Failure analysis of storage tank component in LNG regasification unit using fault tree analysis method (FTA) Cukup Mulyana, Fajar Muhammad, Aswad H. Saad, Mariah, and Nowo Riveli Citation: AIP Conference Proceedings 1827, 020014 (2017); View online: https://doi.org/10.1063/1.4979430 View Table of Contents: http://aip.scitation.org/toc/apc/1827/1 Published by the American Institute of Physics Articles you may be interested in Black-Litterman model on non-normal stock return (Case study four banks at LQ-45 stock index) AIP Conference Proceedings 1827, 020013 (2017); 10.1063/1.4979429 Geographically weighted poisson regression semiparametric on modeling of the number of tuberculosis cases (Case study: Bandung city) AIP Conference Proceedings 1827, 020022 (2017); 10.1063/1.4979438 Modeling relationship between mean years of schooling and household expenditure at Central Sulawesi using constrained B-splines (COBS) in quantile regression AIP Conference Proceedings 1827, 020021 (2017); 10.1063/1.4979437 Robust geographically weighted regression with least absolute deviation method in case of poverty in Java Island AIP Conference Proceedings 1827, 020023 (2017); 10.1063/1.4979439 Prediction of cadmium pollutant with ordinary point kriging method using Gstat-R AIP Conference Proceedings 1827, 020019 (2017); 10.1063/1.4979435 Winsorization on linear mixed model (Case study: National exam of senior high school in West Java) AIP Conference Proceedings 1827, 020020 (2017); 10.1063/1.4979436
Failure Analysis of Storage Tank Component in LNG Regasification Unit Using Fault Tree Analysis Method (FTA) Cukup Mulyana a), Fajar Muhammad b), Aswad H. Saad c), Mariah d) and Nowo Riveli e) Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia Corresponding Author a) c.mulyana55@yahoo.com b) fajaar.muhammad@yahoo.com c) aswas.saad@ymail.ac.id d) mariah@phys.unpad.ac.id e) nowo@phys.unpad.ac.id Abstract. Storage tank component is the most critical component in LNG regasification terminal. It has the risk of failure and accident which impacts to human health and environment. Risk assessment is conducted to detect and reduce the risk of failure in storage tank. The aim of this research is determining and calculating the probability of failure in regasification unit of LNG. In this case, the failure is caused by Boiling Liquid Expanding Vapor Explosion (BLEVE) and jet fire in LNG storage tank component. The failure probability can be determined by using Fault Tree Analysis (FTA). Besides that, the impact of heat radiation which is generated is calculated. Fault tree for BLEVE and jet fire on storage tank component has been determined and obtained with the value of failure probability for BLEVE of 5.63 x 10-19 and for jet fire of 9.57 x 10-3. The value of failure probability for jet fire is high enough and need to be reduced by customizing PID scheme of regasification LNG unit in pipeline number 1312 and unit 1. The value of failure probability after customization has been obtained of 4.22 x 10-6. INTRODUCTION Liquefied Natural Gas (LNG) is the natural gas which is processed by diminishing residue and hydrocarbon compound, and condensing it into liquid in atmospheric pressure with cryogenic cooling temperature. [1] Liquefaction of natural gas into LNG is efficient as it reduces the volume gas into 1/600 times in order to ease the storage and gas distribution by only using tanker without an expensive piping system. However, one issue which mostly existing in LNG industry is the critical storage tank component in regasification unit in onshore or offshore facilities. The failure mostly because of one or combination of over pressure, failure due to corrosion, material degradation, stress on metal surface, failure in supporting device, i.e. in control valve, pressure safety valve, pump, and compressor, and another failures. These failures potentially happened in the case of Boiling Liquid Expanding Vapor Explosion (BLEVE) in storage tank, which is an explosion due to pressure vessel filled by liquid above the boiling point, the undergoing pressure from its catastrophic failure due to fire exposure, and jet fire due to piping leak around the storage tank. BLEVE and jet fire which is occurred in storage tank has the relation with reliability of safety and security system, the component and equipment, or the existing operation. Which means, a method for determining the cause of risk due to LNG storage tank failure is needed in order to prevent the increasing of failure probability or reduce in Statistics and its Applications AIP Conf. Proc. 1827, 020014-1 020014-9; doi: 10.1063/1.4979430 Published by AIP Publishing. 978-0-7354-1495-2/$30.00 020014-1
a certain point. The objective of the research is to determine the failure probability of BLEVE and jet fire in the storage tank by using Fault Tree Analysis (FTA). By using theory of reliability, it is expected to obtain its failure probability and reduce it if the probability exceed an allowable limit. FAULT TREE ANALYSIS AND RELIABILITY THEORY Failure probability of a system is affected by the failure rate of each component. The failure rate data component on the site could be determined from the average of failed component in certain time. It is also called average failure rate (μ) with the units faults/time.[2] Failure probability of the system is also affected by reliability of each component. The reliability is the probability of certain component to keep working for a certain condition in a certain time. Reliability is given in Poisson distribution: (1) From the equation (1) it is shown the higher failure rate of certain component is, the faster reliability reduced. Complement of reliability is failure probability which is given as : [2] (2) In some complex system the failure could occur due to accumulation of series or parallel of failure components. The system which is arranged in parallel mode uses AND logic gate, that the probability of system is calculated by equation (3) (3) where n is amount of component installed, while P i is failure probability for each component, while the total of reliability for parallel component is given by (4) and failure rate total is given by equation (5) (5) For the system with the series component use OR logic gate, the total probability is obtained by sum of reliability of each component in equation (6). (6) the total failure probability is given as: Knowing the interaction of each component is important, if there are misplaced of component in the arrangement of the system whether it is in parallel or series mode, the failure probability of the system would is also wrong. Table 1 indicates the calculation of failure probability, reliability and failure rate of some component connection system. 020014-2
TABLE1.AND and OR Gate Formulation and symbols Failure Probability Reliability Failure Rate METHOD The method use in this research is started with literature review related with FTA and reliability theory, continue with collecting the data which include data of failure rate component and understanding Piping and Instrument Diagram (PID) of regasification of LNG unit. The next step is identifying failure possibility in storage tank component. In the field there are identified two cases, first failure from BLEVE and second jet fire. After obtaining and identifying failure, the next step is constructing fault tree for each failure, then calculating failure probability of failure. Then, the result is analyzed by referring the Safety Integrity Level (SIL) standard. SIL is the safety standard or failure probability point classification. In this case, is petroleum and gas, safety standard of failure probability is in SIL 3. If the calculation of SIL is out of safety standard, then failure probability should be reduced by customizing PID scheme and then continue with recalculating of failure probability, if the result still out of the safety standard then the PID scheme should be re-customized and recalculated again until obtain the safety standard in SIL 3. The standard SIL value is shown in Table 2. TABLE 2.Safety Integrity Level Safety Integrity Level Probability of Failure 1 10-2 s/d 10-1 2 10-3 s/d 10-2 3 10-4 s/d 10-3 4 10-5 s/d 10-4 RESULTS Data operational is the data indicates parameter of operation and process scheme control from storage tank component in regasification unit LNG PT X. Table 3 shows storage operational data. 020014-3
TABLE 3. Operational Data of Storage Tank Operational Pressure Durability OPERATIONAL DATA Capacity 196,000 m 3 Normal 0.2-0.5 barg Pressure Safety Valve (PSV) 0.7 barg Pressure 15 atm Temperature 650 C Data of component failure is used in failure probability calculation in fault tree which has been constructed. Table 4 shows component rate of failure based on PID scheme with one year operating time assumption. TABLE 4. Average Data Failure of Component COMPONENT μ (Faults/Year) Hydrocarbon Gas Detector 0,05404 Extinguisher 0,14588 Butterfly Valve 0,09386 Fire Detector 0,03704 Smoke Detector 0,02678 Temperature Element 0,21116 Temperature Indicator 0,03836 Pressure Differential Transmitter 0,45507 Pressure Gauge 0,10437 Pressure Safety Valve 0,03822 Pressure Transmitter 0,27155 Pressure Indicator 0,03836 Pressure Alarm Low 0,00034 Pressure Alarm Low Low 0,00034 Pressure Alarm High High 0,00034 Control Logic Unit 0,1977 Pressure Differential Indicator (Field Mounted) 0,10437 Pressure Differential Indicator (Shared Display) 0,03836 Pipe (12 ich) 0,0000306 Flange 0,0509119 Flow Element 0,0704103 Flow Transmitter 0,9279123 Flow Indicator 0,0383615 Electric Spark 0,0277 Rotating Equipment 0,0264993 PID of regasification unit process indicates the piping diagram of regasification process completed with all instrumentation needed in the unit. PID scheme data in PT X regasification unit shown in Figure 1 (a) and (b). The determination of top event of FTA conducted with applying logic process of BLEVE and jet fire. Then determine the top event in fault tree which is shown in Figure 2 (a) and (b). 020014-4
(a) (b) FIGURE 1. (a) PID Storage Tank T-101 (b) PID Pipelinenumber 1312 unit 1 020014-5
T GO1 U1 E1 E2 GA2 E3 GA3 E4 E5 E6 E7 GA6 GA7 GA4 E8 B1 E9 B2 E10 GA8 GA9 0 U2 U3 B4 B5 E18 E19 4 5 E30 E31 E32 E33 GO16 GO17 GO18 GO19 GA5 B3 E11 E12 E13 GO2 GO3 GO4 E20 E21 E22 E23 B6 B7 GO6 GO7 GO8 GO9 B10 B11 B12 B13 B14 B15 B16 B17 E14 E15 E16 E17 1 2 GO5 3 E24 E25 E26 E27 E28 B9 E29 B8 GO10 GO12 GO13 GO14 GO15 6 B18 B19 B20 B21 B22 B23 B24 B25 B26 B27 B28 B29 B30 B31 B32 B33 B34 B35 B36 B37 B38 B39 B40 B41 (a) T E1 E2 E3 GO1 GO2 GO3 B1 B2 B3 E4 B4 B5 U1 U2 GO5 B6 E5 GO6 B7 B8 (b) FIGURE 2. (a) Fault tree of BLEVE case and (b) Fault tree of jet fire case. Probability of failure for BLEVE is 5.63 x 10-19 and 9.57021 x 10-3 for jet fire. These two cases have a significant difference. For BLEVE case, the probability of failure is enormously small that approach zero. This value shows that the PID scheme of storage tank in LNG Unit of regasification is still in very good condition. Then, the components has high reliability, when critical condition occurs it still work well, as example, the temperature element has failure rate 0.21116/year and pressure transmitter has failure rate 0.27115/year. Failure rate in these two components have the value less than 1. From the risk assessment, the fault tree has been constructed well. Most of basic event resulted in fault tree, then the evaluation will be specific, which means, entire lest cause of failure could be calculated and be evaluated. In other hand, the value of probability of failure depends on combination logic gate in fault tree. The usage of AND gate would be benefit as multiplication of two events would result failure probability value which is getting smaller. Which means, when probability of failure values of the system is high, it is necessary to use AND gate in PID scheme. Failure probability which is obtained for jet fire case has the high value which is in 10-3, while in petroleum and gas, target of probability of failure in equivalent SIL 3 as 10-4. This high value is due to insufficient of safety function in piping line in jet fire, while the probability of failure for BLEVE is extremely small that the reduction is not needed. However, for jet fire risk, probability of failure could be conducted with customization of PID scheme, by changing the system or adding safety function in order to change fault tree. Figure 3 shows PID scheme and fault tree after customization. 020014-6
(a) JET FIRE E1 E2 E3 GO1 GA2 GO2 B1 B2 B3 E4 E5 B4 U1 U2 GO3 GO4 E6 B5 E7 E8 B6 B7 GO5 GO6 GO7 B8 B9 B10 B11 B12 B13 B14 (b) FIGURE 3. (a) PID Pipelinenumber 1312 unit 1 after modified and (b) Fault tree after modified. After changing the PID scheme by adding the safety function instruments, the probability of failure is smaller. It indicates that the addition of safety function instruments in scheme process would change the previous fault tree construction, as shown in Figure 3. This addition of logic gate and event in fault tree that multiple result each event would smaller in top event and obtained probability of failure for jet fire in the new system as 4.22 x 10-6. If the value is multiplied by operating time per year which has been assumed before, the failure rate of jet fire is 4.22 x 10-6 per year. The following are comparison of probability of failure before and after PID system customization as shown in Table 5. 020014-7
TABLE 5. Comparison of Failure Probability Before and After Modified SKEMA PID SIMBOL EVENT FAILURE PROBABILITY T Jet Fire 0.009616299 B1 Pipe Leak 0.0000305995 B2 flange leak (36"X12") 0.049637606 B3 Hydrocarbon Gas Detector 0.052604937 B4 Pressure Transmitter 1301 0.237803971 B5 Pressure Indicator 1301 0.037635017 B6 Flow Element 1301 0.067988663 BEFORE B7 Flow Transmitter 1301 0.604621719 MODIFIED B8 Flow Indicator 1301 0.037635017 E1 Gas Release From Pipe 12"-LNG-01-1312-A22K-C 0.680713257 E2 Overpressure Inner Pipe 0.266489231 E3 Ignition Source 0.052756698 E4 Gas Release From Flow Indicator System 0.645371352 E5 Decrease Flow Indication Failure 0.619501788 U1 Static Electricity Spark 0.027319873 U2 Rotating Equipment 0.026151274 AFTER MODIFIED T Jet Fire 0.00000422 B1 Pipe Leak 0.0000305995 B2 flange leak (36"X12") 0.049637606 B3 Hydrocarbon Gas Detector Fail 0.052604937 B4 Pressure Alarm High High Fail 0.000339942 B5 Flow Element 1301 Fail 0.067988663 B6 Pressure Transmitter 1301 Fail 0.237803971 B7 Pressure Indicator 1301 Fail 0.037635017 B8 Butterfly Valve 1305 Fail 0.089589789 B9 Pressure Transmitter Fail 0.237803971 B10 Pressure Indicator Controller Fail 0.130641765 B11 Flow Transmitter 1301 Fail 0.604621719 B12 Flow Indicator 1301 Fail 0.037635017 B13 Pressure Differential Transmitter Fail 0.365596442 B14 Pressure Differential Indicator Fail 0.037633573 E1 Gas Release from Pipe 12"-LNG-01-1312-A22K-C 0.882404816 E2 Overpressure Inner Pipe 9.05909E-05 E3 Heat source 0.052756698 E4 Gas Release fromflowmeter 0.869388185 E5 Pressure Measurement Failure 0.266489231 E6 Shut Off Valve Fail to Close 0.396742716 E7 Flow Decrease Indication Failure 0.619501788 E8 Pressure Decrease Indication Failure 0.389471315 U1 Electric Spark 0.027319873 U2 Rotating Equipment 0.026151274 CONCLUSIONS The FTA has been constructed for BLEVE and jet fire based on regasification unit of LNG. The probability of failure has been obtained for BLEVE as 5.63 10-19 and jet fire as 9.57 10-3. After changing the PID scheme by adding the safety function instruments in pipeline number 1312 unit 1, the high probability of failure value for jet fire case has been reduced, with the probability of failure value as 4.22 10-6. 020014-8
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