CN110508909B

CN110508909B - Welding system and method for stainless steel pipe butt joint automatic superposition pulse single-pass welding

Info

Publication number: CN110508909B
Application number: CN201910727448.6A
Authority: CN
Inventors: 赛鹏; 孙国辉; 王莉; 杨云丽; 张海梅; 王恩泽; 王舒伟; 崔建龙; 隋旭
Original assignee: Harbin Electric Group Qinhuangdao Heavy Equipment Co Ltd
Current assignee: Harbin Electric Group Qinhuangdao Heavy Equipment Co Ltd
Priority date: 2019-08-07
Filing date: 2019-08-07
Publication date: 2021-07-09
Anticipated expiration: 2039-08-07
Also published as: CN110508909A

Abstract

The invention provides a welding system and a welding method for stainless steel pipe butt joint automatic superposition pulse single-pass welding. The system comprises a stainless steel butt joint pipe and a TIG welding machine; during welding, the end parts of the sleeve and the connecting piece and the inner diameter of the melting ring are processed and cleaned; assembling the sleeve, the connecting piece and the melting ring, and performing spot welding; and after the welding equipment is installed and debugged, setting welding parameters and implementing welding. The welding system and the method for the automatic pulse superposition single-pass welding of the butt joint of the stainless steel pipes can effectively realize the effective welding between the sleeve pipe of the electric heater and the connecting piece under the conditions that the electric heaters of the voltage stabilizer are dense, the distance between the pipes is small and the welding operation space is small; the method can also avoid the condition that the workpiece and the tungsten electrode are overheated for a long time, so that the welding process is stable, and good welding seam forming and welding quality can be obtained.

Description

Welding system and method for stainless steel pipe butt joint automatic superposition pulse single-pass welding

Technical Field

The invention relates to the field of welding, in particular to a welding method, specifically relates to a superimposed pulse single-pass automatic welding method for stainless steel pipe butt joint, and particularly relates to an automatic welding method for an electric heater sleeve and a connecting piece with low S (sulfur) content of a voltage stabilizer.

Background

In a nuclear power station, the welding of a sleeve and a connecting piece of an electric heater of a voltage stabilizer is a unique structure of the product. The product sets up four rings of 108 electric heaters altogether, and the interval is little between the pipe, only about 80mm, and the welding operation space is narrow and small, can't adopt filler wire welding, can only adopt the autogenous fusion to realize the two-sided shaping of single-side welding, and this welding seam needs weld in horizontal welding position.

According to the design requirement of the voltage stabilizer, the welding seam is qualified through PT and RT detection after butt welding, and meanwhile, the welding seam forming requirement is harsh. In the welding process, good fusion of the welding line is ensured, the sizes of the outer concave part and the inner convex part of the welding line are required to be controlled, the welding difficulty is high, and the quality requirement is high. However, the content of S in the stainless steel pipe is very low, so that the conventional pulse single-pass automatic welding cannot meet the penetration requirement.

Based on the difficulties, the inventor researches the existing stainless steel pipe welding technology so as to design a welding method which has high welding efficiency, stable welding process and good fusion of welding seams, and the sizes of the inner surface and the outer surface of each welding seam meet the use requirements. Therefore, the invention provides a welding system and a welding method for stainless steel pipe butt joint automatic superposition pulse single pass welding.

Disclosure of Invention

In order to solve the above problems, the present inventors have conducted intensive studies and, as a result, have found that: the austenitic stainless steel butt joint pipe can be welded by adopting specific welding parameters through a TIG welding machine, electric arcs with good compression and straightness can be generated after a specific tungsten electrode and a welding method are selected, the workpiece and the tungsten electrode can be prevented from being in an overheated state for a long time under the condition of ensuring the penetration of a welding seam, the welding process is stable, and good welding seam forming and welding quality is obtained, so that the invention is completed.

The object of the present invention is to provide the following:

in a first aspect, the invention provides a welding method for stainless steel pipe butt joint automatic superposition pulse single pass welding, which comprises the following steps:

(1) processing and cleaning the end parts of the sleeve and the connecting piece and the inner diameter of the melting ring;

(2) assembling the sleeve, the connecting piece and the melting ring, and performing spot welding;

(3) and after the welding equipment is installed and debugged, setting welding parameters and implementing welding.

Wherein, in the step (2), the melting ring is clamped between the sleeve and the connecting piece and fixed for spot welding.

Further, in the step (3), the welding apparatus is a TIG welder in which a tungsten electrode is provided;

the tungsten electrode comprises a tungsten electrode rod, a tungsten electrode end cone and a tip platform arranged on the tungsten electrode end cone.

Preferably, in step (3),

the diameter of the tungsten electrode rod is 2-2.8 mm, preferably 2.2-2.6 mm;

the taper angle of the end cone of the tungsten electrode is 25-40 degrees, preferably 28-38 degrees;

the diameter of the tip platform is 0.1-0.5 mm, preferably 0.2-0.4 mm.

Further, in the step (3), the distance from the tungsten tip to the outer wall of the tube in the welding area is 1.0 to 2.0mm, and more preferably 1.3 to 1.7 mm.

In the step (3), the base current is 40-45A, the peak current is 70-75A, and the superposed current is 90-110A;

the base value time/peak value time is 250-400 ms, preferably 280-350 ms; the superposition time is 90-110 ms;

the welding voltage is 17-20V.

Wherein, in the step (3), the front protective gas is helium, the flow rate of the front protective gas is 10-35L/min, and preferably 12-30L/min;

the back protective gas is argon, and the flow of the back protective gas is 10-45L/min, preferably 15-40L/min.

In a second aspect, the invention also provides an automatic pulse superposition single-pass welding system for stainless steel pipe butt joint, which comprises a stainless steel butt joint pipe, a melting ring and a TIG welding machine;

the stainless steel butt joint pipe comprises a sleeve and a connecting piece which are in butt joint assembly, and the melting ring is arranged between the sleeve and the connecting piece;

the inner walls of the end parts of the sleeve and the connecting piece are circumferentially sunken to ensure that the inner diameters of the end parts of the sleeve and the connecting piece are phi_{Inner part}24-28 mm, preferably phi_{Inner part}25-27 mm, most preferably 26 mm;

the inner diameter of the melting ring being phi_{Inner part}27.5～28mm；

The thickness of the melting ring is 0.4-0.6 mm, preferably 0.5 mm.

Further, the TIG welder includes the tungsten utmost point, the tungsten utmost point includes tungsten utmost point pole, tungsten utmost point end cone and sets up the tip platform on the tungsten utmost point end cone.

Preferably, the system further comprises a positioning tool.

According to the welding system and the method for the stainless steel pipe butt joint automatic superposition pulse single-pass welding, which are provided by the invention, the following beneficial effects are achieved:

(1) the welding system and the method provided by the invention realize the tube butt joint of the stainless steel Z2CND18-12NS material with very low S content, and the melting ring with specific material and size is used as the tube butt joint filling material, thereby effectively ensuring the weld quality and formation under the applicable welding parameters;

(2) the welding system and the method provided by the invention adopt the pulse superposition automatic TIG welding process, pulse is superposed on the basis of normal TIG welding to generate electric arc with good compression and straightness, and the welding system and the method can avoid the situation that the workpiece and tungsten are in an overheated state for a very long time under the condition of ensuring the penetration of a welding seam, can carry out programming control on welding parameters and a welding process, have stable welding process and can obtain good welding seam forming and welding quality;

(3) the welding system and the welding method provided by the invention can realize effective welding between the sleeve pipe of the electric heater and the connecting piece under the conditions that the electric heaters of the voltage stabilizer are dense, the distance between the pipes is small and the welding operation space is small;

(4) the welding system and the method provided by the invention can be used for butt welding the sleeve and the connecting piece, can achieve good weld joint forming and weld joint fusion, and meet the welding quality requirement of an electric heater of a voltage stabilizer product.

Drawings

FIG. 1 shows a schematic structural view of a preferred embodiment of a sleeve, a melt ring and a joint of a workpiece to be welded;

FIG. 2 shows a schematic structural view of a preferred embodiment tungsten electrode;

FIG. 3 is a schematic structural diagram of a positioning tool in accordance with a preferred embodiment;

fig. 4 shows a schematic structural diagram of a base in the positioning tool according to a preferred embodiment.

The reference numbers illustrate:

1-sleeve

2-melting ring

3-connecting piece

4-tungsten pole

5-tungsten electrode tip cone

6-tip platform

11-locking screw

12-pressing plate

13-Stent

14-base

15-hook

16-welding window

Detailed Description

The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention, as illustrated in the accompanying drawings.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

The present invention is described in detail below.

In a nuclear power station, the requirement on butt welding of a sleeve of an electric heater of a voltage stabilizer and a connecting piece is very high, the sunken depth of the outer wall of a welding line is not more than 0.5mm, and the raised height of the inner wall is not more than 1.5mm when the welding line is qualified through PT (liquid permeation detection) and RT (ray detection).

The sleeve 1 and the connecting piece 3 are tubular and made of austenitic stainless steel, preferably nitrogen-controlled stainless steel, more preferably nitrogen-controlled stainless steel Z2CND18-12 NS.

Other workpieces are also accommodated in the tubular spaces of the sleeve 1 and the connecting piece 3, and the inner workpieces are in close proximity to the inner walls of the sleeve 1 and the connecting piece 3. During installation, the sleeve 1 and the connecting piece 3 can be welded and fixed after the internal workpiece is installed. Thermal damage to the inner work piece is easily caused by thermal stresses during welding due to the fact that the inner work piece is located too close to the wall of the sleeve 1 and the connecting piece 3.

In order to facilitate the installation of other workpieces and reduce the heat damage to the internal workpieces when the sleeve 1 and the connecting piece 3 are welded, the inner walls of the end parts of the sleeve 1 and the connecting piece 3 are circumferentially sunken to reduce the thickness of the pipe wall so as to enlarge the internal space of the sleeve 1 and the connecting piece 3 and further accommodate and protect other workpieces in the space.

Preferably, the inner walls of the end portions of the sleeve 1 and the connecting member 3 are circumferentially and smoothly recessed, so that the thickness of the end tube wall of the sleeve 1 and the connecting member 3 gradually decreases towards the end face.

Taking the joint of the sleeve 1 and the connecting piece 3 as a datum line, and forming a welding area of the sleeve 1 and the connecting piece 3 along the positions of two sides of the datum line which are not more than 100mm and not less than 30mm respectively; preferably, the welding area does not exceed 80mm and not less than 20mm on both sides of the reference line.

In the region of the weld, the outer diameters of the sleeve 1 and the connecting piece 3 are Φ_{Outer cover}32.5 mm; inner diameter of phi_{Inner part}24-28 mm, preferably phi_{Inner part}25-27 mm. The inner diameter can meet the use requirements of accommodating and protecting internal workpieces and guaranteeing the stress of the welded pipe wall.

In a preferred embodiment, the outer tube diameter of the welded region between the sleeve 1 and the connecting piece 3 is Φ_{Outer cover}32.5mm, inner diameter of tube is phi_{Inner part}26mm and 3.25mm of wall thickness.

Because of numerous electric heaters in the voltage stabilizer, the welding space of the sleeve 1 and the connecting piece 3 is narrow, and the content of S (sulfur) in the nitrogen-controlled stainless steel Z2CND18-12NS is extremely low, the conventional pulse single-channel automatic welding cannot weld through the stainless steel pipe, and the depression and the protrusion of a welding seam cannot be well controlled.

Based on the above, the invention provides a welding method, which is used for welding the stainless steel pipe in butt joint by automatic superposition pulse single-pass welding; preferably, for welding between stainless steel tubes with a fused ring; in particular for welding between the electric heater sleeve 1 and the connection piece 3 of the pressurizer.

The welding method comprises the following steps:

(1) the end parts of the sleeve 1 and the connecting piece 3 and the inner diameter of the melting ring 2 are processed and cleaned;

(2) assembling the sleeve 1, the connecting piece 3 and the melting ring 2, and performing spot welding;

(3) and after the welding equipment is installed and debugged, setting welding process parameters and implementing welding.

In the welding method provided by the invention, the sleeve 1 and the connecting piece 3 are in butt joint assembly and are fixed by welding, the melting ring 2 is arranged between the sleeve 1 and the connecting piece 3 and is used as a filling material for welding the sleeve 1 and the connecting piece 3, and the sleeve 1 and the connecting piece 3 are in butt joint spot welding fixation, as shown in figure 1.

In the step (1), the first step of the method,

in order to maintain a good fusion of the melting ring 2 and the sleeve 1 with the connection piece 3 during welding, it is preferred that said melting ring 2 is made of ferritic stainless steel, more preferably of Z01CD26-01 ferritic stainless steel, e.g. an annular filler material machined from a rod of this material, depending on the material properties of the sleeve 1 and the connection piece 3. The melting ring 2 made of the material can improve the weld structure and improve the corrosion resistance of the weld.

In addition, after welding, the inner side of the welding seam generally protrudes outwards, and workpieces in the sleeve 1 and the connecting piece 3 can be damaged when the protruding height is high; and the outer side of the welding seam is inwards sunken under the action of gravity, and the strength of the pipe wall can be reduced when the sunken depth is larger.

In order to ensure that the sleeve 1 and the connecting piece 3 are fused well and simultaneously control the height of the bulge and the depth of the recess of the welding line, on one hand, the welding line can meet the use requirement by controlling the inner diameter and the wall thickness of the sleeve 1 and the connecting piece 3; on the other hand, machining and control of the inner diameter, wall thickness and thickness of the melt ring 2 are also required.

Further, the outer diameter of the melting ring 2 is the same as that of the sleeve 1/the connecting piece 3, but the inner diameter is larger, so that the occupation ratio of metal formed by the melting ring 2 in the whole molten pool is reduced, and the penetration effect of a welding seam is ensured.

Preferably, the inner diameter of the melting ring 2 is phi_{Inner part}27.5～28mm。

If the height of the melting ring 2 in the axial direction is taken as the thickness of the melting ring 2, the thickness of the melting ring 2 is 0.4 to 0.6mm, preferably 0.5 mm.

The end faces of the sleeve 1 and the connecting piece 3 are turned flat without processing grooves.

When in welding, the melting ring 2 is clamped between the sleeve 1 and the welding area of the connecting piece 3, which ensures that the welding seam is well fused and improves the welding seam structure. Through the cooperation of the melting ring 2, the sleeve 1 and the connecting piece 3, the operation of conveying welding wires during welding is omitted, the influence of manual operation is reduced, the difficulty of welding operation is reduced, and the control on the welding quality is facilitated.

Before the sleeve 1, the connecting piece 3 and the melting ring 2 are assembled, the welding area of the sleeve 1 and the connecting piece 3 and the whole surface of the melting ring 2 are preferably cleaned, so that the defects of air holes, slag inclusion, incomplete fusion and the like caused by impurities mixed into a welding seam in the welding process are avoided.

The cleaning is strictly performed until the cleaning is performed by dipping the non-woven fabric in acetone for wiping without color change, thereby ensuring the cleaning quality.

Preferably, when cleaning, if there are defects affecting welding such as burrs on the surface of the welding area of the sleeve 1 and the connector 3, the defects are removed by using a file, and then the non-woven fabric dipped in acetone or alcohol is wiped on the inner and outer walls of the sleeve within a range of at least 20mm and the entire surface of the melt ring 2 until the non-woven fabric is not discolored, at which time the welding area is considered to be clean.

In the step (2), the step (c),

when the sleeve 1, the connecting member 3, and the melt ring 2 are assembled, the melt ring 2 is sandwiched and arranged between the sleeve 1 and the connecting member 3.

Preferably, during assembly, the axes of the retaining sleeve 1, the connecting piece 3 and the melting ring 2 are vertically fixed so as to ensure that the three are coaxial, have no misalignment and have no clearance, and ensure the welding quality.

In the invention, the sleeve 1, the connecting piece 3 and the melting ring 2 can be assembled and positioned by adopting a tool. The tool is only required to be used for axial centering and fixing of butt welding of the small-diameter pipe, and a common small-diameter pipe centering device in the prior art can be adopted.

The tooling includes a base and a pressure plate for holding the small diameter pipe to be welded, as well as other related components. The fixture is fixed through a set screw, and the fixture is dismantled after the positioning points are welded.

In a preferred embodiment, the tool is a positioning tool, and as shown in fig. 3, the positioning tool comprises a locking screw 11, a pressure plate 12, a bracket 13, a base 14 and a hook 15.

Wherein the base 14 is a flanged U-shaped structure. The pipe clamp is located U-shaped opening part, and the department of contact with the work piece is fillet structure on base 14, avoids the fish tail pipe.

The U-shaped bottom of the base 14 is not contacted with the pipe, a welding window 16 is arranged on the base, and a welding gun can extend into the tool through the welding window 16 to fix the electric heating element connecting piece 3, the melting ring 2 and the sleeve 1 in a spot welding mode.

Preferably, the base 14 is substantially i-shaped, as shown in fig. 4, the welding window 16 is disposed in the middle of the base 14, and the alignment of the workpieces to be welded can be conveniently observed through the concave portions on the two sides of the base 14, so that the adjustment in time is convenient; and forming a spot welding space and performing spot welding treatment.

Preferably, on one flange of the base 14, the face not in contact with the connector 3/sleeve 1 and close to the bottom of the U is bevelled towards the piece to be welded. The inclined plane is matched with the hook 15, so that the hook 15 is not easy to slide off the base 14.

The other side flange of the base 14 is provided with a slotted structure which is hinged with two supporting legs on the bracket 13.

The support 13 is a two-sided frame structure with a break angle, one side is a flat top structure with two ends recessed inwards, and the other side is two support legs hinged with the flange of the base 14.

Preferably, the flat-top structure with concave ends in the support 13 corresponds to the base 14, and more preferably, the flat-top structure is also substantially i-shaped, so that the alignment degree of the workpieces to be welded can be conveniently observed in the concave parts; and forming a spot welding space and performing spot welding treatment.

The hook 15 is L-shaped, one end of the hook far away from the hook is hinged with the end part of the H-shaped flat top in the bracket 3, the hook is contacted with the inclined surface of the upper flange on the base 14, and when the hook and the locking screw 11 act together, the hook is tightened or loosened to play a role in positioning or disassembling the tool.

Preferably, a locking screw 11, preferably a flat-ended compression screw, is provided in the middle of the i-shaped flat top of the bracket 3.

A pressing plate 12 in the form of a U-shaped groove is arranged at one end of the locking screw 11 close to the pipe, the opening of the U-shaped groove facing the workpiece to be welded. The width of the pressure plate 12 is much smaller than that of the base 14, as shown in fig. 3, the contact part of the pressure plate and the workpiece (the sleeve 1/the connecting piece 3) is of a round-angle structure, so that the pipe can be prevented from being scratched. A threaded hole connected with the locking screw 11 is arranged in the middle of the U-shaped groove, so that the end part of the locking screw 11 is not contacted with a workpiece.

The locking screw 11 connects the bracket 13 and the pressure plate 12 together, and when the locking screw 11 is tightened, the pressure plate 12 is pressed to be in contact with the workpiece, so that the workpiece is fixed.

When the positioning tool is used, the locking screw 11 is loosened, the hook 15 is opened, the side surface of the workpiece is sleeved at the assembled welding position, the hook 15 is closed, the locking screw 11 is fastened until the connecting piece 3, the melting ring 2 and the sleeve 1 do not move on the axis, and at the moment, spot welding is performed for fixation.

The positioning tool forms approximate three-point positioning through a positioning surface on the base 14 and a positioning surface on the pressing plate 12, and the axes of the connecting piece 3, the melting ring 2 and the sleeve 1 are locked on the same central line, so that the positioning of the three parts is realized.

In addition, a spot welding space is formed for spot welding through the concave parts arranged on the base 14 and the bracket 13, and three large spot welding spaces are formed at the distribution position of approximately 120 degrees in total by adding the welding window 16 on the base 14, so that the requirement of spot welding is met.

The positioning tool can be used for welding gun trial assembly and other operations in a spot welding space to determine the clamping position of the welding gun, and under the condition that the spot welding position and the arcing position can meet welding requirements, the positioning tool is fastened, so that the butt joint end of the pipe has no gap and no wrong edge, the tool is welded after being disassembled, and particularly, a TIG (tungsten inert gas) welding machine can be used for completing full-automatic welding.

The positioning tool is small in overall structure and is not limited by the space of the electric heating sleeve and the connecting piece 3/sleeve 1.

The method for assembling the sleeve 1, the melting ring 2 and the connecting piece 3 by using the tool comprises the following steps: firstly, any pipe is placed on a tool base, the position to be welded of the pipe end is adjusted to a set position, then the melting ring 2 and the other pipe are placed, the position is adjusted and then the pressing plate is adjusted and fastened through a set screw, so that the sleeve 1/connecting piece 3 and the melting ring 2 are coaxial, and then spot welding is carried out for fixation, and the structure after assembly is shown in figure 1.

Preferably, the rotation center of the welding head drives the tungsten electrode to rotate around the melting ring 2 for automatic welding or spot welding.

And after spot welding is completed, removing the positioning tool, and then installing and debugging the welding equipment.

In the step (3), the step (c),

the welding equipment is an automatic TIG welding machine, the TIG welding machine can program and store welding parameters in advance, related parameters are finely controlled in the welding process, welding heat input, the size and the shape of a molten pool are effectively controlled, the influence of human factors on the quality of a welding seam in the welding process is reduced, the TIG welding equipment is particularly suitable for single-side welding and double-side forming, and the forming and welding quality of the welding seam can be better ensured.

As the sleeve 1 and the connecting piece 3 need to be subjected to annular welding in butt joint, a welding head of welding equipment can be clamped on the sleeve, and the rotation center of the welding head rotates around the melting ring 2 to be welded.

As shown in figure 1, after the axes of the assembled sleeve 1, the connecting piece 3 and the melting ring 2 are vertically fixed, the tungsten electrode is vertical to the axis of the pipe, and the rotation center of the welding head drives the tungsten electrode to rotate at the transverse welding position for automatic welding of the pipe.

When welding is carried out at a transverse welding position, liquid metal has a tendency of inevitably flowing under the action of gravity and surface tension, and the phenomenon of the outer surface of a welding seam is inevitably generated, so that the welding seam is required to be controlled to be formed while the full penetration of the welding seam is ensured in the welding process.

Preferably, the device positioning device of the welding head ensures that the rotation center of the welding gun is consistent with the center position of the stainless steel pipe to be welded (namely the sleeve 1 and the connecting piece 3). During welding, the axis of the pipe is perpendicular to the horizontal plane, the welding part of the automatic TIG welding machine is clamped on the pipe, and the rotation center on the welding head rotates around the melting ring 2 to complete welding.

For butt welding of the sleeve 1 and the connecting piece 3, the diameter is small, the wall thickness is large, and the S content in the material is extremely low, so that the sleeve and the connecting piece are difficult to weld and sensitive to welding parameters.

Multiple researches find that a pulse welding mode is preferably adopted in the welding process, superimposed pulses are added on the basis of thermal pulses to ensure that the sleeve 1 and the connecting piece 3 are thoroughly melted, electric arcs with good compression and straightness are generated, and under the condition that the weld penetration meets the requirement, the workpiece and tungsten can be prevented from being in an overheated state for a long time, so that the weld joint is uniformly formed, and the welding process is stable.

During welding, the type of the tungsten electrode directly influences the welding effect. In the invention, the tungsten electrode can be selected from lanthanum tungsten electrode or thorium tungsten electrode, and preferably lanthanum tungsten electrode is used.

The electric conductivity of the lanthanum tungsten electrode is close to that of a 2% thorium tungsten electrode, the durable current is high, and the burning loss rate is minimum. The lanthanum tungsten electrode has a longer life than the thorium tungsten electrode, and is non-radioactive as compared with the thorium tungsten electrode, and is easier to strike an arc during welding, and excellent in arc striking and stabilizing performance.

The shape of the end of the tungsten electrode directly influences the emission capability of electrons of the tungsten electrode, thereby influencing the penetration effect of the welding seam. The taper angle of the end part cone of the tungsten electrode is increased, and the arc column is diffused, so that the fusion depth is reduced, and the fusion width is increased; with the reduction of the cone angle, the arc column diffusion tendency is reduced, the fusion depth is increased, and the fusion width is reduced. The size of a platform at the tip of the tungsten electrode is increased, and the arc column is diffused, so that the penetration is reduced; the platform at the tip of the tungsten electrode is too small in size, and the burning loss of the tungsten electrode is serious.

Through a plurality of researches, the tungsten electrode with a specific model is researched according to the materials and specifications of the sleeve 1, the connecting piece 3 and the melting ring 2 and the welding requirements of the sleeve 1 and the connecting piece 3 in the voltage stabilizer of the nuclear power station.

Wherein the tungsten electrode comprises a tungsten pole rod 4, a tungsten pole end cone 5 and a tip platform 6 disposed on the tungsten pole end cone 5, as shown in fig. 2.

Preferably, the tungsten pole 4 has a diameter of 2 to 2.8mm, preferably 2.2 to 2.6mm, more preferably 2.3 to 2.5mm, and most preferably 2.4 mm.

Preferably, the taper angle of the tungsten tip cone 5 is 25 ° to 40 °, preferably 28 ° to 38 °, and more preferably 30 ° to 35 °.

Further, the diameter of the tip platform 6 is 0.1-0.5 mm, preferably 0.2-0.4 mm, and more preferably 0.2-0.3 mm.

The tungsten electrode can ensure the formation and fusion of the welding seam of the sleeve 1 and the connecting piece 3, and the tungsten electrode has small loss.

Researches find that after the welding head is installed, the distance between a tungsten electrode in the welding head and the melting ring 2 directly influences the welding quality of a welding seam and the shapes of the inner surface and the outer surface. When the distance between the tungsten electrode and the melting ring 2 is too small, the outer side of the welding seam is easy to form concave, and the tungsten electrode is easy to burn to cause tungsten inclusion of the welding seam; when the distance between the tungsten electrode and the melting ring 2 is too large, the stability of welding electric arc can not be ensured, and the welding quality is influenced.

Preferably, the distance between the tungsten pole tip and the outer wall of the tube in the welding area is controlled to be 1.0-2.0 mm, more preferably 1.3-1.7 mm, and the tungsten pole tip points to the lower edge of the melting ring 2 in the axial direction of the tube in the welding area.

Said distance ensures that the sleeve 1 and the connecting piece 3 are welded through and reduces the inner convex height and the outer concave depth of the weld.

In the invention, during welding, the welding current is the most main parameter for determining the weld penetration depth, and the welding current is large and the penetration depth is increased; when the welding current is too large, the defects of convex lumps, burning through and the like are easily formed, and the defects of undercut, overlarge size of a welding line outer concave and the like can also be caused; and the current is small, so that defects such as incomplete fusion and incomplete penetration are easily formed.

Because the pipe diameter of the welding area is very small, the welding area is only suitable for single-side welding, and in order to ensure the double-side forming of the single-side welding, short-time peak current is superposed on refractory materials with very low S content in the welding process, so that the welding seam can be ensured to be melted through, the tungsten electrode burning loss caused by long-time overheating is avoided, and the concave forming outside the welding seam is difficult to control.

Preferably, in the invention, the base current is 40-45A, the peak current is 70-75A, and the superposition current is 90-110A, so as to achieve good weld forming and weld fusion.

Further, the base value time/peak value time is 250-400 ms, preferably 280-350 ms, and more preferably 300 ms; the superposition time is 90-110 ms.

Preferably, the welding voltage is 17-20V,

the welding speed is also very important to the welding quality, the atmosphere of the front protective gas can be damaged due to the excessively high welding speed, and incomplete welding and air holes are easily generated in a welding line; when the welding speed is too slow, the welding seam is easy to burn through and undercut. The welding speed is selected to be 55-60 mm/min so as to meet the welding requirement.

In particular, the invention uses two sets of shielding gases to respectively perform welding protection outside the pipe and inside the pipe in the welding area.

Preferably, the front protective gas is helium, and more preferably the purity of the helium is more than or equal to 99.999%. Helium has higher ionization energy and large thermal conductivity, and under the same welding current and arc length, the arc voltage of helium arc welding is high, the energy density of the arc is high, the arc column is thin and concentrated, and the helium arc has larger permeability, so the helium is adopted as the front protective gas in the invention.

Further, the back protective gas is argon, preferably the purity of the argon is more than or equal to 99.999%. Argon gas density is big, is difficult for floating when using and scatters and disappears, and after the argon gas flows out, can form stable air current layer, its thermal capacity and thermal conductivity are very little simultaneously, can avoid welding thermal loss when protecting the welding part, so choose for use the argon gas as the inside back protective gas that lets in.

Researches find that the flow of the protective gas is too small, the air flow stiffness is poor, the capability of removing ambient air is weak, the protective effect is poor because the protective gas can deviate and scatter due to slight side wind. The flow is too large, the laminar flow of the ejected airflow is very thin, even forms turbulent flow, and the protection effect is not good.

Preferably, the flow rate of the front protective gas is 10-35L/min, and more preferably 12-30L/min.

Furthermore, the flow rate of the back side protection gas is 10-45L/min, preferably 15-40L/min.

By strictly setting welding parameters, the control function of a molten pool or liquid metal can be realized, so that the influence of the liquid metal flow on the size of a welding seam can be controlled, and the good fusion of the molten pool and a pipe is ensured. The balance is achieved through the electric arc force, the gravity of the molten pool and the surface tension, so that the welding process is stable, the welding quality is high, and the defects possibly occurring in the welding process are avoided. The electric arc with the parameters just can effectively control the shape of a molten pool and the fusion effect with the pipe, so that the side walls of the sleeve 1 and the connecting piece 3 are fused well, good weld forming and welding quality can be obtained, and the butt joint of the sleeve 1 and the connecting piece 3 of the stainless steel pipe achieves a good welding effect.

Before the pipe butt welding is carried out, welding equipment is preferably installed and debugged, the welding equipment is checked, the correct connection of all lines and the normal functions are ensured, and the requirements of gas for welding and the like are met.

The welding method provided by the invention can achieve good weld forming and weld fusion for butt welding of the stainless steel pipe sleeve 1 and the connecting piece 3, and meet the following quality requirements of welding of an electric heater of a voltage stabilizer product.

The detection result after the stainless steel pipe is welded is as follows:

visual detection: the welded seam is even and has no visible defects.

Liquid permeation: the surface is not shown.

Ray detection: no crack, undercut, no fusion and no penetration welding; no single air hole with the largest dimension larger than 0.75 mm; without any linear or dense pores having a cumulative size greater than 1.6 mm. No single slag inclusion or slag inclusion group with the largest dimension larger than 1 mm; no geometric discontinuities were present in the weld zone.

Stretching at room temperature: the tensile strength is more than or equal to 520 MPa.

Surface bending and back bending tests: the bending angle is 180 degrees, and no crack or defect with a single strip length of more than 3mm exists on the stretching surface in any direction.

Metallographic test: the butt welding seam and the heat affected zone have no defects of cracks, incomplete penetration, incomplete fusion, air holes and the like, the outer wall is sunken by no more than 0.5mm, and the inner wall is protruded by no more than 1.5 mm.

Intergranular corrosion: the welding joint has no intercrystalline corrosion tendency in both welding state and sensitization state.

The welding method provided by the invention can be used for welding the butt weld of the stainless steel pipe without the groove, the welding process is stable, the weld is attractive in shape, and the welding quality meeting the product requirements of the nuclear power station can be obtained. And the automatic TIG welding of stainless steel tube materials with low S content is realized, the welding process is stable, and the weld quality and weld forming can be effectively controlled.

The invention also provides an automatic pulse superposition single-pass welding system for stainless steel pipe butt joint, which comprises a stainless steel butt joint pipe, a melting ring 2 and a TIG welding machine.

The stainless steel butt joint pipe comprises a sleeve 1 and a connecting piece 3 which are in butt joint assembly and welded, and the melting ring 2 is clamped between the sleeve 1 and the connecting piece 3.

Preferably, the inner walls of the ends of the casing 1 and the connection member 3 are circumferentially recessed, preferably smoothly recessed to increase the inner diameter, so that the inner diameters of the ends of the casing 1 and the connection member 3 are Φ_{Inner part}24-28 mm, preferably phi_{Inner part}25-27 mm, most preferably 26 mm.

Wherein the outer diameter of the melting ring 2 is the same as the outer diameters of the sleeve 1 and the connecting piece 3, and the inner diameter of the melting ring 2 is larger than the inner diameters of the sleeve 1 and the connecting piece 3. Preferably, the inner diameter of the melting ring 2 is Φ_{Inner part}27.5-28 mm; more preferably the outer diameter is phi_{Outer cover}32.5mm。

In order to ensure the penetration effect of the welding seam, the thickness of the melting ring 2 is 0.4-0.6 mm, preferably 0.5 mm.

In the welding system provided by the invention, the melting ring with a specific size is used as a pipe butt joint filling material, so that the sleeve 1 and the connecting piece 3 with low S content ensure the formation of a welding seam and good welding quality under the applicable welding condition.

The TIG welding machine comprises a tungsten electrode, wherein the tungsten electrode comprises a tungsten electrode rod 4, a tungsten electrode end cone 5 and a tip platform 6 arranged on the tungsten electrode end cone 5.

Wherein, the diameter of the tungsten pole 4 is 2-2.8 mm, preferably 2.2-2.6 mm, more preferably 2.3-2.5 mm, and most preferably 2.4 mm;

preferably, the taper angle of the tungsten tip cone 5 is 25 ° to 40 °, preferably 28 ° to 38 °, and more preferably 30 ° to 35 °;

the diameter of the tip platform 6 is 0.1-0.5 mm, preferably 0.2-0.4 mm, and more preferably 0.2-0.3 mm.

The tungsten electrode can ensure the formation and fusion of the welding seam of the sleeve 1 and the connecting piece 3, and the tungsten electrode has small loss. The pulse superposition automatic TIG welding process is adopted, pulses are superposed on the basis of normal TIG welding to generate electric arcs with good compression and straightness, under the condition of ensuring the penetration of welding seams, workpieces and tungsten can be prevented from being in an overheated state for an extremely long time, the welding process is stable, and good welding seam forming and welding quality can be obtained.

Furthermore, the automatic pulse superposition single-pass welding system for the butt joint of the stainless steel pipes further comprises a positioning tool.

The welding system and the method provided by the invention can be used for butt welding the sleeve and the connecting piece, can achieve good weld joint forming and weld joint fusion, and meet the welding quality requirement of an electric heater of a voltage stabilizer product.

Examples

Example 1

The inner diameter of the sleeve and the connecting piece made of Z2CND18-12NS steel is 26mm, the inner diameter of the melting ring made of Z01CD26-01 steel is 28mm, and the thickness of the melting ring is 0.5mm, after butt joint, the melting ring is fixed by using a positioning tool shown in figures 3 and 4 and is subjected to spot welding.

The positioning tool comprises a base 14 with a flange U-shaped structure, and a flange at one side is hinged with two supporting legs of the bracket 13; the support 13 is a double-sided frame, the other end of the support is hinged with an L-shaped hook 15, and the hook 15 is hooked with the flange on the other side of the base 14. The opposite side of the bracket 13 and the base 14 is connected with a pressure plate 12 in a U-shaped groove through a locking screw 11 to fix the sleeve, the connecting piece and the melting ring.

And (4) after spot welding, removing the positioning tool, and performing automatic welding by using a TIG welding machine. Wherein, the diameter of the tungsten pole rod 4 is 2.4 mm; the cone angle of the tungsten electrode tip cone 5 is 33 °; the tip platform 6 has a diameter of 0.3 mm.

The welding parameters were as follows:

the distance from the tungsten pole tip to the outer wall of the tube in the welding area is 1.5 mm;

the base value current is 40-45A, the peak value current is 70-75A, and the superposed current is 90-110A; both the base value time and the peak value time are 300 ms; the superposition time is 90-110 ms; the welding voltage is 17-20V.

The front protective gas is helium, and the flow rate is 12-30L/min; the back protective gas is argon, and the flow rate is 15-40L/min.

The detection results of the welded joint after welding are as follows:

visual detection: the welded seam is uniform without visible defects;

liquid permeation: the surface is free of any display;

Stretching at room temperature: tensile strength of 633 MPa;

stretching at high temperature of 360 ℃: the tensile strength is 446 MPa;

surface bending and back bending tests: the bending angle is 180 degrees, and no defect exists in any direction on the stretching surface;

metallographic test: the butt weld and the heat affected zone have no defects of cracks, incomplete penetration, incomplete fusion, air holes and the like, the outer wall is sunken by 0.40mm, and the inner wall is raised by 0.52 mm.

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims

1. A welding method for stainless steel pipe butt joint automatic superposition pulse single pass welding is characterized by comprising the following steps:

(1) machining and cleaning the end of the sleeve (1) and the connecting piece (3) and the inner diameter of the melting ring (2), wherein the inner diameter of the melting ring (2) is phi_{Inner part}27.5-28 mm, wherein the thickness of the melting ring (2) is 0.4-0.6 mm;

(2) assembling the sleeve (1), the connecting piece (3) and the melting ring (2) and performing spot welding;

(3) after the welding equipment is installed and debugged, setting welding parameters and implementing welding;

in the step (2), the melting ring (2) is clamped between the sleeve (1) and the connecting piece (3) and is fixed and then spot-welded;

the base value time/peak value time is 280-350 ms; the superposition time is 90-110 ms;

the welding voltage is 17-20V;

the welding speed is 55-60 mm/min;

the method adopts a stainless steel pipe butt joint automatic superposition pulse single-pass welding system, and the system comprises a stainless steel butt joint pipe, a melting ring (2) and a TIG welding machine;

the stainless steel butt joint pipe comprises a sleeve (1) and a connecting piece (3) which are in butt joint assembly, and the melting ring (2) is arranged between the sleeve (1) and the connecting piece (3);

the inner walls of the end parts of the sleeve (1) and the connecting piece (3) are circumferentially sunken, so that the inner diameters of the end parts of the sleeve (1) and the connecting piece (3) are phi_{Inner part}25～27mm；

The inner diameter of the melting ring (2) is phi_{Inner part}27.5～28mm；

The thickness of the melting ring (2) is 0.4-0.6 mm.

2. The method according to claim 1, characterized in that in step (3), the welding device is a TIG welder, in which a tungsten electrode is provided; the tungsten electrode comprises a tungsten electrode rod (4), a tungsten electrode end cone (5) and a tip platform (6) arranged on the tungsten electrode end cone (5).

3. The method according to claim 2, wherein, in step (3),

the diameter of the tungsten pole rod (4) is 2-2.8 mm;

the cone angle of the tungsten electrode end cone (5) is 25-40 degrees;

the diameter of the tip platform (6) is 0.1-0.5 mm.

4. The method of claim 3,

the diameter of the tungsten pole rod (4) is 2.2-2.6 mm;

the cone angle of the tungsten electrode end cone (5) is 28-38 degrees;

the diameter of the tip platform (6) is 0.2-0.4 mm.

5. The method of claim 1, wherein in step (3), the distance from the tungsten tip to the outer wall of the tube in the welding region is 1.0-2.0 mm.

6. The method of claim 5, wherein the distance from the tungsten tip to the outer wall of the tube in the weld region is 1.3 to 1.7 mm.

7. The method according to claim 1, wherein in the step (3), the front surface shielding gas is helium, and the flow rate of the front surface shielding gas is 10-35L/min;

the back protective gas is argon, and the flow of the back protective gas is 10-45L/min.

8. The method of claim 7,

the front protective gas is helium, and the flow rate of the front protective gas is 12-30L/min;

the back protective gas is argon, and the flow of the back protective gas is 15-40L/min.