TY - CONF A1 - Becker, Amadeus A1 - Schröpfer, Dirk A1 - Kannengießer, Thomas T1 - Consideration of design influences to provide adequate repair concepts for high-strength steel weld joints in offshore support structures N2 - The sustainable and resource-efficient production of offshore wind turbines requires the use of modern high-strength fine-grained structural steels (Martin and Schroeter, 2005). This applies to wind turbines in terms of increasing turbine sizes as well as to maintenance and installation vessels and equipment (Ummenhofer et al., 2013). Without the demanded high load-bearing capacities and boom lengths, the economic realization of these goals would be inconceivable. During the assembly of high-strength steel structures, unacceptable defects can occasionally be found in the weld area, although the welding process was executed in accordance with the specifications. In most cases, the economical solution would be local thermal gouging of the affected areas and re-welding. Corresponding standards hardly provide any information on adequate repair concepts, and there is no uniform scientific data on which to base such concepts. This applies particularly to the consideration and optimization of welding-induced stresses due to the high shrinkage hindrance of the gouging grooves and degradation of the adjacent microstructures by gouging and re-welding. The result, especially in the case of high-strength steel grades, are frequently recurring imperfections as well as a missing consideration of the additionally induced welding stresses in the design of the structure. In this context, at BAM component-relevant investigations focused on welding residual stress evolution and microstructural degradation during repair of weld joints due to local thermal gouging and re-welding are carried out within the scope of a FOSTA project (P1311, IGF 20162N). In this study, several relevant findings are discussed based on examples of structural engineering focusing on mechanical-technological properties and residual stresses, for instance found by (Schasse, 2017). Also experimental and numerical work as conducted by (Wongpanya, 2008) and weld tests under defined shrinkage restraint in special weld test-setups for research projects, e. g. FOSTA-P922 (Kannengiesser and Schroepfer, 2015) and P1011 (Kannengiesser and Schroepfer, 2017) have shown that an optimization of the welding-induced stresses of high-strength structural steels is specifically achievable by means of adapted heat control concepts (Schroepfer, 2017). The present research involves systematic investigations of influences of shrinkage restraint, the number of repair cycles and heat control during repair welding of the relatively new developed offshore-relevant high-strength steel S500MLO (EN 10225-1). For the quantification of the shrinkage restraint of weld joints, the concept of restraint intensity established by (Satho et al., 1973) was applied analogous to recent research, e. g. (Schwenk et al., 2008). By means of structural mechanics calculations, geometries of self-strained specimens were identified, that represent different defined rigidity conditions of repair welds of real components, cf. Fig. 1. It could be shown that with increasing weld joint restraint intensity significantly higher residual stresses in the weld metal and heat affected zone up to 80 % of the nominal yield strength occur, cf. Fig. 2. In relation to existing results, it has been shown that a safe repair of such welds can only be achieved by means of appropriate repair concepts and heat control taking the high welding stresses and special microstructures of high-strength steels into account. Finally, the aim of this research is to derive recommendations for repair concepts appropriate to the stresses and materials involved providing a basis for standards and guidelines, especially for SMEs, in order to avoid damage and, in most cases, expensive reworking and to improve the full utilization of the potential of high-strength steels. T2 - Wind Energy Science Conference 2021 CY - Online meeting DA - 25.05.2021 KW - High-strength structural steels KW - Welding KW - Repair KW - Residual stresses KW - Restraint PY - 2021 AN - OPUS4-53319 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Becker, Amadeus A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Adequate repair concepts for high-strength steel weld joints for offshore support structures considering design influences N2 - The sustainable and resource-efficient production of wind energy plants requires the use of modern high-strength fine-grain structural steels. This applies to both foundation and erection structures. During the assembly of steel structures, unacceptable defects can occasionally be found in the weld area. In most cases, the economical solution would be local thermal gouging of the affected areas and re-welding. Due to the high shrinkage restraint of the joint groove in the overall structure, the superposition of global and local welding-induced stresses may lead to crack formation and component failure, particularly in interaction with the degradation of the microstructure and mechanical properties of high-strength steels during the repair process [1]. Corresponding standards hardly provide any information on adequate repair concepts, and there is no uniform scientific data on which to base such concepts. In this study, several relevant findings are discussed based on examples of structural engineering focusing on mechanical-technological properties and residual stresses, e.g. [1]. Further experimental and numerical work as conducted by [2] and weld tests under defined restraint conditions in special weld test-setups [3] show that an optimization of the welding-induced stresses of high-strength structural steels is achievable by means of an adapted heat control. The present research involves systematic investigations of influences of shrinkage restraint, the number of repair cycles and heat control during repair welding of a recently available high-strength offshore steel S500MLO (EN 10225-1). A quantification of the shrinkage restraint of repair weld joints is achievable by means of restraint intensity concept [4], analogous to previous studies [5]. Using structural mechanics calculations, geometries of self-restrained specimens are identified representing different defined rigidity conditions of repair welds considering actual high-strength steel components. Welding experiments with DIC analyses (digital image correlation) of the occurring strains during welding and XRD analyses (X-ray diffraction) of the resulting residual stresses after welding and cooling show increasing transient loads and significantly elevated residual stress profiles in the weld area with increasing restraint intensity. Especially in the heat affected zone, tensile residual stresses of up to 80 % of the nominal yield strength occur when welding under increased restraint conditions. In relation to the presented existing results, this indicates that a safe repair welding is primarily achievable by means of appropriate repair concepts and heat control taking into account the high welding stresses and special microstructures of high-strength steels. Finally, the aim of this research is to derive recommendations for repair concepts appropriate to the stresses and materials involved providing a basis for standards and guidelines, especially for SMEs, in order to avoid damage and, in most cases, expensive reworking and to improve the full utilization of the potential of high-strength steels. T2 - 74th IIW Annual Assembly and International Conference, C II-A CY - Online meeting DA - 07.07.2021 KW - High-strength structural steels KW - Welding KW - Repair KW - Residual stresses KW - Restraint PY - 2021 AN - OPUS4-53320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Lausch, Thomas A1 - Schroepfer, Dirk A1 - Hannemann, Andreas T1 - In-situ Observation of Stress Evolution and Cracking during High Strength Steel Welding T2 - Proceedings of Visual-JW 2019 & WSE 2019 N2 - Residual stresses are crucial when assessing the performance of welded components. The present work deals with the possibilities of transferring the real-life boundary conditions of welding, which influence the residual stress, into the laboratory. The possibilities of a test system with a load capacity of 2 MN specifically developed for online monitoring of stress formation and cracking are shown. Due to the structural design, global process, geometry and material-dependent stresses are induced, which can be quantified in-situ during welding and post weld heat treatment. Examples are presented how the conditions to be found during production are simulated in the laboratory. It is shown how welding residual stresses in high-strength steels are affected by the heat control. Elevated working temperatures significantly increase the tensile residual stresses in the heat affected zone (HAZ). The effect of mechanical stresses resulting from welding on stress relief cracking is demonstrated by the example of a creep resistant steel. Reheat cracks were monitored online during post weld heat treatment. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Residual stress KW - Restraint KW - Welding KW - Large-scale test KW - Reheat cracking PY - 2019 SP - 83 EP - 84 PB - SEIEI Printing Co., Ltd CY - Osaka, Japan AN - OPUS4-49773 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Lausch, Thomas A1 - Schroepfer, Dirk T1 - In-situ Observation of Stress Evolution during High Strength Steel Welding N2 - Residual stresses are crucial when assessing the performance of welded components. The present work deals with the possibilities of transferring the real-life boundary conditions of welding, which influence the residual stress, into the laboratory. The possibilities of a test system with a load capacity of 2 MN specifically developed for online monitoring of stress formation and cracking are shown. Due to the structural design, global process, geometry and material-dependent stresses are induced, which can be quantified in-situ during welding and post weld heat treatment. Examples are presented how the conditions to be found during production are simulated in the laboratory. It is shown how welding residual stresses in high-strength steels are affected by the heat control. Elevated working temperatures significantly increase the tensile residual stresses in the heat affected zone (HAZ). The effect of mechanical stresses resulting from welding on stress relief cracking is demonstrated by the example of a creep resistant steel. Reheat cracks were monitored online during post weld heat treatment. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Residual stress KW - Restraint KW - Welding KW - Large-scale test KW - Reheat cracking PY - 2019 AN - OPUS4-49763 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröpfer, Dirk A1 - Kannengießer, Thomas A1 - Kromm, Arne T1 - Welding stress control in high-strength steel components using adapted heat control concepts N2 - High-strength steels are increasingly applied in modern steel constructions to meet today’s lightweight requirements. Welding of these steels demands a profound knowledge of the interactions between the welding process, cooling conditions, heat input and the resulting metallurgical occurrences in the weld and its vicinity. Additionally, welding stresses may be detrimental for the safety and performance of high-strength steel component welds during fabrication and service, especially due to the high yield ratio. For a development of strategies to adjust welding heat control, all these effects should be considered, to reach a complete exploitation of the high-strength steel potential. In recent researches at BAM, multilayer GMAW experiments were performed with high-strength steels, in which cooling conditions and resulting microstructure were analysed for varied heat control parameters. The application of a unique 3d-operating testing facility and X-ray diffraction measurements allowed the analysis of local stresses in the weld while welding and cooling under component relevant shrinkage restraints. As a result, correlations between material behaviour, welding and cooling condition and the arising multi-axial stresses and forces were found. Based on this study, statements for the development of adapted heat control concepts were derived, which are presented by means of specific analysis examples. T2 - IIW Intermediate Meeting C-II/CIX CY - Genua, Italy DA - 05.03.2018 KW - Process parameters KW - Residual stresses KW - GMA Welding KW - Restraint KW - High-strength steels PY - 2018 AN - OPUS4-45500 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schroepfer, Dirk A1 - Kromm, Arne A1 - Schaupp, Thomas A1 - Kannengießer, Thomas T1 - Welding Stress Control in High-strength Steel Components Using Adapted Heat Control Concepts N2 - High-strength steels are increasingly applied in modern steel constructions to meet today’s lightweight requirements. Welding of these steels demands a profound knowledge of the interactions between the welding process, cooling conditions, heat input and the resulting metallurgical occurrences in the weld and its vicinity. Additionally, welding stresses may be detrimental for the safety and performance of high-strength steel component welds during fabrication and service, especially due to the high yield ratio. For a development of strategies to adjust welding heat control, all these effects should be considered, to reach a complete exploitation of the high-strength steel potential. In recent researches at BAM, multilayer GMAW experiments were performed with high-strength steels, in which cooling conditions and resulting microstructure were analysed for varied heat control parameters. The application of a unique 3d-operating testing facility and X-ray diffraction measurements allowed the analysis of local stresses in the weld while welding and cooling under component relevant shrinkage restraints. As a result, correlations between material behaviour, welding and cooling condition and the arising multi-axial stresses and forces were found. Based on this study, statements for the development of adapted heat control concepts were derived, which are presented by means of specific analysis examples. T2 - 71st IIW Annual Assembly and International Conference: Commission II-A CY - Nusa Dua, Bali, Indonesia DA - 15.07.2018 KW - Residual stresses KW - GMA Welding KW - Restraint KW - High-strength steels KW - Process parameters PY - 2018 AN - OPUS4-45623 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Load analyses of welded high-strength steel structures using image correlation and diffraction techniques N2 - In an increasing number of modern steel applications high-strength steel grades are demanded to meet specifications regarding a high load bearing capacity and a low operating weight. Lightweight design rules enhance the safety requirements, especially for welded joints. Besides a higher cracking risk for HSLA steel welds, the formation of tensile residual stresses might lead to fracture due to overloading or premature failure if not adequately considered. In codes and standards, therefore, residual stress on the amount of the yield strength are expected, disregarding the circumstance that generally the residual stresses are much lower in HSLA steel welds. Oftentimes this leads to an underestimation of the proof strength in high-strength welded components and economical disadvantages using HSLA steels. In this study, a stress-strain analysis was conducted at component related structures from S960QL using digital image correlation while preheating welding and cooling adjacent to the weld seam. X-ray diffraction analysis of the local residual stresses in the weld seam showed a good comparability with the global analyses. The comparison of two different seam geometries revealed significantly lower multi-axial stresses if a narrower weld groove is used. T2 - IIW Annual Assembly 2017 CY - Shanghai, China DA - 25.06.2017 KW - Residual stresses KW - GMA Welding KW - Restraint KW - High-strength steels KW - Process parameters PY - 2017 AN - OPUS4-41074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Formation of multi-axial welding stresses due to material behaviour during fabrication of high-strength steel components N2 - Today an expanding application of high-strength steels in modern welded constructions can be observed. The economical use of these steel grades largely depends on the strength and reliability of the weldments. Therefore the special microstructure and mechanical properties of these grades have to be taken into account by keener working ranges regarding the welding parameters. However, performance and safety of welded components are strongly affected by the stresses occurring during and after welding fabrication locally in the weld seam and globally in the whole component, especially if the shrinkage and distortion due to welding are restrained. Some extensive studies describe the optimization of the welding stresses and the metallurgical effects regarding an adapted welding heat control. In particular lower working temperatures revealed to be effective to significantly reduce the local and global welding induced residual stresses of the completed weld. However, decreased interpass temperatures cause concurrently higher stresses during welding fabrication. This work shows some strategies to reduce these in-process stresses. With help of multi-axial welding stress analyses in component-related weld tests using a special 2-MN-testing facility differences in stress build-up are described in detail for root welds, filler layers and subsequent cooling to ambient temperature. T2 - IIW Annual Assembly 2017 CY - Shanghai, China DA - 25.06.2017 KW - Residual stresses KW - GMA Welding KW - Restraint KW - High-strength steels KW - Process parameters PY - 2017 AN - OPUS4-41075 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Load analyses of welded high-strength steel structures using image correlation and diffraction techniques N2 - In an increasing number of modern steel applications high-strength steel grades are demanded to meet specifications regarding a high load bearing capacity and a low operating weight. Lightweight design rules enhance the safety requirements, especially for welded joints. Besides a higher cracking risk for HSLA steel welds, the formation of tensile residual stresses might lead to fracture due to overloading or premature failure if not adequately considered. In codes and standards, therefore, residual stress on the amount of the yield strength are expected, disregarding the circumstance that generally the residual stresses are much lower in HSLA steel welds. Oftentimes this leads to an underestimation of the proof strength in high-strength welded components and economical disadvantages using HSLA steels. In this study, a stress-strain analysis was conducted at component related structures from S960QL using digital image correlation while preheating welding and cooling adjacent to the weld seam. X-ray diffraction analysis of the local residual stresses in the weld seam showed a good comparability with the global analyses. The comparison of two different seam geometries revealed significantly lower multi-axial stresses if a narrower weld groove is used. T2 - IIW Intermediate Meeting, C-II-A CY - Trollhättan, Sweden DA - 06.03.2017 KW - Residual stresses KW - GMA Welding KW - Restraint KW - High-strength steels KW - Process parameters PY - 2017 AN - OPUS4-41065 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Formation of multi-axial welding stresses due to material behaviour during fabrication of high-strength steel components N2 - Today an expanding application of high-strength steels in modern welded constructions can be observed. The economical use of these steel grades largely depends on the strength and reliability of the weldments. Therefore the special microstructure and mechanical properties of these grades have to be taken into account by keener working ranges regarding the welding parameters. However, performance and safety of welded components are strongly affected by the stresses occurring during and after welding fabrication locally in the weld seam and globally in the whole component, especially if the shrinkage and distortion due to welding are restrained. Some extensive studies describe the optimization of the welding stresses and the metallurgical effects regarding an adapted welding heat control. In particular lower working temperatures revealed to be effective to significantly reduce the local and global welding induced residual stresses of the completed weld. However, decreased interpass temperatures cause concurrently higher stresses during welding fabrication. This work shows some strategies to reduce these in-process stresses. With help of multi-axial welding stress analyses in component-related weld tests using a special 2-MN-testing facility differences in stress build-up are described in detail for root welds, filler layers and subsequent cooling to ambient temperature. T2 - IIW Intermediate Meeting, C-II-A CY - Trollhättan, Sweden DA - 06.03.2017 KW - Residual stresses KW - GMA Welding KW - High-strength steels KW - Process parameters KW - Restraint PY - 2017 AN - OPUS4-41066 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -