Stress analysis of oil and gas pipeline parallel laying when traversing tunnels

Transcription

1 Avilble online Journl of Chemicl nd Phrmceuticl Reserch, 2014, 6(6): Reserch Article ISSN : CODEN(USA) : JCPRC5 Stress nlysis of oil nd gs pipeline prllel lying when trversing tunnels Kun Hung, Shijun Wu, Liqiong Chen, Hongfng Lu*, Yitng Lv nd Jili Wu School of Petroleum Engineering, Southwest Petroleum University, Chengdu, Chin ABSTRACT Chin-Mynmr oil & gs pipeline project covers 7,676 miles in ll. The project met with complex geologicl conditions, construction types long the line, nd long-distnce oil & gs prllel lying pipeline. Becuse the pipeline lyout nd the construction re more complicted, it is necessry to mke the stress nlysis of oil & gs prllel lying pipeline trversing tunnels. Softwre CAESAR II is used to mke numericl simultion on one section of oil & gs prllel lying pipeline. Through nlysis we cn get the min lod infector effecting oil & gs pipeline stress, nd the loction of the most dngerous section. In the end, some fesible suggestions cn be put forwrd for the security of oil & gs prllel lying pipeline ccording to the nlysis conclusion. Key words: Oil & Gs Prllel Lying Pipeline; Stress Anlysis; CAESAR II; Numericl Simultion INTRODUCTION Chin-Mynmr oil & gs pipeline project is the fourth energy input ccess fter Centrl Asi oil nd gs pipelines, the Chin-Russi crude oil pipeline, nd se-lne. This project concludes oil nd gs pipeline, delivering oil into Chin from Southwest Chin insted of Mlcc. It covers 7,676 miles in ll, long with vriety of geologicl conditions, such s Cstor physiognomy of Yunnn-Guizhou plteu. As result, different kinds of crossing methods re required for different regions. The generl crossing methods re shield method nd mining method when crossing the mountins nd lrge rivers, the structurl form of tunnel is devited well-drift-devited well. According to the current sitution nd reserch dt, tunnel uses the form of pipe rck support, nd import nd export will be respectively instlled with fixed buttresses, which re used to block the outside pipelines effect on the tunnel [1-3]. Design of the tunnel crossing pipe instlltion is divided into three stges: choice of pipeline instlltion, piping rrngement nd pipeline stress nlysis. Terrin limittions nd mintennce inconvenience led to more serious the consequences of the ccident for the crossing pipeline. Crossing pipeline filure for mny resons, in ddition to the unresonble design, construction qulity problems, filure of pipeline corrosion, pipeline ftigue filure nd other resons, there is nother importnt reson is tht the bends cnnot meet the strength requirements. Pipeline design is the bsis of the qulity of construction, the resonbleness of pipeline design is directly relted to the structurl sfety of the pipeline. Mostly recently, the Chin-Mynmr gs pipeline hs put into opertion, sooner will be the oil pipeline. Experts did less study on the stress nlysis of oil & gs prllel lying pipeline crossing tunnels. Additionlly, mintennce repir for pipeline under tunnels is difficult, nd the oil & gs prllel lying pipeline lyout is more complicted. Therefore, filling blnks of this technology s well s improve pipeline sfety, it is necessry to mke stress nlysis in detil towrds oil & gs prllel lying pipeline trversing tunnels. 1248

2 EXPERIMENTAL SECTION Stress nlysis method bsed on the finite element Pipeline stress nlysis usully use the of the finite element softwre, finite element method is to simplify the complex engineering problems to reltively simple problems nd then to solve this problem. As for pipeline stress nlysis, it is hrd to figure out the stress of ny point on pipeline, thus some prticulr points re keys to stress clcultion. Generlly, the shorter the length of the infinitesiml, the results of stress nlysis more ccurte, but on the other hnd, if the infinitesiml length is over-short, then the clcultion process is longer, the computtionl burden hevier s well. In order to blnce clcultion ccurcy nd simplicity, usully stipultes the prcticl length on stress nlysis, s it shows in Tble 1. Tble 1 The finite element infinitesiml length Dimeter (mm) D>304.8 D 304.8mm Length of the djcent nodes L<20D L<30D Pipeline stress checking stndrds Oil & gs prllel lying pipeline in project ws buried build-in pipeline. Becuse of trnsmission medium nd conditions (temperture, pressure,) were different, the stress checking stndrds were different, too. Gs pipeline followed ASME B31.4 Pipeline Trnsporttion Systems for Liquid Hydrocrbons nd other Liquids. According to different cuses of stress, the types of stress cn be divided into first stress, secondry stress nd pek stress. Tble 2 nd 3 re check stndrds for gs nd oil pipeline respectively [4-5]. Tble 2 Check stndrds for gs pipeline Type Check requirements Primry stress σ [ σ ] Secondry stress Pek stress σ σ L E OPE σ σ Tble 3 Check stndrds for oil pipeline Type Check requirements Primry stress σ H 0.72σ Secondry stress σ E 0.90σ Pek stress σ OPE 0.90σ s Tunnel exit in the west S1 Bend1 A Anchor block 1 Anchor buttress 2 C Bend 2 Length of west oblique lne L 1 α Length of horizontl lne L Anchor buttress 3 Buttress Length of west oblique lne L 3 β Anchor buttress 4 Bend 4 D Bend 3 Tunnel entrnce in the est S 2 B nchor block 6 Anchor buttress 5 Section 1 Section 2 Fig. 1 Model for the tunnel structure 1249

3 Tunnel model Common lyout of the pipe buttress nd line in tunnel is shown in figure 1. The input nd output pipeline is generlly horizontl lid, with length t S 1 nd S 2, without buttress; the length of west oblique lne is L 1, tilt ngle is α (<50 ), nd the lines nchor buttress is set in the middle. At distnce of bend 2 nd bend 3 in the horizontl lne is ll set by lines nchor buttress, but mny new pipelines hs cncelled horizontl lne nchor buttress; the length of est oblique lne is L 2, tilt ngle is β (<50 ),t distnce of bend 3 is lso set by lines nchor buttress. The two prts re lmost symmetricl [6-9]. Bckfill Oil Gs 700mm Fig. 2 Oil nd gs prllel lyout pipeline through the tunnel digrm Softwre In order to mke the clcultion simpler, we selected CAESAR II stress nlysis progrm of the COADE, n Americn compny. Its function is very powerful, in ddition to sttic nlysis nd dynmic nlysis of pipeline, it cn lso undertke the seismic nlysis of buried pipeline, stress nlysis of vrious components nd the locl joint, flnge lek nlysis etc, nd considering the friction between the pipe element in the design, the simultion is consistent with rel sitution, then it cn get more ccurte results [10-12]. CAESAR II pipe stress nlysis softwre cn be divided into dt input, choice of clcultion conditions, the output nlysis nd judgments of three prts: (1) Dt clssifiction: when clcultion with CAESAR II, first of ll, we should select nd number the node which need nlyze, to mke the output results from the node dt. Then, input dt. According to the chrcteristics of the difference, input dt is divided into pipe element structure chrcteristic prmeters, bsic prmeters nd boundry conditions. Pipe element structure chrcteristic prmeters minly refer to the shpes, structure chrcteristics, etc. of piping components in pipeline. Bsic prmeters minly refers to the bsic conditions of ech pipe element in the piping, they re: clcultion temperture, instlltion temperture, llowble stress, mteril grdes, elstic modulus, Poisson rtio, medium density, density of piping mteril, thickness nd the density of the therml brrier, etc. Boundry conditions minly refer to the piping system of ech pipe element in the constrint condition, dditionl displcement, pipe endpoints type, cold spring, etc. (2) Progrm opertion: Though the progrm opertion hs been into fixed procedures performed by the computer, it must combine the clcultion of conditions, nd error check in process. (i) Rw input dt check Before the clcultion, computer would wrn the mistkes bout computtion errors, t this time, design personnel re needed to check nd correct the rw dt ccording to the wrning. (ii) Choice of clculted conditions Clculted conditions of pek stress: L 1 =W+T+P, to get thrust of pipeline ginst the border; Clculted conditions of first stress: L 2 =W+P, to get the first stress of ech point in pipeline; Clculted conditions of second stress: L 3 =L 1 -L 2, to get the second stress of ech point in pipeline; 1250

4 Where W is self-weight lod, T is temperture stress, P is inner pressure, F is concentrted lod. (3) Anlysis nd judgment of clcultion results: fter stress clcultion of pipeline, we should nlyze nd judge the result, to confirm whether the dt cn meet with the requirements. (4) Anlysis nd judgment bout displcement: when the first nd second stress in pipeline up to stndrd, displcement judgment hs nothing to do with pipeline strength relibility. RESULTS AND DISCUSSION Project profile According to the design mteril of Chin-Mynmr oil & gs pipeline project section XX, the length, from entrnce to exit of tunnel, is 1260 meters. In the tunnel, it is ll pipe supported, nchor block 4 nd nchor block 7 re set in entrnce nd exit respectively to cut the ffection of outside towrds pipeline inside the tunnel. The entrnce of tunnel is 30 meters in length, one nchor block; the length of west oblique lne is 310 meters, tilt ngle is 25, 16 nchor blocks re set every 18 meters, one line nchor buttress(in the middle of west oblique lne, 144 meters to horizontl lne); the length of horizontl lne is 410 meters, 22 buttress; the length of est oblique lne is 453 meters, tilt ngle t 20, 24 nchor blocks re set every 12 meters, one line nchor buttress(in the middle of est oblique lne, 144 meters to horizontl lne); The exit of tunnel is 34 meters in length, one nchor block; in ddition, gs pipeline rosted bend rdius of curvture R= 6D, crude oil pipeline pipe bending curvture rdius R=10D, D s the pipe dimeter, re grde is 3. Numericl simultion needs two pipeline, the length of model is 1240 meters, in which tilt section is 763 meters, input horizontl length is 33 meters, output lne is 34 meters, nd the distnce between two pipelines is 700mm. Pipeline mteril of gs pipeline is APIX80, with 1016mm dimeter stright sw pipe, the stright pipe nd the bend section thickness is 18.4 mm nd 22.2 mm respectively, opertion temperture is 50,pipe mteril llowble stress is 555 MP, operting pressure is 10 MP, specific pipeline prmeters re shown in tble 4. Pipeline mteril of oil pipeline is APIX70, with dimeter t 1016mm, the thickness is 7.9 mm, opertion temperture is 25,pipe mteril llowble stress is 485 MP, operting pressure is 9 MP, specific pipeline prmeters re shown in tble 5. Tble 6 showed the soil prmeters. Tunnel entrnce in the est 33m Tunnel entrnce in the est 34m Anchor block 1 Input Bend 1 Anchor buttress 2 Oblique lne in the est 310m 25 Horizontl lne 410m Oblique lne in the west 453m 20 Bend 2 buttress Bend 3 Anchor buttress 3 Anchor block 4 Bend 4 E Output N S W Fig. 3 Tunnel trverse in Chin-Mynmr oil & gs pipeline project section XX Tble 4 Gs pipeline prmeters Wll thickness of stright pipe Wll thickness of bend Mteril Dimeter Corrosion API X Fluid Insulting lyer Allowble density[kg/m 3 Pressure[MP] Temperture[ ] ] thickness stress[mp] Tble 5 Crude oil pipeline prmeters Wll thickness of stright pipe Wll thickness of bend Mteril Dimeter Corrosion API X Fluid Insulting lyer Allowble density[kg/m 3 Pressure[MP] Temperture[ ] ] thickness stress[mp]

5 Friction coefficient Soil density (kg/m3) Buried depth to top of pipe (m) Friction ngle( ) Tble 6 Soil prmeters Yield displcement fctor Overburden compction multiplier Therml expnsion coefficient Result nlysis In softwre CAESAR II, one document cn only hve one pipeline, in order to relize the stress nlysis of oil nd gs prllel lying pipeline, we need to use commend coordinte to chnge the loction of the dtum xis so tht to combine two pipeline models together. Figure 4 is the digrm of oil nd gs prllel lying pipelines in the west nd est prt. Tunnel entrnce in the west Anchor block1 Bend 1 Bend 2 Bend 4 Bend 3 Anchor block 4 Tunnel exit in the est Fig. 4 Operting interfce of the section modeling using CAESAR II Through the stress clcultion of ech node from CAESAR II, we collect ll dt into Excel nd drw the polygon. It is esier to know the overll stress distribution of pipeline through imge file. Fig. 5 Stress distribution of gs pipeline 1252

6 Tble 7 Gs pipeline stress check Stress Type Mximum stress vlue (MP) Mximum stress rtio (%) Loction Stress check vlue (MP) Pek stress Bend Primry stress Bend Secondry stress Bend Tble 8 Oil pipeline stress check Stress Type Mximum stress vlue (MP) Mximum stress rtio (%) Loction Stress check vlue (MP) Pek stress Anchor block Primry stress Anchor block Secondry stress Anchor block Fig. 6 Stress distribution of oil pipeline Figure 7 nd figure 8 is stress check sitution of gs nd oil pipeline, figure 5 nd figure 6 is the distribution picture of pek, first, second stress rtio of gs nd oil pipeline, respectively. From contrst, it is obviously tht: (1) From the stresses check of gs nd oil pipeline, the stress of oil nd gs prllel lying pipeline in C-M pipeline project section XX up to the stndrd ASME. (2) From tble 7, we cn figure tht: the pek, first, nd second stress of gs pipeline were ll hppened t Bend 2, tht is to sy, Bend 2 is the biggest dnger section in gs pipeline. (3) From tble 8: the pek, first, nd second stress of gs pipeline were ll hppened t Anchor block 1, tht is to sy, Anchor block 1 is the biggest dnger section in oil pipeline. (4) From figure 5: for gs pipeline, the pek stress is lrger thn the first nd the second stress, then is the first stress, nd the second stress comes to the lst. It mens pipe therml stress cused by temperture chnge ffect little to gs pipeline sfety. (5) From figure 6: for oil pipeline, the first stress is lrger thn the pek stress nd the second stress, it mens lod from outside (including grvity, intrinsic pressure) ffect lot to oil pipeline stress. In the figure, we cn lso see the verge second stress is very smll, the lrgest is MP, 9.95% of the stress check vlue, it mens temperture hs less influence towrds oil pipeline stress. (6) From figure 6, we cn lso know tht: t the strt of pipeline model, tht is to sy the nchor block 1, the pek, the first, the second stress is much lrger thn verge stress, which mens nchor block 1 undertook much stress. CONCLUSION Through the stress nlysis of oil nd gs prllel lying pipeline in C-M pipeline project section XX, we knew the loction of dngerous section nd the min lod ffecting pipeline stress during the process of gs nd oil pipeline crossing tunnel. As for gs pipeline crossing tunnel, bnd 2 is the dngerous section. Therefore, except for reinforcing in bends, the bend of oblique lne bottom on the gs direction should be pid much ttention. If the stresses on bends re not 1253

7 qulified, incresing the wll thickness or djusting the bend ngle is expected. As for oil pipeline, the stress nlysis told us tht the min lods ffecting oil pipeline stress re grvity, inner pressure, etc.; it is becuse the grvity hs put much influence on oil pipeline. As result of therml insultion lyer nd the soil, the second stress cused by temperture is much smller. In word, nchor block 1 undertook huge stress; it is suggested to reinforce nd dd the pipe constrint t tunnel portls, or to chnge the pipeline direction to bsorb prt stress using the nture bends t tunnel portls. This reserch filled the technique blnk of stress nlysis towrd oil nd gs prllel lying pipeline trversing tunnels, nd provided certin foundtion on protecting pipeline sfety s well. Acknowledgment This reserch is supported by Sichun Provincil Key Disciplinry Development Project Fund (SZD0416). And specil cknowledgement should be given to the Project Reserch on stress nlysis of oil pipeline from Southwest Petroleum University. REFERENCES [1] K Abhry; A Nourbkhsh; LLHS Loung, Int J Pres Ves Pip., 1999, 76(8), [2] K Hung; HF Lu; KR Shen; et l., Adv. J. Food Sci. Technol., 2013, 5(9), [3] K Hung; SJ Wu; HF Lu; et l., Nt Gs Oil., 2012, 30(4), 1-4. [4] XN Wu; HW Shu; LF Zn; et l., Nt Gs Ind., 2013, 33(3), [5] XN Wu; HF Lu; K Hung; et l., Nt Gs Ind., 2014, 34(5), [6] T Li; SJ Wu; K Hung; et l., Pip Technol Eq., 2014, 3, [7] XN Wu; Y Jing; HF Lu; et l., Res. J. Appl. Sci. Eng. Technol., 2014, 7(1): [8] XN Wu; HF Lu; SJ Wu; et l., Appl Mech Mter, 2014, 501: [9] XD Sh; XH Chen; K Hung; et l., Nt Gs Oil., 2013, 31(1):1-4. [10] M Abid; M Siddique, Int J Pres Ves Pip., 2005, 82(11), [11] MS Chiodo; C Ruggieri, Int J Pres Ves Pip., 2009, 86(2), [12] Y Joliff; L Belec; E Argon, Comp Mter Sci., 2013, 68,