Do stone size and impaction influence therapeutic approach to proximal ureteral stones?

Background/Aim. Primary therapeutic approach to lumbar ureteral stones is still contraversial. The aim of the study was to investigate the influence of stone impaction and size on the effectiveness of proximal ureteral stone lithotripsy. Methods. A total of 123 patients with proximal ureteral stones were investigated in this prospective study performed in a 10- month period. The patients were divided into the group I - 86 patients treated with extracorporeal shock wave lithotripsy (ESWL) and the group II - 37 patients treated with 'Swiss' Lithoclast. In the group I, 49 stones (57%) were classified as impacted, while 20 stones (23.3%) were larger than 100 mm2. In the group II, 26 stones (70.3%) were impacted, and 11 stones (29.7%) were larger than 100 mm2. Stones were defined as impacted by the radiographic, echosonographic as well as endoscopic findings in the group II of patients. Stone size was presented in mm2. Chemical composition of stones were almost the same in both groups of the patients. Results. Generally, there was no statistically significant difference in the treatment success between the groups. However, stones larger than 100 mm2 were statistically more successfully treated endoscopically, while there was no statistical difference in the treatment success of impacted stones between these two groups. Conclusion. ESWL can by considered as primary first therapeutic approach in treatment of all proximal ureteral stones except for stones larger than 100 mm2 that should primarily be treated endoscopically

Analysis of the estimated remaining service life of gas rectification columns

Gas rectification columns are process apparatuses which are very important part of each onshore plant. Sudden failure of these types of columns causes huge daily losses, while fluid leakage can be very dangerous for the people and hazardous for the environment. For that reason, a regular and correct examination of the column is of great importance for the continual process of leading. Together with the detailed examination of the column, a risk-based inspection was applied to maximize savings, both material, time, and costs. The expected remaining service life of rectification columns was also analyzed, while the corrosion rates were calculated according to the various international standards. The minimum required column wall thickness was calculated according to the most commonly used international standard and the obtained difference was analyzed. Detailed analysis of the total risks of the column due to potential failure is presented

Digital image correlation method in experimental analysis of fracture mechanics parameters

U okviru rada su predstavljeni principi i primeri savremenih eksperimentalnih metoda za određivanje parametara mehanike loma. Metodologija analize i određivanja parametara mehanike loma obuhvatila je analizu ponašanja metalnih materijala u odnosu na lom primenom modifikovanih epruveta mehanike loma, sa inicijalnom prslinom i zateznim opterećenjem, i imala je za cilj pre svega određivanje karaktera tih procesa u slučaju problema tankih pločica, uz korišćenje osnovnih postulata mehanike loma. Metodologija uključuje primenu eksperimentalnih postupaka mehanike loma definisanih standardima, uz primenu metode za trodimenzionalno stereoskopsko merenje mehaničkog ponašanja materijala. Pomoću sistema za korelaciju digitalnih slika (Digital Image Correlation, DIC) za ispitivanje deformacija i pomeranja u materijalu ispitani su parametri mehanike loma metalnih materijala, pre svega epruveta od 316L nerđajućeg čelika i titan legure Ti-6Al-4V. 3D optički sistem GOM i softver Aramis su korišćeni za izvođenje eksperimentalne analize na pripremljenim epruvetama. Pošto se ovaj sistem koristi za merenje deformacija i parametra pomeranja otvaranja vrha prsline CTOD na modifikovanim kompaktnim epruvetama za zatezanje C(T) i epruvetama sa zarezom, dat je i kratak pregled mernih procedura i procesiranja rezultata, kao i moguće primene ovog sistema. Prikazani rezultati daju pregled polja deformacija i pomeranja tokom otvaranja vrha prsline, rasta prsline i u trenutku loma epruvete, što nije moguće putem tradicionalnih metoda merenja. Analizom rezultata pokazano je da je sa velikom preciznošću moguće izmeriti pomeranja tokom otvaranja vrha prsline i dobiti CTOD parametar. Rezultati pokazuju da odabrana metoda pruža dobre rezultate u analizi mehaničkog ponašanja i određivanju parametara mehanike loma metalnih materijala.The principles and examples of state-of-the-art experimental methods for measuring the fracture mechanics parameters are presented in this paper. The methodology of experimental analysis of the fracture mechanics parameters includes investigation of fracture behaviour of metallic materials using modified specimens with initial crack under tensile load, with the primary goal of determining the characteristics of fracture processes for the case of thin plates, using basic fracture mechanics postulates. The methodology also includes the application of experimental fracture mechanics procedures as defined by standards, using three-dimensional stereo-metric mechanical behaviour measurement methods. Fracture behaviour of metallic materials, mainly 316L stainless steel and titanium alloy Ti-6Al-4V specimens, is analyzed by using a digital image correlation (DIC) system for measuring strain and displacement in the material. GOM three-dimensional optical system and Aramis software are used to perform experimental analysis of selected specimens. As this system is used to measure strain and crack tip opening displacement (CTOD) parameter on the modified compact tension specimen C(T) and notch specimens, a basic review of measuring procedures and result processing is given, alongside other possible applications for this system. The presented results show strain and displacement fields during crack tip opening, crack growth, and the moment of fracture of specimens, which are not possible using traditional measurement methods. The analysis of results shows that it is possible to measure displacements during crack tip opening with a great precision, and thus obtain the CTOD parameter. The results show that the selected measuring method obtains good results in the analysis of mechanical behaviour and fracture mechanics parameters of metallic materials

Surface modification of laser welded nimonic 263 sheets

Laser surface treatment is both a thermomechanical and mechanical process, based on the ability of a high energy laser pulse to generate shock waves and plastic deformation in metallic materials. Laser welding is a high energy density process with many advantages such as narrow heat affected zone, lower heat input and lower heat/energy distortion compared to conventional welding processes. In this paper, Nimonic 263 alloy sheets are laser welded by Nd:YAG laser using different laser processing parameters. The microstructure, surface roughness and mechanical properties are investigated. Welded joints are mechanically treated by laser in order to improve the surface and mechanical characteristics. Mechanical characteristics are determined by tensile test, and fractures and laser treated weld surfaces are observed by scanning and optical microscopy. Surface topography is analysed by optical profilometry and micro hardness is measured by Vickers method

Digital image correlation method in experimental analysis of fracture mechanics parameters

U okviru rada su predstavljeni principi i primeri savremenih eksperimentalnih metoda za određivanje parametara mehanike loma. Metodologija analize i određivanja parametara mehanike loma obuhvatila je analizu ponašanja metalnih materijala u odnosu na lom primenom modifikovanih epruveta mehanike loma, sa inicijalnom prslinom i zateznim opterećenjem, i imala je za cilj pre svega određivanje karaktera tih procesa u slučaju problema tankih pločica, uz korišćenje osnovnih postulata mehanike loma. Metodologija uključuje primenu eksperimentalnih postupaka mehanike loma definisanih standardima, uz primenu metode za trodimenzionalno stereoskopsko merenje mehaničkog ponašanja materijala. Pomoću sistema za korelaciju digitalnih slika (Digital Image Correlation, DIC) za ispitivanje deformacija i pomeranja u materijalu ispitani su parametri mehanike loma metalnih materijala, pre svega epruveta od 316L nerđajućeg čelika i titan legure Ti-6Al-4V. 3D optički sistem GOM i softver Aramis su korišćeni za izvođenje eksperimentalne analize na pripremljenim epruvetama. Pošto se ovaj sistem koristi za merenje deformacija i parametra pomeranja otvaranja vrha prsline CTOD na modifikovanim kompaktnim epruvetama za zatezanje C(T) i epruvetama sa zarezom, dat je i kratak pregled mernih procedura i procesiranja rezultata, kao i moguće primene ovog sistema. Prikazani rezultati daju pregled polja deformacija i pomeranja tokom otvaranja vrha prsline, rasta prsline i u trenutku loma epruvete, što nije moguće putem tradicionalnih metoda merenja. Analizom rezultata pokazano je da je sa velikom preciznošću moguće izmeriti pomeranja tokom otvaranja vrha prsline i dobiti CTOD parametar. Rezultati pokazuju da odabrana metoda pruža dobre rezultate u analizi mehaničkog ponašanja i određivanju parametara mehanike loma metalnih materijala.The principles and examples of state-of-the-art experimental methods for measuring the fracture mechanics parameters are presented in this paper. The methodology of experimental analysis of the fracture mechanics parameters includes investigation of fracture behaviour of metallic materials using modified specimens with initial crack under tensile load, with the primary goal of determining the characteristics of fracture processes for the case of thin plates, using basic fracture mechanics postulates. The methodology also includes the application of experimental fracture mechanics procedures as defined by standards, using three-dimensional stereo-metric mechanical behaviour measurement methods. Fracture behaviour of metallic materials, mainly 316L stainless steel and titanium alloy Ti-6Al-4V specimens, is analyzed by using a digital image correlation (DIC) system for measuring strain and displacement in the material. GOM three-dimensional optical system and Aramis software are used to perform experimental analysis of selected specimens. As this system is used to measure strain and crack tip opening displacement (CTOD) parameter on the modified compact tension specimen C(T) and notch specimens, a basic review of measuring procedures and result processing is given, alongside other possible applications for this system. The presented results show strain and displacement fields during crack tip opening, crack growth, and the moment of fracture of specimens, which are not possible using traditional measurement methods. The analysis of results shows that it is possible to measure displacements during crack tip opening with a great precision, and thus obtain the CTOD parameter. The results show that the selected measuring method obtains good results in the analysis of mechanical behaviour and fracture mechanics parameters of metallic materials

Welding safety by using a new model of welders' recertification in the oil and gas industry

The paper presents a solution applied for determining the quality of the welding process in oil and gas industrial plants, as well as reliable verification of professional qualification of welding personnel. By applying the solution, welded joint quality can increase and thus the safety (especially in the field of high-pressure gas plants) and the reliability of the process in oil and gas-, petrochemical and nuclear plants, as a whole. The paper analyses safety aspects in the welding process, depending on the competence in welding and an appropriate qualification, taking into account that high levels of skill and competence are required where safety-critical items are fabricated. The results in the application of the new recertification model are presented and analysed, and it is emphasized that the areas of application of the new solution are wide, mainly applied in the oil and gas-, petrochemical industry, and the construction of nuclear plants. The application of the new model of Welders Recertification enables project savings, but also safety at work since the employer has a constant insight into the qualifications and welding capabilities of each welder

Integrity assessment of tanks with microcracks in welded joints

Tokom eksploatacije rezervoara za skladištenje tečnog ugljendioksida ukazala se potreba za ugradnjom dva nova priključka u jedno od danaca. Rezervoar je izrađen od mikrolegiranog čelika, a priključci od visokolegiranog austenitnog čelika. Za izradu novih priključaka izabrani su isti dodatni materijali i ista tehnologija zavarivanja, koji su korišćeni i pri izradi rezervoara. Ispitivanjima metodama bez razaranja zavarenih spojeva novih priključaka otkrivene su mikroprsline u zoni uticaja toplote mikrolegiranog čelika. Primenom postupka prikazanom u standardu BSI PD 6493 'Uputstvo za ocenu prihvatljivosti grešaka u zavarenim konstrukcijama', ocenjen je uticaj ovih mikroprslina na integritet zavarenih spojeva novih priključaka i time i na integritet rezervoara.During the exploitation of tanks used for storing liquid carbon dioxide there was a need to install two new connectors on one of the lids. The tank is made of micro-alloyed steel and its connectors are made of high-alloyed austenite steel. The same welding technology and added materials are used for both the tank and connectors. Non-destructive testing methods of welded joints in new connectors revealed microcracks in the heat-affected zone of micro-alloyed steel. By applying the procedure given in standard BSI PD 6493 'Manual for assessment of acceptability of flaws in welded structures', it is possible to estimate the effect of these microcracks on the integrity of welded joints in new connectors, and therefore their effect on the integrity of the tank

Welding safety by using a new model of welders' recertification in the oil and gas industry

The paper presents a solution applied for determining the quality of the welding process in oil and gas industrial plants, as well as reliable verification of professional qualification of welding personnel. By applying the solution, welded joint quality can increase and thus the safety (especially in the field of high-pressure gas plants) and the reliability of the process in oil and gas-, petrochemical and nuclear plants, as a whole. The paper analyses safety aspects in the welding process, depending on the competence in welding and an appropriate qualification, taking into account that high levels of skill and competence are required where safety-critical items are fabricated. The results in the application of the new recertification model are presented and analysed, and it is emphasized that the areas of application of the new solution are wide, mainly applied in the oil and gas-, petrochemical industry, and the construction of nuclear plants. The application of the new model of Welders Recertification enables project savings, but also safety at work since the employer has a constant insight into the qualifications and welding capabilities of each welder

Analysis of the estimated remaining service life of gas rectification columns

Gas rectification columns are process apparatuses which are very important part of each onshore plant. Sudden failure of these types of columns causes huge daily losses, while fluid leakage can be very dangerous for the people and hazardous for the environment. For that reason, a regular and correct examination of the column is of great importance for the continual process of leading. Together with the detailed examination of the column, a risk-based inspection was applied to maximize savings, both material, time, and costs. The expected remaining service life of rectification columns was also analyzed, while the corrosion rates were calculated according to the various international standards. The minimum required column wall thickness was calculated according to the most commonly used international standard and the obtained difference was analyzed. Detailed analysis of the total risks of the column due to potential failure is presented

Analysis of geometrical characteristics of pulsed nd:yag laser drilled holes in superalloy nimonic 263 sheets

Owing to their excellent mechanical and physical characteristics, superalloys are the most suitable material for use in hot sections of aircraft engines. Thousands of holes need to be drilled in constructive parts of machines, with laser technique emerging as the most effective. Laser drilling has been used to produce small diameter, accurately positioned holes, with little damage in regions around them, and in various materials. Effective laser employment of drilling of high quality holes for critical applications highly depends on correct selection and optimization of laser drilling parameters. In this work, the holes were drilled by a pulsed Nd(3+):YAG laser, with maximum average power of 160 W, in superalloy Nimonic 263 sheets, thickness 0,7 mm and 1,2 mm. The holes were observed by optical and scanning electron microscope. Geometrical characteristics of laser drilled holes that depend on laser parameters were investigated and analysed. The aim of this investigation was to find optimal laser parameters which would produce as much as possible regular holes