Volume 40, Issue 2

Metallic materials are widely utilized in the fields of industry, agriculture, transportation and daily life for their high mechanical strength, and relatively low cost. However, the microorganisms that are widely distributed in surroundings can have complicated interactive reactions with metallic materials. The microbiologically influenced corrosion (MIC) has caused serious economic losses and resource wastage for human society. To date, great efforts have been made in the mechanism of MIC and control methods. This work describes the research findings on MIC developed in the recent years, and studies on the common microbial species that affect metal corrosion. The other aim of this paper is to review the accelerating or inhibiting mechanism in metal corrosion. Also, it provides an outlook for research on MIC.

Sulfamic acid (H 3 NSO 3 ), which is also known as amino sulfuric acid, sulfamidic acid, amidosulfonic acid, and aminosulfonic acid, is an industrially useful water-soluble colorless crystalline solid. Sulfamic acid solutions of different concentrations are widely used for the removal of scales and metal oxides deposits from the surface of metals and ceramics. Sulfamic acid solutions (5–10%) serve as alternative electrolytes for the removal of rusts and lime scales to replace relatively more irritating and volatile hydrochloric and sulfuric acid-based electrolytes. Sulfamic acid solutions can be regarded as relatively more environmentally friendly and less toxic electrolytes for the cleaning of metallic surfaces. However, similar to the popular acidic solutions, sulfamic acid based electrolytes are corrosive to metal and metallic structures. Therefore, organic compounds based corrosion inhibitors of natural and synthetic origin are widely used to prevent corrosive damage of metallic surfaces in such electrolytes. These compounds become effective by adsorbing on the metallic surface following through the Langmuir adsorption isotherm model. Using electrochemical analyses it was observed that organic corrosion inhibitors in sulfamic acid based electrolytes behave as mixed- and interface-type corrosion inhibitors and they become effective by adsorbing at the metal/electrolyte interfaces. The adsorption of most of the corrosion inhibitors mostly follows physiochemisorption mechanism.

Corrosion, a gradual destruction of metals as they react to their environment, is a daunting issue faced by the oil and gas industry since it has negative impacts on both life and industry applications. Attempts to tackle this problem have involved a myriad of techniques among which, corrosion inhibitors have been found to be the most effective. Corrosion inhibitors adsorb onto metallic surfaces and insulate them from deterioration. Plants being green and abundant in nature, offer a cost-effective replacement to toxic, chemical inhibitors on the market. Investigations of several plant extracts using different variables to quantify their effectiveness reveal that most of them exhibit an excellent inhibition potential, usually above 90%. These outstanding results prove their efficiency compared to traditional methods and necessitate further studies so as to enable implementation on large scale.

A detailed comparative study on inhibitive behaviour against corrosion of mild steel in 1N H 2 SO 4 IN HCl for the Schiff bases 2,6-diphenyl-3-methyl azinan-4-one (D3MA) (S1), 2,6-diphenyl-3-methyl azinan-4-one semicarbazone (D3MAS) (S2), 2,6-diphenyl azinan-4-one (DA) (S3) and 2,6-diphenylazinan-4-one semicarbazone (DAS) (S4) was investigated using gravimetric and potentiodynamic polarisation methods. The thermodynamic parameters for the mild steel corrosion and the synergistic behaviour of the inhibitors in the presence of anions and cations were determined and discussed. It was found that the adsorption of the inhibitors on the mild steel surface obeyed Langmuir adsorption isotherm. Electro chemical studies revealed that all the four inhibitors are of mixed type. We proved that the semicarbazones (Schiff bases S2b and S4) with additional O and N are more effective corrosion inhibitors than their parent keto-amines. As a whole from all the proposed studies it is proved that the explored Schiff’s bases work as a very efficient corrosion inhibitor for mild steel in both the acidic medium.

The purpose of this paper is to predict and mitigate AC interference on buried pipeline systems due to transmission lines. Modeling and field verification of AC interference is done. The article also presents the issue of optimizing the mitigation measures. The paper uses the field data on soil resistivity, transmission line, and pipeline details to develop a model using current distribution electromagnetic interference grounding and soil structure analysis (CDEGS) software to predict the AC interference on the pipeline system. The model is validated with field measurements, and post-mitigation measures are considered. Mitigation measures are optimized to develop an economical mitigation plan. The case demonstrates the use of modeling techniques to predict and mitigate AC interference on pipelines. The field validation of modeling results helps improve the modeling results and plan optimized mitigation measures. The study requires providing comprehensive field data relevant to the pipeline system under consideration. The accuracy of the field data may have a bearing on the outcome of the study. The study enables designing and optimizing mitigation measures using modeling. Comparisons with field measurements help achieve desired pipeline system integrity against AC corrosion.

Anodic dissolution of carbon steel in solution mixtures of simulated CO 2 –H 2 S in the presence of formic acid (0–500 ppm) was investigated using electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that the corrosion rate increases with an increase in the concentration of formic acid. Potentiodynamic polarization data revealed that the increase in cathodic current density plays a significant role in the increase of carbon steel corrosion rate. A combination of equivalent circuits was employed to model the impedance spectra of the carbon steel electrode acquired at open circuit potential and different overpotentials. The EIS data obtained at various overpotentials were further analyzed by reaction mechanism analysis (RMA) approach to interpret the dissolution mechanism. A multi-step reaction model including two dissolution paths and ferrous intermediate adsorbed species determined the dissolution behaviour of carbon steel. The best fit RMA kinetic parameters were retrieved using an optimization technique and the surface coverage of adsorbed species was estimated. Surface morphology of corroded steel surfaces was also examined with field emission scanning electron microscope demonstrating aggressive uniform corrosion of carbon steel in the presence of formic acid.

The corrosion behavior of four uncoated low carbon steels: X52, X60, X65, and X70, and three non-ferrous metals: copper, bronze, and magnesium, buried in a real calcareous soil, after a year of exposure time was studied. Samples were not cathodically protected on gravimetric testing in field conditions. Severe roughness and color changes occurred in metals and surface evidenced the presence of rust and calcareous deposits. Oxide scale was generated when metals were immersed in calcareous soil for nine months. In field conditions, X52 was the most corrosion resistant and X65 the most susceptible to corrosion. At laboratory level, a real calcareous soil tested by electrochemical methods exhibited the same trend, which was ascribed to difference in microstructure and phase distribution in steels. Corrosion enhanced when X65 was exposed to calcareous soil collected in spring (0.031 mm/year) and rainy summer (0.077 mm/year), as rain enhanced ions mobility and corrosion. Non-ferrous coupons suggested that a passivation process occurred as corrosion rates (CRs) decreased (0.0025–0.0052 mm/year) compared with the results of low carbon steels.