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This paper aims to verify the inhibition of the hydrogen permeation effect of the coating and to quantitatively and qualitatively characterize the coating-induced stress.

By means of slow strain rate tensile testing (SSRT) in humid air, thickness measurement, fracture morphology, cross-section morphology and surface morphology, hydrogen content measurements, flow stress difference method.

The results demonstrate that the mechanism of the inhibition of hydrogen embrittlement by the coating is mainly attributed to the repression of hydrogen permeation and the additional coating-induced compressive stress.

It is proven that the micro-arc oxidation (MAO) coating does inhibit hydrogen entry into the alloy, and the stress induced by the MAO coating is compressive stress, which can restrain the hydrogen embrittlement of the alloy. Therefore, the mechanism of the inhibition of hydrogen embrittlement is dominated by the mechanisms of both hydrogen permeation inhibition and coating-induced stress.

The corrosion of buried steel pipelines is becoming more serious because of stress corrosion, stray current corrosion and other reasons. This paper aims to study the various alternating current (AC) interference densities on the stress corrosion cracking behaviors of X80 steel samples under cathodic protection (CP) in the simulated soil electrolyte environment by using an electrochemical method.

The change of corrosion rate and surface morphology of the X80 steel samples at various AC current densities from 0 to 150 A/m² or CP potential between −750 and −1,200 mV in the soil-simulating environment was revealed by the electrochemical methods and slow strain rate testing methods.

The results revealed that with the increase of interference density, the corrosion potential of the X80 steel samples shifted to the negative side, and the corrosion pitting was observed on the surface of the sample, this may cause a danger of energy leak. Moreover, the corrosion rate was found to follow a corresponding change with the stress–strain curve. Besides, with the introduction of the CP system, the corrosion rate of the X80 steel working electrode decreased at a low cathodic potential, while showed an opposite behavior at high cathodic potential. In this study, the correlation between AC stray current, cathodic potential and stress was established, which is beneficial to the protection of oil and gas pipeline.

Investigation results are of benefit to provide a new CP strategy under the interference of AC stray current corrosion and stress corrosion to reduce the corrosion rate of buried pipelines and improve the safety of pipeline transportation.

The purpose of this paper is to clarify the influence of the cathodic polarized potential on the stress corrosion cracking (SCC) susceptibility of X120 steel in a simulated acidic soil solution and the different SCC mechanisms at different cathodic polarized potentials.

The SCC behaviors of X120 pipe steels at various potentials were investigated in a simulated acidic soil solution by slow strain rate tensile tests, electrochemical impedance spectroscopy and surface analysis techniques.

The fracture surface of X120 steel stretched in air showed a ductile fracture. Both elongation and tensile strength of X120 steel in the simulated acidic soil solution decreased compared to that obtained in air. A slight cathodic polarization increased the elongation and tensile strength of X120 steel; therefore, the SCC susceptibility was lower at −0.65 V_SCE than that at OCP, anodic dissolution dominates the corrosion process. However, a strong cathodic polarization induced hydrogen embrittlement, decreasing elongation and tensile strength, therefore, the SCC susceptibility was highest at −1.1 V_SCE, and hydrogen embrittlement became the dominant process.

The paper provides an essential insight into the mechanism of pipeline SCC for X120 steel in acidic soil environments.

The purpose of this study is to develop the existence and mechanism of stress corrosion cracking (SCC) for A517 steel in marine environments.

Slow strain rate test (SSRT) and constant load tests were used to investigate the SCC susceptibility of A517 steel. In addition, the additive stresses caused by the corrosion film and hydrogen entering into steel were applied to reveal the fundamental mechanism of the SCC.

The SCC susceptibility increased due to anodic dissolution and additive stress caused by the corrosion-produced film under anode polarization. Furthermore, the SCC susceptibility increased with increasing cathodic polarization, which is due to the increased additional stress caused by hydrogen entering into the steel. However, when the cathode polarization further increased, the additional stress remained due to the constant hydrogen content, thus the SCC susceptibility did not vary. Moreover, the SCC susceptibility of A517 steel under an alternate immersion environment (AIE) was lower than that under a full immersion environment and the steel under the AIE with 0.5 W/D had the lowest SCC susceptibility.

The stress corrosion behaviors of A517 in marine environments under various conditions were systematically analyzed.

The purpose of this study is to investigate the effect of ferrite on hydrogen embrittlement (HE) of the 17-4PH stainless steels.

The effects of ferrite on HE of the 17-4PH stainless steels were investigated by observing microstructure and conducting slow-strain-rate tensile tests and hydrogen permeability tests.

The microstructure of the ferrite-bearing sample is lath martensite and banded ferrite, and the ferrite-free sample is lath martensite. After hydrogen charging, the plasticity of the two steels is significantly reduced, along with the tensile strength of the ferrite-free sample. The HE susceptibility of the ferrite-bearing sample is significantly lower than the ferrite-free steel, and the primary fracture modes gradually evolved from typical dimple to quasi-cleavage and intergranular cracking. After aging at 480°C for 4 h and hydrogen charging for 12 h, the 40.9% HE susceptibility of ferrite-bearing samples was the lowest. In addition, the hydrogen permeation tests show that ferrite is a fast diffusion channel for hydrogen, and the ferrite-bearing samples have higher effective hydrogen diffusivity and lower hydrogen concentration.

There are a few studies of the ferrite effect on the HE properties of martensitic precipitation hardening stainless steel.

The purpose of this paper is to develop new types of anchor bolt materials by adding corrosion-resistant elements for alloying and microstructure regulation.

Three new anchor bolt materials were designed around the 1Ni system. The stress corrosion cracking resistance of the new materials was characterized by microstructure observation, electrochemical testing and slow strain rate tensile testing.

The strength of the new anchor bolt materials has been improved, and the stress corrosion sensitivity has been reduced. The addition of Nb makes the material exhibit excellent stress corrosion resistance under –1,200 mV conditions, but the expected results were not achieved when Nb and Sb were coupled.

The new anchor bolt materials designed around 1Ni have excellent stress corrosion resistance, which is the development direction of future materials. Nb allows the material to retain its ability to extend in hydrogen-evolution environments.

This study aims to study the formation mechanism of micro-arc oxidation (MAO) coating on AZ31 magnesium alloy and how the annealing process affects its corrosion resistance.

This study involved immersion experiments, electrochemical experiments and slow strain rate tensile experiments, along with scanning electron microscopy, optical microscopy observation and X-ray diffraction analysis.

The findings suggest that annealing treatment can refine the grain size of AZ31 magnesium alloy to an average of 6.9 µm at 300°C. The change in grain size leads to a change in conductivity, which affects the performance of MAO coatings. The MAO coating obtained by annealing the substrate at 300°C has smaller pores and porosity, resulting in better adhesion and wear resistance.

The coating acts as a barrier to prevent corrosive substances from entering the substrate. However, the smaller pores and porosity reduce the channels for the corrosive solution to pass through the coating. When the coating cracks or falls off, the corrosive medium and substrate come into direct contact. Smaller and uniform grains have better corrosion resistance.

This paper aims to make clear the sensitive zone of subsea pipeline to stress corrosion cracking (SCC) under a disbonded coating.

The change of microenvironment under a disbonded coating in artificial seawater was analyzed by using a rectangular crevice cell. The SCC behavior of subsea pipeline was studied by slow strain rate tensile tests.

The microenvironment at the crevice bottom exhibits obvious acidification, Cl- aggregation and cathodic protection potential (CP) rise. Accordingly, the susceptibility of X70 steels to SCC is high due to the intensive anodic dissolution effect. At the opening, hydrogen atom can access into the steel and induce hydrogen embrittlement effect on account of the applied over-protected CP potential, resulting in a relatively high susceptibility to SCC. The corrosiveness of the microenvironment at crevice middle, however, is mild with proper CP potential; thus, the susceptibility of X70 steel to SCC here is lower than that obtained at the opening and the crevice bottom.

A rectangular crevice cell is built to survey the microenvironment evolution under a disbonded coating in situ. The sensitive zone of subsea pipeline to SCC under a disbonded coating is clarified.

The purpose of this paper is to demonstrate the effect of δ-ferrite on the susceptibility to hydrogen embrittlement of type 304 stainless steel in hydrogen gas environment.

The mechanical properties of as-received and solution-treated specimens were investigated by the test of tensile and fatigue crack growth (FCG) in 5 MPa argon and hydrogen.

The presence of δ-ferrite reduced the relative elongation and the relative reduction area (H₂/Ar) of 304 stainless steel, indicating that δ-ferrite increased the susceptibility of hydrogen embrittlement in 304 stainless steel. Moreover, δ-ferrite promoted the fatigue crack initiation and propagation at the interface between δ-ferrite and austenite. The FCG tests were used to investigate the effect of δ-ferrite on the FCG rate in hydrogen gas environment, and it was found that δ-ferrite accelerated the FCG rate, which was attributed to rapid diffusion and accumulation of hydrogen around the fatigue crack tip through δ-ferrite in high-pressure hydrogen gas environment.

The dependence of the susceptibility to hydrogen embrittlement on δ-ferrite was first investigated in type 304 steel in hydrogen environment with high pressures, which provided the basis for the design and development of a high strength, hydrogen embrittle-resistant austenitic stainless steel.

This paper aims to understand the effect of water jet cavitation peening (WJP) on stress corrosion cracking (SCC) behavior of alloy 600 and alloy 182 in high temperature water.

Surface and cross-section morphology, grain boundary microstructure, residual stress and strain distribution, hardness and surface roughness in water jet cavitation peened alloy 600 and alloy 182 were characterized.

A superior stress corrosion cracking resistance was obtained in 600MA, which can be attributed to the formation of the ultrafine grain layer and the higher magnitude residual compressive stress.

Relationship between WJP-induced microstructure and stress state change and SCC susceptibility was conducted. It could provide a theoretical basis for developing application of WJP in nuclear power plants.