CN112548278A

CN112548278A - Boss butt joint structure of reactor core assembly and welding method thereof

Info

Publication number: CN112548278A
Application number: CN202011267809.2A
Authority: CN
Inventors: 李峻宏; 苏喜平; 杜爱兵; 冯伟; 任媛媛; 刘川川; 王明政; 黄晨; 梁田; 郝宪朝; 刘奎
Original assignee: China Institute of Atomic of Energy
Current assignee: China Institute of Atomic of Energy
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2021-03-26

Abstract

The invention belongs to the technical field of welding structures and processes, and relates to a boss butt joint structure of a reactor core assembly and a welding method thereof. The boss butt joint structure comprises a reactor core assembly transition section, a reducing section, a boss and a hexagonal pipe. The boss butt joint structure of the reactor core assembly and the welding method thereof can be conveniently assembled, are simple to weld and have reliable process, so that the quality of the welding and assembling of the reactor core assembly meets the requirements, and the reliability and the use safety in the reactor are improved.

Description

Boss butt joint structure of reactor core assembly and welding method thereof

Technical Field

The invention belongs to the technical field of welding structures and processes, and relates to a boss butt joint structure of a reactor core assembly and a welding method thereof.

Background

Tungsten Inert Gas (TIG) welding is a type of arc welding method in which argon gas or argon-rich gas is used for protection and a tungsten electrode is used as an electrode. Compared with other welding methods, the method has the advantages of stable welding process, good welding quality, wide application range, suitability for thin plate welding, easy realization of automation of the welding process, no slag in a welding seam area and the like, and is widely applied to industrial production. However, the current carrying capacity of the tungsten electrode is limited, the penetration capacity is low, the weld penetration depth is shallow, the welding speed is low, the production efficiency is low, and the use of the welding method is restricted. In some occasions, even if the welding current is increased during welding, the penetration depth of the welding seam is not increased, but the width of the welding seam is obviously increased. Therefore, the problem of the tungsten inert gas shielded welding depth cannot be fundamentally solved only by increasing the welding current. How to increase the self-fusion welding penetration and improve the welding efficiency is an important research content in the field.

In the conventional tungsten inert gas shielded welding process, grooves are required to be formed for welding with the thickness of more than 3mm, and welding wires are added for multi-pass welding, so that the process is complex, and the welding efficiency is low. In order to solve the problem of the shallow depth of TIG welding, the patent application "tungsten inert gas welding process with large depth-to-width ratio (application number 200610134406.4)" of the institute of metals of the chinese academy of sciences proposes a technique of welding with an active agent, i.e., before welding, a layer of active agent is coated on the surface of a workpiece to be welded, and then welding is performed. Although the penetration of TIG welding can be increased by the process, a process of coating the active agent before welding is added, which is not favorable for automation of the welding process. More importantly, the appearance of the welding seam is sensitive to the coating amount of the active agent, and the thickness of the welding flux is difficult to control by manual coating, so that the welding process is unstable, and welding slag is left on the surface of the welding seam and needs to be cleaned.

The self-fluxing welding process is simple, is easy to realize automatic welding, and is very favorable for the condition that operators can not approach the welding object in radioactive occasions. However, the conventional tungsten electrode argon protection welding penetration is shallow (generally not more than 2.5mm), so that during welding of the fast reactor core assembly, a welding root of a transition section with a boss structure and a butt joint part of a hexagonal pipe is easy to have a sharp corner left without penetration, parameters such as welding current are difficult to eliminate even if the welding current is increased, and potential risks are brought to long-term use of the core assembly in a reactor.

Therefore, it is necessary to design a welding structure and method with convenient assembly, simple welding and reliable process, so that the quality of the welding assembly of the reactor core assembly meets the requirements, and the reliability and the use safety in the reactor are improved.

Disclosure of Invention

The invention aims to provide a boss butt joint structure of a reactor core assembly, which can ensure that the quality of welding and assembling the reactor core assembly meets the requirement and increase the reliability and the use safety in a reactor.

To achieve the object, in a basic embodiment, the present invention provides a boss docking structure of a core assembly, the boss docking structure including a core assembly transition section, a reducer section, a boss and a hexagonal pipe,

the cross section of the outer wall of the core assembly transition section and the cross section of the outer wall of the hexagonal tube are regular hexagons (namely regular hexagons) with the same size;

the cross section of the inner wall of the core assembly transition section is circular, and the cross section of the inner wall of the hexagonal pipe is regular hexagon;

the diameter-variable section is connected to the foremost end of the core assembly transition section, and the cross section of the outer wall of the diameter-variable section is a regular hexagon of which the size is slightly smaller than that of the inner wall of the hexagonal pipe;

the radial outer side of the middle part of the reducing section is connected with a circle of lug boss in a regular hexagonal ring shape, the lug boss is welded and connected to the cross section of the most front end of the hexagonal pipe along the side wall on one radial side, and the part of the reducing section at the front end of the lug boss is inserted into the hexagonal pipe.

The relevant principle of the invention is as follows:

argon is a monoatomic inert gas and used as a protective gas for argon tungsten-arc welding has the following advantages:

1) the density of the argon is 1.4 times of that of air and 4 times of that of helium, the argon can be well covered above a molten pool and an electric arc, and the flow speed is low, so that the protection effect is better than that of the helium;

2) the argon is a monoatomic molecule, has lower heat conductivity, and has smaller cooling effect on the electric arc, so the electric arc has good stability and lower electric arc voltage;

3) the cost is low;

4) compared with helium, arc initiation is easy.

But for the boss butt joint structure welding of the fast reactor core assembly, the argon gas is independently used for self-melting TIG, and the melting depth is shallow.

Compared with argon, helium has the following characteristics:

1) when helium is adopted for protection, the heat generating power of the electric arc is large and concentrated, the penetration capacity is large under the same welding speed, and the welding device is suitable for welding thick plates, high-thermal-conductivity or high-melting-point metals; under the same penetration capacity, the heat input is small or the welding speed is high, and the welding speed of the tungsten electrode helium arc welding is 30-40% higher than that of the tungsten electrode argon arc welding;

2) under the same welding current and arc length, helium has higher heat conductivity coefficient and ionization voltage, so the helium arc voltage is obviously higher than argon arc voltage;

3) helium has a low density, about 1/7 of air, and is easy to dissipate, so that the flow rate of helium is usually 1-2 times higher than that of argon to achieve the same protection effect;

4) helium has the disadvantages of low cathode atomization, much higher price than argon, and easy blackening of the surface of the welded workpiece.

The argon arc has the advantages of stable and soft arc, low price and the like, and the helium arc has the advantages of high arc temperature, strong penetration capability and the like, so when the argon-helium mixed gas is adopted, the arc has the advantages of the argon arc and the helium arc, and is particularly suitable for occasions with high welding line quality requirements. The tungsten inert mixed gas shielded self-fusion welding is to form mixed gas by adding part of helium into argon-based inert protective gas, thereby realizing large fusion depth welding of the reactor core assembly boss butt joint structure and improving the quality of a welding joint.

The volume content of the argon in the mixed gas is 70-90%, and the volume content of the helium in the mixed gas is 10-30%. The reactor core assembly boss butt joint structure welded by the protective gas in the range can ensure that the assembly welding position is completely penetrated, can also avoid the phenomenon of generating black dust on the surface of a workpiece caused by excessive helium content, and has less burning loss to a tungsten electrode. Two opposite welding torches are used for simultaneous welding, so that the welding deformation can be ensured to be small.

The boss butt joint structure reasonable in design, changeover portion and hexagonal pipe adopt the grafting structure, but design has a little boss on the changeover portion, are used for carrying out the self-fluxing with the hexagonal pipe and weld. The boss is attached to the hexagonal pipe, the height of the boss is the same as the thickness (radial distance) of the hexagonal pipe, and the width (axial distance) of the boss is also the same as the thickness of the hexagonal pipe. The transition section is inserted into the hexagonal tube and contacts with the hexagonal tube, the unilateral clearance is controlled within 0.1mm, and the hexagonal tube belongs to clearance fit, so that the structure is convenient to assemble and is also convenient for subsequent welding.

The large-penetration tungsten electrode inert mixed gas shielded self-fluxing welding is carried out, and the main process comprises the following steps:

firstly, adjusting the components of protective gas before welding, mixing pure argon and pure helium inert gas, wherein the gas flow rate after mixing is (15-20) L/min, and the components of the mixed gas are in the range of 90% Ar-10% He or 70% Ar-30% He.

And secondly, setting welding parameters and process specifications of a master welding torch and a slave welding torch, wherein the welding current range is 70A-250A, the welding speed is 50mm/min-80mm/min, the arc length is 1mm-7mm, two opposite master welding torches and two opposite slave welding torches respectively perform arc striking, and then starting welding.

And thirdly, cutting the welding line of the boss butt joint structure along the direction vertical to the welding direction, observing the metallographic phase of the welding line after corrosion, measuring the penetration and the width of the welding line, and representing the appearance of a molten pool.

According to the invention, for the butt welding structure of the hexagonal pipe with the wall thickness of the reactor core assembly of 3mm and the lug boss with the height and the width of 3mm, the effective penetration of the obtained welding line is more than 90 percent of the wall thickness of the hexagonal pipe, namely 2.7 mm. By adjusting the program and parameters of the automatic welding machine, the effect of stable welding process can be achieved.

In a preferred embodiment, the present invention provides a boss docking structure of a core assembly, in which:

the shape and the size of the cross section of the boss are the same as those of the cross section of the hexagonal tube;

the unilateral clearance between the part of the variable-diameter section inserted into the hexagonal tube and the inner wall of the hexagonal tube is 0.05-0.1 mm.

The second purpose of the invention is to provide the welding method of the boss butt joint structure, so that the assembly is convenient, the welding is simple, the process is reliable, the quality of the welding assembly of the reactor core assembly meets the requirement, and the reliability and the use safety in the reactor are improved.

To achieve the object, in a basic embodiment, the present invention provides a welding method of the above boss butt joint structure, wherein the welding method is a method combining tig welding and autogenous welding, and comprises the following steps:

(1) mixing argon and helium to obtain welding protective gas;

(2) and welding the boss butt joint structure under a set welding condition.

In a preferred embodiment, the present invention provides the welding method for the boss butting structure, wherein in the step (1), the volume percentage of argon in the welding protection gas is 70-90%, and the volume percentage of helium is 10-30%.

In a preferred embodiment, the present invention provides the welding method of the boss butting structure, wherein in the step (2), the flow rate of the welding shielding gas during welding is 15-20L/min.

In a preferred embodiment, the present invention provides the above method for welding a boss butting structure, wherein in the step (2), the welding current is in the range of 70 to 250A.

In a preferred embodiment, the present invention provides the above method for welding a boss butting structure, wherein in the step (2), the welding speed is 50 to 80 mm/min.

In a preferred embodiment, the present invention provides the above method for welding a boss butting structure, wherein in the step (2), the arc length during welding is between 1 and 7 mm.

In a preferred embodiment, the present invention provides the above method for welding the boss butting structure, wherein in the step (2), two opposite main welding torches and two opposite auxiliary welding torches are used for arc striking respectively, and then welding is started.

The invention has the advantages that the boss butt joint structure of the reactor core assembly and the welding method thereof can be conveniently assembled, are simple to weld and have reliable process, so that the quality of the welding assembly of the reactor core assembly meets the requirement, and the reliability and the use safety in the reactor are improved.

The invention solves the problems of shallow fusion depth and the like when TIG (tungsten inert gas) self-fusion welding is carried out on the hexagonal pipe with the wall thickness of the reactor core assembly being 3mm and the transition section, can obtain a welding seam with a large depth-to-width ratio, has good formation of the welding seam, avoids the multi-pass welding of the groove-opening filler wire with complex process, is easy to realize the automation of the welding process, and is beneficial to the condition that personnel can not approach the welding seam in radioactive occasions or hot-room operation. By using the inert mixed gas protection self-fusion welding process, the reactor core assembly boss and the hexagonal pipe butt joint structure can be completely welded at one time, and the quality of a welding joint is stable and reliable. Two opposite welding torches are used for welding simultaneously, and the whole welding deformation of the assembly can be ensured to be small.

The beneficial effects of the invention are embodied in that:

(1) according to the invention, the large-fusion-depth self-fusion welding of the butt joint structure of the hexagonal pipe with the wall thickness of 3mm and the boss with the height and width of the transition section of 3mm of the fast reactor core assembly is realized by adjusting the mixing ratio of Ar and He gases before welding. Two opposite welding torches are simultaneously and rotatably welded, the welding deformation of the assembly is very small, and the welding quality is stable and reliable.

(2) The invention has stable welding process, is convenient to realize automation of the welding process, and is very favorable for occasions with high radioactivity and inaccessible personnel. The mixing proportion of the inert gas is convenient and controllable, and the defects that the welding seam appearance is sensitive to the coating amount of the active agent and the coating amount of the active agent is difficult to control in the technology of manually coating the active agent on the surface of a workpiece or a test plate are overcome.

(3) By adopting the process, the surface of the welding line is clean and smooth, the forming is good, and the working procedures of slag removal after welding by using an active agent, cleaning of a large amount of black ash generated on the surface of a workpiece during welding by using pure helium and large burning loss of the helium to a tungsten electrode are avoided.

(4) The effective depth of the thinnest part of the butt self-melting welding line can reach more than 2.7mm under the welding current of 200A, and compared with the pure argon gas tungsten inert gas shielded welding, the depth of the thinnest part of the welding line is increased by more than 1 mm. The reliability and the safety of the welding joint are improved.

(5) The invention solves the problem of shallow self-fusion TIG welding depth of the butt joint structure of the core assembly hexagonal pipe and the transition section boss, provides a new practical process and provides reference for developing reliable and efficient welding processes by other self-fusion welding methods.

Drawings

Fig. 1 is a perspective view of an exemplary boss docking structure of a core assembly of the present invention.

Fig. 2 is an axial sectional view of an exemplary boss docking structure of a core assembly according to the present invention, and fig. 3 is a composition structural view of a welding apparatus of an exemplary boss docking structure of a core assembly according to the present invention, which includes a mixed gas 1, a tungsten electrode 2, a ceramic electrode sheath 3, a welding power source 4, a workpiece base 5, an arc 6, and a molten pool 7.

FIG. 4 is a diagram of the phase of the pure argon weld penetration of the embodiment (with "sharp corners" where no melting occurs).

FIG. 5 is a metallographic map of weld penetration for a hybrid gas weld of the present invention in an embodiment (no unmelted "sharp corners").

FIG. 6 is a schematic view of the location of the measurement points before welding of the core assembly in accordance with an embodiment.

FIG. 7 is a schematic diagram of the measurement position of the core assembly weldment three-coordinate position measuring instrument in the embodiment.

Detailed Description

The following further describes embodiments of the present invention with reference to the accompanying drawings.

An exemplary structure of the boss abutting structure of the core assembly of the present invention is shown in fig. 1 and 2, and includes a core assembly transition section 1, a reducer section 2, a boss 3, and a hexagonal pipe 4.

The cross section of the outer wall of the core assembly transition section 1 and the cross section of the outer wall of the hexagonal tube 4 are regular hexagons with the same size.

The cross section of the inner wall of the core assembly transition section 1 is circular, and the cross section of the inner wall of the hexagonal tube 4 is regular hexagon.

The reducer section 2 is connected to the foremost end of the core assembly transition section 1, and the cross section of the outer wall of the reducer section is a regular hexagon slightly smaller than that of the inner wall of the hexagonal pipe 4.

The radial outer side of the middle part of the reducing section 2 is connected with a circle of regular hexagonal annular boss 3. The side wall of the boss 3 at one side in the radial direction is welded and connected to the cross section of the most front end of the hexagonal tube 4, and the shape and the size of the cross section of the boss 3 are the same as those of the cross section of the hexagonal tube 4. The part of the variable-diameter section 2 at the front end of the boss 3 is inserted into the hexagonal pipe 4, and the unilateral clearance between the part of the variable-diameter section 2 inserted into the hexagonal pipe 4 and the inner wall of the hexagonal pipe 4 is 0.05-0.1 mm.

An exemplary welding method of the above-described exemplary boss butting structure of the core assembly of the present invention is as follows, wherein the constituent structure of the welding apparatus used for the welding method is shown in fig. 3.

Before welding, inert gases Ar and He are mixed, and the gas flow rate of the mixed gas is 15-20L/min. The mixed gas 1 passes between the tungsten electrode 2 and the ceramic electrode sheath 3, an electric arc 6 is generated between the electrode 2 and the workpiece substrate 5, and the workpiece is melted as a heat source to form a molten pool 7. Meanwhile, the mixed gas 1 also provides tail protective gas through a protective cover covering the tip of the tungsten electrode 2. In the welding process, the two tungsten electrodes are oppositely and simultaneously welded in a rotating mode, and welding deformation of the assembly can be greatly reduced. In the welding process, the electrode 2 is connected with the negative electrode of a welding power supply 4, and the workpiece material is connected with the positive electrode.

The CN-1515 hexagonal tube/CN-1515 transition section or the CN-FMS hexagonal tube/CN-GD transition section are respectively selected as the base materials of the welding workpiece, and the protective gas is mixed gas of 90% Ar-10% He to 70% Ar-30% He (all volume percentage). The workpiece welding test was performed at a welding current of 210-230A. The assembly of this type of construction is easy to assemble, but the effective penetration during welding using pure Ar gas shielding is very shallow, not reaching 90% of the wall thickness (3mm) of the hexagonal tube (as shown in fig. 4). When partial He gas is added into Ar-based protective gas, the appearance of a molten pool becomes deeper, and the phenomenon of incomplete penetration of a sharp corner does not exist at the butt joint part of the boss and the hexagonal tube (as shown in figure 5).

The invention designs a boss butt joint structure and a welding method for large-penetration tungsten electrode inert gas mixture protection self-fusion welding, which mainly comprise the following steps:

1. by adding part of the inert gas He into the Ar-based inert gas, the characteristics of large and concentrated heat generating power of a helium protective arc and large fusion depth capability at the same welding speed are utilized, and the large fusion depth self-fusion welding of the assembly boss butt joint structure is realized. Meanwhile, the high argon density can well cover a molten pool and an electric arc, and the flowing speed is low, so that the characteristic of good protection effect is achieved, and the defects caused by the independent use of He gas welding are avoided. By adopting the welding process, not only can a welding seam with large fusion depth be obtained, but also the proportion of protective gas is only required to be adjusted in the welding process, the operation is simple and flexible, the automation of the welding process is favorably realized, various welding parameters are convenient to set, and the defect that the coating amount of the active agent is difficult to control due to the appearance of the welding seam in the active agent welding technology is avoided. The welding seam welded by using the mixed gas has clean surface and good forming, and the treatment process of slag removal after welding by coating the active agent is also avoided.

2. Partial inert gas He is added into the Ar-based inert gas, so that the respective advantages of Ar and He gas protection are combined, and the welding line of the large-penetration boss butt joint structure is obtained. The defects that the width of the molten pool is greatly increased but the effective depth of the molten pool is almost unchanged when the effective fusion depth of the molten pool is too shallow and the welding current specification is increased under the protection of pure Ar inert gas are avoided, so that the welding reliability and safety are improved.

3. By utilizing the mixed protective gas, the two tungsten electrodes are relatively and simultaneously welded in a rotating way, and the welding deformation of the assembly can be greatly reduced by combining the characteristics of automatically, conveniently and flexibly setting various welding parameters.

The exemplary welding method of the above exemplary boss butting structure of the core assembly of the present invention is applied as follows.

Example 1:

in the embodiment, CN-1515 stainless steel is used as a base material, a structural mode that a hexagonal tube with a wall thickness of 3mm is butted with a boss with a height and a width of 3mm is adopted, and self-fluxing welding of the butting structure of the hexagonal tube and the boss under the protection of Ar and He mixed gas is performed under different welding specifications (including welding current, welding voltage, welding speed and duty ratio). The gas flow rate in this example was 20L/min. The welding test is carried out on a direct current pulse TIG welding machine, and a direct current reverse connection mode is adopted. The welding current variation range is 60A-240A, the welding voltage variation range is 10V-13V, the welding speed is 50-60mm/min, the duty ratio is 50-60%, and the shape of the weld pool of the obtained weld is shown in figure 5.

Example 2:

in the embodiment, autogenous welding is carried out under the protection of Ar and He mixed gas in a structural mode that a CN-1515 stainless steel hexagonal tube with the wall thickness of 3mm is butted with a boss with the height and the width of 3 mm. The gas flow rate in this example was 20L/min. The welding test is carried out on a direct current pulse TIG welding machine, the change range of welding current is 65A-232A, the change range of welding voltage is 11V-12V, the welding speed is 55mm/min, and the duty ratio is 50%.

The boss butt joint structure obtained by this welding was tested as follows.

Firstly, an assembly model of a hexagonal pipe and a transition section boss is constructed in a Pro-E three-dimensional mode, and data of the three-dimensional model are extracted through a computer. And 3 points are selected on the surface A of the

graph

6, 2 points are selected at the ridge line, and one point is selected at the bottom edge of the surface A, so that the parts and the model are overlapped at the selected points and surfaces, and the outline reference dimension of the welded hexagonal tube is determined. With the mating surfaces of the transition piece and the hexagonal tube as reference surfaces, as shown in fig. 7, 3 regions were selected (X, D, L) to measure the difference between the part and the created model.

Table 1 shows the measured data of the deformation of the components before and after welding. According to the measurement data, the two tungsten electrodes are relatively and simultaneously rotated and welded by using the mixed protective gas, so that the welding deformation of the assembly is greatly reduced.

TABLE 1 measurement data of deformation before and after welding of the components

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations. The above-described embodiments are merely illustrative of the present invention, and the present invention may be embodied in other specific forms or other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims should be construed to be included therein.

Claims

1. The utility model provides a boss butt joint structure of reactor core subassembly which characterized in that: the boss butt joint structure comprises a reactor core assembly transition section, a reducing section, a boss and a hexagonal pipe,

the cross section of the outer wall of the core assembly transition section and the cross section of the outer wall of the hexagonal pipe are regular hexagons with the same size;

2. The boss docking structure of claim 1, wherein:

3. The method for welding the boss butt joint structure according to claim 1 or 2, wherein the welding method is a method combining tungsten inert gas welding and self-fluxing welding, and comprises the following steps:

(1) mixing argon and helium to obtain welding protective gas;

(2) and welding the boss butt joint structure under a set welding condition.

4. The welding method according to claim 3, characterized in that: in the step (1), the volume percentage of argon in the welding protective gas is 70-90%, and the volume percentage of helium is 10-30%.

5. The welding method according to claim 3, characterized in that: in the step (2), the flow of welding protective gas during welding is 15-20L/min.

6. The welding method according to claim 3, characterized in that: in the step (2), the welding current range is 70-250A.

7. The welding method according to claim 3, characterized in that: in the step (2), the welding speed is 50-80 mm/min.

8. The welding method according to claim 3, characterized in that: in the step (2), the arc length is between 1 and 7mm during welding.

9. The welding method according to claim 3, characterized in that: in the step (2), two opposite main welding torches and two opposite auxiliary welding torches are used for arc striking respectively, and then welding is started.