The paper proposes a variant for solving the problem of reduction of longitudinal residual stresses in near-root region of a circumferential welded joint of section of steam pipeline by FEM simulation of the stress-strain state of repaired section of a circumferential weld in the zone of lack of root penetration on a thin-wall shell of 89 mm diameter and 6 mm wall thickness from steel 20. The result of solving the problem is total distribution of stresses and residual plastic deformations in the repaired zone

A. O. Perepichay

A. Čikić

I. Mamuzić

V. M. Prokhorenko

English

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449METALURGIJA 52 (2013) 4, 449-452V. M. PROKHORENKO, A. O. PEREPICHAY, I. MAMUZIĆ, A. ČIKIĆREDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION OF CIRCUMFERENTIAL JOINT OF STEAM PIPELINE IN TECHNOLOGICAL WAYReceived – Prispjelo: 2013-02-06Accepted – Prihvaćeno: 2013-04-15Original Scientifi c Paper – Izvorni znanstveni radISSN 0543-5846METABK 52(4) 449-452 (2013)UDC – UDK 669.14.018:621.181.021:621.791.052:620.16=111V. M. Prokhorenko, A. O. Perepichay, National Technical University of Ukraine “Kyiv Polytechnic Institute”, Kyiv, Ukraine I. Mamuzić, Croatian Metallurgical Society, Zagreb, A. Čikić, Technical College in Bjelovar, CroatiaThe paper proposes a variant for solving the problem of reduction of longitudinal residual stresses in near-root re-gion of a circumferential welded joint of section of steam pipeline by FEM simulation of the stress-strain state of repaired section of a circumferential weld in the zone of lack of root penetration on a thin-wall shell of 89 mm diam-eter and 6 mm wall thickness from steel 20. The result of solving the problem is total distribution of stresses and residual plastic deformations in the repaired zone.Key words: steel, weld, stress, steam pipeline, static strength of weldsINTRODUCTIONResidual stresses and deformations in a near-root re-gion of circumferential welds of steam pipelines with al-lowed by standard lack of root penetration are to be deter-mined, fi rst of all, for evaluation of static strength of the welds and prediction of propagation of natural sharp crack from a tip of lack of penetration in the weld. Propagation of such cracks in the circumferential welds can result in weld failure and damage of the steam pipeline. Considering mentioned-above, study of residual welded stresses in the circumferential joints of steam pipelines with circumferential crack-like defects and evaluation of their static strength is relevant and signifi -cant scientifi c-and-technical problem. Steels 20 of 89, 159 and 219 mm diameters with 6 mm wall thickness are used, as a rule, for manufacture of the technological steam pipelines. Chemical composition and mechanical properties of steel 20 are shown in Tables 1 and 2. Table 1 Chemical composition of steel 20 / %Content of elements / %C Si Mn Ni S P Cr Cu0,2 0,3 0,5 0,25 0,04 0,04 0,2 0,2Table 2 Mechanical properties of steel 20Ultimate strength / МPаYield strength / МPаSpecifi c elongation / %Hardness / НВ420 234 25 130 - 160The investigations showed an area of tensile residual welding stresses appearing over the lack of penetration in the near-root zone of circumferential weld. They open crack faces and promote its propagation deep into the wall thickness of steam pipeline [1]. Finite-element method (FEM) was used for solving of the stated problem. A thin-wall shell of necessary ge-ometry was simulated and calculation for several vari-ants of manual arc welding technology, namely one pass, two and three passes welding, was performed us-ing this method [2]. PROBLEMS OF THE INVESTIGATION The fl owing problems were considered in the present work: -  FEM based solution of a joint temperature elastic-plastic problem on residual stress-strain state from two or three pass welding of circumferential weld; -  analysis of rules and peculiarities of distribution of residual stresses and deformations in the vicinity of section of the circumferential weld where the lack of penetration was simulated; -  selection experimental check of obtained calcula-tion results regarding axial residual stresses in weld on internal and external surfaces; -  formulation of the conclusions on possibility of re-duction of the stress-strain state in the vicinity of tip of the circumferential lack of penetration in technological way and, thus, increase of static strength of the circumferential welds of steam pipelines.SIMULATION OF STEAM PIPELINE SECTION WITH ROOT DEFECTSolving of problems of strained body mechanics for regions with cuts (cracks) is connected with signifi cant 450  METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...mathematical diffi culties due to presence of specifi c (singular) points. Most of these problems can be effectively solved only with computer help. The fi nite-element method obtained the highest dis-tribution among the computational approaches used for solving of fracture mechanics problems. This is, fi rst of all, connected with its versatility, well-developed theory and presence of signifi cant number of powerful compu-tational complexes realizing FEM. Different aspects of the FEM application can be considered in fracture mechanics problems. Firstly, these are the calculation of coeffi cients of stress inten-sity, loop J-integrals etc. for different shape areas [3,4]. Secondly, FEM can be used for simulation of fracture processes or behavior of bodies with stationary cracks under such conditions for which accurate mathematical models are absent. Such calculations are useful, in par-ticular, in combination with the full-scale experiments. The third area of FEM application important for prac-tice is the analysis of strength of the real structures from point of view of brittle fracture resistance. The fi nite-element method is based on the assump-tion that a body can be represented in a form of set of elements connected between each other only in the nodes. Connection of node forces with node displace-ments is set with the help of element stiffness matrix. Conditions of body equilibrium can be obtained joining the stiffness matrix of separate elements in a global body stiffness matrix. Solution of system of algebraic equilibrium equations at set active stresses or displace-ments and known global stiffness matrix allows fi nding all the node forces and then stresses and displacements within the framework of each element. Thus, stress-strain state of the body is determined [5]. Algorithm of FEM calculation for section of steam pipelines of 89, 159 and 219 mm diameter and 6 mm wall thickness with lack of root penetration of circum-ferential weld is given below. Stage of pre-process preparation of the model in-cludes creation of date base necessary for calculation, setting of coordinate system, development of geometri-cal model of cylindrical shell with circumferential weld for two variants of welding (with full penetration and with predetermined lack of root penetration of circum-ferential weld, Figure 1), setting of material properties, type and time of analysis, mode of welding and bound-ary conditions according to Tables (1,2), creation of net of fi nite elements and setting of element type.Further, a joint thermo-mechanical analysis involv-ing large displacements (Nonlinear Geometry) and au-tomatic stabilization of dissipation of energy is per-formed. Time of the analysis, i.e. 3 600 seconds up to complete cooling, is set.Loading is a volume heat source according to J. Goldak model [6]: Temperature on the edges of shell (20 °) and absence of structure fastening are the boundary conditions of the structure. Displacement of the nodes in any directions is allowed. Simulation of the structure for the purpose of solving of joint thermoplasticity problem was performed by vol-ume eight-node elements. Elastic-plastic model with strengthening was taken for the material of welded shell. Distribution of stresses and residual plastic strains in the vicinity of circumferential weld with allowed by standard lack of root penetration is a result of problem solution. The problems were solved for different number of passes (from one to three) in welding of circumferential welds. A diagram of distribution of stresses on line of continuation of lack of penetration (1,2 mm depth) from its tip in direction to shell external surface (Figure 2) was built. Also the diagram of dependence of axial stresses σx on depth of lack of penetration at different technological schemes of welding (Figure 3) was made for one the most close to the tip of lack of penetration point on the weld axis.Besides, simulation of pipe section with the circum-ferential weld made in three passes with complete cool-ing after each next pass as well as without cooling (con-tinuous welding) was performed. Figure 1  Geometrical model of section of pipeline with lack of root penetration in circumferential weld Figure 2  Distribution of longitudinal residual welding stresses on line of continuation of lack of penetration (depth 1,2 mm) from its tip in direction to external surface of thin-wall shell from steel 20 of 89 x 6 mm diameter at diff erent number of passes of circumferential weld 451METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...and internal sides in the vicinity of lack of penetration (Figures 4, 5) and in zone with full penetration (Figures 6, 7) in order to perform comparative analysis of ex-perimental data with calculation results.Stresses on external surface of 219 × 6 mm diameter pipe along its generatrix in the middle of zone of weld with lack of penetration (Figure 4) are negative (com-pressive). Average experimental value of stresses on 25 mm basis makes 270 MPa and average calculation value equals 244 MPa. The difference is around 9,6 %. Presence of the stress raiser in a form of lack of pen-etration (Figure 5) promotes non-uniform distribution of the longitudinal residual stresses on external surface of the pipe. Average value of stresses in this zone on the basis of 25 mm equals + 142 MPa (tensile) according to experi-mental results and their average value makes 217 MPa according to calculation data.  34 % difference appears due to an effect of high lo-cal stress concentration induced by presence of the lack Figure 3  Distribution of longitudinal residual welding stresses depending on depth of lack of penetration on line of its continuation from the tip for thin-wall shell from steel 20 of 98, 159 and 219 mm diameter considering diff erent technological schemes of weldingObtained results provides the possibility for evalua-tion of value of longitudinal axial stresses over the lack of penetration in the whole range of change of lack of penetration depth 0 - 1,2 mm. Curves from Figure 3 can also be used for compari-son of the stresses in one-pass welds and welds made per three passes without pauses and with cooling during 3600 s after each pass. Three following peculiarities of stress-strain state (Figure 3) can be outlined based on calculation results. Firstly, more or less uniform increase of the longitu-dinal axial stresses for all pipe diameters in a point over the raiser is observed with the increase of depth of lack of penetration. Secondly, the axial stresses in zone over the tip of lack of penetration at small lack of penetration (up to 0,5 mm) in multi-pass welds are compressive ones in the level up to “ - ” (50 - 100) MPa with their further transfer in tensile ones at increase of depth of lack of penetration.Thirdly, an effect of equally spaced displacement with stable difference in 50 MPa of the curve for axial stresses in the weld with three passes provided cooling after each pass can be explained by insignifi cant in-crease of the stresses due to their summing at each cool-ing step (Figure 3).SELECTION EXPERIMENTAL CHECK OF CALCULATION RESULTS Deformations were measured and residual longitu-dinal stresses from welding of circumferential weld on 219 × 6 mm diameter pipe were calculated for external Figure 4  Distribution of longitudinal stresses over the lack of penetration on external surface of pipe Figure 5  Distribution of longitudinal welding stresses in the vicinity of lack of penetration on internal surface of pipe 452  METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...of root penetration of circumferential weld from inter-nal side of the pipe. Calculation stresses on pipe section with full pene-tration have good correlation with experimental data on external as well as internal surfaces of the pipe. This fact is explained by absence of the stress raisers on this section of the pipe. Difference between the calculation and experimen-tal data for this section does not exceed 9 %. Therefore, FEM calculations can be considered as such providing suffi ciently accurate determination of distribution of components of the residual stresses from welding of circumferential weld in the vicinity of stress raiser in a form of lack of penetration as well as in the points distant from it. Difference of FEM calculations with experimental data lies in 9 - 10 % range. CONCLUSIONSApplication of the Finite Element Method provided the solution and analysis of the results of joint tempera-ture elastic-plastic problem in multi-pass welding of circumferential weld of technological steam pipeline. Analysis of calculations of the stress-strain state for different technological schemes of welding deter-mined that increase of static strength of the circumfer-ential welds can be achieved due to rise of number of passes from one to three. The latter promotes reduc-tion of the lack of penetration up to 0,5 mm, axial stresses over the lack of penetration and the coeffi -cients of stress intensity at the initial stage of crack propagation, respectively. REFERENCES [1] Prokhorenko V. M., Perepichay A. O., Zvorykin K. O. Technological systems, 59 (2012) 2, 20-26. [2] GOST 5264-80 Manual arc welding. Welded joints. Main types, structural elements and dimensions. [3] Morozov E. M., Nikishov G. P. Finite element method in fracture mechanics, Nauka, Moscow, 1980, pp. 137-194. [4] Morozov E. M., Nikishov G. P. FKhMM, 4 (1982), 13-29. [5] Zenkevich O. K. Finite element method in engineering, Mir, Moscow, 1975, pp. 443-528. [6]  John A. Goldak Computational welding mechanics, USA, 2005, pp. 279-325.[7] NPAOP 0.00-1.11-98 Rules of designing and safe opera-tion of steam and hot water pipelines.Note:  The responsible translator for English language is PEWI, Kiev, UkraineFigure 6  Distribution of longitudinal stresses on external surface of pipe with full penetration Figure 7  Distribution of longitudinal stresses on internal surface of pipe with full penetration

Reduction of longitudinal axial residual stresses in near-root region of circumferential joint of steam pipeline in technological way

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449 METALURGIJA 52 (2013) 4, 449-452V. M. PROKHORENKO, A. O. PEREPICHAY, I. MAMUZIĆ, A. ČIKIĆREDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION OF CIRCUMFERENTIAL JOINT OF STEAM PIPELINE IN TECHNOLOGICAL WAYReceived – Prispjelo: 2013-02-06Accepted – Prihvaćeno: 2013-04-15Original Scientifi  c Paper – Izvorni znanstveni radISSN 0543-5846METABK 52(4) 449-452 (2013)UDC – UDK 669.14.018:621.181.021:621.791.052:620.16=111V. M. Prokhorenko, A. O. Perepichay, National Technical University of Ukraine “Kyiv Polytechnic Institute”, Kyiv, Ukraine I. Mamuzić, Croatian Metallurgical Society, Zagreb, A. Čikić, Technical College in Bjelovar, CroatiaThe paper proposes a variant for solving the problem of reduction of longitudinal residual stresses in near-root re-gion of a circumferential welded joint of section of steam pipeline by FEM simulation of the stress-strain state of repaired section of a circumferential weld in the zone of lack of root penetration on a thin-wall shell of 89 mm diam-eter and 6 mm wall thickness from steel 20. The result of solving the problem is total distribution of stresses and residual plastic deformations in the repaired zone.Key words: steel, weld, stress, steam pipeline, static strength of weldsINTRODUCTIONResidual stresses and deformations in a near-root re-gion of circumferential welds of steam pipelines with al-lowed by standard lack of root penetration are to be deter-mined, ﬁ  rst of all, for evaluation of static strength of the welds and prediction of propagation of natural sharp crack from a tip of lack of penetration in the weld. Propagation of such cracks in the circumferential welds can result in weld failure and damage of the steam pipeline. Considering mentioned-above, study of residual welded stresses in the circumferential joints of steam pipelines with circumferential crack-like defects and evaluation of their static strength is relevant and signiﬁ  -cant scientiﬁ  c-and-technical problem. Steels 20 of 89, 159 and 219 mm diameters with 6 mm wall thickness are used, as a rule, for manufacture of the technological steam pipelines. Chemical composition and mechanical properties of steel 20 are shown in Tables 1 and 2. Table 1 Chemical composition of steel 20 / %Content of elements / %CS i M n N i S PC r C u0,2 0,3 0,5 0,25 0,04 0,04 0,2 0,2Table 2 Mechanical properties of steel 20Ultimate strength / МPаYield strength / МPаSpecifi  c elongation / %Hardness / НВ420 234 25 130 - 160The investigations showed an area of tensile residual welding stresses appearing over the lack of penetration in the near-root zone of circumferential weld. They open crack faces and promote its propagation deep into the wall thickness of steam pipeline [1]. Finite-element method (FEM) was used for solving of the stated problem. A thin-wall shell of necessary ge-ometry was simulated and calculation for several vari-ants of manual arc welding technology, namely one pass, two and three passes welding, was performed us-ing this method [2]. PROBLEMS OF THE INVESTIGATION The ﬂ  owing problems were considered in the present work: -   FEM based solution of a joint temperature elastic-plastic problem on residual stress-strain state from two or three pass welding of circumferential weld; -   analysis of rules and peculiarities of distribution of residual stresses and deformations in the vicinity of section of the circumferential weld where the lack of penetration was simulated; -   selection experimental check of obtained calcula-tion results regarding axial residual stresses in weld on internal and external surfaces; -   formulation of the conclusions on possibility of re-duction of the stress-strain state in the vicinity of tip of the circumferential lack of penetration in technological way and, thus, increase of static strength of the circumferential welds of steam pipelines.SIMULATION OF STEAM PIPELINE SECTION WITH ROOT DEFECTSolving of problems of strained body mechanics for regions with cuts (cracks) is connected with signiﬁ  cant 450   METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...mathematical difﬁ   culties due to presence of speciﬁ  c (singular) points. Most of these problems can be effectively solved only with computer help. The ﬁ  nite-element method obtained the highest dis-tribution among the computational approaches used for solving of fracture mechanics problems. This is, ﬁ  rst of all, connected with its versatility, well-developed theory and presence of signiﬁ  cant number of powerful compu-tational complexes realizing FEM. Different aspects of the FEM application can be considered in fracture mechanics problems. Firstly, these are the calculation of coefﬁ  cients of stress inten-sity, loop J-integrals etc. for different shape areas [3,4]. Secondly, FEM can be used for simulation of fracture processes or behavior of bodies with stationary cracks under such conditions for which accurate mathematical models are absent. Such calculations are useful, in par-ticular, in combination with the full-scale experiments. The third area of FEM application important for prac-tice is the analysis of strength of the real structures from point of view of brittle fracture resistance. The ﬁ  nite-element method is based on the assump-tion that a body can be represented in a form of set of elements connected between each other only in the nodes. Connection of node forces with node displace-ments is set with the help of element stiffness matrix. Conditions of body equilibrium can be obtained joining the stiffness matrix of separate elements in a global body stiffness matrix. Solution of system of algebraic equilibrium equations at set active stresses or displace-ments and known global stiffness matrix allows ﬁ  nding all the node forces and then stresses and displacements within the framework of each element. Thus, stress-strain state of the body is determined [5]. Algorithm of FEM calculation for section of steam pipelines of 89, 159 and 219 mm diameter and 6 mm wall thickness with lack of root penetration of circum-ferential weld is given below. Stage of pre-process preparation of the model in-cludes creation of date base necessary for calculation, setting of coordinate system, development of geometri-cal model of cylindrical shell with circumferential weld for two variants of welding (with full penetration and with predetermined lack of root penetration of circum-ferential weld, Figure 1), setting of material properties, type and time of analysis, mode of welding and bound-ary conditions according to Tables (1,2), creation of net of ﬁ  nite elements and setting of element type.Further, a joint thermo-mechanical analysis involv-ing large displacements (Nonlinear Geometry) and au-tomatic stabilization of dissipation of energy is per-formed. Time of the analysis, i.e. 3 600 seconds up to complete cooling, is set.Loading is a volume heat source according to J. Goldak model [6]: Temperature on the edges of shell (20 °) and absence of structure fastening are the boundary conditions of the structure. Displacement of the nodes in any directions is allowed. Simulation of the structure for the purpose of solving of joint thermoplasticity problem was performed by vol-ume eight-node elements. Elastic-plastic model with strengthening was taken for the material of welded shell. Distribution of stresses and residual plastic strains in the vicinity of circumferential weld with allowed by standard lack of root penetration is a result of problem solution. The problems were solved for different number of passes (from one to three) in welding of circumferential welds. A diagram of distribution of stresses on line of continuation of lack of penetration (1,2 mm depth) from its tip in direction to shell external surface (Figure 2) was built. Also the diagram of dependence of axial stresses σx on depth of lack of penetration at different technological schemes of welding (Figure 3) was made for one the most close to the tip of lack of penetration point on the weld axis.Besides, simulation of pipe section with the circum-ferential weld made in three passes with complete cool-ing after each next pass as well as without cooling (con-tinuous welding) was performed. Figure 1   Geometrical model of section of pipeline with lack of root penetration in circumferential weld Figure 2   Distribution of longitudinal residual welding stresses on line of continuation of lack of penetration (depth 1,2 mm) from its tip in direction to external surface of thin-wall shell from steel 20 of 89 x 6 mm diameter at diff  erent number of passes of circumferential weld 451 METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...and internal sides in the vicinity of lack of penetration (Figures 4, 5) and in zone with full penetration (Figures 6, 7) in order to perform comparative analysis of ex-perimental data with calculation results.Stresses on external surface of 219 × 6 mm diameter pipe along its generatrix in the middle of zone of weld with lack of penetration (Figure 4) are negative (com-pressive). Average experimental value of stresses on 25 mm basis makes 270 MPa and average calculation value equals 244 MPa. The difference is around 9,6 %. Presence of the stress raiser in a form of lack of pen-etration (Figure 5) promotes non-uniform distribution of the longitudinal residual stresses on external surface of the pipe. Average value of stresses in this zone on the basis of 25 mm equals + 142 MPa (tensile) according to experi-mental results and their average value makes 217 MPa according to calculation data.  34 % difference appears due to an effect of high lo-cal stress concentration induced by presence of the lack Figure 3   Distribution of longitudinal residual welding stresses depending on depth of lack of penetration on line of its continuation from the tip for thin-wall shell from steel 20 of 98, 159 and 219 mm diameter considering diff  erent technological schemes of weldingObtained results provides the possibility for evalua-tion of value of longitudinal axial stresses over the lack of penetration in the whole range of change of lack of penetration depth 0 - 1,2 mm. Curves from Figure 3 can also be used for compari-son of the stresses in one-pass welds and welds made per three passes without pauses and with cooling during 3600 s after each pass. Three following peculiarities of stress-strain state (Figure 3) can be outlined based on calculation results. Firstly, more or less uniform increase of the longitu-dinal axial stresses for all pipe diameters in a point over the raiser is observed with the increase of depth of lack of penetration. Secondly, the axial stresses in zone over the tip of lack of penetration at small lack of penetration (up to 0,5 mm) in multi-pass welds are compressive ones in the level up to “ - ” (50 - 100) MPa with their further transfer in tensile ones at increase of depth of lack of penetration.Thirdly, an effect of equally spaced displacement with stable difference in 50 MPa of the curve for axial stresses in the weld with three passes provided cooling after each pass can be explained by insigniﬁ  cant in-crease of the stresses due to their summing at each cool-ing step (Figure 3).SELECTION EXPERIMENTAL CHECK OF CALCULATION RESULTS Deformations were measured and residual longitu-dinal stresses from welding of circumferential weld on 219 × 6 mm diameter pipe were calculated for external Figure 4   Distribution of longitudinal stresses over the lack of penetration on external surface of pipe Figure 5   Distribution of longitudinal welding stresses in the vicinity of lack of penetration on internal surface of pipe 452   METALURGIJA 52 (2013) 4, 449-452PROKHORENKO V. M. et al.: REDUCTION OF LONGITUDINAL AXIAL RESIDUAL STRESSES IN NEAR-ROOT REGION...of root penetration of circumferential weld from inter-nal side of the pipe. Calculation stresses on pipe section with full pene-tration have good correlation with experimental data on external as well as internal surfaces of the pipe. This fact is explained by absence of the stress raisers on this section of the pipe. Difference between the calculation and experimen-tal data for this section does not exceed 9 %. Therefore, FEM calculations can be considered as such providing sufﬁ  ciently accurate determination of distribution of components of the residual stresses from welding of circumferential weld in the vicinity of stress raiser in a form of lack of penetration as well as in the points distant from it. Difference of FEM calculations with experimental data lies in 9 - 10 % range. CONCLUSIONSApplication of the Finite Element Method provided the solution and analysis of the results of joint tempera-ture elastic-plastic problem in multi-pass welding of circumferential weld of technological steam pipeline. Analysis of calculations of the stress-strain state for different technological schemes of welding deter-mined that increase of static strength of the circumfer-ential welds can be achieved due to rise of number of passes from one to three. The latter promotes reduc-tion of the lack of penetration up to 0,5 mm, axial stresses over the lack of penetration and the coefﬁ  -cients of stress intensity at the initial stage of crack propagation, respectively. REFERENCES [1]  Prokhorenko V. M., Perepichay A. O., Zvorykin K. O. Technological systems, 59 (2012) 2, 20-26. [2]  GOST 5264-80 Manual arc welding. Welded joints. Main types, structural elements and dimensions. [3]  Morozov E. M., Nikishov G. P. Finite element method in fracture mechanics, Nauka, Moscow, 1980, pp. 137-194. [4]  Morozov E. M., Nikishov G. P. FKhMM, 4 (1982), 13-29. [5]  Zenkevich O. K. Finite element method in engineering, Mir, Moscow, 1975, pp. 443-528. [6]   John A. Goldak Computational welding mechanics, USA, 2005, pp. 279-325.[7]  NPAOP 0.00-1.11-98 Rules of designing and safe opera-tion of steam and hot water pipelines.Note:   The responsible translator for English language is PEWI, Kiev, UkraineFigure 6   Distribution of longitudinal stresses on external surface of pipe with full penetration Figure 7   Distribution of longitudinal stresses on internal surface of pipe with full penetration

Reduction of longitudinal axial residual stresses in near-root region of circumferential joint of steam pipeline in technological way

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