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Alternating current (AC) corrosion is a type of corrosion that occurs in buried pipelines under AC stray current interference, which can increase the hydrogen embrittlement sensitivity of pipelines. However, rare research works have been conducted on the hydrogen permeability characteristics of pipeline steel under AC stray current interference. The purpose of this paper is to study hydrogen permeation behavior of X80 steel under AC stray current interference.

In this paper, the hydrogen permeation behavior of X80 steel under AC interference is studied by AC hydrogen charging experiment in a dual electrolytic cell. The relationship between hydrogen evolution rate and hydrogen permeation flux is studied using the gas collection method. The difference between AC hydrogen permeability and direct current (DC) hydrogen permeability is also discussed.

The anodic dissolution caused by AC corrosion promotes the chemical desorption reaction of the adsorbed hydrogen atoms on the surface, reducing the hydrogen atom absorption ratio by 70%. When the AC is smaller than 150░ A/m², the hydrogen permeation process is controlled by the hydrogen atom generation rate, and the hydrogen permeation flux increases with the increase in hydrogen atom generation rate. When the AC exceeds 400░ A/m², the hydrogen permeation process is controlled by the absorption ratio. The hydrogen permeation flux decreases with the decrease in the absorption ratio. Under AC interference, there is a maximum hydrogen permeation flux that linearly correlates to the H⁺ concentration in the solutions.

The high-strength steel is very sensitive to hydrogen embrittlement, and X80 steel has been widely used in oil and gas pipelines. To date, no research has been conducted on the hydrogen permeation behavior of pipeline steel under AC interference, and the hydrogen permeability characteristics of pipeline steel under AC interference are not clear. The research results of this paper are of great significance for ensuring the intrinsic safety of high-strength pipelines under AC stray current interference.

This paper aims to study the effect of temperature on the process and kinetic parameters of the hydrogen evolution reaction of X80 under cathodic protection (CP) in 3.5% NaCl solution.

Potentiodynamic polarization combined with the hydrogen permeation test is used to analyze the hydrogen evolution reaction (HER) process and the rate-determining step for which is diagnosed through the electrochemical impedance spectrum method. Then, the influence of temperature on kinetic parameters of HER can be known from the results obtained by using the Iver-Pickering-Zamenzadeh model for data analysis.

The results show that the HER proceeds through Volmer–Tafel route with the Volmer reaction acting as the rate-controlling step; Increasing temperature gives a higher activity of the HER on X80, it also accelerates the hydrogen desorption and diffusion of hydrogen into the metal.

There exist few studies on the topic of how temperature affects the HER process. It is imperative to conduct a relevant study to give some instruction in cathodic protection system design and this paper fulfills this need.

Zinc pigments corrode in aqueous alkaline paint media (e.g., waterborne anticorrosive paints) with the evolution of hydrogen. Paint resins inhibit this corrosion reaction at a pH value of 8 more effectively than at pH10. An increase of resin addition effects a decrease of hydrogen evolution (i.e., corrosion inhibition increases). The corrosion reaction of spherical zinc dust can be nearly completely inhibited with the addition of a certain epoxy ester resin (EPE 1). The epoxy ester resin looses its corrosion inhibiting properties after film formation, because of loosing its mobility, which seems to a be requirement for corrosion inhibition. So, zinc dust is inhibited in the liquid waterborne paint but still shows its sacrificial action in the solid primer coating.

In aqueous alkaline ink media aluminium pigments react with the evolution of hydrogen, whereas the more noble copper and brass pigments react by the absorption of oxygen, which can be measured gas‐volumetrically. These different corrosion reactions can be inhibited with addition of certain binders for printing inks, such as styrene‐maleic acid resins, maleic resins and to some extent styrene‐acrylate resins. So, certain ink resins inhibit corrosion reactions of different noble metal pigments in a reducing hydrogen atmosphere (aluminium) as well as in an oxidizing oxygen atmosphere (copper and brass). The overall best resin is that with the lowest acid number. Atomic absorption spectroscopy measurements showed that a lower acid number pruduces a lower solubility of copper and zinc in the medium.

Selective laser sintering (SLS) is a solid freeform fabrication process whereby a part is built layerwise by scanning a powder bed. The processability of metal powder varies depending on the state of the powder prior to SLS. A powder thermal pre‐treatment was developed which involved degassing the powder at an elevated temperature in a vacuum. Without powder thermal pre‐treatment, the powder may flow poorly and may “ball” or form molten clumps during the laser exposure rather than wetting into the present and previous layer. These effects result in SLS parts with poor surface finish, mechanical properties and density. The purpose of this study was to identify for titanium alloy powder the mechanisms responsible for the improvements obtained after powder thermal pre‐treatment and to optimize the thermal excursion.

To investigate the inhibitive effect of Delonix regia extracts to reduce the corrosion rate of aluminium in acidic media. The study was a trial to find a low cost and environmentally safe inhibitor to reduce the corrosion rate of aluminium.

The inhibition efficiency was evaluated using the hydrogen evolution technique at 30°C. The mechanism of adsorption inhibition and type of adsorption isotherm was characterised from trends of inhibition efficiency and kinetic data.

Delonix regia extracts inhibited the corrosion of aluminium in hydrochloric acid solutions. The inhibition efficiency increased with increasing concentration of the inhibitor but decreased with increase in exposure time. The acid extracts (hydrochloric acid seeds extract (HSE) and hydrochloric acid leaf extract (HLE)) were found to be more effective than the ethanolic extracts (ethanol seeds extract (ASE) and ethanol leaves extract (ALE)) and the inhibition followed the order: HSE (93.6 per cent) > HLE (83.5 per cent) > ASE (63.9 per cent) > ALE (60.4 per cent). The low negative values of ΔG_ad: −20.14 kJ mol⁻¹ for HSE, −18.08 kJ mol⁻¹ for HLE, −15.96 kJ mol⁻¹ for ASE and −15.12 kJ mol⁻¹ for ALE, as calculated from the Langmuir isotherm, indicated that the inhibitor molecules adsorbed onto aluminium by a physiosorption‐based mechanism. A first‐order type of reaction mechanism was obtained from the kinetic treatment of the H₂ gas evolution data.

Further investigations involving electrochemical studies such as polarization method should shed further light on the mechanistic aspects of the corrosion inhibition.

This paper provides new information on the possible application of Delonix regia as an environmentally friendly corrosion inhibitor under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coatings.

Aluminium and zinc pigments react in aqueous alkaline media (e.g. water‐borne paints) by the evolution of hydrogen which can be measured gasvolumetrically. Certain organic heterocycles are well‐known corrosion inhibitors for different metals. The six different heterocyclic compound which were examined inhibited the corrosion reaction of zinc pigment in aqueous alkaline media. The most efficient inhibitors were 1H‐benzotriazole at pH 8 and 10 and 2‐(5‐aminopentyl)benzimidazole only at pH 10. In contrast, with addition of all heterocycles there was no corrosion inhibition on aluminium pigment. This complete difference in the corrosion inhibiting effect of the heterocycles with respect to the two different metal pigments can be explained with Pearson’s “Principle of Hard and Soft Acids and Bases”.

A lamellar zinc pigment reacts in aqueous alkaline media (e.g. water‐borne paints) with the evolution of hydrogen. This corrosion reaction can be inhibited by certain surfactants. The most important structural part of the examined surfactants is the hydrophilic group; only anionic phosphate or phosphonate hydrophilic groups are effective corrosion inhibitors. Surfactants with carboxylate, sulfonate, amphoteric, cationic and non‐ionic hydrophilic groups are ineffective. There seems to be also an influence of the hydrophobic group of the surfactants because a partial ester of phosphoric acid with a fluorinated hydrophobic group was the most effective corrosion inhibitor in this study.

The purpose of this paper is to investigate the corrosion inhibitive properties of extracts from mature leaves of Combretum bracteosum for the corrosion of mild steel in H₂SO₄.

Acid extracts from mature leaves of Combretum bracteosum are used as mild steel corrosion inhibitors in various tests at 30‐60°C. The gravimetric and hydrogen evolution (via the gasometric assembly) measurements are conducted.

The mature leaves of Combretum bracteosum extracts inhibit the corrosion of mild steel in H₂SO₄ to reasonable extent. Inhibition efficiency increases with the plant extracts concentration and decreases with temperature. Phenomenon of physical adsorption is proposed as the mechanism of inhibition and the Frumkin adsorption isotherm obeyed. Kinetic parameters for the dissolution of mild steel in H₂SO₄ solutions are calculated.

Mature leaves extract from Combretum bracteosum can be used in chemical cleaning and pickling processes.

The research provides new information on the possible use of the leaves of Combretum bracteosum as an eco‐friendly corrosion inhibitor of mild steel in H₂SO₄.

Galvanic corrosion It is commonly held that it is the electrochemical potential between two surfaces that is the controlling factor for the rate of corrosion. Table 1.2 in chapter one of this series lists the standard oxidation potentials. However, the difference between the potentials of the two metals plus the difference in the e.m.f. due to the concentration of ions is the reversible electrochemical potential, which only applies when there is no current flowing. The degree of corrosion that occurs is based on the potential difference existing when there is a known current flowing. Thus the baser of two connected metals can be extremely corrosion‐resistant, even if the potential difference is quite large, provided at least one of them has good polarisation characteristics. Metals that are particularly damaging to ferrous metals not only have a very low potential, but are also to all practical purposes insoluble in the corrosive environment around the steel. Thus it is that one of the worst is copper.