Non-destructive Control Research Articles

Non-Destructive Testing by Magnetic Noise Method of the Quality of Heat Treatment of Steel Samples Obtained by Additive Technology

The manufacture of products using additive technologies is accompanied by the unpredictable appearance of inhomogeneity of properties, anisotropy, residual stresses, porosity, and other defects. Therefore, there is a great relevance of non-destructive quality control of products obtained by additive technologies. The purpose of the paper is the experimental investigation of the possibility of testing and evaluation of the quality of heat treatment of three-dimensional and cast samples by non-destructive control methods.The low-alloy steel 09G2S samples, which was obtained by casting and selective laser sintering different modes of subsequent heat treatments were studied. The method of the Barkhausen effect and the instrumented indentation method for measuring the material hardness were applied.It was experimentally established that both methods are highly sensitive to annealed and normalized three-dimensional samples and their rejection. Compared to the hardness measurement method, which is mainly associated with phase-structural changes, the magnetic noise method due to selectivity to other controlled parameters is additionally sensitive to cast samples (at the same time the microstructures of cast and normalized three-dimensional samples are close to each other according to X-ray data).The magnetic noise method can be used as one of the physical methods for evaluation the quality and control of the heat treatment of 3D samples at the manufacturing stage when testing their types and modes, as well as sorting samples.

Machine-Learning-Based Methods for Acoustic Emission Testing: A Review

Acoustic emission is a nondestructive control technique as it does not involve any input of energy into the materials. It is based on the acquisition of ultrasonic signals spontaneously emitted by a material under stress due to irreversible phenomena such as damage, microcracking, degradation, and corrosion. It is a dynamic and passive-receptive technique that analyzes the ultrasonic pulses emitted by a crack when it is generated. This technique allows for an early diagnosis of incipient structural damage by capturing the precursor signals of the fracture. Recently, the scientific community is making extensive use of methodologies based on machine learning: the use of machine learning makes a machine capable of receiving a series of data, modifying the algorithms as they receive information on what they are processing. In this way, the machine can learn without being explicitly programmed, and this implies a huge use of data and an efficient algorithm to adapt. This review described the methodologies for the implementation of the acoustic emission (AE) technique in the evaluation of the conditions and in the monitoring of materials and structures. The latest research products were also analyzed in the development of new methodologies based on machine learning for the detection and localization of damage for the characterization of the fracture and the prediction of the failure mode. The work carried out highlighted the strong use of these methods, which confirms the extreme usefulness of these techniques in identifying structural damage in scenarios heavily contaminated by residual noise.

Statistical model of processing the results of technological control at testing enamel wire insulation by high voltage during the production process

The results of non-destructive technological control of the number of defects in the enamel wire insulation based on polyetherimide polymer are presented. The application of statistical analysis of the measurement results of control indicators with the help of a mathematical trend model for the use in active technological control is considered. Recommendations for the practical use of the trend function parameters to control the probability of finding several parameters within the established limits are proposed. The main parameter of the trend is the flow parameter of the number of defects exceeding the established technological limit (the failure flow parameter) in short periods of the technological time, for example, for each spool of wire (several thousand meters of wire). The ability to quantitatively assess the tendency of enamel insulation defects for the wire with two-layer insulation with a nominal diameter of 0.63 mm during a continuous technological cycle has been theoretically explained and confirmed by measurements. Quantitative assessment of the tendency of changing the enamel insulation defectiveness allows using a model based on collating the information on a significant number of control parameters. At the same time, one parameter of the spectrum of interrelated ones is allowed to exceed a set technological limit, which ensures sensitivity to changes in this limit. Data on the sensitivity of this model to technological changes are presented

ANALYSIS OF EXISTING APPROACHES AND METHODS OF DIAGNOSTICS OF ON-LOAD TAP CHANGER OF POWER TRANSFORMERS

In electrical networks of almost all voltage classes, the main link in the work on the transmission of electrical energy is a power transformer. At the moment, about 60% of them are operated in our country with a significant excess of service life, which increases the requirements for their technical control and diagnostics of all units. Switching devices are an integral part of power transformers. They are necessary to regulate voltage on substation busbars depending on the load of consumers. Not only the reliability of power supply of industrial enterprises, cities and agriculture, but also the quality of electrical energy depends on their operation. At the same time, they are one of the vulnerable nodes of voltage converters. Although the parameters of diagnostic signs for switching devices are not as extensive as the power transformer itself, they nevertheless require special attention from the operating personnel. This is due not only to the variety of switchgear types that exist, but also to the methods used to diagnose them. For this reason in this work an attempt has been made to analyze the existing approaches and methods of diagnosing these mechanical controlled voltage regulators. We propose a new approach in terms of diagnostics of high-voltage equipment, including power transformers – introdiagnostics. It is based on methods of non-destructive (without opening tanks and draining dielectric liquids) control of parameters that characterize the state of electrical equipment. We present an original method of diagnosing the on-load tap changer, based on oscillography and subsequent analysis of operation of the on-load tap changer contact system without draining transformer oil from the diverter switch’s tank.

Non-Destructive Control of Lubricating Oil Degradation by Using Ultrasonic Through Reflection Method

The control of lubricating oil degradation is usually done by physical-chemical techniques. However, these techniques are not practical because they are time-consuming and destructive. In order to examine the feasibility of quality control in a non-destructive manner, the ultrasonic technique by reflection under normal incidence with immersion in water has been used. In this experimental study, the evolution of the ultrasonic parameters has been followed in different oil samples, taken every 10000 km, i.e. as a function of the mileage covered by the vehicle. In parallel to these ultrasonic measurements, the evolution of the physical parameters (hot and cold kinematic viscosity, dynamic viscosity, viscosity index) has been also followed in order to verify the existence of such a correlation between these parameters and the ultrasonic measurements. The analysis of the experimental results obtained shows the existence of a perfect correlation between ultrasonic attenuation and viscosity. This experimental work enables to find out that attenuation is the most decisive ultrasonic parameter to characterize the quality of lubricating oil.

On the Control of Metal Strength of Structural Elements of Floating Cranes

Introduction. The article is devoted to the issues of non-destructive testing of mechanical characteristics of metal structural elements of cranes. The reliability of cranes largely determines their safety. The main manifestations of operational failures of floating cranes are analyzed on the example of the UMK-2 crane. It is noted that 27% of failures occur due to the loss of metal strength of their structural elements. Determination of the causes of such failures is possible by conducting non-destructive testing of the mechanical characteristics of the failing structural elements metal. The paper provides the principle of one of the methods of non-destructive strength control based on the impact insertion of a conical indenter into the metal under study with the subsequent analysis of the intermediate parameters of this insertion. The results of measurements of the mechanical characteristics of the metal deformed during the operation of the boom strut of a floating crane are given. The current measured values of the mechanical characteristics of the metal obtained at various points of the strut are processed for compliance with the three-parameter Weibull law to obtain the minimum values of these characteristics. As a result of such processing, it is stated that the minimum values of yield strength, strength and elongation are lower than those claimed by the design documentation for the crane. This may be one of the reasons for the deformation of the structural element during operation.Problem Statement. The application of the method of non-destructive testing of the metal of the boom strut is considered in order to assess the mechanical characteristics and establish possible causes of its deformation when analyzing the operational reliability of the crane.Theoretical Part. When identifying possible causes of deformation or destruction of steel elements of crane structures, it is proposed to apply a method of non-destructive testing of mechanical characteristics based on the impact insertion of a conical indenter into the test surface. Further, it is proposed to process the obtained sample of values of the measured characteristic for compliance with the three-parameter Weibull law to estimate the shift parameter or the minimum value of this characteristic.Conclusions. The minimum values of the tensile strength, yield strength and relative elongation of the metal of the deformed boom strut of the UMK-2 crane were obtained on the basis of the application of the method of non-destructive testing with subsequent approximation of statistical information by the Weibull distribution law. A conclusion was made about the reduced strength characteristics of the metal relative to those stated in the technical documentation, which could cause deformation of the crane boom element.

Spin-wave diagnostics of ultrathin ferrite films

A method of nondestructive control of the layered structure of submicron ferrite films comparable to the thickness of the transition (diffusion) layer at the film-substrate interface was proposed. The control technique was based on measurements of spin-wave resonance frequencies and mathematical processing of the measurement results. It was found that the inhomogeneity of magnetization in the transition layer provides the condition of phase synchronism of electromagnetic waves (photons) and exchange spin waves (magnons). In the region of the synchronism points, the effects of hybridization of coupled waves appeared. In this case, hybrid quasi-spin and quasi-electromagnetic waves were excited in the film. The quasi-spin wave at the film-substrate interface had a purely electromagnetic character, which ensured a good matching with the external microwave tract. Near the plane of phase synchronism, there was an intensive redistribution of energy in favor of increasing the power of the quasi-spin wave. At the same time, the excitation region of the spin-wave resonance significantly narrowed. The proposed mechanism of photon-magnon conversion is applicable to any ferrite-dielectric structures with a boundary diffusion layer, and can be useful in the development of superminiature controlled devices for analog processing of microwave information signals.

Diffuse Reflectance Spectrophotometers Based on C12880MA and C11708MA Mini-Spectrometers Hamamatsu

Diffuse reflection spectroscopy with spatial resolution is a promising direction of non-destructive control of the properties of a number of scattering fine-dispersed materials, including food products. It can find wide practical application only in the presence of compact, easy-to-use and inexpensive spectrophotometric equipment. The aim of the article is to investigate the possibility of creating portable spectrophotometers based on Hamamatsu mini-spectrometers, which work together with modern computing facilities.The schematics for connecting the C12880MA and C11708MA mini-spectrometers to portable computing devices are reviewed. Shows the feasibility of using a small-sized microprocessor board ARM STM32F103C8T6 (Blue pill) on the chip STM32F103C8T6. Its use in the connection scheme has simplified data exchange with the control computer via USB interface and the formation of all the signals that are needed to control the mini-spectrometer.Two experimental samples of spectrophotometers based on C12880MA and C11708MA mini-spectrometers and STM32 microprocessors were created and their characteristics were studied. The calibration procedure and features of the software for these spectrophotometers are presented. The described features ensure the efficiency of software modification for the spectrophotometric problem to be solved. The presence of distortions of the registered spectra in the short-wave part of the spectral range of C12880MA was revealed. They arise due to focusing by the concave diffraction grating of a part of the radiation scattered by it into zero order.Approbation of developed portable spectrophotometers based on Hamamatsu mini-spectrometers indicates the possibility of their use in portable spectrophotometric equipment and devices for spectral control of optical properties of scattering materials. The described calibration technique allows you to determine the range of the spectrum, in which the distortions of the recorded spectra are minimal. The proposed solutions significantly reduce the cost of diffuse reflectance spectroscopy devices with spatial resolution and expand the possibilities of their use in various branches of science and industry.

Noninvasive Methods of Active Thermographic Investigation: Short Overview of Theoretical Foundations with an Example of Application

The field of non-destructive testing using thermography (NDT—Non-Destructive Testing and NDE—Non Destructive Evaluation) was established in the 1960s as a competitive and complementary method to ultrasonic or X-ray testing. Non-destructive quality control of objects is essential in modern industry, especially in mass production. It is an integral part of the quality control process. The reason for the introduction of non-destructive testing into diagnostic techniques were disasters and failures of various equipment and structures. Over the years, a division has been drawn between passive and active thermography. The aim of this publication is to present the theoretical basis of non-destructive testing with the use of active infrared thermography methods. It describes selected models of transient heat flow (thermal wave) in objects of various shapes and physical properties. They are the basis for understanding the changes in the surface temperature of the studied objects in time, which are the response to thermal excitation of different nature. An example of their effective application in engineering practice is the author’s software, in which the recorded time response is matched to the analytical solution, and on this basis detected anomalies are parameterized, detected by the fusion of various techniques of thermal image processing and analysis methods.

Investigation of micro-arc oxidation coatings using sub-THz ellipsometry

The paper is devoted to the investigation of the structure and properties of coatings obtained by micro-arc oxidation (MAO). For the first time, the possibility of using sub-terahertz ellipsometry with an operating frequency f = 0.14 THz for non-destructive non-contact determination of the integral values of the thickness, structure, and composition of such coatings is studied. The frequency was chosen since the corresponding wavelength ( λ = 2.14 mm) significantly exceeds the characteristic size of the roughness of the coatings, which makes it possible to use the geometrical optics approximation in the analysis of experimental results. When constructing models of the structure of coatings and determining their parameters, additional independent methods were used, such as optical microscopy, XRD, SEM, terahertz reflectometry, and the theoretical modeling of the electric field distribution during the microplasma oxidation process. The A1 alloy 1100 was used as the material for research. It is shown that ellipsometry is very sensitive to processes on the surface during MAO even at the earliest stages of oxide layer formation. Based on the data of the ellipsometry experiment, several planar models of the surface structure were constructed, and their parameters were determined at different stages of oxidation. The constructed models and their parameters (thickness, phase composition, and optical constants) are in good agreement with the results of independent measurements and do not contradict the physical concepts of the processes occurring during MAO. For the first time, it was proposed to use piecewise models for interpreting ellipsometric measurements of film structures non-uniform over the surface. The proposed model adequately describes the structure of MAO coatings at all stages of the technological process. It makes it possible to use ellipsometry for non-destructive non-contact express control of the state of these coatings during production without resorting to additional more complex analytical methods (XRD, SEM, etc). When analyzing ellipsometric data, estimates for the optical constants of mullite (Al 5 SiO 10− x ) in the terahertz range were obtained for the first time. It is also shown that the main results of the work can be used in the analysis of MAO coatings on other metals. • THz ellipsometry is found to be an efficient non-destructive method for MAO coatings characterization. • Information about the coating parameters was obtained, consistent with the data of structural and other independent studies. • Estimates for the optical constants of mullite in the sub-THz region are obtained. • A new model is proposed for the analysis of ellipsometric measurements of coatings non-uniform over the surface.

Study of reaction-bonded silicon carbide samples using visual-optical and radiographic methods of nondestructive control

Products based on silicon carbide are widely used in different industrial applications due to a high level of their mechanical, thermal, and operational properties. When the reaction sintering procedure is used to obtain silicon carbide materials, the preformed porous samples consisting of silicon carbide powders, carbon filler, and coke binder are subjected to liquid-phase silicizing (silicon melt infiltration (MI) in a vacuum furnace. We present the results of studying samples of reaction-bonded silicon carbide (RBSC) using visual-optical and radiographic methods of non-destructive control. Silicizing of carbon-silicon carbide materials can result in formation of defects on their surface and in the bulk of the material. The visual-optical method is shown to be rather simple and extremely informative procedure which ensures the detection of surface defects in the form of pores, cracks, chips, shells, and can also provide indirect indications of possible presence of internal defects in the form of underimpregnated areas. The samples silicized with a larger number of silicon drops on their surface exhibit a higher density and a smaller number of underimpregnated areas which can be detected using radiographic control. X-ray control carried out for several exposures differing in the angle of sample rotation by 90° provided 95%-probability of detecting internal volumetric and planar defects. The results obtained can be used in the manufacture of RBSC-based parts of tribotechnical duty, shut-off valves and other wear-resistant products.

Effect of Linear Crack Size and Location Relationship to Piston Stress and Damage Tolerance

In the quantitative characterization of linear defect structure of Piston Alloy, non-destructive testing and micro-morphology of defect, shape and outline of prefabricated linear defect are used in this paper. Based on ANSYS finite element software, an experimental simulation of line defect was carried out by using the finite element software of micromechanics. The defects of piston alloy components are assigned with material parameters, the model grid is divided, the boundary condition is defined and the finite element simulation is carried out under ANSYS/Mechanical environment. The calculation of the micro-stress field of the interface with various defects is obtained. Under the service condition of high-power density diesel engine, the local stress concentration caused by line defect is less than the strength limit of alloy material. Therefore, in this location eddy current testing non-destructive testing control line defect size is 0.12 mm×0.2 mm×5 mm. It is suitable for Eddy current nondestructive testing of piston components and can ensure the material safety and work reliability of Piston components under service condition.

К ВОПРОСУ СЕРИЙНОСТИ РАБОТ ПО НАНЕСЕНИЮ ЗАЩИТНЫХ НАНОПОКРЫТИЙ НА РЕСУРСООПРЕДЕЛЯЮЩИЕ ДЕТАЛИ СИЛОВЫХ УСТАНОВОК АВИАЦИОННОЙ И НАЗЕМНОЙ ТЕХНИКИ

The study objective is to develop the scientific foundations for the practical implementation of new methods of serial repair of resource-saving parts with erosion-resistant nanocoatings, which are subjected to increased erosion wear in operation.
 The problem to which the paper is devoted is to study the reliability and technical effectiveness of the developed proposals for making additions to the current regulatory and technological documents for the serial overhaul of gas turbine engines.
 For the study the following methods are applied: application of ion-plasma coatings in vacuum, destructive (measurements of micro-hardness and erosion resistance of coatings) and non-destructive (instrumental) control, manual and other surface treatment of the studied parts, mathematical statistics and expert judgement while conducting and analysing experimental research results.
 The novelty of the work is in the use of information about compressor blades with multi-layer, multi-shade reinforcing nanocoatings worn out in operation during subsequent repair. Their application should be fixed in the reporting production repair documents during the previous repair of the same blades.
 Study results: confirmation of the defined resource characteristics of compressor blades, reduction of production defects during the repair of blades with remnants of high-strength nanocoatings, preservation of the conditions for ensuring the serial overhaul of gas turbine engines.
 Conclusions. The theoretical calculations and practical studies of the proposed methods for repair of resource-saving components with multilayer multi-shade protective nanocoatings provide both the specified requirements for the operational reliability of gas turbine engines and the serial overhaul.

Origin identification of foxtail millet (Setaria italica) by using green spectral imaging coupled with chemometrics

Foxtail millet is an important edible crop in China and its demand continues to increase with the growth of the population. There are differences in the quality of millet from different origins, leading to differences in price. Therefore, an effective and rapid technique is needed to monitor the authenticity of millet origin. This study evaluates the feasibility of hyperspectral imaging (HSI) in identifying the origin of millet. A total of 120 millet samples from four regions in Inner Mongolia of China were analyzed and the hyperspectral data in the wavelength of 900–1700 nm were collected. The support vector machine (SVM) model built on full-band spectral data achieved acceptable results with a discriminative accuracy of 87.50% for the prediction set. Compared with the full-band spectra, the performance of the SVM model built on the basis of data dimensionality reduction was improved. Among them, the principal component analysis (PCA)-SVM model achieved the best discriminative performance with an accuracy of 95.00% for the prediction set. This study demonstrates the feasibility of NIR-HSI for origin traceability of millet, which provides a high-throughput, rapid and non-destructive quality control means to ensure the commodity flow of millet.

Diagnostics of materials by diffraction optical methods

The internal state of the material formed as a result of technological processing, indirectly affects the state of the material surface. A non-contact method of non-destructive control of the state of materials based on a visual analysis of the surface, requires high-quality images which can be obtained either using lens objectives or lenseless technologies. The results of studying image processing obtained by lensless technologies are presented. We used methods for modeling phase masks and image processing based on Gerchberg – Saxton iterative algorithms, adaptive-additive and phase mask rotation based algorithms. Materials such as granite, graphite, sand and carbon steel were analyzed. It is shown that the construction of cameras can provide significant reduction of their dimensions at the same or even improved characteristics. The images obtained using lensless technologies and the proposed methods of image processing also provide a significant increase in the accuracy of visual inspection of materials. The results obtained can be used in refining lensless technologies, improving the quality of images and reducing time of their processing.

Magnetic resonance imaging as a tool for quality control in extrusion-based bioprinting.

Bioprinting is gaining importance for the manufacturing of tailor-made hydrogel scaffolds in tissue engineering, pharmaceutical research and cell therapy. However, structure fidelity and geometric deviations of printed objects heavily influence mass transport and process reproducibility. Fast, three-dimensional and nondestructive quality control methods will be decisive for the approval in larger studies or industry. Magnetic resonance imaging (MRI) meets these requirements for characterizing heterogeneous soft materials with different properties. Complementary to the idea of decentralized 3D printing, magnetic resonance tomography is common in medicine, and image data processing tools can be transferred system-independently. In this study, a MRI measurement and image analysis protocol was evaluated to jointly assess the reproducibility of three different hydrogels and a reference material. Critical parameters for object quality, namely porosity, hole areas and deviations along the height of the scaffolds are discussed. Geometric deviations could be correlated to specific process parameters, anomalies of the ink or changes of ambient conditions. This strategy allows the systematic investigation of complex 3D objects as well as an implementation as a process control tool. Combined with the monitoring of metadata this approach might pave the way for future industrial applications of 3D printing in the field of biopharmaceutics.

Prediction of Solid-State Form of SLS 3D Printed Medicines Using NIR and Raman Spectroscopy.

Selective laser sintering (SLS) 3D printing is capable of revolutionising pharmaceutical manufacturing, by producing amorphous solid dispersions in a one-step manufacturing process. Here, 3D-printed formulations loaded with a model BCS class II drug (20% w/w itraconazole) and three grades of hydroxypropyl cellulose (HPC) polymer (-SSL, -SL and -L) were produced using SLS 3D printing. Interestingly, the polymers with higher molecular weights (HPC-L and -SL) were found to undergo a uniform sintering process, attributed to the better powder flow characteristics, compared with the lower molecular weight grade (HPC-SSL). XRPD analyses found that the SLS 3D printing process resulted in amorphous conversion of itraconazole for all three polymers, with HPC-SSL retaining a small amount of crystallinity on the drug product surface. The use of process analytical technologies (PAT), including near infrared (NIR) and Raman spectroscopy, was evaluated, to predict the amorphous content, qualitatively and quantitatively, within itraconazole-loaded formulations. Calibration models were developed using partial least squares (PLS) regression, which successfully predicted amorphous content across the range of 0–20% w/w. The models demonstrated excellent linearity (R2 = 0.998 and 0.998) and accuracy (RMSEP = 1.04% and 0.63%) for NIR and Raman spectroscopy models, respectively. Overall, this article demonstrates the feasibility of SLS 3D printing to produce solid dispersions containing a BCS II drug, and the potential for NIR and Raman spectroscopy to quantify amorphous content as a non-destructive quality control measure at the point-of-care.

Possibility of using the results of non-destructive testing for assessing occupational risks in the labor protection management system

Introduction. The paper discusses the methods for occupational risks assessment of workers within the framework of the labor protection management system. To date, there is no legally approved methodology for occupational risks assessment. Numerous well-known methods of ORS are advisory in nature. Their main weak point is the influence of the human factor and, consequently, the relative subjectivity of the final conclusions.Problem Statement. The main objective of this work is to study the possibility of occupational risks assessment of workers by the "Bow tie" method in the occupational safety management system.Theoretical Part. The method of risk assessment "Bow tie" was adopted as a basis. The main components of this method are considered. Approbation has been carried out. It is proposed to introduce an additional barrier into the "Bowtie" risk assessment method, which is called "Non-destructive control".Conclusions. As a result, a technique for occupational risks assessment was proposed, taking into account the results of non-destructive testing. The positive aspects of the proposed approach are also identified.

Assessment of macronutrients and alpha-galactosides of texturized vegetable proteins by near infrared hyperspectral imaging

Near infrared (950−1654 nm) hyperspectral imaging (NIR-HSI) was applied for the first time for the prediction of proximate composition (proteins, carbohydrates, lipids, ashes) and alpha-galactosides (verbascose, stachyose, raffinose) content of texturized vegetable proteins (TVP) obtained from different raw materials (four formulations) intended for plant-based meat analogues (PBMA) production. After exploration by Principal Component Analysis, the dataset was split into calibration and test sets and analyzed by Partial Least Squares Regression. In calibration and cross-validation, the R2 was between 0.92 and 0.98, with low error values. The figures of merit of the prediction confirm those results and the good performance of the models. Pixel-by-pixel prediction allowed the tracking of the non-uniform distribution of chemical components. Overall, NIR-HSI showed potentiality to be applied as a tool for rapid, accurate, and non-destructive quality control of TVP, which is fundamental as they strongly affect the nutritional and textural properties of PBMA.

Structural coloration of AISI 321 steel surfaces textured by ultrasonic impact treatment

This work reports the appearance of iridescent spectral patterns in the form of coloured stripes on AISI 321 steel surfaces subjected to ultrasonic impact treatment (UIT). The possible reasons for the UIT-textured surface coloration are considered from the viewpoints of wave (diffraction and interference) optics. According to the XRD analysis, the phase composition of the AISI 321 steel surface layer after UIT is represented by the austenite and martensite iron phases. The chemical composition of the UIT-textured steel near-surface layer is identified using XPS, which includes iron and chromium in the oxidised and metallic states. The thickness of the oxygen-enriched layer after UIT is estimated to be approximately 15 nm. SEM and AFM analysis confirmed that UIT provides the formation of periodic surface structures with characteristic dimensions from several hundreds of nanometres to several micrometres coinciding in order of magnitude with wavelengths in the visible range. Applying different processing modes of AISI 321 steel surface leads to qualitative transformations in the spectral patterns: the position of the coloured stripes, its width, and the total number of the observed diffraction maxima change according to the equation of light diffraction. The obtained results indicate that diffraction of light is the main reason for the appearance of spectral patterns on the UIT-textured AISI 321 steel surface, which is analogous to a reflective diffraction grating. Structural diffraction coloration could be used as a possible basis for a non-destructive spectral control for UIT-textured steel surfaces and indirect monitoring of the performance of UIT equipment.