Research and Application Development

Services Offered:

• Manual and Automated Ultrasonic Inspection System Development
• Inspection Technique Optimization using Laboratory scale Studies and Ultrasonic modeling (CIVA, BeamTool)
• Preparing Technical Justification for Technique Evaluation and Qualification (Probability of Detection and sizing accuracy studies)
• Inspection/Calibration/Analysis Procedure Preparation to Support Field Deployment of Custom Techniques
• Development of Custom Imaging Algorithms to Support Challenging Inspection Applications

Current Projects

1. In-service Inspection of Heavy Walled Vessels (Up to 350°C) for Detection of HTHA, Creep, Thermal and Fatigue Cracks

Heavy walled pressure vessels are commonly monitored for defects which develop and grow while in-service. Often these vessels operate at elevated temperatures (up to 350°C), requiring them to be taken out of service for periodic inspection. Alternatively, specially designed wedges and probes that can withstand exposure to these temperatures can be employed to perform in-service PAUT examinations, however, the quality of the scan data is much degraded compared with room temperature scans. This loss in data quality (noise, couplant flashing, increased grain noise and attenuation, etc.) makes signal interpretation more challenging. In addition, lower frequency probes are generally needed to mitigate sources scan quality loss, making resolution of the most insidious damage mechanisms (Creep, High Temperature Hydrogen Attack, Fatigue Cracks, etc.) challenging if not impossible. To address these issues, we have been working to develop an inspection system capable of providing higher frequency, higher resolution imaging at elevated temperatures. Our approach has been to design smaller, dual array wedges to reduce the wedge path attenuation, in conjunction with custom focal laws implemented in standard phased array units from which data is exported and post-processed. The resulting scans are then analyzed in open source medical imaging software. The prototype system was tested at room and elevated temperatures and is scheduled to be deployed as part of a pilot program for HTHA inspection at 290°C. The Research and Application Development group is seeking industrial partners to validate the technique for creep inspections.

2. Material Purity Testing and Microstructure Characterization with Attenuation Rate Tomography

Defects in production of bulk materials can lead to non-uniformity in the grain structure of materials which is very difficult to detect by ultrasonic means, particularly if the grain size is much smaller than the ultrasonic wavelength (generally the case). Grain structure non-uniformity can also be indicative of gradual damage such as creep or HTHA. Although presence of contrast in grain structure can sometimes be inferred from changes in ultrasonic backscatter, imaging this transition can be challenging, particularly if the grain size is very small compared to the wavelength. An alternative approach to imaging grain structure involves using the rate of attenuation which for scattering materials is directly related to grain size. For grains much smaller than the ultrasonic wavelength, scattering attenuation is a frequency dependent process. The rate of attenuation with respect to frequency is easily determined for any path through a given material. By measuring this rate through a large number of paths it is possible to produce an image of the attenuation rate, similar to computed tomography or seismic tomography. Our technique uses an FMC data capture and measures the attenuation rate for all element pairs bouncing from the backwall of the test piece with respect to an unflawed reference specimen to produce tomographic images of either the average attenuation or the attenuation rate. This process allows even relatively small contrast in microstructure to be imaged.

3. Sizing of Fatigue and SCC Cracks with Phase Based TFM Imaging of FMC Data

Accurate sizing of cracks (fatigue, SCC, etc.) is an area of major practical importance in NDT. Having precise knowledge of the length of a crack is crucial for making fracture mechanical calculations to estimate remaining life of a component. Unfortunately, sizing is often performed by dB drop type approaches which aim to relate the size of the flaw to the spread of the indication in a sectorial scan using a PAUT probe, or worse, the index offset difference required to bring a flaw to 50% of maximum using a conventional UT probe. Diffraction based sizing is known to be much more accurate, however, it is difficult to implement in practice as the relative amplitude of a diffracted signal is typically 20dB lower than the backwall or corner trap signal which makes resolving the tip from these much higher larger reflectors very challenging. Tip diffraction imaging is made easier when imaging FMC data via the TFM algorithm, however, the fact that the backwall and corner trap signals are so much higher in amplitude that the actual tip signal means that the tip can be easily missed or confused with imaging artifacts, surface multiples, etc. We have developed a variant of the standard TFM imaging algorithm which effectively images the uniformity of phase across the probe aperture instead of the coherent sum of all signals. This effectively enhances the strength of the tip signal (seen to have the same phase by all elements). In addition, the algorithm suppresses backwall echoes as magnitude information is removed from the signals prior to summation and therefore the detection deadzone near sample boundaries is greatly reduced. This technique is currently being extended to a TOFD configuration.

4. Case depth measurement using Phase Based TFM Imaging of FMC Data

Certain machine components require surface hardening to provide adequate resilience to wear and deformation during operation. The depth to which the surface is hardened, the so called “Case Depth”, needs to be controlled for optimal performance. Using the phase based TFM algorithm that we’ve developed for HTHA detection and tip-diffraction sizing, it is possible to directly image the transition between the hardened surface and base materials, allowing the case depth profile to be directly measured from the image. Furthermore, since the phase TFM algorithm naturally suppresses specular reflection, the deadzone at the wedge interface is reduced to around 1 mm.

Completed Development Projects

Feeder welds need to be inspected as part of the production plan in order to optimize welding parameters. Traditionally, Radiographic Testing (RT) is performed, however, RT cannot reliably detect planar defects such as lack of fusion. Lack of fusion defects are always considered rejectable regardless of their size as they are likely to grow in-service. Consequently, without inspecting feeder welds with an NDT technique sensitive to planar flaws, a faulty weld procedure which systematically produces lack of fusion defects could be approved for component replacement.

PAUT, on the other hand, is highly sensitive to planar defects. Accordingly, PAUT is commonly used to complement RT for inspection of coupons during weld development. Feeder tubes are small diameter (2-3.5 inch) and thin walled (5 – 9 mm) which was found to produce unique challenges for development of a code compliant PAUT inspection technique. Principally, the tight curvature of the OD surface was found to produce passive aperture sidelobes so that the maximum response from defects was not aligned with the centerline of the probe. Using ultrasonic modeling (CIVA), it was possible to design a custom probe-wedge combination where these sidelobes were not generated in the piece. Additionally, the use of compound scans was employed in order to cover a large HAZ and weld region using a single group. Calibration blocks were designed based on code requirements and modified to facilitate calibration. A motorized scanning system was used to hold PAUT probes in two configurations for feeder-to-feeder (double sided) and feeder-to-nozzle (single-sided) configurations. The system was tested using a set of samples with known defects for Probability of Detection (PoD) study. The study showed 95% detection rate of planar defects with only a 4% false call rate. Inspection/analysis procedures as well as technician training packages were prepared to support use of the tool for in-factory weld qualification.

Sizing of SCC cracks is a challenging application for PAUT. Conventional dB drop sizing methods on the corner trap indication from the base of the crack can lead to very inaccurate sizing (up to 80% under sizing was observed in this application). Using crack tip diffraction typically gives more accurate sizing which was critical for this inspection. Tip diffraction sizing is a well established technique, however, it can be difficult to implement as diffracted signals are generally low amplitude and often hard to unambiguously identify in Ultrasonic scans. To address this issue, we developed both PAUT and FMC based inspection techniques with the aim of promoting strong tip diffracted signals. These techniques were tested on samples featuring SCC colonies in the weld (both axially and transversely oriented) cut from defective vessels. Inspection/analysis procedures are currently being prepared post development/evaluation phase for filed inspection support.

ERW and EFW welds are susceptible to various weld flaws. Some of these are common to any type of weld, e.g. Lack of Fusion and Cracking defects which can be compared against code based acceptance criteria. One type of crack which is specific to ERW/EFW welds, called “hook” or “J” cracks, pose a particular failure risk and need to be assessed differently from ordinary types of planar defects. It is therefore critical that these hook cracks can be distinguished from ordinary weld flaws and then accurately sized. We developed an FMC based inspection system to provide detailed images of ERW/EFW flaws. The technique was based on design of custom contoured wedges and selection of rendering paths to provide the most detailed images of the flaws of interest. The technique was evaluated on a sample with embedded hook cracks, stacked Lack of Fusion and over trim defects with known size, shape and orientation. The technique provided sufficiently detailed images of ERW/EFW weld flaws which allowed for improved characterization. Post development and evaluation phase, support was provided to Acuren SMEs for preparation of inspection and analysis procedures for in filed implementation of the developed technique.

SCC cracks are commonly found on the outer diameter of buried pipelines. For the purpose of fitness of service assessment, precise knowledge of the depth to which these cracks extend is essential. Conventional dB drop sizing estimates are known to be very imprecise for depth estimation (basically this measures the extent of the transducer’s beam size). A further complication arises from the fact that these cracks are tightly packed together in colonies from which only the depth of the deepest flaw is required. For this application, an FMC based inspection scheme was devised to image the diffraction from the tips of the cracks so that the deepest tip signal could be used for maximum flaw depth estimation. Though tip diffraction based sizing is the preferred ultrasonic sizing technique, the self-tandem (TT-T) reflection based imaging mode is collected simultaneously so that dB drop sizing method can be used in cases where tip signals could not be located in the defect image. The accuracy of the FMC based sizing techniques were evaluated on a variety of samples with real SCC cracks as well as calibration samples featuring notches machined to various depths. The FMC based techniques were compared against conventional UT, Phased Array, TOFD and Transverse Eddy Current Array technologies in terms of depth sizing accuracy.

In response to a customer request Acuren was tasked with inspecting the fillet welds on T-joints for Lack of Fusion (LOF) defects systematically produced by a faulty weld procedure. Inspection of fillet welds in for LOF defects is challenging due to limited probe access. During the first phase of this project we developed an FMC based inspection system using custom wedges to direct the sound into the fusion zone from opposite side of the weld. Initial TFM images were analyzed to correlate features in the image to geometrical features in the weld. Fillet weld samples with simulated LOF targets were used to identify pertinent features in the TFM images. TFM images were further enhanced by implementing image processing algorithms. A custom scanning system was developed in order to collect FMC data in the field, while the analysis of the scans was performed via custom TFM image analysis software which automatically detected and sized dis-bonding on the fusion face. The technique was then evaluated on samples with real lack of fusion defects which were subsequently destructively tested. Comparison of the true dis-bond line and the estimated one proved that the technique was capable of classifying samples with major and minor dis-bond regions. Following the development and evaluation phase, the system was successfully deployed in the field.

Currently there is no universally accepted technique for fillet weld inspection. Inspection of these welds is highly dependent on probe access and weld geometry and as a result, the inspection results can be highly variable from piece to piece. In order to address this issue, we have developed a technique which uses wedges made of flexible polymers to scan directly through the weld cap, focusing along the nominal fusion face (for fusion defects) or the center of the weld volume and the center of the weld volume (for volumetric defects). Acceptable coupling is achieved using a thin ethanol film which when pressed between the weld cap and the flexible wedge material. The following image shows the detection of incomplete weld penetration and crack like defects found in a FlawTech T-weld sample. The inspection technique can be easily deployed using any standard phased array unit with wedges purpose built for each weld geometry.

We developed a system for inspection of the first 10 mm of a forged component for detection of small de-laminations (~ 0.5 mm). Using a combination of high frequency, highly focused linear scans as well as relatively low frequency Rayleigh wave inspection, full coverage of the inspection range was demonstrated. Machined targets as small as 0.5 mm in a range of 1-10 mm from the component’s surface were repeatably detected using the proposed PAUT technique, while targets as small as 0.5 mm in the first 3 mm from the surface were reliably detected using Rayleigh wave inspection. A 1 mm target located 2 mm below the component’s surface, detected by both the PAUT and Rayleigh wave techniques is shown in the figure. A custom wedge was designed and manufactured to hold the phased array probe at the top and hold two conventional probes on either side for generation of the Rayleigh waves. Inspection set-up was prepared to collect data on three channels (one PAUT and 2 Rayleigh waves) simultaneously. A full procedure and training program was provided to the client and the technique is currently in use for quality assurance and extended life cycle testing programs.

Acuren’s Research and Application Development group, in partnership with Eclipse Scientific developed a phased array inspection system for use at elevated temperatures. The system includes wedges build from plastics resistant to high temperature degradation and equipped with a cooling jacket around the array. The effects of temperature on the ultrasonic beamset generated in the piece has been exhaustively studied and compensated for using a model of the ultrasonic beam skew pattern due to thermal gradient inside a wedge. The output of this model allows the focal laws for any standard beamset to be corrected for the effects of temperature via the BeamTool high temperature module. Performance of the phased array inspection system has been fully validated including the effects of focal law correction on defect proper positioning of defects detected at elevated temperatures. This system is widely used in industrial sites for inspection of engineering components at elevated temperatures.