Welding of pipelines. Type, technology and weld defect
The use of electric arc welding is found everywhere in our lives; it is characterized by the reliable connection of metal pipes to each other.
Therefore, in our specificity, it is widely used in the heating system, because where there is high pressure and extreme temperatures, no other material will compete with this material.
Such a system provides for the use of seamless pipes, and welding them together requires a special technology that must be strictly followed. It consists in welding the root of the seam.
When welding pipes and equipment elements on a regular water supply, or, say, sewerage system, everything is much simpler. What I describe below directly concerns the steam system, and the process of installation on a high-pressure gas pipeline is similar to it. Are you, dear visitor, interested in such information? Then I invite you to familiarize yourself, I tried to present everything in simple language.
Type of weld
So, we have two pipes of the same or different diameters, let’s consider both options. In the first case, we connect the pipe to the outlet, and in the second, we need to cut a pipe with a diameter of 76 millimeters into a pipe with a diameter of 133 millimeters.
In order for us to achieve absolute (I’m not afraid of this word) tightness of the welded joint, the weld will be double. First, we boil the so-called root of the seam, and then we will cover it with the second one.
Let’s divide the whole process into several stages, each of them is important and is carried out without “jambs”; if something goes wrong, it is better to achieve “ideality” at the initial stage. In our case, the cheerful saying: “Maybe it won’t flow” will not work.
1. Preparation of surfaces to be welded
Includes a thorough adjustment of them to each other. A chamfer is removed on both mating surfaces, ideally at 45 degrees to the pipe axis. It must be removed with the condition that the end is left flat, 2-3 millimeters wide.
Here and further, in order not to particularly search for suitable words, for clarity, I provide the post with photographs and a video.
In this photograph there is a marking on the end of the pipe, following the line of which we need to cut out an element, we call it “making a mustache”, or “cutting out a fish”.
And here is a picture of what the cut and processed surface of the workpiece looks like.
2. Joining of welded surfaces
This photo shows a joint on tacks. Both planes of the surfaces have chamfers and do not touch each other, having a gap of 2-3 mm, this gap is necessary for penetration of the root of the seam.
It is important that the elements being welded are coaxial; there can be no talk of any displacement relative to each other, otherwise the joint will be rejected.
We put them out and grab them together. In case of unequal gap between the surfaces, which occurs when the pipe is cut unevenly, we modify it using a grinder with a cutting disc, achieving uniformity around the entire perimeter.
Pipes with a diameter of up to 50 millimeters are tacked in two places, but for larger diameters - at least three tacks, and you begin to cook from the logical location of the fourth. Already during the welding process, when reaching the next tack, it must be cleaned off.
Root welding
Everything is ready for penetration for the first time, which is what the welder does next.
Upon completion of running in the joint, it is the installer’s turn to work.
3. Selecting the root of the seam
It consists of treating the welding area around the entire circumference to a metallic shine. Literally - there should not be a hint of unevenness of the groove, much less slag residues.
All edges and irregularities are smoothed out, and the surfaces on both sides of the seam are also sanded to a metallic shine, about twenty millimeters in each direction. I do this using the same grinder, with a cleaning disk installed on it.
While performing this stage, I noticed a defect - it’s time, it formed at the site of the welding “lock”.
Here is a visual result:
If the installer notices this “jamb”, it is necessary to clean this place, until a gap appears, while providing for slopes of the chamfers of the surfaces being welded.
Point out the presence of a pore to the welder, he will “throw it in.” Then select the cooked area until it has a metallic shine. As I wrote above, bring everything to perfection.
After this, the welder can proceed to the next stage.
4. Overlapping the root seam
Observing what he wrote above in the box, in paragraph 2, he rolls the joint in a circle. Without saving electrodes, the seam turns out “greasy”. Then the installer processes the seam using the same grinder with a grinding wheel.
In general it looks like this:
Another important point here: when cleaning, “undercutting” of the welded surfaces is unacceptable; to prevent this, grind in one given direction - from the pipe to the seam.
Here the places where “undercuts” may appear are marked in red.
If this “jamb” is present, the joint is rejected.
I'll add a couple more photos to the description. They have a welded joint between a pipe and a flange. On the outside of the flange, penetration is carried out in accordance with the entire process described above, that is, welding the root of the seam, removing it, covering it and cleaning it.
In addition to this, we also weld the joint from the inside of the flange:
Weld defect
Porina, and how to remove it, we looked at it, and now let’s explain the points due to which there is a high probability of its appearance.
Every welder should be aware of the first probability, because they undergo special training. The second and third are characterized by a conscientious attitude towards the performance of their direct duties.
But on the last point a little more detail:
I have had to deal with this problem: the welder is welding, I select the root, there is a porina there - I clean it, he welds again, I select - porina, I clean it, cooks - porina. Then they realized that the pipeline was long and on one side had a connection with the atmosphere, in general, until this connection was plugged with cotton pants, they did not come to a positive result.
Well, that seems to be all I wanted to tell you, I’ll wrap it up. If you follow everything described, you will end up with a perfect joint. No “luminary” will find reasons to reject it, and an x-ray will show compliance with the standards.
Here is the video promised at the beginning of the article, which I edited as clearly as I could:
I don’t stroke my pride, and I don’t consider myself a “master of the pen” at all; I only shared what I know from my experience. For those interested in deeper knowledge in this area, I can recommend studying the book, which can be downloaded by clicking on the picture below.
The book is not free, but the price is not high, only 84 rubles; moreover, you have the opportunity to read a fragment for reference, and make a purchase only if you are interested. The book consists of 510 pages and has 234 illustrations.
You can rest assured that the distributor is trustworthy; there will be no scam when transferring money, I checked it personally.
I recommend that blog guests subscribe to receive new blog articles; to do this, you just need to enter your email address in the form that will open when you scroll to the bottom of the page.
Useful links:
Dimensions of the depth of the “whiskers” for pipes of various diameters.
Sealed thread on high pressure steam line.
Installation of polypropylene water pipes.
If you have any questions or have anything to add to the article, you are welcome to add it to the comments section.
Good luck to everyone in the installation, best regards Andrey.
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Source: http://santehskript.ru/svarka-truboprovodov-vid-texnologiya-defekt-svarnogo-shva/
How to weld pipes using electric welding against light
How to weld pipes is necessary knowledge for every owner and home owner. Since this process is gaining high popularity due to the strength and reliability of the connections.
Today there is a wide range of welding devices for household and industrial use on the market. Plus, the process is do-it-yourself, so many can do the work themselves at home.
In our article we will look at how to properly weld pipes.
Varieties of welding methods
Today there is a huge classification of types of welding for copper pipes
Today there is a huge classification of types of welding for copper pipes. Visually, the branching looks like this:
- The thermal group includes such methods as gas, arc, electron beam, plasma, laser, etc.
- The thermomechanical group are methods that operate using a magnetic arc and resistance welding.
- Mechanical group - the purpose of connection is achieved through explosion and friction.
Depending on such a criterion as the type of energy carrier, welding methods are:
- Arc;
- Gas;
- Plasma;
- Laser.
There is such a branching of methods by which connections are formed:
- Forced method of connecting elements of water pipelines;
- Free creation of a seam by welding.
If we consider the classification according to the method of protection, then there are the following types of welding:
- The connection is made using a wire with a protective electrode;
- Welding of water pipelines is carried out with shielding gases;
- Flux welding of components.
From the literature and videos we studied, we learned that according to GOST for main pipelines it is necessary to make connections using arc methods. In most cases, automatic arc methods are used under flux components. If it is not possible to use mechanical means, then it is necessary to use manual techniques. It is worth noting that this technology can be performed for vertical, bottom and ceiling joints.
Attention! Electrodes for welding pipes in the manual version move around the circumference at a speed of up to 20 meters per hour, and in the automated process - up to 60 meters per hour.
Manual arc welding of pipes with protection gases is used to organize pipe connections in spaces.
Preparatory work for welding
For pipes with a small diameter, you need to use a trimmer, chamfer, grinding machines, devices for cutting steel products
Before starting installation work, you should determine whether the materials comply with GOST and have quality certificates. It is also necessary to select parts that do not contradict the design and technical specifications. The ends of the connection parts must comply with the welding processes. If this norm is not taken into account, then processing must be performed mechanically.
For pipes with a small diameter, you need to use a trimmer, a chamfer, grinding machines, and devices for cutting steel products. For large quantities – milling and grinding machines. In order to make the clearance correctly, you need to use the following thermal techniques:
- The edge can be made by gas-oxygen cutting using an abrasive wheel;
- From numerous literature and videos, we learned that it is possible to use the air-plasma method with further processing at depths of no more than 1 mm;
- GOST allows the use of the air-arc method at a depth of 0.5 mm;
- Special cutting electrodes can be used which eliminate the need for further grinding.
Attention! Before cooking pipes, it is necessary to clean the inner walls of various contaminants.
Perform preheating
Recommendations and video provide for preheating
Recommendations and video provide for preheating. It should be noted that according to GOST, this action is mandatory. The characteristics and components of the weld joint are based on the cooling rate of the steel in the temperature range from 500 to 800 degrees. If this happens quickly, then hardening structural elements that have ductility and strength can be formed.
Attention! If you initially heat the thickness of the device wall, you can control the rate at which the temperature drops.
If the area is heated correctly, the risk of obtaining hardening structures can be reduced, which promotes the activity of hydrogen diffusion evacuation from the zone and seam. Such a connection will increase the level of welding resistance and protect against possible damage to the integrity of the surface. In order to select a temperature that complies with GOST, you need to keep in mind several factors. Such as:
- Chemical components of metal;
- The thickness of the pipe walls;
- Type of electrode coating;
- Temperature conditions of the area.
After looking through a large amount of literature and videos, we found out that for preheating we only need one tool - an electric or gas type device. It is worth noting that the process must be carried out over the entire area of the product. The width of the heating perimeter from the seams is more than 7.5 cm.
Manual arc welding technology
In order to calculate electrodes when performing welding, you need to take into account the mass of the metal and the brand of the electrode
In most literature and videos, most often when there is a large number of jobs, everyone often uses the manual or arc method. It is correct to form the lumen of sections or individual elements into an unbreakable thread. In order to calculate electrodes when performing welding, you need to take into account the mass of the metal and the brand of the electrode.
The method by which the welding is performed gives impetus to the determination of the material to be joined. Based on the conditions of use and the grade of steel, it is necessary to select components to perform the work. After this, we install the equipment and draw up a work plan. Worth considering. What needs to be taken into account is the speed of construction work.
Attention! Sometimes the choice of material directly depends on the dimensions of the wall and the diameter of the product.
According to GOST, if the wall thickness is no more than 6 mm, then an overlay of at least a couple of seams is required, otherwise more than three seams. The gap must be thoroughly melted, forming a reinforced return roller, up to 3 mm thick for the internal seam.
Important! From the video tips, we can highlight the recommendation regarding the external area, it should have small scales and a smooth surface.
The welding process with a diameter of more than a meter involves preliminary work inside the pipe, in the place where the clearance is located. It is worth considering that this must be done after placing the root sutures. In addition, you need to weld the lower part of the circumferential joint area.
The seam layer that is filled must be reliably fused with similar elements. By the way, you need to process the edges of the pipes that are welded. After completing the layers, it is necessary to clean the areas from slag contamination of the seams. This standard must be complied with without fail, in accordance with the requirements of GOST.
The central seam should have smooth outlines and a connection with the surface of the pipeline. This work must be completed without any cuts or damage. Reinforcement of seams should not exceed 3 mm. The cutting width overlaps by 3 mm in both directions from the center. Today, video consultants identify three welding schemes, which differ in the types of electrodes used:
- Welding joints with an electrode with a main coating;
- Connection with a gas-type electrode based on gas;
- Works based on hot passing and containing a gap in the electrode seam.
As we found out, welding pipes is an important and necessary process that requires precision execution and compliance with the standards and requirements of GOST.
Source: https://respect-kovka.com/kak-varit-truby-elektrosvarkoy-na-prosvet/
