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Presence of crack due the constant exploitation of turbine shaft
Get PDFDesigning, constructing and putting into operation a hydroelectric power plant includes complex
tasks. Stresses of turbine and hydromechanical equipment of hydro power plants arise during the
production of parts and assembly of equipment (residual stresses), in the process of performing
functional requirements in exploitation and in the disturbed process of exploitation.
After several decades of constant exploitation of the horizontal bulb turbine, which is an integral
part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine
shaft due to the influence of corrosion, erosion and cavitation.
Through experimental tests and calculations it has been determined that values of bending stresses
of the turbine, which occur due to the action of fatigue and corrosion, as well as stress
concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than
40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks
on the transition radius between the cylindrical part of the shaft and the flange. It has been
determined that stress values in the zone under the influence of bending stresses were bigger than
allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of
those cracks caused the failure of the shaft and of the whole turbine
Science and Technology for Silicate-Based Construction and Building Materials, A special issue of Materials
Get PDFExperimental determination and numerical validation of the critical value of the J-integral ofa low carbon microalloyed steel for elevated temperature application
Get PDFTo evaluate the behavior of a homogeneous material in the presence of a crack-type defect, the
value of the critical stress-intensity factor, KIc, was determined as a measure of the fracture
toughness of the tested steel under the conditions of a plane stress state, at two test temperatures,
20 C and 540 C. The experiments were carried out using the method of testing one specimen with
successive partial unloading, which aims to r
occurs during the test. In addition to the experimental analysis, a numerical simulation of the
behavior of the specimens under static and dynamic loading was performed. The numerical analysis
is based on the experimentally obtained yield strength and tensile strength values of the investigated
steel, and was done in Ansys Workbench R21 software package, which relies on finite element
method, FEM. The results obtained by numerical analysis showed good agreement with the
experimentally obtained results of the J-integral for specimens tested at room and elevated
temperature. Good agreement with the experimental results was shown, confirming the use of FEM for the load cases considered
Ispitivanja zavarenih spojeva niskolegiranog čelika povišene čvrstoće klase 700 MPa
Get PDFZahtevi ekonomične potrošnje energije i sirovina upućuju proizvođače čelika na proizvodnju zavarljivih čelika povišene čvrstoće, a projektante i konstruktore na njihovu primenu u zavarenim konstrukcijama. Primena niskolegiranih čelika povišene čvrstoće (HSLA) u metalnim konstrukcijama je sve zastupljenija pre svega zbog njihovog svojstva oblikovanja gde zavarljivost ima poseban značaj. Stoga se vremenom razvio čitav niz postupaka ispitivanja kojima je cilj da se svojstva zavarenog spoja pomenutih materijala što bolje upoznaju i tako što racionalnije iskoriste. Analizirana svojstva kao što su ispitivanje zatezanjem, udarna žilavost i tvrdoća, daju širu sliku o samim zavarenim spojevima niskolegiranih čelika i njihovim osobinama i upoređuju se sa zahtevima međunarodnih standarda iz oblasti elektrolučnog zavarivanja
Ispitivanje koeficijenta mikro-Deval na uzorcima drobljenog krečnjačkog agregata – očekivani opsezi vrednosti
No full textKvalitet ugradenog kamenog agregata u direktnoj je vezi sa iivotnim vekom kolovoznih
konstrukcija. Kvalitelan agregat mora imati odgovarajuti granulomelrijski sastav, zadovoliavaiuta
Jiziika i mehaniika svojstva i mora biti otporan na vremenske uslove, odnosno smrzavanie i
odmrzwanje. Otpornost kamenog agregata prema habanju metodom milqo-Deval (EN 1097-l) se
na prostoru Srbije primenjuje tek poslednjih nekoliko godina. U radu su prikazani podaci o
rezultatima ispitivanja uzoraka razliiitih kreinjaikih agregata sa prostora Srbiie, sa ciliem
deJinisanja oiekivanog opsega rezultata milvo-Deval koeficijenta i kriteriiuma za niihovu ocen
Quantifying the impact of parameters of chloride-induced reinforcement corrosion on the GPR signal
No full textThe sensitivity of the high-frequency ground penetrating radar (GPR) signal to changes within the reinforced
concrete (RC) makes it a valuable tool for corrosion assessment of RC structures. The most important parameters
in chloride-induced corrosion are moisture content, chloride content, and reinforcement diameter loss. The
objective of this laboratory study was to investigate and quantify the influence of these parameters on the GPR
signal. Of particular interest was to determine which of the observed parameters the GPR is most sensitive to.
Furthermore, particular emphasis was placed on understanding the influence of corrosion products, which has
not met the consensus in the existing literature. The parameters were studied on a total of forty-two specimens
where the reflector of the GPR waves was the reinforcement embedded in the concrete specimen. Based on the
experimental data, values of normalized amplitude related to the evaluation of corrosion by GPR were proposed
Experimental Determination of JIc for a HSLA Steel Welded Joint
No full textMost serious weldment failures have catastrophic consequences in terms of damage to other equipment, loss of production, and risks to worker health and safety. For the above reasons, there is a tendency to find the line between safety and disaster, and this requires a guarantee of the integrity of the welded structure even if a crack is present. The structural and mechanical heterogeneity of a welded joint affects its resistance to cracking in both the elastic and plastic regions. Therefore, it is important to define the test method and the position of the fatigue crack. The behavior of an elasto-plastic material, during stable crack growth can be described by the J-Δa diagram. As the crack propagates, a point on the curve is defined, which represents the critical value of the J-integral. The aim of this experiment is to determine JIC value and the procedure is reflected in the determination of the R-curve, i.e., the J‒Δa curve, which consists of the value of the J-integral for uniform crack increments Δa. In this paper, precracked SEN(B) specimens with the fatigue crack positioned in the weld metal (WM) were tested according to standard ASTM E1820 at room temperature (RT), -20 °C and -30 °C
Effects of Alloying Elements on the Properties of HSLA Steel
Get PDFThe 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
European Directives Through the Integrity Evaluation of the Mechanical Equipment
Get PDFHydroelectric 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
Choice of component materials for concrete from the durability aspect
Get PDFBetonske konstrukcije su često u eksploataciji izložene spoljašnjim uticajima. Preporuke koje definiše evropski stan-dard SRPS EN 206 za korišćenje betona u pojedinim klasa-ma izloženosti nisu dovoljne i iz tog razloga je usvojen i standard SRPS U.M1.206 koji predstavlja nacionalni doda-tak za njegovu primenu. Dejstvo mraza značajno utiče na trajnost betonske konstrukcije jer može da dovede do raza-ranja strukture betona. Zaštita se postiže dodavanjem hemij-skih dodataka koji uvlače vazduh u svež beton. U radu je prikazana mogućnost primene novog dodatka Sika Aer Solid. Ispitivana je otpornost betona na dejstvo mraza, mraza u prisustvu soli za odmrzavanje, prodiranje vode pod pritiskom i koeficijent migracije hlorida u laboratorijskim uslovima i uzorcima izvađenim iz betonskih prefabrikovanih elemenata. Betoni sa Sika Aer Solid su za istu klasu konzistencije u odnosu na aerirane betone imali bolja svojstva i u svežem i u očvrslom stanju.Recommendations defined by the European standard SRPS
EN 206 for use of concrete in certain classes of exposure
are not sufficient, and for this reason the standard SRPS
U.M1.206 was also adopted, which is a national annex for
its application. The effect of frost significantly affects the
durability of the concrete structure because it can lead to
its destruction. Protection is achieved by adding chemical
admixture that entrains air into fresh concrete. The paper
shows the possibility of applying the new additive Sika Aer
Solid. Concrete resistance to frost, freeze-thaw resistance
with de-icing salt, depth of penetration of water under pressure and chloride migration coefficient are tested in laboratory conditions and samples taken from concrete prefabricated elements. For the same class of consistency, concrete
with Sika Air Solid, compared to concrete with air entraining admixture, had better properties both in the fresh and
hardened state