CN-122021203-A - Weight function method for calculating crack stress intensity factor of circumferential weld surface of pipeline

CN122021203ACN 122021203 ACN122021203 ACN 122021203ACN-122021203-A

Abstract

The invention discloses a weight function method for calculating the crack stress intensity factor of the surface of a pipeline girth weld, which comprises the steps of constructing a point load weight function for calculating the crack stress intensity factor of the surface of the girth weld of a pipeline structure; the method comprises the steps of establishing a finite element model of a pipeline structure containing the girth weld surface cracks, calculating a stress intensity factor reference solution under reference load based on an M integral method, solving a weight coefficient of a calculation point of the girth weld surface crack front edge of a point load weight function, optimizing a back propagation neural network through a genetic algorithm, establishing a weight coefficient prediction model, and carrying out double integral operation on the product of the point load weight function and the stress distribution load on the girth weld surface crack surface so as to realize calculation of the stress intensity factor. The method solves the problems that the existing method is only suitable for the situation that the stress distribution load is unidirectionally changed along the crack depth, and the stress distribution which is frequently generated in an actual structure and is bidirectionally changed along the crack depth and the crack length cannot be suitable, the calculation cost is increased, and the calculation precision is reduced.

Inventors

Yuan Kuilin
SHEN CHENYANG

Assignees

大连海事大学

Dates

Publication Date: 20260512
Application Date: 20260414

Claims (5)

1. The weight function method for calculating the crack stress intensity factor of the surface of the pipeline girth weld is characterized by comprising the following steps: S1, constructing a point load weight function of a undetermined weight coefficient of a calculation point of the front edge of the circumferential weld surface crack aiming at a pipeline structure containing the circumferential weld surface crack, and acquiring a stress intensity factor calculation model of the circumferential weld surface crack of the pipeline according to the point load weight function, wherein the stress intensity factor calculation model comprises the following steps: wherein s represents the shortest distance from the load action point P on the crack surface to the crack front edge; Representing the load action point P on the crack surface to the crack front stress intensity factor calculation point And xi represents the calculation point of the stress intensity factor of the crack front The horizontal distance from the crack local coordinate system origin O is h, a represents the horizontal distance from the crack front edge surface point C to the crack local coordinate system origin O, a represents the surface crack depth, C represents the surface crack half width, T represents the pipeline thickness; Representing the radius of the inner wall of the pipeline, theta representing the transition angle of the weld toe, r representing the radius of curvature of the weld toe, rho representing the distance from the load acting point P on the crack surface to the origin O of the local coordinate system of the crack, Representing the distance from the Q point on the crack front edge to the origin O of the crack local coordinate system; Representing crack front calculation points Is to say, with six dimensionless parameters , , , , , A related function; representing the normalized distance of the crack front, and representing the position of the P' point on the crack front; Representing the surface crack shape ratio; representing the ratio of crack depth to pipe wall thickness; indicating the wall thickness of the pipeline inner wall radius ratio; representing the radius of curvature of the weld toe ratio to wall thickness of the pipe; representing crack fronts Stress intensity factor at the point; Representing the stress distribution on the crack face, The point load weight function is expressed, namely the point P on the crack surface is expressed, and the crack front edge is under the condition that single point load is applied at the position x and y S is the area of the whole crack surface area; S2, based on a pipeline structure containing circumferential weld surface cracks, establishing a finite element model and dividing grids, and simultaneously applying stress distribution perpendicular to crack surfaces as load boundary conditions of the finite element model to obtain the finite element model with load boundaries; S3, calculating stress intensity factors of each point of the front edge of the circumferential weld surface crack under the reference load condition based on the finite element model with the load boundary, and taking the stress intensity factors as a stress intensity factor reference solution; s4, solving a undetermined weight coefficient of a calculation point of the front edge of the crack on the surface of the circumferential weld in a point load weight function according to a stress intensity factor reference solution combined with a stress intensity factor calculation model, and obtaining a sample weight coefficient solution; S5, taking dimensionless parameters as input variables, taking the sample weight coefficient solution as an output target to establish a data set, optimizing a back propagation neural network based on a genetic algorithm, and constructing a weight coefficient prediction model according to the data set; And S6, based on the weight coefficient prediction model, inputting a target dimensionless parameter to predict to obtain a corresponding weight coefficient solution, further obtaining a point load weight function, and performing double integral operation on the product of the point load weight function and the stress distribution load on the crack surface of the circumferential weld surface to realize calculation of stress intensity factors of each point of the crack front edge of the circumferential weld surface of the pipeline structure.
2. The method for calculating the weight function of the crack stress intensity factor on the surface of the circumferential weld of the pipeline according to claim 1, wherein the step S2 specifically comprises the following steps: s21, building a finite element model of the girth weld pipeline structure according to three dimensionless parameters related to the girth weld pipeline by adopting ABAQUS finite element software; The three dimensionless parameters related to the girth weld pipeline are , , : S22, inserting a finite element model of the girth weld pipeline structure into the girth weld surface crack according to the fact that the surface crack involves two dimensionless parameters by adopting FRANC D software; the surface crack involves two dimensionless parameters of , : S23, carrying out grid division on the finite element model obtained in the S22, and applying uniform stress perpendicular to the crack surface As a load boundary condition of the finite element model, a finite element model having a load boundary is acquired.
3. The method for calculating the weight function of the crack stress intensity factor on the surface of the circumferential weld of the pipeline according to claim 2, wherein the step S3 specifically comprises the following steps: S31, acquiring an M integral value of a related crack by adopting an M integral method in FRANC D software based on the finite element model with the load boundary; S32, according to the elastic modulus and Poisson' S ratio of the M integral value combined material, obtaining a stress intensity factor K of the front edge of the pipeline girth weld surface crack, wherein the stress intensity factor K is as follows: Wherein E represents the elastic modulus of the material, and v represents the Poisson's ratio of the material; M represents the M integral value obtained by step S31; s33, adopting stress distribution As a reference load, normalizing the front edge of the crack on the surface of the circumferential weld of the pipeline at a distance of And taking values at equal intervals in the range, calculating stress intensity factors of points of the front edge of the crack of the surface of the girth weld under the condition of reference load by executing S31 to S32, and taking the stress intensity factors as reference solutions of the stress intensity factors.
4. A method for calculating a weight function of a crack stress intensity factor on a circumferential weld surface of a pipe according to claim 3, wherein S4 comprises the steps of: s41, constructing a weight coefficient solving strategy, wherein the weight coefficient solving strategy is as follows: S411, integrating a stress intensity factor calculation model as follows: s412, distributing stress When the stress intensity factor calculation model is used as a reference load condition, two numerical integration results of the integrated stress intensity factor calculation model are obtained The method comprises the following steps: s413, according to the numerical integration result Reference solution for combining stress intensity factors Obtaining a crack front stress intensity factor calculation point The weight coefficient of the point load weight function is as follows: S42, performing grid dispersion on the whole area of the crack surface, and repeatedly executing the step S41 to solve the weight coefficient of each calculated point of the crack front edge of the surface of the circumferential weld in the point load weight function, so as to obtain a weight coefficient solution.
5. The method for calculating the weight function of the crack stress intensity factor on the surface of the circumferential weld of the pipeline according to claim 4, wherein the step S5 specifically comprises the following steps: S51, the dimensionless parameters are processed , , , , , As input variables, solving the weight coefficients Establishing a data set as an output target; S52, taking the input variable as the input of the back propagation neural network, taking the output target as the output of the back propagation neural network, performing network training on the back propagation neural network through a data set, And simultaneously, optimizing the weight and the bias of the back propagation neural network based on a genetic algorithm to obtain the optimal combination of the weight and the bias of the back propagation neural network, thereby obtaining a weight coefficient prediction model.

Description

Weight function method for calculating crack stress intensity factor of circumferential weld surface of pipeline Technical Field The invention relates to the technical field of fracture mechanics and oil and gas pipeline damage tolerance design, in particular to a weight function method for calculating a pipeline girth weld surface crack stress intensity factor. Background With the development of the offshore oil and gas resource development industry, pipelines become one of the most dominant modes of offshore oil and gas transportation. Compared with land oil gas pipelines, the marine oil gas pipeline has the advantages of worse service environment, more complex bearing and higher maintenance difficulty. Oil and gas pipelines are typically welded structures, with initial defects being inevitably generated in the vicinity of the girth weld. Under the alternating load of the marine environment, the initial defect of the girth weld stress concentration area is very easy to be changed into a semi-elliptical surface crack which is continuously expanded, and finally, the pipeline structure is broken and failed, and even disastrous accidents occur. Therefore, the girth weld is a weak link in the whole pipeline structure, and a damage tolerance design method is required to evaluate the service safety of the crack-containing structure in the structure. The method is based on line elastic fracture mechanics, and takes a stress intensity factor of a crack tip as a core parameter of pipeline fracture failure evaluation. Therefore, the rapid and accurate calculation of the girth weld surface crack stress intensity factor is critical for the integrity and safety assessment of marine oil and gas pipeline structures. At present, the common surface crack stress intensity factor calculation method in engineering can be divided into an empirical formula method, a finite element method and a weight function method. For oil and gas pipelines, the empirical formula of the stress intensity factor of the circumferential surface crack of the outer wall of the pipeline is provided in annex 9B of the U.S. petroleum Standard API 579-1 'Fitness for Service', but the application range is limited to a simple loading form, and the influences of the shape of a welding seam and the welding residual stress cannot be considered. The finite element method can be used for calculating stress intensity factors of surface cracks in different structures under complex stress distribution load, but in view of the requirements of different crack shapes and sizes, high-quality grids are required to be divided at crack tips, and the problems of large modeling workload and low calculation efficiency are faced. The weight function method is a half-value half-resolution stress intensity factor calculation method, the weight function expression is only related to geometric parameters of the crack body, and after the weight function is determined, the stress intensity factor of the crack body under any load can be calculated by solving the integral of the product of the weight function and the stress distribution of the crack surface. The common weight function proposed by Glinka is most widely applied in the existing weight function method, and has been adopted by a plurality of damage tolerance design software (such as AFGROW software, DARWIN software and the like). However, the general weighting function is only applicable to the case where the stress distribution load varies unidirectionally along the crack depth, and is not applicable to the stress distribution that varies bidirectionally along the crack depth and the crack length, which is often found in an actual structure. Orynyak and Wang propose different point load weight function formulas for calculating the stress intensity factor of an elliptical buried crack under a bi-directional varying stress distribution load. Patent publication number CN 112989659B discloses a method for establishing a surface crack intensity factor database based on a point load weight function method, which adds a correction term on the basis of a Orynyak point load weight function formula, expands the correction term to a flat plate semi-elliptical surface crack problem, obtains stress intensity factors under three reference loads through finite element calculation as reference solutions, solves three weight coefficients in the weight function formula, however, introducing a plurality of weight coefficients tends to increase the calculation cost and reduce the calculation precision, and influences the reliability of subsequent calculation. Disclosure of Invention The invention provides a weight function method for calculating crack stress intensity factors on the surface of a pipeline girth weld so as to overcome the technical problems. In order to achieve the above object, the technical scheme of the present invention is as follows: A weight function method for calculating crack stress intensity factors on the surfac