STRUCTURAL PERFORMANCE OF BURIED STEEL PIPELINES CROSSING STRIKE-SLIP FAULTS. Spyros A. Karamanos Department of Mechanical Engineering,

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1 Proceeding of the 1th International Pipeline Conference IPC14 September 9 October 3, 14, Calgary, Alberta, Canada IPC STRUCTURAL PERFORMANCE OF BURIED STEEL PIPELINES CROSSING STRIKE-SLIP FAULTS Polyniki Vazoura Department of Civil Engineering, Univ. of Thealy, Volo, Greece Pano Dakoula Department of Civil Engineering, Univ. of Thealy, Volo, Greece Spyro A. Karamano Department of Mechanical Engineering, Univ. of Thealy, Volo, Greece kara@mie.uth.gr ABSTRACT The performance of pipeline ubjected to permanent trike-lip fault movement i invetigated by combining detailed numerical imulation and cloed-form olution. A cloed-form olution for the force-diplacement relationhip of a buried pipeline ubjected to tenion i preented and ued in the form of nonlinear pring at the two end of the pipeline in a refined finite element model, allowing an efficient nonlinear analyi of the pipe-oil ytem at large trike-lip fault movement. The analyi account for large deformation, inelatic material behaviour of the pipeline and the urrounding oil, a well a contact and friction condition on the oil-pipe interface. Appropriate performance criteria of the teel pipeline are adopted and monitored throughout the analyi. It i hown that the end condition of the pipeline have a ignificant influence on pipeline performance. For a trike-lip fault normal to the pipeline axi, local buckling occur at relatively mall fault diplacement. A the angle between the fault normal and the pipeline axi increae, local buckling can be avoided e to longitudinal tretching, but the pipeline may fail e to exceive axial tenile train or cro ectional flattening. INTRODUCTION Ground-inced action e fault movement are reponible for ignificant damage in oil and ga buried teel pipeline. Thoe deformation are applied in a quai-tatic manner, and are not necearily aociated with high eimic intenity, but the pipeline may be eriouly deformed, well beyond the elatic range of pipe material and may caue pipeline failure; high tenile tree may caue fracture of the pipeline wall, epecially at weld or defected location or weld, wherea compreive tree may caue buckling, in the form of pipe wall wrinkling, alo referred to a local buckling or kinking. The pioneering work of Newmark and Hall [1] ha been extended by Kennedy et al.[], Wang and Yeh[3], Wang and Wang [4]and Takada et al. [5] through a beam-type approach for decribing pipeline deformation. More recent work on thi ubject have been reported by Karamitro et al. [6] Liu et al. [7]and Trifonov&Cherniy[8]. In addition to the above analytical and numerical tudie, notable experimental work on the effect of trike-lip fault on buried high-denity polyethylene (HDPE) pipeline have been reported in erie of recent paper by Ha et al. [9] and Abdoun et al. [1].The analytical work outlined above have modelled oil condition baed on a pring-type approach. A more rigorou approach ha been followed in mot recent paperof the preent author [11] [1], for buried teel pipeline croing trike-lip fault at variou angle with repect to the fault plane, through a finite element modelling of the oil-pipeline ytem, which account rigorouly for the inelatic behaviour of the urrounding oil, the interaction and the contact between the oil and the pipe (including friction contact and the development of gap), the development of large inelatic train in the teel pipeline, the ditortion of the pipeline cro-ection and the poibility of local buckling, the preence of internal preure. The objective of the preent paper i to develop a refined numerical model, extending the work preented in [11][1] and accounting for appropriate end effect, to invetigate the mechanical behavior of underground teel pipeline croing oblique trike-lip fault ubjected to permanent ground movement. Toward thi purpoe, the rigorou numerical methodology developed in the previou publication i 1 Copyright 14 by ASME

2 combined with a new cloed-form mathematical olution of equivalent nonlinear pring at the model end, allowing for efficient and accurate imulation of pipeline behavior. NUMERICAL MODEL DESCRIPTION The mechanical behavior of a teel pipeline croing a trike-lip fault i imulated uing finite element program ABAQUS [13]. Relative ground diplacement d i applied in a direction that form an angle β with the normal on the pipeline direction, a hown chematically in Figure 1, ranging from zero to 45 degree. relative ground diplacement d Figure 1.Schematic repreentation of buried pipeline ubjected to oblique trike-lip fault diplacement. Figure.Finite element model for angle β equal to 5: Finite element dicretization of the (a) oil prim with tectonic trikelip fault (b) oil prim cro-ection and (c) the teel pipeline. Figure how a numerical model for the oil-pipeline ytem; it ize and dicretization i imilar to the model employed in [11] [1]. It conit of a oil prim having dimenion pipe diameter. The angle between the fault plane and the normal on the pipeline axi in the model hown in Figure i equal to β =5 but different value of β can be alo aumed. The fault movement i conidered to occur within a narrow tranvere zone of width w, a common practice in everal recent numerical tudie of fault-foundation interaction [14][15], alo correponding to a more realitic repreentation of the fault diplacement mechanim. A relevant numerical invetigation in [11] ha hown that a value of w equal to.33m i adequate for the purpoe of the preent analyi. Figure b how the oil finite element meh in the y-z plane and Figure c depict the correponding meh for the teel pipe. Four-node reced-integration hell element (type S4R) are employed for modeling the cylindrical pipeline egment, and eight-node reced-integration brick element (C3D8R) are ued to imulate the urrounding oil. The burial depth i choen equal to about time of pipe diameter, which i in accordance with pipeline engineering practice [16]. The prim length in the x direction i equal to more than 65 pipe diameter, wherea dimenion in direction y and z are equal to 11 and 5 time the pipe diameter, repectively. The central part of the pipeline model, where imum tree and train are expected, conit of a finermeh. A total of 54 hell element around the cylinder circumference in thi central part have been found to be adequate to achieve convergence, wherea the ize of the hell element in the longitudinal direction ha been choen equal to 1/6 of the pipeline outer diameter D. Thi meh ha been hown capable of decribing the formation of hort-wave wrinkling (local buckling) on the pipeline wall [11]. The meh choen for the pipe egment far from the fault location i coarer. Similarly, the finite element meh for the oil i more refined in the region near the fault and coarer elewhere. A large-train von Mie platicity model with iotropic hardening i employed for the teel pipe material. The mechanical behavior of oil material i decribed through an elatic-perfectly platic Mohr-Coulomb contitutive model. The analyi i concted by applying gravity firtand, ubequently, uing a diplacement-controlled cheme, in which the fault diplacement d i increaed graally. The bae and vertical-boundary node of the firt oil block remain fixed in the horizontal direction, wherea the correponding node of the econd oil block are ubject to a uniform diplacement,in a direction parallel to the fault plane. Finally in order to incorporate infinite length in x direction for both the pipe and the oil a cloed-form mathematical olution i preented below. The equivalent nonlinear pring derived from thi olution i attached at both end of the pipe accounting for infinite model length. One free end of the nonlinear pring remained fixed while the other moved according to fault direction NONLINEAR SPRING FOR INFINITELY LONG PIPELINE IN TENSION A pipeline egment i conidered with diameter D, thickne t, length L, made of a material having Young a Copyright 14 by ASME

3 Molu E and Poion ratio ν. The pipeline i buried in a oil with denity, coheion c, friction angle,young Molu E and Poion ratio v (Figure 3a). The pipeline iubjected to a pullout force at the near end, while keeping fixed the far end (Figure 3b). The fixed far end of the pipeline may be at an infinite ditance ( L a ) which i the mot common cae in real application. It hould be noted that in a pullout tet, nonlinearity will occur firt at the pipe-oil interface at which the value of hear trength i quite lower than the yield tre of oil. Thu, the oil will behave elatically, even at very high pullout force, at which the pipeline material may yield. A hown in Figure 3b, when the applied diplacement u at the near end exceed a critical value, part of the pipeline along a ditance L experience liding at it interface, wherea the ret of the infinitely long pipeline remain bonded to the oil that behave elatically. In the following, pipeline repone in the non-liding and liding part i analyzed. Dk u EA (4) Equation (4)may be written a u (5) where Dk (6) EA The olution of equation (5) i given by x x u C1e Ce (7) For x, u and therefore C, wherea for x, u() u C. The axial force along the pipe i equal to 1 x F( x) EA EAu EA u e (8) Figure 4.Shear tre-diplacement relationhip at the pipe-oil interface. Figure 3: Buried pipeline ubjected to tenion (a) perpective view (b) vertical ection and (c) free body diagram of pipeline egment. The total length L may be either infinite or finite. Elatic behavior (non-liding interface) a Figure 3c illutrate a egment of the pipeline ubjected to tenile and hear tree. For hear tre at the pipe interface,the mobilized value of i equal to k u (1) Conidering the axial force change df along the pipeline of length df D Dk u () and uing the tre-train relationhip, df d ( EA ) EA d u (3) the equilibrium equation for the pipeegment become For the limit cae at which liding initiate at x =, the diplacement u() u become equal to the elatic limit diplacement u / e k (Figure 4). Thu, the axial force at x= can be written a F EA (9) k Hence, for linear elatic repone, the equivalent linear pringcontant for an infinitely long pipeline ubjected to tenion i given by K EA (1) t Inelatic behavior (liding interface) When the pipeline i ubjected to a pullout diplacement u u k, a egment of the pipeline lide along a / e ditance L, wherea the ret of the pipeline interface behave 3 Copyright 14 by ASME

4 elatically. For the liding egment, taking the equilibrium of a pipe element (Figure 3c) lead to EA D (11) or m (1) where D m (13) EA The axial train decreae linearly with the ditance x and may be written a ( x) mx C (14) 3 For x, the axial train i equal to () C (15) 3 wherea for e x x L, it become equal to the elatic limit train ( L ) e ml (16) xl Integrating ( x) from x to L, the diplacement difference u u i found equal to 1 1 u ue ( e) L el ml el (17) From(17), the length L i equal to 1 L e mu ue e m (18) Subtituting the imum elatic train obtained from the nonliding ide of the pipeline e ue (19) k equation (18) become 1 L m u m k k k Equation for equivalent nonlinear pring The force at the pipe end i given by e () F D L EAu (1) Conidering the above analyi, from equation (9), () and (1), the force diplacement ( ) relation for an infinitely long pipe become: F u for for u F u, k EAu (), k D F EA m u (3) k m k k k PERFORMANCE CRITERIA FOR STRAIN-BASED DESIGN OF BURIED STEEL PIPELINES Under trong permanent ground-inced action, buried teel pipeline exhibit evere deformation beyond the elatic limit. Steel material i quite ctile and capable of utaining ignificant amount of inelatic deformation, but at location where large tenile train develop, rupture of the pipeline wall may occur. Wrinkling (local buckling) of pipeline wall may alo occur e to exceive compreion at the pipeline wall, followed by pipe wall folding and development of ignificant local train. Furthermore, evere ditortion of the pipeline cro-ection may render the pipeline non-operational. To quantify the amount of damage in a buried pipeline under evere ground-inced action, the following three performance criteria are monitored in the preent analyi [1]: tenile train equal to 3% and 5% in the longitudinal direction of the pipeline, which may caue pipe wall rupture, local buckling (wrinkling) formation, and exceive ditortion of the pipeline cro-ection o that the flattening parameter f,defined f D D ( D i the change of pipe diameter in the flattening direction), reache a value of.15. During the conecutive tage of fault diplacement application, the performance criteria are evaluated, monitoring the imum value of longitudinal train along the pipeline, a well a the cro-ectional ditortion (flattening) at variou cro-ection. Furthermore, the finite element model i capable of imulating rigorouly the formation of pipeline wall wrinkling. NUMERICAL RESULTS FOR PIPELINES CROSSING STRIKE-SLIP FAULTS In thi ection, numerical reult are obtained for the 36- inch X65 buried pipeline that croe trike-lip fault at different angle, with thickne equal to 9.5 mm (3/8 in), o that D/t i equal to 96. Three croing angle were invetigated with 4 Copyright 14 by ASME

5 zero internal preure uing the numerical model decribed above. The yield tre σ y and ultimate tre σ υ are equal to 45 MPa (65 ki) and 56 MPa (81. ki), repectively, with a 3% elongation at the ultimate tre (ε υ =.3).Infinite pipeline length i aumed. The pipeline i buried in the coheive oil, under undrained condition, having a denity = kg/m 3, coheion c =5 kpa, friction angle =,Young Molu E =5 MPa and Poion ratio v =.5. Pipeline performance for fault angle Uing the numerical model, Figure 5a and Figure 5b plot the ditribution of axial train at the tenion and compreion ide of the pipeline repectively, for different value of fault diplacement d. Figure 5c how the evolution of pipeline tre tate and deformation at a tage jut before local buckling, and immediately after buckling. Conidering the convention for local buckling onet in which ignificant ditortion of the cro-ection occur e to the development of a localized wrinkling pattern on the pipe wall, on the compreion ide of the deformed pipeline, a tated in [11][1], local buckling occur at a fault diplacement of about d =.43 m; thi i the mot critical performance criterion for cr the preent cae. The 3% tenile train i reached at d cr =1.13 m, wherea the critical flattening occur at about 1.96 m. Note that both of thee criteria are reached at the buckled location well beyond the formation of the buckle. The 5% tenile train performance criterion i not reached within the imum fault diplacement (4 m) conidered in the analyi; in fact, the tenile train reache a value of about 4.1% in the coure of thi analyi. Pipeline performance for fault angle 5 Figure 6a plot the deformed hape of the pipeline and the ditribution of the axial train at fault diplacement equal to d =1, 1.5, and.5 m. In thi cae, additional pipeline extenion, equal to d in, occur, reulting in ignificant rection of the compreive bending train, and preventing the development of local buckling. Figure 6b illutrate the ovalization of the pipe croection at the fault location ( x ). The critical fault diplacement for ovalization (flattening) given in Table 1 i 1.8 m. Hence, the deformed pipeline hape at d 1.5 m, hown in Figure 6b, have already exceeded the ovalization performance criterion. Figure 7 plot the ditribution of diplacement in the longitudinal x direction at generator A and B (hown in Figure ) of the pipeline in term of the ditance from the fault, for fault diplacement d =1, 1.5, and.5 m. It i evident that the movement along the generator varie e to bending for x <1 m, but it i practically identical for x >1 m, indicating that, outide the mot-trained region near the fault, the pipeline i practically under pure axial tenion. Table 1. Critical fault diplacement for variou performance criteria with repect to fault angle β Critical fault diplacement, m Fault angle β Local buckling Flattening Strain 3% Strain 5% β= >4.* β=5 None β=45 None * Not reached within a imum fault movement of d=4 m Figure 5.(a) Axial train along the pipeline ide under tenion (b) axial train along the pipeline ide under compreion (c) pipeline hape at critical location before and after buckling. (angle β=). 5 Copyright 14 by ASME

6 Figure 6. Finite element reult from model withβ=5:(a) Axial train and (b) pipeline ection deformation at d 1, 1.5, and.5 m. Figure 8. Ditribution of axial train veru ditance from the fault, (β=5) along generator at the (a) left ide and (b) right ide of the pipeline. Figure 7. Ditribution of axial diplacement at the outer generator located at the left and right ide of the pipeline veru the ditance from the fault, (β=5). Pipeline performance for fault angle 45 For a fault angle 45, the pipeline i ubjected to ubtantial extenion ring fault movement in the x direction by d in.in thi cae, local buckling doe not occur, but the other performance criteria are reached at much maller fault diplacement value (Table 1). Flattening occur at 1.1m, wherea the 3% and 5% tenile axial train criteria at 1.8m and 1.4m, repectively. Effect of fault angle on pipeline performance The above numerical reult for the X65-teel infinite length pipeline with zero preure are ummarized in graphical form in Figure 1, where the fault diplacement value correponding to the performance criteria under conideration, are plotted with repect to the croing angle. The reult indicate that for non-poitive and mall poitive (le than 5 ) value of, local buckling i the dominant limit tate. For greater value of, two major limit tate, namely the 3% longitudinal tenile train and the cro ection flattening are mot important. Under increaing angle β, the normalized ultimate diplacement for cro-ectional ditortion remain the ame, wherea 3% and 5% of tenile train decreae. Figure 11 plot the performance criteria for the ame pipeline embedded in the ame oil condition but having now internal preure. It i obviou that with internal preure no ovalization i oberved. 6 Copyright 14 by ASME

7 Figure 11: Normalized critical fault diplacement for variou performance limit at different angle of β for a pipeline of infinite length (X65, D/t=96, Clay I, p=.56p ) Figure 9. Ditribution of (a) axial train and (b) hoop train around the perimeter of the pipeline ection at x, (croing angle β equal to 5). Figure 1: Normalized critical fault diplacement for variou performance limit at different angle of β and infinite pipeline length (X65, D/t=96, Clay I, p=). CONCLUSIONS The pipe-oil interaction and the performance of pipeline ubjected to permanent trike-lip fault movement have been invetigated uing refined model that combine detailed numerical imulation and mathematical olution. A cloedform mathematical olution for the force-diplacement relationhip of a buried pipeline ubjected to tenion ha been developed for pipeline. The cloed-form olution account for the elatic deformation of the oil and pipe, and the development of liding, when the hear tre at the pipe-oil interface reache it hear trength. The cloed-form olution enable the conideration of nonlinear pring at the two end of the pipeline in a refined finite-element formulation, allowing for an efficient nonlinear analyi of the pipe-oil interaction problem at large trike-lip fault movement. The numerical tudy i baed on a large number of refined numerical model correponding to variou value of angle β between the pipeline axi and the direction normal to the fault plane. The main concluion of the tudy can be ummarized a follow: 1. The propoed nonlinear force-diplacement relationhip allow for an efficient, refined numerical imulation of the oil-pipe interaction ring large permanent fault movement, through the ue of nonlinear pring in finite element model that decribe the pipe-oil ytem in a rigorou manner.. Numerical imulation of X65 pipeline with D/t=96 buried in clay oil croing trike-lip fault normal to their pipeline axi ( ) have hown that local buckling of pipe wall occur at mall fault diplacement. 7 Copyright 14 by ASME

8 3. Upon development of local buckling ring eimic fault movement, the location of imum flattening and axial train i at the buckled cro-ection. 4. For value of greater than 15, local buckling doe not occur e to pipeline tretching that rece the compreive tree caued by bending. Thu, if practically feaible, aligning the pipeline o that it form a poitive value of that i jut large enough to avoid local buckling, may improve pipeline performance, allowing larger critical fault diplacement for the flattening or tenile train criteria. 5. A tenion in the pipeline increae with increaing value of the angle, the critical fault diplacement correponding to the flattening performance criterion and, mot importantly, to the 3%- and 5%-tenile train criteria decreae. The methodology in the preent paper i applied to imulate the behavior of pipeline croing trike-lip fault, but can be alo applicable to other type of permanent ground-inced action, uch a normal and revere fault, a well a to buried pipeline ubjected to other type of ground-inced action (landlide, differential ettlement or lateral preading). NOMENCLATURE A : pipeline cro-ectional area c : coheion of oil D : outer pipe diameter d : fault diplacement D/t : pipe outer diameter-to-thickne ratio E : Young molu F : Axial force at x= k : hear tiffne of pipe-oil interface K t : equivalent linear pring contant L e : non-liding pipeline egment L : liding pipeline egment p : pipe internal preure p : imum pipe preure t : pipe wall thickne u : axial pipeline diplacement w : fault width β : fault angle with repect to normal to pipe axi ε : axial train on pipe wall ν : Poion ratio ρ : oil denity σ y : pipe material yield tre σ υ : pipe material ultimate tre τ : hear tre at pipe-oil interface τ : imum hear tre at pipe-oil interface φ : friction angle of pipe-oil interface ACKNOWLEDGMENTS Thi work wa upported by a financial grant from the Reearch Fund for Coal and Steel of the European Commiion, GIPIPE project: Safety of buried teel pipeline under ground-ined deformation., Grant No.RFSR-CT The author would like to thank Mr. Gregory Sarvani for hi help in preparing the manucript. REFERENCES [1] Newmark N. M., Hall W. J. (1975), Pipeline deign to reit large fault diplacement. Proceeding of U.S. National Conference on Earthquake Engineering; [] Kennedy, R. P., Chow, A. W. and Williamon, R. A. (1977), Fault movement effect on buried oil pipeline, ASCE Journal of Tranportation Engineering, Vol. 13, pp [3] Wang, L. R. L. and Yeh, Y. A. (1985), A refined eimic analyi and deign of buried pipeline for fault movement, Earthquake Engineering &Structural Dynamic, Vol. 13, pp [4] Wang L. L. R., Wang L. J. (1995), Parametric tudy of buried pipeline e to large fault movement. ASCE, TCLEE 1995; (6): [5] Takada, S., Haani, N.and Fukuda, K. (1), A new propoal for implified deign of buried teel pipe croing active fault, Earthquake Engineering and Structural Dynamic, 1; Vol. 3, pp [6] Karamitro, D. K., Bouckovala, G. D., and Kouretzi, G. P. (7), Stre Analyi of Buried Steel Pipeline at Strike-Slip Fault Croing.,Soil Dynamic & Earthquake Engineering, Vol. 7, pp. -11 [7] Liu, M., Wang, Y.-Y., and Yu, Z., (8), Repone of pipeline under fault croing, Proceeding Intern. Offhore and Polar Engineering Conference, Vancouver, BC, Canada. [8] Trifonov, O. V. and Cherniy, V. P. (1), A emianalytical approach to a nonlinear tre train analyi of buried teel pipeline croing active fault.,soil Dynamic & Earthquake Engineering, Vol. 3, pp [9] Ha, D., Abdoun T.H., O Rourke, M.J., Syman, M.D., O Rourke, T.D., Palmer, M.C., and Stewart, H.E. (8), Buried high-denity polyethylene pipeline ubjected to normal and trike-lip faulting a centrifuge invetigation, Canadian Geotechnical Engineering Journal, Vol. 45, pp Copyright 14 by ASME

9 [1] Abdoun T. H., Ha, D., O Rourke, M. J., Syman, M. D., O Rourke, T. D., Palmer, M. C., and Stewart, H. E. (9), Factor influencing the behavior of buried pipeline ubjected to earthquake faulting., Soil Dynamic and Earthquake Engineering, Vol. 9, pp [11] Vazoura, P., Karamano, S. A., and Dakoula, P. (1), Finite Element Analyi of Buried Steel Pipeline Under Strike-Slip Fault Diplacement, Soil Dynamic and Earthquake Engineering, Vol. 3, No. 11, pp [1] Vazoura, P., Karamano, S. A., and Dakoula, P. (1), Mechanical behavior of buried teel pipe croing active trike-lip fault, Soil Dynamic and Earthq. Engineering, 41: [13] ABAQUS (1): Uer Manual, Simulia, Providence, RI, USA. [14] Anataopoulo, I., Callerio, A., Branby, M. F., Davie, M. C., Naha, A. El, Faccioli, E., Gazeta, G., Maella, A., Paolucci, R., Pecker, A., Roigniol, E. (8), Numerical analye of fault foundation interaction., Bulletin of Earthquake Engineering, Springer, Vol. 6, No. 4, pp [15] Gazeta, G., Anataopoulo, I. and Apotolou, M. (7), Shallow and deep foundation under fault rapture or trong eimic haking, K. Pitilaki (ed.), Earthquake Geotechnical Engineering, Springer, pp [16] Mohitpour, M., Golhan, H. and Murray, A. (7), Pipeline Deign & Contruction: A Practical Approach, Third Edition, ASME Pre, New York, NY. 9 Copyright 14 by ASME