Crack Location and Height Measurementby 4 Sensor TOFD Method with Pulse Compression

Background/Objectives: Grain structure of Austenitic Stainless Steel (ASS) weld causes difficulty in defect detection while inspecting using Time of Flight Diffraction (TOFD) method. This study aims at comparing segmentation methods to overcome this difficulty based on defect characterization. Methods/Statistical Analysis: This study makes use of TOFD and Radiographic images of ASS weld pads fabricated with defined linear and volumetric defects. The Region-Based Level Set algorithm and Discontinuity Based Segmentation algorithm were explored for achieving flaw segmentation and quantitative characterization and validation of the result with that of standard radiographic results. Findings: The efficiency of the algorithms was analyzed by comparing and validating the size of defect with that of standard radiographic results in the form of error percentage. The consistency of error percentage in defect sizing (up to 11%) achieved by RegionBased Level Set algorithm for all the test images given in the database indicate that, this algorithm is the best as compared to Discontinuity Based Segmentation algorithm(error percentage up to 47%) for defect segmentation and characterization in TOFD images. Application/Improvements: The segmentation algorithm enables automation of measurement process and enhanced detection and characterization of defects at the initial stage. Further, it reduces human fatigue caused by operator while defect detection as the volume of data increases. The future direction is to fully automate the system in order to save time for interpretation and to modify the algorithm to segment images with multiple defects. Keywords: Defect Characterization, Discontinuity Based Segmentation, Flaw Segmentation, Region-Based Level Set Segmentation, Time of Flight Diffraction (TOFD), Weld Defect

Signal quality enhancement using higher order wavelets for ultrasonic TOFD signals from austenitic stainless steel welds

A hybrid particle swarm–Nelder–Mead optimization method for crack detection in cantilever beams

It is difficult to accurately size the defects that are oriented at an angle (that is not normal to the wave) using conventional amplitude based ultrasonic techniques. Since Time of Flight Diffraction (TOFD) is based on the diffraction of ultrasound at defect edges, defect sizing using this technique is amplitude independent. However, most of the TOFD based assessment relies on manual sizing, whose accuracy depends on quality of image and the operator’s experience. Also, the utilization of TOFD for sections less than 15 mm has reportedly several difficulties. In this paper, we report our attempts to size the vertical and inclined defects using an in‐house TOFD system built to inspect thin sections (6–10 mm). To improve sizing, automated defect sizing techniques termed Embedded Signal Identification Technique (ESIT) and Point Source Correlation Technique (PSCT) were developed. A ray tracing based model was also developed for a) optimizing the experimental parameters for thin sections, b) interpreting the r...

Reliability assessment of manual ultrasonic time of flight diffraction (TOFD) inspection for complex geometry components

Simulation trained CNN for accurate embedded crack length, location, and orientation prediction from ultrasound measurements

This paper addresses the estimation of systolic time intervals, namely the pre-ejection period (PEP) and the left ventricular ejection time (LVET), using heart sound. PEP is estimated with a Bayesian approach resorting to the signal's instantaneous amplitude and typical time intervals between atrio-ventricular valve closure and aortic valve opening. As for LVET, aortic valve closure is determined through the analysis of a high-frequency signature of S2. Additionally, LVET has also been estimated from a PPG signal at a peripheral site, for the sake of comparison over a subset of data. We evaluated our algorithms on a set of 658 heartbeats and achieved 10.32 msec average absolute PEP estimation error with 7.3 msec standard deviation and for LVET, 15.8 msec average estimation error with 13.6 msec standard deviation. Current results support our assumption that heart sounds can be applied to detect the onset of the aortic valve movement processes.

A blind approach for estimating the signal to noise ratio (SNR) of a speech signal corrupted by additive noise is proposed. The method is based on a pattern recognition paradigm using various linear predictive based features, a vector quantizer classifier and estimation combination. Blind SNR estimation is very useful in speaker identification systems in which a confidence metric is determined along with the speaker identity. The confidence metric is partially based on the mismatch between the training and testing conditions of the speaker identification system and SNR estimation is very important in evaluating the degree of this mismatch. The aim is to correctly estimate SNR values from 0 to 30 dB, a range that is both practical and crucial for speaker identification systems. Additive white Gaussian noise and pink noise are investigated. The best feature for both white and pink noise is the vector of reflection coefficients which achieves an average SNR estimation error of 1.6 dB and 1.85 dB for white and pink noise respectively. Combining the estimates of 4 features lowers the error for white noise to 1.46 dB and for pink noise to 1.69 dB

New non-destructive examination methods have been available for many years. These include time of flight diffraction and phased array methods. These are routinely used for inspection of welds. Work is ongoing at ISO and CEN for standardization of these methods. First the time of flight diffraction was drafted and now ISO and CEN are working on a standard for phased arrays. These drafts are used for welding inspections. The acceptance criteria is in draft form for time of flight diffraction which will be followed by that for phased array. Standards are already available for base material phased array inspection such as the ASTM document “Standard Guide for Evaluating Performance Characteristics of Phased Array Ultrasonic Examination Instruments and Systems”. Several ASME code-cases have been issued in recent years on weld inspection. Qualification for the ASME code is also planned for this novel technique.

Defect detection using the phased-array laser ultrasonic crack diffraction enhancement method

The purpose of this study was to determine the accuracy of the typical adult's ability to view, then estimate, distances along a roadway. A survey was conducted along a roadway, where 123 subjects were asked to look at, and then estimate the distance to common objects along the roadway. The entire population tended to underestimate distances to objects that were from 20 to 400 feet away. After none outliers were identified and removed, the average estimation error was –23.4%. The variation in performance among individuals was extremely large, with error extremes ranging from –96% to +71%. An analysis of the percentage error in estimation revealed that police performed as well as the rest of the population. The age of the subjects and their rating of their own vision acuity made no statistically significant difference in their average estimation error. Males had significantly lower estimation error than females, as did subjects who rated themselves highly with respect to their distance estimation ability.

Computational tools based on probabilistic fracture mechanics have been developed to enable reliability-based fitness-for-service assessments of flawed girth welds. The same tools are readily adapted for establishing maximum allowable defect sizes to achieve targeted weld reliability. Sensitivity studies have shown that of the various input parameter uncertainties, measured defect height often has the greatest impact on the probabilities of both fracture and plastic collapse. A reduction in sizing uncertainty should thus dramatically improve predicted reliabilities. The increasing use of mechanized ultrasonic testing (UT) in pipeline construction, driven by the demands of engineering critical assessment (ECA) -based acceptance criteria, highlights the need to quantify this uncertainty, particularly for systems incorporating pulse-echo (P/E) and time-of-flight diffraction (TOFD) methods and phased-array (PA) technology. EWI collected third-party independent data and statistically characterized the systematic and random errors in girth weld defect sizing, as measured by mechanized UT using P/E and TOFD methods, as well as PA ultrasonic technology, in support of pipeline reliability assessments.

Pipelines are now using Fitness-For-Service (FFS) for accept/reject of weld defects. FFS requires accurate measurement of defect height for Fracture Mechanics assessments. The standard pipeline weld inspection technique of radiography is incapable of such measurements. However, the newer technique of ultrasonics can measure defect height, in principle. Initially ultrasonic amplitude methods were used for height measurement, but these proved unreliable. Now diffraction methods, especially Time-Of-Flight-Diffraction (TOFD), are being used in conjunction. This paper reviews previous work — mainly large nuclear studies like PISC II — and published pipeline sizing studies. The best nuclear sizing was within a few millimetres, using diffraction. In contrast to nuclear, pipeline AUT uses zone discrimination, focused transducers, much thinner material and simpler analysis techniques. Current accuracies are typically ± 1 mm (terminology undefined), which correlates with the beam spot size and typical weld pass. Requests for accuracies of ± 0.3 mm are probably unachievable, though future R&D should significantly improve pipeline sizing.

When chirp pulse compression technology (PCT) is applied in Electromagnetic Acoustic Transducers (EMATs), the frequency response characteristic of the EMAT testing system may be inconsistent with the chirp signal bandwidth. Furthermore, it causes a loss in the frequency spectrum and distortion of the ultrasonic echo waveform, leading to a decrease in the signal-to-noise ratio (SNR) and range resolution of the pulse compressed signal. To solve this problem which has not been further researched in the previous publications, we proposed a new circuit-field coupling finite element model for ultrasonic wave generation of the spiral coil EMAT for enhancing the pulse compression effect, and the excitation circuit for the EMAT is also considered in this model. Furthermore, the effects of the diameter of the spiral coil wire, matching method of the impedance matching network, and parameter of the matching components on the peak and width of the main lobe after pulse compression were analysed through simulations and experiments. Subsequently, the optimal combination of the EMAT coil conductor diameter, impedance matching method, and matching component parameters were determined and verified by experiments. The results show that the SNR and range resolution of the pulse compressed ultrasonic signal can be largely enhanced when the diameter of the spiral coil wire, impedance matching method, and the parameter of the matching components are chosen carefully. When the aforementioned parameters are appropriately selected, the amplitude of the main lobe can be increased 3.16 times, and the width of the main lobe is reduced by 31.7%.

Defect sizing is required for a quantitative assessment of the quality and reliability of safety relevant components and materials using ultrasonic non-destructive testing. The SAFT (Synthetic Aperture Focussing Technique) and the TOFD technique (Time Of Flight Diffraction) are such promising sizing candidates, extracting more information from the raw ultrasound echo data and the corresponding crack tip response. In this work the phased array technique is used to inspect a clad mock-up model of a pressure vessel section. The full scale model contains artificial test reflectors which are located in the weld and in the cladding region as well. The defects—representing typical flaws at a very early stage—are analysed with different frequencies, beam angles and directions of incidence. For the reconstruction of reflector indications a SAFT algorithm is applied to the phased array measurement results. Additionally the reflectors are analysed by means of the TOFD technique, using different beam angles at the same time. Both analysis methods are performed using different directions of incidence considering the complex cladding structure underneath the inner surface of the mock-up model. A direct comparison of the SAFT and TOFD techniques shows that, besides the clarity of the results, the detection and sizing capabilities of SAFT are far better.