Towards real-time ultrasound driven inspection and control of GTA welding processes for high-value manufacturing

Many industrial sectors, such as nuclear and defence, employ high-integrity welding processes for the manufacture of safety-critical, high-value components. Non-Destructive Evaluation (NDE) techniques are used to ensure the strength and safety of these components both before they reach service and throughout their service-life. Often these welded components are composed of thick-sections which necessitate the use of a multiple-pass weld deposition strategy. As a result of the traditional inspection approach occurring only after the deposition of all weld runs, defects which have been introduced in early weld runs remain undetected and buried until the final inspection. This greatly complicates the re-work procedure, increases material wastage and the associated costs as well as delaying early correction of improper process parameters. With the nuclear sector being called upon to play a significant role in the delivery of low-carbon energy production there has been an increasing drive to reduce manufacturing costs. The development and deployment of innovative in-process inspection and control strategies is one method being explored to help achieve this. Through in-process inspection and monitoring of the welding process, it is possible to detect the formation of defects at the earliest possible point to enable quicker, more efficient, and more cost-effective correction and repair. As the most critical weld run within any multi-pass weld is the root pass, it is vital that this be monitored precisely to ensure integrity of the welded joint. Here, the feasibility of using single element and phased array ultrasonic approaches to interrogate and analyse the molten weld pool during robotic deposition of a Gas Tungsten Arc Welding (GTAW) root pass of a common multi-pass weld joint (90 degree included bevel angle, 1.5 mm root face height and 3.2mm root gap) is explored. Through processing and analysis of the received shear and longitudinal ultrasonic waves, this technique is shown to be capable of screening root pass width and height and joint fusion, critically indicating lack-of root fusion. This capability directly informs in-process inspection and monitoring and enables the potential for closed-loop control with the opportunity to correct for any defects as they are formed. The concept of utilising a similar strategy for upper passes within multi-pass welds is introduced. Along with the wildly varying wave propagation path and associated impedance variations, the challenges encountered during discrimination of the solid lower and upper molten passes are presented along with suitable signal processing techniques to counteract for these

In-process calibration of a non-destructive testing system used for in-process inspection of multi-pass welding

In multi-pass welding, there is increasing motivation to move towards in-process defect detection to enable real-time repair; thus avoiding deposition of more layers over a defective weld pass. All defect detection techniques require a consistent and repeatable approach to calibration to ensure that measured defect sizing is accurate. Conventional approaches to calibration employ fixed test blocks with known defect sizes, however, this methodology can lead to incorrect sizing when considering complex geometries, materials with challenging microstructure, and the significant thermal gradients present in materials during the inter-pass inspection period. To circumvent these challenges, the authors present a novel approach to calibration and introduce the concept of in-process calibration applied to ultrasonic Non-Destructive Testing (NDT). The new concept is centred around the manufacturing of a second duplication sample, containing intentionally-embedded tungsten inclusions, with identical process parameters as the main sample. Both samples are then inspected using a high-temperature robotic NDT process to allow direct comparative measurements to be established between the real part and the calibration sample. It is demonstrated that in-process weld defect detection using the in-process calibration technique can more reliably identify defects in samples which would otherwise pass the acceptance test using a traditional calibration

In-process phased array ultrasonic weld pool monitoring

In recent years, there have been increasing economic and industrial drivers for the development of real-time non-destructive evaluation directly at the point of manufacture. Real-time inspection and monitoring of welding processes can help to reduce fabrication costs by detecting defects as they occur, enabling more efficient and cost-effective builds. This paper shows, for the first time, the use of phased array ultrasonics to monitor and analyse the molten weld pool during deposition of multi-pass gas tungsten arc welds. The received ultrasonic signals are shown to contain information related to key physical transitions occurring within the welding process, namely the melting and solidification of the weldment. Furthermore, the technique used here is shown to be effective for determining weld quality in real-time with significant signal changes occurring when defects such as Lack of Root Penetration are present. The accurate focusing and steering capabilities offered by phased arrays are used to successfully isolate the molten weld pool from the surrounding solidified weldment during deposition of multiple layers of a multi-pass weld

Investigating the effect of residual stress on hydrogen cracking in multi-pass robotic welding through process compatible non-destructive testing

In this paper, the effect of Welding Residual Stress (WRS) on the size and morphology of hydrogen-induced cracks (HIC) is studied. Four samples were manufactured using a 6-axis welding robot and in two separate batches. The difference between the two batches was the clamping system used, which resulted in different amounts of welding deformation and WRS. The hydrogen cracks were intentionally manufactured in the samples using a localised water-quenching method, where water was sprayed over a specific weld pass in a predetermined position. The Phased-Array Ultrasonic Testing (PAUT) system was implemented during the welding process (high-temperature in-process method), to detect the HIC in real-time. The WRS in both batches was measured using the hole-drilling method, where a difference in transversal residual stress of 78 MPa was found between the two samples. Based upon both the PAUT results and microscopic investigations, the batch with higher WRS resulted in larger size and number of HIC. For the first time, the negative effect of WRS on HIC has been monitored in real-time using high-temperature in-process inspection. This was achieved using an innovative approach, introduced in this paper, to repeatably manufacture high and low WRS samples in order to control the size and location of subsequent HIC

Thermal compensation of ultrasonic transmit and receive data for steel welded plates at the point of manufacture

On modern manufacturing production lines, Non-Destructive Testing (NDT) is frequently a bottleneck which could greatly be alleviated by integrating the inspection of components as they are manufactured. By moving inspection to the point of manufacture, greater economic and productivity benefits are realised in terms of reduced rework and schedule slippage, however, new technical challenges emerge. For welded components, high temperatures and the resulting thermal gradients, present challenges when performing ultrasonic inspection at the point of manufacture. The thermal gradients introduce positional misalignment due to “beam bending” effects arising from refraction as the material properties change with temperature. This paper presents for the first time, through simulation and practical experiments, a novel thermal compensation strategy to mitigate for thermal effects when performing ultrasonic inspection of welded components at the point of manufacture. To understand the thermal gradients experienced during standard Tungsten Inert Gas (TIG) welding, 3-dimensional thermal simulations were developed and experimentally-validated with an average error of 1.80%. The output from the thermal simulations in combination with material properties that vary over temperature, allowed for generalised time of flight maps to be created via the Multi-Stencils Fast Marching Method (MSFMM) and the ultrasonic data to be imaged by the Total Focusing Method (TFM). The thermal compensation strategy was initially proved on synthetically generated finite element Full Matrix Capture (FMC) datasets, and it was shown that reflector positional accuracy could be increased by ∼ 3 mm. Experimental results also showed marked improvements with reflector positional accuracy also being increased by ∼3 mm. Over both simulated and experimental datasets, the SNR was shown to be negligibly altered between uncompensated and compensated images. The results show how high-quality ultrasonic images can be generated in-process and help bring inspection closer to the point of manufacture

Development of a phased array ultrasonic system for residual stress measurement in welding and additive manufacturing

Residual Stress (RS) in engineering components can lead to unexpected and dangerous structural failures, and thus represent a significant challenge to quality assurance in both welding and metal additive manufacturing (AM) processes. The RS measurement using the ultrasonic method is based on the acoustoelasticity law, which states that the Time-of-Flight (ToF) of an ultrasonic wave is affected by the stress field. Longitudinal Critically Refracted (LCR) waves have the highest sensitivity to the stress in comparison with the other type of ultrasonic waves. However, they are also sensitive to the material texture which negatively affects the accuracy of the RS measurement. In this paper, a Phased Array Ultrasonic Testing (PAUT) system, rather than the single element transducers which are traditionally used in the LCR stress measurement technique, is innovatively used to enhance the accuracy of RS measurement. An experimental setup is developed that uses the PAUT to measure the ToFs in the weld, where the maximum amount of tensile RS is expected, and in the parent material, stress-free part. The ToF variations are then interpreted and analyzed to qualify the RS in the weld. The same measurement process is repeated for the Wire Arc Additive Manufacture (WAAM) components. Based on the results, some variations between different acoustic paths are measured which prove that the effect of the residual stress on the ultrasonic wave is detectable using the PAUT system

Model-assisted ultrasonic calibration using intentionally embedded defects for in-process weld inspection

Automated in-process Non-Destructive Testing (NDT) systems are rapidly gaining traction within the manufacturing industry as they reduce manufacturing time and costs. When considering calibration and verification of such systems, creating defects of known geometry and nature during the deposition of a weld can: (I) help examine the capability of the automated system to detect and characterise defects, (II) be used to form a database of signals associated with different defect types to train intelligent defect classification algorithms, and (III) act as a basis for in-process gain calibration during weld inspection at high temperatures, where the ultrasound beam can be skewed as a result of velocity gradients. In view of this, this paper investigates two unique methodologies for introducing: (a) lack of fusion weld defects by embedding tungsten in the weld and (b) creating artificial weld cracks by quenching to imitate the real cracking scenarios. According to the results of Phased Array Ultrasound Testing (PAUT) inspections, the methodologies used for embedding the artificial defects were successful. The validity of inspections was also verified by extracting micrographs from the defective sections of the welds, and model-based simulations were carried out to gain a better understanding of the wave propagation path and interaction with the generated defects

word~river literary review (2011)

wordriver is a literary journal dedicated to the poetry, short fiction and creative nonfiction of adjuncts and part-time instructors teaching in our universities, colleges, and community colleges. Our premier issue was published in Spring 2009. We are always looking for work that demonstrates the creativity and craft of adjunct/part-time instructors in English and other disciplines. We reserve first publication rights and onetime anthology publication rights for all work published. We define adjunct instructors as anyone teaching part-time or full-time under a semester or yearly contract, nationwide and in any discipline. Graduate students teaching under part-time contracts during the summer or who have used up their teaching assistant time and are teaching with adjunct contracts for the remainder of their graduate program also are eligible.https://digitalscholarship.unlv.edu/word_river/1001/thumbnail.jp

Shattered pellet injection experiments at JET in support of the ITER disruption mitigation system design

A series of experiments have been executed at JET to assess the efficacy of the newly installed shattered pellet injection (SPI) system in mitigating the effects of disruptions. Issues, important for the ITER disruption mitigation system, such as thermal load mitigation, avoidance of runaway electron (RE) formation, radiation asymmetries during thermal quench mitigation, electromagnetic load control and RE energy dissipation have been addressed over a large parameter range. The efficiency of the mitigation has been examined for the various SPI injection strategies. The paper summarises the results from these JET SPI experiments and discusses their implications for the ITER disruption mitigation scheme