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Maksimov S.Y.,Paton Electrical Welding Institute
Welding International | Year: 2010

Welding is used extensively in the construction and repair of underwater pipelines. Recently, the volume of application of underwater welding in these operations has been expanded considerably. This welding method is used directly in water without expensive caissons and chambers. The development of Hydroweld FS electrodes in 19991 resulted in the introduction of manual wet welding for restoring the load-carrying capacity of structures produced from Cmn steels with a carbon equivalent of up to 0.4. At the same time, the problem of welding steels with higher strength with a high carbon equivalent has not been solved. This is associated with the considerable difficulties of metallurgical nature. The welding pool is enriched with hydrogen, rising from the vapour-gas bubble, and accelerated cooling by the surrounding water results in 'fixing' of hydrogen in the weld metal. This is accompanied by the formation of quenched structures in the heat-affected zone (HAZ). Consequently, the risk of formation of cold cracks greatly increases, especially, in welding low-alloy steels with higher strength of the 17G1S or X60 type, which is used widely for the construction of pipeline systems. At the same time, the weldability of these steels in water has been studied insufficiently, regardless of the fact that underwater welding is used for the repair of metal structures working under water. © 2010 Taylor & Francis. Source


Kompan Y.,Paton Electrical Welding Institute | Protokovilov I.,Paton Electrical Welding Institute | Fautrelle Y.,EPM Laboratory | Gelfgat Y.,University of Latvia | Bojarevics A.,University of Latvia
Magnetohydrodynamics | Year: 2010

Series of titanium alloy remeltings have been performed in an experimental electroslag setup. The typical electrovortical flow pattern in both the slag and the liquid metal pool has been radically modified by imposing an external magnetic field. Several configurations of the applied magnetic field were considered and tested during actual remelting. The best results were obtained during remelting in the presence of a pulse axial magnetic field providing fine-grained titanium alloy ingots of uniform composition. It has been shown that the new process of magnetically controlled electroslag melting is a highly competitive alternative method for the production of multi-component titanium alloys. Further modifications of the process are proposed with an aim to optimize energy efficiency and equipment costs. Source


Stepanyuk S.M.,Paton Electrical Welding Institute | Pokhodnya I.K.,Paton Electrical Welding Institute
18th European Conference on Fracture: Fracture of Materials and Structures from Micro to Macro Scale | Year: 2010

The hydrogen assisted cold cracking (HACCof high strength steel weldments creates the serious technological problems. In this paper the theoretical generalisation and new decisions of this problem are presented. The adequate physical model developed by PEWI was used as the basis of the mechanism of HACC formation. The model is based on advanced ideas of metal physics about a mechanism of steel cleavage fracture. The key elements of the model are dislocation structure evolution and microcrack behaviour that take place during plastic strain. The dislocations have a particular function because their moving is both a main mechanism of the plastic strain and an efficient mechanism of hydrogen transportation in the metal. The model was used to analyze the features of hydrogen embrittlement of high strength low alloy (HSLAsteel. It is shown that under the influence of high temperature the steel structure loosing the positive effect of thermomechanical treatment, becomes highly sensitive to the embrittling action of hydrogen and, therefore, becomes more susceptible to HACC. Source


Ignatenko O.V.,Paton Electrical Welding Institute | Pokhodnya I.K.,Paton Electrical Welding Institute
18th European Conference on Fracture: Fracture of Materials and Structures from Micro to Macro Scale | Year: 2010

Computed calculations of interactions between two edge dislocations in a hydrogen-containing metal have been performed. According to the calculations, diffusible hydrogen concentration within the limits 2.5-10 cm3/100 g results in plasticity localization effect. The key aspect is extremal nature of repulsive force between two dislocations in a hydrogen-containing metal (in contrast to a hydrogen-free metal. Presence of diffusible hydrogen in a metal has been established to decrease the repulsive force between two edge dislocations. Thus, diffusible hydrogen concentration in a metal Co = 10 cm3 /100 g and temperature T=300 K results in 65% decrease of maximal repulsive force between two edge dislocations. That is why microdefects in a diffusible hydrogen-containing metal can appear at much lower external loads, which results in considerable deterioration of its mechanical characteristics. Source

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