Impact of Elbow Angles on Flow-Induced Vibration in Crude Oil Pipelines

ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 1 يف ةيملعلا ةقرولا ملاتسا مت 12/06/2022 Received يف ةيملعلا ةقرولا لوبق مت 16/04/2022 Accepted يف ةيملعلا ةقرولا رشن مت 13/04/2022 Published Impact of elbow angles on Flow-Induced Vibration in Crude Oil Pipelines Ezedine G. Allaboudi*, Khaled M. Ahmida Department of Mechanical and Industrial Engineering Faculty of Engineering, University of Tripoli -Libya Emails: [email protected]*, [email protected].ly Abstract Pipelines carrying fluids are primarily used in oil and gas industry. These pipelines may experience vibrations caused by high-pressure fluctuations in fluids, leading to a turbulent flow scheme. High vibration level poses a serious risk to the pipeline system, as it could cause pipes to vibrate intensely, severely impairing fatigue cracking. The interaction between the fluid and the structure leads to what is known as flow-induced vibrations (FIV). In this paper, a one-way FIV numerical analysis was conducted using ANSYS® Workbench, by modeling flow in elbows with different angles. Elbows are one of the critical parts along a pipeline, as they are mainly used to redirect fluid flow direction. The data regarding the pipe and the crude oil specifications are based on information received from Mellitah Oil and Gas Company. Stress, modal, and CFD analyses were carried out on elbows with three different angles. Two quite distinct flow velocities are considered, one representing the standard flow, and the other representing an extreme case of high flow velocity. Due to this extreme case, changes in modal parameters, in stress, and in deformations were observed along the pipes. This study emphasizes the importance of geometric features and the effect of sudden changes in fluid flow velocity on pipeline structures. Keywords: Flow induced vibration, pipelines, crude oil, static analysis, modal analysis. ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 2 ت تازازتهلاا ىلع عاوكلأا اياوز ريثأحتسملاث نم ة قفدتلايف طوطخ ماخلا طفنلا بيبانأ *يدوبللا ةعمج نيدلا زعخ ،هديمحا دمحم دلا ةيعانصلاو ةيكيناكيملا ةسدنهلا مسق - كلسلبارط ةعماج ،ةسدنهلا ةي - ليبيا ا:صخلمل ل بيبانلأا مدختسُتقن لكشب لئاوسلا ليسيئر ت دق .زاغلاو طفنلا ةعانص يفتضرع هذه بيبانلأالاتازازته نع ةجتانميق يف حجرأت ىلإ يدؤي امم ،لئاوسلا يف ةيلاعلا طغضلا ،بيبانلأا ماظن ىلع اً ريبك اً رطخ يلاعلا زازتهلاا ىوتسم لكشُ ي .برطضم قفدت ماظن ىلإ يدؤي امم ،ةدشب بيبانلأا زازتها يف ببستي نأ نكمي ثيحتاعدصت ريطخ ة ةجتان نع لااداهج رركتملا. ةجتانلا تازازتهلااب فرعُ ي ام ىلإ يدؤي لكيهلاو لئاسلا نيب لعافتلا فدتلا نعق(FIV) . لا هذه يفةسارديددع ليلحت ءارجإ مت ، أهاجتلاا يداح تازازتهلال فدتلا نع ةجتانلا ق(FIV) جمانرب مادختساب Workbench ® ANSYS للاخ نم ، ةجذمن ةينحنملا بيبانلأا يف قفدتلا ةفلتخم اياوز تاذ يهو o 45 ، o 90و ، o 135 . عاوكلأا (elbows ) ربتعت لا ءازجلأا نمةمهم طخ يفطو بيبانلأا، سيئر لكشب مدختسُت ثيح ي لئاسلا قفدت هاجتا ليوحتل لآ هاجتا نمرخ .بوبنأ تافصاومو تانايب ةساردلا تمدختسا تيلم ةكرشب صاخلا ماخلا طفنلا،زاغلاو طفنلل ة ثيحداهجلإا تلايلحت ءارجإ مت (stresses)لا ،روط (modal)لايلحتو ،ت ةيباسحلا لئاوسلا اكيمانيد (CFD) ةثلاثل اياوزةفلتخم ل و عاوكلأنيتفلتخم نيتعرس ،قفدتللىلولأا ايقلا قفدتلا لثمت ،يس امنيب ى رخلأا ةيلاع قفدت ةعرس تاذ ةفرطتم ةلاح لثمت. هذهل ةجيتن ةظحلام مت ،ةفرطتملا ةلاحلا يف تارييغت راوطلاا تاملعم نم لكبوبنلأا لوط ىلع تاهوشتلاو ،تاداهجلإا ،. ُت زرب لئاسلا قفدت ةعرس يف ةئجافملا تاريغتلا ريثأتو ةيسدنهلا صئاصخلا ةيمهأ ةساردلا هذه ىلعةينب بيبانلأا. ةيحاتفملا تاملكلا : وطخ ،قفدتلا نع ةجتانلا تازازتهلااتلا ،ماخلا طفنلا ،بيبانلأا ط ليلح يكيتاتسلاالأا ليلحت ،طاور. 1. Introduction Pipelines carrying fluid may experience undesired vibrations and suffer from serious stresses due to because of vibrations and stresses ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 3 causes by Flow Induced Vibration (FIV). These would affect the performance, safety and service lifetime of these pipelines. Thicker fluid, with high mass density, would have higher effects than gas, for instance, due to its mass. The main cause of FIV is the instability of fluid flow, where flow velocity fluctuations may occur due to high pressure or velocity differences, thus resulting into turbulent fluid flow [1]. The natural frequencies of the pipeline structure, and its dynamics in general, should fall between specific limits to prevent unwanted operational conditions. FIV may result in resonances and fatigue failure problems [2], thus the goal is to prevent these from happening during the design and operation stages. This is mainly a concern in pipelines used oil & gas industry, where crude oil is the transported fluid. The pipeline system usually contains straight-line line, elbows of different types, valves, strainers, and few apparatuses along the line. All these are potential causers of FIV problem [3]. When a fluid encounters unbalanced forces owing to pressure gradients, substantial pressure differences are the cause of vortices, which in turn cause turbulence and undesired structural vibrations [4]. The FIV studies dates back to the early 20th century, where the first notable event that spurred significant research was the collapse of Tacoma Narrows bridge in 1944 due to aeroelastic flutter. Later on, and due to advancement in computational fluid dynamics, more detailed studies surged, where few are mentioned in what follows. Y L Zhang, D G Gorman and J M Reese [5] derived the dynamic equilibrium matrix equation for a separate pipe element holding a flowing fluid using the Lagrange principle and the Ritz approach. The Eulerian approach and the concept of fictitious loads were used for kinematic correction to evaluate nonlinear geometric vibrations and produce a linear mathematical model. The vibratory behavior of a fluid was then investigated. The findings of the linear vibration model for fluid pipes and the experimental data were compared about pipe transit. Additionally, vibration issues with first-stretched fluid-conveying pipes were investigated at different pipe starting axial tensions and flow rates. Peter Vasilyev and Leonid Fromzel [6] gave a thorough study that examined the state of pipe vibration analysis. The most likely source of vibration caused by flow was thought to be the acoustic resonance of the medium (water or steam). The mathematical model and related computer code, NETPULS, were designed for the assessment of an acoustic oscillation in a liquid or gaseous medium. Acoustic excitation, that ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 4 might occur in pipelines, was investigated. The outcome of NETPULS software was used to assess mechanical vibrations in the pipeline. R. Veerapandi et al. [7] addressed the computational and analytical analyses a FIV in a pipeline. The fluid dynamic behavior mainly in angular type valve regions was explored and the modal analysis of the pipe system was examined. The analysis of FIV was carried out by examining the turbulence in the gas flow within the piping system during subcooling. CFD analysis was conducted using Ansys® CFX solver. Yu Jiang and Lei Zhu [8], under the interplay between the fluid and the structure, examined the same issue of a pipeline filled with fluid. A v-shaped pipeline was investigated using Ansys® software. An experimental study was also conducted using liquid-filled pipeline, where frequency measurements were taken and the simulation model was adjusted accordingly to validate it. It was demonstrated that pressure has very little influence on natural frequencies and that the natural frequency of a loaded pipeline reduces dramatically when compared to an empty one, due to extra mass of the fluid. According to the simulated modal analysis, the mode shapes of the pipeline full with liquid and the pipeline empty have the same mode shapes for the first six natural frequencies, but then differ. The simulation model worked as a replica for the experimental model with certain level of accuracy. Etim S Udoetok [9] created a model studying the vibrations brought on by internal fluid movement through pipes. The model was created for situations in which a free pipe section ends are clamped and when they are merely supported. The methodology combined engineering analysis and complicated mechanics to produce new, straightforward equations that compare positively. These equations were verified experimentally with acceptable agreement. Manoj Dangal and Subodh Kumar Ghimire [10] looked at the vibrations in pipes carrying fluids with various end condition configurations and materials. The mathematical formula for the vibration caused by flow in fluid-conveying pipes was created by adopting Hamilton's energy concept. The vibratory characteristics of the fluid utilized in the pipe were studied using FEA. It was found that increasing fluid velocity had the dual effects of increasing damping and reducing hardness. As a result, when fluid flow speed increased, the fundamental vibration frequency dropped. The crucial flow speed is the flow rate, which corresponds to the fundamental vibration frequency. The obtained results could be ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 5 used to reduce vibration-related failures in systems such as HVAC pipe installations, petroleum transportation, and other related sectors. Kamal Haziq and Izzuddin Zaman [11] conducted a study to utilize both one-way and two-way fluid-structure interaction (FSI) techniques to examine the effects of internal pipeline faults on the fluid flow pressure drop and velocity profile. The FSI multiple analysis system, which includes transient structural analysis, fluent analysis, and system coupling, is implemented using the ANSYS® workbench. The mutual interaction between the fluid domain and the pipe structure was studied using the two-way coupling approach. Laminar flow and turbulent flow were used to calculate the structural deformation, structural velocity, von Mises stress, and pressure of the fluid. This study demonstrated that as the fluid input velocity rises, the pipe overall deformation, velocity distribution, and von Mises stresses increases accordingly. The results in both situations showed that, in comparison to the problematic flow, the two-way savory flow had distortions, speeds, strains, and pressures far greater than the pipe structure. 2. Model Description To assess the impact of change in crude oil flow velocity in a are used. o , and 135 o , 90 o with angles of 45 three elbowspipeline, This analysis focuses on demonstrating the effect of fluid flow on the static and dynamic responses of the elbows. The structures are composed of two pipes, each of 3 m length, connected at one of the three angles mentioned before. An extra 0.1m span is used as a fixing area to model displacement constraint at the two ends, as illustrated in Fig. 1 and Fig. 2. All elbows have a radius of 350 mm. The pipes have an internal diameter of 0.1m, wall thickness of 3mm, and made of Nickel alloy Inconel 600. This alloy is typically employed in the Libyan Mellitah oil & gas company, and is used for transporting crude oil due to its known excellent corrosion resistance, high-temperature strength, oxidation resistance, and high tensile strength. The mechanical properties of Nickel alloy Inconel 600 are as given in Table and Table 2. Table 1. Properties of the Nickel alloy. Young’s modulus Mass density Ultimate tensile strength Yield tensile strength Poisson ratio 210 MPa 8474 kg/m3 800 MPa 500 MPa 0.3 ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 6 Table 2. Properties of the crude oil used. (source: Mellitah oil&gas Co.) Mass density Viscosity 850 kg/m3 1.275 kg/m.s Fig. 1. The elbows structural models with angles 45o, 90o and 135o. Fig. 2. Descriptive diagram of the elbows. The ANSYS® analysis model was developed as follows: the geometry was first built, then transferred to the CFD module where pressures on internal surfaces are calculated, then transferred to the static module where stresses and deformations are calculated, then to the modal analysis module with prescribed load imported from the CFD analysis (prestressed model), and finally to the modal analysis module without the effect of fluid loads. In what follows, the obtained results are analyzed for two scenarios: one representing the standard velocity of crude oil flow of 4m/s, and the other representing the extreme case of high flow velocity of 20m/s. 3. Simulation results and discussion The first section of results deals with structural modal analysis of the unstressed structures, i.e., zero effect of fluid velocity is ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 7 considered, thus allowing to observe the effects of fluid pressure presence and investigate its consequences. A structural modal analysis is conducted on the unstressed model and the only the first three mode shapes are demonstrated in Fig. 3. Most of these mode shapes are characterized by a deflection of pipe spans. The first 20 natural frequencies are calculated for the sake of comparison in the following sections. Fig. 3. The first three mode shapes of the three unstressed elbow structures. The second section of results illustrates the three analyzed modules: fluid flow dynamic analysis, stress and deformation analysis, and prestressed modal analysis. The first part demonstrates the results of a fluid flow velocity of 4 m/s. This is selected as an average of crude oil f in pipelines. The second part illustrates the extreme flow velocity of 20 m/s. The case of this extreme velocity could be originated due to wrongful operation of valves thus creating high pressure gradients, or due to faulty pipeline design. In certain scenarios like short pipelines or during pigging operations, the velocity might temporary be elevated to these values [12]. 3.1 Due to flow velocity of 4 m/s 3.1.1 Fluid flow model (CFD model) ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 8 These models (with the three different elbow angles) comprise the structure and the fluid domain filled with crude oil. The meshing was performed with an average element size of 0.05m, resulting in ~17364 nodes and ~2472 elements. The mesh sizes were sufficient to obtain converging and stable solutions. A fluid input velocity of 4 m/s was used as a boundary condition, with the fluid entering the pipe at one end. A zero-gauge pressure condition was imposed at the other end. The velocity profiles inside each of the three pipes, resulting from laminar crude oil flow, are illustrated in fig 4. . The velocity distribution near the relaxed elbows exhibits higher values due to lower flow resistance. Fig. 4. Flow velocity distribution inside the three elbows: v=4 m/s. 3.1.2 Static analysis of the prestressed model Due to fluid flow velocity, the pressure is formed and stresses are exerted by the fluid on the inner walls of the elbow structures. To find the resulting stresses on the inner walls, a static analysis is performed using loads imported from the fluid domain model (CFD model). These loads originate from the pressure profile acting on the inner walls of the pipeline. The same mesh used for the unstressed modal analysis is used here. The equivalent stresses and total deformations are calculated. This stage is crucial for investigating the effects of fluid flow on the structure, which is essential in the design stages of pipelines manufactured for transporting crude oil. It is important to note that the only loads present in this model are due to fluid flow pressure. Fluid dynamics indicate that sharp angles are expected to have higher pressure exerted on their internal walls compared to flat or more relaxed angles. This could clearly be observed in Fig. 5 (a, b and c). The stress distribution is higher at the sharp 45o elbow, ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 9 compared to the other two, and is minimum at the outlet, as per the boundary condition. .: v=4 m/selbow o 45. Stress distribution inside the (a)5 Fig. .elbow: v=4 m/s o 90. Stress distribution inside the (b) 5 Fig. .: v=4 m/selbow o 135. Stress distribution inside the (c)5 Fig. 3.1.3 Modal analysis of the prestressed model This step is crucial to study the impact of the stresses generated by crude oil flow in the pipeline on the dynamic behavior of the entire structure. The loads from the CFD model are imported into this modal analysis. The first 20 natural frequencies are calculated for the sake of comparison in what follows. In general, the maximum change in natural frequencies is found at the elbow angle of 45o, as ددعلا 63 Volume دلجملا2Part International Science and Technology Journal ةينقتلاو مولعلل ةيلودلا ةلجملا http://www.doi.org/10.62341/agkm0504 ةظوفحم عبطلا قوقح للةلجم ل ةيلودلا ةينقتلاو مولعل Copyright © ISTJ 16 [5] Zhang, Y L, Gorman, D. G., and Reese, J. M., "Analysis of the vibration of pipes conveying fluid", Department of Engineering, University of Aberdeen, Scotland, UK (1998):849-860. [6] Vasilyev, P., and Fromzel, L., "Analytical Study of Piping Flow-Induced Vibration: Example of Implementation", 17th International conference on structural mechanics in reactor technology, Prague, Czech Republic, August 17-22, 2003, J280. [7] Veerapandi, R., Karthikeyan, G., Jinu, G. R., and Kannaiah, R., "Experimental Study and analysis of flow induced vibration in a pipeline", International journal of engineering research & technology (IJERT), v. 3, Issue 5, May 2014: 1996-1999. [8] [8] Jiang, Y., and Zhu, L., "Modal analysis of liquid-filled pipeline under fluid-structure interaction by simulation and experiment methods", Defense technology, Changsha, China (2018): 42-47. [9] Udoetok, E. S., “Internal fluid flow induced vibration of pipes”, Journal of mechanical design and vibration, vol. 6, no. 1 (2018): 1-8. doi:10.12691/jmdv-6-1-1. [10] Dangal, M., Ghimire, S. K., "Modeling and analysis of flow induced vibration in pipes using finite element approach", Tribhuvan University, Nepal, Proceedings of IOE graduate conference, (2019): 725-732. [11] Haziq, K., and Zaman, I., "Flow induced vibration analysis in pipeline by using one-way and two-way fluid structure interaction", Journal of complex flow, vol. 5 No. 1 (2023) p. 15. [12] Brill, J P. and Mukherjee, H. K., “Multiphase Flow In Wells”, Henry L. Doherty Memorial Fund of Aime Society of Petroleum, 1999.