Unloading Pressure Research Articles

Mechanical Behavior and Evaluation of Dented Pipe Caused by Cylindrical Indenter

The defect of pipe dent has a great threat to the safety of oil and gas pipe transportation. In this paper, the numerical calculation model of pipe extruded by cylindrical indenter at vertical and transverse direction was established. Effects of indenter displacement, indenter radius and internal pressure on the dent behavior were discussed. The results show that different action forms of the indenter would cause different dent behaviors. A large degree of plastic deformation is formed at the edge of the cylinder end of the indenter when indenter made a vertical action. The larger the indenter radius is, the larger the plastic deformation is. But when the indenter extrudes transversely, the change in the indenter radius has little influence. For pressure pipeline, the strain in the dent fluctuates in a certain degree, and the plastic strain is larger than that in the non-pressure pipeline, but the dent depth would be lower in the end. Under different conditions of internal pressure, the laws of dent with “non-pressure” and “loading pressure” are the same, and the dented laws of “pressure” and “unloading pressure” are consistent. The strain and the depth of the dent achieve an extreme point or maximum near the edge of the dent.

Achieving constant speed of a hydrostatic drive using controlled operation of the pump and enhancing its energy efficiency

Novel ways of regulating the speed of a hydraulic drive through controlled operation of the pump either by loading/unloading the UPRV (unloading pressure relief valve) or by switching on/off of the prime mover driving the pump have been presented in this paper. The UPRV is used to operate the pump with a minimum load by diverting the pump delivery to the tank at low pressure. The energy efficiency of the said two methods adopted for controlling the hydro-motor speed is also compared. In this respect, the MATLAB®/Simulink model of the system is made and validated experimentally. The static and dynamic performances of the system are investigated using the validated model. The results show that the UPRV controlled system demonstrates better dynamic performance and controllability in terms of decreased fluctuations in hydro-motor speed for the small load torque demand. However, by comparing the energy efficiency of the hydraulic system for the two control strategies, it is found that with the increase in the machine torque demand, the intermittent operation of the pump unit may be more preferable with respect to the amount of energy saved for the complete duty cycle of the system.

Energy Evolution and Acoustic Emission Characteristics of Sandstone Specimens under Unloading Confining Pressure

The acoustic emission characteristics of rock specimens under different initial unloading confining pressures were tested to obtain the damage and rupture characteristics of the sandstone unloading confining pressure path. The CT scan and three‐dimensional reconstruction of the fractured rock specimens were carried out to study the differences of energy evolution and acoustic emission characteristics during the failure of sandstone under different initial unloading pressures. The results show that the unloading confining pressure has a significant influence on the deformation and failure of the rock. There is a significant yielding platform for the circumferential strain and the bulk strain at the peak of the unloading pressure. The larger the initial unloading pressure is, the greater the axial absorption strain energy, the dissipative energy, and the elastic strain energy are at the peak point. After the stress peak point, the elastic strain can be quickly converted into the dissipative energy for rock damage. The elastic energy released from the moment of rock failure under high confining pressure is more concentrated. The acoustic emission ringing and b value characteristic parameters of the rock have a good correlation with the internal energy evolution of the rock, which better reflects the progressive damage of the rock under low stress and the sudden failure of high‐stress unloading.

Effects of the Loading and Unloading Conditions on Crack Propagation in High Composite Slope of Deep Open‐Pit Mine

In the process of open‐pit excavation and stacking of dump along the side wall, the rock mass inside the composite slope undergoes complicated loading and unloading effect, which are manifested as triaxial stress → horizontal unloading → axial loading. In this study, a corresponding mechanical model of crack propagation in composite slope under loading and unloading effects was established. The stress‐strain curves and deformation characteristics of rock under different stress paths were studied. A series of different tests under unloading pressure condition were carried out to study the behavior of the rock fracture under different confining pressure paths. The results showed that under the same initial stress conditions, the deviator stress required for rock unloading failure was less than that of the conventional triaxial compression. The axial deformation of rock samples was gradually increased with the increase of unloading, and the unloading easily led to rock failure. By analyzing the crack propagation mechanism under loading and unloading stress field, the analytic relation of the limit height of the composite slope with the crack morphology as the variation was determined when crack propagation occurred near the slope surface. This study provides a technical note on local damage and cracks propagation of a fractured rock mass under the loading‐unloading effects in high composite slope.

Practice of outburst prevention by pre-driving rock roadway unloading pressure of coal roadway strip in Fengcheng mining area

In view of the new characteristics of the coal and gas outburst disaster of single serious outburst dangerous coal seam in the deep mining area of Fengcheng mining area, the article puts forward regional outburst prevention measures of unloading pressure by pre driving rock roadway and constructing wear layer drilling to pump coal roadway strip gas, a complete set of technical system of regional outburst prevention in coal roadway strip by pre driving and unloading floor roadway in the Fengcheng mining area is obtained. The field practice shows that after entering the deep mining stage, under the conditions of high stress, high gas, high temperature and low permeability, the situation of outburst occurrence is more and more serious, and the mechanism is more complicated, although coal roadway of B4 coal seam has taken the measure of construction of drilling for pre pumping gas along B4 coal seam, but the damage of the high ground stress has not been completely eliminated, the proportion of in-situ stress dominated outburst is increased. Regional outburst prevention is carried through pre driving of floor roadway layout in the rang of 8∼12m which just below the coal roadway to carry on the pressure relief combined with crossing drilling drainage gas, it can greatly improve the permeability of coal seam and the effect of pressure relief, and ensure the safe and fast roadway driving.

Hydrostatic Extrusion Experiment on AZ80 Magnesium Alloy Tube-Expanding Forming under Ultra-High Pressure

A series of systematic experiments were completed on self-developed ultra-high pressure hydrostatic extrusion equipment to determine the effects of key process parameters on AZ80 magnesium alloy tube-expanding forming. Compared with other parameters, extrusion ration has a significant impact on maximum extrusion pressure and unloading pressure. Through material performance tests, highest average tensile ultimate strength (380.0Mpa) and average tensile yield strength (369.3Mpa) was obtained at homogenization temperature of billet 400°C, homogenization time of billet 32h, preheating temperature of extrusion cylinder 180°C, extrusion ratio 2.77 and angle of core die 120°, accompanied by elongation percentage 7%. In the condition of experiment NO.13 (homogenization temperature of billet 400°C, homogenization time of billet 16h, preheating temperature of extrusion cylinder 220°C, extrusion ratio 1.25 and angle of core die 120°), tensile strength, yield strength and elongation percentage achieved a balanced combination with relative low extrusion pressure. Metallographic test also indicates that the ductility of expanding forming tube still has improving potential by annealing recrystallization or other post-treatment processes which is effective to completely eliminate the bulk grain.

A simplified analysis method for evaluating the horizontal deformation of adjacent single pile under tunneling

To analyze the horizontal response regularity of adjacent pile under tunneling, an analytical method is developed considering the shearing effect of pile to assess the horizontal responses of pile due to adjacent tunneling. Firstly, the pile is considered as a Timoshenko beam resting on the Pasternak foundation model, then, combining with the two-stage method, the additional unloading pressure due to the tunneling excavation is loaded on the pile, thus the equilibrium differential equation considering the pile’s shearing effect is established. Secondly, the specific horizontal deformation of pile is given by the finite difference method. Furthermore, through comparing with the boundary element method, the validity of this theory is verified.Finally, using the theory here, a comparison is made between the results based on the Timoshenko beam and Euler-Bernoulli beam, and find the results taking the shearing effect of pile into account are more close to the classical solution, the parameter analysis also suggests: the pile’s shearing effect is closely related with the disturbance, the stronger the disturbance, the more obvious the pile’s shearing effect.

VOCs Emission Inventory of Service Stations in a Subcenter (Tongzhou District) of the City of Beijing

As a subcenter of the city of Beijing, Tongzhou District is faced with enormous pressure from the rapid growth of VOCs emissions from service stations. In this study, a set of bottom-up VOCs inventory estimation methods for service stations in Tongzhou District is established. Using local VOCs emission factors of service stations in Beijing, combined with gasoline and diesel sales from every service station, a high resolution VOCs emission inventory of service stations in Tongzhou District from 2015 to 2022 was established. The results showed the following. ①An online monitoring system (OMS) based on unloading, refueling, and tank pressure vapor emission control measures can reduce the VOCs emission factor from 190 mg·L-1 to 115 mg·L-1, and when the percent onboard refueling vapor recovery system (ORVR) Penetration reaches to about 50%, the emission factors can be reduced to 131 mg·L-1 and 96 mg·L-1, respectively. The VOCs emission factor (13 mg·L-1) of diesel from the service station is 0.8% of the uncontrolled emission factor (1552 mg·L-1) of gasoline. ②The amount of VOCs emissions from service stations in Tongzhou District was 97.8 t·a-1 in 2015, and the emissions of gasoline and diesel were 96.2 t·a-1 and 1.6 t·a-1, respectively, accounting for 98.4% and 1.6%. The emissions were mainly concentrated in the area surrounding the new Beijing Municipal Government site. ③After implementation of the vapor recovery requirements of "Beijing's Clean Air Action Plan from 2013-2017," considering the increase in oil sales from 2017 to 2022, VOCs emissions of gasoline and diesel from service stations will decrease by 9% and 6%, respectively, compared to those of 2015 in Tongzhou District. Assuming that the OMS will also be installed at 28 (2000-5000) t·a-1 service stations by the end of 2022, VOCs emissions of service stations will be reduce by 13% compared to those of 2015. ④The measure of restricting the number of vehicles in operation by 50% can reduce VOCs emissions of service stations by (22±12)% every day during 2014 Asia-Pacific Economic Cooperation conference (APEC). ⑤It is suggested to strengthen vapor recovery supervision on service stations in the area surrounding the new Beijing Municipal Government site, and in summer and refueling idle such as in noon.

Research on mechanism of quantity discharge of firedamp from coal drift of headwork surface reflect coal and gas outburst

The flow of gas in the coal bed is an extremely complex process, and the quantity of gas emission is mainly affected by both gas pressure in coal seam and permeability coefficient of coal seam. The influence factors of quantity discharge of firedamp from coal drift of headwork surface are analyzed, and the characteristics of discharge of firedamp from coal drift of headwork surface are closely related to the factors such as geological structure, gas content, gas pressure and permeability of coal seam. Not only the mathematical and physical model of one-way fluxion of discharge of firedamp from coal drift of headwork surface is established, but also the calculation formula of the quantity discharge of firedamp from coal drift is obtained by applying of variable separation method. According to the formula, the stagnation movement, which is among coal unloading pressure zone of stress, the stress concentration zone and original stress zone stress stagnation and the firedamp package of phenomenon, is analyzed in the coal and gas outburst mine. While the gas permeability of coal seam correspondingly changes variation, the quantity gas discharge also has the corresponding dynamic change. The results show that when the coal body in front of coal drift is in a non equilibrium state in the interaction among the horizontal crustal stress by gravity, gas pressure and mechanical properties of the coal, there is a risk of coal and gas outburst.

Metastable phases, phase transformation and properties of AlAs based on first-principle study

By utilizing an evolutionary methodology on crystal structure search, we propose three new metastable phases for aluminum arsenide (AlAs) as follows: (1) a P6422 symmetric structure (hP6-AlAs), (2) a C222 symmetric structure (oC12-AlAs), and (3) a I4¯3d symmetric structure (cI24-AlAs). By controlling the unloading pressure rate, oC12-, hP6-, and cI24-AlAs may be acquired through quenching NiAs-AlAs. The elastic constants and phonon dispersion spectra are calculated to certify the mechanical and dynamic stabilities of three newly discovered phases. On the basis of first-principle study, we explore phase transformations under pressure for several AlAs polymorphs. The calculation of mechanical properties illustrates that oC12-, and hP6-AlAs possess similar hardness levels, which are higher than that of cI24-AlAs. Meanwhile, oC12-, and hP6-AlAs hold similar shear anisotropic factors, which are smaller than that of cI24-AlAs. Electronic band structure calculation reveals that at zero pressure, oC12-, and hP6-AlAs possess indirect band gaps of 0.468eV and 1.356eV, respectively. cI24-AlAs is a direct semiconductor with a gap value 1.761eV.

Influence of filling atoms on radial collapse and elasticity of carbon nanotubes under hydrostatic pressure

Using molecular mechanics and molecular dynamics simulations, we focus on the influence of filling atoms on radial collapse and elasticity of single-walled carbon nanotubes (SWNTs). It is shown that the filled argon (Ar) and silicon (Si) atoms can effectively improve the resistance to high pressure and radial elasticity of SWNT, which may attribute to the strong repulsive force from the filled Ar(Si) atoms. However, due to the strong interaction of Cu atoms, filling Cu atoms deteriorate SWNT’s radial elasticity. In addition, it is found that the phase transitions of the atoms filled in SWNT occur in the process of loading and unloading pressure, so that the electrical properties of the SWNTs filled with atoms change in the process of loading and unloading pressure. In view of the restorability of SWNT filled with Si atoms upon unloading, the filled SWNTs can be used to develop a new class of nano-electronic devices such as pressure sensor, relay and memory, etc.

Energy conversion of rocks in process of unloading confining pressure under different unloading paths

Based on energy theory and tests of rocks with initial confining pressures of 10, 20 and 30 MPa under different unloading paths, the processes of strain energy conversion were investigated. The absorbing strain energy for axial compression, the dissipating strain energy for plastic deformation and cracks propagation, the expending strain energy for circumferential deformation, and the storing and releasing elastic strain energy were considered. Unloading paths included the condition of fixing axial pressure and unloading axial pressure, increasing axial pressure and unloading confining pressure, as well as unloading axial pressure and confining pressure simultaneously. Results show that expending strain energy for circumferential deformation has mainly evolved from absorbing strain energy for axial compression in three unloading paths during unloading processes. Dissipating strain energy is significantly increased only near the peak point. The effect of initial confining pressure on strain energy is significantly higher than that of unloading path. The strain energy is linearly increased with increasing initial confining pressure. The unloading path and initial confining pressure also have great influence on the energy dissipation. The conversion rate of strain energy in three paths is increased with increasing initial confining pressure, and the effect of initial confining pressure on conversion rate of strain energy is related with the unloading paths.

Evaluating the Unloading Gradient Pressure in Continuous Gas-lift Systems During Petroleum Production Operations

Evaluating the performance, applicability, and field testing of various artificial lift methods, in particular continued gas-lift, can be time consuming and costly. To overcome these drawbacks, it is needed to propose a reliable model to estimate gas-lift applicability in advance of the installation under specific well operational conditions such as tubing size and design oil rate. In this study, the robust least square modification of support vector machine (LSSVM) methodology is implemented to propose a computer program, by which the unloading pressure gradient region can be determined in various design oil production rates and also tubing sizes. The developed LSSVM model results indicate 1.084% average absolute relative deviation from the corresponding unloading pressure gradient literature values, and squared correlation coefficient of 0.9994.

Off-rift volcanism in rift zones determined by crustal unloading

When continents are stretched over a long period of time, deep elongated rift valleys form at Earth’s surface and zones of ponded magma, centred beneath the rift, form at the crust–mantle boundary1, 2. Ascending magma sometimes erupts within the rift valley3, 4 or, counterintuitively, at volcanic fields away from the rift valley that are offset by tens of kilometres from the source of magma at depth5, 6, 7, 8. The controls on the distribution of this off-rift volcanism are unclear. Here we use a numerical model of magmatic dyke propagation during rifting to investigate why some dykes reach the surface outside the rift valley, whereas others are confined to the valley. We find that the location of magmatism is governed by the competition between tectonic stretching and gravitational unloading pressure, caused by crustal thinning and faulting along the rift borders. When gravitational unloading dominates over tectonic stretching forces, dykes ascending from the ponded magma are steered towards the rift sides, eventually causing off-rift eruptions. Our model also predicts the formation of stacked magma sills in the lower crust above the magma-ponding zone, as well as the along-rift propagation of shallow dykes during rifting events, consistent with observations of magmatism and volcanism in rift zones globally. We conclude that rift topography-induced stress changes provide a fundamental control on the transfer of magma from depth to the surface.

Pressure-induced phase transition and polymerization of tetracyanoethylene (TCNE)

We have studied the pressure-induced physical and chemical transformations of tetracyanoethylene (TCNE or C6N4) in diamond anvil cells using micro-Raman spectroscopy, laser-heating, emission spectroscopy, and synchrotron x-ray diffraction. The results indicate that TCNE in a quasi-hydrostatic condition undergoes a shear-induced phase transition at 10 GPa and then a chemical change to two-dimensional (2D) C=N polymers above 14 GPa. These phase and chemical transformations depend strongly on the state of stress in the sample and occur sluggishly in non-hydrostatic conditions over a large pressure range between 7 and 14 GPa. The x-ray diffraction data indicate that the phase transition occurs isostructurally within the monoclinic structure (P21∕c) without any apparent volume discontinuity and the C=N polymer is highly disordered but remains stable to 60 GPa-the maximum pressure studied. On the other hand, laser-heating of the C=N polymer above 25 GPa further converts to a theoretically predicted 3D C-N network structure, evident from an emergence of new Raman νs(C-N) at 1404 cm(-1) at 25 GPa and the visual appearance of translucent solid. The C-N product is, however, unstable upon pressure unloading below 10 GPa, resulting in a grayish powder that can be considered as nano-diamonds with high-nitrogen content at ambient pressure. The C-N product shows a strong emission line centered at 640 nm at 30 GPa, which linearly shifts toward shorter wavelength at the rate of -1.38 nm∕GPa. We conjecture that the observed red shift upon unloading pressure is due to increase of defects in the C-N product and thereby weakening of C-N bonds.

WELL DELIVERABILITY PREDICTIONS OF GAS FLOW IN GAS-CONDENSATE RESERVOIRS, MODELLING NEAR-CRITICAL WELLBORE PROBLEM OF TWO PHASE FLOW IN 1 -DIMENSION

Production of gases from gas-condensate reservoirs are known to bear certain challenges largely due to the formation of retrograde condensates that hinder gas flow. The drop out of this liquid creates flow regions that are characterized by the liquid saturation as it affects the mobility of the two phase flow, thereby preventing the effective modeling of well productivity. In this study, a predictive model based on an analytical approach is developed to predict gas flow in gas condensate reservoirs. This study compares the estimated gas flow from the developed model for gas-condensate reservoirs to the flow of an existing model for gas reservoirs. This study observes the effects of liquid drop-out on productivity at low pressures and the condensate unloading pressure, which is comparable to that of commercial software.

Working process study of a novel scroll type multiphase pump for the transportation of gas-liquid mixtures

A novel scroll type multiphase pump was proposed to transport gas-liquid two-phase mixture. There is a pressure unloading gap from compression chambers to the discharge port by constructing scroll wrap profile with variational meshing clearance in this scroll multiphase pump. In the working process when the volume of working chamber decreases, the pressure of gas-liquid mixtures increases gradually, at the same time small amounts of gas-liquid mixture are pushed to the discharge port from compression chambers through the pressure unloading gap. Therefore, this multiphase pump has an advantage of unloading pressure method automatically, and the frequently problem of liquid impacting in volume multiphase pump is solved. The safety and reliability of volumetric multiphase pump are improved, and the scope of multiphase pump of the gas-liquid ratio is expanded. The working process and the performance characteristics of scroll multiphase pump were analyzed too, and the generation method of scroll wrap profile with variational meshing clearance was investigated. The equations of the profile were obtained, and the changing principle of the working volume and the meshing clearance were analyzed. The geometric theory of scroll multiphase pump was formed. All of that lay the theoretical foundation for engineering design of this novel scroll.

Implications of the idea of effective tip shape on nanoindentation unloading curves: AFM measurements and FE simulation

Abstract

Simulation of the Unloading Pressure and Recovery Pressure of Internal Unloading Valve for Emulsion Pump Station

Automatic unloading valve is the critical pressure control element of emulsion pump station, the unloading pressure and the recovery pressure after unloading of the pump are two important technical parameters of the emulsion pump station. The working performance of the unloading valve can be improved by research and simulation of the two parameters, making clear the state of the unloading valve for emulsion pump station when working, calculating the electromagnetic thrust when the pilot valve and main valve core act as well as the response speed of the unloading pressure, checking and correcting the original spring force. The variation range of pump station pressure can be controlled within ±0.5MPa through the effective control on the unloading pressure and recovery pressure of the automatic unloading valve for emulsion pump station, which ensures the stability, reliability and sensitivity of the pump station when working. The improvement of the automatic unloading valve technology of internal unloading type is adaptable to the development needs of high-yield and high-efficiency modern mine for high pressure and super larger flow pump station.

Mutation of three amino acids in the disulfide-ring of a CNP based chimeric natriuretic peptide alters its vascular properties

Clinical background C-type natriuretic peptide (CNP) is a 22-amino-acid peptide produced mainly in the endothelium with potent cardiac unloading and blood pressure lowering actions, but minimal renal actions. Based on our previous knowledge, we recently fused a 6 aa sequence from BNP to the C-terminus and a 5 aa sequence from ANP to the N-terminus of CNP. This novel hybrid peptide, CBA-NP, has cardiac unloading actions and mild hypotensive effects similar to CNP. Importantly however, the N and C terminus alterations resulted in potent renal excretory actions. Here we test the hypothesis that the 3 aa GSM15–17 in the disulfidering mediate the vascular and hypotensive actions of CBANP. We therefore mutated GSM 15–17 to REA15–17, which we named ABC-NP and compared its in vivo and in vitro actions to CBA-NP.