Volume 34, Issue 1-2

Microbial-influenced corrosion (MIC) has been known to have economic, environmental, and social implications to offshore oil and gas pipelines, concrete structures, and piped water assets. While corrosion itself is a relatively simple process, the localised manner of corrosion makes in situ assessments difficult. Furthermore, corrosion assessments tend to be measured as part of a forensic investigation. Compounding the issue further is the impact of microbiological/biofilm processes, where corrosion is influenced by the complex processes of different microorganisms performing different electrochemical reactions and secreting proteins and metabolites that can have secondary effects. While traditional microbiological culture-dependent techniques and electrochemical/physical assessments provide some insight into corrosion activity, the identity and role of microbial communities that are related to corrosion and corrosion inhibition in different materials and in different environments are scarce. One avenue to explore MIC and MIC inhibition is through the application of omics-based techniques, where insight into the bacterial population in terms of diversification and their metabolism can be further understood. As such, this paper discusses the recent progresses made in a number of fields that have used omics-based applications to improve the fundamental understanding of biofilms and MIC processes.

The control of multiphase flow corrosion during oil production is a challenging task. In this review, the impact of crude oil on pipeline corrosion is broadly discussed, with the notion to reduce corrosion risks of pipelines in aggressive field conditions. First, the properties, emulsion stability, and multiphase flow patterns of crude oil fluids are concisely summarized and correlated to the corrosion behavior. Second, for proper evaluation of the corrosiveness of the oil-brine mixtures, related corrosion test methods and experimental techniques are critically evaluated. Third, the effects of crude oil on corrosion inhibition are conceivably attributed to four aspects, i.e. the entrainment of water, the wetting by crude oil, the partitioning effect, and the modification of the corrosion product layers. Fourth, the presence of crude oil may consume more corrosion inhibitors; however, the inhibitors can produce additional benefits on corrosion mitigation in oil-brine mixed conditions, such as altering the surface wettability to hydrophobic and enhancing the entrainment of water. Finally, some ideas to reduce pipeline corrosion are proposed and future research viewpoints are discussed.

Sulfate-reducing bacteria (SRB), an anaerobic bacterial group, are found in many environments like freshwater, marine sediments, agricultural soil, and oil wells where sulfate is present. SRB derives energy from electron donors such as sulfate, elemental sulfur or metals, and fermenting nitrate. It is the major bacterial group involved in the microbiologically influenced corrosion (MIC), souring, and biofouling problems in oil-gas-producing facilities as well as transporting and storage facilities. SRB utilizes sulfate ions as an electron acceptor and produce H 2 S, which is an agent of corrosion, causing severe economic damages. Various theories have been proposed on the direct involvement of H 2 S and iron sulfides in corrosion; H 2 S directly attacks and causes corrosion of metals and alloys. Many reviews have been presented on the aforementioned aspects. This review specifically focused on SRB corrosion and the role of molecular biology tools in SRB corrosion studies viz. cathodic and anodic depolarization theories, corrosion characteristics of thermophilic SRB and influence of hydrogenase, temperature, and pressure in thermophilic SRB corrosion, SRB taxonomy, molecular approaches adopted in SRB taxonomical studies, sulfate and citrate metabolism analyses in completed SRB genomes, and comparative studies on SRB’s dissimilatory sulfite reductase structures.

Metallic implants have been successfully used in medicine for the past 60–70 years. Historically, implants were designed only as mechanical devices, whereas the biological aspects of their application were beyond the researchers’ interest. The improvement of living conditions and the increase of the average life span have changed the situation. The clinical requirements for medical implants rise up substantially. Presently, it seems impossible to imagine the use of metallic implants in the human body without preliminary surface modification to modulate the interaction between the surrounding biological environment and the implant. The review highlights the most recent advances in the field of functional coatings formed on implants by the plasma electrolytic oxidation technology. Special attention is dedicated to the principles of surface modification of the commercially pure titanium, titanium nickelide, and Mg-Mn-Ce magnesium alloy. The advantages and disadvantages of the method and the characteristics of these materials are discussed from this point of view. Some aspects of this review are aimed at corrosion protection of implants with application of polymer materials.

Phosphoric acid (PA) is an important industrial chemical used as an intermediate in the fertilizer industry, for metal surface treatment in the metallurgical industry, and as an additive in the food industry. Wet-process PA (WPA) is produced by the attack of sulfuric acid (H 2 SO 4 ) on phosphate rock (PR). Other wet processes use HCl and posterior solvent extraction technology. The corrosivity of phosphate ores, during the production of WPA, depends on two main factors: the chloride content and the interaction between HF formed in the WPA reaction slurry with SiO 2 , Al 2 O 3 , and MgO present in the ore. Many forms of corrosion, mainly localized, are encountered in the PA production plants and facilities such as erosion-corrosion (EC), selective corrosion, pitting, stress-corrosion cracking, intergranular corrosion, and corrosion at high temperature. Laboratory and plant corrosion tests were performed to recognize the corrosion types; EC measuring instruments were developed, built, and applied. The PA industry is spread out worldwide in Europe, Asia, Africa and America, including countries that operate PR mines and produces PA, phosphatic fertilizers, and phosphate-based products. Cases of corrosion in PA industrial equipment and plants are presented and discussed, based on the authors’ experience and knowledge.

Electrochemical hydrogen permeation tests using pure Fe sheet specimens were performed under various galvanostatic hydrogen charging conditions commonly applied to tensile test specimens used for evaluation of hydrogen embrittlement property to obtain a guideline for efficient hydrogen charging method for a wide range of hydrogen content. Aqueous NaCl solutions containing varied concentrations of ammonium thiocyanate and a 0.1- m NaOH solution were used as electrolytes for relatively high and low hydrogen content, respectively. Addition of ammonium thiocyanate changes the mechanism of hydrogen evolution reaction and enhances hydrogen entry. By changing the concentration of ammonium thiocyanate and by changing cathodic current density, a wide range of hydrogen content can be covered. The hydrogen content in an AISI 4135 steel estimated from hydrogen permeation current density obtained for a pure Fe specimen was in good agreement with the hydrogen content experimentally measured by hydrogen thermal desorption analysis for the AISI 4135 steel. The hydrogen permeation current density data in various hydrogen charging conditions can be used as a reference for hydrogen charging of specimens.

Motivated to reduce the costs incurred by corrosion in material science, this article presents a combined model based on artificial neural networks (ANNs) to predict pitting corrosion status of 316L austenitic stainless steel. This model offers the advantage of automatically determining the pitting corrosion status of the material. In this work, the pitting corrosion status was predicted, with the environmental conditions considered, in addition to the values of the breakdown potential estimated by the model previously, but without having to use polarization tests. The generalization ability of the model was verified by the evaluation using the experimental data obtained from the European project called “Avoiding Catastrophic Corrosion Failure of Stainless Steel”. Receiver operating characteristic space, in addition to area under the curve (AUC) values, was presented to measure the prediction performance of the model. Based on the results (0.994 for AUC, 0.980 for sensitivity, and 0.956 for specificity), it can be concluded that ANNs become an efficient tool to predict pitting corrosion status of austenitic stainless steel automatically using this two-stage procedure approach.