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We develop statistical methods for the comparative analysis of the accuracy of relations used for the determination of the residual strength of plastic pipes with rectangular surface defects. In the existing approaches, the accuracy of relations is established for the entire set of experiments as a single generalized value. At the same time, in the present work, the corresponding values are established separately for every fixed collection of the sizes of defects (points of interest). For each test, we determine its weight, which is not larger than one at every point of interest. The statistical analysis of accuracy is performed separately for each point of interest, which enables us to smooth out the experimental errors and determine the error of the formula itself more precisely. [ABSTRACT FROM AUTHOR]

The stress state of pipelines in mine working zones, where the main loading factor is longitudinal soil displacements caused by the gradual filling of mine voids, has been calculated. Differential equations of pipe deformation have been formulated, for the solution of which the method of internal response function is proposed, which takes into account the mutual displacement of the pipe and soil in each iteration using a classical three-part nonlinear model of pipe–soil interaction. The type of interaction is determined on the basis of the concept of the basic displacement of the pipe, which is refined using displacements calculated in the previous iteration. The procedure of refining the basic solution is an important component of the method, where the basic solution in the next iteration is found as the sum of the previous solution and the difference between the calculated and previous solutions, multiplied by the convergence-control factor of the iterative procedure. To check the convergence accuracy and rate of the proposed iterative procedure, a comparative analysis with other existing procedures and results, obtained with the aid of commercial finite element programs, has been performed. To diagnose the stress state of pipelines during the working of longwall faces, a system for their continuous monitoring has been created. The correctness of the results of the performed numerical modeling of the stress state of a gas pipeline and the effectiveness of the measures that are developed to reduce the high stress level in its individual zones have been confirmed by relevant monitoring data, which are important both for refining the physical characteristics of pipe–soil interaction and for further taking into account the relaxation of these relations in time. [ABSTRACT FROM AUTHOR]

Complex studies on the in-service metal fracture in weld joint No. 111 of the steam generator of a WWER-1000 power unit elucidated the micromechanisms of crack propagation (combination of corrosion cracking and corrosion fatigue). Quantitative measurements of fatigue striation spacings were performed. Real in-service loading conditions of the collector 'pocket' zone where corrosion fatigue cracks originate and propagate were estimated. [ABSTRACT FROM AUTHOR]

We propose an original physically justified method for the evaluation of the spread of values of the critical temperature of brittleness. Its principal distinction from the standard method and advantage over this method is that the spread of data is determined according to the source data used for the evaluation of the critical temperature of brittleness but not according to the set of values of this temperature. We introduce quantitative characteristics of a series of impact-toughness tests aimed at finding the critical temperature of brittleness: the effective number of experimental points and the weight (degree of influence) of each of these points on the critical temperature of brittleness. A criterion of sufficiency of the number of values of impact toughness for the adequate determination of the critical temperature of brittleness according to these values is also proposed. We describe numerous experiments that reveal good correlation between the spread of values of the critical temperature of brittleness obtained by the proposed method and the corresponding standard deviations. [ABSTRACT FROM AUTHOR]

The method of calculating the frequencies and amplitudes of acoustic vibrations, induced by fluid moving in long pipelines with closed branches, was proposed. Resonant frequencies are supposed to correspond to local maxima of the functional containing the ratio of energy in the vibrating system and absorbed energy from the system boundaries. The energy approach is carried over to analysis not only of vibration frequencies but also of their amplitudes. For determining vibration amplitudes, the balance of input (as a function of the Strouhal number) and absorbed energies was written. Preliminary analysis of forced vibrations of secondary steam lines (Unit No. 1 of Zaporozhye Nuclear Power Plant with a WWER-1000 reactor), induced by turbulent vortices in closed toroidal sections, was completed. Resonant frequencies and amplitudes of acoustic vibrations were evaluated. With the equations of fluid-pipeline interaction, vibration stresses and velocities of pipelines were computed and compared with measuring data. [ABSTRACT FROM AUTHOR]

An analytical model for assessment of the limit plastic state of a pipe branch T-junction subjected to the internal pressure loading with a longitudinal surface defect of constant depth located at the outer surface of the main pipe in the branch pipe welding zone is proposed. The comparative analysis of the theoretical calculated results on the internal pressure with the test results obtained for full-scale notched pipe T-junctions statically loaded until failure is provided. [ABSTRACT FROM AUTHOR]

The crack opening area of a through-wall crack in a shell is one of the main design parameters in the leak-before-break concept. The available methods for determining this parameter essentially consider the shell as a plane body and disregard the linearly varying component of the displacement field (as in the plate theory). Based on a combined method of weight functions, a simple procedure is put forward to derive an approximate expression for the fundamental field of displacements under the action of a concentrated force and moment onto the crack faces in the form of a sum of a uniform component and a component that linearly varies through the wall thickness. This provides, in particular, convenient formulas to find the crack opening area in a polynomial field of membrane stresses as well as linear ones. For a cylindrical shell with a longitudinal or transverse crack, the calculated values of the crack opening area are compared with those reported elsewhere. The contribution of the linear component to the total crack opening area is assessed. [ABSTRACT FROM AUTHOR]

The experimental equipment has been upgraded and requirements to geometrical sizes of edge notches of pipe specimens are formulated. A series of tests until fracture have been performed for static loading by internal pressure and bending moment of straight pipe specimens having longitudinal and circumferential edge notches, as well as for a pipe bend with a longitudinal edge notch. Experimental data are compared with the theoretical calculation results. The conditional boundary line between leak and break has been theoretically predicted and experimentally verified for internal pressure loading of a straight pipe with a longitudinal surface defect. [ABSTRACT FROM AUTHOR]

The problem of reconstruction of a continuous spatial line of a pipeline by the discrete points measured with some error is solved. For the problem solution, a non-iteration numerical algorithm is proposed, according to which each measured point of the pipeline is treated as a compliant support. The algorithm is based on the method of initial parameters and accounts for the concept of 'an incompatibility angle' between two adjoining measured sections of a pipeline axis. Using methods of the probability theory, the analysis is performed, which allows one to assess the accuracy of the reconstructed position of a pipeline and obtained stress values. Accuracy of calculations executed by means of the developed algorithm has been verified using the results obtained by analytical methods. [ABSTRACT FROM AUTHOR]

The paper addresses forced vibrations in piping subsystems, which are induced due to the formation and separation of turbulent vortices in the flow of a fluid being transported. The excitation frequency is not a constant number but can take on values from a certain range, thus leading to difficulties and ambiguities in the vibration analysis of piping. To solve this problem, a so-called energy approach is put forward which enables one to determine the most physically governed frequencies of forced vibrations. The approach essentially consists in searching for the natural frequencies and modes of the fluid hydrodynamic vibrations whereby the minimum amount of energy leaves the piping subsystem, while the maximum one remains inside. The validity of the proposed approach is verified by test examples. The proposed methods have been used to analyze piping forced vibrations induced by turbulent vortices in the steam flow in the secondary coolant piping of nuclear power plants with WWER-1000 reactor. Natural frequencies and modes of mechanical, hydrodynamic, and coupled hydrodynamic vibrations have been determined; some recommendations of how to minimize the level of vibrations have been worked out. [ABSTRACT FROM AUTHOR]

The basic peculiarities of stress corrosion fracture cases of main pipelines are analyzed. The authors consider structure, mechanical properties, Charpy energy, fracture toughness, corrosion fatigue, and fracture mechanisms of steel Kh70 (from transit gas pipeline 'Urengoy-Pomary- Uzhgorod') in three conditions: as received (archive), after 24 and 26 years of service. The service degradation of steel is revealed, which manifests itself in considerable drop of Charpy energy, fracture toughness and resistance to the corrosion fatigue crack growth. The analysis is performed of the resistance of the pipeline steels to the corrosion fatigue crack nucleation and growth and the respective recommendations are provided concerning the avoidance of the stress corrosion failure of transit gas pipelines. [ABSTRACT FROM AUTHOR]

The paper presents a modification of the method of initial parameters as employed to allow for harmonic vibrations of a fluid transported in piping. The existing parameters that describe mechanical vibrations of piping are supplemented with the parameters representing the fluid displacement and pressure pulsation. For these hydrodynamic parameters the authors have derived equations of coupling within the design elements and equations of conjugation of parameters at the boundaries between the elements. Equations of conjugation of hydrodynamic and mechanical parameters are derived which allow for their mutual influence and make it possible to analyze the coupled hydromechanical vibrations. In general, the algorithm of the method of initial parameters and the method for constructing a design model have remained unchanged. Some examples are presented which demonstrate the accuracy of the proposed methods as used for the analysis of natural and forced vibrations of a fluid in a pipeline, with and without mutual influence of the fluid and the pipe. [ABSTRACT FROM AUTHOR]

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects of irregular shape, based on simulation of global and local ultimate plastic states are proposed for the case of loading by axial force, internal pressure and bending moment. The comparative analysis of the results calculated by the proposed procedure and the experimental data is performed. [ABSTRACT FROM AUTHOR]

The paper describes the method of initial parameters which is used for stress analysis of complex branched piping systems under static loading as well as under natural and forced harmonic vibrations, including the case of kinematic loading by displacement amplitudes. For the purpose of modeling arbitrary curved elements, in particular three-dimensional ones, the authors propose an inertialess rotary element of zero length, which turns coordinate axes of neighbor elements. The paper demonstrates the potentialities of the method for vibrodiagnostics of piping. [ABSTRACT FROM AUTHOR]

nalytical and numerical methods have been developed for the solution of stress-strain and limit state problems of piping systems (in the case of the presence of flaws in them as well). The fracture strength of pipe steels during long-term service has been studied. A methodology and a software have been developed for the assessment of stress-strain state to extend the life of active pipelines. The developments made are used to increase the reliability of Ukrainian piping systems. [ABSTRACT FROM AUTHOR]

We have performed calculations of stress-strain state of cable-stayed aerial pipeline crossing in the operation state and of the additional effect of the inspection gauge application. In order to assess efforts in the pipe and cable stays of the aerial crossing, we apply analytical solutions combined with numerical simulations using the 3D PipeMaster software system. This comprehensive analysis allows one to assess stresses in the critical zones of the crossing, as well as to develop recommendations on strengthening the structure of the aerial crossing before its in-line inspection. [ABSTRACT FROM AUTHOR]

We review the currently available approaches, applicable codes and standards for assessment of defects in trunk pipelines and discuss advantages and disadvantages of the National pipeline regulations. The paper outlines the main principles of the newly introduced normative document that regulates the assessment of strength and remaining life of pipelines containing service defects. [ABSTRACT FROM AUTHOR]

We propose a procedure for the numerical analysis of the stress-strain state and criteria of its admissible state in the course of repairs of the air crossings of gas mains with regard for possible defects of the pipe metal. Using the “3D PipeMaster” software complex, we compute different versions and present recommendations concerning the optimal location of pipe-laying machines with an aim of realization of the possibility of lifting the pipe to a height required for repair works with guaranteed validity of the prescribed conditions of strength. The values of tractive forces in the pipe-laying machines are determined. The optimal sites of fixing the pipeline in the transverse direction are indicated and the corresponding forces acting in the cables used to prevent the transverse motions of the pipeline are calculated. [ABSTRACT FROM AUTHOR]

Analytical models are proposed for the limiting plastic state of heavy-walled pipes with axial surface defects, which are located at the outer and inner surface. The corresponding model of a thin-walled pipe is used. On this basis, the effect of radial stresses is taken into account. An analysis of the models and a comparison with the experiment results are carried out. [ABSTRACT FROM AUTHOR]

We study the decrease in the strength of a pipe containing an artificial defect. On the basis of the analytic and numerical models, we consider the influence of the structural features of a split sleeve on its load-carrying ability. We also analyze the joint operation of a sleeve and a pipe containing an artificially made axial surface defect. The results of the numerical analysis are compared with the experimental data. [ABSTRACT FROM AUTHOR]

Based on the analytical model for the plastic limit state, a numerical procedure for estimating the remaining strength of a complex-shaped defect has been developed. Comparison of the calculation results obtained by the proposed procedure with the experimental data and the calculation results obtained by other methods showed its efficiency. [ABSTRACT FROM AUTHOR]

An analytical method is proposed for the solution of geometrically nonlinear Brazier problem for thin-mall pipes with initial cross-sectional shape imperfection in the case of action of pressure. Geometrical equations relating displacement components to strains and equilibrium equations taking into account change in the curvature of pipe cross section and axis have been derived. A solution in a first approximation for dimensionless flexibility parameter is presented, the exactness of which is illustrated by numerous examples. For the case of joint action of external bending moment and pressure, a limit curve of the critical moment value as a function of pressure value has been obtained. [ABSTRACT FROM AUTHOR]

To calculate stress intensity factors in elastic pipes with long flaws, the known Cheng-Finnie method is used. A universal description of the mode of behavior of beam is proposed, for which equations of the method of initial parameters with allowance for geometric nonlinearity (effect of axial force on lateral deformation) have been derived and are employed. This allowed us to determine, apparently for the first time, the values of stress intensity factors in thin-walled pipe in a geometrically nonlinear formulation, when increase in pressure leads to their somewhat “ retarded” increase. The results have been generalized for a more complex flaw-crack starting from the dent tip. [ABSTRACT FROM AUTHOR]

Refined results of the stress-strain state evaluation for the hot header-steam generator connector weldment of small-and large-series WWER-1000 reactors with three-dimensional models are presented. The layout of the steam generators in the reactors is shown to influence maximum stresses in the vicinity of the weld. [ABSTRACT FROM AUTHOR]

We developed analytical models of the buckling failure of initially rectilinear pipeline in the environment. We specify the drawbacks of available analytical methods, which take no account of the possible longitudinal displacement of the pipeline points or the limited length of the pipeline portion, as well as, in the limiting case, fail to describe the experimental results of buckling failure in the air. The proposed models make it possible to provide analytical evaluation of the critical load, length and shape of the deformed pipeline in cases of its horizontal and vertical transversal deformations with the account of the above factors. The results obtained are corroborated by the numerical simulation of the deformation process, based on the procedure described by the authors in Part 1, as well as by the full-scale test results. [ABSTRACT FROM AUTHOR]

An effective numerical iteration procedure has been worked out for the analysis of the stress-strain state of a flat pipeline in a medium with allowance for possible presence of supports and branches. The governing equilibrium equations and geometrical equations used have been written in geometrically nonlinear formulation and supplemented with boundary conditions, obtained analytically for a semi-infinite pipeline under transverse-longitudinal elastic bending. The article considers an elastoplastic law of interaction between pipeline and the ground with the possibility of additional limitation of absolute pipeline displacements. The computational algorithm is based on the concepts of corrective and basic solution. Basic solution is refined in each iteration step using corrective solution. Corrective solution is direct solution of a system of linearized equations, in which, e.g., basic displacements of pipeline are used to determine forces of interaction between the pipe and the ground. The algorithm uses an efficient method of run in each iteration step, which minimizes the number of unknowns. The results of the calculations are compared with numerical and theoretical solutions presented in publications: cantilever curling by the action of end bending moment; laying of an underwater pipeline; stability loss in air, etc. [ABSTRACT FROM AUTHOR]

The notion of the dynamic flexibility factor of a pipe bend to be used in problems on the calculation of harmonic vibrations of pipelines is formulated. Based on the Vlasov semi-momentless theory, simplifying hypotheses are introduced that make it possible to reduce the problem statement to the solution of the quartic differential equation. Using the results of the dynamic analysis for toroidal shells, the procedure for taking into account the increased flexibility of pipe bends under dynamic loading has been developed. The expression for the flexibility factor is derived as a function of both the geometrical parameters of the bend and the vibration frequency. The efficiency of the derived expression for the flexibility factor is illustrated by a great number of examples. [ABSTRACT FROM AUTHOR]

A new analytical method is proposed for the analysis of boundary effect in a pipe bend portion loaded by bending moment combined with internal pressure. The proposed method is based on the simplifying hypotheses, which make possible to represent all deformation- and force-related parameters in terms of the tangential displacement assumed in the form of the Fourier series expansion by the circumferential coordinate. A set of quadric differential equations by axial coordinate containing unknown displacement expansion coefficients is derived. We obtained an analytical approximate solution for a pipe bend portion and precise solution for a straight pipe, which are expressed via Krylov functions. We formulate the application procedure for the method of initial parameter, where the values of tangential and longitudinal displacements, axial and tangential forces are used as boundary conditions. We present the equations relating the above-mentioned parameters in the initial and end sections of the pipe bend portion. The results obtained are compared with the available published data. [ABSTRACT FROM AUTHOR]

A problem of deformation of a curved shell loaded by internal pressure, axial force, and temperature difference is discussed. Physical equations are derived whereby the displacements and angles of rotation of the line of centers of mass of cross sections of a shell are related to loading parameters. A general constitutive set of equations for a curved element during its deformation is given. Using a method of initial parameters, an analytical solution is obtained for the differential equations for displacements and angles of rotation of the center line allowing for the action of distributed forces and moments. [ABSTRACT FROM AUTHOR]

We analyze a problem of determination of stressed state and flexibility of a pipe bend under a combined action of internal pressure and bending moments applied both in and out of plane of the bend curvature. This problem is referred to as a geometrically nonlinear one where an increase in internal pressure brings about a decrease in ovalization stresses induced by bending moments. A unique method of allowing for the pressure is put forward, which is based on the consideration that the pressure-induced circumferential stresses greatly exceed the stresses due to bending moments. A general set of equations for all displacements and stress components is derived. The present results are compared with those reported elsewhere. [ABSTRACT FROM AUTHOR]

A new method for analysis of stress-strain state in elastic cylindrical toroidal shells is put forward, whereby forces and displacements are chosen as unknown junctions. The method enables a study of the bend ovalization phenomenon that occurs when three-dimensional bending moments are applied. The authors have derived geometrical equations relating displacement components and strains, and introduced smallness hypothesis, which makes it possible to neglect some combinations of displacements during the shell deformation analysis. The Karman hypothesis of nondeformability of a pipe median surface is demonstrated to be applicable only after the circumferential force is excluded from equilibrium equations. The authors have established the limits of applicability of the solutions obtained, depending on the order of approximation of the flexibility parameter. Beam differential equations have been derived for a curvilinear bar, which relate angles of rotation and center-line displacements with applied loading factors. The results obtained are compared to those reported elsewhere. [ABSTRACT FROM AUTHOR]

General methodological approaches to solving the problems of strength and life of NPP equipment and results recently obtained in this field at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine are outlined. The urgency of the strength and life issues for reactor pressure vessels and steam generator shells is demonstrated. Application of a comprehensive calculation and experimental approach to the stress-strain state analysis is illustrated by the example of steam generator joints with defects. [ABSTRACT FROM AUTHOR]

The authors consider edge effects in buried pipelines that occur in the region of joining of a straight buried pipe and a bent insert (factory bend, elbow, or an elastically bent segment). The action of those effects results in the appearance of additional bending moments, which are proportional to the difference between the axial force in an infinite straight pipeline and that in a closed-end pipe, and depend on the geometrical parameters of the pipeline and physical-mechanical characteristics of the soil. Specific examples of analysis of elastic interaction of a pipeline with the soil for pipe bends with various radii of the bend arc are offered. It is shown that additional bending stresses may exceed appreciably the stresses from the axial force, and therefore, they should be taken into account when designing and building pipelines. The solution for an elastically bent segment has been obtained and analyzed. [ABSTRACT FROM AUTHOR]

We study two different approaches to the evaluation of the stress intensity factors (SIF) for circular cracks one of which is based on the Rice integral formula and the second (Panasyuk) approach deals with the analysis of the stressed state outside an imaginary circular crack. It is shown that the Panasyuk approach is more accurate from the mathematical point of view as it is physically grounded and based on the three-term approximation of the stress field. The proposed practical procedure for the evaluation of the SIF proves to be very efficient and gives good results for irregular cracks. [ABSTRACT FROM AUTHOR]

We propose a method for the analysis of stable crack-length increment Δ a (where Δ a is regarded as a function depending on the parameters KI and σ r of the two-criterion approach). It is shown that the K Rcurve consists of two portions: {K′} R and {K′ ′} R curves, which in the framework of the fracture evaluation diagram correspond to two portions of the loading curve – prior to and after its intersection with the limit curve of the fracture evaluation diagram. We propose an analytic description of the {K′} R curve as the first approximation, while the shape of the {K′ ′} R curve is shown to be fully determined by the limit curve of the fracture evaluation diagram. The method has been verified by using the experimental data of the ASTM Round Robin tests performed in 1979–1980 and predicting the maximum fracture load P f of cracked specimens made of various materials: compact specimens, center-cracked specimens and special specimens with three holes. Good agreement between predicted and experimental data is demonstrated. [ABSTRACT FROM AUTHOR]

Urgent requirements for the determination of the ductile-fracture ultimate load for defects of the indentation type in pipelines are pointed out. The authors propose an idealized model of the limiting plastic state of a pipe with a longitudinally infinite indentation. To assess the influence of the finite length of the indentation, an approximate model for rectangular indentation has been developed. Practical formulas for the calculation of residual strength in the case of the absence of axial stresses have been derived and analyzed. [ABSTRACT FROM AUTHOR]

We show the urgency of developing methods for prediction of the ultimate load of ductile fracture for defects of the dent type in pipelines. We propose an idealized model of the limiting plastic state of a pipe with infinite dent along it. We obtain formulas for engineering calculations and analyze them. [ABSTRACT FROM AUTHOR]

On the basis of an analysis of the known solutions for a circular and for a semiinfinite normal-separation crack with straight front in an infinite body we constructed, in analogy to the method of Burns and Oore, a weight function for elliptical cracks. Its use for finding the stress intensity factors K at the point of minimal curvature under conditions of uniform loading leads to a maximal error of 10%; at the point of minimal curvature of the crack front the error increases with decreasing ratio of the semiaxes of the ellipse. With the aid of this solution the weight function is found in bounded bodies with a quarter-elliptical, semielliptical, and elliptical crack. A comparison of the data obtained by this method with the values of K calculated by the finite-element method under nonuniform loading showed that the suggested method is very accurate. [ABSTRACT FROM AUTHOR]

Problems of the correct derivation of crack-resistance characteristics under longitudinal or transverse shear are examined. It is proposed that effective values of the stress intensity factor, which are calculated in accordance with the theory of maximum tensile stresses, can be used to calculate the limiting state and critical brittleness temperatures for a cracked body under a combined load. It is recommended that the limiting load of ductile failure be calculated in accordance with the theory of limiting equilibrium using the Tresca strength condition. An approximate method of plotting the weighting function for cracks subject to nonsymmetric loading is developed. [ABSTRACT FROM AUTHOR]

An approximated method is proposed for constructing the weight function for flat solids with a crack based on the available exact solutions for an infinite plane and the available values of the stress intensity factor at the crack tip in the examined solid for any distribution of the load at its edges. Examples are given of determining the weight function for edge and central cracks in right-angled plates and disks. [ABSTRACT FROM AUTHOR]

The article considers problems of finding the limit pressure leading to ductile failure of a cylinder with an axial crack. Actual formulas are obtained for a thin-walled shell and for cylinders with considerable thickness. The article shows their satisfactory agreement with the results of full-scale tests. [ABSTRACT FROM AUTHOR]

The authors are grateful to Doctor of Technical Sciences, Sh. U. Galiev for useful discussion of the work. [ABSTRACT FROM AUTHOR]

We propose a new method for the approximate description of the crack opening displacement caused by the action of two symmetric forces applied to the opposite faces of a crack originating from a concentrator. The solution is sought in the form of a sum of asymptotic and correction terms. The asymptotic term is obtained by applying the operation of inversion to the well-known solution for a half plane with edge crack. The correction term contains unknown coefficients and is negligibly small as compared with the first term if either the point of application of a force or a current point of the crack surface is located near the crack tip. It is shown that the realization of this method reduces to several arithmetic procudures. The high accuracy of the proposed method is demonstrated by analyzing various examples. [ABSTRACT FROM AUTHOR]