CN108856989A - Consumable electrode MIG is welded in the method for priming in pipeline welding - Google Patents

Abstract

The invention relates to a bottoming method for MIG welding in pipeline welding, which belongs to the technical field of pipeline welding. During welding, the two pipes to be welded are respectively provided with welding grooves on the butt end faces, and are arranged opposite to each other to form a V-shaped groove. 35°, the welding machine for bottom welding adopts semi-automatic melting electrode MAG welding equipment, and the shielding gas adopts a mixture of argon and carbon dioxide. Calculated according to volume percentage, argon accounts for 95% and carbon dioxide accounts for 5%. The invention adopts common semi-automatic melting electrode MAG welding equipment to realize the effect of MIG welding, can reduce construction cost, improve construction efficiency, and avoid welding defects in conventional operation methods.

Description

The bottoming method of MIG welding in pipeline welding

technical field

The invention relates to a bottoming method for MIG welding in pipeline welding, which belongs to the technical field of pipeline welding.

Background technique

The chemical industry has high requirements on the strength and compactness of pipelines and tanks, so it has strict requirements on the welding quality of pipelines, and the requirements for radiographic flaw detection of some pipelines reach the first grade. In the prior art, argon arc welding is used for one-sided welding and double-sided forming of the root pass, and manual welding is used for filling and covering welding. However, when welding large-diameter pipes, the lower half of the large pipe is almost in the position of overhead welding and climbing Yang welding, and the operation of argon arc welding must hold the welding torch with one hand and feed the welding wire with the other. The two hands must cooperate and coordinate to ensure Weld quality. There are two wire feeding methods for conventional argon arc welding welding pipes: internal wire filling (Figure 1) and external wire filling (Figure 2). However, if a large-diameter pipeline uses internal filling wire, it cannot be completed by one person, and two people must cooperate to complete the operation. Moreover, the tacit understanding and operational proficiency of the two people are also very high, and the investment in welders has increased significantly. According to the situation of the enterprise and the preparation of personnel, we all use external filler wire for welding. When the external wire filling method is used, the hands are suspended in the overhead welding position, and there is no leaning and support point to ensure the stability of the hands, and the head is still in a long-term upward position. Such an operating posture naturally increases the difficulty of welding. If the operator's hands are unstable, the welding wire cannot be correctly sent to the root of the weld. If the welding wire is only sent to the middle of the groove, when the welding wire is melted and combined with the base metal, the welding seam will be formed due to the self-weight of the molten iron in the overhead welding position. It will collapse naturally, and there will be a natural depression on the back. To avoid this phenomenon, it is necessary to ensure that the gap between the grooves must be greater than the diameter of the welding wire, so as to ensure that the welding wire can be sent to the back of the weld through the groove normally. Even if there is a certain slump behind the pool, it can ensure that the reinforcement on the back of the weld is flush with the base metal and slightly higher than the base metal. However, due to various factors such as the welding position, the operation difficulty increases, and the welding of the overhead welding position always appears different. Deep and shallow depressions (as shown in Figure 3) make the welding quality unable to be guaranteed.

Using molten electrode MIG welding instead of manual tungsten argon arc welding for bottom welding can ensure the stability of the hand, because molten electrode MIG welding is semi-automatic welding, and the welding wire is automatically fed through the welding torch, so it does not need to be sent separately like argon arc welding At this time, both hands can be used to hold the welding torch, and the arm of one hand can also lean against the pipe wall, which greatly increases the stability of the welding operation. In addition, the welding wire of MIG welding is thin, and it is easy to reach the root of the groove. The short existence time of the molten pool during welding can also avoid the phenomenon of molten pool collapse, which can effectively avoid the depression of the upward welding part of argon arc welding bottom welding, and also It can significantly improve the construction efficiency, and at the same time, the heat-affected zone of MIG welding is narrow, the cooling speed of the weld seam is fast, and the deformation of the weldment is small.

At present, the melting electrode MIG welding process has been widely used in oil and natural gas pipelines at home and abroad, but the cost of the welding machine itself is relatively large. The minimum price of a professional melting electrode MIG welding machine is more than 50,000 yuan, and some equipment is semi-automatic. One piece of welding equipment is worth hundreds of thousands, and the equipment is more complicated than ordinary melting electrode equipment. It is not directly proportional to the construction cost and profit return of general industries, and the use of this equipment is also limited in places where the construction site is relatively complicated.

Contents of the invention

The technical problem to be solved by the present invention is to provide a bottoming method for MIG welding in pipeline welding, which uses ordinary semi-automatic MIG welding equipment to achieve the effect of MIG welding, so as to reduce construction costs.

In order to solve the above-mentioned technical problems, the technical solution adopted by the present invention is: the bottoming method of molten electrode MIG welding in pipeline welding. During welding, two pipes to be welded are respectively provided with welding grooves on the butt joint end faces, and are arranged in opposite directions so that Form a V-shaped groove, the root gap of the V-shaped groove is 3mm~5mm, and the angle of the single side groove is 30°~35°. The welding machine for bottom welding adopts semi-automatic melting electrode MAG welding equipment, and the shielding gas adopts argon and The mixed gas of carbon dioxide is calculated according to the volume percentage, the proportion of argon is 95%, and the proportion of carbon dioxide is 5%.

Further: when the welded pipe is in the horizontal fixed position, in the circumferential direction of the weld, mark the lowest point as M, the highest point as N, take a point on the weld on one side of the straight line MN and mark it as P, and mark it on the straight line MN A point on the weld on the other side of MN is marked as Q, the central angle of arc MP is marked as a, the value of a is 55°～65°, the central angle of arc MQ is marked as b, and the value of b is 55°～65°;

When rooting welding, use the straight line MN as the dividing line to divide the weld into two halves for welding, and start from point M when welding; the welding current is 150A~180A, and the voltage is 14V~17V.

The welding seam within the range of point M to point P, and the welding seam within the range of point M to point Q are all welded by the forward tilting method of the welding torch. Each time the arc is struck in the middle of the weld, the arc is immediately extinguished after observing the fusion between the molten pool and the grooves on both sides, and the wire feeding position is at the root of the pipe skin;

The welding seam between point P and point N, and the welding seam between point Q and point N are all welded by the backward tilting method of the welding torch. The method of arc ignition and arc extinguishing on both sides, the arc is ignited at the groove of the tube skin once and immediately swings to the other groove, and the arc is extinguished immediately after observing that the groove on the other side is fused, and then the arc is ignited at the arc extinguishing place and moves to the other groove. After the side groove swings and fuses well, the arc is extinguished, and this action is repeated until the bottoming welding of the entire weld seam is completed.

Further: when the outer diameter of the pipe is Φ>400mm, the weld is divided into four sections from point M to point P, from point M to point Q, from point P to point N, and from point Q to point N for backing welding.

Further, when the welding pipe is in the vertical fixed position, the welding current for bottom welding is 120A~130A, and the voltage is 13V~14V; When the thickness of the tube skin is more than 16mm, continuous arc welding is adopted, and when the thickness of the tube skin is less than or equal to 16mm, arc-breaking welding is used, and the arc is extinguished every time an oblique circle is completed. , and then ignite the arc from the arc extinguishing position and do the next oblique circle operation, so that the welding of the bottom bead is completed in turn.

A further step is: before bottoming welding, positioning welding is carried out at the welding seam, the length of the positioning welding seam is 20 mm to 30 mm, and the two ends of the positioning welding seam are ground with an angle grinder to form a gentle slope.

The beneficial effects of the present invention are: the practice shows that the quality of the welding seam of the present invention can meet the service performance. The present invention adopts appropriate welding methods and effective operation methods, and the effect of MIG welding can be realized by using ordinary semi-automatic melting electrode MAG welding equipment, which not only solves the welding quality problem, reduces the deformation and stress of the weldment, but also improves the welding efficiency. Production efficiency not only shortens the construction period but also saves construction costs. The invention is especially suitable for the complex construction environment and limited construction site, can meet the construction requirements of argon tungsten arc welding, and can also avoid the phenomenon of indentation in the overhead welding position when argon tungsten arc welding welds large-diameter pipes It is suitable for all metallurgical, construction industries and private enterprises to use in the welding of large-diameter pipes, which is conducive to improving the pass rate of flaw detection and construction efficiency, and reducing labor costs.

Description of drawings

Fig. 1 is a schematic structural view of welding in the prior art when using an inner wire filling method;

Fig. 2 is a structural schematic diagram when welding with external wire filling in the prior art;

Fig. 3 is a structural schematic diagram of a concave defect in an overhead welding part of a weld seam in the prior art;

Fig. 4 is the segmented welding structure schematic diagram among the present invention;

Fig. 5 is the structural representation of the welding torch angle change among the present invention;

Fig. 6 adopts the schematic diagram of the welding method of one-point wire feeding in the present invention;

Fig. 7 is a schematic diagram of the welding method adopting arc ignition on both sides and arc extinguishing on both sides in the present invention;

Fig. 8 is a schematic diagram of the method of transporting the gun in an oblique circle in the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

The bottoming method of molten electrode MIG welding in pipeline welding. During welding, two pipes to be welded are respectively provided with welding grooves on the butt end faces, and are arranged oppositely to form a V-shaped groove. The root gap of the V-shaped groove is 3mm to 5mm, single-side bevel angle is 30° to 35°, the welding machine for bottom welding adopts semi-automatic melting electrode MAG welding equipment, and the shielding gas is a mixture of argon and carbon dioxide. Calculated according to volume percentage, the proportion of argon 95% and 5% carbon dioxide.

Before bottoming welding, position welding is carried out at the weld. The length of the position weld is 20mm~30mm. The two ends of the position weld are ground with an angle grinder to make a gentle slope to ensure the quality of the joint. Before welding, the rust and oil stains within the range of 10mm to 20mm on both sides of the weld groove should be cleaned up. The welding wire is ER49-1Ф1.2mm welding wire, which should be consistent with the formal weld when performing tack welding.

As shown in Figure 4 to Figure 7, when the welded pipe is in the horizontal fixed position, mark the lowest point as M and the highest point as N in the circumferential direction of the weld, and mark a point on the weld on one side of the straight line MN P, take a point on the weld on the other side of the straight line MN and mark it as Q, mark the central angle of the arc MP as a, the value of a is 55°～65°, mark the central angle of the arc MQ as b, The value of b is 55°～65°; the values of a and b are usually the same value;

When rooting welding, use the straight line MN as the dividing line to divide the weld into two halves for welding, and start from point M when welding; the welding current is 150A~180A, and the voltage is 14V~17V.

The welding seam within the range of point M to point P, and the welding seam within the range of point M to point Q are all welded by the forward tilting method of the welding torch. Each time the arc is struck in the middle of the weld, the arc is extinguished immediately after observing the fusion between the molten pool and the grooves on both sides, and the wire feeding position is at the root of the tube skin; here, the wire feeding position cannot only be sent to the middle of the groove, otherwise due to Due to the effect of gravity, it is easy to have the phenomenon that the weld seam on the inner side of the groove is too high and the back of the weld seam is too deep.

The welding seam between point P and point N, and the welding seam between point Q and point N are all welded by the backward tilting method of the welding torch. The method of arc ignition and arc extinguishing on both sides, the arc is ignited at the groove of the tube skin once and immediately swings to the other groove, and the arc is extinguished immediately after observing that the groove on the other side is fused, and then the arc is ignited at the arc extinguishing place and moves to the other groove. After the side groove swings and fuses well, the arc is extinguished. Repeat this action until the bottom welding of the entire weld seam is completed, so as to avoid the phenomenon of internal welding flash.

In addition, in order to further ensure the welding quality, when the pipe diameter is large, the weld seam can also be divided into multi-stage welding. The four sections from point to point P, from point M to point Q, from point P to point N, and from point Q to point N are used for backing welding.

When the welding pipe is in the vertical fixed position, the welding current of the bottom welding is 120A~130A, and the voltage is 13V~14V; As shown in Figure 8, the trajectory of the gun movement finally forms a spiral; when the thickness of the tube skin is greater than 16mm, continuous arc welding is used, and when the thickness of the tube skin is ≤16mm, interrupted arc welding is used. The arc is extinguished, and then the arc is ignited from the arc extinguishing position and the next oblique circle operation is performed, so that the welding of the bottom bead is completed in sequence.

After the bottoming bead is welded, in order to avoid slag inclusion and incomplete fusion between layers, the joint and the parts with clamping grooves on both sides of the local middle protrusion should be smoothed with an angle grinder before welding in the next process , The welding of the interlayer and the cover layer can choose manual welding and MIG welding according to the actual situation.

Embodiment one:

Welding base material: the material of the pipe is 20, the outer diameter of the pipe is 273mm, and the wall thickness is 8mm; the horizontal fixed position welding is used between the two pipes.

Welding equipment and materials: The welding machine adopts conventional NBC-350 carbon dioxide gas shielded welding machine, and the shielding gas adopts a mixture of argon and carbon dioxide. Calculated according to the volume percentage, the proportion of argon is 95%, and that of carbon dioxide is 5%. ; Welding wire adopts ER49-1Ф1.2mm welding wire.

Groove setting: adopt V-shaped groove, the root gap is 4mm, and the single-side groove angle is 30°.

Working parameters of welding equipment: welding current is 150A~180A, voltage is 14V~17V.

Welding operation: In the circumferential direction of the weld, mark the lowest point as M and the highest point as N, take a point on the weld on one side of the straight line MN and mark it as P, and take a point on the weld on the other side of the straight line MN One point is marked as Q, the central angle of arc MP is marked as a, the value of a is 60°, the central angle of arc MQ is marked as b, and the value of b is 60°;

When bottoming welding, use the straight line MN as the dividing line to divide the welding seam into two halves for welding, and start from point M when welding;

The welding seam within the range of point M to point P, and the welding seam within the range of point M to point Q are all welded by the forward tilting method of the welding torch. Each time the arc is struck in the middle of the weld, the arc is immediately extinguished after observing the fusion between the molten pool and the grooves on both sides, and the wire feeding position is at the root of the pipe skin.

The welding seam between point P and point N, and the welding seam between point Q and point N are all welded by the backward tilting method of the welding torch. The method of arc ignition and arc extinguishing on both sides, the arc is ignited at the groove of the tube skin once and immediately swings to the other groove, and the arc is extinguished immediately after observing that the groove on the other side is fused, and then the arc is ignited at the arc extinguishing place and moves to the other groove. After the side groove swings and fuses well, the arc is extinguished, and this action is repeated until the bottoming welding of the entire weld seam is completed.

Welding quality inspection: no visual inspection is adopted on the outside, no porosity, slag inclusion, unfused, and undercuts with a depth greater than 0.5mm are qualified, and radiographic flaw detection is used for internal inspection of pipe welds, and all welds can reach level two or above Radiographic quality.

Embodiment two:

Welding base material: the material of the pipe is 20, the outer diameter of the pipe is 600mm, and the wall thickness is 6mm; the horizontal fixed position welding is used between the two pipes.

Welding equipment and materials: The welding machine adopts conventional NBC-350 carbon dioxide gas shielded welding machine, and the shielding gas adopts a mixture of argon and carbon dioxide. Calculated according to the volume percentage, the proportion of argon is 95%, and that of carbon dioxide is 5%. ; Welding wire adopts ER49-1Ф1.2mm welding wire.

Bevel setting: V-shaped bevel is adopted, the root gap is 4mm, and the bevel angle on one side is 35°.

Working parameters of welding equipment: welding current is 150A~180A, voltage is 14V~17V.

Welding operation: In the circumferential direction of the weld, mark the lowest point as M and the highest point as N, take a point on the weld on one side of the straight line MN and mark it as P, and take a point on the weld on the other side of the straight line MN One point is marked as Q, the central angle of arc MP is marked as a, the value of a is 60°, the central angle of arc MQ is marked as b, and the value of b is 60°;

Divide the weld seam into four sections from point M to point P, from point M to point Q, from point P to point N, and from point Q to point N for backing welding, with point M as the initial starting point for welding;

The welding seam within the range of point M to point P, and the welding seam within the range of point M to point Q are all welded by the forward tilting method of the welding torch. Each time the arc is struck in the middle of the weld, the arc is immediately extinguished after observing the fusion between the molten pool and the grooves on both sides, and the wire feeding position is at the root of the pipe skin.

The welding seam between point P and point N, and the welding seam between point Q and point N are all welded by the backward tilting method of the welding torch. The method of arc ignition and arc extinguishing on both sides is to ignite the arc at the groove of the tube once and swing it to the other groove immediately, observe that the groove on the other side is fused and extinguish the arc immediately, and then ignite the arc at the arc extinguishing place and move to the other groove. After the side groove swings and fuses well, the arc is extinguished, and this action is repeated until the bottoming welding of the entire weld seam is completed.

Welding quality inspection: visual inspection is adopted on the outside, and undercuts with no pores, slag inclusions, unfused, and depths greater than 0.5mm are qualified. Ultrasonic is used to inspect the internal quality of the pipeline, and the welding quality can reach the ultrasonic level.

Embodiment three:

Welding base material: the material of the pipe is 20, the outer diameter of the pipe is 325mm, and the wall thickness is 6mm; the vertical fixed position welding is used between the two pipes.

Welding equipment and materials: The welding machine adopts conventional NBC-350 carbon dioxide gas shielded welding machine, and the shielding gas adopts a mixture of argon and carbon dioxide. Calculated according to the volume percentage, the proportion of argon is 95%, and that of carbon dioxide is 5%. ; Welding wire adopts ER49-1Ф1.2mm welding wire.

Groove setting: adopt V-shaped groove, the root gap is 4mm, and the single-side groove angle is 30°.

Working parameters of welding equipment: welding current is 120A~130A, voltage is 13V~14V.

Welding operation: The arc starting position is close to the edge of the upper bevel, and welding is carried out in an inclined circle from top to bottom. As shown in Figure 8, the trajectory of the torch finally forms a spiral; arc-breaking welding is adopted.

Welding quality inspection: no visual inspection is adopted on the outside, no porosity, slag inclusion, unfused, and undercuts with a depth greater than 0.5mm are qualified, and radiographic flaw detection is used for internal inspection of pipe welds, and all welds can reach level two or above Radiographic quality.

Claims (5)

1. consumable electrode MIG is welded in the method for priming in pipeline welding, when welding, two pipes to be welded are set respectively in docking end face Welding groove is set, and in positioned opposite to form double V-groove, it is characterised in that：The root gap of double V-groove is 3mm~5mm, Angle of bevel is 30 °~35 °, and the welding machine of bottom welding uses semi-automatic consumable electrode MAG welding equipment, and protective gas uses The mixed gas of argon gas and carbon dioxide, calculates according to percent by volume, and argon gas accounting is 95%, and carbon dioxide accounting is 5%.

2. consumable electrode MIG as described in claim 1 is welded in the method for priming in pipeline welding, it is characterised in that：Welded pipe line In horizontal busy hour fixed, on the circumferencial direction of weld seam, minimum point is labeled as M, highest point is labeled as N, straight line MN's It takes a little labeled as P, is taken on another side weld of straight line MN a little labeled as Q, the center of circle footmark of camber line MP on one side weld It is denoted as a, the value of a is 55 °~65 °, and the central angle of camber line MQ is labeled as b, and the value of b is 55 °~65 °；

When bottom welding, two halves are divided to weld weld seam using straight line MN as line of demarcation, using M point as starting point when welding；Weldering Connecing electric current is 150A~180A, and voltage is 14V~17V.

In the weld seam in M point to P point range, the weld seam in M point to Q point range, it is all made of welding gun and leans forward method welding, welding gun and pipe The angle of skin is 100 °~105 °, and welding manner is some wire feeds, and each striking is among weld seam, observation molten bath and two sides groove Blow-out immediately in fusion, wire feed position is in pipe dermatome portion；

In the weld seam in P point to N point range, the weld seam in Q point to N point range, it is all made of the welding of welding gun hypsokinesis method, welding gun and pipe The angle of skin is 80 °~90 °, and the method that welding manner uses two sides striking and two sides blow-out is once ignited electricity in pipe skin groove Arc is swung to another secondary groove immediately, observes the fused blow-out immediately of other side groove, and the electric arc that then ignites at blow-out is to another Side groove swings blow-out after fusion well, repeats bottom welding of such movement up to completing entire weld seam.

3. consumable electrode MIG as claimed in claim 2 is welded in the method for priming in pipeline welding, it is characterised in that：When outside pipe Diameter Φ>When 400mm, M point is divided the weld into P point, M point to Q point, P point to N point, Q point to four sections of progress bottom weldings of N point.

4. consumable electrode MIG as described in claim 1 is welded in the method for priming in pipeline welding, it is characterised in that：Welded pipe line In vertical busy hour fixed, the welding current of bottom welding is 120A~130A, and voltage is 13V~14V；Striking position is close Upper bevelled edge is welded in a manner of the fortune rifle of oblique circle from top to bottom, and fortune rifle track ultimately forms a spiral shape；When pipe skin depth Degree>When 16mm then using even arc welding, when pipe skin thickness≤16mm if use current interruption to weld, current interruption welding often around complete one tiltedly Circle, that is, blow-out, then next oblique circle running is done again from the blow-out position electric arc that ignites, it is sequentially completed the weldering of backing run in this way It connects.

5. the consumable electrode MIG as described in any one of Claims 1-4 is welded in the method for priming in pipeline welding, feature It is：Before bottom welding, positioning welding is first carried out in commissure, tack weld length is 20mm~30mm, tack weld both ends Go out gentle slope with electric angle grinder reconditioning.