Color flaw detection of welds: features and description

The quality of welding work is determined by how strong the seam has turned out. In this case, the connection control must be non-destructive, which forces the masters to refer to special verification methods after the operation is completed. In some cases, an external inspection without instruments is allowed, but in the case of responsible structures, visual control can not be limited. It can be supplemented with colored defectoscopy of welded joints - one of the most effective, convenient and reliable methods of analyzing such compounds.

Features of the verification method

This method of testing welds is capillary, but focuses exclusively on external defects. That is, it can not be used to verify the internal structure of the bond zone, in contrast to, for example, ultrasonic flaw detection. Usually, metals that are prone to cracking are subjected to such testing. In addition, color control makes it possible to effectively detect discontinuities emerging on the surface.

As for the verification principle, it is based on the sensitivity of metals to interaction with flaw detection materials. Contrary to popular belief, analysis as controlled information uses not the characteristics of the workpiece surface, but changes induced by chemical structure irritation. The process of chemical exposure is based on the method of color defectoscopy, which allows you to process information about changes and to provide data on identified defects in the output.

The method itself is rarely used alone. Usually it is used in the overall test complex - together with ultrasound. First, a color analysis followed, followed by ultrasonic flaw detection.

Materials used

As already mentioned, flaw detection can not do without the use of special chemicals. A standard set for color flaw detection includes three types of components: indicator penetrant, cleanser and developer. That is, the color sensitivity control will be activated due to the three-stage processing of the working area. At each stage, special materials are used.

Penetrants are, as a matter of fact, coloring substances which can be presented in different kinds. Powder means are also used, but for their use additional operations of thermal impact or mixing with liquids should be introduced. Suitable metal penetrants for color flaw detection are selected on the basis of several operational properties. In particular, fire resistance, environmental friendliness and toxicity are taken into account, eliminating the need for subsequent stripping, etc.

Requirements for the place of inspection

The defectoscopy operation can only be carried out in a specially prepared room. It is important to take into account the requirements for the communication equipment of the place, the air characteristics, technical support, etc. The room should be ventilated, without sources of open flame or intense heating. The lighting should be general and local, the fixtures close to the place of operation should be protected against heat exposure.

It is necessary to take care of the creation of an optimal microclimate from the very beginning - only in favorable conditions, color defectoscopy can be carried out qualitatively. GOST 18442-80, in particular, indicates that the air must be dry and warm - if necessary, you can use an infra-red heater to achieve these characteristics, which will ensure the drying of the developer at a level of 5 ° C. The technical equipment will depend on the methods of applying chemical components. In particular, for application of the same penetrant, paint sprayers, aerosol cans, brushes, etc. can be used.

Preparation of the base of the seam

The connection section is also prepared for the flaw detection operation. If there are severe roughness or dirt on the surface, then it is possible to use fine-grained material and make easy processing. Then degrease is carried out. For this task, one of the components of the flaw detection kit can be used, but it is important that it provides the degreasing effect, or even better, the sensitivity of the control. It is not recommended to use kerosene for such purposes, but you can use gasoline and acetone. If there is no ventilation in the room, degreasing is performed only by aqueous solutions based on powdered synthetic low-concentration products. If a color defectoscopy is planned for a small part, you can also apply a full immersion in the degreasing compound. In other cases, either the spraying technique is applied to the target area, or by applying a rag soaked in the solution.

Application of penetrant

First of all, an indicator penetrant is applied. As with degreasing, this procedure can be carried out by spraying, dipping or brushing - this depends on the characteristics of the workpiece. And the application should be carried out in several layers (4-6) and so that each previous layer of the composition does not have time to dry. Also, in order to ensure that the color defectoscopy of the welds shows an optimally accurate result, each successive layer should cover a larger area relative to the previous one. This is due to the fact that each new layer will dissolve the outline of the previous spot, avoiding abrupt transitions and incrustations, which can be perceived as false cracks. If the operation is performed under conditions of negative temperature, then the penetrant itself should have a state of the order of 15 ° C.

Removal of penetrant

Immediately after delivery, the test film should be removed using a clean cloth or cloth that does not have coarse pile. Previously, the material should be soaked in ethyl alcohol and clean the surface until the coating is completely eliminated. Problems can arise if the work is carried out on the surface of a rough metal - in which case it makes sense to use light abrasives. Further, an oil-kerosene mixture is used. It covers the entire target area, and then it is also removed with rags or napkins. During the two described stages, the color defectoscopy must preserve the cleanliness and dryness of the surface around the seam. This is important to maintain the accuracy of further monitoring procedures.

Application of the developer

As in the cases with indicator layers and cleaning compositions, the developer is stacked in various ways - from brush to spray guns. The main thing at this stage is to observe the uniformity and solidity of the coating being formed. Therefore, it is necessary to carefully check spraying tools, nozzles and other elements of devices that affect the quality of delivery of the product to the target site. All this in the future will affect the control of color flaw detection, as well as the quality of subsequent verification operations. After the developer is applied, drying is carried out. It can and should not be performed, waiting for polymerization in natural conditions, but for the acceleration of the process it is allowed to use low-power point heaters.

Inspection of the controlled area

When the developer dries, you can prepare for his examination, after waiting another 30 minutes. Further control by the method of color flaw detection involves the use of a magnifying glass, providing a minimum 5-fold increase. If a layer control technique is used, the test can be performed as early as 2 minutes after the developer has processed it.

In the evaluation process, the operator captures the characteristics of the stain left - in particular, logs the size of the contours, the shape, etc. The main task that color defectoscopy poses is to detect surface flaws that clearly manifest themselves after the procedure is completed. Mechanical damages, and traces of corrosive effects, as well as cracks with excessive sags can be identified.

Safety in the performance of flaw detection

Requirements for safety measures are caused by fire and explosion hazards during flaw detection. Therefore, it is necessary at least to prepare the overalls, including a cotton robe, headdress and rubber gloves, the surface of which must be covered with talc. At the site should be fully complied with security measures. During the procedure, there should be neither open sources of fire nor sparks. If color capillary flaw detection is performed on a regular basis in the same room, it is necessary to install appropriate signs on the prohibition of smoking and the observance of fire protection measures. Rags, napkins and flammable products should be stored in a fireproof container.

Conclusion

It will be wrong to consider this method of assessing the quality of the weld as optimal, choosing it from the general spectrum of other methods. This is a specially directed survey method, which is oriented precisely to analyzing the surface of the billet. That is, color flaw detection is not a comprehensive control measure, but with relatively high efficiency gives information about external flaws. If this method is supplemented by other methods of studying the internal structure of the seam, then one can obtain complete information about the structure of the metal. Further, a decision is already made about a possible correction of the detected defects. In some cases, secondary welding is done - this will depend on the number and significance of the defects in terms of the effect on the strength of the structure of the workpiece. Sometimes a defect of this type is used to analyze the structure of old joints and joints in operated structures.