The results of using a nitrogen protection system for 15 years in a sour crude oil storage park equipped with Hazmat class II and III vertical storage tanks with a stationary roof without pontoons are analyzed. Under nitrogen protection conditions, the rate of localized corrosion of the inner surface of the roof of raw and commercial crude oil storage tanks is 0.013–0.015 mm/year, which is ∼100 times lower than the rate of corrosion under natural gas phase conditions inside the tank. Continuous operation of the nitrogen protection system ensures fire and explosion safety of the tanks. Interruptions in the nitrogen protection do not have any practical effect on the efficiency of through perforation of the roof until the end of the regulated service life of the tanks, but increase fire and explosion hazard due to the formation of pyrophoric corrosion deposits.

Creation of a nitrogen atmosphere within a tank gas space with sulfurous oil leads to a reduction in steel corrosion rate and pyrophoric deposit formation rate. A reduction in oxygen content in the gas phase to a level of 3 vol.% or less makes it possible to avoid pyrophoric iron sulfide formation.

The state of various areas of the surface of a test melt of carbon steel containing 0,2% of carbon and 0,75% of chrome was analyzed by means of methods of energy-dispersive analysis and scanning tunneling microand spectroscopy. Without corrosion-active sulfide inclusions, the local corrosion spots are inert chromium carbides and oxides of aluminum. Spots of localized corrosion occur in places where above mentioned carbides and oxides brake the surface due to accelerated etching of the metal/inclusion boundary, where are seen a rapid increase of the tunneling activity.

In neutral (рН 7,55) and alkalescent (pH= 8,74) chloride-containing solutions there was examined the electrochemical corrosion behavior of carbon steel model containing up to 1,05 % Cr. It is shown that the chromium containing in carbon steel hampers their passivation, but microalloying it with titanium has a beneficial effect on their passivity and pitting resistance. The view is suggested that the observed effect of chromium and titanium on passivity and pitting resistance of low-alloy steels is connected with the change of the energy state of the surface of the metal.

In neutral (рН 7,55) and alkalescent (pH= 8,74) chloride-containing solutions there was examined the electrochemical corrosion behavior of carbon steel model containing up to 1,05 % Cr. It is shown that the chromium containing in carbon steel hampers their passivation, but microalloying it with titanium has a beneficial effect on their passivity and pitting resistance. The view is suggested that the observed effect of chromium and titanium on passivity and pitting resistance of low-alloy steels is connected with the change of the energy state of the surface of the metal.

Method of electrochemical noise is adapted to determination of carbon steels resistance to pitting and ulcerous corrosion on example of carbon steel 20 of industrial smelting. At the electrochemical tests the pitting formation should be prevailing process proceeding on the metal surface. When the indicated condition is kept, the electrochemical noise intensity is proportional to maximum depth and density of pitting and can be used as criterion of metal resistance against local corrosion.

FIELD: instrumentation. SUBSTANCE: proposed device consists of corroding metal plates of different thickness smaller than that of metal structure wall made of the same material as said metal structure. Note here that one side of every plate faces the corroding medium. Opposite side of the plate is jointed electrically and mechanically to protector of the same sizes as said plate and made of metal with more negative potential of corrosion in said corroding medium than metal plate. Every plate and every protector make transducers electrically isolated one from another while protector is isolated from said medium by antirust dielectric coating. Note here that every transducer is fitted in case made of antirust dielectric material. Said every transducer stays in electric contact with metal structure via set of switches and ammeter. EFFECT: reliable remote diagnostics irrespective of pressure, temperature, medium transfer and structure type. 2 cl, 1 dwg, 1 tbl

Changes in the background intensities in giant Raman scattering spectra for silver surface in silver sulfate solutions, appeared at the varying of the silver galvanostatic deposition current near the silver electrode equilibrium potential, are measured. The connection between the silver adatom concentration and the intensity of the giant Raman scattering background allowed determining the absolute cross-section for the giant Raman scattering involving adatom-metal complexes: 1.02 × 10−27 cm2/adatom in sulfate solutions.

The measurements of electroreflection of freshly generated metal surface in aqueous solution of electrolyte allowed to determine duration of the formation of metal-water adsorption complexes. The role of water molecules and OH − ions in dissolution of iron group metals is elucidated.

Analysis of results of steady-state potentiostatic measurements on iron in the neutral and nearly neutral borate solutions is complicated by the fact that the metal is in the state of active-passive transition near the free-corrosion potential. This difficulty is overcome using the method of neural network simulation. The study of the behavior of neural-network model shows that chloride and sulfate ions can promote or inhibit iron dissolution depending on their concentration and the pH value of solution. The ambiguous effect of anions is explained by the fact that, when they are adsorbed at the metal, they prevent its cations from passing to the solution, and, entering into the metal-water adsorption complexes, they assist the decomposition of complexes thus promoting the dissolution. Sulfate ions, compared with chloride ions, are, probably more adsorption-active with respect both to iron and to water adsorbed on it.

In neutral and close-to-neutral solutions, which contain no surface-active substances, iron dissolves via a two-step scheme. The transfer of the first electron across the interface involves water molecules that dissociate during the adsorption; the transfer of the second electron limits the process under steady-state conditions. In parallel, a passivator, namely, adsorbed oxygen is formed via a similar scheme. The passivator is removed from the surface due to its chemical reaction with hydroxonium ions, water molecules, or hydroxide ions. The process is adequately described by a mathematical model based on an assumption that the metal dissolves from an energy-uniform surface free from passivating species.

The causes of the formation and the conditions for self-ignition of pyrophoric deposits in the vapor zone of tanks during the storage of sour crude oil were considered. It was demonstrated that creation of an oxygen-free atmosphere inside oil storage tanks seems to be the most promising approach to prevention of self-ignition and corrosion. This approach was effected in practice by supplying oil tanks with nitrogen from a membrane gas separator.

A jumpwise improving of the passivation ability and pitting-resistance of the Fe-(8–13)% Cr-(0.32–2.7)% Si alloys upon surpassing the limit of ∼14–15 at % by the chromium and silicon summary concentration is found. It is suggested that the nature of the critical summary concentration C Cr + C Si is identical to that in Fe-Cr binary alloys; it is caused by the silicon building-in to the alloy’s crystal lattice and its substitution for chromium in the statistical proportion to its atomic part in alloys. When the summary concentration C Cr + C Si approaches ∼14–15 at %, each elementary cell in the Fe bcc lattice must necessarily contain either a Cr atom or the proportional number of Si atoms. The improved passivation ability and pitting-resistance of the Fe-Cr-Si alloy, compared with the Fe-Cr alloys, is explained by the fayalite formation at the alloy surface.

In neutral aqueous media containing 0.4 g/l [Cl−], steel 04X14C2б, in the form of mono-or bimetal with a weld, retains its steady passive state unlike steel 08X13. This is due to stabilizing the ferrite phase by silicon and the absent tendency to the grain growth and precipitation of chromium carbides when heated below 1025°C because of modifying with niobium. In aqueous media close to neutral which contain ∼10 g/l [Cl−], the cladding layer of X18H10T steel, in contrast to the massive metal of the same composition, is insusceptible to pitting because of the absence of manganese sulfide in its structure due to its low sulfur content insufficient for the manganese sulfide concentration in the metal to reach the solubility product.

Regularities of the electrochemical dissolution of freshly formed surface (FFS) of iron and nickel are similar as a whole, but exhibit a number of distinctions. At an oxidation stage Me0-Me+, a water molecule chemisorbs to form a surface complex with charge transfer; however, a mean fraction of transferred charge in the complex of nickel (0.8) is significantly higher than that of iron (0.5). In weakly acid sulfate solutions (pH 1.7–3.2), the iron FFS dissolution is predominantly inhibited by hydrogen atoms formed by the discharge of hydroxonium ions and adsorbed at the dissolution centers. On nickel at pH > 2.7, the inhibition is caused by the formation of adsorbed oxygen corresponding to more positive potentials in a range of active nickel dissolution.

Potentials stabilized at the anode and cathode of a differential aeration cell (DAC) under free corrosion conditions, electric contact, and cathodic polarization are analyzed. It is shown that the soil conductivity limits the possibility of cathodic protection. The shallow pit formation at the cathode and pitting at the anode are the main corrosion types in the half-cells. The rate of development of local corrosion centers on the surfaces of both half-cells is virtually independent of the conditions of DAC operation.