Nondestructive testing of welded joints: equipment, GOST

Welding is usually used in assembly activities, if it is necessary to ensure a high degree of reliability of the connections. In many cases, there is no alternative to thermal fusion, but there are many different techniques for its implementation, not to mention the working conditions. Accordingly, there are also different ways of checking the quality of the seam obtained. Specialists use non-destructive testing of welded joints, which allows to preserve the structure of the material in the joint area and the overall performance of the structure.

Regulatory standards (GOST)

The implementation of non-destructive testing methods is carried out in accordance with established technical standards. Specially for welding there is a section GOST under number 3242-79. Guided by the rules of this section, the master can apply this or that method of control. The standards describe not only the technique of verification, but also equipment. In some cases, deviation from the requirements provided for in this GOST is allowed. Nondestructive testing of welded joints in this case is already guided by the quality assessment methods that are recommended for defect detection operations for specific metals and alloys. However, in such situations it is necessary to rely on the requirements of GOST, but in another section - 19521-74.

What defects are revealed?

There are several groups of defects that help to detect technologies for nondestructive testing. At the base level, surface defects of the seam are revealed. Such deviations from the norm can be fixed already with an external examination, even without the use of special equipment. For example, external non-destructive testing of welded joints helps to fix the zones of discontinuities emerging on the surface. Internal defects, however, can not be detected without adequate technical means. It determines the shape of the seam, its characteristics and the degree of reliability.

In this case, not always the presence of a defect as such indicates the unfitness of the structure or product for future use as intended. Again, according to regulations, the welding seam can have critical and insignificant deviations. The task of control is precisely to detect critical defects, which are defined as not meeting the requirements for the operation of the material.

Equipment for acoustic control method

This method of checking structures for defects in welds is one of the most technological, accurate and effective. Compared with other modern control techniques, it is also characterized by its versatility. It can be used both indoors and in the field without power supply. The test involves an ultrasonic flaw detector consisting of several functional modules. In particular, this non-destructive testing of welded joints involves the use of piezoelectric transducers, which contain hardware components for receiving and dispersing ultrasonic waves. The device generates pulses of ultrasonic vibrations, and also receives reflected signals, which are presented to the operator in a form convenient for analysis. When examining the amplitude of signals, the equipment user determines the parameters of the defects.

Equipment for radiation monitoring

This technique is called radiation defectoscopy of welded joints. The very principle of research is based on the supply of ionizing radiation. During the passage of rays through the seam, their intensity decreases, depending on the thickness and density of the material. Occurring changes in the radiation indices allow the operator to determine the presence of discontinuities in the thickness of the connection. Various x-ray sources are used in this operation . The most common equipment for nondestructive testing of welded joints of this type in the form of electron accelerators and gamma-defectoscopes. These devices are combined to be capable of working with radioisotope radiation. Russian manufacturers of X-ray machines for testing welded joints produce equipment that provides the ability to control the range of photon energy from an average of 15 keV to 30 MeV.

Thermal control equipment

Evaluation of the quality of the weld by thermal scanning allows us to work with a wide range of alloys used in industry and in the construction industry. As for detectable defects, thermal analysis reveals hidden cavities, cracks, areas of impurities, foreign inclusions, etc. Radiometer directly heats and registers suspicious zones. This device, which implements non-destructive testing of welded joints of metal structures throughout the area. In the process of analysis, the operator checks both the basic undeformed structure and the location of the connection. By comparing untouched sections and seams, the reliability of the structure is determined. Today there are different directions of this method. In particular, the vibro-thermal imaging method involves the analysis of oscillations in the transmission of energy to the object.

Equipment for electrical control

The formation of an electric field around the object under study also makes it possible to determine the characteristics of the internal structure of the structure at the junction points. To use this method, electric capacitive converters of different types are used. For example, overhead systems are characterized by high heterogeneity of the electrostatic field formed by them. This property is useful in that the operator fixes oscillations against a background of high sensitivity in the supply of back pulses from the material. Electrical non-destructive quality control of welded joints in linear-drawn structures involves pass-through converters. Such equipment, in particular, is used in assessing the quality of seams made on wire, metal bands, rods, etc. Depending on the electrodes, different current feeding schemes can be used.

Apparatus for capillary control

This is an extensive set of methods that are aimed at detecting and determining the parameters of internal defects. Capillary flaw detectors are used as working equipment. They record the characteristics of the same cavities, their structure, direction, depth and spatial arrangement. In this case, their function is impossible without the use of penetrants. These are liquid or granular substances, which, if possible, are introduced into the seam and spread along its internal cavities. Capillary methods for nondestructive testing of welded joints provide for the use of penetrants of different characteristics. These are some kind of developers who give information about the structure of the connection to capillary flaw detectors. There are substances that are activated by ultrasonic, magnetic, color and other impulses. Some formulations have a pronounced chemical activity, so immediately after the control is performed, seams must be treated with so-called absorbers. They exclude the negative impact of capillary penetrants on the material of the object, which makes it possible to relate this method to non-destructive ones.

Sequence in seam as a method of control

This technique is largely related to the principles of the previous control technology, but it has several significant differences. If the capillary method is focused on the accurate determination of the parameters of the internal cavities, the leak test aims to find in principle where the leak is broken. In this case, the welding seam can be checked not only with the help of liquid substances, but also through air and gas mixtures. Often this method is used before capillary technique, because in itself leak detection only registers the fact of leakage in the joint node, but does not give information about the characteristics of defects.

How is the optimal method of control chosen?

Specialists start from tasks that need to be performed with the help of control. For example, if it is a question of superficial verification, then it is possible to do with this leak detection technology or an experienced visual inspection. For a deeper and more accurate analysis, ultrasound, electrical and X-ray machines are used. Further, it is taken into account how much any non-destructive testing of welded joints can be effective when implemented under specific conditions. So, the ultrasonic technique can be used practically in any conditions, but it costs more. The electric defect scanning method is more affordable, but it can only be used when there is a stable current source.

Conclusion

The control of joints in joints of metal structures is the most important operation of reliability testing. If the test results are positive, you can use the product or design for the intended purpose. In addition, non-destructive testing of welded joints can provide information on old operated facilities. Over time, even quality seams are exposed to wear, so testing should be done regularly. After it, and based on the analysis results, an opinion is given on the technical condition of the structure. On the basis of this document, the responsible engineer decides whether to rectify the defects, or to allow the object to be used further.