Technological features of welding galvanized pipes
The service life of a steel pipe increases by an order of magnitude if it is coated with a protective layer of zinc. However, the process of welding galvanized pipes has its own technological features, non-compliance with which leads to rapid wear of the pipe at the joint and threatens the health of the welder. There are several ways to safely and efficiently weld galvanized metal. The choice of a specific technology depends on the location of the work, the qualifications of the welder and the availability of certain welding equipment.
Problems connecting zinc pipes using welding
There are three sides to the problem of welding galvanized metal. The first is that zinc, if inhaled by a worker, can cause respiratory arrest. The welding temperature of steel fluctuates around 1200 degrees. In this case, the zinc coating begins to evaporate at a temperature just above 900 degrees.
Note! Welding work on galvanized materials must be carried out in special protective clothing: a respirator, a welding mask and heat-insulating gloves.
If welding work is carried out indoors, it is necessary to ensure effective ventilation.
The second problem is that the presence of molten zinc degrades the quality of the joint. Galvanizing is mixed with the base alloy, embedding itself into the crystal lattice and weakening it. Intense evaporation of the zinc coating causes the formation of bubbles, cavities, and inhomogeneity of the weld seam.
https://www.youtube.com/watch?v=HXHPhmkAN5M
It would seem that by removing the galvanization at the joint, you can safely and efficiently connect the pipes. However, here lies the third problem - local removal of galvanization leads to rapid wear of communications at the joint.
Welding technologies for galvanized products
Technologists offer several ways to solve the problem of welding galvanized pipes:
- preliminary removal of the protective coating and its subsequent restoration;
- reduction of welding temperature;
- reduction of welding time;
- preventing zinc evaporation by using flux.
Cleaning of the work area is carried out either mechanically or chemically. In the first case, use a grinder with a metal brush or an abrasive wheel. Here it is difficult to control the locality of protection removal. Chemical removal of galvanization is carried out by treating the joint with a solution of hydrochloric acid. It is applied carefully, in small portions, without damaging the base metal.
Selecting Electrodes
The process of welding galvanized pipes differs little from welding ferrous metal. The technological feature of the work is to reduce welding time while simultaneously increasing the current strength of the process. This can be achieved using rutile-coated electrodes.
Rutile electrodes
Rutile electrodes are electrodes whose coating consists of titanium oxide with admixtures of aluminosilicates and carbonates.
Note! Welding work with rutile electrodes can be started only after they have been preheated at a temperature of 200 degrees and held for a day afterward.
Advantages of rutile coated electrodes:
- the presence of titanium oxide facilitates the process of igniting the electrode at the beginning of operation or when it fades during operation;
- the characteristics of the welding arc make it possible to obtain a high-quality seam, without lack of penetration, cracks, and with high resistance to wear;
- minimal metal spattering reduces the loss of molten metal.
The presence of iron powder in the rutile coating reduces the alloying level of the steel, which increases the strength of the resulting joint.
Explanation and designation of electrodes
Main electrodes
Electrodes with a basic coating are used for welding thick-walled low-alloy steel pipes. The powder coating here has a complex composition of ferroalloys, calcium fluoride, and magnesium compounds.
The cooking process is accompanied by the release of carbon oxides, which protect the molten metal from the destructive effects of atmospheric oxygen and hydrogen.
Electric arc welding technology for galvanized pipes
In addition to the correct choice of the type of electrodes, the quality of the weld is influenced by the qualifications of the welder. The process requires careful but fast work. When the process slows down, it is easy to burn through the connection. When moving the electrode quickly, the seam results in lack of penetration.
We recommend that you read: Methods for making the transition from HDPE pipe to metal
The same joint defects result from an incorrect choice of electrode diameter. The power of the electric arc directly depends on the thickness of the electrode wire. For pipes with a wall of 1.5-3 mm, the optimal diameter will be a wire of 2-3 mm.
Note! The optimal welding speed for galvanized pipes is not established by decree. A qualified welder acquires the skills of electrode welding through experience.
Features of connecting galvanized pipes using the welded method:
- Thin-walled pipes are connected without pre-processing the ends.
- To connect thick-walled pipes, you will need to first chamfer. This must be done partially, without forming a sharp edge. A partial bevel of the edge when joining the ends end-to-end should ensure the formation of a groove, which is filled during welding.
- Electrodes are selected according to the thickness of the pipe wall. The gas torch number for galvanizing is chosen two sizes smaller than when welding ferrous metal.
- During the soldering process without removing the zinc layer, care should be taken to ensure that the spraying does not “boil.”
- When using a torch, the flame is directed at the solder, not at the pipes.
- After welding, excess flux is removed.
Getting flux inside a pipe when working on water supply lines is safe for humans, since it is easily washed out with water and is not toxic.
Galvanized gas welding
Welding of galvanized pipes without damaging the protective coating is carried out with a gas torch using HLS-B flux. It is applied to the ends of the pipes to lower the heating temperature of the zinc layer. As a result, the zinc does not evaporate during the process, but melts under flux, remaining on the surface of the pipe.
The edge of the pipe needs to be pre-cleaned and degreased. The ends of the pipes are heated at a distance of up to 30 cm from the edge. The flux is applied at a distance of 2 cm from the end of the pipe in a thick layer. Its initial consistency is a thick paste. By heating it is brought to a semi-liquid consistency. The readiness of the flux to begin work can be determined by changing its color.
Note! When heated, the flux first acquires a yellowish tint, then becomes milky white. Welding should begin after the flux becomes transparent and gel-like.
Application of protective coating
Restoration of galvanization in a factory workshop is carried out using cathode sputtering. The process is of an electrochemical nature and is therefore not applicable in field conditions. When installing household communications, an alternative protection is painting the pipes. The coating requires constant monitoring and renewal when pipes rust.
Paint with a zinc dust content of more than 90% has a more lasting protective effect. Apply it using an ordinary brush. There is a way to restore the zinc coating by fusing chemically pure zinc wire onto the joint surface.
Source: https://InfoTruby.ru/soedinenie/svarka-otsinkovannyh-trub
Options for welding galvanized pipes - advantages and disadvantages of methods
:
Pipes made of galvanized steel are very widely used for laying various communications and constructing all kinds of metal structures, since they have good performance qualities. Installation of such products can be done in several ways. This material will tell you how to weld a galvanized pipe, and what features of this process may be important during the work.
Methods for welding galvanized steel pipes
The technology of electric welding of metal products involves heating the working surface of the seam to 1200 degrees, while the boiling point of zinc is only 906 degrees. Such a difference in performance in some cases leads to burnout of the zinc layer.
Among the undesirable consequences of the welding process of galvanized pipes are:
- Zinc fumes are extremely harmful to health. If the room is not well ventilated, inhaled vapors can cause poisoning or temporary respiratory arrest for the worker.
- The zinc layer on the welding seam is damaged during operation, so corrosion processes can begin in this place, and the profile galvanized pipe will no longer last as long as it could.
- If intense zinc evaporation occurs during welding of a galvanized pipe with an electrode, the surface of the pipe may become covered with pores and cracks. As a result, the seam will not be sufficiently tight and strong.
Thus, compliance with safety rules when working with these products is a prerequisite. The face must be protected with a special respirator and a mask made of dielectric materials. Rubberized gloves with thermal insulating fabric on top are put on your hands.
If you pre-treat the working surface of the pipe with hydrochloric acid, you can avoid foaming of the zinc layer. Please note that ideally it is advisable not to allow the zinc coating to evaporate, so as not to deprive the pipe of corrosion protection. This can be achieved using several welding methods.
The first method is to mechanically clean the galvanized layer using an abrasive wheel with emery or a metal brush. All further welding work will be carried out as with ordinary black pipes.
The disadvantage of this technology is that it eliminates the corrosion protection that the zinc coating provides, so that the service life of such a pipeline is significantly reduced (read: “Types of pipe welding technologies - advantages and disadvantages of methods”).
Due to contact with liquid, such a pipe will quickly begin to rust and very soon it will need to be repaired or completely replaced, which will entail additional labor, material and time costs.
However, if the area without a zinc layer is small, it can be protected by the cathodic method - apply zinc sputtering to the cleaned area using an electrochemical method (read: “Options for cathodic protection of pipelines - advantages and disadvantages of methods”).
An alternative technology for welding galvanized pipes is the use of special fluxes for soldering. In this case, there is no need to remove the zinc coating. This method is widely used in situations where it is impossible to clean the pipe. To connect pipes, UTP 1 alloy and HLS-B flux are required. It is noteworthy that flux completely dissolves upon contact with water, it is safe for health, so this method is quite acceptable for assembling plumbing systems.
Method of welding galvanized pipes using flux
Before welding galvanized pipes by electric welding using flux, the edges of the pipes must be cleaned until the metal shines and degreased, and both the external and internal parts of the pipe should be treated (read also: “How to properly weld pipes by electric welding - theory and practice from the master” ).
The prepared pipe sections need to be heated to a length of 20-30 cm on both sides of the future seam. At the same time, there is no need to perform any manipulations with the edges of pipes whose wall thickness does not exceed 3 mm - the joint will be of high quality. In this case, the gap between the ends will be 2-3 mm.
If the walls of the pipe are thicker, then the size of the gap can be left the same, but the opening angle of the edge will be 80-90º with a blunting at a height of 1-1.5 mm.
Before welding, the flux must be heated to a state intermediate between solid and liquid, and then applied to the future joint in a fairly thick layer. At the same time, to join galvanized pipes, you will need twice as much flux as to work with pipes made of ordinary steel. The purpose of the flux is to draw off excess heat during the welding process so that the zinc layer does not boil and begin to evaporate from the edges of the pipe.
When heated, the flux changes its color - first, from yellow to white, and then becomes completely transparent. This means that you can start soldering the pipes.
Please note that the size of the nozzle in the burner will depend on the wall thickness of the galvanized pipe.
In particular, if the pipe wall thickness is in the range of 2-6 mm, and its cross-section does not exceed 250 mm, then a nozzle with a diameter of 1-2 mm will be sufficient. This also applies to filling joints on any pipelines.
If the diameter of the galvanized pipe is more than 250 mm, and its walls are more than 2-6 mm thick, you will need a burner with a 2-4 mm nozzle.
Such close attention is paid to the burner nozzle because its too large diameter will lead to overheating of the working surface, as a result of which the zinc will begin to evaporate. In addition, the presence of molten zinc on the surface of the pipe leads to the formation of pores, which reduces the product’s resistance to corrosion and shortens its service life.
On the contrary, a nozzle diameter in the torch that is too small will not allow the metal to be heated to the temperature required for welding, which will inevitably lead to solder sticking.
Soldering of galvanized pipes is carried out with an oxygen-acetylene flame adjusted to excess oxygen. This is done so that during the soldering process, when the solder interacts with silicon, its oxide is formed, which prevents the evaporation of zinc.
Please note that the burner flame must be stable, and it must be focused on the gap between the workpieces and on the edges. Otherwise, the pipe at the connection may overheat.
The optimal method for welding a galvanized pipe when using a gas torch is the “left” technique, that is, placing the solder in front of the flame so that it does not hit the metal surface. When making a remelting seam, the burner must be held at an angle of 70-75º. If you need a filling seam, then the angle of inclination will be 15-30º. It is easiest to observe the weld pool if the torch is in the down position, although this is not essential.
In one pass, you can connect pipes with a cross-section of up to 4 mm, but for products with a large diameter, multi-pass welding will be required.
At the end of the job, remove all excess solder with a wire brush and water. When doing this, you should be careful not to damage the zinc coating. The inside of the pipe is left with water for a day and washed.
If everything is done correctly, the seams are of high quality and do not require additional protection against corrosion.
Connecting zinc-coated pipes using manual electric arc welding
To prevent porosity in butt and fillet welds, you can increase the current and reduce the welding speed. To do this, you will need electrodes for galvanized pipes, which are selected depending on the grade of steel. In particular, the brand of electrodes for welding galvanized high-carbon steel pipes is selected with a rutile coating. And if low-alloy steel is used for pipes, then electrodes with a basic coating are quite suitable.
Electrodes with rutile coating have a whole list of advantages:
- Due to the presence of titanium oxide in the electrode, the arc can be ignited very easily and quickly, and repeatedly.
- Welds with such an arc are sealed, durable and of very high quality, without any defects.
- There is virtually no splashing during operation, so material losses are negligible.
The rutile coating of the electrode may contain inclusions of iron powder. It helps reduce the specific gravity of carbon in the zinc layer and increases resistance to cracking.
It is worth noting that to perform welding work using electric welding, you need at least minimal practical experience (for more details: “How to weld pipes using electric welding correctly - a step-by-step guide”). In addition to the outer coating of the electrode, its thickness also affects the arc power.
In particular, an electrode that is too thick will produce an arc that will quickly burn through the material. On the contrary, it is unlikely that it will be possible to make a sufficiently powerful and high-quality seam with an electrode that is too thin.
Since work is most often carried out with pipes with a wall thickness of 1.5-5 mm, the optimal electrode diameter will be 2-3 mm.
The speed at which the electrode passes over the surface also plays an important role in the welding process. If you do this too slowly, there is a high chance of burning the pipe. And if the speed of movement of the electrode is higher than necessary, the weld will be weak. The optimal speed can only be determined experimentally.
Do not forget to treat the seams with an anti-corrosion compound upon completion of welding work.
The anti-corrosion agent must meet the following parameters:
- have good adhesion to the surface;
- provide protection against oxidation on zinc coating;
- be convenient and easy to apply without special tools.
A good option for protecting galvanized products is a special paint containing about 94% zinc dust. This composition is easy to apply and holds well on a vertical surface due to the presence of unsaponifiable binders in it.
An alternative method of anti-corrosion surface protection is surfacing wire containing 99.99% zinc or zinc-cadmium rods.
Other methods of joining galvanized products
Another way to connect galvanized pipes without heating them is threaded joining. Cutting threads on galvanized pipes is quite difficult, so this method is practiced mainly on products with a small cross-section. In addition, this method is financially more expensive compared to conventional welding. Another important point is that in the thread cutting area the zinc layer will be destroyed, so the pipe will begin to rust faster.
To assemble water supply and heating communications, non-welded sets of pipes with fittings, reminiscent of a construction set, can be used. This kit contains a special coupling with a sealing ring, which is secured with bolts to the groove along the edges of the pipe. Although this method of pipe assembly is not yet widespread in our country, it provides a strong connection and is performed very quickly.
To summarize, we can say that the answer to the question of whether it is possible to weld galvanized pipes will be positive, provided that safety precautions and work technology are followed, as well as experience. Remember that it is very important to avoid overheating of the pipes and evaporation of zinc. These phenomena can be prevented using flux and rutile electrodes. Alternative methods of joining pipes, although they have a right to life, however, are significantly more expensive.
Source: https://trubaspec.com/soedinenie-trub/varianty-svarki-otsinkovannykh-trub-preimushchestva-i-nedostatki-sposobov.html
Principles of welding galvanized pipes
Heating networks are often made of elements coated with a layer of zinc. Welding galvanized pipes has many nuances that must be taken into account during installation. This is due to the characteristics of the material and its technical characteristics.
Welded galvanized pipe
Is it possible to weld galvanized pipes?
The rules for assembling pipelines are determined by GOSTs. However, the standard requirements are not suitable for working with galvanized pipes. The protective layer of zinc boils at a temperature of 906 degrees Celsius. However, the base must be heated to 1200 degrees. Because of this, innovations were introduced, which identified two possible ways to solve the problem:
- Welding using flux. The composition should not contain components that dissolve in water.
- Reduced welding time. This way the zinc will not have time to evaporate. To complete the work faster, you need to increase the temperature using the current regulator.
The welder chooses a method depending on the situation and technical requirements.
Welding methods
There are two technologies for welding galvanized pipes:
- Gas burner. This method involves the use of special alloys for welding and flux.
- Electric arc apparatus. To perform the work, you need to use special electrodes that have a rutile coating. The optimal current range is 100–160 A.
When using an electric arc apparatus, the thickness of the pipes plays an important role. If it does not exceed 3 mm, the elements are welded immediately. If it is larger, before welding it is necessary to chamfer the edges to be welded. After completing the work, the seams are cleaned with a metal brush. Next, a zinc-based protective coating is applied.
Gas torch welding technology
Not every novice welder knows how to weld galvanized pipes at home. To do this, you need to take into account several features:
- Select a burner depending on the diameter of the pipe to be connected. Equipment with numbers 1, 2, suitable for working with pipes with a diameter of up to 250 mm, wall thickness up to 6 mm. Numbers 3, 4 for other sizes.
- Maintain a constant flame when welding.
- Increase oxygen supply.
We must not forget that zinc vapor is poisonous. You need to work using a welding mask and a respirator.
Torch for welding galvanized pipe
Preparation
Before turning on the welding equipment, you need to prepare:
- Cut the pipes to the required size. Clean the ends from metal burrs.
- Remove the chamfer if the wall thickness exceeds 3 mm. The opening angle should be 80 degrees.
- Clean dirt from the joints and degrease them.
- Lay two pipes opposite each other with a gap of 3 mm for the seam. Secure them in a vice or other holding device.
- Apply flux to the surfaces to be joined. The optimal layer thickness is 2–3 mm.
After completing the preparation, you can start welding.
A little about welding galvanized pipes
How to weld galvanized steel correctly?
The process of working with a welding machine:
- Turn on the burner. Start heating the galvanized surfaces at a distance of 30 cm.
- The flux must be heated to such an extent that it turns from yellow to transparent.
- Insert the filler wire into the heating zone so that when melted, it fills the voids, forming a seam.
- Bring the torch closer to the filler wire so that it begins to melt. To do this, just heat it to 950 degrees.
Welding galvanized pipes (rotary seam)
It is important to control the burner to avoid overheating areas without flux. This will damage the zinc coating. To make it convenient to regulate the oxygen supply to the work area, welders recommend using a three-position gearbox.
How to weld galvanized pipes (fixed seam)
Completion of welding
After completing the work, you need to wash off the flux. For this, a soap solution is used. Next you need to clean the finished seam. To do this, use a metal brush. The movement should not be too intense. This may damage the zinc layer. The last stage is coating the cleaned seam with anti-corrosion paint, which contains a large amount of zinc.
Welding galvanized pipes (horizontal seam)
Galvanized welding has many nuances that are unknown to beginners. Before starting work, you need to select equipment and electrodes. The use of personal protective equipment cannot be ignored. They will protect the body from the harmful effects of zinc vapor. Beginning welders need to practice on rough tubes.
Source: https://trubyda.ru/svarka/otsinkovannyh-trub
How to cook galvanized pipes
23.09.2018
Galvanized steel pipes are often used for laying heating networks, water supply and sewerage systems. When installing a pipeline, it is necessary to take into account a number of nuances associated with the difference in the melting temperature of zinc and steel. If you connect protected metal using conventional methods, the quality of the coating will suffer.
Zinc fumes are very harmful; it is easy to get poisoned when working with them. Peeling off the protective coating is also not an option; the line will begin to rust at the seams; this must be taken into account when welding galvanized pipes.
Is it possible to weld galvanized pipes?
GOST provides rules for the assembly of water pipelines. Instead of traditional welding methods, others are provided that do not violate the protective zinc coating during the installation process. The protective layer boils at 906°C, and the alloy must warm up to 1200°C. How to weld a galvanized pipe in this case:
- Speed up the welding time so that the zinc does not have time to evaporate. To do this, you need to increase the temperature in the melt zone by adjusting the currents. If the steel quickly reaches condition, the coating will not be damaged.
- Weld using flux - a special protective composition that can preserve the integrity of the zinc coating. Fluxes must meet certain requirements and not contain harmful components that can dissolve in water.
Welding galvanized pipe
Technologies for welding galvanized pipes
Steel pipes without a protective coating quickly corrode and fail. Therefore, a technology for applying a protective zinc layer was developed, which increases the service life of the material by almost ten times.
Galvanized pipes are used everywhere today; they are cheaper than stainless steel products and are not inferior to them in terms of technical characteristics. But there is a negative point associated with the melting point of zinc and other properties of this metal.
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 technologies are used
Taking into account all the above-mentioned disadvantages of welding galvanized pipes, two special technologies have been developed in which the welding process is carried out so that the galvanization does not collapse.
In the first technology, the welding zone is treated with a special material - flux, which covers the joint and prevents the zinc from burning out, that is, going into a gaseous state.
It absorbs part of the thermal energy onto itself, and inside, under the flux, the zinc melts and becomes viscous-liquid. This metal envelops the connection of two galvanized pipes, evenly covering their ends. The protective layer is thus not damaged.
The second technology uses special electrodes that can withstand high current. This method is based on the position of reducing welding time, during which the zinc does not have time to evaporate.
That is, the welding process is carried out so quickly and without reducing the quality of the connection that the protective coating does not have time to turn into gas.
These technologies are used everywhere today when it comes to welding galvanized pipes. And not only those that are assembled into gas pipelines or into supporting structures in construction.
In the water supply, under the influence of running water, zinc dissolves and is partially removed. So it does not pose a danger to human health.
Rutile coating
Electrodes with rutile coating are used. Rutile is a mineral in the form of titanium oxide. It is powder coated and used as a concentrate with a content of more than 50%. The composition also includes aluminosilicates and carbonates.
The slag obtained during welding has high alkalinity, so the metal of the joint has such characteristics as high impact strength and increased protection against the formation of hot cracks.
The only requirement for rutile electrodes for welding galvanized pipes is to dry them for an hour at a temperature of +200 °C before starting the process. But you can use consumables only after a day.
Basic coating
Basic coated electrodes can be used. This powder layer has a complex formulation, which includes a large number of different chemicals: magnesium, calcium, fluorspar and ferroalloys.
When burned inside the welding zone, the powder releases carbon dioxide and carbon monoxide, which protect the molten metal from oxygen and hydrogen. The last two reduce the quality of welding. Typically, these electrodes are used to weld pipelines made from thick-walled pipes.
Process nuances
As for the welding process itself, it is based on the thickness of the pipe wall. If this indicator does not exceed 3 mm, then the ends of the pipes are connected with an electrode without preliminary preparation, leaving a gap of 2-3 mm between them.
Of course, the cleanliness of surfaces (both external and internal) must be ideal, so they are cleaned of dirt and degreased with alcohol or solvent.
If the thickness is more than 3 mm, then a chamfer is made at the ends of the galvanized pipes with a blunting of 1.5-2 mm, depending on the wall thickness. During the cooking process, the space between the chamfers is filled with molten metal from the electrode rod.
It is important to select the correct current strength on the welding machine and the diameter of the electrode. High current will lead to burning of the connected products.
The same applies to electrodes with large diameters. And vice versa, if the current is small or the diameter of the consumable is small, then lack of penetration will occur. And this reduces the quality of the joint.
Much will depend on the speed of movement of the electrode along the welding zone. Here, as in previous cases, slow movement means there is a possibility of burning through the steel and galvanized layer.
High speed means the same lack of penetration. Suitable welding speed comes with experience. And the more often you have to weld galvanized pipes, the better the quality of the seam.
Subsequent processing of the joint
After welding is completed, it is recommended to treat the joint of two galvanized pipes with an anti-corrosion compound. It must have three main qualities:
- adheres well to metal surfaces;
- be resistant to corrosion processes, at least at the level of zinc coating;
- Easy to apply without the use of special equipment or tools.
A special paint that contains more than 94% zinc dust is popular for covering joints. Essentially, it is zinc in the form of dust, into which unsaponifiable binders are added.
Therefore, the paint can be easily applied with brushes or rollers to any surface: horizontal, vertical or inclined, where it adheres well and does not run off.
Application of a gas burner
You can connect two galvanized pipes using a gas torch. The technology labeled “UTP”, which was once invented by the Germans, is increasingly being used.
To do this, they used HLS-B flux, which protects the zinc coating from fading. Today, rods of the UTP-1 brand are offered using this technology - this is copper-zinc solder in the form of a rod 2 mm thick. With its help you can cook not only galvanized products, but also copper alloys and cast iron.
Preparation and soldering
Preparation for the process is identical to that used for welding galvanized pipes with electrodes. But there are certain features and standards that are established by GOSTs and SNiPs.
The heating pad number is selected 1-2 positions less than when welding conventional steel pipes.
More oxygen is added to the acetylene flame. This is done so that silicon, which is a component of solder, combines with oxygen to form an oxide.
It is the latter that is the main protective ingredient in the process of inhibiting zinc evaporation. In this case, the flame must be stable, it should not jump, which will lead to temperature changes in the welding zone.
The ends of the pipes are preheated to a width of up to 5 cm.
As for the burner number, there is a direct relationship with the pipe diameter:
- diameter up to 250 mm with a wall thickness of 2-6 mm - burner number 1 or 2;
- more than 250 mm with the same thickness - burner number 3 or 4.
Soldering itself is the introduction of a solder rod into the joint area, where it is heated by a torch and melted. In this case, it is very important to direct the fire not at the ends of the galvanized pipes being connected, but at the solder rod .
For this technology, it is better to use welding towards yourself, when the rod moves in front of the torch. By the way, it should be brought to the joint at an angle of 40°.
Flux application
But before welding, the junction of two galvanized pipes is filled with “HLS-B” flux. This is a paste-like substance that is applied to the ends so that it fills an area on each side of the joint with a length of at least 2 cm.
It should be taken into account that the thickness of the flux layer should be two or three times greater than when soldering conventional pipes.
Final stage
If galvanized pipes up to 4 mm thick are connected by soldering, then welding is carried out in one pass. If it is more than this indicator, then for two or three. After the work is completed and the joint has cooled, the flux that remains on top of the joint is removed with water and a wire brush.
There is no need to be overzealous so as not to damage the zinc coating. The inner surface of the connected products is washed with water, which fills the pipeline for a day.
Welding galvanized pipes is not as easy as it might seem at first glance. A small deviation from the rules and regulations will lead to serious defects that will affect the quality of the final result.
Source: https://svaring.com/welding/detali/svarka-ocinkovannyh-trub
How to weld galvanized pipes?
Currently, galvanized steel is widespread and is often used in the construction of pipelines, in the creation of various structures and in all kinds of industrial work.
The popularity of this material is due to the high anti-corrosion properties of zinc, reliability and low cost of this material. In addition, the technical and operational characteristics of galvanized steel are quite good.
Welding galvanized pipes is a process characterized by a number of features that will be described in this article.
Rules for performing welding work
In order to ultimately obtain a reliable welded joint when welding galvanized steel pipes, you must comply with a number of rules and requirements for this process:
- during work, monitor the condition of the zinc, make sure that it does not overheat, this will protect the pipes from corrosion processes,
- the area where galvanized products are connected must be thoroughly cleaned and degreased; to protect the layer, coat it with flux,
- if the welding process uses pipes with a wall thickness of less than 3 mm, then the edges of the product do not need to be pre-prepared; it is enough to make bevels and edges,
- the torch used for welding galvanized parts must be smaller in size than that used for welding conventional steel pipes,
- the gas flame must be adjusted so that excess oxygen remains,
- Before starting welding work, the workpieces must be heated,
- the coated rod must be positioned at the joint in such a way that at the moment of melting, the flame hits only the rod and not the material,
- At the end of welding, the flux must be removed.
To make the seam as resistant to possible cracks as possible, during the welding process it is necessary to reduce the amount of silicon at the joint.
After all the work is done, the seam must be covered with a protective layer.
You can use paint with 94% or more zinc dust, or zinc wire with 100% zinc.
Source: https://svarkaed.ru/svarka/izdeliya-i-konstruktsii/kak-svarit-otsinkovannye-truby.html
Welding galvanized pipes: how it is done, technique, equipment and materials, features
Galvanized steel is often used in construction work, pipeline structures and industry.
It easily withstands difficult environmental conditions, since zinc makes the metal resistant to oxidation and corrosion.
In addition, this type of steel is inexpensive and durable, but its processing requires special knowledge, which we will share with you in this article.
Galvanized pipe welding technology
Steel pipes without a protective coating quickly corrode and fail. Therefore, a technology for applying a protective zinc layer was developed, which increases the service life of the material by almost ten times.
Galvanized pipes are used everywhere today; they are cheaper than stainless steel products and are not inferior to them in terms of technical characteristics. But there is a negative point associated with the melting point of zinc and other properties of this metal.
Do-it-yourself welding of galvanized pipes - technology and rules
Hello, dear readers!
From some sources you can get unreliable information that welding galvanized pipes is prohibited in principle. In reality, this is not entirely true: there are ways to properly weld such pipes.
Today I will tell you about well-known and widely used welding technologies.
Welding methods
Taking these features into account, special technologies have been developed that provide complete safety of galvanized pipes:
- submerged;
- special electrodes.
Using flux
Welding points are coated with a special substance - flux. It prevents the zinc coating from fading and turning into a volatile gas. The flux takes up some of the heat, and the zinc underneath melts, turns into a viscous-liquid state and evenly envelops the welded joint, connecting the ends of the galvanized sections.
Manual electric arc
In this method of welding galvanized surfaces, special electrodes for high currents are used. The essence of the technique is to reduce the time of thermal exposure on the workpieces being joined, when the zinc does not reach the point of transformation into gas during welding and does not evaporate.
This technology is most often used not only in the construction of gas pipelines and building structures, but also in the laying of water pipelines.
Alternative connection methods
Galvanized pipes can be connected with threads and couplings. In the latter case, the result guarantees 100% tightness only with regular maintenance of the joints. Cutting threads on galvanized pipe is not so easy. There is an option to use factory threads and fittings. But, again, they need to be welded. All this can significantly increase the cost of work.
Which way is better
Welding and submerged arc brazing are preferable to other methods of joining galvanized pipes. And here are the reasons:
- Work is carried out quickly if it is performed by qualified welders.
- Compared to threaded or flanged, it provides a permanent connection that does not require further maintenance.
- Welding allows you to perform large volumes of work in a short period of time - for example, when laying many kilometers of pipelines.
On galvanized pipelines, detachable connections - threaded, flanged, using compression and overhead couplings - are not used so often and only in cases where little needs to be done. For example, when replacing a radiator in an apartment, it is necessary to extend the hose. Then a thread is cut on a section of the existing galvanized pipe and a coupling is used, and another section is connected using corner fittings.
A detachable connection, instead of welding, is used to connect additional devices, such as meters, to the pipeline. It is important to understand that such a connection, unlike welding and soldering, does not provide 100% tightness and requires periodic maintenance, regardless of what working medium circulates through the galvanized pipeline - liquid or gas.
Technology of work execution
Mainly taken into account is the wall thickness:
- up to 3 mm - pipes are welded without preparatory work, leaving an allowance in the joint of 2–3 mm.
- over 3 mm - a chamfer is made at the ends of the pipes being welded, blunting the edge by 1.5–2 mm.
The correct choice of current and electrode nozzle diameter are of great importance.
High currents in combination with too small a diameter lead to burning through the galvanized pipe, and in the opposite situation there will be undercooking. Another factor is the speed of movement of the electrode. If it moves slowly, there is a risk of damaging the ends being welded. Excessive speed of electrode movement is fraught with undercooking.
Preparation for work and soldering
Choose a burner 1-2 positions less than if you were to cook regular steel. There must be more oxygen in the acetylene flame so that the silicon in the solder and the oxygen can combine to form an oxide. It is that important protective element that prevents the evaporation of zinc.
Before cooking, sections of galvanized pipes are heated to a length of 5 cm away from the soldering area. During welding, a solder rod is inserted at an angle of 40° into the joint gap, where it melts and the seam is filled with molten metal. It is better to use the “pull” method, holding the rod not behind, but in front of the burner. The flame does not heat the pieces themselves, but the solder.
Conclusion
In conclusion, I would like to emphasize that it is still possible to use welding in the case of galvanized pipes. Technologies make it possible to preserve the protective coating and not expose the pipeline at welding points to the risk of rapid corrosion. It is enough to follow the rules and regulations that are enshrined in SNiP, use suitable electrodes, fluxes, and solders.
With this, let me say goodbye to you. I hope the article was useful. Subscribe to our other articles and share useful materials on social networks.
(1 5,00 out of 5)
Source: https://vseotrube.ru/montazh-i-remont/svarka-otsinkovannyh-trub
