Relief Pipes Research Articles

Review of Oil–Water Flow Characteristics of Emptying by Water Displacing Oil in Mobile Pipelines

Water displacing oil is one of the main emptying methods for mobile pipelines. It has the advantages of being a simple process and highly safe. At present, the determination of a water displacing oil scheme of mobile pipelines is based on the oil–oil alternating transport theory of product oil pipelines. However, the insolubility of the oil phase and the water phase results in a great difference between the flow characteristics of water displacing oil and the oil–oil alternating transport of a product oil pipeline. In addition, due to the effect of buoyancy, the oil phase gathers at the high point of the pipeline and forms a liquid accumulation, which is difficult to carry away by water flow, resulting in the low emptying efficiency of the mobile pipeline. The essence of water displacing oil in a mobile pipeline is an oil–water two-phase unsteady displacement flow, involving liquid–liquid displacement flow, oil–water two-phase flow and water carrying oil. Aiming at such problems, domestic and foreign scholars have carried out a large number of theoretical and experimental studies, established the oil–water mixing model of water displacing oil and the relationship between macroscopic quantity (flow pattern, pressure drop and water content) and microscopic quantity (local flow field and droplet dispersion pattern, etc.) under each flow type, and explored the influence of pipeline diameter, oil phase velocity, pipeline inclination angle and other parameters on the capacity of carrying liquid accumulation. On this basis, this paper analyzes the shortcomings of the current research on the oil–water flow characteristics of water displacing oil in a mobile pipeline from three aspects: the formation mechanism of the oil–water mixture, displacing flow characteristics of immiscible fluids and flow characteristics of water carrying oil. Five future research directions are proposed, including the interface morphology and flow field characteristics of oil–water two-phase layered flow, local mixing characteristics of an oil–water two-phase dual continuous flow interface, droplet distribution and flow characteristics of oil–water two-phase dispersed flow, unsteady flow characteristics of the oil–water mixture of water displacing oil and oil accumulation and flow characteristics in topographic relief pipes.

Peran Crude Oil Washing System (COW) Pada Kapal Tanker

Crude Oil Washing System adalah sistim yang menggunakan Crude Oil atau minyak mentah sebagai medium pencuci. Tanki-tanki muatan diusahakan bersih dari sisa-sisa muatan minyak mentah sehingga balas bersih dapat dimuat dalam tanki yang sudah dibilas tadi dengan hanya mengadakan sedikit pembilasan lebih dahulu dengan air sehingga akibat pollusi akan sangat terbatas. Pipa yang digunakan yang dihubungkan dengan pipa muatan harus dibuat dari pipa baja atau sejenisnya yang kekuatannya cukup untuk menahan tekanan minyak yang diperlukan, dan juga harus terpasang (fixed) dan diperkuat dengan baik. Crude Oil Washing System harus dipasang permanent dan terpisah sama sekali dari system pipa-pipa yang lain kecuali yang disambung kepipa muatan. Juga pipa-pipa tersebut harus dilengkapi dengan relief system guna mengontrol tekanan dalam pipa jangan sampai berlebih, relief pipe system ini harus dihubungkan kembali dengan bagian isap dari Supply Pump. Sedangkan keuntungan menggunakan Crude Oil adalah sudah tersedia dikapal dengan cara resirkulasi, efektif untuk menghilangkan sediment dan sisa-sisa minyak yang melekat dalam tanki (good Carrier) dan dibongkar bersama-sama dengan muatan, tidak menimbulkan karat serta tidak ada kemungkinan emulsi air dan minyak jadi mengurangi bahaya pollusi. Semua pekerjaan Crude Oil Washing harus sudah selesai sebelum kapal meninggalkan pelabuhan bongkar muatan terakhir.Jika sampai dilaksanakan Crude Oil Washing antara dua pelabuhan bongkar pada tanki-tanki tersebut harus tetap kosong untuk pemeriksaan pada pelabuhan-pelabuhan berikutnya sebelum diisi dengan air balas.

Pipe size sensitivity in pressure relief networks using genetic algorithms

This paper utilizes a stochastic optimization approach using genetic algorithms, for conducting rigorous pipe size sensitivity assessments onto the design of pressure relief networks. By sampling high performance candidates, only the finest options can survive. The pressure relief network system that was investigated in this work was previously reported in literature. The problem is constrained and involves minimizing a cost objective function that evaluates the overall network performance, in which the best pipe size combination should be selected for each segment within the network. The overall goal of this paper was to seek cost-effective designs for the pressure relief piping system by exploring different ranges of pipe diameters that are available for each segment in the network and comparing how the overall design of the system is affected, when the number of pipe size options to select from is varied.

Analysis of the Ingress of Coolant Event tests performed in the upgraded ICE facility aimed at the ECART code validation

The activities on the validation of the ECART code against the eight Ingress of Coolant Event (ICE) tests performed in the upgraded ICE facility are discussed. These analyses have been carried out to extend the ECART validation to incidental sequences related to future fusion plants, specifically - in the case of ICE - versus Loss Of Coolant Accident (LOCA) in volumes with near vacuum conditions. The upgraded ICE facility consists of a boiler, injecting water at high pressure inside a low-pressure tank simulating the Plasma Chamber (PC). This PC is in turn connected to the Vacuum Vessel (VV) through the divertor, and to the pressure Suppression (ST) by means of several relief pipes. Finally, the VV is connected with the Drain Tank (DT). Eight tests were performed investigating different numbers of relief pipes, different initial PC and VV temperatures, and different injected water mass flow rates, pressures and temperatures. The ECART results show an overall good agreement with the experimental data, confirming that ECART is also a valuable tool for the safety analysis in future fusion plants, as already pointed out in previous works.

Sizing of the Vacuum Vessel Pressure Suppression System of a Fusion Reactor Based on a Water-Cooled Blanket, for the Purpose of the Preconceptual Design

A methodology to preliminarily evaluate the size of the suppression tank and the relief pipes for a Vacuum Vessel Pressure Suppression System, to be adopted in a fusion reactor based on a water cooled blanket, is presented. The volume of the ST depends on the total energy of the water cooling system and it can be sized based on a required final pressure at equilibrium, by a simple energy balance. The pressure peak in the VV depends mainly on break area and the flow area of the relief pipes and some suggestions about the method for a preliminarily evaluation of their size are discussed. The computer code CONSEN has been used to perform a parametric study and to verify the methodology.

Numerical Simulations of LNG Vapor Dispersion from LNG Jetting in Different Directions

LNG jetting release in emergency pressure relief or storage tank leakage accident is common. Computational fluid dynamics model of LNG vapor dispersion from LNG jetting is established, and we performed numerical simulations in a more general situation of three jet directions, then we got the result of CH4 concentration distribution in jet diffusion area. Depending on the results of the comparison, we found that LNG vapor diffusion distance is the farthest when jetting along the direction of the wind. The results provide technical support for LNG storage unit emergency relief pipe installation choices and jet leakage accident emergency management.

Numerical study of choked two-phase flow of hydrocarbons fluids through orifices

Valves and orifices are the most widely devices of flow control used in oil and gas industry. In particular, they are installed in relief piping system in order to control the discharge flow during potential plant overpressuring scenarios, thus ensuring plant safety. It is a common practice to flow liquid and gas mixtures through such restriction devices.Rigorous models are available to precisely size pressure relief devices operating in single phase flow; however for two-phase flow, no models are considered sufficiently reliable for predicting the relevant flow conditions.In the present paper, two-phase flow of hydrocarbons fluids through an orifice under critical conditions has been numerically investigated.The existing literature has been analyzed and data on two-phase flow of highly volatile mixtures of hydrocarbons through openings have been collected. A comparison has been carried out with numerical simulations carried out by the multiphase flow simulation tool OLGA by SPT.The Henry–Fauske model has been used as orifice choke model and the orifice discharge flow coefficient, required as input by OLGA, has been calculated by Chisholm's model.Comparison between OLGA's results and experimental data shows that Henry–Fauske model markedly underestimates the mass flow rate through the orifice, if Chisholm's model is used to calculate discharge coefficient. It was found that the error of the model could be minimized using different values of orifice discharge coefficient (Cd).A new discharge flow coefficient model, suitable for choked two-phase flow across orifices, is proposed in this study and it has been determined to match the above mentioned experimental measurements.

The Danger of Piping Failure Due to Acoustic-Induced Fatigue in Infrequent Operations: Two Case Studies

Failure in piping due to acoustic-induced fatigue can be considered catastrophic as it could happen only after a few minutes of operation. Acoustic-induced fatigue occurs mainly in gas piping systems with high velocity where high energy is dissipated through pressure reducing stations and pipe branch connections. It usually results in pipe through wall longitudinal cracks, pipe detachment from saddle supports, and complete shear off of branch connections. There are existing design criteria to avoid acoustic-induced fatigue based on comparison of generated power level to an acceptable power level. This criterion is normally used for the design of pressure relief and flare piping where high gas velocity exceeding 50% of the speed of sound (i.e., 0.5 Mach) is expected. However, acoustic-induced fatigue has been experienced in systems due to intermittent operations. Two case studies are presented in this paper. The first one is during a steam-out operation to clean a newly constructed steam header. During the cleaning operation, an orifice plate was used to control the flow in the steam header. Several pipe vents and drains failed due to fatigue in less than 1 h. The second case is for drainage of compressed natural gas during process upset condition. Because of the high level buildup in the liquefied gas separator vessel, the drain valve was opened to release the pressurized liquefied gas to the relief system to reduce the level buildup. Wall cracks and several pipe support detachments were found in the system after the upset condition. This paper presents the engineering analysis and material failure analysis conducted to find the root causes of the failures. Moreover, it highlights the recommendations and lessons learned from these two failures.

Overpressure characteristics of aluminium dust explosion vented through a relief pipe

A parametric experimental study of an aluminium dust explosion, initiated in a vessel and vented through a relief pipe, was performed. The aim is to clarify the overpressure characteristics in a vessel and relief pipe, during aluminium dust explosion venting, especially when a burn-up phenomenon occurs. For a vessel of fixed size, the influence of pipe diameter and pipe length on burn-up was discussed. Results demonstrate that burn-up occurs shortly after flame only enters the initial part of the relief pipe when the original dust concentration in the vessel is at relatively high level, which is usually higher than the optimum concentration obtained from the confined vessel. When burn-up occurs, the maximal overpressure continues to increase rather than to decay along the initial part of the relief pipe. If burn-up is vigorous, a second peak on overpressure-time curve in the vessel could appear. By adding 0.1 g aluminium powders on the membrane, the second overpressure peak may even surpass the first peak. Extending pipe lengths can strengthen the overpressures around the position where burn-up occurs in the relief pipe. Reducing the pipe diameter can increase the burn-up severity in the relief pipe owing to the increased dust concentration and the pressure accumulation.

Vented Gas Explosion In A Cylindrical Vessel With A Relief Pipe

Kajian tentang letupan gas/udara di dalam tangki silinder dengan panjang/garis pusat adalah 2, dilaporkan di mana tangki silinder bersambung dengan paip dengan panjang/garis pusat ialah 6. Kajian ke atas kesan tekanan koyakan penutup ventilasi dan kedudukan pencucuh dijalankan untuk mengetahui nilai tekanan maksimum di dalam tangki, halaju nyalaan gas serta halaju gas tak terbakar. Gas propana dan metana di dalam udara digunakan dalam kajian ini dengan kadar persamaan gas/udara antara 0.8 hingga 1.6. Keputusan kajian menunjukkan bahawa tekanan dan halaju nyalaan udara di dalam tangki silinder adalah lebih tinggi jika kedudukan pencucuh berada jauh dari ventilasi berbanding jika pencucuh berada pada bahagian tengah tangki. Selain itu, sebelum gas dialirkan keluar ke bahagian paip, aliran gas dihalang untuk memasuki bahagian paip disebabkan oleh aliran sonik yang terbentuk pada bukaan paip. Kata kunci: Letupan gas; tekanan koyakan penutup ventilasi; kedudukan pencucuh; aliran sonik A study of vented explosions in length/diameter (L/D) of 2 of cylindrical vessel with a duct pipe (L/D = 6) is reported. The influence of vent burst pressure and ignition locations on maximum overpressure generated inside the vessel, flame speeds and unburnt gas velocities ahead of the flame were systematically investigated. Propane and methane–air mixtures with equivalence ratio, Φ of 0.8 to 1.6 have been used. Results show that rear ignition exhibits higher maximum overpressures and flame speeds in comparison to central ignition. It is confirmed that prior to the flame entry to the duct, the flow is chocked due to the sonic flow created at the duct entrance. Key words: Vented explosion; vent burst pressure; ignition location; sonic flow

CFD analysis of gas explosions vented through relief pipes

Vent devices for gas and dust explosions are often ducted to safe locations by means of relief pipes. However, the presence of the duct increases the severity of explosion if compared to simply vented vessels (i.e. compared to cases where no duct is present). Besides, the identification of the key phenomena controlling the violence of explosion has not yet been gained. Multidimensional models coupling, mass, momentum and energy conservation equations can be valuable tools for the analysis of such complex explosion phenomena. In this work, gas explosions vented through ducts have been modelled by a two-dimensional (2D) axi-symmetric computational fluid dynamic (CFD) model based on the unsteady Reynolds Averaged Navier Stokes (RANS) approach in which the laminar, flamelet and distributed combustion models have been implemented. Numerical test have been carried out by varying ignition position, duct diameter and length. Results have evidenced that the severity of ducted explosions is mainly driven by the vigorous secondary explosion occurring in the duct (burn-up) rather than by the duct flow resistance or acoustic enhancement. Moreover, it has been found out that the burn-up affects explosion severity due to the reduction of venting rate rather than to the burning rate enhancement through turbulization.

Experimental results of functional performance of a vacuum vessel pressure suppression system in ITER

An integrated Ingress-of-Coolant Event (ICE) test facility was constructed to investigate quantitatively effectiveness and functional performance of a vacuum vessel pressure suppression system (VVPSS) during the ICE in International Thermonuclear Experimental Reactor (ITER). The integrated ICE test facility simulated structural components of the ITER VVPSS with a scaling factor of 1/1600. From the present study it was clarified experimentally that the ITER VVPSS is very effective to reduce the pressurization during the ICE because the condensation of vapor within a suppression tank is enhanced and the pressure rise characteristics strongly depend on the cross-sectional area of the relief piping, and then the pressure rise rate in ITER is expected between 100 and 200 kPa s −1.

Numerical Analysis on Ingress of Coolant Event in Vacuum Vessel of Fusion Reactor Using Modified TRAC-BF1

The semi three-dimensional numerical analysis model of the FDR-ITER to simulate the in-vessel LOCA or the ICE was constructed using the modified TRAC-BF1 code in which the vacuum vessel, the pressure suppression tank and the relief pipe header are modeled using one VESSEL component. Analytical results obtained from the modified TRAC-BF1 code were compared with those from the MELCOR code concerning pressure in the vacuum vessel when a cooling pipe of 0.6 m2 flow area breaks in it. The mass flow rate of the injected water into the vacuum vessel and the initial wall temperature in the modified TRAC-BF1 input data were the same as those calculated in the MELCOR analysis. The maximum pressure in the vacuum vessel obtained from the modified TRAC-BF1 code is 10% higher than that from the MELCOR code, but it is still below the design pressure 0.5 MPa of the FDR-ITER vacuum vessel. The semi three-dimensional analysis using the modified TRAC-BF1 obtained that the maximum delay in opening time among the four rupture-disks is within 3 ms. The maximum pressure in the vacuum vessel does not exceed the design pressure, even if one of rupture-disks is not opened.

Analysis of Pressure Rise in an ITER-Like Fusion Reactor During In-Vessel LOCA by A Modified TRAC-PF1 Code

Damage of cooling tubes of plasma facing components (PFCs) results in water discharge into a vacuum vessel (W) of a fusion reactor. Flashing in vacuum, water pool boiling and impingement-jet on a surface of the PFC are the main heat transfer phenomena responsible for steam production that causes a rapid pressurization of the W. This is called an in-vessel loss-of-coolant accident (LOCA) event or ingress-of-coolant event (ICE). The ICE event is one of the most severe accidents in the fusion reactors.The integrated ICE test facility was constructed to demonstrate the safety design approach of International Thermonuclear Experimental Reactor (ITER) and obtain validation data for the ITER safety analysis codes. Then, an experimental study was performed using the integrated ICE test facility and at the same time the code validation study with the TRAC code was carried out. The pressure rise characteristics in the current ITER machine during the ICE event were analyzed numerically using the verified TRAC-PF1 code and the effects of the relief pipe diameter and suppression tank volume regarding to the pressure rise due to the ICE events were clarified quantitatively from the present analytical results.

Numerical Analysis on Ingress of Coolant Event in Vacuum Vessel of Fusion Reactor Using Modified TRAC-BF1.

The semi three-dimensional numerical analysis model of the FDR-ITER to simulate the in-vessel LOCA or the ICE was constructed using the modified TRAC-BF1 code in which the vacuum vessel, the pressure suppression tank and the relief pipe header are modeled using one VESSEL component. Analytical results obtained from the modified TRAC-BF1 code were compared with those from the MELCOR code concerning pressure in the vacuum vessel when a cooling pipe of 0.6 m2 flow area breaks in it. The mass flow rate of the injected water into the vacuum vessel and the initial wall temperature in the modified TRAC-BF1 input data were the same as those calculated in the MELCOR analysis. The maximum pressure in the vacuum vessel obtained from the modified TRAC-BF1 code is 10% higher than that from the MELCOR code, but it is still below the design pressure 0.5 MPa of the FDR-ITER vacuum vessel. The semi three-dimensional analysis using the modified TRAC-BF1 obtained that the maximum delay in opening time among the four rupture-disks is within 3 ms. The maximum pressure in the vacuum vessel does not exceed the design pressure, even if one of rupture-disks is not opened.