PIPELINEROUTESURVEYRESULTSINPIPEBENDINGRADIUSCALCULATION

1、s.p. sushchev, doctor of technical sciences,v.i. larionov, doctor of technical sciences(moscow state technical university named after n.e. bauman),p.v. klimov, candidate of technical sciences (intergaz central asia oao),ya.r. idrisova (institute of energy resources transportation gup)pipeline route

2、survey results in pipe bending radius calculationbackgroundto assess the impact of groundwater changes on the stress state of underground pipelines it is required to inspect periodically the horizontal and vertical position and to determine the bend radius of the route.aims and objectives to review

3、existing methods for determining the underground pipes bending radius, to establish their characteristics and weaknesses, to develop improved method for calculating the bending radius according to the survey. methods the mathematical analysis, finite element method and laws of thermodynamics are use

4、d. results there are some disadvantages of using a geometric approximation in results measurement. a new method that uses the physical modeling of the deformation of the pipeline under the influence of soil reaction is offered. conclusion the simulation method allows to calculate the bending radius

5、with greater accuracy, not only in the plane but in space. key words: underground pipeline, ground, bend radius, tension, calculation, modeling, horizontal and vertical position.nowadays the task to find out the depth of the underground pipeline on the basis of the survey results is highly relevant.

6、 there some reasons for its.1. improving and everywhere installation of the satellite based navigation tool results in the highly accurate pipeline location determination and its coordinates recording on the digital devices. in order to provide it, it is necessary to improve the existing methods of

7、survey information analysis.2. pipeline net expansion towards the east siberia and far east, considering their complicated geotechnical conditions results in necessity of supervision of the ground deformation and its influence on the underground pipelines.3. pipelines lifetime nowadays is over 40 ye

8、ars or more, and it is twice more than the maximum pipeline age. for their further exploitation their reliability and safety should be proved. with this purpose pipelines should be inspected, defects should be detected and their changes, such as material ageing, defects progress, depth change, stres

9、sed zones and stress concentrators, should be analyzed.4. in the last few years it is highly relevant to provide the internal diagnostics of the main pipelines. the internal diagnostics is provided after the pipeline construction first and then periodically every 5 years. such method helps to find s

10、uch metal defects as corrosion, dents, metal layering, abnormal welds, etc. however, there are no internal diagnostics devices which show the underground pipeline depth, so it is the actual task for scientists now.thus, the aim of the work is to analyze the existing methods of pipeline depth data tr

11、ansformation into stress-state condition.it is well known, that stress in every pipeline wall point is composed of three parts: circumferential, axial and bending stresses 1, 2. such stresses can change circumferentially or axially. circumferential stresses depend on the pipeline sizes (diameter d a

12、nd wall thickness d), operating pressure p and atmospheric pressure. the axial stresses depend on the climate conditions, operating pressure and ground deformation. the bending stresses of the underground pipelines are highly influenced by the ground features. supposing the straight pipeline part, r

13、elation between bending stress and bending radius r:,(1)e steel youngs module.its necessary to remark, that under the influence of the ground changing the underground pipeline bending radius r can change depending on the pipeline length and depending on time. so the task is to find out the bending r

14、adius of the underground pipeline as the result of periodical surveys.analyzing the literature and normative documents, there were found out three main methods:1. «circumferential method», used in most documents, including the temporary guidelines 39-1.10-026-2001 «methods of assessin

15、g underground pipeline's actual position and condition» 3. determination of bending radius is based on the circles composition y three points (picture 1).the errors value depends on the points chosen. in addition to that, it is necessary to account the depth calculation error, which always

16、exists. it is shown on the picture 1, on the 3-4 there are 2 circles, characterizing the pipeline bending with different radius.h1, , h6 pipeline depth in different pointspicture 1 the bending radius determination scheme 22. «regulating methods», offered by tyumen scientists 4, is based on

17、 the approximation (regulation) of the depth coordinates by means of particular analytical function. the depth is measured in field conditions on the particular pipeline points with the 40 m step., (2)where a, b, l, z0 should be determined by means of infinitesimal square method based on the measure

18、d values vi. then the smooth approximating function line w(z) is used for bending radius calculation:.(3)however, this method is characterized by some disadvantages. there are no answers on such questions, as: why this function was chosen? are there any demands for initial data preparation? the calc

19、ulated value is lower than theoretical because of approximation. so the calculating error evaluates not the strength margin but vice versa, breaking the main strength calculating principles.3. «modeling method», offered by ufa scientists 5, 6, uses not the geometrical construction but the

20、deformation modeling using physical laws. in this method the main thermodynamical law is used, according which the mechanical system is in the stable equilibrium and the potential energy is minimum. as a system it is offered to considere the pipeline section divided on finite elements 1. the final e

21、lement in this case is the ring which size is z (z = 1 m is recommended). the aim of the calculation is to find the finite element model equilibrium state (picture 2) which satisfies the boundary conditions. the boundary conditions are the geometrical height in the particular pipe points vi. under c

22、onsideration there are forces acting on the pipeline including the ground reaction qi. in equilibrium state the geometrical height of the finite elements and the bending radius in this sections satisfy these conditions:,(4).(5)picture 2 pipeline finite element model in this method the only error rea

23、son is the initial data route survey data. for example, the calculation by this method is shown below.the underwater pipeline is considered, its diameter is 720 mm, pipe wall thickness is 19,5 mm. the calculation is provided in 10 points, step is 20 m (table 1). the geometrical height calculation er

24、ror is not more than 10 sm.table 1 the pipeline survey datadistance z, mdepth h, mdistance z, mdepth h, 100- 3,20200- 4,10120- 3,30220- 4,00140- 3,50240- 3,00160- 3,40260- 2,90180- 4,80280- 2,80the solution is based on the system of equations (4), written for all the finite elements in the model (i

25、= 1, 2, 3, , 280). on the basis of this pipe route survey data there were found out the pipeline equilibrium state, bending radius and bending stress with the 1 m step by the formulas (4), (5), (1). the corresponding graphs are shown in the picture 3. h pipeline depth; s - bending stress (lower gene

26、ratrix); r - bending radiuspicture 3 pipeline stress state on the basis of the 20 m step calculationobviously, this model is not characterized by the disadvantages of other models. because other models are based on geometrical laws, which are just mathematical instrument, in spite of physical laws.

27、on the geometrical basis the circle could be composed by three points. in the case of the pipeline the circle is not the only geometrical figure could be composed by three points, and the geometrical form depends on the minimum energy condition (thermodynamic law). from the picture 3 it is obvious t

28、hat stress is continuous piecewise-linear function. due to temporary guidelines 39-1.10-026-2001 the stress distribution is discontinuous piecewise-constant function. the main model feature is that the calculation errors as the part of initial data form the boundary condition. basing on comparison o

29、f the calculations based on different initial data for one pipeline section the demand for geometrical depths measuring devices could be formed.the methods, considered above, allow finding out the bending radius in the vertical plane. in fact, the pipeline axis might get out of one plane and to beco

30、me the surface line, so it can be written parametrically:; ; ,(6)where x, y, z spatial coordinates of pipeline; s a parameter, which change changes the x, y, z coordinates, i.e. the point moves due to the pipe axis. in our case s is the path from the initial point 0, which is the coordinate origin.

31、so the formula for bending radius r 7:.(7)if the pipeline axis line is in vertical plane, then parameter s equals to z coordinate (along the pipeline axis) and formulas (6) and (7) transform to the formula (5):;®. (8)by the analogy, use of this formulas for the straight line pipe section, which

32、 under the ground water influence changes its x and y coordinates, and taking parameter s equal to z coordinate, gives the following formula:;®. (9)last equation shows how to use the modeling method for the pipeline deformation in two space directions (spatial problem). for this task shifts on

33、x and y axis are considered separately, then it is necessary to find the corresponding bending radius rx and ry, the total bending radius r and cumulative bending stress: .(10)lets find the bending radius in x and y directions by means of modeling method, using scheme, shown in the picture 2, and eq

34、uations (4) and (5), written separately for each shift direction:; ; .summarythere is developed the improved method of bending radius determination using pipeline depth survey data. the method is based on the basic physical laws and allows to calculate the pipeline stress state under the ground defo

35、rmation influence.this method in aggregate with magnetic location method 8-10 allows to automate the process of pipeline depth determination, so this method is highly relevant being used in the non-stable grounds. literature1. gumerov a.g., gumerov r.s., gumerov k.m. bezopasnosty dlitelyno ekspluati

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