TY - JOUR A1 - Czeskleba, Denis A1 - Rhode, Michael A1 - Wandtke, Karsten A1 - Irfan, Muhammad Dary A1 - Kannengiesser, Thomas T1 - Hydrogen diffusion in thick-walled S690 SAW joints: part 2 – predictive modeling of heat input and microstructure influence N2 - High-strength low-alloy (HSLA) steels such as S690 are widely employed in thick-walled welded structures, where hydrogen-assisted cold cracking (HACC) remains a persistent concern. While microstructure-specific hydrogen diffusion coefficients (DH) for weld metal (WM), heat-affected zone (HAZ), and base material (BM) were experimentally established in Part 1 of this study, their quantitative influence on hydrogen accumulation and effusion has not yet been fully clarified. This work presents a transient, spatially resolved numerical model for simulating hydrogen transport in multi-pass submerged arc welds. The model integrates experimentally determined DH values with realistic thermal cycles and temperature-dependent boundary conditions. Developed in Python, the simulation tool is purpose-built for hydrogen diffusion in welded joints. It offers a focused, transparent alternative. It offers a focused, transparent alternative to general-purpose finite element platforms. Parametric analyses demonstrate that, although the diffusion coefficients vary by up to 50%, their impact on overall hydrogen retention is minor. In contrast, plate thickness, bead geometry, cooling time (t₈/₅), and interpass temperature exert a dominant influence on hydrogen distribution. Despite clear microstructural differences between the thermomechanically rolled (S690MC) and quenched and tempered (S690Q) variants, including opposite HAZ hardness responses (softening in S690MC, hardening in S690Q) in the (pen)ultimate weld bead, the simulations confirm that their diffusion behavior and hydrogen solubility are closely aligned. Consequently, differences in DH and solubility exert only a minor influence on hydrogen retention compared to thermal exposure and joint geometry. These findings support the interchangeable use of both steel grades in terms of HACC risk due to hydrogen diffusion kinetics under comparable welding conditions. KW - Hydrogen assisted cracking KW - Numerical simulation KW - Diffusion KW - Submerged arc welding PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-655721 DO - https://doi.org/10.1007/s40194-026-02395-1 SN - 0043-2288 SP - 1 EP - 16 PB - Springer Science and Business Media LLC AN - OPUS4-65572 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Czeskleba, Denis A1 - Rhode, Michael A1 - Wandtke, Karsten A1 - Irfan, Muhammad Dary A1 - Kannengiesser, Thomas T1 - Hydrogen diffusion in thick-walled S690 saw joints: part 1—experimental determination of microstructure-dependent diffusion coefficients N2 - High-strength low-alloyed steel S690 is widely used in heavy-duty applications, such as structural components, mobile cranes, and industrial plant construction, owing to their high strength and weldability. However, thick-plate submerged arc welding (SAW) can introduce elevated hydrogen levels and residual stresses that promote time-delayed hydrogen-assisted cold cracking (HACC). Accurate, microstructure-specific diffusion data are scarce, limiting predictive HACC assessments. This study presents an experimental determination of hydrogen diffusion coefficients (DH) in two S690 variants: thermomechanically rolled (S690MC) and quenched and tempered (S690Q). Multi-layer SAW welds were produced from 30 mm thick plate material at three heat input levels, and diffusion membranes were extracted from weld metal (WM), heat-affected zone (HAZ), and base material (BM). Hydrogen permeation tests, conducted in accordance with DIN En ISO 17081, yielded flux curves normalized in time from which DH was derived using the inflection-point method. At room temperature, DH values ranged from 6 × 10−5 mm2/s to 9 × 10−5 mm2/s across all regions and heat inputs, with no significant difference between S690MC and S690Q. Weld metal exhibited marginally lower DH, attributed to enhanced hydrogen trapping, while base material measurements showed greater variability. These microstructure-resolved diffusion coefficients add quantitative data for modern S690 SAW welds and provide internally consistent input parameters for the numerical simulations presented in part 2. The results support improved parameterization for subsequent assessments of HACC risk through the optimization of welding parameters. KW - Hydrogen assisted cracking KW - Submerged arc welding KW - Diffusion KW - Electrochemical permeation KW - Microstructure PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-655711 DO - https://doi.org/10.1007/s40194-026-02400-7 SN - 0043-2288 SP - 1 EP - 15 PB - Springer Science and Business Media LLC AN - OPUS4-65571 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Numerical simulation of weld heat input effect on microstructure and hydrogen diffusion in thick-walled S690 submerged arc welded joints N2 - 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 presents 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. SAW was performed on specimens of both steel grades to produce weldments consisting of weld metal, heat-affected zone (HAZ), and base metal. Electrochemical hydrogen permeation tests (ISO 17081) were performed to determine the microstructure specific coefficients. Using the obtained coefficients, a numerical model was developed to identify the time- and microstructure-dependent local hydrogen diffusion and its influence on the distribution within the welds. The results showed that the TM grade exhibited slightly accelerated hydrogen diffusion compared to the QL grade, which is beneficial for hydrogen reduction and increases the HACC resistance. However, the further simulations with different ply sequences showed that the welding heat input (i.e. welding ply sequence) had a significantly higher effect on hydrogen accumulation. Specifically, increased welding heat input and increased thicknesses decrease hydrogen diffusivity. For this reason, microstructure-specific hydrogen diffusion played a minor role in thick-layer SAW joints compared to the need to control the welding parameters (layer sequence, individual layer thickness, welding heat input). T2 - FEMS Euromat 2025 - 18th European Congress and Exhibition on Advanced Materials and Processes CY - Granada, Spain DA - 15.09.2025 KW - Hydrogen assisted cracking KW - Welding KW - High strength steels KW - Numerical simulation KW - Electrochemical permeation PY - 2025 AN - OPUS4-64158 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Effect of Ti and Nb on hydrogen trapping in welded S690 HSLA steel and effect on delayed cold cracking N2 - Fine-grain, high-strength, low-alloy (HSLA) structural steels with yield strengths > 600 MPa are now the state of the art in construction applications such as mobile cranes and civil engineering. HSLA grades derive their strength from a combination of specific heat treatment and the underlying chemical composition. In this context, Ti or Nb are essential to obtain a fine-grained microstructure as well as the necessary carbides or nitrides for precipitation strengthening. In this context, the specific effect of Ti or Nb-rich compounds on hydrogen trapping and diffusion is well known for special laboratory cast alloys, but unknown for realistic steel compositions. For this reason, a series of S690Q-based alloys were synthesized, close to a real steel composition, but with well controlled Ti or Nb additions in different amounts. Specimens were obtained from these alloys by electrochemical discharge machining (EDM). The specimens were tested using the well-established electrochemical permeation technique. From the experimental results, the hydrogen diffusion coefficients and the analytical subsurface hydrogen concentration were calculated. In addition, the hydrogen trapping behavior at elevated temperatures was interpreted by thermal desorption analysis (TDA) using different heating rates of hydrogen charged samples. The results showed that in contrast to metallurgically "pure" laboratory cast alloys, realistic chemical compositions were similar in their hydrogen trapping behavior, despite some small differences. All investigated steel grades exhibited shallow and reversible hydrogen trapping, regardless of their chemical composition. Of course, the experiments only allowed the calculation of effective diffusion coefficients and trapping energies, which represent an average of the entire microstructure. Nevertheless, HSLA steels are typically joined by arc welding, which includes the risk of delayed hydrogen assisted cracking. From the point of view of welding practice, however, a more or less identical hydrogen diffusion behavior means that no special "metallurgically specific", justifiable measures need to be considered, despite the well-established processes such as "soaking" or dehydrogenation heat treatment. Of course, a closer look at the heat-affected zone (HAZ) or the weld metal of the specific welds is necessary. However, especially in the case of thick-walled welds, it is assumed that the weld metal and HAZ are similar to the base material due to the multi-layer welding, which results in multiple annealing cycles of the weld metal and HAZ. T2 - FEMS Euromat 2025 - 18th European Congress and Exhibition on Advanced Materials and Processes CY - Granada, Spain DA - 15.09.2025 KW - Hydrogen assisted cracking KW - HSLA KW - Diffusion KW - Electrochemical permeation PY - 2025 AN - OPUS4-64156 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Hydrogen diffusion in thick-walled S690 SAW joints: Part 1 - Experimental determination of microstructure dependent diffusion coefficients N2 - S690 steels are widely used in heavy-duty applications, such as structural components, mobile cranes, and industrial plant construction, owing to their high strength and weldability. However, thick-plate submerged arc welding (SAW) can introduce elevated hydrogen levels and residual stresses that promote time-delayed hydro-gen-assisted cold cracking (HACC). Accurate, microstructure-specific diffusion data are scarce, limiting pre-dictive HACC assessments. This study presents an experimental determination of hydrogen diffusion coeffi-cients (DH) in two S690 variants: thermomechanically rolled (S690MC) and quenched and tempered (S690Q). Multi-layer SAW welds were produced from 30 mm-thick plate material at three heat input levels, and diffusion membranes were extracted from weld metal (WM), heat-affected zone (HAZ), and base material (BM). Hydro-gen permeation tests, conducted in accordance with DIN EN ISO 17081, yielded time-normalized flux curves from which DH was derived using the inflection-point method. At room temperature, DH values ranged from 6 × 10⁻⁵ to 9 × 10⁻⁵ mm²/s across all regions and heat inputs, with no significant difference between S690MC and S690Q. Weld metal exhibited marginally lower DH, attributed to enhanced hydrogen trapping, while base mate-rial measurements showed greater variability. These microstructure-resolved diffusion coefficients fill a critical data gap and provide essential input for the numerical simulations presented in Part 2. The results also support practical guidelines for mitigating HACC risk through the optimization of welding parameters. T2 - 78th IIW Annual Assembly, Meeting of Commission II-C CY - Genoa, Italy DA - 22.06.2025 KW - Hydrogen assisted cracking KW - Submerged arc welding KW - High strength steels KW - Hydrogen Diffusion KW - Electrochemical permeation PY - 2025 AN - OPUS4-63540 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Weld heat input effect on microstructure and hydrogen diffusion in thick-walled S690 submerged arc welded joints N2 - 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. T2 - 78th IIW Annual Assembly and International Conference CY - Genoa, Italy DA - 26.06.2025 KW - Hydrogen assisted cracking KW - Submerged arc welding KW - Diffusion KW - Electrochemical permeation KW - Microstructure PY - 2025 AN - OPUS4-63543 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Hydrogen diffusion in thick-walled S690 SAW joints: Part 2 - Predictive modeling of welding heat input and microstructure influence N2 - High-strength low-alloy (HSLA) steels such as S690 are widely employed in thick-walled welded structures, where hydrogen-assisted cold cracking (HACC) remains a persistent concern. While microstructure-specific hydrogen diffusion coefficients (DH) for weld metal (WM), heat-affected zone (HAZ), and base material (BM) were experimentally established in Part 1 of this study, their quantitative influence on hydrogen accumulation and effusion has not yet been fully clarified. This work presents a transient, spatially resolved numerical model for simulating hydrogen transport in multi-pass submerged arc welds. The model integrates experimentally determined DH values with realistic thermal cycles and temperature-dependent boundary conditions. Developed in Python, the simulation tool is purpose-built for hydrogen diffusion in welded joints and offers a focused, transparent alternative to general-purpose finite element platforms. Parametric analyses demonstrate that, although the diffusion coefficients vary by up to 50 %, their impact on overall hydrogen retention is minor. In contrast, welding parameters such as plate thickness, bead geometry, cooling time (t₈/₅), and interpass tem-perature exert a dominant influence on hydrogen distribution. Despite clear microstructural differences between the thermomechanically rolled (S690MC) and quenched and tempered (S690Q) variants, including hardness softening versus hardening in the heat-affected zone of the (pen)ultimate weld bead, the simulations confirm that their diffusion behavior and hydrogen solubility are closely aligned. Consequently, differences in diffusivity and solubility exert only a minor influence on hydrogen retention compared to thermal exposure and joint geometry. These findings support the interchangeable use of both steel grades in terms of HACC risk due to hydrogen diffusion kinetics, under comparable welding conditions. T2 - 78th IIW Annual Assembly, Meeting of Commission II-C CY - Genoa, Italy DA - 22.06.2025 KW - Hydrogen assisted cracking KW - Numerical simulation KW - Hydrogen diffusion PY - 2025 AN - OPUS4-63541 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Rhode, Michael A1 - Mente, Tobias A1 - Kannengießer, Thomas A1 - Czeskleba, Denis T1 - Simulation of hydrogen distribution in submerged arc welded heavy plates as tool for evaluating cold cracking sensitivity for offshore structures N2 - Foundation structures for offshore wind turbines are typically made of heavy plate struc-tural steels, such as S420ML, welded by submerged arc welding. Due to the welding process conditions, higher amounts of hydrogen can be introduced. In this context, large plate thicknesses result in long diffusion paths and a prolonged diffusion time for hydrogen at ambient temperature and possible delayed hydrogen-assisted cold cracking. As a result, hydrogen can accumulate in areas of high mechanical stress and strain. Due to the delayed diffusion, a minimum waiting time of up to 48 h must be observed before non-destructive testing can be performed. In addition, the assessment of possible cold crack locations is very complex. For this reason, a numerical model of a component-like weld test was developed to simulate the temperature field during welding and subsequent cooling. A hydrogen diffusion model based on the temporal-local temperature distribution was established. It was applied to simulate the change of hydrogen distribution as a function of temperature cycle during multi-layer welding and further for the entire waiting time interval ≤ 48 h. As a result, crack critical areas could be evaluated in terms of accu-mulated hydrogen. An advantage of the diffusion model is the simulation of a normalized concentration, i.e. between "0" (no hydrogen) and "1" (max. concentration), which can be scaled to experimentally determined hydrogen concentrations. Finally, selected results for increased real hydrogen ingress are presented, which confirm the relatively high crack resistance of the S420 submerged arc welded joint. KW - Hydrogen assisted cracking KW - Diffusion KW - Numerical simulation KW - Offshore steel PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-632416 DO - https://doi.org/10.21268/20250507-6 SP - 1 EP - 12 PB - Technische Universität Clausthal CY - Clausthal-Zellerfeld, Deutschland AN - OPUS4-63241 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Reliable hydrogen determination in metallic materials and their weld joints: Parameters and challenges N2 - In the course of tomorrow's hydrogen-based energy transition, the construction of the corresponding infrastructure will play a central role. The majority of materials used to date are typically welded for component fabrication. In that context, steels are widely applied and can be prone to hydrogen embrittlement. This includes the classical delayed cold cracking during welding processing as well as embrittlement phenomena during operation. For the evaluation of any hydrogen effect on, for example, the mechanical properties of a welded metallic material, the hydrogen content must be precisely determined. In the case of welds, for example, according to ISO 3690, this is the isothermal carrier gas hot extraction (CGHE). CGHE is based on accelerated hydrogen degassing due to thermal activation of hydrogen at elevated temperatures. In addition to the pure quantification of hydrogen, thermal desorption analysis (TDA) with varied heating rates can be used to determine and evaluate the bonding state at microstructural defects in the material. For both techniques, experimental and measurement influences have to be considered, which have a great effect on the result. For CGHE, for example, ISO 3690 suggests different sample geometries as well as minimum extraction times. The present study summarizes results and experiences of numerous investigations with different sample temperatures and geometries (ISO 3690 type B and cylindrical TDA samples) regarding: the influence of the sample surface (polished/welded), measurement accuracies depending on the sample volume as well as the insufficient monitoring of the effect of the PI controller on the extraction temperature. In particular, a deviating extraction temperature to the set temperature, can significantly falsify the measurement results. Based on the results, methods are shown to quickly reach the desired extraction temperature without having to physically interfere with the measurement equipment. This serves to substantially improve the reliability of hydrogen measurement through increased signal stability and accelerated hydrogen desorption. In general, an independent temperature measurement with dummy samples for the selected heating procedure is advisable to exclude possible unwanted temperature influences already before the measurement. In addition (and way more important), the methods described can be transferred directly to industrial applications. T2 - 47th MPA-Seminar CY - Stuttgart, Germany DA - 10.10.2023 KW - Hydrogen assisted cracking KW - Carrier gas hot extraction KW - Welding KW - ISO 3690 KW - Metals PY - 2023 AN - OPUS4-58677 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Large scale hydrogen assisted cracking test for thick walled SAW joints for offshore applications N2 - Offshore wind turbines continuously increase in size and weight and demand adequate offshore foundations concepts like monopiles, tripods or jackets. These components are typically submerged arc welded (SAW) high-strength thick steel plates like the S420ML. During welding, the occurrence of delayed hydrogen assisted cracking (HAC) must be anticipated. HAC is a critical combination of the local hydrogen concentration within a susceptible microstructure under certain mechanical load, i.e., the occurring (welding) residual stresses. The welding sequence of the thick-walled plates complicate the residual stress distribution due to the necessary repeated thermal cycling, i.e., welding seam / layer deposition to fill the joint. For that purpose, SAW with two-wire-technique was used to weld a specially designed and prototype-like mock-up of a real component with a thickness of 50 mm, filled with 22 passes and a seam length of 1,000 mm. Additional welded stiffeners simu-lated the effect of a high restraint, to stimulate critical HAC conditions. The necessity of a minimum waiting time (MWT) before the NDT can be conducted (to exclude HAC) was critically verified by the application of ultrasonic testing of the welded joint at different time-steps of the NDT of 48 h after welding. The residual stresses were determined by a robot XRD goniometer. Tensile residual stresses up to the yield limit are found both in the weld metal and in the heat-affected zone. Numerical modelling allowed the qualitative estimation of the hydrogen diffusion in the weld. A remarkable HAC occurrence was not identified and proves both, a certain resistance of the weld joint to HAC and the (questionable) duration of the MWT. T2 - IIW Annual Assembly, Meeting of Commission II-C CY - Singapore DA - 19.07.2023 KW - Mock-up KW - Hydrogen assisted cracking KW - Submerged arc welding KW - Offshore KW - Steel PY - 2023 AN - OPUS4-57977 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -