Root crack sizing using phased array inspections and autoregressive spectral extrapolation signal processing

Critical welds need inspecting, because of either code requirements or structural integrity. Automated ultrasonics has proven more reliable than other techniques, such as radiography or manual techniques. Recently, portable phased arrays have become a dominant method of inspecting as they offer high speed, repeatable inspections. Techniques are available for a wide variety of vessels and pipes using commercial equipment. In addition, ASME section V now has five code cases available for phased array inspections of welds. One aspect of phased array inspections is that the coverage must be demonstrated using a scan plan, which can be a ray tracing programme showing the beam coverage, inspection angles, etc. This approach has big advantages for a flexible technology such as phased arrays; specifically, unusual weld profiles can be inspected using tailored scan plans. Unlike conventional ultrasonics or radiography, angles can be selected to optimise defect detection. Also, phased arrays can be adapted to austenitic welds by switching to longitudinal beams, dual arrays or combinations. For ferritic steel welds, time-of-flight diffraction can be used concurrently to improve detection, sizing and for off axis defect detection.

A series of ultrasonic elements arranged in a phased array transducer can provide the capability to activate each element separately but in a programmed sequence. This will help the acoustic signal to be generated at desired focusing distances and anticipated angles for specific materials and structures. In case of composite material inspection, this characteristic of the phased array method can improve the undesirable effects of the high attenuation and anisotropic structure of composite materials on response signals. In this study different phased array probes and wedges which are commercially available were evaluated for their response signals’ characteristics. First, the capability and resolution of bulk wave generation were studied for each set of probe and wedge, and the response signals were compared to that of the conventional single element ultrasonic transducers for different thicknesses composite plates. Then the resolution of the response signals and their sensitivity to defect size were evaluated and compared to the single element transducers as well. Next, each phased array probe and wedge set was used to generate plate waves in aluminum plates based on plate wave propagation theory, probe and wedge physical properties and the definition of delay law. Results show a general improvement in response signals’ strength and resolution for phased array method in comparison to the single element transducers. Also some plate wave modes could be generated with optimized signal generation parameters in phased array system.

As part of efforts by Rolls‐Royce to evaluate the use of ultrasonic phased arrays for inspection of titanium billets, a series of ultrasonic phased array inspections were performed at the Center for Nondestructive Evaluation (CNDE). The inspections were performed using a sectorial‐annular array designed especially for titanium billets by R/D Tech and supplied to Rolls‐Royce. The billet test piece is seeded with thirteen yttria disks, each located at successive depths below the outer diameter surface to just past the billet centerline. The phased array inspections employed both fixed‐focus and dynamic‐depth‐focus (DDF) focal laws in conjunction with several depth gating schemes. Aperture and focal parameters were changed as a function of depth when using fixed‐focus focal laws. Results include characterization of transducer performance and delay‐time correction of imperfections, signal‐to‐noise measurements for the yttria disks in the billet test piece, and effects of probe misalignment on flaw sensitivity.

The increasing use of high-speed trains, resulting in higher stress to the material and serious accidents with human injuries in the past, lead to a demand for shorter inspection intervals, extended scope of inspection and more stringent test requirements to be applied to the critical components. One component, which is inspected in regular intervals, is the axle of the railway wheel set. Critical areas for cracks are mainly the wheel and brake disc seats and the cross section transition areas. The manual ultrasonic inspection of used axles by experienced personal is time-consuming (since several sound beam angles have to be used to cover the complete test area), expensive and, of course, subjective. It represents a bottleneck in the inspection line. One way to overcome this bottleneck is the automation of the test process and the use of phased array probes. GE Inspection Technologies, in co-operation with the German railways (DB) and the 'Bundesanstalt fur Materialprufung'(BAM), developed a system to automate this inspection. This system applies the phased array technique to detect transversal cracks in the most critical areas of the axle. The different angles of several conventional probes are replaced by steering the beam angle of one phased array probe accordingly. Mechanical movement is substituted by software control. Two of these automated systems have been delivered to the German Railways. When taking these systems into operation, several problems arose, caused by the variety of the axles, coupling surface conditions and differences in the sound attenuation even within the axle. This paper describes the technical concept and reports some practical experience, problems and solutions in the commissioning phase of the automatic inspection lines.

The welding quality of the GIS shell is critical to preventing SF6 gas leakage in the Gas Insulated Switchgear（GIS） equipment of the substation, and phased array ultrasonic testing（PAUT） technology can intuitively and efficiently inspect the butt welds of the GIS shell. Since the GIS shell is mostly non-magnetic aluminum alloy material, the scanning process can not use the magnetic wheel to allow the scanning device to adsorb on the detection surface.in order to solve the problem of coupling between the phased array probe and the surface of the GIS shell during the inspection process, automatic scanning device for PAUT of butt welds of GIS shell was developed. The scanning device uses the main frame, straps, probe lifting assembly and waterway tap assembly to effectively fix the phased array probe and the curvature wedge on the GIS shell, on the one hand, to ensure the close fit between the probe and the detection surface in the inspection, on the other hand, to ensure that the data can be automatically collected along the established trajectory during the inspection process.The scanning device ensures the quality of the collected data while improving the detection efficiency, and the feasibility of the scanning device is verified by experiments.

The marriage of welding and Non-Destructive Testing (NDT) processes at the point of manufacture has enabled the detection and correction of defects during the welding process. This has demonstrated clear financial and production benefits by reducing weld rework and ensuring schedule certainty, however this is yet to be demonstrated for use with narrow-groove welding practises. Narrow-groove welds are notoriously difficult to inspect using traditional Phased Array Ultrasonic Testing (PAUT) techniques due to large thicknesses and the vertical nature of Lack-of-Sidewall Fusion (LOSWF) defects. This is further complicated by the presence of partially-filled weld geometries during in-process inspection, which cause geometric reflections which can mask or falsely indicate the presence of a defect. A solution to this is proposed in this work, by adapting a dual-tandem phased array imaging system for the imaging of LOSWF defects in a partial weld geometry. This considers a two array system utilising a phased array probe on each weld side, coupled with an advanced dual-aperture Full Matrix Capture (FMC) acquisition technique. Advanced multi-mode image processing algorithms such as the Total Focusing Method (TFM) and Phase Coherence Imaging (PCI), with adaptive delay law calculation, have shown high sensitivity to LOSWF defects in a mock partial weld geometry. Additionally, an adaptive Probe Centre Spacing (PCS) technique is defined for in-process inspection based on amplitude and phase coherence sensitivity in partial weld geometries, with the effects of partial weld reflections analysed and discussed. These results have demonstrated the effectiveness of a dual-tandem phased array approach to imagine LOSWF defects during the in-process inspection of narrow-gap welds.

Ultrasonic testing of metal welds has been in use for many years. Scanning methods using both contact and immersion methods are often used at the time of manufacture and also during periodic in-service inspection programs. But because of a variety of component configurations and potential flaw geometries it is often necessary to perform several inspections, each with a different probe configuration to assure adequate defect delegability. It is possible that a properly designed phased array probe can perform several different inspections without changing hardware thereby reducing inspection times. This presentation reviews the design and operation of ultrasonic phased array transducers and the necessary features to achieve the desired performance. Situations in which these probes have already been implemented effectively are also discussed.

The requirements of Ultrasonic Testing, such as DNV, ISO specification etc., for longitudinal submerged arc weld (SAW) seam of UOE pipe become severe to the offshore steel line-pipe with high grade and heavy wall thickness. In order to satisfy the requirements, testing method with multi-probe arrangement have been widely applied in the pipe manufacture. Recently, the phased array technique has been applied for inspection of girth welds of pipeline and longitudinal ERW (electric resistance welded) seam instead of multi-probe method. But the inspection system with conventional phased array probe has many difficulty to apply for inspection longitudinal SAW seam of UOE pipe, because of defect detection capabilities, array elements arrangement, and so on. The authors have developed an applicable ultrasonic phased array probe to satisfy the severe requirements for longitudinal SAW seam of UOE pipe. This paper presents the results of our original designed array probe, which has been composed of 32-transducer elements mounted on cylindrical-shaped plastics, and also compares the inspection results to those obtained on the conventional multi-probe and our developed array probe in the UOE pipe mill.

Hybrid bearings, consisting of silicon-nitride ceramic rolling elements (e.g., balls) and a metal race, are a critical enabling technology for advanced gas turbines. A primary factor for reliable manufacturing of ceramic bearing balls is to establish an affordable nondestructive inspection method to detect flaws on the ball surface and subsurface. The current inspection method is based on fluorescent penetrant examination under ultra-violet lights, which is a slow process. A nondestructive evaluation (NDE) method, based on ultrasonic Rayleigh waves that are generated/detected by phased array probes, is being investigated for detection and characterization of these flaws, including Hertzian C-cracks. Both detection sensitivity and speed are important parameters to evaluate the performance of this NDE method. This paper describes the principle of this method and presents recent results on detection capability for various flaws in bearing ball specimens.

The digitalization of testing procedures is one of the challenges in the development of modern non-destructive testing systems. In order to guarantee a high level of inspection reliability, the assignment of measurement data to the measurement position plays an important role as well as the optimal inspection hardware. In a cooperative research and development project, an optical tracking system has been developed with which it is possible to determine the positions of different ultrasonic probes in space without contact. Thus, the position of the measurement is linked to the measurement results directly. Infrared LED markers attached to the ultrasonic probes are used for this purpose. The position of the markers are tracked in space with a camera. By linking several cameras and trackers, a positional accuracy of a few millimeters can be achieved for a camera specimen distance of 2 m. The more cameras are used the bigger the investigated part can be. For the tracking system, an existing optical camera system is coupled with a conventional of the shelve ultrasonic phased array device by means of a newly developed universal encoder. Different single transducer probes or phased array probes can be used. The costly and time consuming use of mechanical encoders is thus eliminated. This combination enables the further digitalization of hand-guided ultrasonic testing precisely in those areas where robot-based testing is not feasible. Additionally, a much easier way of documentation is possible. Due to the exact position determination a better evaluation of the measurement data can be carried out via a subsequent 3D display of the ultrasound data.

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.

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.

A novel sparse representation based multi-source localization method is presented in this work. We envision a wireless network infrastructure containing multiple phase arrays of acoustic sensors. With multiple arrays, direct estimation of a set of source locations is achieved using a new joint sparse representation of array covariance matrices (JSRACM). This representation transforms the source location estimation problem into a spatial sparse signal representation (SSSR) optimization problem. To mitigate the high computation complexity of JSRACM, a novel binary sparse indicative vector (SIV) is introduced to represent the support of joint SSSR of array covariance matrices. As such, the multiple source locations may be estimated by solving an unconstrained optimization problem of the SIV vector using existing FOCUSS-like algorithms. The resulting SIVR-JSRACM algorithm does not require prior information of the number of sources nor initial source location estimates. It promises super-resolution, robustness to noise, and low computing complexity which is independent of the number of sensor phase arrays. Simulation results demonstrate superior performance of the proposed algorithm.

Hollow axle inspection can be performed without demounting the axles and without dismantling the wheels and the brake discs by using the drilling for the scan. To increase inspection reliability and inspection speed, the application of phased array systems instead of conventional probes is a good choice. For solid shaft inspection phased array setups became standard in the recent years. Nevertheless, for hollow axle inspection typically a number of conventional probes rotating through the axles drilling are applied.The new approach uses an electronically steered rotating sound field from a phased array for the circumferential scan. This is realized by a cone shaped phased array which operates in immersion technique. That allows a significant increase in inspection speed and a reduction of the mechanical effort of the inspection system. The inspection can be carried out by a linear movement of the probe setup along the axles drilling. Applying additional focal laws allows exact inclination and focusing of the sound beam in the plane vertical to the specimen axis to concentrate the sound in the zones close to the external surface. An additional focus in the plane of incidence increases overall resolution and sensitivity.The cone type phased array probe has been optimized to detect transversal flaws in and close to the outer surface of the hollow axle with orientation in the radial-radial plane. The prototype probe system, sound field simulations and measurement results are presented.

Calibration procedure for performance evaluation of clinical Pulsed Doppler Systems