IIW Genoa 2025 International Conference
26 e 27 Giugno 2025
Sala Grecale e Sala Modulo 7 Piano 1°
26 Giugno 2025
Sala Grecale, ore 14.00 - 18.00
- 14.00 - 14.30: Performance of ferritic steel weldments in gaseous hydrogen
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As hydrogen gains momentum as viable energy carrier in a decarbonized economy, performance of hydrogen container materials becomes a keystone for design.
Given the low density of hydrogen, high pressures are required to achieve a useful energy density in storage and transportation. Along with pressure, the embrittling effect of hydrogen on material also increases.
For high pressure service, design by analysis based on fracture mechanics is mandatory to safely predict the vessel lifetime based on expected operating conditions. In fact, this approach is prescribed by the ASME Boiler and Pressure Vessels Code, Section VIII, Division 3, Article KD-10; and ASME B31.12 Hydrogen Piping and Pipelines Code, which remands to the former. This design requires accurate and reliable input data from material testing, in terms of resistance to fracture and fatigue crack propagation. For base materials, design curves for commonly used quenched and tempered vessel steels and linepipes are provided in ASME B&PV Code Case 2938-2 and B31 Code Case 220.
For welded construction, fracture resistance of weldments has to be properly determined, identifying and testing the most critical portion of the weld, both in terms of microstructure and potential defect occurrence. As of today, while Article KD-10 prescribes testing base metal, weld metal, and heat-affected zone, no specific prescription is given on the positioning of specimens across the latter. - 14.30 - 15.00: Hydrogen Embrittlement in Pipeline Steels: A Chemical and Mechanical Approach
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Hydrogen embrittlement (HE) is a well-known phenomenon that primarily affects steels, compromising their strength and durability under stress. This issue is particularly relevant in the context of the ecological transition, where hydrogen is considered a potential substitute for natural gas to fuel more sustainable energy transportation networks. However, integrating hydrogen into existing infrastructures, such as pipelines, presents significant challenges in terms of the long-term resistance of the materials. Therefore, it is crucial to thoroughly study how hydrogen affects the mechanical properties of the steels used in pipelines, ensuring safety and efficiency.
In this project, two complementary approaches were pursued: one chemical and one mechanical. On the chemical side, the focus was on the direct measurement of diffusible hydrogen using a custom permeation setup. This technique allowed for a comparison between gaseous hydrogen charging, which simulates real pipeline conditions, and electrolytic hydrogen charging, commonly used in laboratory settings due to its simplicity and safety. The aim was to establish a quantitative correlation between the two methods, using X52 pipeline steel as a case study.
Simultaneously, the mechanical aspect was investigated through fracture toughness tests with SENB (sigle edge notch ben) specimens of the same steel, tested in a hydrogenated environment. These tests highlighted the impact of hydrogen on fracture toughness in different regions of the material (base metal, heat affected zone, and fusion zone), using the same electrochemical parameters as the permeation experiments.
This combination of approaches provided a comprehensive understanding of hydrogen’s effects, from its diffusion into the material to the degradation of mechanical properties, offering a solid foundation for assessing the in-service performance of this steel in hydrogen environments. - 15.00 - 15.30: Repair and Hot Tapping of Pipelines in Hydrogen and Blended Gas Service
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In-service welding allows for safe, cost effective installation of full-encirclement repair sleeves and hot tap branch connections while a pipeline remains in service. Upon the wide-scale use of hydrogen and blended gas pipelines, in-service welding will continue to be an important aspect of pipeline operations. When steel is exposed to hydrogen gas, atomic hydrogen can be adsorbed at the surface, which may occur rapidly at elevated temperatures, such as those encountered during in-service welding. While the primary defense against hydrogen cracking during in-service welding is to strictly limit the introduction of hydrogen into these welds, the ability to safely weld onto an in-service pipeline in hydrogen or blended gas service could be adversely affected by the uptake of hydrogen.
The objective of an on-going joint industry project (JIP) at DNV is to experimentally determine if welding onto an in-service pipeline that contains hydrogen or blends of natural gas and hydrogen results in an increased risk of hydrogen cracking and, if so, to develop guidance for measures that can be taken to mitigate the increased risk. The results have shown that various increases in weld hydrogen level can occur depending on the pipe wall thickness, the weld heat input, and the partial pressure of hydrogen. Burnthrough experiments were also conducted using pipe sections pressurized with hydrogen and blended gas. The results indicate that ignition is more likely with blended gas than with natural gas alone, and that ignition is highly likely with pure hydrogen.
The results of this project will allow in-service welds to be safely made onto pipelines that transport hydrogen and blended gas so that full-encirclement repair sleeves and hot tap branch connections can be installed while the pipeline remains in service. - 16.00 - 16.30: Assessment of in-service welding conditions for pressurized hydrogen pipelines via component test
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Hydrogen is the energy carrier of tomorrow for a fossil-free future. This requires a reliable transport infrastructure with the ability to carry large amounts of hydrogen e.g. for steel industry or chemical industry. The conversion of existing natural gas (NG) grids is an essential part of the worldwide hydrogen strategies, in addition to the construction of new pipelines. In this context, the transportation of hydrogen is fundamental different from NG as hydrogen can be absorbed into the pipeline material.
Given the well-known effects of hydrogen embrittlement, the compatibility of the materials for the intended pipelines must be investigated (typically low alloy steels in a wide range of strengths and thicknesses). However, pipelines require frequent maintenance, repair or the need for installation for further outlets. In some cases, it is necessary to perform welding on or onto the pipelines while they are still in service, i.e. with active gas flow under high pressure, e.g. such as the well-known “hot tapping”, see Fig. 1a. This in-service welding causes challenges for hydrogen operations in terms of additional hydrogen absorption during welding and the material compatibility. The challenge can be roughly divided into the possible austenitization of the inner pipe material exposed to hydrogen, which can lead to sufficient hydrogen absorption, and the welding itself, which causes an increased temperature range. Both lead to a significant increase in hydrogen solubility and diffusivity of the respective materials compared to room temperature. In this context, knowledge about hot tapping on hydrogen pipelines is scarce due to the lack of operating experience. Fundamental experimental investigations are required to investigate the transferability from NG to hydrogen pipeline grids. For this reason, the present study introduces a specially designed mock-up / demonstrator concept for the realistic assessment of the welding processing conditions, see Fig. 1b. The mock-up was designed to enable in-situ temperature measurement during welding as well as ex-post extraction of samples for the quantification of the absorbed hydrogen concentration, see Fig. 1c. For safety measures, the necessary pressurized hydrogen volume was limited by the insertion of a solid cylinder ensuring a 1 cm hydrogen gas layer. Welding experiments on the pressurized mock-ups with the diameters DN60 and DN200 have shown that the austenitization temperature can be reached on the inner surface of the pipeline, especially on thin walled pipelines, using current - 16.30 - 17.00: Characterization of hydrogen trapping in a CoCrFeMnNi high-entropy alloy charged up to 1000 bar high-pressure hydrogen
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First studies on the mechanical behavior of high-entropy alloys (HEAs) in high-pressure hydrogen environment are available. In contrast, the underlying hydrogen absorption, diffusion and trapping in these HEAs like the Cantor-alloy was less in the scientific scope so far. For that reason, the CoCrFeMnNi-HEA was compared to a conventional AISI 316L austenitic steel, by exposing to high-pressure hydrogen charging at 200 bar and very-high pressure at 1,000 bar. Thermal desorption analysis (TDA) was applied with different heating rates (0.125 K/s to 0.500 K/s), see Fig. 1a to d. The underlying TDA spectra were analyzed in terms of a reasonable peak deconvolution to into a defined number of peaks and the calculation of the activation energies for the respective and predominant hydrogen trap sites. Both materials show a comparable hydrogen diffusivity. The obtained activation energies (see Fig. 2a to d) suggest that in case of the CoCrFeMnNi-HEAs an interaction of the austenitic phase as well as the direct atomic bonding of hydrogen to the metal atoms are the dominant traps, since “impurities” such as carbides or inclusions are only present in trace amounts [1,2]. Available literature [3,4] suggests that the Cr and Mn-content is here of special interest for the direct hydrogen bonding at solute atoms. In addition, the trap occupancy rate must be considered in terms of a pressure-related hydrogen absorption. The derived apparent hydrogen solubility was in the order: 316L 70 wt.ppm for the AISI 316L and >130 wt.ppm for the CoCrFeMnNi. In fact, both the hydrogen diffusion and trapping data on gaseous high-pressure hydrogen charged HEAs are rare so far. The results of the present study allow a deeper understanding of hydrogen trapping in the regarded CoCrFeMnNi-system.
- 17.00 - 17.30: Cryogenic Performance of Conventional and Novel Welding Materials for Liquid Hydrogen Applications
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The growing demand for sustainable energy solutions has led to increased interest in hydrogen as a clean energy carrier. Consequently, the development of efficient and safe liquid hydrogen storage systems has become a critical area of research. As new steels are being developed for liquid hydrogen storage, it is essential to assess the performance of welding materials under cryogenic conditions. This study presents a cryogenic property evaluation of both conventional welding materials used in LNG storage tanks and newly developing welding materials specifically designed for liquid hydrogen environments. Our research focuses on assessing the mechanical properties of these welding materials under extreme cryogenic conditions characteristic of liquid hydrogen storage. We conducted a series of tests including tensile strength, impact toughness, and fracture toughness at temperatures as low as -253°C. This study contributes valuable insights into the selection and optimization of welding materials for future liquid hydrogen storage tank construction, contributing to the advancement of hydrogen infrastructure development.
- 17.30 - 18.00: Soluzioni hydrogen ready per la prevenzione delle perdite di idrogeno
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In un’era caratterizzata da una crescente enfasi sulla sostenibilità e sulla ricerca di alternative energetiche pulite, l’idrogeno verde spicca come soluzione particolarmente interessante. Su tutto il suo ciclo di vita – dalla produzione alla distribuzione – grava la necessità di ridurre al minimo o eliminare le perdite, una sfida che implica oneri economici oltre a potenziali rischi per la sicurezza.
Superare le sfide rappresentate dalle minuscole dimensioni delle molecole di idrogeno, creando collegamenti efficaci e garantendo al contempo la sigillatura, può rivelarsi un compito arduo. I raccordi filettati vengono spesso evitati nei sistemi a idrogeno. Gli ingegneri preferiscono ricorrere a costosi processi di assemblaggio, come la saldatura, o a metodi di collegamento più onerosi.
In questo studio dimostreremo l’efficacia dei sigillanti anaerobici, prodotti eccezionali per la prevenzione delle perdite nei raccordi filettati e nelle flange, in grado di offrire un contributo cruciale per l’integrazione dell’idrogeno verde nella nostra ricerca di soluzioni energetiche sostenibili.
26 Giugno 2025
Sala Modulo 7 Piano 1°, ore 14.00 - 17.30
- 14.00 - 14.30: Wire arc additive manufacturing of CNT coated AISI316L stainless steel
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In this study, wire arc additive manufacturing (WAAM) was employed to fabricate AISI 316L stainless steel components coated with carbon nanotubes (CNTs). CNT nanoparticles were selected as the coating material due to their exceptional specific modulus and strength. The coating process was carried out using thermal chemical vapor deposition (CVD) in an acetylene gas environment. Following the successful deposition of CNTs onto the AISI 316L wire, bead-on-substrate experiments were conducted by depositing a single bead onto a mild steel substrate. For comparative analysis, similar bead-on-substrate experiments were performed using uncoated AISI 316L wire. To evaluate the impact of CNT incorporation in AISI 316L stainless steel, X-ray diffraction (XRD) analysis and nano-hardness testing were performed. The results indicated a significant enhancement in nano-hardness for CNT-coated AISI 316L stainless steel sample compared to the uncoated sample. XRD analysis further confirmed the formation of a cementite (Fe₃C) phase in the CNT-coated AISI 316L samples. This study demonstrates the potential of WAAM in fabricating components with enhanced wear resistance, expanding its applicability in advanced manufacturing.
- 14.30 - 15.00: Study on WAAM-based dissimilar metal additive manufacturing through multi-robot control
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The Wire Arc Additive Manufacturing (WAAM) process utilizes an arc plasma heat source to melt metallic wire and fabricate components through an additive manufacturing approach. This technology is particularly suitable for producing large-scale components and has gained significant attention in industries such as aerospace and nuclear power. Components used in these advanced industries are exposed to extreme environments, including high temperatures and high pressures, necessitating superior mechanical properties. However, conventional manufacturing methods such as machining and casting often involve long processing times and excessive tool wear. Moreover, uniformly applying high-performance materials across an entire component can lead to over-engineering, as different regions may not require the same level of performance. This inefficiency reduces manufacturing efficiency and increases production costs. To address these challenges, this study proposes a WAAM-based dissimilar metal additive manufacturing technique using multi-robot control with Inconel 718 and Stainless Steel 316L. A multi-robot control system was developed by synchronizing digital I/O signals between robots, allowing precise control over the distance between wires fed by each robot to fabricate dissimilar metal beads. Abrupt material transitions at the bonding interface between dissimilar metals can induce residual stress and deformation issues. Therefore, this study analyzed the bonding characteristics by observing the microstructure and Nb composition variations at the interface using SEM and EDS analysis. Based on the analysis results, dissimilar metal additive structures were fabricated, and the high-temperature tensile properties of Inconel 718 and the dissimilar metal additive structures were evaluated and compared at temperatures above 650°C. Additionally, the distribution of dissimilar metals within the cross-section of the deposited structures was examined.
- 15.00 - 15.30: Estimation of Charpy energy for SUS316L at cryogenic temperature based on temperature-lateral expansion relationships
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Environmental regulations are being strengthened worldwide to transition to a Net-Zero, and the applicability of various eco-friendly energies is being reviewed accordingly. Among the various eco-friendly energies, hydrogen is known as a carbon-free energy source that can be produced in an eco-friendly manner. There are three main types of hydrogen energy storage, and high-pressure storage is currently the most widely used method. However, liquefied hydrogen storage is essential for mass storage and transport, and thus securing the core technologies related to the production of storage tanks capable of storing liquefied hydrogen is becoming increasingly important. The one of the most important part for manufacturing a liquefied hydrogen storage tank is to ensure excellent mechanical properties of the materials used at -253°C (20K), which is the hydrogen liquefaction temperature. Impact toughness has been widely used as a performance check item due to the cost of producing test specimens and the simplicity of testing, but additional verification is required due to several problems occurring at -253℃.
In this study, the aim is to predict the Charpy energy at the hydrogen liquefaction temperature through the relationship between the lateral expansion that can be confirmed at the fracture surface after impact test and the Charpy energy derived at each temperature. In addition, the goal is to confirm the impact toughness by deriving a prediction equation for the weld metal and heat affected zone (HAZ) according to the welding process. Also, we would like to examine whether it is possible to derive a master curve for SUS316L by considering the strength parameters of the material. - 16.00 - 16.30: Development of an In-Situ Welding CCT Diagram for HSLA S960MC Steel and Comparison with the Existing CCT Diagram
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High-strength low-alloy (HSLA) structural steel S960MC is widely used in the manufacturing of cranes, trucks, trains, ships, and other heavy-duty applications. Due to thermomechanical controlled processing (TMCP), the steel achieves high strength, excellent ductility, and good cold formability without requiring increased carbon content or additional alloying elements, as is common in conventional mild steels. However, any thermal effect from the welding process irreversibly degrades the microstructure and properties of any TMCP steel (incl. S960MC), necessitating strict control and optimization of the welding process. In production, in-situ continuous cooling transformation (CCT) diagrams serve as a basis for developing welding procedures. In this study, dilatometric measurements were performed based on real arc welded and laser welded joints to develop an in-situ CCT diagram for S960MC steel. The accuracy of this diagram was verified by comparison with an existing CCT diagram for S960MC.
- 16.30 - 17.00: Heat-affected zone simulations of P355NH pipeline steel
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Transporting large quantities of hydrogen could be possible in high-pressure steel pipelines. Nowadays, many countries already have an established natural gas transportation system which could be used for hydrogen transport (mixed with natural gas). Although high-strength pipeline steels are available, one of the most commonly used pipeline steels is P355NH. As the weakest part of a welded joint is often the heat-affected zone (HAZ), it is important to examine it. The long-term goal of our research is to investigate the effect of hydrogen on the HAZ of different pipeline steels, however, in order to determine the effect of hydrogen exposure on the HAZ, it is necessary to investigate first the properties of it without hydrogen. Physical simulation can be used to produce the investigated part of the HAZ at a sufficiently large scale for subsequent material testing. In the present paper the properties of the coarse-grained (CGHAZ), intercritical (ICHAZ) and the intercritically reheated coarse-grained (ICCGHAZ) subzones of the P355NH material grade are investigated by Gleeble 3500 physical simulator. For the physical simulation, the chosen t8/5 cooling times were 5, 15 and 30 s to simulate welding with low, medium and high heat input in accordance with the widely used arc welding processes. Thus, after the physical simulation, optical microscopy, Vickers hardness measurements and instrumented impact tests were performed. Significant hardening was observed in CGHAZ at short cooling time, while softening did not occur in any subzones and cooling times. The impact energy significantly dropped down compared to the relatively tough base material.
- 17.00 - 17.30: A Study on Residual Stresses of Multilayer Welded SUS316 Steel with Surface Machining using Double Exposure Method
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In this study, the influence of surface machining on the residual stress near the surface of multilayer welds of austenitic stainless steel SUS316 was investigated by measuring the residual stress using the double exposure method (DEM). The results revealed that the residual stress introduced by surface machining disappeared due to the heat of welding, and no influence remained on the residual stress near the weld metal. In addition, the results of the residual stress simulated by FEM analysis correspond to the measured results, and the location of the maximum tensile residual stress is found to be in good agreement with the occurrence of stress corrosion cracking (SCC) in the weld. It follows that surface machining has no obvious influence on the residual stress after multilayer welding, and our result supports that surface machining is not the cause of SCC in actual welds.
27 Giugno 2025
Sala Grecale, ore 09.00 - 12.30
- 09.00 - 09.30: Modern filler metal development for liquid hydrogen cryogenic application
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The climate change is one of the key challenges of the modern society.
Upcoming environmental legislations aim for reducing greenhouse gases emission, whereby one of the most promising solutions from a long-term perspective is the adaption of alternative fuels such as hydrogen to decrease especially the CO2 emissions in the transportation and power generation sector. Hydrogen can be also used as energy carrier and feedstock and shows highest volumetric capacity in liquid condition. To store liquid hydrogen, special tanks are needed. Predominantly, these tanks are welded and made from austenitic stainless steels due to the very low liquefaction temperature of the hydrogen (-253°C).
However, many factors such as the welding process, the related welding parameters as well as the requirements arising from the Standards have to be taken into account by the manufacturers to deliver a reliable product which is suitable for liquid hydrogen applications. The objective of this work is to implement optimized filler metals for welding processes such as GTAW, GMAW and SAW to weld the austenitic stainless steel AISI 316L and AISI 304L(N).
The development of suitable filler materials not only aim on fulfilling the requirements of ISO and ASME Standards, but also to outline predominant influences on the welding performance and the corresponding mechanical properties. - 09.30 - 10.00: Development of austenitic stainless steel welding filler metals and weld properties for liquid hydrogen storage applications
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Gaseous hydrogen is liquefied by cooling it below -253°C (20°K), reducing its volume by a ratio of 1:848.
Once hydrogen is liquified it can be much more easily stored and transported. In recent years, with the rapid transition of the energy industry, the demand for liquefied hydrogen as one of the main fuel sources is growing rapidly. This trend leads to the requirement for storage facilities and associated piping systems capable of working at extremely low temperatures down to -253°C, which requires high toughness for both the base alloy and weld metal.
Low carbon 316L and 304L austenitic stainless steels are currently the preferred choices for base alloys due to their toughness properties at the service temperature. Challenges have arisen in the filler metals for matching the required toughness. One of the most stringent requirements of ASME Section VIII UHA-51 and ISO 21028-1 is that, to qualify the toughness of weld metal for service at as low as 4°K (- 269°C), it needs to meet a minimum Charpy impact lateral expansion of 0.53mm (21 mils) when tested at -196°C (77°K). This is based on the correlations between fracture toughness and impact data at these temperatures. In most projects, it is mandatory to demonstrate this for every lot of welding
consumables using the actual production welding procedure.
It has been recognized that 316L and 308L grade consumables of standard compositions, or even those with a controlled -ferrite content through targeted modifications of the chemical compositions within the specified ranges of relevant AWS/EN ISO classifications of these grades, are not capable of producing weld metals consistently meeting the lateral expansion of the Charpy impact test at specified testing temperature. Special consumable designs with optimized alloy and flux systems that deposit chemical composition with a ferrite-free full austenite microstructure are required.
The current paper presents the development and evaluation of a full range of welding consumables for GTAW, SMAW, FCAW and SAW processes. These consumables aim to produce welds that overcome the toughness limitations of standard filler metals for hydrogen storage applications. The work shows, by
optimizing alloy additions and flux systems, the corresponding welds possess a ferrite free full (nonferrite) austenite microstructure, and the impact lateral expansion requirements at cryogenic temperature are met. The effects of slag types connecting with different welding processes are explored. The results also show that non-ferrite weld metals minimize the toughness variations typically
associated with traditional filler metals, leading to greater predictability and reliability in welding performances which in turn improves the safety and service life of liquid hydrogen facilities. - 10.00 - 10.30: Resistance Welding for future Hydrogen Economy – Challenges in the Comeback of an old Welding Technique for modern Applications
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Hydrogen is currently regarded as a key element of the energy transition and a versatile alternative to fossil fuels. Hydrogen can be produced in electrolysis in various ways. One of the most efficient methods is the PEM electrolysis (PEM-EL), the core of which is the so-called proton exchange membrane (PEM). This hydrogen-permeable membrane is bordered on both sides by gas-permeable structures (porous transport layers, PTL) through which water and gas flow during electrolysis. In PEM-EL, the activation potential needed for the electrolysis reaction process, an electric field is applied. Of the chemical reaction products (hydrogen and oxygen), oxygen in particular leads to a highly oxidative environment within the cell on the anode side, the components must withstand during hydrogen electrolysis. This is why PTLs are produced of materials with high corrosion resistance, mainly titanium.
However, if hydrogen electrolysers are to be scaled up economically to meet the forecast hydrogen demand, production costs must be significantly reduced. One approach is to reduce production costs by substituting expensive individual components with alternative semi-finished products, which in turn are assembled using cost-efficient and automatable joining processes. Regarding PTLs, cost intensive sintered bodies are replaced by expanded metal that is joined with resistance welding to form permeable sandwich structures and easy to produce in a line-to-line process.
As part of the research project “HyInnoLyze2” (03ZU211AC), funded by the German ministry of education and research (BMBF), cross-industry research is being carried out in collaboration with various partners from industry. The research is focused on upscaling the individual processes that are production steps for PEM-electrolysers, including upscaling the resistance welding of PTL. Due to its reliability, its high economic efficiency and the locally limited heat input, capacitor discharge technology was chosen to join titanium expanded mesh into multi-layered structures in just one process step. But, as determined previously, the welding process and the weld quality itself have a significant influence on the subsequent cell performance.
This work focuses on the challenges in capacitor discharge welding of multi-layered, permeable structures in order to meet the high quality requirements when upscaling PTL production for PEM electrolysers. Next to mechanical tests, light and electron optical analysis and electric conductivity tests are included to investigate the influence of the welding parameters and the layer structure on the composite properties. - 11.00 - 11.30: Hydrogen Embrittlement Behavior in API X52 Steel for High-pressure Hydrogen Transportation
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The purpose of this study is to understand hydrogen penetration, hydrogen-induced deformation, and fracture behavior in API X52 steel. Microstructural analysis of API X52 steel was conducted, followed by the slow strain rate test (SSRT) and the small punch test (SPT) in nitrogen and hydrogen atmospheres. The obtained results were evaluated to assess the susceptibility of the material to hydrogen embrittlement. The SSRT revealed predominantly ductile fractured surfaces in the nitrogen atmosphere specimen, whereas brittle fractured surfaces were observed at the edges. The specimen in the hydrogen atmosphere exhibited elongated dimples and some internal cracks in the central region. The SPT revealed circular cracks and dimples in the nitrogen atmosphere specimen. In contrast, hydrogen atmosphere specimens displayed fractures in the form of a mix of cleavage fractures, dimples, and internal, circumferential, and radial cracks. Brittle fractures were mainly observed at the grain boundaries of ferrite and pearlite, the primary microstructural constituent, or within ferrite grains.
- 11.30 - 12.00: Weld heat input effect on microstructure and hydrogen diffusion in thick-walled S690 submerged arc welded joints
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High-strength, low-alloy (HLSA) steels such as S690 are an attractive option for heavy industries such as offshore wind turbines and peripheral equipment due to their combination of excellent mechanical properties and weldability. The construction of these thick-walled structures requires highly efficient welding processes such as submerged arc welding (SAW). However, SAW faces challenges related to delayed hydrogen assisted cold cracking (HACC). Despite its importance, the effect of different diffusion coefficients on the cold cracking susceptibility of different microstructures within SAW-welded S690 steels is not fully understood. For this reason, the present study focuses on comparing the cold cracking susceptibility of thermomechanically rolled (TM) or quenched and tempered (QL) variants of S690 steel. Submerged arc welding was performed on both steel grades at different welding heat inputs. From these thick-walled welds, metallic membranes were extracted from the weld metal, the heat-affected zone (HAZ), and the two base metals. The specimens were subjected to electrochemical hydrogen permeation tests (according to ISO 17081) to determine the microstructure-specific hydrogen diffusion coefficients. In general, increased welding heat input and thickness decreased the hydrogen diffusion coefficients, i.e., the time required for hydrogen diffusion increased. In addition, the results showed that the TM grade exhibited slightly accelerated hydrogen diffusion coefficients compared to the QL grade, which is beneficial for hydrogen reduction and increases the HACC resistance. As a result, the microstructure-specific assessment of hydrogen diffusion in the BM, HAZ or WM of the SAW joint was less important for a given set of welding parameters compared to other welding processes such as gas metal arc welding (GMAW). The reason is that in multilayer SAW, the relatively large welding heat input and multiple annealing resulted in similar microstructures, resulting in very close hydrogen diffusion coefficients. From this point of view, it is sufficient to characterize the hydrogen diffusion coefficients of both the weld metal and the base material.
- 12.00 - 12.30: Hydrogen embrittlement evaluation of welded joints in low-alloy carbon and austenitic stainless steels for hydrogen applications
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Hydrogen technologies play a crucial role in the transition toward a fossil-free society. Steel applications are a key enabler in this transformation particularly with the use of high strength carbon steels.
(HSCS) and austenitic stainless steels (ASS). These steels are essential for long- and short-range pipelines and pressure vessels, supporting future hydrogen transport and storage infrastructures. However, the presence of hydrogen in structural materials can lead to hydrogen embrittlement (HE), posing challenges to their long-term performance and reliability. In this study, we evaluate the suitability of different welding filler materials for hydrogen-related applications in both low alloy carbon steel and austenitic stainless steel. Being welds and heat affected zones (HAZ) suitable spots for hydrogen accumulation, leading to premature failure.
To assess their performance in hydrogen environments, welded joints of low-alloy carbon steel and austenitic stainless steel were subjected to slow strain rate tensile (SSRT) testing using the Hollow Specimen Method (HSM) under 200 bar pressurized hydrogen gas exposure. Additionally, fracture surface analysis and microstructural characterization with scanning electron microscopy (SEM) were conducted to investigate hydrogen embrittlement mechanisms.
The results demonstrated that both material groups exhibited promising resistance to hydrogen embrittlement, suggesting their potential suitability for hydrogen-related applications. The insights gained from this study contribute to the ongoing development of welding consumables optimized for the hydrogen economy.
27 Giugno 2025
Sala Modulo 7 Piano 1°, ore 09.00 - 12.00
- 09.00 - 09.30: Assessment of hydrogen effect on failure mechanisms of welded low alloy carbon steel
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The expected increase of clean hydrogen production will be a great challenge for transport infrastructures and the conversion of existing gas pipelines to hydrogen is a promising and cost saving solution. To assess the suitability of pipelines repurposing, a study has been conducted aiming at providing a better understanding of the failure mechanisms of low alloy carbon steel under gaseous hydrogen environment (30 bar). To this end, an original approach based on post-mortem advanced characterization on laboratory tested samples has been performed.
First, statistical fractography is used to evaluate the local damage parameters and to calculate the fracture toughness. To check the accuracy of the model, the calculated fracture toughness is compared with the experimentally measured values. In order to characterize the interactions between the crack and the microstructure in the presence of hydrogen, Electron Backscatter Diffraction (EBSD) mapping is performed. The objective is to discern the nature of cleavage planes susceptible to failure under the influence of hydrogen. Lastly, nanoindentation tests are performed to assess the localization of plastic deformation associated with hydrogen-induced embrittlement. - 09.30 - 10.00: Fusion joining of advanced and dissimilar metals — Processes, challenges and experimental insights (Inconel-Copper)
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In recent years, there has been an increasing trend and demands for exploring various joining processes for dissimilar advanced metals in several industrial applications due to their better strength and economic advantages. However, joining process of dissimilar metals is a challenging task due to differences in their chemical, physical and mechanical properties like chemical composition, thermal conductivity, coefficient of thermal expansion, hardness, strength etc. The formation of undesirable intermetallic phases is another major concern. This paper provides a concise overview of the current fusion joining processes, with a focus on their application to advanced materials and the challenges associated with it. Further, the paper presents preliminary experimental insight from the fusion welding of dissimilar metals specifically Inconel-Copper (Ni-Cu) joints, using electron beam welding (EBW). EBW has gained attention and an important topic of interest for joining dissimilar metals in recent years due to its unique characteristics like high energy density, beam with various dynamic effects, precise beam control etc. Many dissimilar metals have already been joined successfully using this process, but many combinations still under investigation for further improvement and optimization and new combinations requires exploration to assess their weldability and potential improved applications. The paper concludes by highlighting future extended research directions with these dissimilar metals in the extended article.
- 10.00 - 10.30: Data Analytics Approaches for Yield Strength Prediction of Austenitic Stainless Steel Welds
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With the increasing demand for fabricating liquefied gas storage containers made of low-temperature base metals such as 9Ni steel and high-Mn steel, predicting the mechanical properties of stainless steel weld metal has become increasingly important. In this study, two types of predictive models for the yield strength of austenitic stainless steel weld metal were successfully developed using conventional multiple regression analysis and machine learning techniques, based on 100 data points. The models incorporate chemical composition and welding heat input per unit length as input variables. The multiple linear regression model (MLR) achieved a high coefficient of determination (R²) of 0.93. Machine learning models, including stepwise linear regression, linear support vector machine, and Gaussian process regression, also demonstrated similar R² values but lower mean absolute percentage error (MAPE) than that of the MLR model. Verification with an additional 27 data points confirmed that the MLR model was statistically more reliable, exhibiting a higher R² and lower MAPE than the machine learning models. Furthermore, the developed models effectively predicted the yield strength of weld metal, demonstrating their potential as powerful tools for the development of stainless steel filler materials.
- 11.00 - 11.30: Investigation of Split Crack in Cryogenic CT Test of A5083-O Aluminum Alloy
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A5083-O aluminum alloy, widely used in liquefied natural gas (LNG) tanks, is now being considered for liquified hydrogen (LH) storage at an extreme cryogenic temperature. However, split crack, which has not been reported in A5083-O, occurred in compact tension (CT) tests under 4K. To clarify the mechanism of this phenomenon, this study investigates the fracture behavior of A5083-O through CT tests at temperatures from 293K (RT) to 4 K in L-T and S-L orientations. For L-T CT tests, split crack exclusively occurred in 4K specimen. By SEM and EDS analysis, we recognized split crack propagating along grain boundaries decorated with Al₆(Mn,Fe) precipitates. The fracture toughness in L-T orientation exhibited an 87.7% increase from RT to 123K, followed by a subsequent 38.9% reduction at deeper cryogenic condition of 4K, with spliting identified as the dominant degradation mechanism. Across the entire temperature range, the fracture toughness in S-L orientation consistently exhibited over 40% lower values compared to L-T orientation, indicating the weakness in short-transverse direction. In addition, based on the results of cryogenic uniaxial tension tests, crack growth in the CT test was simulated by finite element method, and the mechanism of split crack and the influence on fracture toughness was discussed. This study provides a new insight for the development and application of Al-Mg alloys.
- 11.30 - 12.00: Techniques for Improving the Fatigue Strength of Thin Laser-Welded Butt Joints
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Welding thin high-strength steel sheets using laser beam welding (LBW) presents challenges related to fatigue strength, as the resulting weld geometry and distortion can significantly affect fatigue performance. While post-weld treatments such as high-frequency mechanical impact (HFMI) or grinding are effective for fatigue enhancement, they may not be optimal for thin sheets due to potential distortion and material removal. This study investigates the effectiveness of laser dressing and filler metal application as improvement techniques for laser-welded butt joints in 3 mm thin S960MC steel. Fatigue testing demonstrated that laser dressing significantly enhanced fatigue strength by modifying weld geometry and introducing beneficial compressive residual stresses. In contrast, the use of filler metal did not yield notable improvements, likely due to excessive weld penetration and increased stress concentration at the weld root. These findings highlight laser dressing as a promising method for improving the fatigue performance of laser-welded thin-sheet structures.