| Abstract | Od samih početaka svoje djelatnosti, naftna industrija se susreće s problemom korozije s obzirom da je većina procesne opreme i cjevovoda u naftnoj industriji izrađena od ugljičnog čelika. U većini slučajeva, ovisno o tipu ležišta, proizvodnja ugljikovodika podrazumijeva i proizvodnju određene količine slojne vode. Uz slojnu vodu, proizvedeni fluid u sebi može sadržavati nečistoće poput pijeska, aditiva koji su bili primijenjeni tijekom procesa proizvodnje (biocidi, inhibitori stvaranja kamenca, deemulgatori i sl.), ali i otopljenog plina, ugljikova dioksida (CO2) i sumporovodika (H2S). Kako s godinama dolazi do starenja proizvodnih polja tako se udio vode u proizvedenom fluidu povećava. Spomenuti ugljikov dioksid i sumporovodik, otopljeni u vodi, stvaraju korozivnu sredinu. Zbog starosti polja i zastarjelosti proizvodne infrastrukture, korozija je jedan od velikih problema u naftnoj industriji u Hrvatskoj. Dijelovi proizvodno-transportnog sustava, koji su najizloženiji korozivnom mediju, su niz proizvodnih cijevi te priključni i sabirni cjevovodi i slanovodi. Jedan od načina usporavanja korozije je upotreba inhibitora korozije. Kako je u novije vrijeme, zbog njihove toksičnosti, ograničeno korištenje konvencionalnih inhibitora korozije, sve se više ispituju ekstrakti biljaka kao tzv. zeleni inhibitori korozije koji bi se mogli primjenjivati i za zaštitu dijelova proizvodno-transportnog sustava izloženih koroziji. U doktorskom radu prikazani su rezultati laboratorijskih ispitivanja odabranih ekstrakata biljaka iz hrvatskog podneblja s ciljem utvrđivanja njihove primjenjivosti kao inhibitora korozije u sabirno-transportnom sustavu ugljikovodika. Ispitivanja uzoraka čelika od kojih su izrađeni priključni cjevovodi i slanovodi provedena su u simuliranoj slojnoj vodi zasićenoj s ugljikovim dioksidom (CO2), kako bi se simulirali realni (terenski) uvjeti. U okviru istraživanja provedena su elektrokemijska mjerenja (potenciodinamička polarizacija s Tafelovom ekstrapolacijom, elektrokemijska impedancijska spektroskopija) u stacionarnim i u dinamičkim (protočnim) uvjetima, površinska ispitivanja (SEM, FTIR) kako bi se odredio način vezanja ekstrakata na površinu metala, te određivanje toksičnosti i biorazgradivosti kako bi se utvrdio utjecaj ekstrakta na okoliš. Od ispitivanih ekstrakata najdjelotvornijim su se pokazali ekstrakt cvijeta vrkute i ekstrakt korijena maslačka. Oba ekstrakta su gotovo 100 % biorazgradiva. |
| Abstract (english) | From its very beginning the petroleum industry is facing the problem of corrosion since most of the equipment and pipelines in the petroleum industry are made of carbon steel. In most of the cases, depending upon the type of the reservoir, production of hydrocarbons includes the production of certain amount of brine. Besides brine, produced fluid can also contain impurities such as dissolved gasses, sand, additives applied during production etc., but also carbon dioxide (CO2) and hydrogen sulphide (H2S). With maturing of the production fields, the share of the produced brine increases. Earlier mentioned carbon dioxide and hydrogen sulphide, dissolved in water (brine) cause corrosion and damage the equipment. Due to the maturity of the production fields and obsolescence of the infrastructure, the corrosion problem is one of the major issues in the Croatian petroleum industry. Parts of the oil and gas gathering and transportation system, which are most exposed to the corrosive fluid, are the production pipelines (tubing) and the flowlines, the gathering pipelines, and the pipelines for extracted brine transport. One of the ways to minimize the corrosion problem is application of corrosion inhibitors. Since nowadays there are some limitations in usage of conventional corrosion inhibitors due to their toxicity, plant extracts, among other things, have been studied as so-called green corrosion inhibitors. The green corrosion inhibitors could have great potential in application in petroleum industry. For this doctoral thesis, several plant extracts from Croatia were chosen. With the aim of selecting plant extracts as efficient corrosion inhibitors, which could potentially be applied in petroleum industry, electrochemical measurements (polarization measurements with Tafel extrapolation, electrochemical impedance spectroscopy), in brine with saturated CO2 in static and in flow conditions were made. Lady’s mantle extract was added to the brine solution at concentration 1 to 5 g/L for measurements conducted under static conditions. Maximum inhibitor efficiency (92,68 %) was achieved at 4 g/L. For measurements performed under static conditions, dandelion root extract was added at concentration 10 to 13 ml/L, and at concentration of 12 ml/L, extract achieved maximum efficiency (98,37 %). For measurements done under dynamic (flow) conditions, concentration of lady’s mantle, added to the brine solution, was 3 to 6 g/L, and concentration of dandelion root added to the brine solution was 11 to 15 ml/L. Highest efficiency of lady’s mantle extract, 92,57 %, was achieved at 5 g/L, and highest efficiency of dandelion root extract, 84,79 %, was achieved at 14 ml/L. Due to electrochemical measurements, both plant extracts behaved as mixed type corrosion inhibitor. Surface analyses (SEM, FTIR) were also made for determining adsorption to metal surface. Both analyses confirmed that lady’s mantle extract and dandelion root extract adsorb onto metal surface. For analysing the effect of the chosen plant extracts on the environment, biodegradability and toxicity tests were conducted. Both plant extracts are almost 100 % biodegradable. Biodegradability of both lady’s mantle extract and dandelion root extract is 0,96 (out of 1). Toxicity of lady’s mantle extract is 19,34 % while toxicity of dandelion root extract is 2,38 %. |
