IJSTE - International Journal of Science Technology & Engineering Volume 3 Issue 07 January 2017 ISSN (online): 2349-784X Mitigations to Flow Induced Vibration (FIV) in Control Valve Piping System using Visco-Elastic Dampers & Neoprene Pads Mr. Bhagwat B. Kedar Ms. Jayshri S. Gulave M. Tech. Student (CAD/CAM & Automation) M. E. Student (Heat Power) Department of Mechanical Engineering Department of Mechanical Engineering Veermata Jijabai Technological Institute Mumbai, India Matoshri College of Engineering & Research, Nashik, India Abstract The control valve piping is vibrating due to high flow rate and high velocity, also this line is running at different flow rate condition. The generic calculations based on Energy Institute Guidelines [1] indicate that the flow is Turbulent and Likelihood of Failure is more than one. This number is alarming and detailed analysis considering change in flow, pipe route, supports etc. is recommended to be performed. This Paper aims to study the 12-inch Control Valve Piping Vibrations observed at site due high flow rates and high velocity. and also attempts to find probable cause of the vibration and the solution to minimize these vibrations. Keywords: FIV, CAESAR II, LOF, Visco-Elastic Damper, Vibration Pads I. INTRODUCTION Pipe will exhibit a series of natural frequencies which depends on the distribution of mass and stiffness throughout the system, and the distribution are influenced pipe diameter, material properties, wall thickness, location of lumped masses (such as valves), pipe supports and also fluid density. Each natural frequency will have unique deflection shape associated with it, which is called mode shapes, which has the locations of zero motion (node) and maximum motion (Antinodes). The response of the pipe work to an applied excitation is dependent upon the relationship between the frequency of excitation and the system s natural frequencies. Vibration generated in the pipe work may lead to high cycle fatigue of components (such as Small bore connections) or the failure at welds in the main line itself. II. FLOW INDUCED VIBRATION Flow-induced vibration, or vortex shedding, is due to high flow velocities and High mass flow rates such as in a piping dead leg of a centrifugal compressor system. with certain flow conditions, piping systems will develop high levels of noise and vibration that can damage the pipes and related systems such as tube bundles, side cavities, and bluff or tapered bodies in flow streams. Pipe damage compromises plant safety, forces shutdowns, increases maintenance, and reduces efficiency and capacity. Fig. 1: Example of vortex shedding from an object in the flow stream. III. VISCO-ELASTIC DAMPER Viscoelastic dampers reduce vibrations by converting kinetic energy into heat thus damping the motion of the system. Damping, as a method to reduce unwanted vibrations, is most effective in cases where the vibratory system is excited with a frequency close to its natural frequency. [3] Viscoelastic dampers may be used to solve very different vibration problems. A typical example is the damping of operational vibrations in an industrial piping system e.g. in a power plant. Whenever the piping systems cannot be isolated from the source of vibration, damping might be an adequate measure to reduce the motion of the piping to an acceptable level. The Construction and mounting of the Visco-Elastic Damper is shown in Fig. 2. All rights reserved by www.ijste.org 40
Fig. 2: (a) Visco-Elastic Damper at site (b) Construction of Visco-Elastic Damper Top Connection plate Bottom connection plate Serial Number plate Position Indicator Housing Fluid Piston IV. CASE STUDY System Description The system consists of 12-inch control valve piping which is observed to be vibrating at site. Also this line is running at different flow rate condition. [5] The line serves between Potassium carbonate solutions to the rich solution flash tank. Points at which Amplitude of Vibration is noted in the System were noted as A, B, C, D, E, F, G, H, & I as shown in Fig. 3. Fig. 3: Typical System from Vibration Report Approach towards Solution Following approach has been applied to find most probable solution to Vibration problem in 12- inch control valve. A Qualitative Analysis has been carried out to identify the potential Excitation Mechanism that may exist. (LOW to HIGH). A Quantitative Analysis of an LOF score for each identified excitation mechanism from Qualitative Analysis and Periodic flow frequency calculation. Based on LOF score (0-1) Recommendation & corrective Actions have been recommended. Dynamic stress Analysis of the system using CAESAR-II to simulate analysis model with site observations. To propose corrective actions using results. All rights reserved by www.ijste.org 41
Input Data Mitigations to Flow Induced Vibration (FIV) in Control Valve Piping System using Visco-Elastic Dampers & Neoprene Pads Table - 1 Input Data Sr. No Input Unit Case 01 Max Flow Case 02 Max Flow Case 03 Max Flow 1 Fluid Density kg/ m 3 1169 1169 1169 2 Viscosity Pa-s 0.25 0.25 0.25 5 Operating Temperature 0 C 124 124 124 6 Upstream Pressure of the control valve Pa 1372931 211823.6 267721.5 7 Downstream Pressure of the control valve Pa 200546 197113.7 197113.7 8 Mass Flow Rate kg/sec 325.45 148.75 310.16 9 Pipe Size mm 323.85 323.85 323.85 10 Wall Thickness of Main Line mm 10.3124 10.3124 10.3124 11 Fluid Velocity m/sec 4.278 2.32 3.95 12 Maximum Span Length between supports on line of interest m 3.21 3.21 3.21 13 Speed of Sound in Fluid m/sec 2000 2000 2000 14 Length of Side branch m 3.21 3.21 3.21 Likelihood of Failure (LOF) Calculation Flow Induced Turbulence a) Step 1: Determine ρv 2 For single phase flow ρv 2 = (actual density) x (actual velocity) (1) Kinetic Energy =1169 4.278 2 Kinetic Energy =21934.201 kg/m-s 2 b) Step 2: Determine Fluid Viscosity Factor As the fluid in this example is gas the fluid viscosity factor (FVF) must be calculated; this requires the gas dynamic viscosity (µ gas). Fluid Viscosity Factor (FVF) = 0.25 µ 1 10 3 (2) Fluid Viscosity Factor (FVF) = 1 10 3 Fluid Viscosity Factor (FVF) = 15.82 c) Step 3: Determine Support Arrangement The pipe support arrangement must now be determined. This requires the maximum span lengths between supports to be identified and compared with the criteria. In all cases the support classification is Stiff (14-16Hz). d) Step 4: Determine Flow Induced Vibration Factor Fv Flow Induced Vibration Factor (Fv) = 686540 ( 323.8 10.35 ) 0.80 Flow Induced Vibration Factor (Fv) = 44183 e) Step 5: Calculation of Likelihood of Failure (LOF) Finally, the LOF for each line is calculated using: Flow Induced Vibration Factor (Fv) = α ( D ext T )β (3) Likelihood of Failure (LOF) = ρv2 FVF (4) Fv Likelihood of Failure (LOF) = 21394.20 44183 15.82 Likelihood of Failure (LOF) = 7.661 As the value of Likelihood of Failure (LOF) for both the PSV is greater than 1, some corrective Actions should be taken to reduce the value of LOF below 1. Flow Induced Pulsation a) Step 1: Determine critical side branch diameter Critical Diameter (d crit) = 1000 ( 400 πρv 2)0.5 (5) 400 Critical Diameter (d crit) = 1000 ( π 21394.20 )0.5 Critical Diameter (d crit) = 77.145 mm b) Step 2: Determine Reynolds Number For the two side branches the Reynolds Number of the flow in the main line is calculated using: Reynold s Number (Re) = ρvd char (6) 1000μ All rights reserved by www.ijste.org 42
Reynold s Number (Re) = 1169 4.278 303.15 1000 0.25 Reynold s Number (Re) = 6064.19 Where D Char is internal diameter of main line The Reynolds Number is below 1.6x10 7 and therefore S 1 needs to be calculated. c) Step 3: Calculate Strouhal Number Strouhal Number (S 1) = 0.420 ( d int D int ) 0.316 ( v c ) 0.083 ( Re 10 6) 0.065 (7) Strouhal Number (S 1) = 0.420 ( 303.15 303.15 )0.316 ( 4.278 2000 ) 0.083 ( 6064.19 10 6 ) 0.065 Strouhal Number (S 1) = 0.97491 Note, as the ratio of d int/d int not equal to 1 Strouhal Number (S 1) = fundamental Strouhal Number (S) = 0.97491 d) Step 4: Calculate Fundamental Excitation Frequency Fundamental Excitation Frequency (Fv) = S v (8) d int Fundamental Excitation Frequency (Fv) = 0.97491 4.278 1000 303.15 Fundamental Excitation Frequency (Fv) = 13.75 e) Step 5: Calculate fundamental acoustic natural frequency of side branch c Fundamental Acoustic Natural Frequency (Fs) = 0.206 Fundamental Acoustic Natural Frequency (Fs) = 0.206 2000 3.25 Fundamental Acoustic Natural Frequency (Fs) = 126.76 f) Step 6: Obtain LOF score The ratio of F v/f s is calculated: Ratio Fv/Fs=13.75/126.769=0.1084 Therefore, ratio of Fv/Fs is less than 1 scores an LOF of 0.29. Pulsation: Flow Induced Excitation LOF = 0.29 FIV Analysis Results L branch (9) From the Qualitative Assessment we get the value of Kinetic Energy (ρv 2 ) between 5000 & 20000 which falls under MEDIUM probability of failure due to Flow Induced Turbulence & Flow Induced Excitations, to calculate Likelihood of Failure (LOF). There is also possibility of Acoustic Induced Vibration (AIV) for Case-1 as pressure ratio is greater than 1.8. But, the possibility of failure due to AIV is ruled out as the Fluid used in the system is Liquid [1]. The support span founds to be adequate with respect to Quantitative Analysis. However, the requirement of additional supports or change in the supports can be obtained post Dynamic Stress Analysis results. Table - 2 Summary of Likelihood of Failure (LOF) score for FIV Sr. No. Excitation Mechanism Maximum Flow Normal Flow Minimum Flow 1 Flow Induced Turbulence 7.665 6.546 1.982 2 Flow Induced Pulsation 0.29 0.290 0.290 Dynamic Stress Analysis using CAESAR II The static model is generated to check the overall behavior of the pipe and supports. It has been informed that no supports at site are lifting off. Hence it can be concluded that all the rest supports are active. This is due to the fact that the supports are resting on platform connected to Flash Tank. The problem is then needs to be solved mainly for vibration purpose considering linear boundary conditions. The original model is shown following Figure 4. Fig. 4: Original CAESAR II Model All rights reserved by www.ijste.org 43
Based on vibration analysis report the harmonic analysis has been performed to simulate site conditions. The Vibration Survey Report has been used to simulate the model. The result obtained at 265kg/sec flow rate nearest to the control valve (Point D as per vibration measurement report) as shown in Fig. 3 (a) has been considered as bench mark results for comparison near to the control valve LV6301. The Vertical displacement of 215.4 microns found to be the largest amplitude [5]. Following table provides the comparison between actual data and calculated values. Table - 3 Comparison of results as per CAESAR II model and vibration report CAESAR II node Vibration Reading HD: Horizontal Displacements as per CAESAR II Frequency, Hz no. Point report, mm results, mm 340 A 0.114 5.6 0.005 300 B 0.084 11.9 0.02 310 C 0.084 14, R 0.014 210 D 0.215 15 0.217 220 E 0.131 15.6 0.14 150 F 0.114 4.4, R 0.12 160 G 0.085 4 0.15 Since the most probable source of vibration is the Flow Induced Turbulence in the control valve, the permanent solution may call for flow change and piping layout changes. However, at present the scope is to make minimum changes in the existing piping and that too without taking shut down. Hence, the scope is limited to avoid vibration transferring to the structure. The Detailed harmonic analysis suggested providing a viscoelastic damper to isolate the vibrations transferred to the structure. However, the before implementing this big change it is recommended to explore the option of Isolating pads. Recommendations The following recommendation shall be implemented in sequence one after another. It means First set of recommendation shall be implemented & vibration shall be observed. In case of unsatisfactory results implement second set. This approach may save cost. First Set of Recommendations Provide Temporary support to the pipe. Cut the trunnion at node 5020 next to the valve LV-6301 and attach a base plate to it and provide 2 Neoprene rubber pads each of 1 thickness using clamps [4]. Provide an additional clamp shoe at node 175. Insert 2 nos. of Neoprene isolating rubber pads each 1 thick to the base plate of shoe for isolation purpose. The assembly of support to be provided at node 175. Following diagram shows the general arrangement of the supports as per Solution 1. Fig. 5: Supports as per Solution 1 Following Table-4 provides a data sheet for selection of Isolation pads located at support Table - 4 Isolation or Neoprene Pad Data Sheet Material of the isolation pad to be used Neoprene rubber or Equivalent Operating temperature ( C) 124 C Excitation frequency (Hz) 4 Hz to 16Hz Load on each pad 0.6 N / sq.mm Stiffness of isolation pad 120 kn/mm Thickness of the isolation pad (mm) 2" THK pad. 1 Nos for each support All rights reserved by www.ijste.org 44
Permissible deformation 0.1 mm to 0.13 mm Application To isolate Pipe base from Supporting platform in event of Flow induced vibrations Second Set of Recommendations Keep support provided at node 5020 as it is. At node 175 instead of Neoprene pads, provide a viscoelastic damper [2]. The following diagram shows general arrangement of pipe supports. Fig. 6: Supports as per Solution 2 Following Table-5 provides a data sheet for selection of Damper located at support Table - 4 Isolation or Neoprene Pad Data Sheet Operating Temperature ( C) 124 C Critical frequencies at which vibration experienced 15 Hz Hot cold thermal displacement (mm) 1 mm to 2 mm Vertical damping resistance 335 kns/m Thermal movement of pipe in vertical direction 2 mm Maximum damping force 2000N to 4000N Application To isolate Pipe base from Supporting platform in event of FIV Damping fluid Bitumen based fluids allowing high damping parameters more than 2000lb-sec/inch at 16Hz V. RESULTS The displacement observed at various points after implementing the Solution 1 is as follows: Table - 4 Comparison of results as per Soln. 1 CAESAR II model and vibration report CAES AR II node no. Vibration Reading Point HD: Horizontal Displacements as per report, mm Frequency, Hz CAESAR II results, mm Solution 1 340 A 0.114 5.6 0.001 300 B 0.084 11.9 0.001 310 C 0.084 14, R 0.001 210 D 0.2154 15 0.036 220 E 0.131 15.6 0.05 150 F 0.114 4.4, R 0.026 160 G 0.085 4 0.034 The amplitude of vibration found to be reduced down considerably, after implementing the recommended Solutions with reference of previous vibration report. All rights reserved by www.ijste.org 45
VI. CONCLUSION The vibration measurement report has been considered as a reference to simulate the Piping system in stress analysis software CAESAR II. The bench mark results of vibration measurement at 265kg/sec have been compared against CAESAR II results. A harmonic analysis has been performed and solutions have been recommended. By considering the fact that those are to be implemented while system is in running condition. The solutions 1 suggest providing isolating rubber pads of higher frequencies at two locations. If solution one does not yield satisfactory results, then a viscous damper has been recommended as solution 2. Solution 2 results are predicted to be better than Solution 1. However, cannot be predicted as actual Damper properties will be available by vendor at later stage. ACKNOWLEDGMENT Author would like to thank Mr. Rajiv Desai and whole staff of the Protton Engineering for their direct or indirect support and contribution for this work. REFERENCES [1] V. A. Carucci and R. T. Mueller, Acoustically Induced Piping Vibration in High Capacity Pressure Reducing Systems, ASME 82-WA/PVP-8; 1982. [2] Energy Institute, Guidelines for the Avoidance of Vibration Induced Fatigue in Process Pipework 2 nd Edition, 2008. [3] F. L. Eisinger, Designing Piping Systems against Acoustically-Induced Structural Fatigue, ASME 1996, PVP-vol. 328; 1996. [4] Frank P. Barutzki, Extending the Service Life of Piping Systems through the Application of Viscous Fluid Dampers GERB Vibrations Control Systems, Inc. [5] VICODA- Product Boucher, Vibration Control Devices and Application UK. [6] WARCO-BILTRITE, Rubber Product Catalogue USA, November 1, 2014 [7] Vibration Survey Report EG 2- LV 6301 Provided by Vendor. All rights reserved by www.ijste.org 46