RU2094781C1 - Method of gas sorption flaw detection - Google Patents

Abstract

FIELD: examination and analysis of materials. SUBSTANCE: object under test is kept in atmosphere of mixture of nonradioactive gases at least one of which improved sorption of the remaining gases on object surface. Residual distribution of sorbed gases on object surface is registered within preset time by means of superposed and removable indication coating which is applied to surface under test for preset time. Presence, location, type and size of defects are judged by change in coating color. Ammonia and water and/or alcohol vapors may be used as mixture of nonradioactive gases. This mixture can be obtained by evaporating the solution in closed space. EFFECT: improved test results. 3 cl

Description

 The invention relates to non-destructive testing methods and can be used in various industries to detect through and surface microdefects such as pores, cracks, zones of increased porosity.

 A known method of non-destructive testing of surface defects based on the use of the capillary properties of a liquid in which a volatile penetrant is used [1] According to this method, the penetrant is applied to a controlled surface with a brush or tampon, or sprayed with a spray gun. Under the action of capillary forces, the penetrant is absorbed into surface defects. The surfaces are allowed to dry until wet spots disappear, after which an indicator shell is applied on it, which changes color when absorbing penetrant evaporating from defects. As a result, colored spots appear on the surface of the indicator shell adjacent to the controlled surface of the product, which are enlarged mirror images of the mouths of surface defects. The shape and size of the mouths of surface defects are determined by the shape and size of the colored spots on the indicator shell.

 The use of an evaporated penetrant and a removable indicator shell makes it possible to obtain information about the depth of the defect and the size of its mouth, as well as to exclude the operations of cleaning the surface from defectoscopic materials.

 However, like all capillary non-destructive testing methods, the known method is not applicable for detecting defects whose cavities contain impurities that impede penetrant penetration. In addition, the use of vaporized penetrant limits the ability to detect defects whose depth does not exceed 0.3 mm.

 A known method for determining the presence and location of surface defects [2] is based on keeping the controlled part in a radioactive inert gas and observing a pattern of the distribution of radioactivity on the surface due to adsorption of gas on the surface of the defects, which effectively detects surface defects whose cavities contain solid contaminants that cannot be removed during cleaning surface of the part.

 The disadvantages of the method are the low reliability of the detection of defects having a shallow depth and a large opening width, as well as radiation hazard.

 A known method of radioactive gas sorption flaw detection [3] in which to prevent rapid desorption from the cracks of the indicator (working) gas krypton-85 before control they are filled with a substance with good sorption properties.

 As a result, the residual radioactivity of the surface of the controlled object in the locations of the defects increases, which makes it possible to increase the sensitivity of the method.

 However, this increases the radiation hazard when using the method, which greatly limits the scope of its application.

 In addition, the known method does not allow to obtain information about the depth and disclosure of detected defects, since in this method scattered β-particles are recorded.

 The problem solved by the invention is the creation of a gas sorption defectoscopy method that allows you to register non-radioactive gas sorbed in defects and evaluate the sorption capacity of defects.

 The technical result is the elimination of radiation hazard, increasing control performance, expanding the scope of the method, increasing the information content of the method.

 The technical result is achieved due to the fact that the controlled part is kept in the atmosphere of a mixture of non-radioactive gases, of which at least one improves the sorption of the remaining gases on the surface of the part. Then, the controlled part is kept in air for a predetermined time to ensure desorption of gases from the outer surface of the part, after which a removable indicator shell sensitive to sorbed gases is applied to the controlled surface for a specified time to register defects.

 Gases filling the defect cavity and adsorbed on its walls escape from it due to diffusion, thereby creating a diffusive gas flow. As non-radioactive gases, for example, ammonia and water and / or alcohol vapors are used, of which water and / or alcohol vapors improve the sorption of ammonia.

 After the outer surface of the part is degassed, a removable indicator shell, for example, filter paper (or fabric) impregnated with an indicator composition sensitive to ammonia, is imposed on the controlled area of this surface and provide a tight fit of this shell to the surface. When ammonia molecules emerging from the defect due to diffusion are absorbed, an indicator trace of this defect in the form of a colored spot appears on the surface of the indicator shell adjacent to the controlled surface of the part. The shape of this spot repeats the shape of the mouth of the defect with an increase that depends on the time of registration, i.e. from the time during which the indicator shell is on a controlled surface and absorbs the diffusion flux of ammonia from the defect.

 After a predetermined registration time, the indicator shell is removed from the surface of the part and the presence of indicator traces on the shell is used to judge the presence of defects on the surface being monitored. The shape and size of the indicator traces judge the type and size of their disclosure. To assess the depth of defects, which is associated with the sorption capacity of the defect, indicator shells are applied repeatedly at fixed intervals for a given time and the continuation of desorption and the presence of diffusion flows of sorbed gases from deeper defects and the termination of diffusion flows of these gases from smaller defects are recorded.

 Example 1. At the bottom of the desiccator is placed a bottle with a 20% aqueous solution of ammonia. Above it, on a ceramic stand, a crack standard is placed with an opening of 0.8 1.2 μm 0.3 mm deep, which is a stainless steel plate about 3 x 6 cm in size and about 3 mm thick with a nickel coating 0.3 mm thick. The desiccator is closed with a lid and kept at room temperature for 30 minutes.

 Then the standard is removed from the desiccator, kept for 1 min in air, an indicator shell of filter paper impregnated with an ammonia-sensitive composition is applied to the surface of the standard, and defects are recorded for 60 s. After that, the indicator paper is removed from the surface of the standard and the indicator traces of the reference cracks are observed. The width of the crack marks is proportional to the crack opening.

 Example 2. In a desiccator, a turbine blade of a gas turbine engine is placed, on the concave surface of which near the root by the prototype method an extended defect is detected. The desiccator is closed with a lid and a vacuum of about 0.01 atm is created inside the desiccator, after which a mixture of water and ammonia vapors is injected into it to a partial pressure of ammonia of 200,250 mm Hg. Art. incubated for 5 min at room temperature, after which the blade is removed from the desiccator and incubated in air for 1 min.

 The test areas on the convex and concave surfaces on both sides of the inlet edge near the root of the scapula, including the inlet edge, are applied with indicative paper, sensitive to ammonia, and defects are recorded for 30 s. After that, indicator paper is removed from the surface and indicator traces of an extended defect on the concave surface of the scapula are observed in the form of a thin line about 15 mm long, erosion ulcers in the form of round spots with a diameter of 0.3 to 1.0 mm and mechanical damage (risks) in the form of a stroke with a width 0.5 mm and a length of about 5.0 mm.

 The use of non-radioactive gases eliminates the radiation hazard, especially when monitoring products from materials with a large sorption capacity, which also allows you to expand the scope of the method by expanding the range of tested products.

 The use of a mixture of gases, of which at least one improves the sorption of the others, eliminates the intermediate stage of filling defects with an adsorbent before holding the part in the working gas, which simplifies the method and thereby increases the control performance.

 The use of an invoice and a removable indicator shell, which is highly sensitive to ammonia, allows, if necessary, to repeat the control by applying a new indicator shell on the same surface of the part without re-saturation, which allows to increase the information content of the method.

 As can be seen from the above examples, the full control cycle takes 10-35 minutes. Moreover, the main cost of time associated with the first stage of the cycle - aging in a gas environment. The performance of the control can be increased by reducing the time spent in the first stage of the cycle by placing several parts of the gas mixture in the atmosphere at the same time.

 The sensitivity of the proposed method of gas sorption flaw detection is not worse than the sensitivity of the capillary ink method and gas sorption radiographic method.

 Sources of information.

 1. Indicator capillary-diffusion method for non-destructive defectoscopy of composite materials, Proc. Moscow Intern. composites Conf. Nov. 14-16, 1990, Elsevier Applied Science, London New York, 773-776.

 2. Rumyantsev S.V. and other Isotopes in the USSR, N 44, 1975.

 3. Rumyantsev S.V. Shtan A.S. Goltsev V.A. Handbook of radiation non-destructive testing methods. -: M. Energoizdat, 1982, p. 151 prototype.

Claims (3)

 1. The method of gas sorption flaw detection, which consists in the fact that the defects of the controlled object are filled with a substance that improves the sorption of the working gas, the object is held in the working gas medium with its subsequent removal from the external surface of the object, and the residual distribution of the working gas over the object surface is recorded, characterized in that as a substance that improves the sorption of the working gas and the working gas itself, a mixture of non-radioactive gases is used, of which at least one improves the sorption of the remaining gases by the surface of the object, and registration is carried out after a predetermined time using an invoice and a removable indicator shell, which is applied to the surface to be monitored for a predetermined time and judged by the color change of the presence, location, type and size of defects.  2. The method according to PP.1 and 2, characterized in that as a mixture of non-radioactive gases using ammonia and water vapor and / or alcohol.  3. The method according to claims 1 and 2, characterized in that the filling of the defects of the controlled object with a mixture of non-radioactive gases, of which at least one improves the sorption of the remaining gases, is carried out in a closed volume by evaporation of a mixture of non-radioactive gases from the solution.