MODELLING OF NON-STATIONARY PROCESSES IN WELDED CONNECTION OF THE PIPELINE

Transcription

1 382 UDC MODELLING OF NON-STATIONARY PROCESSES IN WELDED CONNECTION OF THE PIPELINE E.M. Fedoseevа 1, T.V. Olshanskаyа, M.N. Ignatov Perm State Technical University, Perm, Russia 1 lyalyaf@mail.ru A.P. Shestakov Institute of continuous media mechanics UB RAS, Perm, Russia Abstract. Modeling of non-stationary processes in welded connection of the pipeline has been realized. Change of intensity of pressure in welded connection of a pipe, formation of flexural waves at passage of a longitudinal wave through nonmetallic inclusions is considered. It is shown that on certain sites pulse changes of intensity of pressure which can promote occurrence of critical pressure are possible. Keywords: pipeline, stress intensity, nonmetallic inclusions, welded connection, ANSYS High demands are made to pipelines on maintenance of reliability and safety of their functioning. Welded connections, especially a root of a seam of the main pipelines are in severe constraints under the influence of pressure while in service [1]. Influence of nonmetallic inclusions in welded connections, as primary center of origin of the defect leading to formation of the main crack, and as consequence to destruction of the pipeline [2] is established. In an industrial practice of experts of the enterprises of pipeline transport and the corresponding supervising organizations program modules take root and developed for all-around automation of procedure the numerical strength analysis of pipelines in the environment of program ANSYS at the difficult intense-deformed condition of a linear part of the pipeline by a finite element method (FEM). In this connection the analysis of processes of change of intensity of pressure in nonmetallic inclusions of welded connections of pipelines by numerical modeling is actual. The work purpose was modeling of non-stationary processes in welded connections of pipelines. Modeling of non-stationary processes by a finite element method is carried out by means of settlement-program complex ANSYS. We believe that: the pipe material isotropic, elastic also follow the Hooke law law; deformations are small and are described by linear geometrical relationships. Geometrical and physical parameters of a pipe and a welded seam (Table 1) are set for intensity calculation.

2 383 Nonmetallic inclusions represent some congestions (the area is equal approximately mm 2 ), located any way in a welded seam. Physical characteristics of nonmetallic inclusions: Е = N/m 2, Poisson's ratio is equal Table 1. Parameters for calculation of intensity of pressure Geometrical parameters of a seam Physical parameters of a seam Width N sh, m Length L sh, m Е, N/m 2 Poisson's ratio ρ, kg/m 3 Н sh1 = ; L sh1 = ; 2 10 Н sh2 = L sh2 = Geometrical parameters of a pipe Physical parameters of a pipe Width N t, m Length L t, m Е, N/m 2 Poisson's ratio ρ, kg/m In work the case when the non-stationary action to a wall of a pipe looks like (Fig. 1) is considered: Fig 1. The operating loading scheme (where Р 0 Amplitude of power action ( Pa); t V duration of power action) Loading reflected on Fig. 1 mathematically is expressed so: F(t)=(P 0 /t 3 ) ((t-t 0 ) h (t-t 0 ) - (t-t 1 ) h (t-t 1 ) - (t-t 2 ) h (t-t 2 ) + (t-t 3 ) h (t-t 3 )), (1) where h(t) Heaviside step function, t 0 = 0, t 1 = t 3, t 2 = t V - t 3, t 3 = t V. The finite element method is applied to the task in view decision. The given problem is non-stationary, for its decision the direct method of integration on time is used. For pipe approximation it is used flat, 4 coal, 8 central, with square-law approximation of movings, finite elements. The settlement scheme of a problem is shown on Fig. 2.

3 384 Fig. 2. The settlement scheme of a problem: H т a thickness of a pipe; L т length of a pipe; L ш1 width of a seam; L ш2 width of a root of a seam; H ш1 seam height; H ш2 height of a root of a seam; R т pipe radius; Р operating loading (pressure); Y an axis of action of longitudinal pressure; R an axis of action of radial pressure; by digits 1, 2, 3 and 4 places of transition of the basic metal in a seam, being concentrators of pressure are shown On Fig. 3 the variety of the waves arising at action of loading, change of front and wave refraction at change of a configuration of a pipe in a welded seam is shown. The non-uniform is intense-deformed condition in a welded seam, on border of the basic metal and a seam in points 1, 2, 3 and 4 (see Fig. 2) there is an increase in pressure. The greatest increase (to the Pas) occurs in a seam root (Fig. 4а). Theoretical the factor of concentration of pressure Кσ, equal as the relation of settlement pressure to operating, has made 1.8. The seam root has the smaller sizes in comparison with a facing layer of a seam, and accordingly is the concentrated concentrator of pressure in the pipeline. Because of distinction of physical characteristics of a steel matrix and nonmetallic inclusions near to inclusions on border of section with a pressure matrix grow, there is an increase in intensity of pressure (Fig. 4b). The maximum deflection characterizing change of moving of a longitudinal wave owing to a meeting with border metal inclusion is established. Besides, it is revealed the races, characterizing formation of a flexural wave and its subsequent pulsations. In nonmetallic inclusions of welded connection of a pipe under the influence of the set loading there is an increase in intensity of pressure on the average from 18 to 35 %. The greatest increase in pressure is observed on border metal nonmetallic inclusions in a seam root (to %) that is connected with change of the sizes in a seam root. The theoretical factor of concentration of pressure has made 1.3 (Fig. 4b).

4 385 Fig. 3. Character of change of a longitudinal wave and intensity of pressure at change of a configuration of a pipe in a welded seam ( 10**-5) а ( 10**-5) b Fig. 4. Quantitative changes of pressure in welded connection; a on border base. metal - a seam root ; b on border metal - nonmetallic inclusions Taking into account Кσ the estimation of working capacity of pipelines with ring seams is executed, using criterion of cyclic durability. Supposed working pressure in the pipeline is defined by a technique offered by M.Kh. Muftahov [3] and defined: 0( П =П n n D Kσ 2/ (1+c (1 c)/(1+c))1 ) ε вн p раб m с Np, (1) 2 χ Е δ (n σ ψ 1 ) where П 0 a relative indicator of structural damageability of metal; n reliability factor on loading; ψ relative narrowing; p раб working pressure, MPa;

5 386 n ε yield factor on deformation; N p the minimum number of cycles prior to the beginning of destruction at lowcycle fatigue; δ pipe wall thickness, mm; n σ pressure yield factor; D вн internal diameter of pipe, mm; m c factor of working conditions of metal; E modulus of elasticity, МPа; χ factor characterizing plastic properties of metal; c strain-hardening coefficient; Kσ stress-concentration factor. Taking into account a relative indicator of damageability of metal of a pipe in the concentrator of pressure the factor of change of working pressure in the pipeline is defined: m y =(1 П ) m c (1+c )/2. (2) Supposed working pressure in the pipeline with ring seams in this case is defined: p= p раб m y, (3) Entering in (1), (2) and (3) parameters are characteristics of a pipe and are defined by service conditions under standard documents, except Kσ which is defined on researches of the is intense-deformed condition in the pipeline. The carried out calculation has shown that for maintenance of safe operation of the pipeline taking into account ring welded seams for a pipe in the size in diameter of 1220 mm and thickness of a wall of 11 mm supposed working pressure makes 6.1 МPа, and for a pipe in diameter of 1420 mm and thickness of a wall of 15.7 mm 7.9 МPа (at standard 9.8 МPа). Thus, modeling of non-stationary processes in welded connections of pipelines is realized. Influence nonmetallic inclusions on change of pressure in metal of a seam of welded connections of pipelines is defined, the theoretical factor of concentration of pressure is equal 1.3. Near to inclusions, on border of section with a matrix, pressure grow because of distinction of physical characteristics of a steel matrix and nonmetallic inclusions. It is established that for a linear part of pipelines with ring seams the nonuniform is intense-deformed condition is characteristic. The maximum values of pressure are created on border of transition of the basic metal to strengthening of a root of a seam. The theoretical factor of concentration of pressure is equal 1.8 which is necessary for considering at calculation on cyclic durability of a linear part of pipelines that allows to correct working supposed working pressure in the pipeline for safe operation.

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