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Low-temperature corrosion relevant to oil and gas wells was investigated. Casing cement was exposed to brine in contact with CO2 at 4 °C and 10 MPa. Pore water was extracted from wet cement using a die press, and a cement simulated pore solution (CSPS) was developed to be used for corrosion studies. High levels of chloride similar to the original brine solution were found. The sodium content was well below that of the original brine, with the change in charge mostly balanced by an increase in dissolved calcium. The calcium content was above predictions for brine-CO2-Ca(OH)2 equilibrium, suggesting that sodium was displaced in favor of calcium. Corrosion measurements were performed on casing steel using linear polarization resistance, electrochemical impedance spectroscopy, and mass loss samples with H2S:CO2 ratios from 0 to 0.001. The corrosion rate was found to decrease slightly with increasing sulfide content from 0.02 to 0.01 mm y-1.

Brazing of stainless steels is commonly carried out using nickel-based brazing fillers, which provide a high corrosion and oxidation resistance of the resulting joints. These brazed stainless steel joints are mostly used for manufacturing of heat exchangers for energy and air conditioning technologies. The joints of the study were produced at temperatures of 1000 °C, 1125 °C and 1150 °C in vacuum furnaces or continuous furnaces. In both cases, the parts interact with process gases like nitrogen within the brazing process, especially during cooling. The amount of nitrogen in the braze metal as well as in the base material was determined by the carrier gas hot extraction technique. The occurring diffusion of nitrogen into the braze metal and the base material causes a shift in the corrosion potentials. In this work, the influence of the nitrogen enrichment on the corrosion behavior was investigated using a capillary microcell. The corrosion measurements were carried out on the braze metal and the base material. The results of samples, brazed with and without the influence of nitrogen, were compared.

A microelectrochemical cell housed in an optical microscope and custom-made accessories have been designed and fabricated, which allows performing spatially resolved corrosion measurements. The cell assembly was designed to directly integrate the reference electrode close to the capillary tip to avoid air bubbles. A hard disk along with an old optical microscope was re-engineered into a microgrinder, which made the vertical grinding of glass capillary tips very easy. A stepper motor was customized into a microsyringe pump to dispense a controlled volume of electrolyte through the capillary. A force sensitive resistor was used to achieve constant wetting area. The functionality of the developed instrument is demonstrated by studying ?-electrochemical behavior of worn surface on AA2014-T6 alloy. � 2015 AIP Publishing LLC.

Cilj ovog istraživanja je zaštita niskougljeničnog čelika API X65 od korozije u prisustvu CO2 primenom organskog inhibitora korozije, imidazolinskog derivata smeše viših masnih kiselina i dietilentriamina, TOFA/DETA imidazolina, u tečnoj, kao i u gasovitoj fazi u uslovima kondenzacije uz primenu pene (natrijum C14-16 olefin-sulfonat) kao nosača inhibitora. Konvencionalne metode zaštite, poput ubrizgavanja inhibitora korozije nisu efikasne jer uslovi toka fluida onemogućavaju inhibitor da formira zaštitni sloj u delovima cevi gde dolazi do kondenzacije. Primenom spektroskopije elektrohemijske impedancije (SEI), metode polarizacione krive, gravimetrijske metode i metode određivanja gubitka mase na osnovu električne otpornosti za ispitivanje procesa korozije pokazano je da gustina struje korozije i brzina korozije niskougljeničnog čelika u 3 mas. % NaCl rastvoru zasićenom sa CO2, značajno opadaju sa povećanjem koncentracije TOFA/DETA imidazolina. U prisustvu 90 ppmv TOFA/DETA imidazolina u rastvoru izmerena je vrednost efikasnosti inhibicije preko 90 %. Na osnovu rezultata metode potencijal-vreme i metode linearne polarizacione otpornosti pokazano je da TOFA/DETA imidazolin u 3 mas. % rastvoru NaCl zasićenom sa CO2 deluje kao mešoviti inhibitor korozije, sa izraženijim anodnim dejstvom, pri čemu je vrednost polarizacione otpornosti do 40 puta veća u odnosu na sistem bez inhibitora. Primenom metode ciklične voltametrije (CV), pokazano je da se u prisustvu 90 ppmv TOFA/DETA imidazolina u 3 mas. % vodenom rastvoru NaCl zasićenom sa CO2 smanjuje vrednost gustine struje na celom toku voltamograma usled fizisorpcije molekula inhibitora na površini elektrode. Na osnovu dobijenih rezultata može se zaključiti da je TOFA/DETA imidazolin stabilan u opsegu korozionog potencijala niskougljeničnog čelika. Na osnovu termodinamičke analize procesa adsorpcije TOFA/DETA imidazolina na kristalima kvarca sa prevlakom od Au, kao i na niskougljeničnom čeliku, pokazano je da je proces adsorpcije spontan, endoterman, praćen porastom entropije najverovatnije usled reakcije desorpcije molekula vode sa površine metala. Pokazano je da ispitivani proces... The aim of the present study was to investigate the inhibition effect of talloil diethylenetriamine imidazoline (TOFA/DETA imidazoline) on corrosion of API X65 mild steel in the presence of CO2 for both continual immersion and top of the line corrosion (TLC) when injected within foam matrix (C14-16 olefin sulfonate). Conventional mitigation methods, like injection of corrosion inhibitors, can fall short in protecting the top of the line, since the conditions do not allow the inhibitor to reach the top sections of the wall where the condensation occurs. Electrochemical impedance spectroscopy (EIS), potentiodynamic sweep (PDS) measurements, weight loss and electrical resistance (ER) measurements on mild steel in CO2-saturated 3 wt. % NaCl solution without and with different concentrations of TOFA/DETA imidazoline showed a significant decrease in corrosion current density and consequently corrosion rate with the increasing concentrations of TOFA/DETA imidazoline. In the presence of 90 ppmv or more of TOFA/DETA imidazoline in the solution the inhibition efficiency, was calculated to be above 90 %. Linear polarization resistance (LPR) measurements showed that TOFA/DETA imidazoline is a mixed-type corrosion inhibitor with the predominant anodic effect. The values of polarization resistance in CO2-saturated 3 wt. % NaCl solution in the presence of inhibitor increased 40 times compared to the bare steel. The results of cyclic voltammetry (CV) measurements revealed inhibited electrode processes in the presence of 90 ppmv TOFA/DETA imidazoline due to the physical adsorption of inhibitor molecules on mild steel electrode active sites. Accordingly it can be concluded that corrosion inhibitor, TOFA/DETA imidazoline is stable in the range of mild steel corrosion potential. The adsorption of TOFA/DETA imidazoline from 3 wt. % aqueous NaCl solution saturated with CO2 investigated on both gold coated quartz crystals and mild steel from CO2-saturated 3 wt. % aqueous NaCl solution is spontaneous, endothermic, driven by entropy gain, due to the gradual replacement of water, molecules initially adsorbed on the...

Conference of 2013 SPIE Conference on Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2013 ; Conference Date: 10 March 2013 Through 14 March 2013; Conference Code:97276; International audience; Corrosion of reinforced bar (rebar) in concrete structures represents a major issue in civil engineering works, being its detection and evolution a challenge for the applied research. In this work, we present a new methodology to corrosion detection in reinforced concrete structures, by combining Fiber Bragg Grating (FBG) sensors with the electrochemical and physical properties of rebar in a simplified assembly. Tests in electrolytic solutions and concrete were performed for pitting and general corrosion. The proposed Structural Health Monitoring (SHM) methodology constitutes a direct corrosion measurement potentially useful to implement or improve Condition-Based Maintenance (CBM) program for civil engineering concrete structures.