α + β Ti6Al4V samples were exposed to a phosphate buffer saline (PBS) solution containing 1 M of H2O2 for short durations (30 min) to investigate the initial stage of the β phase dissolution. Electrochemical impedance spectroscopy (EIS) measurements and post-mortem scanning electron microscopy (SEM) analysis of the samples revealed randomness in the initiation of β phase dissolution. Bright-field transmission electron microscopy (BF-TEM) imaging and scanning kelvin probe force microscopy (SKPFM) measurements suggested a galvanic coupling between the α and β phases

This work aims to assess the susceptibility to stress corrosion cracking (SCC) of additively manufactured (AM) 316L stainless steel by laser-based power bed fusion (PBF-LB) and compare its performance with conventional manufacturing (CM), i.e. wrought 316L. Also, the influence of different surface conditions was analyzed. Potentiodynamic polarization tests in artificial seawater were used to obtain electrochemical properties, such as pitting breakdown potential (E<inf>bd</inf>) and corrosion potential (E<inf>corr</inf>). Stress corrosion cracking susceptibility was measured using U-Bend specimens, using concentrated artificial seawater droplets, simulating non-rinsing atmospheric conditions in marine environments. The specimens were exposed to temperatures between 40 and 60 °C and relative humidity of 40 %. For the AM specimens, two surface conditions were tested: as built and after machining process. A higher threshold temperature was observed for 316L-AM, indicating a better SCC resistance, than the 316L-CM, hence L-PBF can be used as an alternative manufacturing route for replacing 316L-CM as better properties were achieved. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and superficial residual stress measurements were used to aid the discussion of the SCC results. These tests revealed better passive layer properties in the AM material and formation of strain-induced martensite in the CM after bending, leading to higher residual stress

With the international drive to deploy green energies and decarbonized intermediates in the place of fossil fuel sources, a large number of developed countries are actively preparing for a future where hydrogen plays a strategic role as an energy storage medium. Producing and using hydrogen requires the rapid expansion of a dedicated, economically viable industrial sector. Nevertheless, questions on how to safely store, transport and distribute hydrogen remain an important priority today. In countries with existing natural gas transport grids, the possibility to retrofit these networks to store and transport hydrogen-natural gas blends is being studied. A key challenge is to evaluate how pressurized H2 would interact with steel structures with regards structural embrittlement of the latter, with a view to exploiting existing transport infrastructures for storage and transport applications. In this work, we evaluate the H2-performance of a non-hydrogen service ×65 pipeline steel. The cracking susceptibility of this steel grade has been evaluated at 100 bar H2 using slow strain rate testing, Constant strain testing and fracture toughness measurements. Accompanying hydrogen permeation tests under pressure provide diffusion data and elucidate the discussion. Exposures were carried out in dry or wet H2 and with or without H2S contamination at levels representative of biogas. The results underline that the impact of dry or wet hydrogen on this grade are moderate. The presence of traces of H2S together with humidity could risk seriously degrading the mechanical performance of the ×65 steel grade. © 2023 The Authors

Dense buried pipelines network, such as in implemented in parallel, can be installed in different process and storage mills, such as geological gas and hydrocarbon storages. Their corrosion resistance is ensured by a combination of organic coating and cathodic protection (CP). For maintenance operation on a specific pipeline, the CP can be turned off for safety reasons. Thus, the operated pipeline can be affected by CP influence from other surrounding protected ones. This phenomenon is supported in the field by different pigging inspections, highlighting local corrosion induced by output stray current on coating defects. In the literature, many studies focused on CP influences by finite and/or boundary element modeling. However, usually the foreign structures considered (under influence) are limited to bare steel or fully coated pipeline. Moreover, most of these studies are not confronted with experimental works. To our knowledge, the actual influence between the different pipelines is not much documented in the literature and not quantified. In this study, an experiment consisting in 3.00 x 1.80 x 0.80 m sand tank, equipped with 4 full scale parallel pipelines, with 17 model defects were realized. The model defects reproduce uniformly degraded coating and local defects. The experimental work allows i) measuring the DC influence under different CP configurations, and ii) providing stray current data for finite element modelling (FEM). The FEM was performed in a two steps i) a CP distribution in terms of current demand and electric field on protected pipelines, and ii) application of this electric field to the foreign pipeline. The good agreement obtained allows a validation the proposed approach and globally assess the riskier scenario in terms of nature of the defect, applied CP and soil environment.

The deliquescence of the corrosion species produced by nuclear waste incineration, in particular ZnCl2, makes wet corrosion possible even in dehumidified atmosphere complicating the corrosion risk management of the equipment. A specific cyclic corrosion test was used to assess the compatibility of corrosion resistance alloys to such conditions. Thereby, AISI 316 L welds resisted somehow to pitting but experienced severe stress corrosion cracking, while UR66™ showed only pitting in the heat affected zone. Hastelloy® C22 exhibited better performance, with localized corrosion only in the fusion zone, that was greatly influenced by the composition of the filler materials and welding techniques.

Additive manufacturing (AM) allows for optimized part design, reducing weight compared to conventional manufacturing. However, the microstructure, surface state, distribution, and size of internal defects (e.g., porosities) are very closely related to the AM fabrication process and post-treatment operations. All these parameters can have a strong impact on the corrosion and fatigue performance of the final component. Thus, the fatigue-corrosion behavior of the 3D-printed (L-PBF) AlSi10Mg aluminum alloy has been investigated. The influence of load sequence (sequential vs. combined) was explored using Wohler diagrams. Surface roughness and defects in AM materials were examined, and surface treatment was applied to improve surface quality. The machined specimens showed the highest fatigue properties regardless of load sequence by improving both the roughness and removing the contour layer containing the highest density of defect. The impact of corrosion was more pronounced for as-printed specimens as slightly deeper pits were formed, which lowered the fatigue-corrosion life. As discussed, the corrosion, fatigue and fatigue-corrosion mechanisms were strongly related to the local microstructure and existing defects in the AM sample.

Steels with high mechanical performance are prone to hydrogen embrittlement and environmental assisted cracking. Under atmospheric corrosion conditions, the source of hydrogen can be the steel corrosion process itself or galvanic coupling with a metallic coating. Electrochemical behaviour of Press Hardened Steel (PHS) under electrolyte films of different thicknesses using local electrochemical techniques was studied on a fundamental level. Scanning Vibrated Electrode Technique (SVET) was applied to study the evolution and localization of the corrosion process during PHS immersion in NaCl electrolyte. Kelvin Probe (KP) was used as a reference electrode to obtain cathodic and anodic polarization curves on PHS surfaces which were covered by thin electrolyte films (60 to 500 µm) of 0.1 M NaOH and 0.6 M NaCl. For both electrolytes, a strong increase in the oxygen reduction rate due to the decreasing of electrolyte thickness has been clearly demonstrated. Data are correlated well with a theoretical plot determined by Nernst-Fick equation. The influence of the rust layers on the kinetics of corrosion reactions under thin electrolyte films was investigated using KP. © 2023

The atmospheric corrosion of high-strength steels can lead to hydrogen absorption directly linked to hydrogen embrittlement or delayed fracture phenomena. A scanning Kelvin probe (SKP) and electrochemical permeation technique (EPT) were applied to correlate the potential of an oxidized surface with the flux of hydrogen across a thin steel membrane. The side of the membrane opposite the corroding or electrochemically charged area was analyzed. The potential drop in the oxide was calibrated in terms of surface hydrogen activity, and SKP can be applied in situ for the mapping of hydrogen distribution in the corroding metal. A very low flux of hydrogen can be characterized and quantified by SKP, which is typically observed under atmospheric corrosion conditions. Therefore, hydrogen localization that drives steel durability under atmospheric corrosion conditions can be evaluated.

Scanning Kelvin probe (SKP) can be applied for mapping of subsurface hydrogen in steels. The good spatial resolution is combined with poor quantification. Controversy, the electrochemical permeation technique (EPT) is extremely sensitive to hydrogen flux but has low spatial resolution. Thus, a local hydrogen quantification method using SKP measurements calibrated by EPT was developed. The fixed amount of hydrogen flux in mild steel membrane was obtained by cathodic polarization and was detected using the two methods. A semi-logarithmic relationship between SKP potential drop and the hydrogen sub-surface concentration underneath of the corroding surface was established. SKP quantification was applied for mapping the subsurface hydrogen in steel corroding under various atmospheric corrosion conditions. 

Hydrogen, due to corrosion processes, can degrade high strength steels (HSS) through embrittlement and stress corrosion cracking mechanisms. Scanning Kelvin probe (SKP) mapping of surface potential was applied, to visualize the locations with an increased subsurface concentration of hydrogen in mild steel and martensitic HSS. This work can help to determine the reasons behind hydrogen localization in a steel microstructure, leading to embrittlement and hydrogen-assisted cracking. Cathodic charging was used to insert hydrogen, which decreased the steel potential. Hydrogen effusion in air passivates steel, increasing the potential of HSS and mild steel. The passivation of steels was monitored depending on different conditions of cathodic pre-charging and the amount of absorbed hydrogen. The SKP could determine the area of diffusible hydrogen and the area of cracks. In addition, low potential locations linked to the hydrogen trapped in the deformed HSS microstructure were also determined, which delayed the steel passivation. Mild steel showed a uniform potential distribution related to interstitial hydrogen, without potential extremes attributed to locally accumulated hydrogen. Thus, SKP sensing can detect locations containing increased concentrations of hydrogen and sensitive to steel cracking.