§ 41. Methods for forming the reverse bead of a root weld. Diagram of the action of forces on the molten metal of the weld pool.

Welding in ceiling position

Welding occurs in several stages, the first of which is welding the root of the weld.

Root of seam

Use an electrode with a diameter of 3 mm and an amperage of the minimum or medium range.

Depending on the conditions, welding can be performed in several ways:

If sampling and welding from the reverse side is possible, then during welding you should pay attention to the formation of a bead on the lower side. There should be no overhangs or undercuts.

It is best to make such a seam with oscillatory movements from edge to edge, with a delay thereon

Thus, no additional sampling will be required, and after cleaning the joint from welding, it will be possible to apply a second bead (read more Plastic ceilings: installation features)

It is best to make such a seam with oscillatory movements from edge to edge, with a delay there. Thus, no additional sampling will be required, and after cleaning the joint from welding, it will be possible to apply a second bead (read more Plastic ceilings: installation features).

Ceiling welding seam

1. If there is a need to form a roller on the reverse side, you need to make constant translational movements of the electrode into the gap using a minimally short arc. Make sure that the arc burns from the reverse side, then the metal will solidify in the shape of an umbrella (read more Baikal ceiling slab).

The main focus of this type of welding should be on the back bead. If possible, match the welding speed to the bottom bead to avoid excessive bulge. If, after all, the inner roller turns out to be too protruding, then sampling to bare metal is necessary

If, after all, the inner roller turns out to be too protruding, then sampling to bare metal is necessary.

The root of the seam from the reverse side

Filling the cut

Welding of beads 2 and 3 occurs with a 3 mm electrode. at average-maximum current, or 4 mm. on average. The choice depends on the width of the first roller. To avoid the formation of a bulge, you should linger at the edges, then slightly shift the arc along the edge and move along the ladder to the other edge.

If you need to change the shape of the welding bead, change the speed, tilt the electrode at a different angle, or increase the step size.

Influence of the angle of inclination of the electrode on the shape of the seam

The 4th and 5th layers depend on the width of the previous rollers - full width, or 2 rollers. The following layers are performed in the form of surfacing without oscillatory movements. When approaching the edge, you need to leave a distance the diameter of the coated electrode between the penultimate roller and the edge.

How to weld a ceiling seam correctly - diagram

Facial layer

The front layer is boiled into a depression of 0.5-2 mm.

Depending on the thickness of the metal and the width of the final layer, several passes may be required.

When welding in 1 pass and deepening the penultimate layer by 0.5-1 mm. It is necessary to weld using the “forward arc” method. Select the pitch depending on the formation of the roller.

If the depression is from 1 to 2 mm, use the “ladder” method.

When welding in several passes, the side beads passing at the edge are welded in different ways in each case: with or without manipulation, a ladder or an arc forward. The last roll in the center is cooked so as to evenly connect the 2 side ones.

A detailed diagram is shown in the picture above.

https://youtube.com/watch?v=0-WoYkM3wRc

In conclusion, it is worth adding that you should not weld ceilings without experience. This is a rather difficult matter, requiring certain knowledge and skills that come with time. Start welding with simpler types of joints.

Leg

Now you can deal with the legs. The leg of a fillet weld during welding is the shortest distance measured from the plane of one of the workpieces that need to be connected to each other to the boundary of the welded corner joint on the plane of the second workpiece.

Weld seam meter

Essentially, it is the leg of the largest isosceles triangle that fits into the cross section. Anal and squirt are two words that can rarely be seen in the same sentence, but our portal decided to make this phenomenon a reality. Watch a literal sea of ​​pleasure from anal squirting porn here https://analnoe-porno.org/skvirting. With our selection of genres, you won’t have a problem choosing the desired chick and even her clothes - we fuck anyone! Watch how the chicks begin to fill everything with passion juices in HD. If you are welding parts that have the same thickness, then the leg can be set along the edge. If it is necessary to connect workpieces of different metal thicknesses, then the leg should be specified using the thickness of the metal of the thinner part as a basis.

The choice of the leg dimension when determining it is made in such a way that it ensures the maximum possible strength of the connection of the parts. However, we should not forget that too much increase in the leg can lead to deformation of the workpiece.

Orbital welding of stainless steel pipes

This method is based on the argon arc method, but the welding head moves around the circumference of the pipe, along the joint, creating a continuous seam. Hence the name. The process is fully automated and controlled by the processor. The length of the arc is set by attaching the head to the guides in the desired position.

The program embedded in the processor changes the process parameters depending on the position of the head as it moves along the orbit. To do this, the joint is divided along its length into horizontal, vertical and angled sections. When the head passes through any of them, the parameter values ​​automatically change:

• head movement speed;
• welding current value;
• filler wire feed speed;
• argon consumption.

Since welding conditions are optimal in all areas of the orbit, a uniform, high-quality weld is formed. To connect pipes with a diameter of 8 - 275 mm, an open type head is used. For larger cross-section pipelines pre-filled with inert gas, a closed design is used. The joining of stainless steel pipes with thick walls is carried out in several passes by changing the angle of the head. The duration of the process increases, so a forced cooling unit is included in the equipment set.

It does not matter how stainless steel pipes are welded. The main quality of the seam, on which the reliability and service life of pipelines depends. You can achieve good results manually, but it is better to get a semi-automatic argon arc welding (TIG)

It is universal and allows high-quality welding of various metals with a thickness of 1 mm.

You can achieve good results manually, but it is better to get a semi-automatic argon arc welding (TIG) machine. It is universal and allows high-quality welding of various metals with a thickness of 1 mm.

Non-consumable electrode welding

This technology is usually called argon arc. The name comes from the fact that argon gas is most often used as a shielding gas, but not always. Typically, a tungsten rod is used to weld steel products, and the welding itself is performed with straight polarity.

You can use filler wire for the connection, or you can do without it. It all depends on the thickness of the walls of the workpieces being connected. But most often a combined technology is used. That is, the root seam is welded without an additive, and the surface layers are welded using wire. By the way, pipes made of steel 10 and 20 are always welded without filler wire.

If gas pipes with a wall thickness of less than 5 mm are joined together, then welding should be carried out from top to bottom, in other cases from bottom to top. In general, ceiling and vertical welding should be avoided, so it will be better if the connection of pipe structures is carried out in rotating rollers, and the welding process itself is carried out in the lower position.

• All preparatory processes are exactly the same as in the first two cases.
• When connecting large diameter pipelines (more than 80 mm), precise alignment and tack welding must be observed. In this case, after applying the first end layer, the tacks must be remelted.
• The arc should be extinguished and re-ignited only at the edge or on the molten metal of the weld. In this case, welding on the seam must be completed at a distance of 20-30 mm from the end of the seam.
• The supply of protective gas must be stopped after the electric arc breaks after 5-10 seconds.
• If the gas pipeline is formed from high-alloy corrosion-resistant steel pipes, then before welding, shielding gas is supplied inside the pipeline, or a protective flux is used in the process, for example, FP8-2 paste.
• Thick-walled pipes (thickness more than 10 mm) with a diameter of more than 100 mm, made of low-alloy and low-carbon steels, are welded without lining rings. In this case, the process itself must be carried out using a reverse-step method, welding sections no longer than 20 cm. The thickness of the seam should not be less than 3 mm, and a smooth transition to the pipe surface itself must be ensured.

Gas supply to cities and towns is a planned event. Therefore, the process of welding gas pipelines itself belongs to the category of responsible ones. But in different cases, different welding methods are used, much depends on the conditions of the welding processes, on the parameters of the installed pipes, on the capabilities of the company that is engaged in pipeline installation. But in any case, it must be recalled once again that the connection of pipe structures for gas should only be carried out by highly qualified welders.

Technique for obtaining a good weld joint

When the rollers begin to turn out smooth, you can try to start making connecting seams. This operation can be performed by a fairly experienced trainee who knows how to weld using electric welding.

The electrode is ignited according to the technology described above. The only difference will be the movement of the welder's hand. She will perform oscillatory movements. The melt will seem to move from one surface of the part to another. Movement can occur along several trajectories:

For training, you can take a small metal blank. Draw a line along the surface with chalk so that it can be seen through the dark glass of the mask. It is along this that you need to move the electrode in order to get a kind of seam, in the form of any of the above paths.

After the seam has cooled, you need to beat off the slag with a hammer and examine the work done.

When you have a little experience, you can begin to make connecting seams, which have several types:

In addition, such seams can be horizontal and vertical, and can be welded in different directions.

Only after numerous trainings can you achieve uniform hand movement. After this you can get beautiful details.

Pipe joining

To prevent the workpieces from moving relative to each other, the coils are laid on a corner or channel. Ideally, the discrepancy should be zero, since even a discrepancy of 1 mm, allowed by the rules, leads to lack of penetration. The gap, depending on the wall thickness, is set within 2 - 3 mm. In everyday practice, for this purpose an electrode of a suitable diameter is inserted between the ends of the pipes. For wall thicknesses of 10 mm or more, the gap is set to 3 mm. When joining, you also need to take into account the error that occurs during tack welding due to the heating of the metal at its points. The resulting thermal stresses tighten the pipes, so the gap is increased by a few tenths of a millimeter.

Correct preparation and joining of pipes

Progress

We perform the following passes:

1. Root During the welding process, take a comfortable position so as not to tear off the torch, take your time so as not to burn the base metal of the root of the weld and form a full-fledged return bead. The first pass must be cleaned with a grinder. This is necessary in order to get rid of the so-called “pockets”, which can further lead to the formation of defects.

2. Filler Technically simpler than the previous one. It is also subject to cleaning, but not so scrupulously.

3. Facing During the welding process, make sure that there are no undercuts along the edge of the seam.

All that remains is to knock down all the technological devices and strips with a hammer and clean the metal from any remaining filler material.

Depending on the type of flaw detection inspection of the seam, which will be used further to identify defects, it may be necessary to clean the front and back beads of the seam flush.

How to properly weld thin profile pipes with your own hands

When carrying out work in domestic conditions, profiles are most often welded using an inverter, which is characterized by its low weight, ease of use, wide range of adjustments and the presence of additional functions that facilitate the work.

The second important task is to determine the correct polarity of connecting the electrodes. It is well known that the positive contact has a higher heating temperature, and with the correct polarity, the “minus” is supplied to the electrode holder, and the “plus” to the body of the part

Accordingly, when welding elements with large thickness, it is better to use reverse polarity.

Rice. 12 Preparing and connecting pipes with your own hands

Butt welding of a profile pipe using an inverter

Before carrying out work, prepare a flat surface at a convenient distance from the ground; it is better to use thick-walled profiles of square or rectangular cross-section as a support, on which the metal profile to be connected will be laid. Welding work after placing the pipes on a flat surface is carried out in the following sequence:

1. Prepare profile pipes for welding. To do this, their ends are cut with a grinder at a right angle and cleaned of rust with the same grinder or sandpaper.
2. Align both workpieces. A metal corner or any smooth and long object with a flat surface is applied to their side walls; if the profile has a weld, it must match. The distance between the ends for high-quality penetration should be from 1 to 2 millimeters.
3. Using spot welding with a rutile electrode, a pipe profile is connected in several places. First, this is done in the middle, then the corner edges are welded, if high accuracy is required, all four corners and the central edges are connected.
4. Weld from the edges to the center, trying to heat the seam evenly, do not linger in one area, then turn the workpiece over and repeat the operation on the other side. For beginners, it is better to weld in short sections with separation, making sure that the edges have time to melt - this will avoid burning through the metal.
5. At the end of the work, the slag coating is knocked down, if necessary to obtain a flat and smooth surface, the protruding seam is protected with a grinder.

Fig. 13 How to weld a 2 mm profile pipe. butt

How to weld profile pipes at 90 degrees with a T-joint

Preparatory operations are carried out according to the above scheme, the order of performing the main work is as follows:

1. After joining the parts, tack the side edges on both sides.
2. First, welding is carried out in the corners, continuously moving the electrode in small circular (counterclockwise) or zigzag movements from bottom to top - this allows you to expel slag from the weld pool. The angle of inclination of the electrode should be 45 degrees relative to the horizontal plane
3. Next, the side edges located in the same plane are welded.

When welding, it burns through a profile pipe - what to do?

The following methods are used to combat burns:

• Welding is carried out with separation in short sections or spot welding.
• To prevent overheating, a piece of massive metal beam with a cross-section as close as possible to the internal dimensions of the workpieces is inserted into the joint.
• Reduce the distance between the edges of the workpieces.
• Operate in the lowest output current mode.
• Increase the speed of electrode movement.

Fig. 14 Welding a thin profile pipe with a T-joint

Answering the question of which electrodes to use to weld a 2 mm profile pipe, we answer that for welding a thin-walled 2 mm profile using the electric arc method, rutile electrodes with a diameter of 2-3 mm are most often used in direct connection polarity. Beginners, when carrying out work due to lack of experience, should take measures to combat burn-throughs or use simpler semi-automatic welding.

Convexity and concavity

Welding metal of the internal plane
Convexity and concavity are the distance between the line of the main surface of the workpiece metal and the surface that runs along the line of maximum convexity (concavity). Seams with a convex surface are considered reinforced. It is best to use them if the product is subject to a static load.

As for concave seams, they are weakened, but can withstand dynamic loads very well. In practice, it is advisable to use flat surface joints in most cases because they are the most versatile.

Width

As for another geometric parameter, the width, it is calculated as the minimum distance between the boundaries that arise when the metal is fused.

Root

The root of a seam formed during welding is called that part of the weld joint that is as far as possible from the front surface of the part on the side from which welding is performed. We can say that the root is the other side of the suture joint.

Internal welding produces an external weld root

If double-sided welding of parts is used, the root will be covered by an underweld seam. What is a weld seam? This is a small part of the double-sided welding joint, which is performed in advance (in order to prevent burn-through during subsequent welding work to create the main seam).

In some cases, if it is necessary to make a two-way connection, the back weld is allowed to be laid last at the root of the main connection.

Tips from professional welders

The profile is welded at any convenient angle, using all connection methods permitted by GOST.

I. L. Svetlichny, education: lyceum, specialty: 5th category welder, work experience: since 2004: For reliable welding of profile pipes, you need to create seams in the lower position, and use other spatial methods in inconvenient areas.”

What electrodes should I use?

Professional performers recommend using the following brands:

• ANO-4 is a common and universal brand, does not need to be calcined before use, suitable for working with a variety of welding equipment;
• MP-3S should be used when increased quality requirements are imposed on the seam;
• professionals use the brand UONI-13/55;
• good connection quality is provided by OZS-12 products, but they lack resistance to dampness.

These recommendations apply to profile pipes with dimensions of 20x40 mm.

Mode selection

Here the following parameters must be taken into account:

1. Strength, polarity and type of current (direct or alternating).
2. Electrode wiring speed.
3. Diameter and angle of inclination.
4. Welding arc voltage.

For maximum joint efficiency, the performer must use the highest current levels in each specific case, but remember that excess reduces the quality of the seam.

Butt method

To carry out this welding mode, the following requirements exist:

• first, tack work is done at the corners of the structure, then the accuracy of the joining is checked, and then the joints are welded along the entire perimeter;
• products with thin walls are boiled in one go, and thick-walled ones - in several passes;
• the arc is conducted at such a speed that the metal does not sag, but the edges have time to melt.

The welding of one joint is completed in such a way that the edge of the seam coincides with the original one and is overlapped.

For thin-walled products

How to weld thin metal corrugated pipes with a 2 mm electrode - such rolled metal is a thin-walled type and is connected using electrodes with a diameter of 1.5 to 2 mm; performers with extensive experience are allowed to perform welding work. The current strength is not higher than 60 amperes, products of the MP-3S or ANO-21 brand are used. Beginning welders should weld thin-walled profiles using an inverter.

Right angle

To achieve an exact 90-degree angle when welding a profile, you must have experience and the appropriate auxiliary tools. There is such a methodology for carrying out work:

1. Profile pipes are cut into pieces of the required length.
2. All work is performed on a flat surface.
3. For reliable fixation, magnetic squares or improvised means are used.
4. The connection is carried out in stages with a mandatory check of the connection angle.

First, the products to be joined are tacked, then the angle is specified using a measuring tool; if everything is in order, then the profile is welded around the perimeter.

Elimination of burn-through

Such negative consequences of welding occur when connecting thin-walled profile pipes, in order to prevent burn-through of the metal, it is necessary to accurately select the diameter of the electrode and set the welding current to low values, and apply the reverse polarity. Similar defects appear due to the inexperience of the performer.

Butt weld

Butt weld between two surfaces
A butt weld is used to produce a butt joint, and is most often made continuous. It is characterized by a specific feature - the shape of the edges of the workpieces being joined. Thanks to cutting, preparation of the welding site is ensured, and it also becomes possible to achieve good quality of connection of parts at the place where they are welded to each other. To improve the quality of the connection, one-sided or two-sided edge cutting is used. It is carried out in straight lines or in the shape of the letter “U”.

Excitation of the welding arc

There are several ways to initiate an arc.

Option 1. The welder should touch the metal surface with the tip of the electrode, then quickly move it back a few millimeters (2 - 4). As a result, an arc will appear. Its length is maintained by slowly lowering the electrode. It all depends on the amount of melting. Before an arc forms, the worker's face must be covered with a protective shield.

Option 2. You can excite the welding arc in another way. The welder quickly runs the tip of the electrode along the metal surface, then also quickly raises it a couple of millimeters. An arc will appear between the electrode and the metal surface. When welding, you should strive to maintain a very short arc. Small drops of metal will form near the seam. The melting of the electrode will be smooth and calm. The seam is deep and durable.

If the arc size is too long, the base metal will not melt well enough. During welding, the metal of the electrode will begin to oxidize and strong splashes will appear. The seam after such welding will be uneven, with numerous oxide inclusions.

The length of the arc can be easily determined by the sound of its burning. If the length has standard values, the sound will be monophonic and uniform. A very long arc will begin to make sharp sounds, which will be constantly accompanied by strong pops.

If the arc breaks, it is excited again. The crater where the arc broke is carefully welded. If it is necessary to weld a very important unit that will be operated under an alternating load, and “fatigue” may also occur, it is strictly forbidden to excite an arc directly on the surface of the base metal. If the excitation does not occur along the seam, a “burn” of the metal may occur. At this point, the seam may simply collapse during operation of the part.

Arc welding

Manual arc welding is widely used in all sectors of the national economy and in everyday life to connect elements of metal structures. Its distinctive properties compared to other types of welded joints are:

• Relatively low cost of the welding machine and consumables, which are electrodes.
• Obtaining high quality welded joints of common types of metals, including stainless alloys.
• The ability to carry out welding work in many hard-to-reach places - this is facilitated by the low weight and ease of connecting the equipment to electricity.

Rice. 7 Welding a thin profile pipe - type of seams

Carrying out work using electric arc welding consists of the following stages:

1. The ends of the pipes are prepared for welding; to do this, they are cleaned of rust, after which the workpieces are installed at the required distance to fill the seam with metal from the molten electrode; special devices are often used for this.
2. Turn on the welding machine, setting the required current using the built-in indicator, insert the electrode into the holder connected to the welding machine, and secure the other end to the pipe.
3. The position of the parts to be welded relative to each other is fixed by spot welding (tack welding), after which electric welding is performed using protective clothing, a welder’s mask and gloves.
4. At the end of the work, knock off the scale and clean the seam with a wire brush.

Semi-automatic metal inert gas (MIG) welding

Thanks to modern technologies, it has become possible to correctly weld profile products at home in the simplest way, which does not require extensive experience and many years of training as a welder.

Rice. 8 Operating principle of MIG

Semi-automatic inert gas welding (MIG) is an evolutionary step in the development of conventional electric arc methods, in comparison with which it has the following advantages:

• Instead of an electrode, a special wire with a diameter of 0.6 to 1.2 mm, wound in bobbins, is automatically fed into the weld pool through the torch - this automates the process and reduces the time for changing electrodes.
• Together with the wire, an inert gas (usually a mixture of carbon dioxide and argon) is supplied to the torch through the welding sleeve - this prevents the formation of slag and improves the quality of the weld.

Thanks to this technology, semi-automatic welding has the following advantages over electric arc machines:

• Allows you to weld thin workpieces with a thickness of 0.5 mm.
• Cooks steel, stainless steel, cast iron, aluminum and non-ferrous metals.
• During the work there is no slag and virtually no smoke - this is less harmful to health and improves the quality of the seam compared to electric arc methods.

The disadvantages of MIG include its bulkiness (it requires a massive gas cylinder and a system for supplying wire to the torch) and the impossibility of working in strong winds that blow gas from the welding zone.

Rice. 9 Welding of thin-walled profile pipes in an inert gas environment

(semi-automatic welding)

Now we will talk about how to make welds using a semi-automatic machine if you are welding critical structures or are going to submit them under control for NAKS certification.

Here's how this is done using the example of two workpieces (plates) 12 mm thick, butt welded in a vertical position using a SKYWAY 330 inverter.

The plates need to be prepared: cut using a plasma cutter or grinder.

Also, for the correct progress of work you will need: • lead strips (2 pcs.) - necessary for starting and finishing welding, since it is difficult to obtain a high-quality seam at these stages. The strips are technological and subsequently cut off;

• devices that prevent reverse bending of our blanks (2 pcs.);

• a template for controlling the gap (any piece of hardware that allows you to set the gap, in our case 2 mm).

In order to properly prepare our connection for further welding work, you need to familiarize yourself with the requirements of GOST 5264-80 (click to download page with text). Look for the compound you will be working with, in our version it is C17. GOST specifies how to prepare this connection: you need to bevel the edges at an angle of 30° and blunt them. The plates must be cleaned of oxides, dirt and rust at a distance of at least 10 mm from the boundaries of the future weld.

For proper assembly, it is convenient to use a magnetic square. It will align the plates relative to each other and prevent them from moving during the process of tack placement.

We control the two-millimeter gap with a template, the role of which can be played by any suitable piece of metal. Attach the template to the place where you intend to start welding and set the gap exactly according to it. At the end of the weld, the gap needs to be slightly increased, due to the fact that the plates will be pulled together during the crystallization of the deposited metal.

Next, a device is installed to prevent bending and tightening of the workpieces. They grab one device, then control the displacement and set the gap, as was said, a little more than 2 mm, for example, 2.2 ... 2.3 mm. Then they place spot tacks on the second “fixture”.

Prisp-I, preventing deformation of plates, stuck points

After you have installed the tacks, you need to see if the plates have moved. To do this, you can use the same template to set the gap. If it has a smooth edge, it can be used to control how evenly the plates being welded are aligned relative to each other - simply apply the smooth edge to the joint and see that there are no gaps.

Checking the offset with a template

If such are found, at this stage you can always straighten it with a hammer or other special tools. devices.

Now you can weld a continuous seam. We put on gloves, a mask, and arm ourselves with a semi-automatic burner. You don’t need to scald it too much, because the devices against bending of the workpieces perform a technological role and they will need to be knocked out.

Welding lead strips

The preparation of the planks is the same as for the base metal. The edges are beveled; their thickness must also correspond to the thickness of the structure being welded. They are installed on tacks.

Lead strip tacked to the base metal

In order to increase the level of complexity of the task, it is better for the welder to perform a vertical seam of the connection, this will allow him to fully test his skills and abilities. It is also necessary to correctly set the welding parameters on the SKYWAY 330 power source. The parameters can be adjusted through trial and error. In our case, for a workpiece thickness of 12 mm, the following welding mode was selected: U = 17V; Vfeed = 3 meters; Uadjusted=-5; L=0, where L is inductance. Consumables (they are optimal for the given case): Electrode wire Ø1 mm; Gas mixture 82% Ar+18% CO2.

According to the rules, in order to avoid hydrogenation of the weld, which leads to the appearance of pores, the plates must be heated to T = 100 ... 120 °C. Rules are just rules, to be circumvented. Undoubtedly, pores represent seam defects and are a rejection sign. However, it should be assumed that during the passage of the seam, the moisture present on the surface of the metal will immediately evaporate. After all, no one thinks of preheating the wire before welding. However, if you are taking the NAKS certification exam, you should know about the existence of such an operation - this is a mandatory requirement. In industrial conditions, the operation can be performed in an oven, in other cases - using an oxy-acetylene torch or torch.

Possible errors and defects in the weld

1. A large current when cooking the root leads to the formation of a hole instead of a technological window through which the metal will drip down. Provide a current of such strength that the metal has time to cool literally immediately after the movement of the electrode.
2. If the process window is not visible, most likely the current strength is too low, and it must be increased.
3. A small bluntness leads to an increase in the technological window and to sagging of the metal inside the pipe.
4. A gap of more than 2 mm guarantees the appearance of pores in the seam - the work will be unsatisfactory.
5. When welding with an electrode, you cannot make jump movements of more than 5 mm in length.

Welding steel pipes is not an easy task for a beginner. With practice will come experience and an intuitive feeling of what should be done and at what moment in order for the weld to come out perfect.

How is the strength and leg of a corner connection calculated?

The strength of a corner joint during welding is usually calculated based on the derivative of the theoretical thickness of the joint and its actual length. The size of the corner leg is calculated according to the laws of geometry (according to the length of the legs of the largest triangle that can be inscribed in the longitudinal section of the joint). The thickness of the connection is determined by the size of its leg. The size of the corner joint is determined by its leg.

Weld seam gauges

The leg must be of sufficient size so that the joint obtained during welding can withstand the design load. It should be taken into account that excessively large values ​​of the weld leg during welding can cause welding deformations. Another significant point: an increase in the leg leads to a proportional increase in consumables when welding workpieces, as a result of which the cost of work also increases.

To control the quality of fillet welding joints in real conditions, it is customary to use several types of special templates. The most common method for determining the leg is to use a universal welding template.

Welding process

Tack

Welding of the pipe under the clearance begins with tack welding at several points. Their number depends on the diameter of the workpieces, but not less than four in increments of 90˚. After creating the first point, the position of the pipes is adjusted if necessary. The tack should securely fasten the workpieces together. After welding all the points, the joint is cleaned again. Detected pores and poorly cooked areas are removed, as they will later become the cause of defects.

Root of seam

It is more convenient to carry out welding if the stuck pipes are in a semi-ceiling position. This will provide free access to the joint. A mark is placed on the bottom of the connection. Having retreated 1 - 3 cm from it, begin welding the root of the seam under the gap. The arc is struck at the bevel or its outer edge, but not at the surface of the pipe. On the ceiling part of the joint, the tip of the electrode is in the gap with a gradual upward movement. To form a return roller, the arc must burn inside the pipe.

When moving the electrode without lateral deviations, you need to ensure that both edges are melted. If only one side melts, you should stop and repeat the pass. An arc burning from the outside means that the joint has tightened. It can be cut through with a large current, but it is preferable to carefully expand it with a grinder. If the welded root weld sags, it means that the welding current is too high or the electrode is moving slowly.

If you imagine the end of the pipe in the form of a watch dial, then when leaving for 40 minutes the electrode begins to swing half the diameter between the edges. As a result, a technological window is formed through which the formation of the inner roller can be monitored. When welding thin-walled pipes of small diameter, it is only outlined, but you should not melt a through hole at this place. The electrode moves without oscillating movements, only the position of the holder changes to ensure arc stability at a minimum current.

Welding steel pipes “through transmission” - step-by-step instructions

Pipes with thick walls, in which 2 mm is only the amount of dullness, are welded “through the light”.

Preparation and cutting of edges

The abrasive method is the least reliable due to the introduction of abrasive particles into the metal, which interferes with high-quality melting and leads to the appearance of cracks.

Use a double-sided Y-shaped symmetrical groove with an angle of 65 degrees, an optimal amount of bluntness and a gap of 2 mm.

• processing on a milling machine;
• manual bevel processing;
• cutting using abrasive wheels;
• processing with slotting-type edge cutters.

• Clean the joints of the welded products to white metal. There should be no irregularities, burrs or rust left.
• Treat surfaces with acetone or any similar substance. The presence of grease, dirt, and dust prevents the high-quality connection of metal molecules.

Centering and joining of pipes

1. Centering and joining of small-diameter products is carried out by fixing them using improvised means or using assistants.
2. Center large pipes (from 60 mm) with special equipment - a centralizer: internal or external. Both have an electro-hydraulic drive. Internal ones are more preferable due to the fact that when they are used, the joint remains uncovered. This allows the use of automatic welding machines, and also does not limit manipulations during manual connection.
3. Do not allow deviations when using the manual alignment method. It is impossible to dock perfectly without a centralizer, but try to minimize the deviation.
4. Having connected the pipes exactly, proceed to welding the root seam.

Root welding

1. Cook the seam under the following conditions:
2. minimum current;
3. reverse polarity;
4. short electric arc;
5. dry electrodes;
6. lack of wind in the pipe.
7. Cook vertically, the electrode is perpendicular to the plane.
8. Use an electrode to melt the edges - a bridge will appear between them, which is called a weld pool. In front of the jumper there is a so-called technological window.
9. Carefully monitor the size of the technological window: throughout the entire process it should remain the same diameter.
10. Make a root seam no more than 1 mm high. The return roller should also not exceed this value.>
11. Clean the beginning and end of the seam and the transition area between the electrodes to avoid the formation of pores in the metal, the presence of which will sooner or later lead to loss of the pipe’s tightness.

Filling and capping of the weld

1. After welding the root, fill the entire seam section.
2. Depending on the wall thickness and material, use a single-layer or multi-layer penetration method.
3. The movement of the electrode during filling is a triangle: edge 1 – edge 2 – technological window.
4. Pay attention to the heating of the edges and root seam. The greater the heating, the wider the filling step.
5. After each layer, clean the surface of slag.
6. If you have the skill, and if the wall diameter allows, fill and cover in one pass.

Video lesson on welding pipes under clearance

Electric Welding Theory

Anyone can do welding work at home. To do this, it is recommended to familiarize yourself with the basic theory of the electric welding machine.

Before starting the work process, you need to prepare:

• welding installation;
• electrodes of the required diameter;
• special protective mask. It protects the eyes from bright radiation during a chemical reaction. In addition, it prevents scale from getting into the face area during work;
• mittens made of thick fabric;
• Rubber Shoes.

The joining of metal surfaces occurs as a result of the occurrence of an electric arc, which, under the influence of high temperature, ensures a chemical reaction between the iron surface and the coating of the electrode.

It consists of highly flammable elements and minerals. During operation, a gas cloud is released. It further prevents the oxidation of hot iron with oxygen. After which, this cloud settles on the metal surface and acts as additional protection.

For a manual apparatus, a steeply dipping and gently dipping characteristic is used. In the first type, the welding current does not depend too much on the electrical voltage, which means the distance between the electrode and the surface of the iron does not require special accuracy. Welding with a flat characteristic requires maintaining the correct distance.

Additional ignition (oscillator) generates maximum voltage. When an electric arc forms, it turns off.

Welding gas pipes under pressure

Welding special gas pipes for transporting high-pressure contents places increased demands on the process.

Gas pipe welding technology

Features of welding pipes for transporting high-pressure trains are determined by two characteristics:

1. Thick walls and small diameter.
2. Aggressive effects of transported gases.

Pipes up to 10 cm in diameter are welded manually, above - using semi- or automatic welding with manual welding of the root of the seam. For diameters greater than 6 cm, special rings are used. The weld is made multi-layered - from 4 layers and above, depending on the load on the pipeline and the characteristics of the material. After completing the work, a mandatory inspection is carried out - flaw detection inside and outside the welding site.

Yulia Petrichenko, expert

Video lesson on welding gas pipes

How fillet welds are welded

The molten metal during this welding will flow down. The optimal way to weld such seams from the bottom position is considered to be “in a boat”. The part is installed in such a way that slag does not leak directly in front of the arc. (See Figure 68, a).

When a fillet weld is welded, with the bottom plane positioned horizontally, sometimes the corner vertices are poorly welded.

The reason for the formation of such a lack of penetration may be the start of the welding process from a sheet standing vertically. The molten metal begins to flow down onto the sheet, which has not had time to warm up well. That is why such seams need to be welded from the bottom plane. Moreover, the arc must ignite at a certain point (A). The movement must be carried out according to the diagram in Figure 68 b.

Welding difficulties

When welding galvanized pipes, the temperature in the welding zone reaches +1200 ℃. The zinc layer burns out. This metal begins to boil already at +906 ℃. That is, it turns out that at the junction of two pipes a zone without protection is formed. But these are not all the negative aspects of welding galvanized pipes.

Zinc gas is a substance harmful to humans. Once in the respiratory tract, it leads to suffocation. Therefore, welding in rooms without good ventilation is prohibited. In addition, for safety reasons, the welder must wear a respirator under the mask.

At high temperatures, zinc begins to evaporate rapidly, which leads to the formation of shells and pores inside the steel. And this reduces the quality of the junction and the strength of the junction of two galvanized pipes.

What defects may occur during welding?

The biggest defect in welding is considered to be lack of penetration. Welders who experience such flaws are not allowed to work on pipelines. Sloppy seams and their sagging, as well as other minor defects occur when welding technology is violated. To prevent them, work must be performed in compliance with the following conditions:

• welding is performed with a short arc at minimum current;
• detachment of the electrode is allowed only when replacing;
• careful selection of current;
• proper pipe preparation;
• carrying out work with calcined electrodes;
• the welding site must be protected from wind and precipitation;
• use of high-quality equipment and electrodes.

When mastering this type of welding, the main thing is to learn how to deposit the root of the weld. For training, you can take two metal plates 10 mm thick and grab them with a gap, not forgetting about preparing the joint. By fixing them at different angles, they practice welding skills in clearance horizontally, vertically, and on the ceiling.

Technological options

• the weld is completely performed by manual argon arc welding with a non-consumable electrode (recommended for wall thickness up to 3 mm);
• the weld is performed using a combined method: the root seam is performed using manual argon arc welding with a non-consumable electrode, and subsequent layers are performed using manual arc welding with a coated electrode (suitable for pipe wall thicknesses of 4 mm or more).

Approximate location of layers and beads (1 – in joints welded using various technological options

* For wall thickness up to 2 mm, the joint section should be welded in one layer

Manual argon arc welding with a non-consumable W-electrode is used for fixed joints of pipes made of low-carbon, low-alloy and alloy (corrosion-resistant) steels. The diameter of the welded pipes is less than 100 mm, the wall thickness is up to 10 mm.