum of the modules of actually measured TEMF of all possible variants of pairs of blanks in the panels [3] to the average integral minimum of modules of the calculated and experimental values of TEMF of the same possible options for pairs of blanks found on the basis of measurements of the own potentials of blanks. The number of measurements of the potentials of the workpieces is small and is equal to the number of workpieces in the panel n, which is much less than the number of measurements of possible variants of the TEMF of pairs of workpieces. In addition, the measurement of the potentials of the workpieces is carried out in an arbitrary sequence, which makes it possible to abandon the constant labor-intensive, targeted search for the required workpieces during the measurement and bring them together during the measurement. So, instead of measuring the TEMF of pairs of blanks, it is proposed to use the measurement of the intrinsic potentials of blanks. In this case, the calculated TEMF values of all possible pairs of blanks are found by simple subtraction of the intrinsic potentials of these blanks.

The invention is aimed, first of all, at improving and reducing the labor intensity of protection against electrochemical corrosion of a welded metal structure from interchangeable workpieces by simplifying the selection of each pair of workpieces with similar physical and chemical properties included in welded joints, as well as reducing the number and labor intensity of the required measurements.

Experimental refinement of the duration (time) of heating made it possible to refine the setting of the parameters of the heating mode of the workpieces and more accurately set the temperature of the local areas of measurement of the workpieces - shells (rings) of heating the workpieces.

Determination of the radii of the heating shell (ring) - internal R ₁ and external R ₂ made it possible to set the location of the contact of the crocodile with the local heating area on the heating shell (ring) of each workpiece.

The application of a control point on the outer surface of each workpiece, corresponding to the location of the axis of symmetry of the electrodes of the tongs, made it possible to establish on each workpiece the location of the axis of symmetry of the electrodes of the tongs, and hence the axis of symmetry of the shell (ring) of heating.

Marking the inner and outer radii of the heating shell (ring) relative to the control point on the outer surface of each part made it possible to fix the place of installation (engagement) of the crocodile on it.

The application of a control point and the radii of the shell (ring) of heating with a scribe on the outer surface of each workpiece made it possible to maintain high electrical conductivity of the contacts of the electrodes of the tongs with the workpieces, as well as the crocodile with each workpiece. This made it possible to exclude errors in measuring the intrinsic potentials of the workpieces associated with instability and an increased value of the electrical resistance of the contacts.

Fixing the control point by the intersection of the coordinate axes made it possible to more accurately determine the location of the control point.

Installing (engaging) the crocodile in the middle of the shell (ring) wall of heating the workpiece made it possible to fix it in the local area of the workpiece measurement - the place where the workpiece was heated to the temperature T _back (i).

Setting the heating time and pressure of compressed air in the electrode compression system of the tongs on the control panel of the tongs made it possible to set the heating mode of the workpiece.

Measurement of the ambient temperature T ₀ before assembling the welded metal structure made it possible to find the potential of the reference electrode in real measurement conditions.

The measurement of the potential difference in the contact of each workpiece with the reference electrode made it possible to measure not the potential difference (thermoelectromotive forces) in all variants of the workpiece contacts, but to measure the potential differences between each workpiece and the reference electrode, which are much smaller in number and required labor costs.

Heating the local area of measurement of the workpiece to the temperature T _back made it possible to reproduce the operating temperature of the welded metal structure when measuring. Thus, the average temperature inside the vessel is assumed to be 20 ° C higher than outside. For the operating conditions of the hull of the ship, T _{back is} conventionally defined as the sum (20 + T ₀ ) ° C, where T ₀ is the ambient temperature.

The measurement in each contact is duplicated (repeated 2-3 times) to increase the statistical reliability of the measurement. The measurement results are averaged.

Adding the measured potential difference of each contact with the potential of the reference electrode at a temperature T ₀ made it possible to determine the intrinsic potential of each i-th workpiece at a given heating temperature of the workpieces T _back (i).

Finding the difference between the intrinsic potentials of the blanks contacting in the metal structure made it possible to determine the maximum values of thermoelectromotive forces in a given blank contact.

The ranking of the blanks according to the value of the measured intrinsic potentials of the blanks in a decreasing row made it possible, during assembly, to expand the blanks along the metal structure so that, on average, over it, the differences in the measured potentials between all pairs of adjacent blanks were minimized.

The measuring instruments are used to measure the ambient temperature and the potential difference between the intrinsic potential of the workpiece and the reference electrode at the ambient temperature.

The introduction of a thermometer into measuring instruments made it possible to measure the ambient temperature during measurement. This made it possible, according to the table, to find the numerical value of the potential of the reference electrode precisely at the measurement temperature.

The introduction of a reference electrode into the measuring instrument made it possible, using a simple and technologically advanced measuring instrument, a microvoltmeter, to measure the potential difference in each specific contact of the workpieces between the own potential of the given workpiece and the potential of the reference electrode. That further made it possible for each workpiece to add the resulting difference with the potential of the reference electrode and obtain its own potential of the workpiece.

The connection of the reference electrode through the switch with a switching wire to the second terminal of the device (microvoltmeter) made it possible to apply the potential of the reference electrode to this terminal.

The use of a single clamp for heating made it possible to heat only the workpiece subject to measurement.

Pliers 9 cover the workpiece 1 with electrodes 10 and 11 on both sides. In this case, the heating shell (ring) 13 has the form of a shell (otherwise, a ring) with an inner radius R ₁ and an outer R ₂ with an axis of symmetry coinciding with the axis of symmetry of the electrodes 10 and 11 of the tongs. It is heated to the average set temperature T _back . Crocodile 12 also covers the workpiece from both sides in the local measurement area in the middle of the formed wall of the heating shell (ring) 13. The thermometer 20 is located on the housing 14 at a distance from the recorder 15, excluding the influence of the latter on the thermometer readings.

As a reference electrode, for example, a standard silver chloride reference electrode is used.

As a crocodile, for example, a powerful steel crocodile in rubber insulation from REXANT brand U 2303-1 for a current of up to 20 A.

As a device for measuring in the contact of the workpieces of the device, as well as a potentiometer for measuring the thermoelectromotive force of a thermocouple when setting the heating duration of the clamps, for example, millivoltmeters of the Sh-4541 brand can be used. The metrological characteristics of the millivoltmeter provide the ability to verify and calibrate exemplary thermoelectric converters of the 2nd and 3rd categories. The precision millivoltmeter is designed to measure DC voltage in the range from - 300 mV to 300 mV and statistically process the measurement results. The millivoltmeter is used in laboratories of state metrological services and metrological services of legal entities for accurate voltage measurements.

A chromel-copel thermocouple in accordance with GOST R 585-2001 can be used as a thermocouple to adjust the heating duration of the workpiece.

The wire going from the crocodile to the recorder can be made of insulated single-core flexible copper wire of increased temperature resistance and strength. This is due to the working conditions of the wire, coupled with its direct contact with the raw edges of the workpieces, the possibility of impacts on it, thermal effects, etc. At the same time, in order to ensure high measurement accuracy (given the small value of measured voltages), it must have a high electrical conductivity. For example, a wire made of a flexible power assembly copper single-core wire of increased temperature resistance of the RKGM brand. It contained copper, multi-wire, cross-section - 4-6 mm ² . Silicone rubber insulation, fiberglass sheath impregnated with heat-resistant enamel or varnish. This wire is resistant to vibration, high humidity (up to 100% at a temperature of + 35 ° С), heat-resistant (operating temperature range - from -60 to + 180 ° С). In addition, the wire is protected from the harmful effects of varnishes, solvents and mildew.

For example, an ASW-07D toggle switch with illumination is used as a switch.

The method is implemented as follows.

, мм, где

- толщина листа заготовки, мм. Причем меньшее значение нахлеста соответствует толщине заготовки ≤ 20 мм, а большее - толщине ≥ 20 мм. Это необходимо с целью исключения значимых погрешностей измерения вследствие образования цепей шунтирования. Собирают средство измерения в контакте заготовок. Подсоединяют источник переменного тока для питания клещей, клещи запитывают сжатым воздухом. На пульте управления клещами устанавливают расчетное время нагрева. Устанавливают давление сжатого воздуха в системе сжатия электродов клещей. Термометром измеряют температуру окружающей среды.After carrying out the blanking operations, the manufactured interchangeable blanks of metal structures are numbered. Preliminarily, by calculation, the duration (time) of heating and the radii of the shell (ring) of heating are determined - internal R ₁ and external R ₂ . In the center of the wall of the heating shell (ring) on the outer surface of each part, the coordinate axes are applied with a scribe and the location of the control point is set. The workpieces are placed so as to exclude, when overlapping, the convergence of the measurement areas of neighboring workpieces closer (15-20)

, mm, where

- thickness of the blank sheet, mm. Moreover, the smaller value of the overlap corresponds to the workpiece thickness ≤ 20 mm, and the larger value corresponds to the thickness ≥ 20 mm. This is necessary in order to eliminate significant measurement errors due to the formation of shunting circuits. Collect the measuring instrument in the contact of the blanks. Connect an alternating current source to power the clamps, supply the clamps with compressed air. The estimated heating time is set on the tick control panel. Set the compressed air pressure in the electrode clamping system of the tongs. A thermometer is used to measure the ambient temperature.

Experimental adjustment of the duration of heating the workpieces with tongs is performed. For this, the inner radius of the heating shell (ring) R ₁ and the outer R _{2 are} laid from the calculated control point of one of the blanks. A chromel-copel thermocouple is installed on the upper plane of the workpiece in the middle between R ₁ and R ₂ . It is pressed against the surface of the workpiece with a crocodile. The thermocouple is connected to a potentiometer. Turn on the clamp and read off the potentiometer either immediately the temperature in ° C (if the potentiometer scale is graduated in ° C), or the voltage in millivolts. In the second case, the voltage for the installed thermocouple is converted to ° C according to conversion tables. If the measured temperature of the heating shell (ring) does not coincide with the preset temperature T _back , then by iteration find the specified heating duration (time) at which the actual and preset heating shell (ring) temperatures coincide.

Further, the tuned pliers are sequentially randomly set on the control points of the blanks. In the middle of the wall of the shell (ring) heating the workpiece hook (set) a crocodile. At each control point, the clamp is turned on and the potential difference is measured in the contact of each workpiece, heated to the temperature T _ass (i), with the reference electrode. The measurement in each contact is duplicated to increase the statistical reliability of the measurement. Also, to increase the reliability of the measurement, the sequence of the workpieces is changed during the measurements. The measurement results are averaged over each local measurement area. From the known dependence of the potential of the reference electrode used on the measurement temperature, the potential of the reference electrode is found at the found ambient temperature. The measured potential difference of each contact is added to the found potential of the reference electrode at temperature T ₀ , thus determining the intrinsic potential of each i-th workpiece at a given heating temperature of the workpieces T _ass (i).

Then the workpieces are ranked according to the value of their own potential in a decreasing series, according to which, when assembling a metal structure, the maximum values of thermoelectromotive forces in a given contact of workpieces are found as the difference between the own potentials of the contacting workpieces. On the basis of the resulting decreasing series, the best option for the location of the blanks in the metal structure is found. To do this, the absolute differences in the measured natural potentials between all pairs of adjacent workpieces (included in future welded joints) are minimized using various well-known ordering procedures. After that, when assembling the metal structure, the workpieces are laid out according to the found location, other operations for the production of the metal structure are performed.

Example 1.

Consider the production of welded metal structures in the manufacture of the hull of a sea vessel. It is assembled from panels, each of which, in turn, is assembled from standard interchangeable sheet blanks.

The technological process of production of each panel begins with the performance of procurement operations. The blanks are edited, cleaned and marked. They are numbered and a control point is put on each sheet with a scribe.

In the measurement area, the workpieces are laid out in isolation from each other, which allows an independent measurement of the potential of each workpiece separately. This is required to evaluate options for their assembly and subsequent welding in order to reduce the tendency of all joints to electrochemical corrosion.

In the local measurement area of each workpiece, its own electric potential is measured. A microvoltmeter is used for measurement. One input terminal of the microvoltmeter is connected to the local measurement area of the workpiece, and the other is connected to the reference electrode. The measurement result u (i), where i is the workpiece number, is expressed in microvolts.

To measure the potential of the sheets, we use an F-136 microvoltnanoammeter. Its accuracy is down to fractions of a microvolt. We use an accurate and easy-to-use silver chloride electrode as a reference electrode. We measure the ambient temperature. We find the potential φ of the _{ES of the} reference electrode according to the table for the measured ambient temperature. We add φ _ES with u (i) and get the intrinsic potential of the i-th workpiece φ _ZAG (i).

For each welded joint of a metal structure, the potential difference of two assembled and then welded workpieces will drop. It is the averaged set of these stress differences over the entire plurality of welds that is further minimized using an ordering procedure. For this, all blanks of the panel are ranked according to the found potentials - they are arranged in descending order of the potential value.

On the basis of the resulting decreasing series of potentials during assembly, the workpieces are laid out over the object so that, on average, throughout the entire metal structure, the absolute differences in the measured potentials between all pairs of adjacent workpieces are minimized. For this, when searching for the optimal arrangement of sheets in a given panel, all possible options for their layout are considered. And in each considered weld seam, the expected thermoelectromotive force (TEMF) is found, obtained by subtracting the potential of one workpiece entering the welded joint from the potential of the second workpiece entering the welded joint. Then the resulting voltage is taken modulo.

After finding the optimal arrangement of sheets in the panel, other operations for the production of metal structures are performed: assembly, welding, improvement, etc.

The assembly and welding of the ship's skin from the fabricated panels is carried out in the same way.

Only panels are considered as assembly elements.

Example 2. As an example, let us give the values of standard potentials of a silver chloride reference electrode at different temperatures [6]:

Example 3.

Let us determine, for example, the parameters of the heating mode of a billet with a thickness of δ = 10 mm = 10⋅10 ^-3 m made of 09G2 steel with a heating duration τ _c = 0.3 s, which corresponds to a mild heating mode of the billet (part) with tongs. The purpose is to determine the mode of heating the workpiece with the tongs to the temperature of the shell (ring) heating 40 ° C.

Let us take as a hypothesis the heating of the central column of the workpiece (located between the electrodes of the tongs) T = T _n = 640 ° C.

The total amount of heat spent on heating the workpiece and the electrodes of the tongs [7, pp. 30-31]:

where Q ₁ is the energy spent on heating the central column. Its height is equal to the thickness of the sheet of the workpiece δ, and the diameter corresponds to the diameter of the working surface of the electrodes of the tongs d _E :

where c and ρ are the heat capacity and density of the billet steel.

The diameter of the pliers electrodes is determined from the ratio [8, p. 34]:

d _E = δ + 2 = (10 + 2) ⋅10 ^-3 = 12⋅10 ^-3 m.

Q ₁ = (3.14⋅12 ² ⋅10 ^-6 / 4) ⋅10⋅10 ^-3 ⋅0.67⋅7800⋅640 = 3.780 kJ.

Q ₂ is the energy spent on heating the metal in the form of a ring with a width of x ₂ , surrounding the central column. The average temperature of the ring, according to the recommendation [7, p. 30], is taken equal to 0.25⋅T _n = 0.25⋅640 = 160 ° C.

Where k ₁ is a correction factor, k ₁ ≈ 0.8;

x ₂ - ring width:

where a is the thermal diffusivity of the billet steel;

τ _s = 0.3 s. - heating duration (welding time).

For low alloy steels:

Similarly, the temperature in the workpiece will drop by 4 times at a distance of X ₂ from the boundary of this ring. In this case, the average temperature in the larger ring will be about 40 ° C. Thus, the final distance of the middle of the heating shell (ring) from the surface of the electrode of the tongs will be 2X ₂ = 2⋅6.6⋅10 ^-3 = 13.2⋅10 ^-3 m. That is, with a crocodile hook thickness of 5 mm, the inner radius of the shell (rings) heating R ₁ will be 17 mm, and the outer R ₂ - 22 mm.

Q ₂ = 0.8⋅3.14⋅6.6⋅10 ^-3 ⋅ (12⋅10 ^-3 + 6.6⋅10 ^-3 ) ⋅10⋅10 ^-3 ⋅0.67⋅7800⋅160 = 2.578 kJ.

Q ₃ - energy losses spent on heating the electrodes of the tongs:

where k ₂ is a coefficient that takes into account the shape of the electrode. For cylindrical electrodes k ₂ = 1;

d _E - diameter of the electrodes of the tongs;

with _E and ρ _E - heat capacity and density of the metal of the electrodes;

x ₃ - electrode heating height:

where a _E is the thermal diffusivity of the metal of the electrodes;

τ _s = 0.3 s. - heating duration (welding time).

For bronze electrode pliers:

Q ₃ = 2⋅1⋅ (3.14⋅10 ^-4 / 4) ⋅18.1⋅10 ^-3 ⋅0.38⋅8900⋅640 / 8 = 0.771 kJ.

The total amount of heat spent on heating the workpiece and the electrodes of the tongs:

Q _EE = Q ₁ + Q ₂ + Q ₃ = 3.780 + 2.578 + 0.771 = 7.129 kJ.

Welding current (heating current):

where for steels coefficient m ₁ ≈1;

r _dk - resistance of the workpiece in the transition from one electrode to another at the end of heating.

m ₁ - coefficient taking into account the change in resistance during welding. For low-carbon steels k ₃ = 1.0-1.1,

where A _d ≈ 0.87 is the coefficient of electrical resistance of the workpiece at the end of the heating process;

k _p - coefficient taking into account the uneven heating of the workpiece, for steels k _p = 0.85;

ρ _1, ρ ₂ - the resistivity of the material pieces at temperatures 0,8⋅T _n and T _n, i.e., when 0,8⋅640 = 512 ° C and 640 ° C, respectively.

For these temperatures ρ ₁ = 4 μOhmcm, ρ ₁ = 6 μOhm⋅cm [7, p. 17, Fig. 1.8].

r _dca ^{= 0,87⋅0,85⋅1⋅ (4⋅10 -6 + 6⋅10 -6} ) / (3,14⋅ (12⋅10 -1) ^2/2) = 32,71⋅10 ^{- 3} ohm.

Then

For different thicknesses of workpieces, the settings are selected, for example, according to the method [7, pp. 30-31].

The welding force can be found by the expressions [8, p. 115, table]:

F _St = 10 daN / mm ² ⋅πd _e ^2/4 (daN) - for soft heating modes.

F _CB = 10⋅3,14⋅10 ^2/4 = 785 daN.

The reading of the potential difference according to the readings of the microvoltmeter is carried out at the maximum voltage, i.e. at the moment of inflection of the potential versus time.

The invention makes it possible to expand the technological possibilities of protecting a welded metal structure from interchangeable workpieces against electrochemical corrosion, to increase its efficiency and significantly reduce the labor intensity of protective measures.

The invention can be used in the production and repair of welded metal structures for a wide range of purposes, primarily sheet, shell, tank, pipe, as well as hull, lattice and other metal structures resistant to electrochemical corrosion and made from interchangeable workpieces. In particular, the invention can be used in the manufacture of hulls for sea vessels, as well as deck decks, bulkheads, tanks using butt, tee and fillet welds.

Sources of information

1 - Method of control of the mode of operation of the protective protection of steel hulls of ships and vessels [Text]: US Pat. 2589246 Rus. Federation: IPC G01N 17/00 / Shevtsov V.A., Korostylev D.V., Belozerov P.A., Belavina O.A., Adelshina N.V .; applicant and patentee Federal State Budgetary Educational Institution of Higher Professional Education "Kamchatka State Technical". - No. 2015104363/28; declared 02/10/2015; publ. 10.07.16. Bul. 19 - 3 p.

2 - GOST 9.056-75. Steel hulls of ships and vessels. General requirements for electrochemical protection during long-term standby operation. M .: Gosstandart. - 14 p.

3 - Method and device for protection against electrochemical corrosion of welded metal products [Text]: Pat. 2571293 Rus. Federation: IPC C23F 13/00 / Verevkin V.I .; applicant and patentee Federal State Budgetary Educational Institution of Higher Professional Education "Kaliningrad State Technical University". - No. 2014105150/02; declared 02/15/2014; publ. 20.12.15. Bul. 35 - 23 p.

4 - Andreev, N.T. Ship repair [Text]: monograph / N.T. Andreev, O.A. Borchevsky, V.G. Lugovykh [and others]. - L .: Shipbuilding, 1972 .-- 568 p.

5 - Verevkin V.I. Increase of resistance to corrosion of ship metal structures [Text] / V.I. Verevkin, V.F. Igushev, S.A. Teryusheva - Marine and Intelligent Technologies. - No. 4 (38). T. 2. - 2017.S. 69-75.

6 - Handbook of Electrochemistry. / Ed. A.M. Sukhotina. - L .: Chemistry, 1981 .-- 488 p.

7 - Technology and equipment of resistance welding [Text]: textbook for engineering universities / B.D. Orlov, A.A. Chakalev, Yu.V. Dmitriev [and others]. // Under total. ed. B.D. Orlova. - 2nd ed. - M .: Publishing house of mechanical engineering, 1986 .-- 352 p.

8 - Kabanov, N.S. Welding on contact machines [Text]: monograph / N.S. Kabanov. - M .: Higher. school, 1979 .-- 215 p.

Claims (2)

1. A method of manufacturing a welded metal structure subjected to electrochemical corrosion, made of interchangeable workpieces having a similar thickness and physical and chemical properties, including cleaning the surfaces of the workpieces, placing them in close proximity to each other, sequential measurement of the maximum values of thermoelectromotive forces created in thermocouples, formed in the contacts of the blanks of the metal structure, while the said blanks are heated with the help of tongs for double-sided spot contact welding to the same temperature, which is equalized at each measurement by preliminary settings of the tongs, after which the optimal distribution of the blanks in the welded metal structure is determined from the condition of minimizing the maximum values in modulus thermoelectromotive forces generated across all contacts and the absence of excess in contact of at least one pair of workpieces of the maximum permissible value of thermoelectromotive forces, which is 5- 8 mV, then assembly and welding operations are carried out and an anti-corrosion coating is applied to the welded metal structure, characterized in that for the mentioned measurement of the values of thermoelectromotive forces, the eigenvalues of the contacting workpieces are determined, while on the outer surface of each i-th workpiece, a control is set at the intersection of the coordinate axes the point corresponding to the location of the axis of symmetry of the electrodes of the tongs, relative to which the inner R ₁ and outer R ₂ radii of the heating ring of the workpiece to a given temperature T _back are marked, a crocodile-type contact clip is installed in the local area of the workpiece in the middle of the obtained ring of its heating, the heating time of the electrodes is set welding tongs, the pressure of compressed air in their compression system, measure the ambient temperature T ₀ and determine the potential difference in contact of each i-th workpiece with the reference electrode, and the measurement is carried out in the said local area of the workpiece, n aggregated to a temperature T _back (i), and duplicate the measurement in each contact to increase the statistical reliability, then, taking into account the dependence of the potential of the reference electrode used on the measurement temperature, find the potential of the reference electrode at the found ambient temperature T ₀ and add to the measured potential difference of each contact the found potential of the reference electrode to determine the intrinsic potential of each i-th workpiece at a given heating temperature T _ass (i), and to determine the optimal distribution of the workpieces in the welded metal structure, the workpieces are ranked by their own potential in a decreasing series, according to which the maximum values of thermoelectric forces as the difference in their own potentials of the contacting workpieces. 2. A device for the manufacture of a welded metal structure subject to electrochemical corrosion, made of interchangeable workpieces having a similar thickness and physicochemical properties, containing assembly and welding devices, an AC power source, a control unit and means for measuring thermoelectromotive forces in the contact of workpieces, including a heater , made in the form of pincers for double-sided spot contact welding with high-conductive electrodes, designed to pass current and heat the clamped workpiece, a device for measuring thermoelectromotive forces of workpieces and a contact clip of the "crocodile" type for its engagement on the workpiece at a given distance from the electrodes of the mentioned tongs a switching wire with the first terminal of the said device, characterized in that the means for measuring thermoelectromotive forces additionally comprise a thermometer and a reference electrode connected through a switch with a switching wire to the second adhesive mm of the above-mentioned device, providing measurement of thermoelectromotive forces in the contact of the workpiece with the said reference electrode.

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