Non-Destructive Testing Technology
Year:2018 | Volume:2 | Issue:2|Papers Count:10

Digital shearography is widely used as a nondestructive inspection method in detection of subsurface defects and strain measurement in experimental mechanics. In addition, full field measurement and low vibration isolation requirements cause to higher application of this method in quality control applications. In this paper, the application of digital shearography in inspection of metallic samples has been studied. The subsurface defects of aluminum samples have been investigated by using a proper setup of digital shearography. The thickness of samples is 3mm and 5mm and the shear size in experiments is equal to 4mm. The samples are irradiated by a 660nm diode laser and recorded shearograms before and after thermal load have been analyzed by means of appropriate software. The results showed that, the diameter to depth ratio of defects employs important role in detectability of subsurface defects. By using this method, the minimum detectable diameter of defect is 2. 5 times of its depth.

Considering day to day increase in cost of gasoline for Iranian customers; the interested for using dual fuel automobiles are increasing. It is common to use steel CNG vessels in Iranian dual fuel cars. Nowadays; there are millions of CNG vessels with more than 10 years of commissioning time in Iran. Recently, periodic inspection regulations are issued by the Iranian Standard bureau. In this regulation, visual inspections are considered as the main method of inspection, however, for critical vessels it is strongly recommended to use ultrasonic inspections and/or hydraulic tests. Because of the importance of the topic for the safety of the citizens, this paper dedicated to investigate the statistics of the CNG vessels and their most common defects in country. In addition, the periodic inspection procedure of the Iranian regulations is compared with international counterparts. According to the discussion, inspection measures which considered by the Iranian standard bureau are enough and useful for standard CNG vessels; however, more than 25% of all CNG vessels in Iran are manufactured in nonstandard manners and they need more inspection measures. It seems that reducing of the inspection period from 36 months to 24 months will be of value.

Inspection of oil and gas and chemical materials pipelines is one of the most important problems in the material transfer industry. Lack of corrosion detection in these pipes causes irreparable human and financial accidents. Due to the under loading of these pipes, kind of tests are needed that can be achieved to location of corrosion without any damage to the tube. One of these destructive tests is industrial radiography, which is used in this case. In this method, the sensitive plate is closed around the tube and transmitted X-rays or gamma-ray and the location of corrosion are recorded the sensitive plate. Due to the scattering, the resulted images need to be processed in order to clear the areas of defect and corrosion regions. Interpreter and radiographers need images with better quality and contrast to detect areas of defects. Image processing algorithms can help. The complex wavelet algorithm, using image decomposition into various phase and domain components and removing some of these components, can be effective in improving image contrast. In this research, the complex wavelet method was used to remove the background and clarity of images. The results show that this method has acceptable performance in improving the contrast of radiographic images in corrosion areas of ammonia tubes. And the evaluation of industrial radiography also confirms the improvement of images with a high percentage.

Edge flaw detection is a complicated task in ultrasonic testing, thus, majority of automatic testing system makers exclude this feature from their products. As a rule of thump, a span of 10 to 20 cm of each end of objects is defined as the area that needs an alternative testing solution by the user. The reason for this is the geometrical limitations that a probe holder suffers in covering the body of to-betested parts. Owing to the fact that an array of search units implanted in a large housing (holder) ought to scan the surface of the object all together, some of them miss the edges when the holder positions on the extremities. This is an inevitable issue in manual approach too when the wave projection and scan direction are same. To resolve the problem, full-immersion method can be applied where both the object and probes are submerged in a liquid. Although, the need for sinking parts in a couplant makes it slow and costly for sizable parts like pipes and cylinders. This paper proposes a new contact technique for ultrasonic of edges based on extension of the objects’ ends that offers a higher speed and less complexity compared to the full-immersion method.

The use of Eddy Current (EC) technique has proved to be a viable means for crack detection and sizing in metals. In this technique, a crack is evaluated from the observation of probe impedance changes due to the interaction between induced current in a metal and the crack. Since the growth of fatigue crack in metals is a stochastic process, the cracks do not have a constant predetermined shape. Detection and Sizing of the cracks from probe signals witch called inverse problem is important for predicting the life of the workpiece. In this paper, an inverse algorithm based on the particle swarm optimization (PSO) technique is proposed for predicting the crack depth profile from EC probe signals. The validity of the proposed algorithm is demonstrated by comparing the actual and reconstructed depth profiles from measurement EC probe signals.

In this paper, the eddy current nondestructive testing method was presented to evaluate the residual austenite in the microstructure and hardness of high chromium cast iron mill balls. For this purpose, some 40 mm high alloy cast iron balls with 30 wt. % Cr and 3 wt. % C nominal composition were selected after sand casting process. To achieve the different hardness and different residual austenite contents in the microstructure, the balls were heat treated at different austenitzing and tempering temperatures. The microstructural studies using by optical and scanning electron microscopies, XRD and Vickers hardness were performed on the samples. Then, the microstructures of the samples were evaluated using an eddy current device at 50 to 200 kHz frequencies. The result showed that, using the eddy current method, different microstructures of the balls with different values of residual austenite and hardness can be identified and separated, rapidly and nondestructively. To the purpose, the eddy current inspection at 150 kHz frequency is selected using the impedance index as a nondestructive evaluation method. This index decreases with increasing residual austenite content.

Although pesticides which are used to control plant pests and diseases increase the productivity, they have the potential to contaminate the environment and foods. By using pesticides excessively or incorrectly during production, ignoring the degradation period of pesticides and early harvesting, transferring to the market and selling the products immediately or a few days after spraying, the pesticides residue will exceed the maximum residue limits, thus indicating a potential risk to consumer health and safety. To ensure public health, it is essential to detect and determine pesticides contamination of agricultural products especially fruits and vegetables. Currently, several different destructive technologies are used to determine the concentration of pesticides residue which are destructive, have a highly time-consuming sample preparation, are very expensive, and require welltrained personnel and advanced laboratories. Therefore, development of a non-destructive, fast, simple, low-cost, environmentally friendly and reliable detection technique of pesticides residue is imperative. In this paper, some advances in non-destructive testing technology which can use for rapid detection of pesticides-contaminated product are presented and a novel portable system designed based on visible/near-infrared spectroscopy is introduced for this end.