SU1520763A1 - Method of resistance butt welding of fuel cell shell pipe with plug - Google Patents

Abstract

The invention relates to mechanical engineering and can be used in the technology of flash butt welding, used mainly for sealing the zirconium shells of fuel rods of nuclear power reactors. - The purpose of the invention is to increase productivity by eliminating the need for annealing the welds of the fuel rods and improving the quality of the welded joints by reducing the residual tensile stresses in the interface between the shell and the plug. A method of welding a casing pipe with a plug, the diameter of which is made smaller than the outer diameter of the pipe being welded, is proposed. The casing pipe and the plug are clamped in the welding zone in coaxially arranged annular separable electrodes. Further, a compression force is applied to the electrodes and a pulse of welding current is passed through the parts to be welded. The fuel cladding pipe in the weld zone is clamped at its site equal to the length of the weld along the pipe being welded and increased by no more than the wall thickness of the pipe-shell. In addition, the working diameter of the plug is large. The inner diameter of the welded is large. my pipe is 1 / 2-2 / 3 wall thickness. the last one. The pipe is additionally clamped at a distance of one to two diameters of the pipe being welded from the welding zone. 2 hp f-ly, 3 ill., 2 tab.

Description

O1 145

The invention relates to mechanical engineering and can be used in the technology of flash butt welding, used mainly for sealing the zirconium shells of fuel rods of nuclear power reactors.

The purpose of the invention is to increase productivity by eliminating the need for annealing welds of fuel rods and improving the quality of the welded joint, either by reducing the residual tensile stresses in the interface of the shell and the plug.

- -. f.j

Figure 1 shows the stages of the welding process: a - clamping of the pipe-breaking and plug, b - passing a current pulse, c - forming a joint after precipitation, d - releasing the weld zone from the clamp, where the welded pipe 1 is marked, weldable plug 2 and annular detachable electric | year 3; Fig. 2 shows the temperature distribution in the cross section of the heating section of the pipe and the outer elephant of the working part of the bottom; on fig.Z - constructive design method: a - clamp in the ring electrode

sj

O) od

with a conical (2-3) surface in combination with a cylindrical additional clamp J 6 - narrow, equal to the width of the seam clamp in an annular electrode with a cylindrical surface and with an additional cylindrical clamp; in - a wide ring clamp with a groove, which simultaneously performs the role of a conventional narrow clamp and additional clamp

., working in the elastic region.

The welding cycle consists of the following steps.

In the initial state, the co-ferrous pipe 1 and the plug 2 are in the position shown by & figa. In the process of clamping the tube (fig. 1a) in the electrode, its end is deformed within the limits of elastic deformation. After passing a pulse of welding current (Fig. 1c), a press-fit is made into the heated end of the tube of the plug heated over the outer layer. At the end of the pressing-in phase, the welding zone is cooled due to heat transfer to the electrode.

If the length of the section of the pipe clamped in the annular current lead exceeds the length of the pressed part of the plug by more than the wall thickness of the pipe, if the annular electrical lead is released after welding due to the occurrence of elastic return forces, the stress can reach a value in which the pipe in the heat-affected zone will begin to deform, which would entail the occurrence of cracks. It is possible to avoid the occurrence of a bending moment in the heat-affected zone by limiting a section of the pipe clamped in the current lead that is not longer than the length of the weld, along the pipe axis increased by the thickness of the pipe wall. In this case, when the current-supply sectors are opened, only shrinkage thermal stresses take place, the magnitude of which, as experiments show, the type of welding is not significant (2 ... 2.5 times less than the stresses from the elastic return of the shell). This allows you to avoid long-term additional annealing of the parts being welded and to carry out the welding process on automated lines.

In addition, when choosing the diameter of the working part of the plug (the pressed-in area), the following relation should be followed: the diameter of the working part of the plug

g

0

 ( five (

to be more than 1/2 ... 2/3 of the pipe wall thickness. When this ratio is fulfilled, the quality of mutual diffusion of the materials being joined in the contact zone is improved. This is explained by the temperature distribution in the cross sections of the heated pipe sections and the outer layer of the working part of the plug. In the first approximation, this temperature distribution can be expressed by the straight lines A and .B (see Fig. 2).

It can be seen from Fig. 2a that an increase in the diameter of the working part of the plug leads to a decrease in the average temperature at the junction of the parts being joined, which leads to the appearance of point and line defects in the form of undissolved oxides on the connecting line at this junction.

Reducing the diameter of the working part of the plug to a certain limit

d

tr.

| .In.

 five)

0

five

five

0

improves the quality of study of the joint. A further decrease in d y, Hz. leads to a rather sharp increase in defects, as shown in curve D in Fig. 2b, which is explained by the lack of compressive stress in the weld metal, as well as misalignment of the parts to be welded, which in reality always takes place. Therefore, there is an optimum for the diameter of the working part of the plug. This optimum coincides with the minimum of the dependence of residual tensile stresses on the stub diameter or

Zatl, 1 Tr. yn ,

(curve B in Fig.26).

The method also proposes the use of 5 additional clamps (Fig. 3). Without it, when the length of the main clamp is 3 mm, it is impossible to weld,. as the pipe will slip. The additional clamp is better to be placed as close as possible to the main one - this reduces the size of the welding device.

The minimum length over which the additional clamp should be located is chosen such that the action of this clamp is not in the area of the pipe, in which the elastic return of the pipe can affect the coupling.

51520

No pipe with a cap. If the additional clamp is located close to the main one, then this will be equivalent to welding with a long current lead, i.e. In this zone, the residual stresses of tension are again in TC. That is why the minimum length of the additional clamp removal from the main one should be at least one to two diameters of the pipe being welded. The design of the method may be different (see FIG, Pro, b, c).

Example. Welded sealed samples of fuel rod simulators. For this, a zirconia HI alloy tube with a length of 120 mm and a size of 13.6 x 0.95 mm into which crystalline iodine was loaded after welding on one side.

in the amount of 20 mg / dm of internal tio-20 cracks is reduced. The same dependences of the sample surface, filled after, are also observed with a zagluiyu diameter

pre-vacuum helium under pressure of 30, BO, 90 MPa at room temperature and sealed the open end by welding the second plug.

The iodine was placed in a thin-walled glass ampoule, which, after welding the second plug, was broken by a butt end.

sample on a metal plate. The end of the zone Rusheni in the compound under load

The pipes were clamped in a detachable ring stop-cooler (KUH) consisting of a set of heat-conducting plates 0.3 mm thick connected to a ring split-off current lead, the effective pressure of 60 MPa (at C). In connection with: - with this, for both diameters of zelicia, the area of the pipe clamped in PCT over the length of the weld should not be greater than 1 L, and the effect of

tive (in contact with the pipe), the frequency of decreasing the diameter is in which it was; 0.5; 1.0; 1.5; a larger stock of loading pressure of 2.0 and 5.0 mm. The diameter of the working part before the appearance of germs of cracks. When the plugs were chosen equal to 12.3 and 12.6 mm with a length of 5 mm.

40

the occurrence of nuclei of cracks, values of 1 large 1 & In the seams, cracks are generated when donating gels inside the ATI samples at C, which is not allowed by the existing technical conditions.

the occurrence of nuclei of cracks, values of 1 large 1 & In the seams, cracks are generated when donating gels inside the ATI samples at C, which is not allowed by the existing technical conditions.

In addition, experiments were carried out. During welding, the samples (pipes) were clamped in the pipe electrode (KUH + current lead) so that the distance from the pipe end to the plane of the KUH connection with the current lead was 3 mm using an additional cable clamp. stub.

The welding mode (by welding force) A pipe being welded with a length of 120 mm of compression tOO kg and a current of 25 kA) was chosen from a zirconium alloy with 1% niobium (E 110) wounds so that it was provided with a diameter of 1.0 mm and a wall thickness the joint seam along the axis of the joint, equal to sp 1 mm was clamped in an annular 3 mm ring (the current for plugs with a diameter of three sectors, the current lead from a bronze 12.6 mm was 27 "A)

At each selected pressure, the gels under the sample shell (at each value of the current-supply ring of the pipe 1 mm, the length of the current supply and diam. Pa-., (I.e., the barrel part of the plug was clamped in the current lead) was welded through a pipe of length 1, 5 mm).

In this case, the internal working diameter of the current lead ring was bored out

ZB NBT 2.5 mm thick with a groove end of the welded pipe relative to

5 samples. All samples were placed in an oven and kept for 100 h.

at.

The test results of the samples in the furnace at ,,,, ZZO C and h are given in Table 1 Ldr (log 12.3 mm) and Table 2 (for dio, rA 12.6 mm). At that () l.1 and 2, the following conventions are accepted: no cracks; F initiation of cracks (depth 0.1 mm); + cracks deeper than 0.1 mm,

From Table 1 it can be seen that, with a plug diameter of 12.3 mm, the cracks begin to nucleate at 1 electrical power supply equal to 0.5 and 1.0 mm at the pressure (gels inside the sample) of the VO alti.

With an increase in the length of the electrical power supply from 1.5 to 5 mm, the tendency to the formation of cracks and their depth increase. D. decreasing the pressure of the gels inside the samples the tendency to form

12.6 mm. However, they are shifted to lower pressures, i.e. In this case, the propensity for patterning cracks 25 increases.

According to the technical conditions, the performance indicator of the welded assembly of the fuel rods of power reactors is the absence of corrosion damage in the joint under load conditions.

pressure of 60 MPa (at C). In connection with: - with this, for both diameters of zelicia, the area of the pipe clamped in PCT over the length of the weld should not be greater than 1 L, and the effect of

  a reduction in diameter is found in a larger stock of loading pressure before the appearance of nuclei of cracks. With

40

the occurrence of nuclei of cracks, values of 1 large 1 & In the seams, cracks are generated when donating gels inside the ATI samples at C, which is not allowed by the existing technical conditions.

In addition, experiments were conducted on the use of an additional clamp when welding a pipe with a plug.

 A welded pipe of 120 mm length made of zirconium alloy with 1% niobium (Ø 110 with a diameter of 1.0 mm and a wall thickness of 1 mm was clamped in an annular, consisting of three sectors, current lead from armor

the end of the current-supply ring of a pipe of 1 mm (i.e., a 1.5-mm-long pipe section was clamped in the current lead).

ZB NBT 2.5 mm thick with a groove end of the welded pipe relative to

closed sectors compressed

7152076

at a diameter of 13 ,, and the pipe was clamped with a force exceeding the force required for its deformation-settlement in diameter, i.e. with an effort to ensure the closure of the electrode sectors without gaps between them.

After that, the d / f excluding the slippage of the pipe being welded in its electrode was additionally clamped. in two half-ring sponges on a site with a length of 80 mm, with the end of these sponges located at a distance of 30 mm from the end of the ring electrode to prevent the pipe from bending in the zone between the main welding and additional clamps.

J5

20

Further, in focusing to the end of the clamped pipe let down the cap from the same material

with a working diameter equal to mm, a welding force of 350 kg was applied to it and a welding pulse of current with an amplitude of 25 kA and a duration of 0, c was passed. (Previously 25 it was determined that when welding in tacr mode, the weld width, or its length along the j-joint axis, is equal to, 5 mm). Then, a pipe section d (120 mm long) welded on one side, on the other hand, in the same mode, the same plug was welded in with a central through hole 1.5 mm in diameter and outwardly facing by a nozzle with a diameter of mm and a length of 5 mm. After that, the resulting welded sample was evacuated (in a special chamber), filled with argon, and 10 mg of crystalline iodine was poured into it.

Then, on a spot welding machine, the sample was clamped on the lower console instead of the lower electrode in a vertical position (with the second socket up), the upper electrode with a tapered recess from below and an axial hole, tightly attached by a metal pipeline to the helium balloon, the gas pressure equals 90 ati.

Next, a welding force was applied to the sample through the top 50 electrode, helium balloon was opened, the internal cavity of the sample was filled with this gas under a pressure of 90 MPa, and a welding current pulse was passed through the electrodes of the point machine 55, sealing the nipple on the second plug. Then

40

45

.

five

0

5 d

50 55

40

45

eight

The helium balloon was closed and the brewed sample with iodine and under pressure the helium under the shell 90 ati was removed from the machine.

Similarly, it was welded 10 sealed samples of the proposed method and 10 sealed samples in a known manner. After that, all - 20 samples were placed in one oven, heated to 350 ° C and kept at this temperature for 100 hours. After the samples were removed, the welds from them were cut off and longitudinal (along the axis of the samples) metallographic sections were prepared, on which cracks 60–80 m deep in wall thickness (similar to those shown in Fig. 2) were found only on joints welded along known method. At the joints welded by the proposed method, there were no cracks,

Claims (3)

1. A method of contact butt welding of a pipe of a cladding with a plug, the diameter of which is made smaller than the outer diameter of the pipe being welded, including the clamping of the pipe being welded and plugs in coaxially arranged annular detachable electrodes, the application of compression force to the electrodes and the transmission of a welding current pulse through the parts to be welded, that is, the pulses of the current | that, in order to increase productivity by eliminating the need for annealing the welds of the fuel rods and improving the quality of the welded joint by reducing the residual tensile stresses in the interface between the sheath and the plug, the tubular sheath pipe is clamped at a section equal to that of the weld along the weld pipes increased by no more than wall thickness. last. 2. Method according to claims 1, 1, and T l and h and w - y and, and so, Mto, the working diameter of the plug is made larger than the inner diameter of the pipe being welded 1/2 - 2/3 wall thickness of the latter, 3. Method according to PP.1 and 2, from l and h.yu shchi And with the fact that the pipe is additionally clamped at a distance of one to two diameters of the welded pipe from the welding zone. 0.5 1.0 2.0 fF -f-f ® ® + + + + +. 5.0® + + + “- + + + h1520763 10 t a b l and i (a 1 That 6l and c and 2 ® © @ ® + + .f R with  sas / t.mmufi  with / TO I / 2G ° C S) rush. Comchesto strocheche9ig .2 J