Leakage Hole Research Articles

R290 leakage hazards assessment of a 1 HP split-type household air conditioner by concentration detection and ignition experiment

Propane (R290) is a promising alternative natural refrigerant for refrigeration, air conditioning and heat pump systems to replace hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), but its highly flammable and explosive properties require specific attention and hinder the replacement process. A fire and/or an explosion may occur once R290 leaks. This paper evaluated the fire hazards of a 1 HP split-type household air conditioner (STHAC) with a charge of 260 g to 350 g not only by measuring the R290 concentration distribution 1.5 m above the floor after a leakage occurred in the indoor unit (IDU) under various situations, but also by ignition experiment to examine the validity of concentration distribution results. A new method for reducing fire hazards was provided by installing a check valve near the gas-liquid separator with a solenoid valve installed after the capillary to prevent the transference of refrigerant from the condenser to the evaporator, which was validated to effectively decrease the fire hazards. The effects of charge, leak hole diameter and valve arrangement on the R290 concentration profiles were studied. It was found that under a fast-leaking rate, a fire occurred though the maximal concentration was 73% LFL detected by infrared gas detectors. This indicated that the detected R290 concentration may be lower than the actual concentration at a fast-leaking rate, and the ignition test was probably the most accurate method for fire hazards assessment. The low-risk application boundaries of the 1 HP STHAC were confirmed both by concentration detection and ignition test.

A New Function for Frequency Analysis in the Risk Assessment of Offshore Oil-Related Platforms

_ Risk assessment of offshore oil-related platforms such as the floating production storage and offloading system (FPSO) is extremely important. In earthquakes prone to target sea areas, earthquakes should be considered as one of the important external forces that cause severe damage. In such risk assessments, for estimating the appearance frequency of seismic energy, the complementary cumulative distribution function (CCDF) of seismic energy of a considered area is usually based on the Gutenberg–Richter law. Furthermore, it is important to estimate the CCDF of the leak hole diameter when estimating the damage caused by an oil spill accident in an offshore oil-related platform. Some ship classification societies recommend using a formula based on the power law distribution as used in those processes. However, the power law distribution has a drawback in that, i.e., it is essentially impossible to accurately estimate the CCDF over the entire domain of the random variables. The authors have developed an enhanced power law distribution function that eliminates such defects in the power law distribution function and some practical methods for estimating its parameters. In this study, the developed function is applied to the CCDFs of the seismic energy and leak hole diameter. The results demonstrate that the function fits the existing data with sufficient accuracy. Therefore, the new function introduced here can be well used in the frequency analysis of the risk assessment of offshore oil-related platforms. Introduction In the risk assessment of offshore oil-related platforms like floating production storage and offloading system (FPSO), it is necessary to estimate probabilistic characteristics of external forces against them. Earthquakes are a major external force. Furthermore, it is necessary to estimate the damage when an external force is applied. The frequency of external forces, such as earthquakes, is low, but the damage is extensive. However, damage to offshore oil-related platforms is caused by not only these external forces, but also oil leaks resulting from some factors, such as operation errors and corrosion, that may cause accidents such as fire and explosion. Therefore, it is also essential to estimate the probabilistic characteristics of such damage for the risk assessment of offshore oil-related platforms.

Leakage simulation and acoustic characteristics based on acoustic logging by ultrasonic detection

The detection of casing leakage in oil and gas wells or water injection wells is an important element of wellbore integrity management. Ultrasonic technology is suitable to detect and identify the position of leakage in oil and gas well shafts, providing engineering guidance for subsequent treatment. In this paper, the finite element calculation model of casing leakage in oil and gas wells is established by using the computational fluid dynamics method, and the large eddy simulation model and Ffowcs Williams-Hawkings acoustic model are utilized to simulate the casing leakage condition. The acoustic pressure signals of each monitoring point on the inner axis of the pipeline are obtained, and the influences of the pipeline pressure difference, the leakage hole diameter and the pipeline fluid on the leakage acoustic field are analyzed. The simulation results indicate that the acoustic pressure level measured on the pipeline axis rises with the increase of pipeline pressure difference and leakage hole diameter. The size and variation rule of acoustic pressure level also vary with the type of pipeline fluid. Overall, the results obtained show that ultrasonic logging can accurately locate and detect tubing leakage, and they provide theoretical guidance for practical casing leakage detection, assisting with wellbore integrity management. Cited as: Li, J., Wan, J., Wang, T., Yuan, G., Jurado, M. J., He, Q. Leakage simulation and acoustic characteristics based on acoustic logging by ultrasonic detection. Advances in Geo-Energy Research, 2022, 6(3): 181-191. https://doi.org/10.46690/ager.2022.03.02

Research on natural gas leakage and diffusion characteristics in enclosed building layout

There are many people in urban construction areas, and natural gas leakage can potentially cause serious accident consequences. Predicting the consequences of gas dispersion is important to react rapidly and adequately in the event of an incident. Currently, computational fluid dynamics (CFD) models are an important tool to predict gas dispersion. However, in most cases, considering computational cost, the building layouts is ignored, so the flow field influence near the building area cannot be considered. In this research process, a realizable k-ε turbulence model is used to simulate the natural gas leakage process in a typical building layout (enclosed building layout), while focusing on wind speed and the leakage position. The validity of realizable k-ε turbulence model is verified by experimental data. The results show that under conditions of high wind speed (wind speed≥ 6 m/s), the reverse vortex formed by the shear flow of wind can cause the natural gas cloud to sink. When the leak hole is located in the influence area of the turbulent vortex, it easily induces R-H instability. When combined with the stronger K-H instability at high wind speeds, natural gas clouds may accumulate. This then leads to serious leakage accidents, knowledge of which may be the key component of emergency management during an accidental natural gas leakage. The research results can guide the building layout plan and gas pipeline construction to prevent accidents.

Innovate and Precise Machining

Laser machining specialist GFH has developed a process for medical and pharmaceutical manufacturers which allows the drilling of high precision leak holes

Leakage Effect on the Transmission Properties of a Duct Loaded with a Helmholtz Resonator

The characteristics of transmitted acoustic field have important significance to the leakage detection and the acoustic metasurface technology. When the additional leak holes are present, the conventional single neck Helmholtz resonator will naturally become the one with multiple necks. Based on such a background, in this paper, the effects of leakages on the transmission properties of a Duct Helmholtz Resonator (DHR) device is investigated both analytically and numerically. A set of closed-form formulas are derived to analytically predict the transmission spectra of the DHR device with leakages. The theoretical results are compared with COMSOL predictions. The simulation results show that the number and width of leak holes have significant influences on the amplitude, phase shift of the transmitted wave, and resonance frequency of the DHR system.

Plastic Pipeline Leak Localization Based on Wavelet Packet Decomposition and Higher Order Cumulants

This paper presents a plastic pipeline leak localization method based on wavelet packet decomposition and higher order cumulants. The hydrophone sensors are used to capture the acoustic signals generated by the water leakage in the plastic pipe. The feature frequency band containing the most leak information is subsequently extracted by performing wavelet packet decomposition on the signals. The most suitable wavelet packet basis function for leak signals is obtained by comparing the effects of varieties of wavelet packet basis functions. Furthermore, the higher order cumulant method is used to estimate the time delay between the two sensors signals, from which the leak hole can be located. The simulation and experimental results show that, compared with the basic cross-correlation method (BCC) and the generalized cross-correlation method (GCC), the higher order cumulant method has higher leak localization accuracy. The relative error of the third-order cumulant method is 2.99% in experiment 1 and 7.58% in experiment 2, while the relative localization error of the fourth-order cumulant method is 1.96% in experiment 1 and 1.23% in experiment 2.

In-line detection of defects in steel pipes using flexible GMR sensor array

Steel pipes serve as the main source for transporting water, gas, and other petrochemical substances for longer distances. These pipes were able to withstand extreme weather conditions and hostile environments because of their remarkable properties such as higher strength, durability, lower cost, and improved wear and corrosion resistance. However, prolonged usage of these pipes in such environments may lead to the initiation of defects in their inner surface such as leak holes, cracks, corrosion, etc. In overtime, these defects may become more severe, resulting in component failure and property losses. Hence, earlier detection of defects is highly recommended to avoid these failures. In this work, an in-line robot system has been proposed for detecting the defects in the steel pipes. This robot utilizes a non-destructive way for evaluating the flaws by means of the magnetic flux leakage (MFL) technique. A 3D finite element model has been developed with the aid of ANSYS Maxwell 3D software for evaluating the generated magnetic field and optimizing the lift-off distance. The permanent magnet is preferred as the magnetizing material for implementing local magnetization in the inspection area. The magnetic flux leakage from the defect region is sensed by using a flexible GMR sensor array of six sensors. Artificial defects were introduced in a 6-inch diameter steel pipe in various shapes and the Arduino UNO controls the overall process. The data from the sensor array were collected using the Arduino and plotted as the waveform graph. From this graph, the voltage variations among the sensors represent the defect region. In addition, the higher peak in amplitude denotes that the flux is influenced by the defect’s depth. Thus, the waveform graph for the introduced defects was analyzed and all graph represents a better signal to noise ratio (SNR) for identifying the defects.

Leak hole sizes from refrigeration, air conditioning and heat pump systems

• First major study which gathered hole data from over 1000 leaks. • Taken from a variety of refrigeration, air conditioning and heat pump systems. • 95% of all leaks and >99% of uninterfered leaks were smaller than 0.5 mm 2 . • 0.5 mm 2 corresponds to a mass flow of 70 g min −1 of R290 at standardised conditions. Knowledge of sizes of leak holes arising in refrigeration, air conditioning and heat pump systems is critical for safe application of flammable refrigerants, especially hydrocarbons such as R290. Data for leak hole sizes is currently lacking so safety standards have used a range of assumed leak rates that maybe unreasonable and lead to severe restrictions on charge limits and/or high costs for addressing potential ignition sources. Over 1000 leak holes have been measured from various systems. The leak hole areas were found to be clustered around very small values with more than 90% below 0.10 mm 2 and 98.8% smaller than 1.0 mm 2 , irrespective of type, age and size of the system. The largest leak hole size that should be considered for safe design of systems is around 0.5 mm 2 , or about 70 g min −1 of R290 vapour or adjusted according to the system operating conditions or type of refrigerant.

Numerical and experimental study on leakage detection for buried gas pipelines based on distributed optical fiber acoustic wave

Buried natural gas pipeline leakage can cause severe environmental pollution and human casualties. The currently used fiber optic temperature sensors cannot detect pipeline leakage in all directions, and there are monitoring blind spots. Besides, there is a lack of field tests and verification of the acoustic characteristics caused by leakage. In this work, a sound wave attenuation model considering gas flow in viscous porous media is established based on the Φ-optical time-domain reflectometry (Φ-OTDR) principle, combined with fluid dynamics and acoustic wave propagation mode in porous media (soil). The attenuation characteristics of acoustic wave propagation in soil are studied by varying the leakage hole size and leakage pressure. It is found that the acoustic source of buried natural gas pipeline leakage belongs to broadband noise. The acoustic signals detected by optical fiber acoustic sensors are vary with different leakage holes and leakage pressures. In particular, the leaked acoustic wave’s energy is prominent in the low-frequency band of 15 kHz, and the sound pressure level (SPL) oscillates and attenuates with the increase in frequency. With the increase in the transmission distance, the amplitude of the pipeline leakage signal gradually attenuates. Eventually, the acoustic wave decays to the point where the fiber-optic acoustic sensor cannot detect it. The optimum frequency of acoustic wave propagation in soil is obtained through experimental research. The propagation characteristics of acoustic waves in the soil are not a fixed value. The simulation results are in good agreement with the experimental results, indicating that the SPL in the low-frequency band is significant for pipeline leakage monitoring. The above research results can provide valuable guidance for field optical fiber installation.

A new real-gas model to characterize and predict gas leakage for high-pressure gas pipeline

High-pressure gas pipe leakage is a topic of great concern in the risk assessment and safety management of pipeline systems. Traditional ideal-gas models with the assumption of fully ruptured leak loss are valid for a large leak hole in low-pressure gas pipelines (3–14 bar). This paper developed a new model for small leaks in high-pressure gas pipelines, which improves the traditional models in two aspects: the introduction of a mass fraction to characterize the proportion of leaked gas flow to in-pipe gas flow, and the integration of the real-gas thermodynamics into the fundamental governing equations to include the gas compressibility factor in the high-pressure conditions (>14 bar). To examine the validity and practicality of the new real-gas model, comprehensive comparison tests were carried out with the results of the benchmark numerical simulations and the hazard modelling software ALOHA, respectively. In the light of prediction accuracy, the new real-gas model shows its advantage over the traditional ideal-gas model, the improved ideal-gas model, and the semi-empirical correlation proposed by previous research. The virtues of high accuracy and short computational time confirmed the effectiveness of the new real-gas model in the responsive evaluation of high-pressure gas pipe leakage with small leak holes.

Investigation on diffusion characteristic of leaked oil in the thermal insulation layer of submarine pipe-in-pipe

ABSTRACT Submarine pipe-in-pipe with thermal insulation layer plays a crucial role in the offshore oil and gas transportation system. This paper presents pollutants distribution in thermal insulation layer of damaged submarine pipe-in-pipe by computational fluid dynamics method. The numerical model has been validated through comparing with other simulation data. In order to considerably mitigate the leakage damage, the influence factors analysis is performed. Finally it is identified that macropores thermal insulation material and larger leakage hole with higher leakage velocity can significantly make the damage more serious. In addition, it is under consideration to install monitoring system on the bottom of the jacket pipe for easier and faster detection of the leaked pollutants, which helps to offer a valuable guidance for formulation of emergency response and protect seawater from direct contamination.

Identification of energy wastes through sound analysis in compressed air systems

This paper proposes a new approach which is able to identify energy losses of compressed air in any CAS based on acoustic energy emission. By means of a previously validated mathematical model, the inverse problem that finds air power lost over time from the sound generated by air expansion is solved. The developed method is tested in a laboratory scale while a tank is being emptied through artificial holes with different diameters in a pipe. Two supplying cases: continuous supply of compressed air to the tank and single filling of the tank are considered. All measurements are made in an anechoic chamber to record pure air expansion noise without any background sounds. The analysis shows that over certain range of leakage hole diameters there is a dependence between the generated sound pressure level and the mass flow and, therefore, the power loss. Thus, acoustic monitoring could be effective in leakage diagnosing in CASs, which is important for production energy efficiency management.

Acoustic method of high-pressure natural gas pipelines leakage detection: Numerical and applications

Leak detection is one of the most important issues in natural gas pipelines operation, major accidents can result from pipe gas leaks in pipelines that transport high-pressure gases. Natural gas pipeline leakage can cause huge economic losses and affect public health. Currently, pipeline leak detection relies on the semi-empirical formula based on the traditional basis. However, such methods have obvious limitations. It is impossible to predict the new process in a forward-looking way, which leads to a sharp increase in cost. The infrasonic wave method offers the possibility of continuous acoustic monitoring of pipelines and remote detection of leaks. In this work, the time-frequency signal of pipe leakage acoustic wave was studied by using the method of “acoustic - pipe and acoustic - pressure” multi-physical field coupling. Finally, the acoustic leakage monitoring method was applied to the field pipeline. The results show that: 1) natural gas pipeline leakage is a kind of broadband noise. With the increase of frequency, the energy tends to oscillate and decay; 2) the acoustic wave propagates from the leakage hole, and the amplitude decreases rapidly. 3) the leakage acoustic energy is mainly concentrated below 20 Hz, and the mean sound pressure increases with the increase of internal pressure and leakage diameter; 4) ultra-low frequency sound pressure level (SPL) is of great significance to the detection of natural gas pipeline leakage by the acoustic method. The field experiment demonstrates that this method can improve the detection ability of small leakage. Hence, the proposed method provides a new approach for the detection of pipeline leakage in technology popularization and engineering applications.

Numerical Study on Extent of Hazardous Area for Sonic Jet Release Using Equivalent Leak Diameter

In this study, three-dimensional K - E turbulence numerical simulations were conducted to analyze the extent of hazardous area for the sonic jet leakage of flammable gas. Incompressible fluid flows were simulated based on an inlet boundary condition estimated using the theory of “equivalent leak diameter” to prevent the direct simulation of sonic flows near the leakage hole. Numerical simulations of 20 methane leakage scenarios providing the lower explosive limit contour showed shapes of the hazardous area with a maximum height of approximately 12-14 times larger than the maximum width, owing to convection. The extents of hazardous area determined using computational fluid dynamics (CFD) were approximately 5%-10% lower than the results obtained with 1 m over based on IEC 60079-10-1. For scenarios in which quantitative data were not calculated using IEC 60079-10-1 due to low release rates, CFD provided quantitative data for the extent of hazardous area, showing nonlinear relationships with the pressure and diameter of leak holes.

Vortex suppression of the tip leakage flow over a NACA0009 hydrofoil via a passive jet induced by the double-control-hole

Tip leakage vortex (TLV) frequently occurring in bladed energy conversion machines may induce flow loss as well as cavitation. The double-curved-hole (DC hole) structures located at the 10%–25% chord near the leading edge of the foil are adopted to induce a passive jet thus suppressing the tip leakage vortex structures in this paper. The control effects and the control mechanisms of three DC hole positions are illustrated by numerical analyses based on the rotation-curvature corrected shear stress transport (SST) k-ω turbulence model and the Zwart-Gerber-Belamri (ZGB) cavitation model. The results demonstrate that the passive jet from the DC hole could divide the TLV into several parts and induce new vortical structures. The newborn vortical structures can be classified into three types: weakened tip leakage vortex (WTLV), newborn secondary tip leakage vortex (NSTLV) and hole separation vortex (HSV). The control effects for different tip clearance are greatly related to the DC hole location. Once the DC hole locates near the merger point of the tip leakage vortex and the tip separation vortex, it could achieve the best control effects. Besides, TLV core pressure could be improved thus suppressing the local cavitation, and the lift-drag ratio for different inlet velocities can be slightly reduced.

Cause Analysis of the Large-Scale LPG Explosion Accident Based on Key Investigation Technology: A Case Study.

Blending dimethyl ether (DME) into liquefied petroleum gas (LPG) has become a common phenomenon. On December 3, 2019, an LPG/DME explosion occurred in Beijing, resulting in 4 deaths and 10 injuries. To deeply investigate the cause and explosion process of the explosion accident, the accident investigation method combining on-site inspection, material evidence analysis, experimental verification, and logical reasoning was used. In addition, the location of the ignition point, the explosive substances, the cause of the gas leakage, the process and the distribution characteristics of the gas leakage, and the ignition process were successively reasoned and analyzed in detail. The results show that the LPG/DME-blended gas can effectively corrode silicone flange gaskets, forming laminar fractures and radial cracks on the gasket. As a result, the tensile strength of the gasket decreased. Under the action of the gas pressure inside the pipeline, the gasket was torn and a leakage hole was formed. The leaked combustible gas formed at least 305 m3 of the explosive gas mixture inside and outside the refrigerated storage. The investigation and research results have important scientific guiding significance for revealing the cause and preventing similar accidents.

ИССЛЕДОВАНИЕ ПРОЦЕССА НАТЕКАНИЯ ВОЗДУХА В ВАКУУМНУЮ СИСТЕМУ ЧЕРЕЗ ОТВЕРСТИЯ РАЗЛИЧНОЙ ФОРМЫ

The paper presents the results of the control of air leaks into a vacuum system and the dependence of its value on the parameters of the leak hole. To obtain these data, an experimental installation based on a capacitive pressure sensor was created. The process of air leak into the vacuum system through various calibrated holes is experimentally investigated. It is established that the change in the air pressure in the system can be described by an exponential function. Moreover, the nature of the leakage for all holes is the same, only the value of the exponent changes, which depends on the parameters of the hole. Analysis of the obtained data showed that this parameter decreases with increasing hole length and increases with increasing its cross-sectional area.

등가누출직경을 적용한 도시가스 감지기의 설치 위치에 대한 수치 해석적 연구

In this study, the location of gas detectors installed in urban gas-using facilities was investigated by using Computational Fluid Dynamics(CFD). Three-dimensional incompressible flow fields coupled with a κ-ε turbulence model were solved by using the equivalent leakage diameter to efficiently analyze the sonic jet leakage. Numerical simulation consisting of twenty methane gas leakage scenarios with various leakage hole sizes and gas pressures provided quantitative data of a detectable height that depends on an alarm set concentration. Lowering the alarm set concentration from 25% of Lower Explosive Level(LEL) to 20% of LEL was found to increase the detectable heights by 23∼31%. Although the maximum width of 20% contour of LEL was increased by 16%~30% compared to that of 25%, it was found that the width of the 25% contour of LEL predicted by CFD was as quite a small as about 30 ㎝.

Notable difference between rapid-thermal and microwave annealing on Ge pMOSFETs

Effects of rapid-thermal-annealing (RTA) and microwave annealing (MWA) on Ge pMOSFET with GeOx interfacial layer (IL) and HfO2 gate dielectric were studied in this work. High gate leakage and low hole mobility may be induced by the diffusion of GeOx during RTA thermal process. A high hole mobility of ~510 cm2/V-s, low equivalent oxide thickness (EOT) of ~0.7 nm, and very low gate leakage density of ~10−4 A/cm2 at V = VFB + 1 V in Ge pMOSFET can be simultaneously achieved with the efficient annealing effects of MWA on hydrogen plasma (H*) treated GeOx IL due to the suppression of GeOx out-diffusion. The notable difference between RTA and MWA can be attributed to good annealing effects on gate stack by using a MWA with low effective thermal budget.