RU2364483C2 - Electrode for underwater welding - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention can be used for maintenance of hand arc welding of fabricated metals of high-duty, including pipelines from low-carbon and low-alloy steel, exploited under water. Bar of electrode is implemented from steel CB08. Coating contains components in a following ratio, wt %: fluorite 19.5-28.0, rutile concentrate 18.0-33.5, ferric oxide 13.0-28.0, feldspar 8.0-12.0, metallurgical magnesite 4.0-8.0, metallic manganese 5.0-10.0, ferrosilicon 0.5-2.0, nickel powder 0.5-3.5, carboxymethylcellulose 1.5-2.0. Coating mass factor is 22-25%.

EFFECT: invention provides qualitative forming of weld metal during welding in all attitude position and high indices of its mechanical properties.

1 dwg, 5 tbl

Description

The invention relates to the field of fusion arc welding, in particular to the development of welding materials for manual underwater wet welding of low carbon and low alloy steels. It can be used in gas and other industries.

The problem of welding underwater metal structures in all spatial positions has not yet been resolved. The slag coating system of existing electrodes provides high-quality formation of the weld metal mainly in the lower position. When welding on a vertical plane and especially in the ceiling position, the welding and technological properties of the electrodes deteriorate, since the physical properties of the slag formed during the melting of the electrode coating do not provide reliable protection of the molten metal, do not prevent it from draining, as well as the formation of undercuts and sag. As a result, the formation of deposited metal becomes unsatisfactory, the mechanical properties of such welds are sharply reduced. At the same time, the majority of work in the repair of underwater metal structures (the underwater part of the ship’s hull, pipelines, vertical platform supports and walls of port facilities) must be performed precisely in spatial positions other than the lower one. Therefore, the possibility of welding in all spatial positions is one of the key issues in the creation of electrode materials, the development or improvement of the underwater welding process. In addition, the level of mechanical properties of the weld metal does not meet the requirements of the ANSI / AWS D3.6 "Specification for Underwater Welding", which limits the use of wet underwater welding in a narrow circle of mild steels.

Known electrode EPS-52 (N.M. Madatov. Underwater welding and cutting of metals. - Leningrad: Shipbuilding, 1967, p.142) with a coating of ore-acid type, designed for welding under water carbon and low alloy steels, the coating of which contains wt.%:

Titanium dioxide 35 Feldspar 10 Marble 10 Zirconium ore 5 Ferromanganese 5 Ferrotitanium 12 Ferrosilicon 3 Potash 10 Liquid glass twenty

Its main disadvantages are unsatisfactory welding and technological properties and a low level of mechanical properties due to the very high content of diffusion hydrogen and slag inclusions.

As a prototype, we chose the EPS-AN1 electrode (USSR Author's Certificate No. 1706821, IPC V23K 35/365), which allows wet underwater welding in all spatial positions and the coating of which contains:

Feldspar 6 ... 11 Marble 3 ... 7 Ferromanganese 5 ... 20 Cellulose 1,5 ... 2,5 Rutile concentrate rest.

But the specified electrode does not provide high-quality formation of multipass butt joints. The coating of the prototype electrode is purely rutile type and creates short slags with a high hardening temperature, which causes the formation of deposited rollers with a low shape factor - the rollers are almost triangular, rather high, do not have a smooth transition to the surface of the previously deposited welds. When surfacing the following seams, this leads to defects in the form of fusion, slagging, undercuts, etc. In addition, these electrodes do not provide a sufficient level of mechanical properties of the weld metal.

The objective of the invention is the provision during welding in all spatial positions of the qualitative formation of the weld metal and indicators of the mechanical properties of the weld metal in accordance with the requirements of "Specification for underwater welding" ANSI / AWS D3.6.

The problem is solved in that the electrode consists of a rod of Sv08 wire and a coating containing rutile concentrate, feldspar and ferrosilicon, in which fluorite, iron oxide, metallurgical magnesite, metallic manganese, nickel powder and carboxymethyl cellulose are added with this ratio of components (wt. .%):

Fluorite 19.5-28.0 Rutile Concentrate 18.0-33.5 Iron oxide 13.0-28.0 Feldspar 8.0-12.0 Metallurgical magnesite 4.0-8.0 Manganese metal 5.0-10.0 Ferrosilicon 0.5-2.0 Nickel powder 0.5-3.5 Carboxymethyl cellulose 1.5-2.0

Coefficient of coating mass is 22 ... 25%.

A decrease in the hardening temperature of the slag, its elongation, as well as an increase in the wetting angle of the base metal with molten metal, was achieved by introducing a balanced amount of fluorite and iron oxide into the coating. The introduction of a significant amount of fluorides provides a decrease in the hydrogen content in the weld metal, desulfurization of the molten metal, a high degree of assimilation of easily oxidizable elements, and together with feldspar, promotes the formation of a slag crust, which reliably protects the weld from the environment, and provides a good formation. This technical solution is the result of a thorough study of the influence of the components of the CaF ₂ -TiO ₂ -FeO ternary system on the welding and technological properties of electrodes for underwater wet welding.

The essence of the experiments is illustrated in figure 1, where the concentration triangle qualitatively reproduced the nature of the influence of the ratio of the ingredients of the CaF ₂ -TiO ₂ -FeO system on the welding and technological properties of the electrodes. Here A is the region of optimal electrode coating compositions that meet the requirement of wet underwater welding of multi-pass butt welds in all spatial positions.

Direction 1 - with such a change in the ratios of ingredients, the tendency to form weld beads of a triangular shape, the formation of a solid ceramic slag crust with a tendency to jam during multilayer welding of butt joints, an increase in the coefficient of reinforcement of joints, coarsening of flakes, the formation of defects in the form of undercuts, slag inclusions during welding increases multipass seams.

Direction 2 - with such a change in the ratios of the ingredients, the tendency to form a solid ceramic slag crust, high uneven coarse-scaly crusts, and finally cast round rollers increases, separation of the slag crust worsens, large drops appear near the seam, the arc voltage increases, the mode becomes unstable .

Direction 3 - with such a change in the ratios of the ingredients, the tendency to form rollers with low gain, a finely scaled surface and a smooth transition to the surface of the base metal or previously deposited rollers increases, the transfer of molten metal becomes small-droplet, the formation of an amorphous slag coating of the deposited rollers is observed, which is easily removed by brush , the possibility of high-quality welding in spatial positions other than the lower one is limited.

Thus, the boundaries of the content of fluorite, rutile concentrate and iron oxide, as well as their ratio in the coating of the electrode, which is proposed as an invention, were determined during the study of the slag system CaF ₂ -TiO ₂ -FeO and correspond to the values of region A of the optimal composition of the system.

In order to improve the stabilization of the arc gap and ensure stable arc burning both on the direct and reverse polarity, as well as a certain increase in the shape factor of the seam, magnesite (in the form of metallurgical magnesite) was introduced into the coating, which also practically prevents spatter. The introduction of magnesite in an amount that exceeds the accepted limit leads to coarsening of the scaly shape of the rollers and their unevenness in height.

Iron oxide, when CaF ₂ -TiO _{2 is} introduced into the slag system, lowers its melting temperature and the surface tension coefficient, which leads to the droplet transfer of the molten metal and the formation of rollers with a finely scaly surface and a smooth transition to the base metal or the metal of the previously deposited rollers. The introduction of the coating of the proposed electrode FeO in an amount less than stated, leads to the formation of "hump" rollers. Exceeding the amount of FeO above the proposed limit contributes to the formation of low-melting slag, which makes it impossible to qualitatively form vertical and ceiling joints. The introduction of FeO in the proposed amount in the presence of calcium fluoride causes the formation of iron fluorides, which also provide an additional reduction of diffusion hydrogen in the weld metal.

The introduction of feldspar at the indicated boundaries causes the formation of a sufficiently dense slag crust and, together with magnesite, stabilizes the arc gap. An increase in the content of feldspar over the specified limit leads to the formation of more fluid slags of large mass, which makes it difficult to weld in spatial positions.

The introduction of manganese and nickel within the accepted limits provides a weld metal, the strength properties of which are not lower than those for the welded metal.

Ferrosilicon provides the transition of the required amount of manganese into the weld metal. But increasing its content above the proposed limit leads to a decrease in the plasticity value of the deposited metal, which is due to solid-solution hardening of the ferrite matrix with silicon.

For experimental verification of the proposed technical solution, 5 batches of electrodes with rods from Sv08 welding wire with a diameter of 4 mm were made, the coating composition of which is shown in Table 1.

To evaluate the welding and technological properties, a diver-welder in the laboratory pool at a depth of 2 m in all spatial positions welded butt samples of steel St3 14 mm thick. The formation of the deposited metal was evaluated using a three-point system, Table 2, taking into account the appearance, separability of the slag, the nature of the slag crust, spatter, combustion stability, etc. Analysis of the results allows us to conclude that the electrodes coated with the proposed composition provide satisfactory formation of multilayer welds in all spatial positions.

Table 1. The coating composition of the electrodes, wt.% Coating
Components one 2 3 four 5 fluorite 17 19.5 23 28 thirty rutile concentrate 35 33.5 26 eighteen 16 iron oxide 10 13 twenty 28 thirty magnesite 10 8 7 four 3 feldspar fourteen 12 10 8 7 manganese metal 8 8 8 8 8 nickel powder 2 2 2 2 2 ferrosilicon 2 2 2 2 2 carboxymethyl cellulose 2 2 2 2 2 Table 2. Welding and technological properties of electrodes Coating
Welding technologist. the properties one 2 3 four 5 Possibility of welding in the lower (n), vertical (in) and ceiling (p) positions nvp nvp nvp nvp nv The formation of metal seams, points (three-point system): lower 3 3 3 3 3 vertical 2 3 3 3 2 ceiling one 2 3 2 -

To determine the mechanical properties of the weld metal during welding of St3 steel, electrodes with rods from Sv08 wire were made on the basis of coating No. 3, Table 1, in which the alloying elements varied within the limits shown in Table 3.

Table. 3. Coating composition of electrodes with cores made of Sv08 wire for testing the mechanical properties of weld metal Coating one 2 3 four 5 Components base charge 86 87 86.5 87.5 88 manganese metal 12 10 8 5 3 nickel powder 0 0.5 2 3,5 four ferrosilicon 0 0.5 1,5 2 3 carboxymethyl cellulose 2 2 2 2 2

From welded joints made in the lower position, in accordance with the requirements of "Specification for underwater welding" ANSI / AWS D3.6, samples of the type Mi12, GOST 6996-66 were made. The test results are shown in table 4. Their analysis indicates that the electrodes with coatings No. 2-4 provide high rates of plastic and strength properties of the weld metal and meet the requirements of ANSI / AWS D3.6 "Specification for Underwater Welding" (δ≥12%, limit the strength of the weld metal is higher than the tensile strength of the base metal).

Table 4. Mechanical properties of metal seams made with electrodes with rods from wire Sv08 Coating one 2 3 four 5 Fur. properties. metal seam Tensile strength, σ _b , MPa 420 425 445 460 475 Yield Strength, σ _t , MPa 340 355 370 410 445 Elongation, δ,% 8 12 fourteen 13 9

To determine the mechanical properties of the weld metal during welding in all spatial positions, electrodes with a coating of No. 3 were used, Table 3. The results obtained are shown in Table 5.

Table 5. Mechanical properties of weld metal during welding in all spatial positions Spatial position Mechanical properties σ _t , MPa σ _b , MPa δ,% Lower 370 445 fourteen Vertical 360 430 12 Ceiling 365 425 12

Thus, the proposed electrode makes it possible to obtain a high-quality welded joint in all spatial positions with the required level of mechanical properties when welding under carbon mild and low alloy steels and can be recommended for use in the repair of underwater pipelines.

Claims (1)

The electrode for underwater welding, which includes a rod of wire Sv08 and a coating containing rutile concentrate, feldspar and ferrosilicon, characterized in that the coating additionally contains fluorite, iron oxide, metallurgical magnesite, metallic manganese, nickel powder and carboxymethyl cellulose in the following ratio of components, wt.%:
fluorite 19.5-28.0 rutile concentrate 18.0-33.5 iron oxide 13.0-28.0 feldspar 8.0-12.0 metallurgical magnesite 4.0-8.0 manganese metal 5.0-10.0 ferrosilicon 0.5-2.0 nickel powder 0.5-3.5 carboxymethyl cellulose 1.5-2.0
while the coating mass coefficient is 22-25%.