With the improvement of welding technology, the risks of the formation of various kinds of defects and deviations from regulatory parameters are reduced. Nevertheless, even automatic and robotic welding machines do not completely eliminate the risks of producing poor-quality joints. Therefore, regardless of the applied technology for the production of welding operations, after its implementation, a comprehensive weld quality check procedure is implemented. The visual inspection method is the initial step in the overall process of welding troubleshooting.
Key Points
Welding control should be understood as a technological procedure that can be performed at different stages of the production process, but in any case it should be carried out in accordance with regulatory guidelines. The basic principles of this operation include:
- Control is carried out in relation to parts, blanks and finished products in order to determine the compliance of this object with design characteristics.
- When performing the control, the current status of the object of study, the features of structural and dimensional parameters should be taken into account.
- Only qualified personnel familiar with the technical rules of visual inspection in accordance with GOST R EN 13018-2014 is allowed to check. In addition, the vision of the direct participants in the test should meet the requirements of ISO 9712.
- In the process of performing control operations, the target object should not be subjected to destruction and mechanical stress, which, in principle, can lead to changes in the structure of the material and its operational characteristics.
Principles and objectives of the method
The essence of this control method is to study the surfaces of target objects by external inspection. At the initial level, the operator studies the weld zone using his own vision, but special technical devices can also be used. For example, optical instruments make it possible to study surfaces in conditions of approaching and accenting a zone by means of light radiation. This makes it possible not only to visual inspection, but also to fix certain parameters of an already identified defect.
As a result of the inspection, a defectological map should be formed indicating the places of damage, flaws and deviations in the place of the welded joint. Based on the data obtained, the seam is finalized or the part is disposed of, depending on the possibilities of site restoration.
Target defects to identify
The main defects and deviations of the weld, which are detected during external control, include:
- Lack of fusion. Leaks or partial misalignment of the surfaces of the two parts due to insufficiently molten edges.
- Concavity. On the contrary, excessive penetration of the weld root was allowed, as a result of which the base structure was deformed. In this case, the visual control only fixes the fact of the presence of a defect, and its characteristics are detected by the methods of internal non-destructive testing.
- Undercuts. Deepening along the alloy line. Allowed due to improper arc direction during welding or due to external mechanical damage.
- Bulges. Usually formed due to improper supply of a protective gas mixture or in violation of the temperature regime during the melt.
Applied Control Tool
At the basic level, the simplest means of visual inspection are used, including magnifiers, vernier calipers, rulers and squares. Eddy current and ultrasonic thickness gauges, which give an idea of the dimensional parameters of defects, can be classified as specialized devices for professional control.
Widely used for visual inspection and patterns, by which and without specific measurements, you can determine the deviation of the weld characteristics from the standard values. In this comparison method, the shapes of gaps, edges and assembled parts are usually determined for subsequent joining. Specially for determining the degree of waviness and surface roughness, profilographs-profilometers are used.
Features of laser visual inspection
Both human vision and the capabilities of optical instruments have their limitations when examining surfaces with increased accuracy of observation. The most effective means of deep visual inspection of welded joints is a laser scanning system with a high-precision camera. Such devices allow you to take three-dimensional graphical images of the observation sites with the instant calculation of joint errors. That is, in the operational analysis mode, a defect map is made in the form of a computer model.
Moreover, the device not only gives the necessary list of initial parameters for subsequent analysis, but depending on the data processing algorithms it can independently classify the connection based on geometric parameters, type of defect, etc. The scanning module with a microprocessor makes a decision on the possibilities of further use of the part, taking into account severity of detected abnormalities.
Site preparation
According to the regulations, work is carried out on a stationary site equipped with special platforms, stands and tables to accommodate the object under study and equipment. Often, control is carried out within the production site, due to the minimization of logistics costs when moving parts from the immediate place of welding to the control zone. In this case, special attention is paid to fences from the site where technological operations are performed. A place for research is also selected taking into account the sanitary and environmental conditions, which is especially true for enterprises in the chemical and metallurgical industries.
The better the work area is illuminated, the more accurate will be the results of the visual and measuring control of the welds. Lighting should be bright enough for a reliable study of the controlled surface, but not exceed 500 lx in terms of luminous intensity.
Preparation for the inspection
Regardless of the type and characteristics of the investigated object, its surfaces must be properly cleaned. Any foreign coatings that are not part of the natural weld structure are subject to removal. This applies to scale, paint, dirt, traces of rust and slag remaining after welding. Not always allowed to control and objects, the surfaces of which have a color tint. If the controlled surface is part of the working equipment, then the unit must be stopped for the duration of the study.
As a rule, this applies to technological equipment that has undergone repair by welding. We are talking about ventilation, cooling systems, compressor units, etc. Particular attention in the preparation is given to the visual inspection tool kit and consumables that will be used during the work. Instruments must be properly configured, calibrated, tested for operability and accuracy of readings.
The procedure for conducting input control
The first stage of external control as part of the production process, which aims to check the workpieces and parts before assembly operations. At this stage, cracks, sunsets, nicks, delaminations and weld shells are revealed that are incompatible with the requirements of further technological operations. According to the instructions for visual inspection at the stage of the entrance inspection, the length of sections that can be checked without auxiliary equipment can be no more than 100 mm.
Otherwise, measuring devices are used, which allow fixing the geometric parameters of defects in the stream mode. By the way, in addition to directly welds, at this stage, the condition of the edges of the parts that will still be assembled by welding can be evaluated.
Accounting for controlled parameters after welding
The main stage of work on the visual inspection of parts, which is carried out after completion of the assembly of structures by thermal welding. The main object of study is surfacing in the form of a finished joint. As a rule, a layer-by-layer visual inspection of welds with fixation of surface defects is performed. If it is not possible to accurately identify and evaluate the parameters of fistulas, cracks and signs of destruction of the suture roller, then an internal structure analysis is performed with the connection of radiation or ultrasound equipment.
Measured parameters during monitoring
From the point of view of the requirements for the technological assembly of metal parts and structures, it is more important not to fix the fact of a defect itself, but its dimensional indicators. In accordance with the instructions for visual and measuring control, a comprehensive study should record the following values:
- Width, length and depth of the seam.
- The size of the bulge of the seam.
- Parameters of chips, cracks and shells.
- Undercut depth.
- Leg of the fillet.
- The length of the discontinuities.
On an individual basis, according to the design requirements, a map of the mutual arrangement of seams can also be drawn up. For example, maintaining a certain distance between the connection points is often a condition for ensuring the reliability of the entire structure, therefore, taking into account the gaps is considered as one of the primary control values.
Control as part of the remedial action
In the process of repairing defective joints and when restoring the damaged structure of metal parts, control operations are also performed, the purposes of which include:
- Tracking the completeness of the elimination of the defect.
- Identification of new defects caused by the use of seam structure correction tools.
- Control of the general shape of the defective area.
- Control of site cleanliness - in particular, monitoring of contamination of the junction with oil, corrosion products, technical dust, etc.
Also, the visual control method allows you to keep in the regulatory framework the parameters of the mechanical operations required to fix the structure of the welded joint. In particular, the depth of sampling of the defective seam, the width of the stripping zone, the amount of cutting edges, the bevel angles, etc., are controlled.
Recording Results
The control data is entered in a special accounting journal, after which the documentation is compiled in the form of an act, protocol or opinion based on the results of the survey. When performing visual quality control, a marking is also put on the surface of the target area indicating the results of the inspection. For example, it may be a mark with admission to further technological operations as part of the production process. Otherwise, the workpiece is sent for repair or revision.
Conclusion
The technologies for organizing and conducting control and verification operations in relation to solid-state parts and materials are constantly being improved, allowing the smallest defects to be detected without damage to the object of study. Nevertheless, the simplest methods of visual inspection are still actively used, significantly limited in the possibilities of point monitoring.
This practice is really incomparable in terms of efficiency with modern means of non-destructive internal analysis of the same welds. But, as noted in the instructions for visual and measuring control, external inspection affects only the most pronounced surface defects, some of which can be eliminated without the use of specialized apparatus and consumables. In other words, with the minimum cost of organizing control and technical measures, the most rude marriage is revealed. Further, the workpiece is sent to the next stages of more precise control, which requires the use of specialized magnetic, x-ray and ultrasound devices, which are impractical to use in the initial control of obvious surface defects.