Effect of operating temperature on the resistance of low carbon microalloyed steel for thermal power plants to crack initiation and growth

Svrha inženjerskog projektovanja je da konstrukcije budu izrađene tako da efikasno, sigurno i ekonomično ispunjavaju predviđene eksploatacione funkcije. Da bi se to postiglo, inženjer polazi od pretpostavljenih radnih opterećenja i eksploatacionih uslova, izračunava napone u nosećim elementima konstrukcije i upoređuje ih sa dozvoljenim naponima za odgovarajući oblik oštećenja koji može da se pojavi. Ukoliko su projektovana opterećenja manja ili jednaka opterećenjima u toku rada, vek konstrukcije će zavisiti od izbora materijala čiji kvalitet i osobine treba da odgovaraju nameni konstrukcije, tehnologiji proizvodnje i tehnologiji i izvođenju zavarivanja. Parovodi pripadaju visoko odgovornim konstrukcijama koje su tokom radnog veka izložene puzanju. Osnovno svojstvo čelika za parovode je otpornost na lom puzanjem u predviđenom radnom veku. Predmet istraživanja ove disertacije je bio da se prikupe podaci o uticaju radne temperature na mehaničke i strukturne osobine niskougljeničnog mikrolegiranog čelika za rad na povišenim temperaturama, koji će poslužiti za ocenu veka komponenata termoenergetskih postrojenja. Materijal je analiziran ispitivanjem uzoraka izrađenih od novog, nekorišćenog materijala na dve temperature, temperaturi okoline i radnoj temperaturi od 540 ℃, pri delovanju statičkog i dinamičkog opterećenja. Glavni cilj istraživanja je bio da se odredi otpornost analiziranog materijala prema nastanku prslina i lomu. Rezultati eksperimentalnih istraživanja su nam takođe pružili i sliku o ponašanju prsline na radnoj temperaturi. Pored eksperimentalne analize urađena je i numerička simulacija ponašanja epruveta pri statičkom i dinamičkom opterećenju. Numerički proračun je rađen metodom konačnih elemenata (MKE) u softverskom paketu ANSYS. Simulacije su bile zasnovane na eksperimentalno određenim vrednostima J-integrala kao i na vrednostima koeficijenata iz Parisove jednačine. Pokazano je dobro slaganje sa eksperimentalnim rezultatima, čime je verifikovana primena MKE za razmatrane slučajeve opterećenja. Dobijenim rezultatima ispitivanja dat je praktičan doprinos oceni uticaja radne temperature na ponašanje ispitivanog materijala u uslovima statičkog i dinamičkog opterećenja, a u cilju procene integriteta i preostalog veka konstrukcije. Takođe su date i smernice za produženje radnog veka procesne opreme izrađene od čelika za rad na povišenim temperaturama.Purpose of engineering design is to construct structures to efficiently, safely and economically fulfill the estimated purposes in exploitation. To achieve this, the engineer starts from the assumed loads and operating conditions, calculates the stressesin the load-carrying structure elements’ and compares them with the allowable stresses for type of damage that may occur. If the designed loads are less than or equal to the loads acting during operation, the structure’s life will depend on the materials’ selection whose quality and properties should correspond to the function of the structure, manufacturing technology and welding technology and performance. Steam pipes belong to highly responsible constructions that are exposed to creep during their service life. The basic property of steel for steam lines is creep resistance in the expected service life. The subject of research of this dissertation was to collect data on the effect of operating temperature on the mechanical and structural properties of low carbon microalloyed steel for elevated temperature service, which will be used to assess the life of components of thermal power plants. The material was analyzed by testing specimens made of virgin, unused material at two temperatures, ambient temperature and operating temperature of 540 ℃, under static and dynamic loading conditions. The main goal of the research was to determine the resistance of the analyzed material to crack initiation and its fracture resistance. The results of experimental research also helped us to understand the crack behavior at operating temperature. In addition to the experimental analysis, a numerical simulation of specimens’ behavior under static and dynamic loading was performed. The numerical calculation was done by the finite element method (FEM) in the ANSYS software package. The simulations were based on experimentally determined values of the J-integral as well as on the values of the Paris law coefficients. Good agreement with the experimental results was shown, which verified the application of FEM for the considered load cases. The obtained test results give a practical contribution to the assessment of the operating temperature effect on the behavior of the tested material exposed to static and dynamic loading, in order to assess the integrity and the remaining life of the construction. Guidelines for extending the service life of process equipment made of steel for elevated temperatures operation are also given

Experimental Determination of the Critical Value of the J-Integral that Refers to the HSLA Steel Welded Joint

Fracture mechanics, as a scientific discipline dealing with the study of cracks in welded structures, has defined parameters and introduced new test methods in order to better determine the tendency to crack growth, critical conditions for rapid fracture development, material resistance to rapid crack propagation and better definition of other parameters for assessing the behaviour of the material and the safety of the structure in the presence of cracks. In this paper, the focus is on determination of the parameter of elastic-plastic mechanics of J-integral, more precisely, on examination of the critical value of J-integral (JIc) of the welded joint of HSLA steel. The position of the tip of the fatigue crack and the properties of the region where fracture propagation occurs are main indicators of influence of the heterogeneity of the NN-70 welded structure and mechanical properties. Resistance to cracking in the welded joint shows that the heterogeneity has a major impact on the resistance to crack initiation and propagation, in elastic as well as in the plastic region

Determination of the Coffin-Manson equation under low-cycle fatigue conditions

The cycle loading of a material results in the modification of its properties and so in this paper is presented the behaviour of the fatigue life using low-cycle fatigue parameters. By applying the Coffin-Manson equation in fatigue loading of the tested specimens, the crack initiation has been computed. The stabilized hysteresis loop is a characteristic of all hystereses and it is used to determine all of the parameters for the low cycle fatigue (LCF) assessment. The experimental results have given us important information on the understanding of fatigue behaviour of high strength low-alloyed steel (HSLA) and its welded joints

Оптимизација хроматографског раздвајања арипипразола и нечистоћа: приступ квантификовања односа структуре и ретенционог понашања

A new optimization strategy based on the mixed quantitative struc- ture–retention relationship (QSRR) model is proposed for improving the RP- HPLC separation of aripiprazole and its impurities (IMP A-E). Firstly, experi- mental parameters (EPs), namely mobile phase composition and flow rate, were varied according to Box–Behnken design and thereafter, an artificial neural network (ANN) as a QSRR model was built correlating EPs and sel- ected molecular descriptors (ovality, torsion energy and non-1,4-van der Waals energy) with the log-transformed retention times of the analytes. Values of the root mean square error (RMSE) were used for an estimation of the quality of the ANNs (0.0227, 0.0191 and 0.0230 for the training, verification and test set, respectively). The separations of critical peak pairs on chromatogram (IMP A- B and IMP D-C) were optimized using ANNs for which the EPs served as inputs and the log-transformed separation criteria s as the outputs. They were validated by application of leave-one-out cross-validation (RMSE values 0.065 and 0.056, respectively). The obtained ANNs were used for plotting response surfaces upon which the analyses chromatographic conditions resulting in optimal analytes retention behaviour and the optimal values of the separation criteria s were defined. The optimal conditions were 54 % of methanol at the beginning and 79 % of methanol at the end of gradient elution programme with a mobile phase flow rate of 460 μL min-1Нова оптимизациона стратегија заснована на грађењу мешовитих модела за кван- тификовање односа структуре и ретенционог понашања (QSRR) предложена је за уна- пређење RP-HPLC раздвајања арипипразола и његових нечистоћа (IMP А-Е). Експери- ментални параметри (EP), састав мобилне фазе и брзина протока, варирани су најпре у складу са Box–Behnken дизајном, а затим је награђена вештачка неуронска мрежа као QSRR модел који повезује ЕP и одабране молекуларне дескрипторе (овалност, торзиона енергија и не-1,4-ван дер Валсова енергија) са логаритамски трансформисаним ретен- ционим временом аналита. Вредности средње квадратне грешке (RMSE) коришћене су за процену квалитета мреже (0,0227, 0,0191 и 0,0230 за тренинг, верификацију и тест сет, редом). Раздвајање критичних парова пикова на хроматограму (IMP А-B и IMP D-C) оптимизовано је коришћењем мрежа за које су ЕP послужили као улази, а логаритамски трансформисани критеријуми сепарације s као излази. Ове мреже су валидиране при- меном унакрсне валидације изостанка (RMSE вредности, редом, 0,065 и 0,056). На основу награђених мрежа, конструисани су дијаграми површина одговора чијом ана- лизом су дефинисани услови при којима се постиже оптимална ретенција аналита, односно вредности критеријума сепарације s, а који су подразумевали 54 % метанола на почетку и 79 % на крају програма градијентног елуирања са брзином протока мобилне фазе од 460 mL min -

Processing of Data Obtained by the Testing of Steel under Low Cyclic Fatigue (Part I)

The design of mechanical components exposed to fatigue load, at a low number of cycles, requires knowledge of the behaviour of the material under the impact of variable load in conditions of controlled strain when cyclic plasticity is present. The aim of testing the quality of the material of the components exposed to low cycle fatigue (LCF) in many industries: nuclear, aerospace, mechanical, civil engineering and shipbuilding. In order to ensure the reliability and consistency of the results from different laboratories, it is necessary to collect all test data using test and data processing methodologies that are in accordance with a number of key points of ISO 12106:2017 and/or ASTM E 606-04 standards. This paper defines a new data processing methodology after the LCF testing of steel

Zaštita od korozije brodskih konstrukcija

Hull maintenance is one of the most important aspect in ships lifetime. Ship maintenance represents prevention of ship system failures, dealing with them and extending ships lifetime. Corrosion has been a common cause of damage in ships for years. The most widely used method for protecting ship structures is application of coatings. Ships age, size and navigation area all influence in choosing the right protective coating system. Hull protective coating can be applied either during navigation or during ship repair works in shipyard

European Directives Through the Integrity Evaluation of the Mechanical Equipment

Hydroelectric generating units at hydro power plants consist of turbine and hydromechanical equipment, which components could be subject to a large number of European Directives. Responsibility of turbine manufacturer is to make sure that certain components of equipment are in agreement with requirements of the specific Directive. This paper offers the opportunity to perceive the possibility of applying the Pressure Equipment Directive 97/23/EC, Simple Pressure Vessels Directive 2009/105/EC, Machinery Directive 98/37/EEC and Low Voltage Directive 2006/95/EC for turbine equipment at hydro power plants ‘Djerdap 1’ and ‘Djerdap 2’, because components of the turbine regulator and of the lubrication system, of the runner and measurement and regulation system are individually subject to different Directives. The overview of the possible approach regarding the standardization and technical harmonization of turbine equipment components for easier assessment of their integrity is also presented in this paper

Uticaj tipa poremećaja pisanja na školski uspjeh učenika sa disgrafijom

Introduction. Dysgraphia is a term used for problems with transcription in children without intellectual disabilities, untouched eyesight and hearing, age-appropriate education and appropriate socioeconomic conditions. Writing disorder can be manifested by both handwriting deficiency and language stage deficiency. The aim of this study was to identify the influence of writing disorder type on school success of students with dysgraphia. Methods. The study sample consisted of 461 third-grade, fourth-grade and fifth-grade students from three city schools in the Republic of Srpska. Using the scale for the assessment of handwriting maturity, as well as the language analysis of each handwriting in turn, the subsample consisting of 42 male and female students with dysgraphia, aged 8 to 11, was isolated. The research was conducted in Foča from April to May 2015. Results. Out of a total of 461 examined students, 42 (9.1%) had dysgraphia that was more frequently present in boys (7.6%) than in girls (1.5%). There was no statistically significant difference in the degree of dysgraphia severity between the students of different sex and school age. Severe deviations/ delays in handwriting maturity with respect to chronological age were only found in respondents with dysgraphic handwriting. There was a considerably higher percentage of graphomotor dysgraphia (71.4%) compared to language dysgraphia (28.6%). School success, as well as grades in Serbian language, were considerably lower in students with language dysgraphia than in children with graphomotor dysgraphia. Conclusion. The results show a significant presence of dysgraphia in school-age children. It is found more frequently in boys than in girls. Graphomotor dysgraphia is found more frequently in schoolage students compared to language dysgraphia, while there is a greater negative effect of the latter on school success.Uvod. Disgrafija je poremećaj u ovladavanju vještinom pisanja kod djece očuvanih intelektualnih sposobnosti, očuvanog vida i sluha, adekvatne obuke u školi i odgovarajućih socio-ekonomskih uslova. Poremećaj pisanja može da se manifestuje oštećenjem rukopisa i jezičkim deficitima. Cilj ispitivanja je bio da se utvrdi uticaj tipa poremećaja pisanja na školski uspjeh učenika sa disgrafijom. Metode. Uzorak se sastojao od 461 učenika trećih, četvrtih i petih razreda tri gradske škole na području Republike Srpske. Pomoću testa za procjenu disgrafičnosti rukopisa i na osnovu jezičke analize svakog pojedinačnog rukopisa, izdvojen je poduzorak od 42 ispitanika sa disgrafijom, uzrasta od 8 do 11 godina, oba pola. Istraživanje je realizovano u aprilu i maju 2015. godine. Rezultati. Među ispitanim učenicima 42 (9,1%) ima disgrafiju koja je u značajno većem procentu prisutna kod dječaka (7,6%) nego kod djevojčica (1,5%). Nije uočena statistički značajna razlika između ispitanika različitog pola i školskog uzrasta u pogledu stepena disgrafije. Teži stepen odstupanja/kašnjenja u zrelosti rukopisa u odnosu na hronološki uzrast prisutan je isključivo kod ispitanika sa izrazito disgrafičnim rukopisom. Pronađen je značajno veći procenat grafomotornih (71,4%) u odnosu na jezičke disgrafije (28,6%). Djeca sa jezičkom disgrafijom postižu značajno niži uspjeh u školi i nižu ocjenu iz srpskog jezika u poređenju sa djecom sa grafomotornom disgrafijom. Zaključak. Rezultati pokazuju prisustvo disgrafije kod djece školskog uzrasta koja se značajno češće javlja kod dječaka nego kod djevojčica. Grafomotorna disgrafija se statistički značajno više ispoljava kod djece školskog uzrasta o

Effects of Alloying Elements on the Properties of HSLA Steel

The first industrial application of elevated and high-strength steel in the form of hot-rolled strips and sheets was the manufacture of pipes and vessels under pressure, as it was possible to reduce the thickness, i.e. to reduce the weightof welded structures. The high-strength low-alloy steels used today are usually obtained by suitable chemical composition and thermomechanical treatment. Our investigated steel NIOMOL 490 K belongs to the class of molybdenum microalloyed steels, where the microalloying with molybdenum serves to increase the heat resistance of the steel and at the same time strengthen the influence of other alloying elements. This steel grade is designed for the manufacture of welded pressure vessels fabrication and is mainly used for dynamic loading conditions at low operating temperatures. In the present paper, the tensile and hardness tests were used to determine the effects of alloying elements on the mechanical properties of NIOMOL 490K steel in the temperature range from -60°C to +60°C

Evaluation of the behavior of welded structures under low-cycle fatigue loading

Welded structures are exposed to constant variable loads during their exploitation in real conditions. A variable load affects the integrity and life of a welded structure; therefore, it is of practical importance to understand fatigue behavior, especially the behavior of welded structures under the impact of low-cycle fatigue. The effect of low-cycle fatigue is very prevalent in structures and an assessment of cyclic loading of a material entails modifications of its properties and characteristics related to the dependence of stress and strain. Since the stress-strain response during low-cycle fatigue is in the form of a hysteresis loop, this paper presents the application of one of the two most common relations for testing resistance to low-cycle fatigue, the Ramberg-Osgood relation, which is used to evaluate the behavior of a material, in this case a high-strength low-alloy steel welded joint