MOGUĆNOST PRIMJENE BILJNIH EKSTRAKATA KAO ZELENIH INHIBITORA KOROZIJE U NAFTNOJ INDUSTRIJI

In this paper, preliminary studies of ten different plant extracts as potential corrosion inhibitors of carbon steel were examined. For each extract, the concentration range in which it shows anti-corrosion action was first determined, and then the most effective concentration was determined for each extract. The tests were performed in a brine solution saturated with CO2 at room temperature. The aim of this study was to isolate extracts with high effectiveness and subsequent electrochemical and surface methods to determine the mechanism of inhibitory action. For this purpose, potentiodynamic polarization was performed with Tafel extrapolation. Among all the tested extracts, lady’s mantle (92.17%) and dandelion root (95.07%) stood out with their effectiveness. Both tested extracts showed the behaviour of a mixed corrosion inhibitor with a dominant influence on the anode process.U ovome radu provedena su preliminarna ispitivanja deset različitih biljnih ekstrakata kao potencijalnih korozijskih inhibitora ugljičnoga čelika. Za svaki ekstrakt najprije je određen raspon koncentracija u kojemu pokazuje antikorozijsko djelovanje, a potom je za svaki ekstrakt određena najdjelotvornija koncentracija. Ispitivanja su provedena u sintetskoj slojnoj vodi zasićenoj s CO2 pri sobnoj temperaturi. Cilj rada bio je izdvojiti ekstrakte s visokim djelotvornostima te naknadnim elektrokemijskim i površinskim metodama utvrditi mehanizam inhibitorskoga djelovanja. U tu svrhu provedena je potenciodinamička polarizacija s Tafelovom ekstrapolacijom. Od svih ispitanih ekstrakata sa svojim djelotvornostima izdvajaju se vrkuta (92,17 %) i korijen maslačka (95,07 %). Oba ispitana ekstrakta pokazala su ponašanje mješovitoga korozijskog inhibitora s dominantnim utjecajem na anodni proces

Tracing nitrate nitrogen input-output dynamics at the Padež stream watershed

The sensitivity of ecosystems to changes in the amounts of nitrogen in the environment is large. In order to protect them against overloads of nutrients and to allow their healthy development, the knowledge of the nitrogen mass balance is crucial. Differences in the amount of nitrogen occur because of increasing inputs from anthropogenic sources, but they are also due to meteorological, hydrological, geological and biological factors or, in other words, to biogeochemical circulation between the biotope and organisms. The data on stream water nitrate concentrations and nitrate concentrations in precipitation together with measurements of precipitations and Padež stream discharge were used to analyze nitrate-nitrogen input-output dynamics. The analysis is presented as a difference between inputs and outputs of nitrate-nitrogen per hectare of catchment area. The impact of seasonality could be observed. Watershed behaves as a sink or as a source of nitrate-nitrogen depending on the hydrological conditions and the amount of potentially available nitrate-nitrogen in soil which is flushed towards the stream and its concentrations in precipitation

LABORATORIJSKA ISPITIVANJA ZAGAĐENJA SILIKATNE ISPLAKE KALCIJEM

The silicate-based drilling fluid is a low solids KCl/polymer system with the addition of soluble sodium or potassium silicate to enhance inhibition and wellbore stability. Silicate-based drilling fluids exhibit remarkable shale and chalk stabilizing properties, resulting in gauge hole and the formation of firm cuttings when drilling reactive shales and soft chalks. Silicates protect shales by in-situ gellation when exposed to the neutral pore fluid and precipitation, which occurs on contact with divalent ions present at the surface of the shale. Also, silicates prevent the dispersion and washouts when drilling soft chalk by reacting with the Ca2+ ions present on chalk surfaces of cutting and wellbore to form a protective film. The silicate-based drilling fluid can be used during drilling hole section through shale interbeded anhydrite formations because of its superior shale stabilizing characteristics. However, drilling through the anhydrite can decrease the silicate concentration and change rheological and filtration fluid properties. So, the critical concentration of calcium ions should be investigated by lab tests. This paper details the mechanism of shale inhibition using silicate-based drilling fluid, and presents results of lab tests conducted to ascertain the effect of Ca2+ ions on silicate level in the fluid and the fluid properties.Silikatna isplaka je KCl/polimerna isplaka s malo čvrstih čestica i s dodatkom topivog natrijevog ili kalijevog silikata radi povećanja inhibicije i stabilnosti kanala bušotine. Silikatne isplake pokazuju izvanredna svojstva u stabiliziranju šejla i krede, čime se postiže nominalan promjer kanala bušotine i stvaranje čvrstih krhotina tijekom bušenja kroz reaktivne šejlove i meke krede. Silikati štite šejlove in-situ geliranjem u kontaktu s neutralnim slojnim fluidom i taloženjem do kojeg dolazi uslijed reakcije silikata s dvovalentnim ionima prisutnim na površini šejla. Tijekom bušenja kroz meku kredu silikati sprečavaju disperziju i proširenja jer reagiraju s Ca2+ ionima koji su prisutni na površini krhotina krede i stijenki kanala bušotine i formiraju zaštitni film. Zbog njenih superiornih svojstava u stabiliziranju šejla silikatna isplaka se može koristiti tijekom bušenja kroz naslage anhidrita sa proslojcima šejla. Međutim, bušenje kroz anhidrit može dovesti do prevelike potrošnje silikata odnosno smanjenja njegove koncentracije u isplaci, te promjene reoloških i filtracijskih svojstava isplake. Zbog toga je neophodno provođenje laboratorijskih ispitivanja radi utvrđivanja kritične koncentracije iona kalcija u isplaci. U, radu se opisuje mehanizam inhibicije šejla kad se koristi silikatna isplaka, i prikazuju rezultati laboratorijskih ispitivanja provedenih radi određivanja utjecaja Ca2+ iona na razinu silikata u isplaci i na njena svojstva

ULOGA RAZLIČITIH REOLOŠKIH MODELA U PRECIZNOM PREDVIĐANJU SMANJENJA TLAKA

Hydraulics play an important function in many oil field operations including drilling, completion, fracturing, acidizing, workover and production. The standard API methods for drilling fluid hydraulics assume either power law or Bingham plastic rheological model. These models and corresponding hydraulic calculations do provide a simple way for fair estimates of hydraulics for conventional vertical wells using simple drilling fluids, such as bentonite fluids. However, nowdays with many wells drilled deep, slim or horizontal using complex muds with unusual behaviour (such as tested MMH mud), it is necessary to use appropriate rheological model for mathematical modelling of fluid behaviour. Oil and gas reservoirs in Croatia have been under production for quite a while and the probability to discover new deposits of hydrocarbons is rather small. Therefore attempts have been made to maintain the gas and oil exploitation at the present level. One of possible ways to meet this target is re-entry wells drilling. The diameter of such wells in reservoir is smaller than 0,1524 m (6 in). Accurate modelling of annular pressure losses becomes therefore an important issue, particularly in cases where a small safety margin exists between optimal drilling parameters and wellbore stability, what is the case in re-entry wells. The objective of the paper is to show the influence of well geometry and accuracy of fluid rheological properties modelling to the distribution of pressure losses in a slimhole well.Hidraulika ima vrlo važnu ulogu pri izvođenju velikog broja postupaka u bušotini uključujući bušenje, opremanje, frakturiranje, kiselinske obrade, održavanje i proizvodnju. Razmatranje hidraulike bušaćeg fluida prema API postupcima podrazumijeva primjenu ili eksponencijalnog ili Bingham plastičnog reološkog modela. Ti modeli i odgovarajući proračuni hidraulike osiguravaju jednostavan način dobivanja podataka prihvatljve točnosti za slučaj primjene u konvencionalnim vertikalnim bušotinama i kod primjene bušotinskih fluida jednostavnog sastava, kao što su bentonitne isplake. Međutim, danas, kada se izrađuje veliki broj dubokih bušotina, bušotina velikog dosega ili malog promjera, koje mogu biti usmjerene ili horizontalne, a za njihovu izradu koriste se fluidi složenog sastava i neobičnog ponašanja (kao što je slučaj s ispitanom MMH isplakom), neophodno je za modeliranje ponašanja fluida primijeniti odgovarajući reološki model. Budući se iz postojećih ležišta u Hrvatskoj nafta i plin proizvode već dulje vrijeme, a vjerojatnost otkrivanja novih ležišta je mala, nastoji se zadržati proizvodnju nafte i plina na današnjoj razini. Jedan od mogućih načina da se to ostvari je i izrada bočnih ("re-entry") bušotina. Promjer takve bušotine unutar ležišta najčešće je manji od 0,1524 m (6 in). U takvim slučajevima vrlo je važno precizno modeliranje smanjenja tlaka u prstenastom prostoru. Posebno se to odnosi na slučajeve gdje postoji mali sigurnosni zazor između postizanja optimalnih bušaćih parametara i kanala bušotine, kao što je to slučaj kod izrade bočnih bušotina. U radu je prikazan utjecaj geometrije bušotine i preciznosti modeliranja reoloških svojstava fluida na smanjenje tlaka u kanalu bušotine malog promjera

Extended FEM analysis of fatigue crack growth in Ti-6Al-4V orthopaedic plates

The extended finite element method (xFEM) was used to analyse fatigue crack growth in orthopaedic locking compression plates (LCP), made of Titanium alloy, Ti-6Al-4V, loaded in four-point bending. The optimal geometry was defined previously in respect to the remaining life of LCP used for patients with different body weights (BW - 60, 90 and 120 Kg). The plate with optimal geometry is analysed in more details here to assess the effect of BW and get better insight into fatigue crack growth path

Extended FEM analysis of fatigue crack growth in Ti-6Al-4V orthopaedic plates

The extended finite element method (xFEM) was used to analyse fatigue crack growth in orthopaedic locking compression plates (LCP), made of Titanium alloy, Ti-6Al-4V, loaded in four-point bending. The optimal geometry was defined previously in respect to the remaining life of LCP used for patients with different body weights (BW - 60, 90 and 120 Kg). The plate with optimal geometry is analysed in more details here to assess the effect of BW and get better insight into fatigue crack growth path

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

Numerical Simulation of Fatigue Crack Growth in Hip Implants

In this paper numerical analysis of hip replacement implant behaviour from a fracture mechanics perspective is presented. It is necessary to understand the fatigue crack initiation and propagation characteristics in order to prevent catastrophic failure of the implant. For the simulation of crack propagation extended finite element method (XFEM) was used, as being one of the most advanced modeling techniques for this type of problem. Short theoretical background information on the XFEM is provided, as well as the representation of crack and the stress intensity factors computation. For chosen titanium alloy hip implants numerical modeling and analysis were done in ABAQUS software. It is shown that is possible to assume hip implant mechanical behaviour to the existence of defects such as cracks by application of numerical simulation crack behaviour. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in complicated biomedical structures, without the need to re-mesh during the propagation if the finite element mesh is well defined

Numerical Simulation of Fatigue Crack Growth in Hip Implants

In this paper numerical analysis of hip replacement implant behaviour from a fracture mechanics perspective is presented. It is necessary to understand the fatigue crack initiation and propagation characteristics in order to prevent catastrophic failure of the implant. For the simulation of crack propagation extended finite element method (XFEM) was used, as being one of the most advanced modeling techniques for this type of problem. Short theoretical background information on the XFEM is provided, as well as the representation of crack and the stress intensity factors computation. For chosen titanium alloy hip implants numerical modeling and analysis were done in ABAQUS software. It is shown that is possible to assume hip implant mechanical behaviour to the existence of defects such as cracks by application of numerical simulation crack behaviour. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in complicated biomedical structures, without the need to re-mesh during the propagation if the finite element mesh is well defined