In this investigation, the effect of microstructural changes and phase equilibria on corrosion behavior and hydrogen induced cracking (HIC) sensitivity of an API X65 pipeline steel was studied. For this purpose, heat treatment was performed at 850 °C, 950 °C, 1050 °C and 1150 °C to engineer the desired microstructure of this pipeline steel. Then, the microstructural evolution was performed by optical microscopy, and Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Corrosion properties were evaluated in H2S environment by open circuit potential (OCP), Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). As well, HIC sensitivity of the API X65 pipeline steel was assessed by hydrogen charging of the cathode and immediately conducting the tensile test. Microscopy analyses showed that the microstructure of the steel is ferritic-pearlitic together with the islands of martensite/austenite constituents. Increasing the heat treatment temperature reduced the amount of pearlite and increased ferrite grain size. It also stabilized the ferrite content. Corrosion results indicated that no active layer was formed on the surface of this pipeline steel. Also, increasing the heat treatment temperature increased the corrosion resistance and reduced sensitivity to micro-galvanic localized corrosion. As well, results suggested that the sensitivity to HIC in the API X65 pipeline was substantially increased with increasing the amount of pearlite and reducing the amount of ferrite; i.e. at lower heat treatment temperature.

Sensitivity to hydrogen induced cracking, and corrosion performance of an API X65 pipeline steel in H2S containing environment: influence of heat treatment and its subsequent microstructural changes

Influence of electrochemical hydrogenation parameters on microstructures prone to hydrogen-induced cracking

The present study is attempted to investigate the inﬂuence of multicomponent Ni-alloy (BNi-2) on the hydrogen embrittlement (HE) behavior of AISI 1018 steel by using cathodic protection and tensile test. The results show that the HE indexes (HEI) decrease notably when AISI 1018 steel is coated with BNi-2 alloy by DC sputtering process. This coating processes leads to decrease in HE susceptibility of the AISI 1018 steel, which can be rationalized to the enhancement in corrosion resistance and the decrease in hydrogen absorption of the AISI 1018 steel after coating.  The tensile strengths of bared samples were decreased with increasing charging time until 24 hours when stable at values 350 MPa. while the coated samples showed an increasement in the tensile strength from 570 MPa to 750 MPa. stabilization in strength at value of 600 MPa was observed after exceeding 48 hours. Also, the tensile test for uncoated specimens indicated a clear reduction on the modulus of elasticity compared with other coated ones.

https://qu.edu.iq/journaleng/index.php/JQES/article/download/842/669

Studying the effect of multicomponent nano-coating alloy on hydrogen embrittlement of AISI 1018 steel by gas-phase process

Simultaneously enhancing strength and hydrogen embrittlement resistance of pure iron via gradient microstructure

The exposure of metal surfaces to energetic particles originating for example from a plasma can lead to the formation of blisters. These features are caused by hydrogen-filled gas bubbles near the surface and can influence the diffusion and retention of hydrogen atoms in the bulk material during plasma exposure. No comprehensive theory of the underlying processes governing these effects has been developed so far. A major constraint to the investigation of blisters has been the effort that is required to identify and characterize a statistically relevant ensemble of blisters. Therefore, the analysis of a limited number of blisters in isolated observations before and after plasma exposure has been state of the art so far. In this article, a framework is presented that allows to automatically analyze blisters in image data with the aid of convolutional neural networks (CNNs) which are trained with artificial training data. It thereby resolves the limitations of existing analysis methods that prevented the large-scale and in-situ investigation of blistering up to now. Automated routines are used to identify and localize blisters, estimate important blister parameters such as size, and track individual blisters over time. Apart from discussing the principles underlying this approach and describing the implementation of the framework in detail, this article also presents first results acquired with a molybdenum sample that was exposed to a cold deuterium plasma. The results indicate a blister identification accuracy of the framework of more than 80% within the considered parameter ranges and overall demonstrate the feasibility of the approach in general.

Convolutional Neural Networks for the In-Situ Investigation of Blistering on Plasma-Exposed Metal Surfaces

The effect of surface roughness on hydrogen-induced blister behavior in pure iron was explored using optical microscopy and microcomputerized tomography. Hydrogen was introduced into the samples by electrochemical precharging methods with various hydrogen charging times. It is found that grinded surface exhibits higher roughness and compressive residual stress compared to those of polished surface. With increasing hydrogen charging time, hydrogen-induced blister height, blister width and blister area fraction increase, regardless of the grinded surface and polished surface. Further, hydrogen blister height and width of grinded surface are comparative to polished surface under the same hydrogen charging time. However, the blister area fraction and the number of blister on polished surface are considerably higher than the grinded surface, indicating that polished surface is more susceptible to the formation of blisters than that of grinded surface, both of surface and interior of the samples. This is dominantly rationalized in terms of the suppression effect of hydrogen invasion in grinded surfaces due to their higher residual compressive stress and higher dislocation density.

Jin Zhang

Papers

Effect of Surface Roughness on Hydrogen-Induced Blister Behavior in Pure Iron