Papers by Keyword: Local Corrosion

Abstract: Aspects of the development of local corrosion on the metal surface under the influence of aggressive media containing chloride ions are presented. The main mechanisms leading to the formation and development of local damage of the surface of metals are described. The process of electrochemical corrosion of steel under the influence of chloride-containing medium is experimentally investigated. By constructing corrosion diagrams, the main indicators of steel corrosion in a 10% sodium chloride solution were determined, which allows one to judge the rate of development of corrosion processes with local damage to the protective coating and the degree of steel resistance depending on the aggressiveness of the medium. It is shown that protective coatings, such as modified phosphate and oxide-phosphate films, prevent the penetration of an aggressive medium to the surface of the protected metal and, accordingly, the anodic dissolution of the metal.

Abstract: The reason for perforation leakage of gathering pipeline in an oilfield was investigated by size measurement, mechanical properties, metallographic structure, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). The results showed that the failure form of the spirally submerged arc welded pipe (SAW) was the corrosion perforation caused by local corrosion. The main cause of corrosion perforation was due to the existence of chlorine ion, H₂O and O₂ in the pipeline transportation medium. A large cathode and small anode electrode corrosion formed in the pipe marking area and the base metal, which eventually led to the perforation of the steel pipe.

Abstract: This work deals with localized electrochemical impedance spectroscopy (LEIS) which is an improved technique of the commonly used electrochemical impedance spectroscopy (EIS). Thanks to modern structural solutions, the LEIS technique ensures local impedance measurement. Therefore, it is used in the research into point corrosion, such as the pitting corrosion, and in the research into protective coatings or into alloys including alloy steels. This review paper presents the basic theory and the usability of the LEIS based on the literature on the newest research in the field of corrosion.

Abstract: In the two last decades, the Electrochemical Microcell Technique (EMT) was used in various electrochemical surface investigations. The diameter of microcapillaries was in the range between few and few hundred microns. This technique was commonly used in corrosion research. Indeed, metallic alloys exhibit a complex microstructure consisting of different metallic and intermetallic phases, inclusions, precipitates... The use of microcapillaries based techniques like EMT makes possible to perform local electrochemical measurements in individual phases. Therefore, it was possible to get information about the behavior of a single grain, inclusion, precipitate... From these information, precursor sites can be identified and criteria leading to corrosion can be proposed.

Abstract: Influences of temperature and CO₂ partial pressure on CO₂ corrosion behaviors of 25CrMnVA steel were investigated in the simulated oil field environments. The corrosion rates were measured under high temperature and high pressure condition. SEM, EDS and XRD were used to analyze the morphologies and characteristics of corrosion scales on the steels. The results shows that the corrosion rates of 25CrMnVA steel change little below 65°C, the corrosion feature is uniform corrosion. The corrosion rates increase rapidly after 65°C, mesa corrosion is found on the surface of steel. The corrosion rates decrease firstly and increase subsequently with the rising of CO₂ partial pressure, and the minimal corrosion rate presents near CO₂ critical pressure. The compactness of corrosion scale improves with the increase of CO₂ partial pressure below 8MPa, which causes uniform corrosion rate reduced. Under supercritical CO₂ condition, the local defects in the surface of corrosion scale increase, and the compactness of corrosion scale reduces,which cause the increase of corrosion rate sharply. The corrosion rate and corrosion morphology are closely related to the state of corrosion scale.

Abstract: Hysteretic loops were used to study the influence of several ions in sedimentary water of oil tank on local corrosion at the bottom of crude oil tank, which were measured by the electrochemical station CHI660. The results indicated that the pitting increased firstly and then decreased with the increasing of the concentrations of each ion. The most serious pitting corrosion occurred under the following condition: the concentration of Cl-, SO42-, HCO3-, Mg2+, Ca2+ were 10.0 g/L, 1.0 g/L, 0.75 g/L, 0.35 g/L, 0.2 g/L, respectively.

Abstract: In this work, the Scanning Reference Electrode Technique (SRET) was used to visualise the pyrite corrosion by atmospheric oxygen and its inhibition by a thymol derivative. SRET has the advantage over the potentiostatic and galvanostatic techniques of enabling in situ operation without imposing any potential or current to the sample under study. SRET revealed that the inhibiting effect is effective only if the sample is oxidised beforehand. It also revealed that pyrite corrosion by oxygen is a localised process whereas that by Fe(III) is not local, thus the oxidation of pyrite by atmospheric oxygen is not only due to the oxidative role of Fe(III). Adsorption of oxygen plays probably a determining role. Studies are now carried on to evidence the intervention of galvanic processes or catalysis phenomena occurring during the corrosion of natural conducting minerals and industrial wastes. Their aim is to better understand the mechanisms and to propose remediation processes.

Abstract: The pitting corrosion behavior of sintered SUS 444 stainless steels (P/M specimens) with different kinds of porosity ratios of 13.3, 9.11 and 6.88 % was studied in an aqueous solution containing MgCl2 compared with a conventionally processed SUS 444 stainless steel(I/M specimen). The pitting corrosion potential decreased almost linearly as porosity ratio increased, and the I/M specimen showed the best resistance against the initiation of pitting corrosion. The pitting corrosion morphology by SEM observation showed that more small pits were observed on the specimen with larger porosity ratio while less number but larger diameter pits were observed on the specimen with smaller porosity ratio, and it was also confirmed that the I/M specimen had the least number but the largest and deepest pits.