CN113188929B - A method for testing the impact strength of metal welded pipe fitting joints - Google Patents

Abstract

A method for testing the impact strength of a metal welding pipe fitting joint comprises a first constant magnetic field coil and a second constant magnetic field coil, wherein the first constant magnetic field coil and the second constant magnetic field coil are used for generating a radial constant magnetic field at the end part of the metal welding pipe fitting to be tested; first and second pulsed magnetic field coils for generating induced eddy currents at ends of the metal welding pipe fitting to be tested; first and second ring-shaped yokes for constituting a constant magnetic field magnetic circuit; the sections of the first and the second ring-shaped magnetic yokes are rectangular frame-shaped with gaps; annular through grooves are formed in the middle of the first pulse magnetic field coil and the second pulse magnetic field coil; the annular through groove type annular magnetic yoke is provided with a gap corresponding to the gap; the upper end of the upper half part of the metal welding pipe fitting to be tested is positioned in the gap of the first annular magnetic yoke; the lower end of the lower half part of the metal welding pipe fitting to be tested is positioned in the gap of the second annular magnetic yoke. The invention can provide uniform unidirectional stretching pulse electromagnetic force for the metal welding pipe fitting to be tested; meanwhile, by changing the pulse width of electromagnetic force, loading with different strain rates can be realized.

Description

A method for testing the impact strength of metal welded pipe fitting joints

Technical field

The invention belongs to the field of metal material testing, and specifically relates to a method for testing the impact strength of metal welded pipe fitting joints. It is mainly used for testing the impact strength of metal welded pipe fitting joints.

Background technique

The quality of metal welded pipe joints directly affects the mechanical properties of the entire component, and the unidirectional tensile impact strength test can verify its impact strength. However, in the existing unidirectional tensile test, mechanical force loading is used, which has the following problems: stress concentration exists at the mechanical clamping force application point, which will affect the unidirectional tensile test results; the loading speed is slow, which belongs to quasi-static loading and cannot simulate the unidirectional tensile impact strength under high strain rate.

The Chinese patent "A method for stretching large-size metal welded pipe fittings (CN 106424176 A)" discloses a method for stretching large-size metal welded pipe fittings. During the tightening process, it is not easy to deform the parts of the metal welded pipe fittings that do not have auxiliary grooves. However, mechanical loading inevitably causes stress concentration at the clamping point.

The Chinese patent "Carbon Fiber Reinforced Resin-based Thin-walled Composite Pipe Fittings Tensile Properties Test Method (CN105403457B)" discloses a carbon fiber reinforced resin-based thin-walled composite pipe fittings tensile properties test method, which uses adhesive connection technology instead of mechanical connection technology to prepare carbon fiber reinforced resin-based thin-walled composite pipe fittings mechanical tensile test pieces, and designs a transfer fixture to clamp the tensile test piece on the mechanical testing machine, and then loads the tensile test piece, and finally obtains the breaking load and corresponding deformation value. This invention solves the problem that the existing carbon fiber reinforced resin-based composite pipe mechanical properties test method is not suitable for thin-walled composite pipe fittings. By adopting a new tensile test piece preparation method, it avoids the problem of metal joints damaging pipe fittings due to mechanical connection, and provides a new test method for carbon fiber thin-walled composite pipe fittings. However, this method is only applicable to carbon fiber materials, not to metal welded pipe fittings.

The Chinese patent "An electromagnetic impact dynamic tensile test method and device (CN 102109436 B)" provides an electromagnetic impact dynamic tensile test method and device. The tensile specimen is passed through the center hole of the electromagnetic pulse device. The electromagnetic pulse The device excites a strong pulse magnetic field and generates electromagnetic force between the target and the electromagnetic pulse coil, so that the tensile specimen installed between the target and the bracket obtains direct instantaneous tension, completing the dynamic tensile test of the tensile specimen. . However, this method is not suitable for applying electromagnetic force to metal welded pipe fittings.

Contents of the invention

In order to solve the above technical problems, the present invention provides a device and method for testing the impact strength of metal welded pipe fittings joints, which can provide uniform unidirectional tensile pulse electromagnetic force for the metal welded pipe fittings to be tested; because there are no clamping points, There is no stress concentration at the clamping point; at the same time, by changing the pulse width of the electromagnetic force, loading at different strain rates can be achieved.

The technical solutions adopted by the present invention are:

A device for testing the impact strength of metal welded pipe fitting joints, including:

A first constant magnetic field coil and a second constant magnetic field coil for generating a radial constant magnetic field at the end of the metal welded pipe to be tested;

A first pulse magnetic field coil and a second pulse magnetic field coil used to generate induced eddy currents at the end of the metal welded pipe fitting to be tested;

A first annular magnetic yoke and a second annular magnetic yoke for forming a constant magnetic field magnetic circuit;

The first and second ring-shaped magnetic yokes include a cavity, and the cross-sections of the first and second ring-shaped magnetic yokes are rectangular frames with gaps, the gaps of the first ring-shaped magnetic yoke are opened at the bottom, and the gaps of the second ring-shaped magnetic yoke are opened at the top;

The first constant magnetic field coil is located at the upper part of the first ring-shaped magnetic yoke cavity, and the second constant magnetic field coil is located at the lower part of the second ring-shaped magnetic yoke cavity; the constant magnetic field coil is connected to a DC power supply;

The first pulse magnetic field coil is located at the lower part of the first annular yoke cavity, and the second pulse magnetic field coil is located at the upper part of the second annular yoke cavity; the pulse magnetic field coil is connected to a pulse power supply;

An annular through groove is provided in the middle of the first and second pulse magnetic field coils; the annular through grooves of the first and second pulse magnetic field coils correspond to the gaps provided in the first and second ring-shaped magnetic yokes respectively;

The upper end of the upper half of the metal welded pipe fitting to be tested is located in the gap of the first annular yoke; the lower end of the lower half of the metal welded pipe fitting to be tested is located in the gap of the second annular yoke.

The inner annular edge of the gap of the first annular yoke is 0.2-0.5 mm smaller than the inner diameter of the upper half of the metal welded pipe fitting to be tested, and the outer annular edge of the gap of the first annular yoke is smaller than the inner diameter of the upper half of the metal welded pipe fitting to be tested. The outer diameter is 0.2-0.5mm larger; the inner annular edge of the gap of the second annular yoke is 0.2-0.5mm smaller than the inner diameter of the lower half of the metal welded pipe fitting to be tested, and the outer annular edge of the gap of the second annular yoke It is 0.2-0.5mm larger than the outer diameter of the lower half of the metal welded pipe fitting to be tested.

The first and second ring-shaped yokes are made of insulating silicon steel sheets with a thickness of 0.2 mm.

The inner annular edge of the annular slot of the first pulse magnetic field coil is 0.2-0.5mm smaller than the inner diameter of the upper part of the metal welding pipe to be tested, and the outer annular edge of the gap of the annular slot of the first pulse magnetic field coil is smaller than the inner diameter of the metal welding pipe to be tested. The outer diameter of the upper half of the pipe is 0.2-0.5mm larger; the inner annular edge of the annular slot of the second pulse magnetic field coil is 0.2-0.5 mm smaller than the inner diameter of the lower half of the metal welded pipe to be tested. The outer annular edge of the gap of the annular groove is 0.2-0.5mm larger than the outer diameter of the lower half of the metal welded pipe fitting to be tested.

The ratio of the number of turns of the first pulse magnetic field coil to the number of turns of the second pulse magnetic field coil is equal to the ratio of the inner diameter of the lower half of the metal welded pipe fitting to be tested to the inner diameter of the upper half of the metal welded pipe fitting to be tested.

A method for testing the impact strength of metal welded pipe fitting joints,

The first constant magnetic field coil is placed in the upper region of the cavity of the first annular magnetic yoke, and the second constant magnetic field coil is placed in the lower region of the cavity of the second annular magnetic yoke; the first pulsed magnetic field coil is placed inside the first annular magnetic yoke, and the annular groove of the first pulsed magnetic field coil is aligned with the gap of the first annular magnetic yoke; the second pulsed magnetic field coil is placed inside the second annular magnetic yoke, and the annular groove of the second pulsed magnetic field coil is aligned with the gap of the second annular magnetic yoke;

The upper end of the upper half of the metal welded pipe to be tested is placed in the gap of the first annular magnetic yoke, and the lower end of the lower half of the metal welded pipe to be tested is placed in the gap of the second annular magnetic yoke;

The central axes of the first constant magnetic field coil, the first pulsed magnetic field coil, the metal welded pipe fitting to be tested, the second constant magnetic field coil, the second pulsed magnetic field coil, the first annular magnetic yoke, and the second annular magnetic yoke coincide with each other;

A DC power supply is used to supply power to the first and second constant magnetic field coils connected in series to generate a radial constant magnetic field in the gap of the annular yoke;

A pulse power supply is used to supply power to the first and second pulse magnetic field coils connected in series to generate a pulse current and a changing magnetic field. The changing magnetic field generates circumferential induced eddy currents in the metal welded pipe fittings to be tested;

The radial constant magnetic field interacts with the circumferential induced eddy current to generate axial pulse electromagnetic force;

The upper end of the upper half of the metal welded pipe fitting to be tested is subjected to an upward axial electromagnetic force. At the same time, the lower end of the lower half of the metal welded pipe fitting to be tested is subjected to a downward axial electromagnetic force, completing the impact strength test of the welded joint.

The radially outward constant magnetic field interacts with the clockwise circumferentially induced eddy current to produce an upward axial electromagnetic force; or the radially inward constant magnetic field interacts with the counterclockwise circumferentially induced eddy current to produce an upward axial electromagnetic force. .

The radially outward constant magnetic field interacts with the counterclockwise circumferentially induced eddy current to produce a downward axial electromagnetic force; or the radially inward constant magnetic field interacts with the clockwise circumferentially induced eddy current to produce a downward axial electromagnetic force. Electromagnetic force.

Adjusting the pulse current of the pulse magnetic field coil can achieve loading of different electromagnetic forces and strain rates.

The present invention is a device and method for testing the impact strength of metal welded pipe fitting joints. The advantages are:

1. It can provide uniform unidirectional tensile pulse electromagnetic force for the metal welded pipe fittings to be tested;

2. Because there are no clamping points, there is no stress concentration at the clamping points;

3. At the same time, by changing the pulse width of the electromagnetic force, loading of different strain rates can be achieved.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and examples:

Figure 1 is a 2/3 cross-sectional view of the device used to test the impact strength of metal welded pipe fitting joints.

Figure 2 is a schematic diagram of the pulse current of the pulse magnetic field coil.

in:

1.1-the first constant magnetic field coil, 1.2-the second constant magnetic field coil;

2.1-the first pulse magnetic field coil, 2.2-the second pulse magnetic field coil; 2.3-the annular through slot of the first pulse magnetic field coil; 2.4-the annular through slot of the second pulse magnetic field coil.

3.1-The first ring-shaped yoke, 3.2-The second ring-shaped yoke; 3.3-Gap;

4- Pulse power supply;

5-DC power supply;

6.1-The upper part of the metal welded pipe fitting to be tested, 6.2-The lower part of the metal welded pipe fitting to be tested, 6.3-Welded joint; 7-Pulse current of the pulse magnetic field coil.

Detailed ways

A device for testing the impact strength of a metal welded pipe joint, comprising:

The first constant magnetic field coil 1.1 and the second constant magnetic field coil 1.2 used to generate a radial constant magnetic field at the end of the metal welded pipe to be tested;

The first pulse magnetic field coil 2.1 and the second pulse magnetic field coil 2.2 used to generate induced eddy current at the end of the metal welded pipe fitting to be tested;

The first annular yoke 3.1 and the second annular yoke 3.2 are used to form a constant magnetic field magnetic circuit.

The first and second annular magnetic yokes include a cavity. The cross-section of the first and second annular magnetic yokes is in the shape of a rectangular frame with a gap. The gap of the first annular magnetic yoke 3.1 is opened below, and the second annular magnetic yoke 3.1 has a gap at the bottom. The gap of yoke 3.2 is opened at the top;

The first constant magnetic field coil 1.1 is located at the upper part of the cavity of the first annular magnetic yoke 3.1, and the second annular magnetic yoke 3.2 is located at the lower part of the cavity of the first annular magnetic yoke 3.1; the constant magnetic field coil is connected to a DC power supply 5; the first and second constant magnetic field coils have consistent geometric parameters and are connected in series to be provided with DC current by a DC power supply 5.

The first pulse magnetic field coil 2.1 is located at the lower part of the cavity of the first annular yoke 3.1, and the second pulse magnetic field coil 2.2 is located at the upper part of the cavity of the second annular yoke 3.2; the pulse magnetic field coil is connected to the pulse power supply 4. The first and second pulse magnetic field coils are connected in series, and the pulse power supply 4 provides pulse current.

The first constant magnetic field coil is a traditional coil, wound by copper wire, and its geometric size is limited to being able to simultaneously place the first constant magnetic field coil and the first pulse magnetic field coil inside the rectangular frame cavity of the first annular yoke 3.1.

The second constant magnetic field coil is a traditional coil, wound by copper wire, and its geometric size is limited to being able to be placed inside the rectangular frame cavity of the second ring-shaped yoke 3.2 at the same time as the second pulsed magnetic field coil.

The first pulse magnetic field coil is a traditional coil, wound by copper wire, and its geometric size is limited to being able to simultaneously place the first constant magnetic field coil inside the rectangular frame cavity of the first annular yoke 3.1.

The second pulsed magnetic field coil is a conventional coil wound with copper wire, and its geometric dimensions are limited to being placed inside the rectangular frame-type cavity of the second annular magnetic yoke 3.2 together with the second constant magnetic field coil.

Pulse power supply 4 uses a pulse capacitor of 100uF.

The DC power source 5 adopts a 400V DC battery.

An annular through slot is provided in the middle of the first and second pulse magnetic field coils; the annular through slots of the first and second pulse magnetic field coils respectively correspond to the gaps provided by the first and second annular yokes.

The upper end of the upper half 6.1 of the metal welded pipe fitting to be tested is located in the gap of the first annular yoke 3.1; the lower end of the lower half 6.2 of the metal welded pipe fitting to be tested is located in the gap of the second annular yoke 3.2.

The annular edge inside the gap of the annular yoke is 0.2-0.5mm smaller than the inner diameter of the metal welded pipe to be tested, and the annular edge outside the gap of the annular yoke is 0.2-0.5mm larger than the outer diameter of the metal welded pipe to be tested.

There is an annular through slot in the middle of the first pulse magnetic field coil to reserve axial space for the upper half of the metal welded pipe fitting 6.1 to be tested when it is stretched upward. At the same time, because the annular through slot is located in the middle of the winding of the first pulse magnetic field coil, so The radial electromagnetic force can be reduced as much as possible; the annular slot in the middle of the second pulse magnetic field coil is to reserve axial space for the lower half 6.2 of the metal welded pipe to be tested when it is stretched downward, and because the annular slot is located The middle part of the winding of the second pulse magnetic field coil can reduce the radial electromagnetic force as much as possible.

The upper end of the upper half 6.1 of the metal welded pipe fitting to be tested is located in the gap of the first annular yoke 3.1; the lower end of the lower half 6.2 of the metal welded pipe fitting to be tested is located in the gap of the second annular yoke 3.2. This is to make it The radial constant magnetic field is large enough to generate sufficient axial electromagnetic force; "The inner annular edge of the gap of the annular yoke is 0.2-0.5mm smaller than the inner diameter of the metal welded pipe fitting to be tested, and the outer annular edge of the gap of the annular yoke is smaller than the inner diameter of the metal welded pipe fitting to be tested. The outer diameter of the metal welded pipe fittings to be tested is 0.2-0.5mm larger" so that the metal welded pipe fittings to be tested have enough moving space within the gap without contact or friction.

The first and second ring-type yokes are made of insulating silicon steel sheets with a thickness of 0.2 mm. There can be no induced eddy current in the first and second ring-shaped yokes, thus reducing losses. If the silicon steel sheet is too thin, the cost will increase, and if it is too thick, the loss will increase.

The inner annular edge of the annular groove is 0.2-0.5 mm smaller than the inner diameter of the metal welded pipe fitting to be tested, and the outer annular edge of the gap of the annular yoke is 0.2-0.5 mm larger than the outer diameter of the metal welded pipe fitting to be tested. In order to ensure that the metal welded pipe fittings to be tested have enough moving space within the gap, there will be no contact and no friction.

In order to ensure that the downward axial electromagnetic force and the upward axial electromagnetic force are equal in magnitude and opposite in direction, the ratio of the number of turns of the first pulse magnetic field coil 2.1 to the number of turns of the second pulse magnetic field coil 2.2 is equal to the ratio of the inner diameter of the lower half 6.2 of the metal welded pipe to be tested to the inner diameter of the upper half 6.1 of the metal welded pipe to be tested.

A method for testing the impact strength of a metal welded pipe joint, wherein a first constant magnetic field coil 1.1 is placed in the upper region of a cavity of a first annular magnetic yoke 3.1, and a second constant magnetic field coil 1.2 is placed in the lower region of a cavity of a second annular magnetic yoke 3.2; a first pulse magnetic field coil 2.1 is placed inside the first annular magnetic yoke 3.1, and its annular groove is aligned with the gap of the first annular magnetic yoke 3.1; a second pulse magnetic field coil 2.2 is placed inside the second annular magnetic yoke 3.2, and its annular groove is aligned with the gap of the second annular magnetic yoke 3.2;

Place the upper end of the upper half 6.1 of the metal welded pipe fitting to be tested in the gap of the first annular yoke 3.1, and place the lower end of the lower half 6.2 of the metal welded pipe fitting to be tested in the gap of the second annular yoke 3.2;

The first constant magnetic field coil 1.1, the first pulse magnetic field coil 2.1, the upper half of the metal welded pipe fitting to be tested 6.1, the welding joint 6.3, the lower half of the metal welded pipe fitting to be tested 6.2, the second pulse magnetic field coil 2.2, the first The pulse magnetic field coils 2.1 are arranged in sequence from top to bottom; and their central axes coincide;

A DC power supply is used to supply power to the first and second constant magnetic field coils connected in series to generate a radial constant magnetic field in the gap of the annular yoke;

A pulse power supply is used to supply power to the first and second pulse magnetic field coils connected in series, generating a pulse current and a changing magnetic field, and the changing magnetic field generates a circular induced eddy current in the metal welded pipe to be tested;

The radial constant magnetic field interacts with the circumferential induced eddy current to generate axial pulse electromagnetic force;

The upper end of the upper half 6.1 of the metal welded pipe fitting to be tested is subjected to an upward axial electromagnetic force. At the same time, the lower end of the lower half 6.2 of the metal welded pipe fitting to be tested is subjected to a downward axial electromagnetic force, completing the impact strength test of the welded joint 6.3.

The radially outward constant magnetic field interacts with the clockwise circumferentially induced eddy current to produce an upward axial electromagnetic force; or the radially inward constant magnetic field interacts with the counterclockwise circumferentially induced eddy current to produce an upward axial electromagnetic force. . F=J×B, the direction is determined by the left-hand rule.

The radially outward constant magnetic field interacts with the counterclockwise circumferentially induced eddy current to produce a downward axial electromagnetic force; or the radially inward constant magnetic field interacts with the clockwise circumferentially induced eddy current to produce a downward axial electromagnetic force. Electromagnetic force. F=J×B, the direction is determined by the left-hand rule.

Adjusting the pulse current of the pulse magnetic field coil can achieve loading of different electromagnetic forces and strain rates. F=J×B. The magnitude of the axial electromagnetic force experienced by the metal welded pipe to be tested is determined by the radial constant magnetic field and the circumferential induced eddy current. At this time, adjusting the pulse current size of the pulse magnetic field coil can change the axial electromagnetic force on the metal welded pipe to be tested, thereby realizing the loading of different electromagnetic forces; adjusting the pulse current pulse width of the pulse magnetic field coil can change the size of the axial electromagnetic force to be tested. The pulse width of the axial electromagnetic force experienced by the metal welded pipe fittings achieves strain rate loading;

Example:

As shown in FIG1 , the first constant magnetic field coil 1.1 is placed in the upper region of the cavity of the first annular magnetic yoke 3.1, and the second constant magnetic field coil 1.2 is placed in the lower region of the cavity of the second annular magnetic yoke 3.2;

Place the first pulse magnetic field coil 2.1 in the lower area of the cavity of the first annular yoke 3.1, and align its annular slot with the gap of the first annular yoke 3.1;

Place the second pulse magnetic field coil 2.2 inside the second annular yoke 3.2, and align its annular slot with the gap of the second annular yoke 3.2;

Place the upper end of the upper half 6.1 of the metal welded pipe fitting to be tested in the gap of the first annular yoke 3.1, and place the lower end of the lower half 6.2 of the metal welded pipe fitting to be tested in the gap of the second annular yoke 3.2;

The first constant magnetic field coil 1.1, the first pulse magnetic field coil 2.1, the upper half of the metal welded pipe fitting to be tested 6.1, the welding joint 6.3, the lower half of the metal welded pipe fitting to be tested 6.2, the second pulse magnetic field coil 2.2, the first pulse The magnetic field coils 2.1 are arranged in sequence from top to bottom; and their central axes coincide;

A DC power supply is used to power the first and second constant magnetic field coils connected in series, generating a radial constant magnetic field in the gap of the annular magnetic yoke; a pulse power supply is used to power the first and second pulse magnetic field coils connected in series, generating a pulse current 7 and a changing magnetic field, and the changing magnetic field generates annular induced eddy currents in the metal welded pipe to be tested; the radial constant magnetic field interacts with the annular induced eddy currents to generate an axial pulse electromagnetic force; the upper end of the upper part 6.1 of the metal welded pipe to be tested is subjected to an upward axial electromagnetic force, and at the same time, the lower end of the lower part 6.2 of the metal welded pipe to be tested is subjected to a downward axial electromagnetic force, thereby completing the impact strength test of the welded joint 6.3.

Impact strength refers to the maximum load that the metal welded pipe to be tested can withstand under impact load, and the weakest link of the metal welded pipe to be tested is the welding joint; therefore, in this method, pulse electromagnetic force is applied to both ends of the metal welded pipe to be tested, and the maximum electromagnetic force that its welding joint can withstand is observed to determine its impact strength.

Claims (4)

1. A method for testing the impact strength of metal welded pipe joints, characterized by: placing the first constant magnetic field coil (1.1) in the upper area of the cavity of the first annular yoke (3.1), and placing the second constant magnetic field coil The magnetic field coil (1.2) is placed in the lower area of the cavity of the second ring-shaped magnetic yoke (3.2); the first pulse magnetic field coil (2.1) is placed inside the first ring-shaped magnetic yoke (3.1), and the first pulse magnetic field coil is placed inside the first ring-shaped magnetic yoke (3.1). The annular slot (2.3) of the coil is aligned with the gap of the first annular yoke (3.1); place the second pulse magnetic field coil (2.2) inside the second annular yoke (3.2), and make the second pulse The annular slot (2.4) of the magnetic field coil is aligned with the gap of the second annular yoke (3.2); the gap of the first annular yoke (3.1) is opened below, and the gap of the second annular yoke (3.2) is opened on the top; place the upper end of the upper half of the metal welded pipe fitting to be tested (6.1) in the gap of the first annular yoke (3.1), and place the lower end of the lower half of the metal welded pipe fitting to be tested (6.2) in the second Within the gap of the ring yoke (3.2); The central axes of the first constant magnetic field coil (1.1), the first pulsed magnetic field coil (2.1), the upper half of the metal welded pipe to be tested (6.1), the welded joint (6.3), the lower half of the metal welded pipe to be tested (6.2), the second pulsed magnetic field coil (2.2), the second constant magnetic field coil (1.2), the first annular magnetic yoke (3.1), and the second annular magnetic yoke (3.2) coincide with each other, and the first constant magnetic field coil (1.1), the first pulsed magnetic field coil (2.1), the upper half of the metal welded pipe to be tested (6.1), the welded joint (6.3), the lower half of the metal welded pipe to be tested (6.2), the second pulsed magnetic field coil (2.2), and the second constant magnetic field coil (1.2) are arranged in sequence from top to bottom; The ratio of the number of turns of the first pulse magnetic field coil (2.1) to the number of turns of the second pulse magnetic field coil (2.2) is equal to the inner diameter of the lower half (6.2) of the metal welded pipe fitting to be tested and the upper half of the metal welded pipe fitting to be tested. Ratio of inner diameter of part (6.1); A DC power supply is used to supply power to the first and second constant magnetic field coils connected in series to generate a radial constant magnetic field in the gap of the annular yoke; A pulse power supply is used to supply power to the first and second pulse magnetic field coils connected in series to generate a pulse current and a changing magnetic field. The changing magnetic field generates circumferential induced eddy currents in the metal welded pipe fittings to be tested; The radial constant magnetic field interacts with the circumferential induced eddy current to generate axial pulse electromagnetic force; The upper end of the upper half of the metal welded pipe fitting to be tested (6.1) is subjected to an upward axial electromagnetic force. At the same time, the lower end of the lower half of the metal welded pipe fitting to be tested (6.2) is subjected to a downward axial electromagnetic force, completing the welded joint (6.3 ) Impact strength test. 2. According to claim 1, a method for testing the impact strength of metal welded pipe joints is characterized in that: a radially outward constant magnetic field and a clockwise annular induced eddy current act to generate an upward axial electromagnetic force; or a radially inward constant magnetic field and a counterclockwise annular induced eddy current act to generate an upward axial electromagnetic force. 3. A method for testing the impact strength of metal welded pipe joints according to claim 1, characterized in that: the radial outward constant magnetic field and the counterclockwise circumferential induced eddy current generate downward axial electromagnetic force. force; or the interaction between the radially inward constant magnetic field and the clockwise circumferential induced eddy current produces a downward axial electromagnetic force. 4. A method for testing the impact strength of metal welded pipe joints according to claim 1, characterized in that: adjusting the pulse current of the pulse magnetic field coil can realize the loading of different electromagnetic forces and strain rates.