Features of heat treatment of welded joints and methods for its implementation

An essential step in the construction of metal structures is the heat treatment of welded joints. To improve their mechanical qualities and reduce internal stresses, it entails heating and cooling the welded areas. This procedure guarantees that the welded joints are robust, long-lasting, and able to withstand a range of stresses and environmental factors.

The ability of heat treatment to enhance the weld’s microstructure is one of its primary advantages. The extreme heat generated during welding can alter the metal’s composition, resulting in flaws like hardness or brittleness. By improving the grain structure, heat treatment helps to fortify and strengthen the weld. This is particularly crucial in sectors like aerospace, automotive, and construction where dependability and safety are top priorities.

Heat treatment can be applied in a number of ways, each of which is appropriate for a particular kind of material and welding technique. Annealing, normalizing, quenching, and tempering are examples of common techniques. In order to soften the metal and increase its ductility, annealing entails heating the welded joint to a specified temperature and then gradually cooling it. Similar techniques are used for normalizing, but air cooling is used to balance the weld’s strength and hardness.

Fast cooling through quenching strengthens and hardens the welded joint, but if tempering isn’t done next, quenching can make the joint more brittle. Reheating the quenched metal to a lower temperature is known as tempering, and it is used to increase toughness and decrease brittleness. To achieve the desired properties in the welded joint, each method necessitates meticulous control over temperature and timing.

The longevity and quality of welded structures depend on knowing and using the proper heat treatment technique. Manufacturers can create welds that withstand strict requirements and function dependably in a range of scenarios by carefully regulating the process and choosing the right technique.

Feature	Description
Purpose	Heat treatment reduces residual stress and improves the strength of welded joints.
Methods	Common methods include post-weld heat treatment (PWHT) and local heat treatment.
Temperature	The specific temperature and duration depend on the material and welding process used.
Equipment	Ovens, furnaces, and localized heating devices are commonly used for heat treatment.
Safety	Proper protective equipment and procedures are necessary to prevent accidents during heat treatment.

The main methods of processing welds

After welding, there are three ways to remove the welds:

• Heat treatment. Using this method, the residual voltage in the metal is eliminated, which occurs as a result of welding. Thermal processing of the weld is carried out using local and general technology. In the first case, we are talking about heating with further cooling of only welded joint. As for the total heat treatment, the entire details are heated directly here. This method is often used for small structures.
• Mechanical restoration. The essence of this method is to eliminate the compounds and adjacent sections of the remnants of toxins. Also, in the process of processing, the joint is checked for the strength. So, the classic option is to clean up welds using certain tools or tapping the seam. The connection of the connection is very careful, since this will depend on this. If cracks arose as a result of tapping, then the design is rejected, since the connection strength is violated. As for the remnants of slag, if it is not removed, then this will lead to the occurrence of corrosion of the site. For this, grinding welds are grinded.
• Chemical processing. With this method, applying to the connection of the protective coating is performed. This prevents the corrosion of the metal during the operation of the structure. The most affordable option is the use of a primed paintwork.

Many considerations should be made when selecting a welded seam processing method. This first has to do with whether the approach is reasonable in a given situation. It is crucial to understand why the design is being used. Certain products and connecting seams are subject to stricter standards for dependability and strength.

Heat treatment

Pipeline highway construction frequently involves the application of heat treatment to welded joints. They are made by using pipes with a substantial wall thickness and a large inner diameter. This will guarantee the system’s robustness and dependability while it is in use. However, this leads to a new issue: it is challenging to interpret pipes with such geometric features in a high-quality manner.

A tiny portion of the product is welded during the process. This consequently causes several physical processes that have a negative impact on the structure’s ability to function.

There are various steps involved in the extremely heat treatment of welded joints:

• Medgoding of products for welding. The strength of the connection depends on how well this work is done.
• Heat treatment of the junction of the products during welding.
• Walking after welding.

Metal structures cannot be improved by welding without heat treatment. First and foremost, however, annealing and high leave affect products and seams.

Why is needed?

The filler material from the electrode and an electric arc work together to facilitate welding. The temperature range in this instance is 1500–5000 0 with. Such heating on thick metal causes a number of undesirable phenomena that need closer examination:

• A large overheating occurs at the junction of the welded and additive material. As a result, crystallization of metal increases, which has a large structure. This significantly reduces its plasticity. Also, in the process of heating, manganese and silicon is burned out. The site of the metal product becomes rigid and loses its original technical characteristics.
• There is a hardening zone near the seam, it also experiences heating. Of course, it has a lower temperature than in the environment of a direct connection of the additive and basic material. As a result of this, certain elements are injected in the metal. The site loses its original plasticity and becomes more solid. Also changed by shock viscosity material.
• The begging zone is located at a remote distance from the place of direct welding of metal products. It lends itself to moderate temperature that the electronic arc emits. Due to the lack of this process, the material retains its plasticity. But with regard to strength, it decreases somewhat.

The residual voltage that results from the welding of the metal to metal can cause deformation. This may make installing volumetric structures more challenging. This is particularly valid for locations where new nodes are going to be added.

The risk associated with residual stress is that it may eventually lead to the development of cracks. This particularly applies to welding. This is intolerable because it will eventually cause the compound to be destroyed.

When high temperatures are appropriate for welding while the structure is in operation, the situation gets worse. As a result, the metal’s cyclical strength and resistance to corrosion processes decline. This also holds true for the metal’s resistance to the fragility that results from exposure to low temperatures.

Features of the conduct

Thermal processing, which involves raising the temperature to between 700 and 1000 0 C, is done on welded joints. As a result, the effects of the uneven heating that occurred during arc welding can be completely eliminated. This is particularly valid for metal goods with substantial thickness. They provide a structure that is comparable to the remainder of the material as a result of processing the seam.

There are three steps involved in heat treating welded joints:

1. The site is heated near the connection. For this, special equipment is used, which we will talk about later.
2. The site or the entire product is maintained under a certain temperature for a certain time.
3. At the final stage, systematic cooling of the material is performed to normal temperature.

Through this process, residual phenomena from arc welding can be eliminated, the metal’s structure can be aligned, and voltage, which frequently causes deformation, can be relieved. There are several ways to carry out the procedure. The thickness and kind of material determine the technology used to implement it. Though it’s not always done, there are situations in which processing is just required.

How the heat treatment process works is shown in the video.

Advantages and disadvantages

There are some benefits and drawbacks to the thermal method’s combined processing. Among the benefits, the following are noteworthy:

• As a result of the process, welded joints acquire new properties. As a result of this, parts will become more suitable for operation in certain conditions. This is especially true for the protection of metal from corrosion.
• Processing allows us to eliminate some negative points that arose as a result of welded work.
• Heat treatment relieves the residual voltage that occurs during the welding process.

Of course, you have to approach the processing correctly to get such a result. This is particularly true when it comes to following certain rules. Regarding the drawbacks of this processing technique, they separate out the following:

• The process must perform an experienced specialist. This is due to the fact that processing by heating is irreversible. And this means that it is almost impossible to eliminate the mistakes made.
• For processing, special equipment may be needed, for which certain skills are needed. Especially when the welds of pipelines are protected.
• The procedure should be carried out exactly with the requirements.
• In each case, their processing parameters are selected.

There won’t be any issues when cleaning the junction if you follow a few guidelines.

What is subjected to processing?

Pipelines are frequently constructed using heat treatment for a variety of reasons. This first applies to pipes with a diameter greater than 10 cm and a wall thickness of at least 1 cm. Induction heating by current, with a frequency of 50 Hz, is used in the process.

Pipes can be thermally treated quite easily. Use special electric heating wires with enough elasticity and muffle stoves to achieve this. The product is processed using gas-flaming heating if its thickness is no more than 2.5 cm. Here, distributing the temperature uniformly around the connecting seam is crucial.

Heat treatment is applied to connections with a different shape in addition to ring seams.

It is important to take the metal’s characteristics and thickness into account when processing welds. For example, the process needs to be completed right away after welding if the pipeline is composed of steel pipes with 45 mm wall thickness. In this instance, the material shouldn’t cool down to 300 0 with. This also holds true for goods that are 25 mm thick.

Thermal insulation material is used to protect the seam in the event that processing cannot be completed. Immediately upon arising, they are cleaned. The procedure needs to be completed in three days starting on the welding date.

The parameters of the process

Steel type and thickness have a direct impact on heat treatment characteristics. Thus, induction or radiation methods are used in the case of chromomoliden steel and its alloy.

Therefore, the processing process will take the following amount of time, depending on the material’s thickness and the method used:

Metal gauge, in millimeters

Radiation technique, minimum

Induction technique, minimum

It is evident from an analysis of the table that the induction method’s metal processing is faster. This is a result of the process’s characteristics.

What equipment is used?

Welds are thermally processed via a variety of techniques. When making a decision, consideration is given to the metal’s thickness as well as the feasibility of utilizing specific pieces of equipment in a given location. The peritial site can now be heated using three primary techniques. Think about each one of them.

Induction

On the spot, a specialized device that generates alternating high frequency voltage is installed. It is connected to a heating element via a flexible wire. It is wound on a welding connection that has been covered with asbestos that insulates against heat. Processing of both horizontal and vertical seams is done with this technology.

The wire is tightly wound around the insulator. In this instance, the space between the turns is 2.5 cm thick. Consequently, 25 centimeters of the product are covered on both sides of the seam. The device is turned on once the turns are installed in accordance with all standards and requirements. Here, the equipment’s functionality is taken into consideration. It is directly influenced by the metal’s thickness. A voltage travels through the turns of the apparatus during operation, heating the metal and producing induction.

Additionally common are special belts with a specific number of wires for processing. This makes it possible to quickly and easily get the product ready for stripping after welding.

The pipes are heated by induction in the video.

Radiation

Equally popular is the radiation processing method for welds. As a heating element, special nichrome wires are utilized. They allow the voltage to pass through, which causes them to heat up. It is important to note that induction is not involved in the procedure. A hot wire is used to heat the material. The material used for thermal insulation determines how tenas are laid.

Gas -flaming

It is the least expensive method. Heat treatment of the welded areas is done using an oxygen and acetylene mixture. Materials with a maximum thickness of 10 cm are processed using this method. Large holes in a burner that holds a flammable mixture are used to install a mouthpiece. An asbestos funnel is placed on the nozzle to guarantee a consistent supply of heat to the processed surface. This enables you to spread the flame across a 25 cm width.

There are a few features to consider when applying this method. Thus, simultaneous heating of the nearby sewing sites is required to achieve high-quality heat treatment. This implies that two burners are involved in the process simultaneously.

Types of heat treatment

There are multiple methods to perform the thermal effect on the combination of welding. In this instance, the goal of the procedure is considered. Among the primary techniques, they differentiate:

• Thermal rest. In this case, the material is heated to 300 0 from. This temperature is maintained for two hours. As a result of the process, hydrogen decrease in the welding seam, and the residual voltage is removed. This method is often used to materials that have thick walls, as well as where there is no way to use other technologies.
• High vacation. With this technology, the product gives in heating at a temperature of up to 700 0 s. This processing lasts about three hours. The time of heat on the material directly depends on its thickness. This method allows you to remove the residual voltage by almost 90%. If we are talking about the processing of low -alloy steel, then as a result there is a destruction of the hardening structure and carbides become larger. Thus, you can achieve an increase in plasticity and shock viscosity. Often this technology is applied to perlite steels.
• Normalization. This method implies the simultaneous heating of the material and the weld to a temperature of 800 0. At the same time, heat treatment should not exceed 40 minutes. Using normalization, you can partially remove the residual voltage. But the main advantage is that as a result of processing, a homogeneous and fine -grained structure is obtained. This, in turn, improves the mechanical properties of the seam and near -sewing sites. Normalization is often used on materials that have a small thickness.
• Austenization. The material is heated to a temperature of 1100 0 s. Thermal exposure continues for two hours. After that, the material is cooled in the air. It is not recommended to perform forced cooling, as this will lead to a decrease in the strength of the metal, and as a result to the appearance of cracks. Austenization is used on highly alloyed steels. With its help, the plasticity of the material increases, and the residual voltage decreases.
• Stabilizing anneal. The method is used to process materials with a stamked seam. It is heated by a temperature of 970 0 C for three hours. After the time of this time, the material gives to natural cooling in the air. With the help of stabilizing annealing, it is possible to prevent the occurrence of intercrystalline corrosion. Often, the technology is used on highly alloyed steels. This will protect areas from corrosion.

A variety of metal products are subjected to heat treatment. They extend their lives with its assistance. The selection of the operating temperature, the heating technique, and the heat treatment time must all be done with great care in order to perform the process correctly. To prevent further damage, the cleaned products must be handled with extreme caution.

What way to choose?

The physicochemical properties of the material directly influence the technology selected for the thermal processing of welded joints. The steel brand is proof of this. Experts advise that special attention be paid to the technological requirements. If not, the weld’s quality will be greatly diminished, which could eventually result in its total destruction.

It is important to consider the following factors when heat treating the welded joint:

• the width of the site that will succumb to processing;
• the uniformity of thermal influence on the material, both in thickness and in width;
• heating duration;
• Features of cooling the material after heat treatment.

By considering each of these aspects, you can select a heat treatment technique that will raise the connection’s quality. This is particularly valid in terms of its power.

Temperature control

As was previously mentioned, close attention to the heating temperature is required during the heat treatment process. Thermal carandas and thermal coloring are two examples of the specialized instruments used to accomplish this aim. They undergo a dramatic color shift when a particular temperature is reached. These thermostats can be chemical or melting, depending on how they work.

Chemical temperature controllers undergo color changes due to component reactions when a specific temperature is reached. Both pressure variations and the length of time the material is exposed to heat have a direct impact on the measurement accuracy.

The measurement error won’t exceed 10 0 from if heating is done for three minutes. It is important to remember that at critical temperatures, heat controllers’ color changes.

The second kind of pencils and paints have a shift in color due to the melting of a material that is extremely sensitive to temperature changes. These products undergo changes independent of the length of thermal exposure, in contrast to chemical thermal indocatives. This enables you to adjust the heating temperature more precisely. The error in this instance is less than two zero seconds.

The advantages of melting thermal indicators are numerous, but it’s important to note that they include inertia to temperature variations, resolution to solar radiation, sea fog, and other unfavorable environmental factors that could compromise measurement accuracy.

There are two categories for melting thermal paints and thermal pencils:

• Adsorbent. The indicator consists of a pigment in a connecting solution and a suspension of a substance, which is sensitive to an increase in temperature during the heating of the material. As a result of thermal exposure, thermal substance melts, after which its adsorption with a color pigment occurs.
• Melting varnishes. They have a certain melting point. The substance is applied directly to the processed surface. It dries quickly, after which a rough surface forms. As a result of achieving a certain temperature, it will become glossy.

Thermal indigors are still produced in paint factories today. They also offer details on the critical melting points of various materials. This can greatly enhance the welds’ heat treatment quality.

It is essential to comprehend the heat treatment of welded joints in order to guarantee the robustness and longevity of different kinds of structures. This procedure modifies the mechanical and physical characteristics of the welded area by carefully regulating the heating and cooling processes. It can reduce internal stresses, increase toughness, and strengthen resistance to breaking and other types of failure by doing this.

Effective heat treatment is accomplished through the use of multiple techniques. Hard and brittle structures can be reduced to a minimum by preheating the base metal prior to welding. Annealing, normalizing, and tempering are examples of post-weld heat treatments that aid in further microstructure refinement and ductility restoration. Various methods have different applications based on the material and the properties needed for the final product.

Using the proper heat treatment method is crucial to getting the best performance out of welded joints. Considerations include the kind of material, the design of the joints, and how the welded structure will be used. In addition to extending the life of the welds, properly applied heat treatment guarantees application safety and dependability.

In conclusion, one of the most important steps in the fabrication process is heat treating welded joints. It has a major effect on the longevity and quality of welds, so experts in the field must take this into account. Welded joints with superior quality and durability can be consistently produced by using suitable techniques and closely monitoring the process.

For welded joints to be stronger and more durable, heat treatment is necessary to reduce stresses, refine the microstructure, and improve mechanical qualities. Depending on the kind of metal and the welding technique employed, this process requires controlled heating and cooling to produce the desired effects. Three important methods, each suited to a particular material and application, are stress relieving, annealing, and post-weld heat treatment (PWHT). The longevity and dependability of welded structures across a range of industries are guaranteed by the proper application of these techniques.

Video on the topic

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