CN106001825B - Anticorrosion superalloy pipe tube sheet connection method and heat exchanger - Google Patents

Abstract

The invention discloses a corrosion-resistant superalloy tube-tube-sheet connection method. The method includes: 1. Process a tube hole on the tube plate, process a U-shaped annular feeding groove for placing a solder ring around the tube hole on the upper side of the tube plate, and the inner diameter of the U-shaped annular feeding groove Not less than the outer diameter of the pipe + 1mm, and set a plurality of feeding holes connecting the U-shaped annular feeding groove and the pipe hole and evenly distributed along the circumference of the pipe hole; 2. Pass the pipe through the pipe hole and make the lower end of the pipe protrude Plane the lower side of the tube sheet, then expand the protruding part of the lower end of the tube, and finally press the protruding part of the lower end of the tube into the tube hole; 3. Fusion welding is performed on the joint between the lower end of the tube and the lower side of the tube plate, and the weld penetration depth is not less than that of the tube 4. Put the solder ring in the U-shaped annular feeding groove and perform vacuum brazing. The invention also discloses a corrosion-resistant superalloy heat exchanger. The present invention can ensure full-thickness metallurgical bonding between the tube and the tube sheet.

Description

Corrosion-resistant superalloy tube-tube-sheet connection method and heat exchanger

technical field

The invention relates to a tube-tube sheet connection method, in particular to a corrosion-resistant superalloy tube-tube sheet connection method.

Background technique

The fourth-generation nuclear reactor-molten salt reactor has become an important development direction in the future nuclear power field because of its inherent safety and high efficiency. The reactor operates at a temperature of 600°C~700°C, uses highly corrosive molten salt as the coolant, and uses a nickel-based superalloy that is resistant to molten salt corrosion (such as the Hastelloy N alloy developed by the Oak Ridge Laboratory in the United States or developed by a scientific research institution in my country. GH3535 alloy) as a structural material, the construction of a nuclear reactor needs to ensure the manufacture of high-quality nuclear equipment, and the molten salt heat exchanger is the core equipment of the reactor, the reliability of its manufacture, especially the reliability of the heat exchanger tube-tube sheet connection appears to be particularly important.

There are three main connection methods for traditional heat exchanger tube-tubesheet joints: (1) Tungsten argon arc welding between the end of the tubesheet and the tube. This welding method only obtains a weld with a certain penetration depth, and there are large tube The gap between the tube sheet and the tube sheet, the existence of this gap leads to a large stress concentration at the root of the weld and the risk of crevice corrosion, and the tube-tube sheet joint is prone to failure in harsh and harsh service environments; (2) the tube and tube sheet Expansion welding, that is, the method of expansion + welding, this welding method is applied to the evaporator of the pressurized water reactor with an operating temperature below 350 °C, but the expansion joint is a mechanical combination rather than a metallurgical combination. The material will undergo creep and relaxation, so the expansion joints are prone to loosening, which will lead to the stress concentration of the weld and cause failure; (3) the welding technology of the inner hole of the tube and the tube plate, this welding method needs to be equipped with a special welding torch to penetrate into the tube For welding, since the inner diameter of the heat exchange tube of the molten salt reactor heat exchanger is only about 10mm, there is no mature welding torch on the market that can be used for inner hole welding.

Therefore, according to the material characteristics of corrosion-resistant superalloys and high-temperature and high-corrosion working conditions, how to provide a tube-tube-sheet connection method to avoid the risk of stress concentration cracking and crevice corrosion at the joint, improve the service life of the heat exchanger and Security is a problem to be solved by those skilled in the art.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, and provide a corrosion-resistant high-temperature alloy tube-tube-sheet connection method, which can ensure a full-thickness metallurgical bond between the tube and the tube sheet, avoid stress concentration cracking of the joint, and prevent Crevice corrosion occurs, thereby improving the service life and safety of equipment such as molten salt reactor heat exchangers.

The corrosion-resistant superalloy tube-tube-sheet connection method proposed by the present invention comprises the following steps:

Step 1. Process a tube hole with a diameter 0.08 to 0.16 mm larger than the outer diameter of the tube on the tube plate, and process a U-shaped annular feeding groove for placing a solder ring around the tube hole on the upper side of the tube plate, The inner diameter of the U-shaped annular feeding groove is not less than the outer diameter of the pipe + 1 mm, and a plurality of feeding holes connected to the U-shaped annular feeding groove and the pipe hole are arranged and evenly distributed along the circumference of the pipe hole;

Step 2. Pass the tube through the tube hole so that the lower end of the tube protrudes from the lower plane of the tube sheet, and then expand the part where the lower end of the tube protrudes from the lower plane of the tube sheet, so that the largest outer diameter of the tube after expansion is larger than the diameter of the tube hole 0.5mm, and finally press the lower end of the tube into the tube hole until it is flush with the lower plane of the tube sheet;

Step 3. Fusion welding is performed on the joint between the lower end of the tube and the lower side of the tube sheet, and the penetration depth of the weld is not less than the wall thickness of the tube;

Step 4. Vacuum brazing is performed after inserting a solder ring in the U-shaped annular feeding groove.

Preferably, the material of the solder ring is gold-nickel alloy; the preferred mass ratio is 82% Au and 18% Ni.

Preferably, the process parameters of the vacuum brazing are specifically as follows: the vacuum degree of vacuum brazing is above 10 ^-2 Pa, the heating rate is not greater than 10°C/min, the intermediate process is kept at 900°C for 20 minutes, and the brazing temperature is 1000-1020°C. The holding time is 20 to 60 minutes, and the temperature is lowered to below 400°C at a cooling rate of no more than 5°C/min before being released from the furnace.

Preferably, the axis of the feeding hole forms an angle of 30° with the axis of the pipe hole.

Preferably, in step 2, a cemented carbide indenter with a taper of 30° is used to hydraulically expand the part of the lower end of the tube protruding from the lower plane of the tube sheet, and then a hydraulic press is used to press the lower end of the tube into the tube hole.

Further, a U-shaped ring groove for reducing fusion welding stress is pre-processed around the tube hole on the lower side of the tube sheet, the inner diameter of the U-shaped ring groove is not less than the outer diameter of the pipe + 2 times the wall thickness of the pipe, The width of the groove of the U-shaped ring is not less than the wall thickness of the pipe, and the depth of the groove of the U-shaped ring is not less than the wall thickness of the pipe. Adopting this scheme can effectively reduce the welding stress of fusion welding.

The corrosion-resistant superalloy can be various existing or future corrosion-resistant superalloys, such as HastelloyN alloy or GH3535 alloy. The corrosion-resistant superalloy materials used for the tube sheet and the tube can be the same or different.

According to the same inventive idea, a corrosion-resistant superalloy heat exchanger can also be obtained, which includes a group of tubes connected to the tube sheet, and the tube sheet and the tubes are connected by the connection method described in any of the above technical solutions.

Compared with the prior art, the present invention has the following beneficial effects:

The invention can realize the full-thickness metallurgical connection between the corrosion-resistant high-temperature alloy tube sheet and the pipe with a large thickness, and the thickness of the tube sheet can reach 130mm, which is beyond the reach of the prior art;

The tube-tube-sheet joint connected by the method of the invention avoids the risk of stress concentration cracking and crevice corrosion, and effectively improves the service life and safety of molten salt reactor heat exchangers and other equipment used in high-temperature and high-corrosion environments.

Description of drawings

Fig. 1 is the schematic diagram of a preferred embodiment of the method of the present invention; Wherein, 1 is a tube plate, 2 is a tube hole, 3 is a pipe, 4 is a U-shaped ring groove on the lower side of the tube plate, and 5 is a U on the upper side of the tube plate Type annular feeding groove, 6 is the feeding hole, 7 is the argon arc welding seam at the junction of the tube plate underside and the pipe, and 8 is the brazing seam.

Detailed ways

The technical scheme of the present invention is described in detail below in conjunction with accompanying drawing:

Aiming at the problem of reliable connection between corrosion-resistant superalloy tubes and tube sheets, which is difficult to complete in the prior art, the present invention proposes a new connection method, which organically combines expansion joints, fusion welding, brazing and other processes, thereby realizing variable thickness. The tube sheet up to 130mm is connected to the full thickness of the tube, and the tube-tube sheet joint avoids the risk of stress concentration cracking and crevice corrosion, and the connection performance fully meets the requirements of equipment used in high-temperature and high-corrosion environments such as molten salt reactor heat exchangers safe operation requirements. Technical scheme of the present invention is specifically as follows:

Step 1. Process a tube hole with a diameter 0.08 to 0.16 mm larger than the outer diameter of the tube on the tube plate, and process a U-shaped annular feeding groove for placing a solder ring around the tube hole on the upper side of the tube plate, The inner diameter of the U-shaped annular feeding groove is not less than the outer diameter of the pipe + 1 mm, and a plurality of feeding holes connected to the U-shaped annular feeding groove and the pipe hole are arranged and evenly distributed along the circumference of the pipe hole;

Step 2. Pass the tube through the tube hole so that the lower end of the tube protrudes from the lower plane of the tube sheet, and then expand the part where the lower end of the tube protrudes from the lower plane of the tube sheet, so that the largest outer diameter of the tube after expansion is larger than the diameter of the tube hole 0.5mm, and finally press the lower end of the tube into the tube hole until it is flush with the lower plane of the tube sheet;

Step 3. Fusion welding is performed on the joint between the lower end of the tube and the lower side of the tube sheet, and the penetration depth of the weld is not less than the wall thickness of the tube;

Step 4. Vacuum brazing is performed after inserting a solder ring in the U-shaped annular feeding groove.

In order to facilitate the public's understanding, the technical solution of the present invention will be described in detail below with a preferred embodiment.

In this embodiment, the connection between the tube sheet and the tube of the molten salt reactor heat exchanger is taken as an example. The material used for the tube sheet and the tube is GH3535 alloy. The thickness of the tube sheet of the heat exchanger reaches 130 mm, and the outer diameter of the tube is 13.72 mm; The connection process between the tube sheet and the tube in the example is shown in Figure 1, and the details are as follows:

Step 1. Processing of the tube plate: process a tube hole on the tube plate with a diameter 0.08 to 0.16 mm larger than the outer diameter of the tube, and process a U-shaped ring around the tube hole on the upper side of the tube plate for placing the solder ring Feeding groove, the inner diameter of the U-shaped annular feeding groove is not less than the outer diameter of the pipe + 1mm, and a plurality of feeding pipes connecting the U-shaped annular feeding groove and the pipe hole and evenly distributed along the circumference of the pipe hole are provided. hole;

In this embodiment, as shown in Figure 1, firstly, the tube hole 2 is processed on the 130mm thick tube plate 1, and the diameter of the tube hole 2 is 13.80mm; Annular feeding groove 5, the specific size of the groove depends on the solder required for brazing. In this embodiment, the inner diameter of the groove 5 is 16mm, the width is 2.5mm, and the depth is 2.5mm; along the pipe hole 2 weeks To every 120 ° process a feed hole 6 that communicates with the U-shaped annular feed groove 5 and the tube hole 2 and is 30 ° with the tube hole axis. The diameter of each feed hole 6 in the present embodiment is 2.3mm.

The present invention can further process a U-shaped ring groove around the tube hole on the lower side of the tube plate to reduce the welding stress of argon arc welding. The inner diameter of the U-shaped ring groove is not less than the outer diameter of the pipe + 2 times the pipe wall thickness, U Type ring groove width is not less than pipe wall thickness, and U-shaped ring groove depth is not less than pipe wall thickness; The depth is 2.3mm.

Step 2. Pass the tube through the tube hole so that the lower end of the tube protrudes from the lower plane of the tube sheet, and then expand the part where the lower end of the tube protrudes from the lower plane of the tube sheet, so that the largest outer diameter of the tube after expansion is larger than the diameter of the tube hole 0.5mm, and finally press the lower end of the tube into the tube hole until it is flush with the lower plane of the tube sheet;

First pass the tube 3 through the tube hole 2 so that the lower end of the tube 3 protrudes from the lower plane of the tube sheet 1, and then expand the part where the lower end of the tube 3 protrudes from the lower plane of the tube sheet 2. In this embodiment, the tube 3 and the tube sheet 1 are cleaned with detergent, acetone, etc., and a cemented carbide indenter with a taper of 30° is used to hydraulically expand the part of the lower end of the tube 3 that protrudes from the lower plane of the tube sheet 2. The pressure is about 15KN, so that the largest outer diameter of the expanded tube 3 is 0.5mm larger than the diameter of the tube hole 2; The plane of the lower side of the plate 1 is flush; try to ensure that the tube 3 and the tube hole 2 are concentric during hydraulic pressure, so as to ensure a reasonable gap for brazing.

Step 3. End fusion welding: fusion welding is performed on the joint between the lower end of the pipe and the lower side of the tube sheet, and the penetration depth of the weld is not less than the wall thickness of the pipe;

Argon arc welding, plasma arc welding, laser welding and other fusion welding methods can be used to weld the joint between the lower end of the tube and the lower side of the tube sheet. In this embodiment, argon tungsten arc welding is used, and the process parameters are as follows: The high-purity argon shielding gas is 15L/min, the distance from the electrode to the workpiece is 1mm, the welding current is 45A, and the welding speed is 10mm/s. As shown in FIG. 1 , the penetration depth of the obtained argon arc welding seam 7 is slightly larger than the wall thickness of the pipe 3 . The U-shaped ring groove 4 pre-set on the lower side of the tube plate 1 can effectively eliminate the welding stress of fusion welding.

Step 4. Vacuum brazing of tubes and tube sheets: vacuum brazing is carried out after inserting a solder ring in the U-shaped annular feeding groove;

In view of the material properties of corrosion-resistant superalloys and their special use environment, the present invention preferably adopts gold-nickel alloy solder to carry out vacuum brazing on the tube and tube sheet, wherein the preferred mass ratio of gold-nickel alloy solder is 82% Au and 18%Ni. Specifically, after argon tungsten arc welding is completed, an 82Au-18Ni solder ring is placed in the U-shaped annular feeding groove 5 on the upper side of the tube plate, and then the tube plate and the tube are put into a vacuum brazing furnace as a whole Carry out vacuum brazing, the process parameters of vacuum brazing: the vacuum degree is above 10 ^-2 Pa, the heating rate is not more than 10°C/min, the intermediate process is 900°C for 20min, the brazing temperature is 1020°C, and the holding time is 60min, but not more than 5 The cooling rate of °C/min is lowered to a temperature below 400 °C before being released from the furnace. During the brazing process, the solder of 82Au-18Ni turns into a liquid state, fills into the gap between the tube sheet 1 and the tube 3 through the feeding hole 6, and interdiffuses with the GH3535 alloy of the tube sheet 1 and the tube 3, finally forming Fig. 1 Brazing welds in 8.

In order to verify the effect of the above connection method, the tube-tube-sheet joints that have been connected are inspected, specifically: liquid penetrant testing and ultrasonic testing are performed on the tube-tube-sheet joints, and the quality of the joints meets the acceptance requirements of ASME NB Class I components. In addition, , Carry out a water pressure test of 5.5MPa and 10 minutes of pressure on the joint, and the joint has no leakage. The test results prove that the quality of the heat exchanger tube-tubesheet connection fully meets the operating requirements of the molten salt reactor.

The above examples fully illustrate that the method of the present invention can fully satisfy the reliable connection between corrosion-resistant superalloy tubes and tube sheets, which is of great significance for the development of advanced nuclear reactors; especially the method of the present invention can realize the large-thickness tube sheet and tube sheet with a thickness of 130 mm. The safe and reliable connection of the pipes can greatly improve the service life and safety of the molten salt reactor heat exchanger, which cannot be realized by the prior art.

Claims (11)

1. anticorrosion superalloy tube-plate connection method, it is characterised in that comprise the following steps：

Step 1, the pore for processing on tube sheet diameter 0.08~0.16mm bigger than tube outer diameter, around described on the upside of tube sheet The machining of drilling is used to placing the U-shaped ring-type feeding groove of solder ring, the internal diameter of U-shaped ring-type feeding groove not less than tube outer diameter+ 1mm, and the U-shaped ring-type feeding groove of connection and pore are set and along the circumferentially equally distributed multiple feed holes of pore；

Step 2, pipe is passed through into pore and causes pipe lower end to protrude tube sheet underside plan, tube sheet then is protruded to pipe lower end The part of underside plan carries out tube expansion so that tube outer diameter maximum is bigger 0.5mm than pore diameter after tube expansion, finally by under pipe Side pressure enters pore, makes pipe lower end until concordant with tube sheet underside plan；

Step 3, fusion welds are carried out to junction on the downside of pipe lower end and tube sheet, weld penetration is not less than the wall thickness of pipe；

Step 4, carry out vacuum brazing after inserting solder ring in the U-shaped ring-type feeding groove.

2. tube-plate connection method as claimed in claim 1, it is characterised in that the material of the solder ring is golden nickel alloy.

3. tube-plate connection method as claimed in claim 2, it is characterised in that the quality proportioning of the golden nickel alloy is 82%Au And 18%Ni.

4. tube-plate connection method as claimed in claim 3, it is characterised in that the technological parameter of the vacuum brazing is specific such as Under：The vacuum 10 of vacuum brazing^-2More than pa, programming rate is not more than 10 DEG C/min, 900 DEG C of insulation 20min of pilot process, pricker 1000~1020 DEG C, 20~60min of soaking time of temperature is welded, less than 400 DEG C are down to the rate of temperature fall no more than 5 DEG C/min Come out of the stove after temperature.

5. tube-plate connection method as claimed in claim 1, it is characterised in that add in advance around the pore on the downside of tube sheet Work has the U-shaped ring groove for reducing fusion welds stress, and the internal diameter of the U-shaped ring groove is not less than+2 times of tube walls of tube outer diameter Thickness, U-shaped ring groove width are not less than pipe wall thickness, and U-shaped ring groove depth is not less than pipe wall thickness.

6. tube-plate connection method as claimed in claim 1, it is characterised in that the axis of the feed hole and tube bore axis it Between into 30 ° of angles.

7. tube-plate connection method as claimed in claim 1, it is characterised in that using hard alloy pressure head to pipe in step 2 The part that lower end protrudes tube sheet underside plan carries out hydraulic expanding tube, and pipe lower end then is pressed into pore using hydraulic press.

8. tube-plate connection method as claimed in claim 1, it is characterised in that the fusion welds are argon tungsten-arc welding, its work Skill parameter is specific as follows：The flow of argon gas is 15L/min, electrode to workpiece distance 1mm, welding current 45A, speed of welding 10mm/s。

9. tube-plate connection method as claimed in claim 1, it is characterised in that the anticorrosion superalloy is used for MSR Nickel base superalloy.

10. tube-plate connection method as claimed in claim 9, it is characterised in that the MSR is with nickel base superalloy Hastelloy N alloys or GH3535 alloys.

11. a kind of anticorrosion superalloy heat exchanger, including one group of pipe being connected with tube sheet, it is characterised in that the tube sheet It is connected with pipe by the connection method of any one of claim 1~10.