Welding in the World—update 2021 Lippold, John C.; Böllinghaus, Ing Thomas; Scotti, Américo
Welding in the world,
02/2021, Letnik:
65, Številka:
2
Journal Article
Potentiodynamic measurements are used to determine key potentials to classify certain corrosion properties. The material selection for components (e.g. shafts) in corrosive environments is widely ...based upon these potentiodynamic measurements. Criticism for using these potentials for component design has been expressed in literature. Potentiostatic measurements are known to represent the long term corrosive impact experienced by components in a more realistic manner but are prone to scatter. Therefore a statistical approach called staircase method was adapted to the given electrochemical problem.
With using this staircase method, a reliable value for the median potential (threshold potential) can be determined. This potential defines the threshold between anodic dissolution and cathodic protection. For the first time, this newly defined potentiostatic threshold potential is offering a validated median potential value for corrosion prediction in a given corrosion system based on potentiostatic measurements. Threshold potentials for the stainless steel grades 1.4057 and 1.4542 were investigated in aerated electrolytes at 25°C with different chloride ion concentrations.
Welding in the world – update 2018 Lippold, John C.; Böllinghaus, Ing Thomas; Richardson, Ian
Welding in the world,
01/2019, Letnik:
63, Številka:
1
Journal Article
The high potential of hydrogen as a key factor on the pathway towards a climate neutral economy, leads to rising demand in technical applications, where gaseous hydrogen is used. For several metals, ...hydrogen-metal interactions could cause a degradation of the material properties. This is especially valid for low carbon and high-strength structural steels, as they are commonly used in natural gas pipelines and analyzed in this work.
This work provides an insight to the impact of hydrogen on the mechanical properties of an API 5L X65 pipeline steel tested in 60 bar gaseous hydrogen atmosphere. The analyses were performed using the hollow specimen technique with slow strain rate testing (SSRT). The nature of the crack was visualized thereafter utilizing μCT imaging of the sample pressurized with gaseous hydrogen in comparison to one tested in an inert atmosphere.
The combination of the results from non-conventional mechanical testing procedures and nondestructive imaging techniques has shown unambiguously how the exposure to hydrogen under realistic service pressure influences the mechanical properties of the material and the appearance of failure.
•Visualization of hydrogen induced crack propagation using μCT.•Orientation of cracks differs in hydrogen gas compared to inert gas atmosphere.•Spread of cracks differs in hydrogen gas compared to inert gas atmosphere.
Metals that are exposed to high pressure hydrogen gas may undergo detrimental failure by embrittlement. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals ...is crucial for avoiding hydrogen embrittlement. In this study, the effect of stress-enhanced gaseous hydrogen uptake in bulk metals is investigated in detail. For that purpose, a generalized form of Sievert's law is derived from thermodynamic potentials considering the effect of microstructural trapping sites and multiaxial stresses. This new equation is parametrized and verified using experimental data for carbon steels, which were charged under gaseous hydrogen atmosphere at pressures up to 1000 bar. The role of microstructural trapping sites on the parameter identification is critically discussed. Finally, the parametrized equation is applied to calculate the stress-enhanced hydrogen solubility of thin-walled pipelines and thick-walled pressure vessels during service.
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•Improvement of Sievert's law to consider trapping sites and stress states.•Calculation and validation of gaseous hydrogen solubility under extreme conditions.•Hydrogen uptake measured for L450 steel at 200 and 1000 bar.•Calculation of the hydrogen solubility in pipes and pressure vessels.•Comprehensive literature survey of gaseous hydrogen solubility.
Welding in the World Update Lippold, John C.; Böllinghaus, Ing Thomas; Norrish, John
Welding in the world,
04/2020, Letnik:
64, Številka:
4
Journal Article
High-temperature slow strain rate testing (SSRT) - ductility data from cathodic hydrogen charging of 10CrMo910 and 7CrMoVTiB1010 are implemented into a mathematical model of stress corrosion cracking ...(SCC) at various operational conditions including temperatures, pH, and dissolved hydrogen/ oxygen contents as well as global stresses and material properties. The results show that, as a consequence of experimentally verified local acidification at initial anodic path corrosion, subsequent local hydrogen-assisted cracking can be a controlling factor for SCC in high-temperature water. As a particular effect at global stresses close to the yield point, operational temperatures around 270 degree C exhibit peak crack growth rates depending on dissolved hydrogen, oxygen, pH, and global stress, which has been found to be consistent for both experimental studies and mathematical modeling.
Hydrocarbons fuel our economy. Furthermore, intermediate goods and consumer products are often hydrocarbon-based. Beside all the progress they made possible, hydrogen-containing substances can have ...severe detrimental effects on materials exposed to them. Hydrogen-assisted failure of iron alloys has been recognised more than a century ago. The present study aims to providing further insight into the degradation of the austenitic stainless steel AISI 304L (EN 1.4307) exposed to hydrogen. To this end, samples were electrochemically charged with the hydrogen isotope deuterium (
H, D) and analysed by scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that deuterium caused a phase transformation from the original γ austenite into ε- and α'-martensite. Despite their low solubility for hydrogen, viz. deuterium, the newly formed phases showed high deuterium concentration which was attributed to the increased density of traps. Information about the behaviour of deuterium in the material subjected to external mechanical load was gathered. A four-point-bending device was developed for this purpose. This allowed to analyse in-situ pre-charged samples in the ToF-SIMS during the application of external mechanical load. The results indicate a movement of deuterium towards the regions of highest stress.
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