Transient Impact of Valve Closure Times: Disagreements Between Design and Application

2017 ◽  
Author(s):  
Ilker T. Telci ◽  
Shesh R. Koirala
Keyword(s):  
Transient Analysis ◽  
Lag Time ◽  
Field Conditions ◽  
Dynamic Loads ◽  
Design Stage ◽  
Pressure Waves ◽  
Valve Closure ◽  
Pipe Network ◽  
Transient Pressure ◽  
Transient Event

Many pressurized liquid systems require emergency shut down procedures in order to prevent damage to the piping and components, environmental contamination and fire hazard. The emergency shutdowns (ESDs) are facilitated by fast closing on-off valves installed at various locations along the piping system. When these valves close they create transient pressure waves traveling through the pipe network. These waves can be reflected at the dead-ends or closed valves. At locations where the pressure decreases below the vapor pressure, liquid column separation followed by a rejoining can cause creation of new transient pressure waves. As these waves travel, they may meet and superpose. These complex surge pressure wave behaviors require modeling of the pipe network and simulation of the transient event as the first step of a transient analysis. The second step of the transient analysis is to pin point the problems such as excessive surge pressures and dynamic loads that may occur in the system. The third step is to provide recommendations to prevent undesired transient consequences. One of the most important components of these recommendations include valve closure times during ESDs. Recent field measurements on the valve closure rates showed that the valve closure times recommended by the transient analysis were not accurately implemented. One reason for this disagreement between the designed closure rates and the applied closure rates is that the actuators of the valves introduce a time lag between the shutdown signal and start of valve closure. Another reason comes from the decision taken by the operator adjusting the actuator timing. Some operators may adjust the actuators such that the valves close within the prescribed time including the lag time which may result in very fast valve closures depending on the lag of the actuators. Other operators may choose to close the valves within the prescribed time including the lag time or even slower than the recommended rates. This may impair the orchestrate of the valve closure events designed in the transient analysis resulting in excessive surge pressures or dynamic loads. This study investigates (i) the discrepancies between the recommendations from transient study made early in the design stage and (ii) the transient impact due to the deviation and/or misinterpretation of those recommendations. Specifically, in this study, these problems are demonstrated in a case study from LNG - Ship loading systems. The results indicated that transient analysis is the essential tool in finding critical components of the system in the field conditions providing a variety of solutions such as valve closure rate adjustments, flow rate reduction at the beginning of ESDs via pump trips and pipe size increase at dead legs. This study showed that the pressure piping systems can deviate from initial design under dynamic field conditions and frequent inspections of the ESD valves are crucial for safe operations of these systems.

A Calculation Model for Leak Detection and Location of Single Pipeline With Two Leaks

2018 ◽  
Author(s):  
Xu Diao ◽  
Juncheng Jiang ◽  
Lei Ni ◽  
Yong Pan ◽  
Qiang Chen
Keyword(s):  
Linear Equations ◽  
Time Domain Analysis ◽  
Economic Loss ◽  
Calculation Model ◽  
Pressure Waves ◽  
Transient Pressure ◽  
Transient Event ◽  
Leak Location ◽  
Pipeline Valve ◽  
Transportation Modes

Pipeline, as one of the transportation modes, is playing an increasingly important role in national economy. But leakages in pipelines may cause severe problems, such as environmental damages and economic loss. Therefore, how to calculate the leak location and leak size has been investigated for last decades. This paper presents a calculation model based on time-domain analysis solution for detecting and locating two leaks in the pipeline. The model is based on a transient event that is generated by fast closure of the valve at the end of a reservoir-pipeline-valve (RPV) system. The presence of leak causes continuous drops in pressure waves and leak information can be revealed by analyzed the leak transient pressure waves. The time of reflection wave represents the leak location and the magnitude of the piezometric head represents the leak size. The governing equations for calculating the leak size are derived as a system of linear equations based on the Method of Characteristics (MOC). The first transient pressure wave was analyzed to obtain the calculation parameters. Then the applicability of this method is verified on simulated pressure data. The results indicate that this model can perfectly solve two leaks problem in a single pipeline.

scholarly journals Protecting a Pumping Pipeline System from Low Pressure Transients by Using Air Pockets: A Case Study

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1786 ◽  
Author(s):  
Rafael Bernardo Carmona-Paredes ◽  
Oscar Pozos-Estrada ◽  
Libia Georgina Carmona-Paredes ◽  
Alejandro Sánchez-Huerta ◽  
Eduardo Antonio Rodal-Canales ◽  
...  
Keyword(s):  
Design Stage ◽  
Pipeline System ◽  
Pressure Waves ◽  
Transient Pressure ◽  
Transient Simulations ◽  
Transient Control ◽  
Water Pipeline ◽  
Potential Damage ◽  
Air Pockets

This paper presents a case study of an existing water pipeline with five pumping stations each equipped with five pumps. In order to study the pipeline behavior prior to putting the system into operation, several transient simulations for different scenarios were developed. Results revealed that the most serious situation occurred when a simultaneous failure of the five pumps occur at each station caused by power cut, producing negative pressure waves because the system for control of hydraulic transients of the pipeline was insufficient to suppress downsurge pressures, due to the moment of inertia of all the pumps being erroneously considered during the design stage. The necessity to start supplying water to the population led to attempt an unconventional form of protecting the line against low pressures. The solution was to operate two of the five pumps per plant, and permit air to enter through combination air valves located along the pipeline. Air entrained formed pockets that remained stationary at the air valves locations, acting as air cushions that absorbed the energy of transient pressure waves. Computational simulations were conducted considering that two pumps are in operation at each plant and suddenly these fail simultaneously caused by power failure. The program was verified by comparing the calculated results with those registered during field pressure measurements. It was noticed that the surge modelling results are in good agreement with the measured data; furthermore, these show the air pockets in combination with existing devices for transient control protect the system adequately, avoiding potential damage to the pipeline.

Starting Processes in Electric Drive of a Passenger Elevator

2021 ◽  
Vol 1 (1) ◽  
pp. 40-49
Author(s):  
S. Rachev ◽  
K. Dimitrova ◽  
D. Koeva ◽  
L. Dimitrov
Keyword(s):  
Coordinate System ◽  
Induction Motor ◽  
Electric Drive ◽  
High Speed ◽  
Induction Motors ◽  
Dynamic Loads ◽  
Design Stage ◽  
Motor Drive ◽  
Induction Motor Drive ◽  
Electric Induction

During the operation of electric induction motors used to drive passenger elevators, electro-mechanical transient processes occur, which can cause unacceptable dynamic loads and vibrations. In this regard, research is needed both at the design stage and for operating elevator systems to determine the arising impact currents and torques, in order to propose solutions for their limitation within pre-set limits. Paper deals with starting processes in a two-speed induction motor drive of a passenger elevator. The equations for the voltages of the induction motor are presented in relative units in a coordinate system rotating at a synchronous speed. The values have been obtained for the torques, the rotational frequencies and the currents when starting at a high speed and passing from high to low speed.

Transient Analysis on Helium Coolant Tube Break Accident of Dual-Functional Lithium Lead Test Blanket Module

2016 ◽  
Author(s):  
Qian Sun ◽  
Tianji Peng ◽  
Zhiwei Zhou ◽  
Zhibin Chen ◽  
Jieqiong Jiang
Keyword(s):  
Pressure Wave ◽  
Transient Analysis ◽  
Structural Integrity ◽  
Maximum Pressure ◽  
Pressure Waves ◽  
Operating Pressure ◽  
Pressure Shock ◽  
Dual Functional ◽  
Short Time ◽  
Helium Coolant

Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM) was proposed by China for testing in the International Thermonuclear Experimental Reactor (ITER).When an in-TBM helium coolant tube breaks, high pressure helium will discharge into the Pb-Li breeding zones. The pressure shock in the TBM will threaten the structural integrity and safety of ITER. Simulation and analysis on helium coolant tube break accident of DFLL-TBM was performed, and two cases with different break sizes were considered. Computational results indicate that intense pressure waves spread quickly from the break to the surrounding structures and the variation of pressure in the TBM breeding box is drastic especially when the pressure wave propagation encounters large resistance such as at the bending corner of the flow channel, the inlet and outlet of Pb-Li, etc. The maximum pressure in the TBM breeding box which is even higher than the operating pressure of helium also occurs in these zones. Although the pressure shock lasts for a very short time, its effect on the structural integrity of DFLL-TBM needs to be paid attention to.

scholarly journals An approximation of behind-casing hydraulic conductivity between layers from transient pressure analysis

DYNA ◽  
2019 ◽  
Vol 86 (210) ◽  
pp. 108-114
Author(s):  
Freddy Humberto Escobar ◽  
Angela María Palomino ◽  
Alfredo Ghisays Ruiz
Keyword(s):  
Hydraulic Conductivity ◽  
Transient Analysis ◽  
Test Interpretation ◽  
Well Test ◽  
Transient Pressure ◽  
Pressure Transient Analysis ◽  
Pressure Transient ◽  
Transient Pressure Analysis ◽  
Pressure Analysis

Flow behind the casing has normally been identified and quantified using production logging tools. Very few applications of pressure transient analysis, which is much cheaper, have been devoted to determining compromised cemented zones. In this work, a methodology for a well test interpretation for determining conductivity behind the casing is developed. It provided good results with synthetic examples.

Anticipated Transient Without Scram Analysis for an ABWR Using RETRAN

2008 ◽  
Author(s):  
Chiung Wen Tsai ◽  
Shu Ming Yang ◽  
Chunkuan Shih ◽  
Jong-Rong Wang ◽  
Shao Shih Ma ◽  
...  
Keyword(s):  
High Pressure ◽  
Control System ◽  
Neutron Flux ◽  
Transient Analysis ◽  
Valve Closure ◽  
The Third ◽  
The Core ◽  
Main Steam ◽  
High Neutron ◽  
High Neutron Flux

A RETRAN02/MOD5 model was developed for Lungmen ABWR and applied for ATWS transient analysis. Three ATWS events including Main Steam Isolation Valve Closure (MSIVC), Loss of Offsite Power (LOOP), and Inadvertent Opening of all Turbine Bypass Valves (IOTBV) are analyzed in this study. During the first two transients, the vessel pressure is increased as a result of steam flow reduction due to the closure of main steam isolation valves (MSIVs) and Turbine Control Valves (TCVs) respectively. In the third transient, the vessel pressure is reduced because of the open of Turbine Bypass Valves (TBVs) and turns to be increased because of the closure of MSIVs. All of the above transients suffer high neutron flux as a result of void reduction. There are several equipments and procedures to mitigate ATWS transient such as feedwater trip, Reactor Internal Pumps (RIPs) runback and trip, and the depressurization of relief valves. After the ATWS high pressure signal is initiated and permissive for 180 seconds, Standby Liquid Control system is initiated to inject boron liquid into upper plenum to shutdown the reactor. The results conclude that equipments and procedures mitigate the event effectively and the core is brought to shutdown state.

Design of Water Hammer Protection for FPSO Domestic Water System Based on AFT-Impulse

2020 ◽  
Author(s):  
Zhang Huan ◽  
Zhang Qipeng ◽  
Wang Chao ◽  
Xu Jiangguo ◽  
Kong Weiwen
Keyword(s):  
Working Conditions ◽  
Transient Analysis ◽  
Water System ◽  
Water Hammer ◽  
Network System ◽  
Pipe Network ◽  
Safe Operation ◽  
Domestic Water ◽  
Pipe Length ◽  
Control Factors

Abstract Due to the limitation of cabin space, FPSO domestic water pipe network system has the characteristics of long water delivery distance, more bending of pipeline and frequent opening and closing of valves, etc. The above characteristics are very likely to cause water hammer in the pipeline, resulting in increased risk of safe operation of pipe network system. In this paper, a FPSO domestic water system was taken as the research object. In view of the water hammer problem in the pipe network system, the model of FPSO domestic water system was established by using dynamic fluid analysis software AFT-Impulse, combined with the factors affecting the water hammer phenomenon (such as pipe diameter, velocity of wave, pipe length, pipeline roughness and valve closing time), the steady state analysis and transient analysis of multi-working conditions and multi-scenarios were realized to determine the main control factors. Based on the influence of main control factors, a comparison scheme of water hammer protection in FPSO domestic water system was proposed. Through the transient analysis of AFT-Impulse software under multi-working conditions, the optimal scheme of water hammer protection for FPSO domestic water system was obtained, which provided guarantee for the safe operation of the system.

The Whole-Engine Model for Clearance Evaluation

2009 ◽  
Author(s):  
Alexander N. Arkhipov ◽  
Vladimir V. Karaban ◽  
Igor V. Putchkov ◽  
Guenter Filkorn ◽  
Andreas Kieninger
Keyword(s):  
Steady State ◽  
Transient Analysis ◽  
Operating Experience ◽  
Operating Conditions ◽  
Design Stage ◽  
Fe Model ◽  
Engine Operation ◽  
Engine Model ◽  
Operation Conditions ◽  
3D Effects

The evaluation of the blading clearance at the design stage is important for heavy duty gas turbine efficiency. The minimum clearance value at base load is limited by the pinch point clearance during startup and/or shutdown. Therefore, transient analysis is necessary for different operating conditions. 3D transient analysis of a whole engine is labor-intensive; however 2D axisymmetric analysis does not allow consideration of different 3D effects (e.g. twisting, bending, ovality, rotor alignment). In order to overcome these cost and time limitations, the combination of 2D, axisymmetric, whole-engine model results and the scaled deflections caused by different 3D effects is used for the axial and radial clearance engineering assessment during engine operation. The basic rotor and stator closures are taken from the transient analysis using a 2D finite element (FE) model composed of axisymmetric solid and plane stress elements. To take into account 3D effects of airfoil twisting and bending, the 3D FE displacements of the blade are included in the clearance evaluation process. The relative displacements of airfoil tip and reference point at the blade or vane hub are taken from 3D steady-state FE analyses. Then the steady-state displacements of the airfoils are scaled for transient conditions using the proposed technique. Different 3D rotor / stator effects (cold-build clearances and their tolerances, rotor position with respect to stator after assembly, casing bending, deformations of compressor and turbine vane carrier inducing of casing ovalization, exhaust gas housing movements, movements of the rotor in bearings and CVC and TVC support, etc.) are also included as a contributor to the clearances. The results of the calculations are analyzed and compared with good agreements to the clearances measured in engine testing under real operation conditions. The proposed methodology allows assessing the operating clearances between the stator and rotor during the design phase. Optimization of the running clearance is one key measure to upgrade and improve the engine performance during operating experience.

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