Development and Experimentation of Magnetostrictive Sensors for Inspection and Monitoring of Piping Systems

Nondestructive Evaluation – NDE, is an important aspect of the integrity management of industrial plants, where pipe systems are the dominant component. During the last decade Ultrasonic Guided Waves (UGW), have started to be used as a useful instrument for on-stream long range inspection of pipes. Various procedures and systems have been proposed for the generation and detection of UGW. Presently, they are based on piezoelectric (PZT) or magnetostrictive (MT) transducers or electromagnetic acoustic transducers (EMAT). It is generally known that PZT based systems have elevated diagnostic capacities due to their high transduction efficiency. However, the elevated costs of installation of such devices make their use for long-term monitoring of piping systems quite improbable. On the other hand, the MT based systems have the advantage of the reduced costs of the composing materials, simplicity of attaching it to the pipe wall and flexibility regarding the diameters of the pipes that can be inspected. Still, its single-element configuration limits the capacity to characterize the detected discontinuities in terms of geometry, thus being unable to distinguish between possible flaws from symmetrical features, normally located on pipes, like welds or flanges. Furthermore, its reduced capability to geometrically characterize flaws makes the classification of their severity particularly difficult. The improvement of the diagnostic capacity of MT based systems in order to make practically possible and economically convenient its use in monitoring applications is the main purpose of this thesis. In this dissertation multiple laboratory and field experiments are described and the magnetostrictive technology is evaluated. Furthermore, a new magnetostrictive transducer for UGW acquisition is presented. It allows step-by-step data acquisition around the pipe circumference revealing important information on the geometry and circumferential position of flaws. The new sensor was validated by computer simulations as well as further laboratory and field tests. The resulting data was used as input for various digital signal processing techniques to describe geometrically the features detected in the acquired signal. The final results outline the potential of MT based long-range inspection to reach also a good sensitivity and a good defect sizing and classification with respect to conventional techniques, making it an important candidate for monitoring activities for the integrity management of industrial plants

Corrosion behavior of carbon steel in presence of sulfate-reducing bacteria in seawater environment

The influence of sulfate-reducing bacteria (SRB)on the corrosion behavior of carbon steel was studiedin a laboratory test-loop, continuously fed with nutrient supplemented North Sea seawater. The mainparts of the test-loop, represented by two separated flow cells, were fitted with steel specimens. The test-loop was operating anoxically for 2200 h and each flow cell was three times inoculated with Desulfovibrioalaskensis or Desulfovibrio desulfuricans species. Additionally, each flow cell was two times perturbed with antimicrobial treatments. Steel specimens exposed in flow cells exhibited comparable appearance andsystems responding similarly to inoculations and antimicrobial treatments. The effect of the inoculations in both flow cells on the steel coupons electrochemical behavior was materialized as lower resistanceto corrosion and higher surface activity or occurrence of localized pitting events. The localized surfaceattacks recognized in both flow cells after inoculations continued to progress with the time, althoughbacterial activity was temporarily suppressed by antimicrobial treatment. Post-exposure sample evalu-ations might suggest that, some particular steel surface areas have been subjected to a dramatic change in the corrosion mechanism from initial localized attack to general corrosion. The long-term exposureof the carbon steel specimens resulted in identifiable formation of biofilms and corrosion products. Cor-rosion deposits were characterized by a specific structure built of iron sulfides (FeS), sulfated green rust(GR(SO42−)), magnetite (Fe3O4), Fe(III) oxyhydroxides (FeOOH), chukanovite (Fe2(OH)2CO3), carbonatedgreen rust (GR(CO32−)) and some calcareous deposits. Presented factual evidence reinforced the idea thatsulfidogenic species in natural seawater environment may cause localized damage with a specific surfacepattern; however, this does not necessarily lead towards significantly elevated corrosion rates

Electrochemical and fractographic analysis of Microbiologically Assisted Stress Corrosion Cracking of carbon steel

This study was carried out to evaluate the effect of microorganisms on the corrosion behavior of carbon steel when exposed to mechanical axial stress. Open Circuit Potential (OCP) and Electrochemical Frequency Modulation (EFM) response were measured on the tensile specimens while applying a constant load in various environments inoculated with different sulfidogenic or iron reducing microorganisms. The fractographic analysis revealed a noticeable impact of the enriched environments on the topography of tensile specimens; however, after the tests were carried out, it was not possible to detect any indications of a Stress Corrosion Cracking (SCC) failure mechanism for the tensile specimens

Corrosion of carbon steel by bacteria from North Sea offshore seawater injection systems: Laboratory investigation

Influence of sulfidogenic bacteria, from a North Sea seawater injection system, on the corrosion of S235JR carbon steel was studied in a flow bioreactor; operating anaerobically for 100 days with either inoculated or filtrated seawater. Deposits formed on steel placed in reactors contained magnesium and calcium minerals plus iron sulfide. The dominant biofilm-forming organism was an anaerobic bacterium, genus Caminicella, known to produce hydrogen sulfide and carbon dioxide. Open Circuit Potentials (OCP) of steel in the reactors was, for nearly the entire test duration, in the range − 800 45), suggested pitting on steel samples within the inoculated environment. However, the actual degree of corrosion could neither be directly correlated with the electrochemical data and nor with the steel corrosion in the filtrated seawater environment. Further laboratory tests are thought to clarify the noticed apparent discrepancies

Micropatterning and microelectrochemical characterisation of biological recognition elements

Eine piezoelektrische Mikrodosierpumpe wurde über das Versprühen von pl-Tröpfchen für die Mikrostrukturierung von Gold- und Glasoberflächen mit biologischen Molekülen eingesetzt und dabei optimale Parameter für die Erzeugung von Enzym-, Laminin- und DNA-Mikrostrukturen ermittelt. Auf Lamininmikrostrukturen konnten Neurone zum gerichteten Wachstum veranlasst werden. Glucoseoxidase-Mikrostrukturen wurden mittels elektro-chemischer Rastermikroskopie (SECM) untersucht und die Enzymaktivität hochauflösend visualisiert. Für die Detektion von Hybridisierungsereignissen auf DNA-Chips wurde ein neuer SECM-Abbildungsmodus entwickelt, der die Abstoßung zwischen negativ geladenen Redoxmediator-Molekülen und Phosphatgruppen der DNA-Stränge ausnutzt. Für SECM-Messungen in kleinsten Elektrolytvolumina (<1\$\mu$l) wurde eine koaxiale Pt/Ag-Mikroelektrode realisiert, indem die Silberabscheidung nach Tollens zur Abscheidung eines Ag-Films auf der Glasisolierung von Pt-Scheibenmikroelektroden verwendet wurde.Microscopic arrays of biomolecules such as glucose oxidase (GOx), laminin and oligonucleotides were created using piezo-assisted microdispensing of picoliter volumes of solutions of these compounds for their deposition onto suitable substrates. The optimal parameters for the preparation of the different biological microstructures were evaluated. Micropatterns of laminin were further used to promote directed growth of neurons. GOx microarrays were visualised and characterised with scanning electrochemical microscopy (SECM) for high resolution imaging of the enzyme's activity. The repelling mode of SECM was introduced as a new approach for imaging spots of single and double stranded oligonucleotides, and for the efficient detection of DNA hybridisation on DNA chips. Moreover, a novel coaxial microelectrode was developed for advanced microelectrochemical measurements in ultrasmall electrolyte volumes and microenvironments

The impact of the surgical technique on stenosis after laparoscopic sleeve gastrectomy: a single center study on 5235 patients

Background: Laparoscopic Sleeve Gastrectomy (LSG) has gained worldwide popularity in the last 10 years as self alone bariatric procedure. Symptomatic Stenosis (SS) is a potential severe postoperative complication and it can be divided in organic stenosis (OS) and functional stenosis (FS). The aim of this paper is to propose a modified surgical technique to prevent FS. Methods: A retrospective review on 5235 LSG performed in Ponderas Academic Hospital between January 2011 and December 2019, searched FS in two consecutive patients groups, divided based on the modified surgical technique introduced in 2015, with fixation of the gastric tube to the pre-pancreatic fascia and stapler line's over-sewn running suture. Results: Group A (2011-2014) included 1332 LSG, 16 SS were registered (1.2%), 7 OS and 9 FS; 3903 LSG included in group B (2015-2019), counting for 37 SS (0.95%), 27 OS and 10 FS. A statistically significant difference between the 2 groups was observed for the FS incidence (p=0.03), while it was non-significant for the OS (p=0.52) and the total number of SS (p=0.43). The endoscopic approach was used in forty-eight SS (90.5%) with a successful rate of 83%, while specifically for the FS it was 100%; only one complication was registered during endoscopic treatment, that required further surgical solution. Conclusions: fixation of the gastric tube to the pre-pancreatic fascia and stapler line's over-sewn running suture during LSG, introduced lately, are beneficial in preventing the postoperative functional stenosis of the LSG, contributing to the improvement of the patient's quality of life