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Composite materials are created by combining different substances, each contributing specific properties that enhance the material's overall performance. Given the diversity of composite types, a range of Non-Destructive Testing (NDT) techniques has been developed for their inspection, each offering unique benefits. Among these, Computed Microtomography (micro-CT) emerges as a particularly powerful method for volumetric analysis, providing highly detailed three-dimensional (3D) imaging of internal structures. This study aims to develop a methodology for analyzing the joints of polymer composite tubes. To achieve this, the volumes of the matrix, reinforcement, and any defects within the selected samples were meticulously evaluated. The findings reveal that the micro-CT technique, when integrated with advanced image processing tools, is highly effective for detecting, locating, and quantifying defects.

This paper reports on the results of the second part of a round-robin programme designed to assess the accuracy of TFM (Total Focussing Method) sizing as it relates to probability of detection truth values. Part 1 of the programme involved analysis of flaw responses simulated using the FMC (Full Matrix Capture) method of acquisition in CIVA simulation software. The report [1] noted that the mean standard deviation of height-sizing error for all participants 0.56mm and the mean standard deviation of error for ligament sizing was 0.88mm. CIVA simulation software is well known for its ability to reproduce ultrasonic results; however, software simulation cannot fully represent the human factors of uncertainty. To address the human factors, a second part to the programme was organised whereby welds with seeded flaws were provided to volunteers from several labs. Their task was to scan the welds using an acquisition format compatible with a TFM algorithm and analyse the data using the TFM algorithm of their choice. Height, length and smallest ligament was to be reported. This report summarises the statistical findings of Part 2 of the programme.

The petrochemical industry heavily relies on steam reforming furnaces for large-scale hydrogen production. Centrifugally cast HP stainless-steel tubes constitute the majority of components in these furnaces, enduring temperatures ranging from 600 to 1000 ºC for extended periods. These tubes manifest distinct aging states, characterized by specific microstructural markers linked to the exposed wall temperature. Given their significant cost and importance, monitoring the service life of these tubes is crucial. The current aging state is particularly relevant due to the correlation between creep damage and advanced aging stages. Hence, this study aims to assist in assessing the remaining life of HP stainless-steel tubes by employing a portable Eddy Current Testing (ECT) inspection system, coupled with real-time Support Vector Machine (SVM) classification of aging states. Two 12.6-meter-long tubes, aged for 160,000 hours, underwent inspection using the portable ECT inspection system to evaluate the progression of aging states along their height, considering the expected vertical temperature gradient. Results underscore the efficacy of the SVM classification in identifying the various aging states present along the studied tubes, highlighting promising in situ applications.

Commercial bulk hydrogen is mainly produced in petrochemical steam reforming furnaces inside centrifugally cast Nb-modified HP austenitic stainless steels tubes, which operate at temperatures above 900 °C. In-service aging causes well known microstructural modifications such as the transformation of primary niobium carbides, NbC, into the G-phase (Ni16Nb6Si7). Unexpected operational problems, such as reduced feedstock flow may, in a few minutes, cause severe overheating. These short-time temperature surges, can lead tubes to premature failure often through the formation of large longitudinal cracks. Little is known about the integrity of the tubes that undergo a temperature surge without cracking. Thus, understanding the microstructural changes brought upon by these events becomes extremely important when assessing the reuse of these tubes. In the present work, by means of optical microscopy, scanning electron microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy, two Nb and NbTi-modified HP steels tubes, which cracked due to high temperature surges, were analyzed. Results show that insitu dissolution of the G-phase in the thermally affected regions causes this phase to be replaced by fine NbC or (NbTi)C precipitates. These microstructural transformations suffered by the tubes during the short-time overheating and cooling cycles are thus presented and discussed in terms of their practical consequences.

Reliability of non-destructive (NDT) procedures is usually assessed using probability of detection (POD). However, the reliability of the POD is rarely questioned. A POD usually produces a curve that relates the size of a defect to the likelihood that it will be detected by the NDT procedure. PODs are often used in conjunction with fracture mechanics that can relate the severity of a flaw to the service life of a component (Fitness for Service or FFS). To this end, it is the flaw vertical extent relative to the component thickness that is important. Closely related to the concern for flaw height is how close the flaw is relative to the surface of the component. Proximity to a surface can increase the stresses raised by the flaw and make it more critical to the fitness for service. Use of full matrix capture (FMC) techniques in ultrasonic testing, in conjunction with the postprocessing use of Total Focussing Method (TFM), has shown good potential to provide accurate flaw sizing. This paper examines the results of a round-robin trial using CIVA simulated data that were configured to assess flaw height and ligament in simulated welds. Results suggest that FMC with TFM post-processing can provide sizing estimates as good or better than manufacture estimates and can be used as the actual measured values for POD assessments.

The use of composite materials has been an option increasingly used in various industry sectors. However, the degradation process by which these materials are subjected due to operational conditions is a reality that makes monitoring a challenge. In this work, conventional ultrasonic technique was used to analyse the behaviour of GFRP pipes under different aging conditions (temperature and pressure). The pipes were submitted to aging for 2, 6 and 18 months and acoustic measurements were performed in certain areas of each pipe in order to monitor the relevant locations, both in circumference and in length. The gathering of these signals was carried out periodically throughout the aging process. Through the methodology presented in this work regarding ultrasonic inspection, it was possible to correlate the acoustic properties obtained with the mechanical properties of the material during aging. Additionally, after the end of the aging process and occasional failures, some samples were extracted to perform tensile tests, which were able to indicate residual Young Modulus in the axial direction. Sound testing for mechanical characterization were also performed and their results were compared to the ones calculated by ultrasonic results. Microstructure of the material and its manufacturing process were also found to be important parameters that must be considered. The experimental database obtained were analysed using statistical tools to evaluate the feasibility of a trend model in the behaviour of material properties during aging.

In the petrochemical industry, steam reforming furnaces play a crucial role in large-scale hydrogen production. These furnaces are equipped with centrifugal cast HP-modified austenitic stainless-steel tubes, which are exposed to temperatures ranging from 600 to 1000ºC for extended periods. As a result, the wall temperature profile of these tubes exhibits a vertical gradient of distinct aging states, labelled as state I to VI in the literature, each characterized by specific microstructures. Given that the reformer tubes are expensive components of the furnace assembly, it is imperative to monitor their service life. Non-destructive testing is a vital tool for evaluating the structural integrity of industrial components. Hence, the objective of this study is to establish a real-time classification system for determining the aging states of HP-modified stainless-steel tubes using a non-destructive magnetic system and the machine learning technique Support Vector Machine (SVM). Two tubes, each measuring 12.6 meters in length, were removed from the same steam reforming furnace after 160,000 hours of service. The inspection was conducted using an eddy current hybrid probe adapted to an inspection vehicle, allowing for real-time data acquisition. The results demonstrated that the developed classification system was capable of accurately identifying the different aging states present along the studied tubes.

Pipelines for fuel transportation range in length from hundreds to thousands of kilometers, with part of their length underground. Due to the high cost of the fluids and products transported an increasing number of criminal activities are taking place all over the world. In addition to causing great economic and environmental losses the illegal activity brings risks to the surrounding population. For example, the accident in Tlahuelilpan, Mexico, due to illegal tapping, resulted in the tragedy of hundreds of deaths. In order to combat such activities, many efforts have been employed to early detect and locate illegal tapping in pipelines. The great challenge of such inspections is the unpredictable activity of the clandestine taps, requiring frequent inspections. Usual pipeline inspection tools, such as ultrasound or MFL (Magnetic Flux Leakage) PIG’s, are sensitive for detecting and positioning the anomalies, however, the high operating costs make the recurring application of such tools unfeasible. Focusing on these challenges, a low-cost inspection tool embedded with a minimalist eddy current instrumentation was developed. The results achieved show the capability to detect and differentiate the components existing in the pipeline and illegal taps of different diameters as well as, in a complementary way, the detection of corrosion on the internal surface of the pipelines.

The cavitation phenomenon in polymers, commonly known as whitening, has been quite studied in the last two decades due to its relevance to the plastic deformation process and the overall behavior of the material. Its occurrence has been proposed to be either on equatorial or at polar region of the spherulite during deformation. The detection techniques usually employed are small angle X-ray scattering (SAXS) or light scattering, and neither one is suitable for field inspection. The present study focused on nondestructive methodologies to detect the cavity phenomenon in two grades of poly(vinylidene fluoride), comparing simple visual inspection (VI), optical densitometry (OD) and ultrasound velocity (US). The results showed that the last two techniques were able to identify the existence of voids very earlier along the deformation path, about 2%–5% strain, where visual whitening was not even detected. The OD and US showed to be highly effective in distinguishing the effect of the processing conditions on the occurrence of cavitation, via simple and fast methods. The use of ultrasound technique for cavity detection becomes a very promising approach for the production inspection of the pressure sheath of raisers, polymer pipes and other products, as well as for evaluating the integrity of the component that may be affected by occurrence of cavities.

Glass Fiber Reinforced Polymers (GFRP) laminated joints combine properties such as high mechanical resistance, low specific weight and high corrosion resistance, features that allow their application in harsh environments. The structural integrity of these components must be ensured; therefore, their inspection through non-destructive methods capable of certifying such integrity is necessary. This work evaluates the phased array inspection of GFRP laminated joints, in order to detect defects frequently found in this material. For the development of the study, artificial flaws representing interply delamination were inserted in the material. The experiments were conducted with a 32 elements matrix probe (500 kHz frequency). Two focal laws were applied aiming the detection of the existing defects. Results indicated that the proposed methodology is adequate for the detection of the flaws, highlighting the performance of focal laws with focal spots in the back wall of the joint. Keywords: Phased array, Ultrasonics, GFRP, Non-destructive inspection, Composites

This work presents the characterization of the external oxide scale of a centrifugally cast HP steel tube, modified with Nb and Ti, after 90,000 h of operation in a steam reforming furnace, showing different aging states as a function of the column height and exposure temperature. The objective was to relate the oxide microstructural morphology to its magnetic response for three different microstructural aging states. The morphological and compositional characterization was performed by high resolution scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. The magnetic response of the external surface was analyzed by magnetic force microscopy and scanning magnetic susceptometer. The results showed the formation of a multilayer oxide scale with different compositions along its thickness. In addition, a microstructural modification was identified in the scale-matrix interface, due to the depletion of chromium. It was also observed that the magnetic response is dependable both on the oxide scale thickness and the chromium carbides depleted zone. Magnetic force microscopy was able to identify the origin of the magnetic response resulted from the steel tube surface. Keywords: Oxide scale, High temperature oxidation, Modified HP steel, Steam reforming tubes

Superduplex stainless steel is a widely used material in many industrial areas, due to its significant properties in terms of mechanical and corrosion resistance. In order to guarantee the quality of these steels, the ferrite evaluation is an important analysis since many properties depend on the control of the ferrite content. During equipment manufacturing or field inspections, the most conventional way to evaluate the ferrite content is through ferritoscope measurements, due to its portability and easy interpretation. However, it has been observed that the calibration pattern used for ferritoscope calibration can lead to inaccurate ferrite quantification in superduplex inspection. In order to analyze this influence, different characterization techniques were performed in superduplex samples, such as optical microscopy, X-ray diffraction, and vibrating sample magnetometer, to compare with the measurements obtained by a ferritoscope. It was concluded that for high ferrite values, with the calibration made from the calibration pattern provided by the ferritoscope manufacturers, the ferrite values measured showed significant deviations from the real values. The current work presents a solution for using the ferritoscope for a more accurate quantification of the ferrite content in superduplex stainless steels. Keywords: Superduplex stainless steel, Ferrite content meter, Calibration procedures, X-ray diffraction