Pipe Outer Diameter Research Articles

Feasibility of coaxial deep borehole heat exchangers in southern California

This paper investigates the feasibility of coaxial deep borehole heat exchanger (CDBHE) applications to the University of California San Diego (UCSD) campus. By collecting different geophysical source data for various formations and well logs around the UCSD campus, a multilayered thermophysical model for the ground on the site is established. Water circulation within a closed coaxial loop system considers the geothermal energy extraction under uncertainty consideration of the unknown deeper layers heat flow gradient as coupled with the variation of pipe insulation properties, flow rates, outer pipe diameter, grout, and depths between 1 and 4 km. A finite-element framework models the Navier–Stokes fluid flow and heat transfer in the CDBHE system, validated with a field test on CDBHE from the literature. Results show that a 4-km CDBHE could produce a thermal power of 600 kW under the optimum geological conditions at the UCSD site: the water flow rate of 2.78 L/s and a ground thermal gradient of 60 ℃/km. Thermal power shares from different layers indicate that deeper formation layers contribute more to the thermal power than the shallower layers because increasing the CDBHE length from 1 to 4 km can lead to a maximum of 900% increase in thermal power and a 50% expansion in thermal plume for a CDBHE with an insulated inner pipe between the upper and lower bound heat flow bounds. An inner pipe with an insulated depth of 2 km produces only 1–6% less power than a fully insulated inner pipe for the 4-km CDBHE, and thus, a partially insulated vacuum-insulated tube (VIT)-plastic inner pipe is suggested as the best practice. Furthermore, the CDBHE thermal power increases by 5% when the grout thermal conductivity increases from 1 to 3.65 W/(K∙m), close to the formation thermal conductivity, and then maintains almost the same, and the 4-km CDBHE with flow rates of 2.78–6.94 L/s at the UCSD site can directly supply a low-temperature heating radiator system for room heating. This study suggests practical ranges for geothermal energy extraction for southern California. A CDBHE with a well-insulated inner pipe of 0.05 W/(m∙K), the thermal power of lower and upper-bound heat flow cases can vary by 60% from the mean. Finally, water as the working fluid is more efficient than CO2, doubling CDBHE's thermal power. The effects of the investigated factors provide guidelines for future geothermal resource exploitation in southern California.

Zero-Net Liquid Flow Simulation Experiment and Flow Law in Casing Annulus Gas-Venting Wells

Under casing annulus gas venting, the annulus of the well is in a special state of zero-net liquid flow (ZNLF), leading to gas production without liquid at the wellhead, resulting in significant holdup issues. Therefore, conventional two-phase flow models cannot be used for calculation. To study the flow characteristics of ZNLF in the annulus of the well, this study established a visual experimental device with a total height of 5.4 m, an outer pipe inner diameter of 140 mm, and an inner pipe outer diameter of 72 mm. The flow characteristics of ZNLF were studied by controlling the casing pressure, initial liquid level, and bottom gas injection rate. The experimental results showed that the flow patterns of ZNLF are mainly bubbly flow and churn flow. Bubbly flow occurred at lower gas rates, while churn flow occurred at higher gas rates. In addition, the experiment found that when the gas injection rate and initial liquid column height were controlled to be the same, the liquid holdup decreased as the casing pressure increased. Analysis of the data patterns indicated that the slip velocity is related to the casing pressure. Based on the experimental results of ZNLF in the annulus, this study established standards for flow pattern transitions, holdup, and a pressure drop calculation model. The model results showed good agreement with the experimental results, with errors not exceeding ±5%.

Heat transfer performance and optimal design of shallow coaxial ground heat exchangers

The heat transfer performance of coaxial ground heat exchangers (GHEs) can be strongly influenced by their structure parameters and improved by the optimal design. To improve the heat transfer efficiency, this study proposed a coaxial GHE with large pipe diameters and thick inner pipe insulation for shallow ground source heat pump systems, which had heat transfer rates of more than 120 W/m in 12 h during both heat injection and extraction experiments. The validated three-dimensional CFD model was used to numerically investigate the influence of various structural parameters on the heat transfer efficiency considering the thermal short-circuiting effect. The thermal short-circuiting effect could be alleviated with thicker inner pipe insulation, while the decreasing annular space occupied by the insulation would reduce the borehole heat transfer rates, thus, an inner pipe with a 35 mm-thick insulation obtained the optimal heat transfer rate. The inner pipe diameter increase contributed to a more severe thermal short-circuiting and poor heat transfer performance. Increasing the outer pipe diameter improved the heat transfer efficiency and an optimal outer pipe diameter of 155 mm existed when considering the heat transfer performance and its efficiency. Therefore, increasing the inner pipe insulation thickness and outer pipe diameters can be regarded as an efficient method to improve the thermal performance of coaxial GHEs.

Optimal design of medium-buried pipe with horizontal wells

In this paper, based on the emergence of medium-depth cased buried pipe with horizontal wells, a kind of optimization design for this buried pipe is designed. Firstly, a semi-analytical model and related evaluation indexes are established for the model, and three different schemes are used for simulation and comparison, which are: changing the inner and outer diameters of the buried pipe at the same time, changing the outer pipe diameter while keeping the inner pipe diameter unchanged, and changing the inner pipe diameter while keeping the outer pipe diameter unchanged, which are of great significance for the optimization of the design of the new type of buried pipe. In this paper, the establishment of the model mainly adopts the establishment and discretization of the energy equation of heat transfer and uses Fortran software to realize. Ultimately this paper comprehensively consider its temperature distribution, heat storage capacity and its economic type, can be concluded that the above three options in option two of the investment is relatively small, the temperature enhancement is more significant. The results and conclusions of the optimization are very helpful for the optimal design of this kind of buried pipe.

Improving the Quality of Environmentally Friendly Liquid Smoke Distillation Process to Increase Artisan Income

The problems the Smoke-liquid Craftsman Group often faces are production capacity, product quality, and low selling prices. Low production capacity due to the limited ability distillation machine. The low quality of smoke-liquid products is due to the absence of standard quality. The smoke produced from the coconut shell charcoal production process has the potential to disturb the environment, so it has been carried out the process of melting smoke into liquid, which is then called smoke-liquid. However, the resulting smoke-liquid is still mixed with ash, brown colour, and intense aroma, and still contains much tar, so it does not meet the standard quality for food preservatives the price is low. The objective of this activity is to apply appropriate technology is carried out by enforcing standard product quality and repairing distillation machines to produce high-quality smoke liquid. This one is to support renewable and environmentally friendly energy programs while being able to increase revenue. Appropriate Technology (TTG) is in the form of improvements in distillation technology, which was previously a distiller using annular pipes, where the inner pipe is 1/2 inch. The outer pipe diameter is 1.5 inches and is changed with parallel heat pipe exchanger technology using an inner pipe with a diameter of 1 inch and an outer pipe with a diameter of 4 inches. The result of this service is prototyping a new distillation machine that can increase the production capacity and quality of liquid smoke that meets the specified standard quality and increase the selling price four times.

Comparative study of different meta-heuristics on optimal design of a heat exchanger

AbstractThe paper compares different metaheuristics for using heat exchangers as a benchmark to estimate the best design parameter values using optimization efficient algorithms. Many MATLAB algorithms are used in this study. Also, an engineering equation solver, which is commercial software, is used to solve the issue. The design calculates three variables, which are the length, and inner and outer pipe diameter of the heat exchanger. The results showed that the best algorithms are particle swarm optimization, and when using this algorithm, the optimal design of the double pipe heat exchanger is as follows: the pipe length is 5.6734·10−1 m, the pipe inner diameter is 8.0203·10−3 m, and the pipe outer diameter is 2.2439·10−2 m.

An Analytical Calculation Method and Mechanical Response Laws of Buried Pipelines Subjected to the Impact of Transverse Landslides

When the buried gathering and transportation pipelines cross the landslide area transversally, the migration of the landslide mass can cause the pipelines to be subjected to lateral thrust, which can seriously affect the safe operation of the buried pipelines. In order to study the mechanical response laws of the buried pipelines under the impact of transverse landslides, based on the elastic-plastic foundation beam theory, the mechanical models of buried pipelines are established for three situations, and the analytical solution of pipeline displacement is obtained by genetic algorithm. The influences of landslide thrust, landslide width, soil resistance coefficient, the pipe outer diameter and wall thickness on pipeline peak displacement and peak stress are also investigated. The results show that under the impact of the transverse landslide, with the increase of landslide thrust, the maximum displacement and maximum tensile stress of pipeline increase exponentially, and the failure risk of pipe increases. Secondly, with the increase of landslide width, the maximum displacement of pipeline increases in the beginning and then decreases to be constant, and the maximum tensile stress decreases sharply to be constant. Thirdly, with the increase of soil resistance coefficient, the maximum displacement and maximum tensile stress of pipeline decrease in a negative power trend, and the pipeline is safer. Fourthly, when the pipe outer diameter increases to a certain value, the maximum displacement and maximum tensile stress of the pipeline change very little, hence, pipe outer diameter can be optimized when designing pipe structure. Fifthly, the smaller the pipe wall thickness is, the greater the maximum tensile stress of the pipe is, therefore, pipe corrosion protection should be paid attention to. Sixthly, when the landslide thrust is large, the landslide width is small, or the pipeline outer diameter is small, the maximum tensile stress of the pipeline is located at the centre of the landslide, otherwise, it is located at 0.56L ~ 0.7L away from the landslide centre. In order to ensure the safe operation of the pipeline, the stress state of these two positions should be focused on. It is concluded that the study can provide the basis for the evaluation of pipeline safety status and has practical significance for ensuring the safe operation of buried pipelines.

Analysis of axial force transmission characteristics and contact mechanism of coiled tubing in the spoolable compliant guide during injection

The spoolable compliant guide (SCG) maintains S-shaped dynamic stability in the marine environment. At present, limited studies have been reported on the mechanical laws of coiled tubing (CT) injection by employing SCG. In this study, an experimental platform was developed to simulate the CT injection process in SCG. The axial force transmission characteristics, buckling laws, and contact mechanism of the CT were investigated. The results showed that an increase in the diameter of the inner pipe delayed the occurrence of sinusoidal and helical buckling and improved the transmission efficiency by 13.0%. An increase in the outer pipe diameter showed no significant effect on the efficiency, however, it increased the injection length of the inner pipe by 30.4%. The friction force increased significantly after the helical buckling of the inner pipe. Based on the results, the presented research is beneficial in establishing CT's theoretical framework and enhancing operational effectiveness.

Modelling of thermal shrinkage of seamless steel pipes using artificial neural networks (ANN) focussing on the influence of the ANN architecture

This paper presents two main novel findings. (1) The first finding is the development of an artificial neural network (ANN) model for thermal shrinkage of seamless steel pipes, which represents a new application for ANNs. Mill operators need such fast and accurate models to predict the final pipe outer diameter at ambient temperature based on the hot state immediately after rolling. The goal of this work was to lower the reject rate. However, small relative changes in the diameter are currently difficult to predict by using conventional ANNs. Therefore, a more sensitive target variable and a modified ANN architecture were applied to solve this problem. Data for training and validation were obtained from measurements on a hot-rolling mill. (2) The second finding is based on an investigation performed to determine the number of hidden neurons affected the model response, considering the data used. The knowledge obtained helps to determine the most suitable number of hidden neurons and to prevent overfitting. No generally accepted solution to these problems had previously been proposed in the literature. Consequently, this paper significantly supplements current research studies that describe applications of ANNs.

Steam Boiler Design Using Diesel Motor Exhaust Gas

As it is known that the boiler is a device used to heat water. This research is conducted to propose another alternative in energy saving efforts by utilizing exhaust gas energy from Diesel motors which so far have not received much attention. The exhaust gases is reused to react the boiler. The method used in design this tool uses the literature study method. The data is taken from the exhaust gas of a 9 x 12 x 4 cylinders Diesel engine with a speed of 300 rpm and Mep 80 Psi, engine power (N) 92.4 Hp. From the results of this study, the results show that the size of the steam pipe with pipe outer diameter (OD) is 1 in, spaced 1 in, the number of rows is 2 rows, the number of pipes in one row Z = 12 rows, with carbon steel pipe material SA 106 Grade. Meanwhile, the size and arrangement of the economizer pipes are the outer diameter of the pipe (OD) 1 in, the spacing = 2 in, the number of rows = 6 rows, the total number of pipes Z = 2 x 6 = 12 pieces, the overall length of the pipe is L x 12, the economizer pipe = 644 in, and SA 106 Grade carbon steel pipe material. The thickness of the boiler drum t = 0.245 cm, capacity Q = 536.75 lb/hour, and the boiler drum material is SA 302 Grade B carbon steel.

Numerically analysis of a Phase-change Material in concentric double-pipe helical coil with turbulent flow as thermal storage unit in solar water heaters

This research investigates a 3-D double-pipe helical coil heat exchanger containing Phase-Change Material (PCM) as a thermal storage system in solar water heaters. A concentric double-pipe follows the helical profile upward and creates a heat storage unit. In the unit, water in turbulent mode flows in the inner pipe as a Heat Transfer Fluid (HTF), and RT-50 is considered PCM placed in the annulus. This heat exchanger with all related conditions is modeled in Ansys Fluent 19 software, and we used the k-ε RNG turbulence model to simulate turbulent flow. For evaluating this novel model of thermal storage unit, the impact of some critical geometrical parameters, like helical pitch, inner and outer pipe diameter, and some flow parameters, such as fluid inlet temperature and Reynolds number, have been analyzed. The most important outcomes of the investigation show that inlet temperature and inner and outer pipe diameter are critical factors for the storage system's design. A 1.5 % change in inlet temperature will enhance the melting rate by 27 %. Also, by increasing the inner pipe diameter by 42 %, the melting process was improved by 92 %, while the outer pipe diameter was inversely related to the melting rate. A 20 % increase in this parameter's value showed a 52 % reduction in the melting. Moreover, the change in the helical pitch could not significantly affect the PCM melting process, and for a 300 % increase in pitch size, the melting process increases only by 0.6 %.

Optimasi kinerja reaktor pirolysis biomassa dengan penambahan pipa udara

The pyrolysis reactor is a tool that functions to decompose organic compounds from biomass materials which is carried out by a heating process without or little air with temperatures ranging from 300-600°C. The results obtained from the pyrolysis reactor process are charcoal and liquid smoke. The existing air will accelerate the process of biomass oxidation, but if there is excess air it will cause combustion of the biomass so that most of it will be oxidized and decomposed into smoke and this will cause less charcoal yield. However, without air, the pyrolysis process will take longer. Therefore, an ideal air requirement is needed so that the effectiveness of this biomass pyrolysis process can be maintained because it will produce optimal charcoal and liquid smoke. The purpose of this research is to find out how many air pipes for the pyrolysis reactor are needed in this combustion process and how long the time and temperature of the pyrolysis process combustion and how much charcoal and liquid smoke are obtained. This research was conducted at the Mechanical Engineering Laboratory of the University of Muhammadiyah Metro, this study used a pyrolysis reactor with a diameter of 40 cm, height 50 cm, air pipe diameter inch with variations in the number of 1,3 and 5. Using 8 kg of corncob biomass. Straight pipe condenser with 12 mm diameter copper material 3 m long, outer pipe diameter 4 inch. The results showed that the highest pyrolysis temperature in air pipe 5 was 485°C with a pyrolysis process time of 120 minutes and the lowest temperature in pipe 1 was 353°C with a pyrolysis process time of 185 minutes. The results of the most liquid smoke in air pipe 5 are 0.5 liters or 6.25% and the least liquid smoke results are in air pipes 1 as much as 0.32 liters or 4.0% For the highest charcoal yields in air pipes 1 weighing 4 kg or 50% and for charcoal yields at least on air pipe 5 of 3.2 kg or 42.5%. The highest pH level in the air pipe 1 is 3.43 and the lowest level in the air pipe is 3.11.

Plastic behavior and fracture cross section of coiled tubing in the ram shearing process of subsea blowout preventer

For studying the plastic behavior and fracture cross section of sheared drill pipe are of important aspects for evaluating the rams' shear performance of subsea blowout preventer, the plastic deformation and fracture cross section of drill pipe are analyzed based on the plastic deformation theory and the hypothesis that the deformation process of drill pipe is a four-plastic hinge or an eight-plastic hinge mechanism, respectively, according to different ram structure configuration. The elastic-plastic deformation process of CT90 tube in the simulated shearing process is obtained, the final fracture cross section of CT90 tube is approximately a rhombus circle, which is agreeing with the analytical and experimental results. Furthermore, the structure parameters research shows that ram or pipe structures have limited effect on the peak/terminal value of pipe stress. The major length of rhombus circle increases first and then decreases with the increase of ram's blade mouth thickness, decreases with the increase of ram's V-shape angle and pipe wall thickness, while the minor length shows an opposite trend. The larger pipe outer diameter is, the greater major/minor length of rhombus circle is and the growth rate of major length is significantly faster than that of minor length.

Vibrational analysis of pipes based on the drift-flux two-phase flow model

Linear and nonlinear free vibrations of supported pipes containing two-phase flow were modeled in different flow regimes by including gravitational force, structural and two-phase damping effects. To model the flow, the drift-flux model was utilized. Discretization of the dynamical equation was performed with the help of the Galerkin scheme. The linear vibrational frequency of the system was determined by solving the eigenvalue problem. Also, a mathematical closed-form expression for the nonlinear vibrational frequency is presented. For the validation purpose, theoretical and experimental data were obtained from literature and compared with the results of this work in various operating conditions. A detailed parametric analysis was also carried out to examine the influence of flow parameters, geometry, and physical properties on the dynamics of the system. It was concluded that by increasing the inner and outer pipe diameters, vibrational frequencies of the system decrease and increase, respectively. It was found that a lower liquid phase density leads to an improvement in the vibrational stability of the system. Besides, it was demonstrated that by increasing the void fraction/mixture velocity in the system, linear and nonlinear vibrational frequencies increase/decrease. Furthermore, a higher initial amplitude caused a larger nonlinear frequency shift. The outcomes of the current analysis can be applied as a frame to evaluate and optimize the performance of structures transporting two-phase flows.

Numerical and experimental investigation on a downhole gas-liquid separator for natural gas hydrate exploitation

Natural gas hydrate (NGH) is widely considered as an alternative energy source due to its tremendous reserves, cleanness and high energy density. During the exploitation process, discharging the gas-liquid phase to the surface for separation not only affects the pump performance but also increases the space requirements of the offshore platform. Taking NGH production test data in South China Sea for example, a downhole spiral gas-liquid separator is designed for high gas-liquid ratio (liquid content is less than 10%) in this paper. The forces of droplets in the separator are analyzed and the CFD model for gas-liquid two phase flow is established. The RNG k-ε turbulence model is used for analyzing the velocity field distribution and the pressure field distribution in the separator. The influence of structure parameters (pitch, cycle number of spiral piece, and the outer diameter of spiral pipe) and scale on the separation performance is investigated. The energy loss increases sharply after scaling in the separator and some necessary measures should be taken to avoid the generation of the sale and the secondary hydrate. Based on steepest ascent design, response surface methodology and particle swarm optimization, the optimal structure of the separator with high separation efficiency 87.26% and low pressure drop 2614.19Pa is obtained. The experimental platform is built for testing the gas-liquid separator. The comparison of numerical simulations and experiments show that the calculation model for the hydrate gas-liquid separation is correct and feasible. The separation device with the optimal structural parameters has good separation performance.

Experimental and numerical study of cuttings transport in inclined drilling operations

Directional drilling has become popular in recent decades in both onshore and offshore operations due to reduced drilling costs and improved recovery. In a directional well drilling operation, drill cuttings tend to settle down at the lower side of the inclined annular section. If the generated cuttings are not removed from the hole section properly, it causes a cuttings bed formation in the annular section. Different drilling related problem such as poor rate of penetration, excessive torque and drag, increase differential sticking often associated with a poor hole cleaning which eventually lead to increase in non-productive time (NPT). Therefore, the success of inclined well drilling operation largely depends on effective cleaning of drill cuttings from the annular section. A variety of parameters, including the fluid rheology, mud velocity, cuttings size, drill pipe rotation and drill pipe inclination generally influence the cuttings transport performance. Optimization of these drilling parameters is crucial to ensure proper hole cleaning. In this study, a Computational Fluid Dynamics (CFD) model for the inclined well section is used to investigate the cuttings transport efficiency (CTE). An Eulerian-Eulerian multiphase flow model is proposed and validated with lab scale experimental data. The experiments were performed in a 6.16-m-long annular test section having an outer pipe diameter of 4.5-inch and an inner pipe diameter of 2.5-inch. The setup is equipped with Electrical Resistance Tomography (ERT) system to measure the instantaneous solid volume fraction and a visualization section. A non-Newtonian Heschel-Bulkley (HB) fluid was used as drilling mud and solid glass beads of 2.50 mm–3.00 mm were used as cuttings in the experiment. This study shows a good agreement in visualization of mechanistic three-layer model of cuttings transport in terms of ERT data from experiment and CFD simulation. The validated CFD model is used to perform 5- Factors factorial design and analysis of variance (ANOVA) study. ANOVA shows that the interaction effects of mud velocity-cuttings size, mud velocity-inclination are statistically significant. Finally, this study proposed a statistical model to estimate the CTE of an inclined well considering the two factor and three factor interactions among the variables. Also, the model shows that drill pipe rotation has negligible effect in improving cuttings transport efficiency in the inclined well. The proposed model also reveals that cuttings size and fluid velocity account for 78% contribution in the transport efficiency for an inclined well. Furthermore, an Artificial Neural Network (ANN) method is used to verify the contribution of lower order interaction in the statistical model. Though empirical model shows few lower order two factor interactions (fluid rheology -cuttings size, fluid rheology-inclination), and three factor interactions (velocity-cuttings size-inclination, fluid rheology-cuttings size-inclination); ANN model shows that lower order interaction are significant in model prediction and should not be ignored. The findings of this study can help in better understanding the interaction behaviour among drilling parameters and optimized cuttings transport efficiency in the inclined drilling operation for a wide variety drilling parameters.

A new criterion based on strain determination for dent assessment of pipelines

Dents are one of the most common defects on pipelines and compromise the structural integrity. To date, relevant studies on failure assessment of dented pipelines have been limited, and the existing standard, mainly American Society of Mechanical Engineering (ASME) B31.8, contains major problems, making assessment results not sufficiently accurate and reliable. In this work, a new method based on ductile damage failure indictor (DFDI) criterion combined with improved strain determination by a finite element (FE) model was developed for pipeline dent assessment. Dents with different depths were created by applying a spherical indenter of 100 mm in diameter on a pipe segment of 720 mm in outer diameter and 8.1 mm in pipe wall thickness. The DFDI formula considers the influence of spring-back upon removal of indenter, and the difference between the equivalent strain at dent apex and the maximum equivalent strain at the whole dent area. When the indenter displacement is smaller than 8% of pipe outer diameter, the maximum DFDI can be determined from the equivalent strain at the dent apex. When the initial displacement exceeds 8% of the pipe outer diameter, the maximum equivalent strain at the dent area, which deviates from the dent apex, should be determined by the FE model. Moreover, the limitations of ASME B31.8 in dent assessment were explained.

Boiling simulation and PEC evaluation of helically corrugated tubes in vertical grooves with different pipe diameters

The double tube structure is simulated, R32 in the inner helical corrugated tubes with vertical grooves is heated by the water flowing in the outer tube to make it boil. The influence of pipe diameter and number of vertical grooves on the performance of double tube is analyzed. The evaporation temperature of the refrigerant is 283K. The temperatures of inlet refrigerant and inlet water are 280K and 320K, respectively. The flow velocity of inlet refrigerant and inlet water are 1m/s and 5m/s, respectively. The simulation results show that, compared with the smooth pipe, when the inner pipe diameter is 3, 4, 5, 6, 7mm, the surface heat transfer coefficients of the double tube have been increased by 160%, 150%, 147%, 138%, and 130%, respective. when PEC=1.691, the performance of the inner helical corrugated tube is the best, whose inner pipe diameter is 3 mm, outer pipe diameter is 6.2 mm, number of vertical grooves is 10.

Numerical investigation on sealing performance of drainage pipeline inspection gauge crossing pipeline elbows

AbstractA pipeline inspection gauge (PIG) is routinely passed throughout the long‐distance oil and gas pipelines by pipeline operators to clean the pipeline. Sealing performance is a significant evaluation index for PIG's safety operation. To comprehensively evaluate the PIG's seal performance, nonlinear finite element models were developed, and parametric analysis was conducted in this study. The accuracy of simulation model was validated from numerical and experimental results reported in the literature. The results show that comparing with the pigging in straight pipes, the sealing rubber cups of PIGs can be more easily detached from the pipe wall when passing through elbows, causing smaller sealing areas. For a typical elbow (with curvature radius equals to six times of pipe diameter) widely used in pipeline industry, the minimum sealing area of rubber cup is only 8.07% during common operation conditions. The sealing ability of rubber cups can be obviously enhanced by increasing the curvature radius for the pigging operation of small curvature elbow. Elbow radius slightly affects the cup's sealing behavior when the curvature radius is over six times of pipe's outer diameter. An increment in sealing cup interference can increase the contact area between cup and pipe wall, and the blockage risk of PIGs will be reduced due to the good sealing ability and sufficient driving force. The minimum interference required for the cups is 4% under a most common operation condition; that is, the sealing cup thickness, fluid pressure difference, and friction coefficient are 35 mm, 0.02 MPa, and 0.3, respectively. A proper decrease in sealing cup thickness will reduce the stiffness of rubber cups, indicating that the cups with a smaller thickness are more prone to deformation. Thus, an increase in differential pressure over PIG can enhance the sealing performance of cups when the cups are separated from pipe wall. A large friction coefficient is risky for a safe pigging due to the decrease in sealing region with the increase in friction coefficient. In engineering practice, proper measures should be taken to reduce friction force. Above all, the results obtained in this study provide a reference for the structural design of PIGs.

Buckling resistance of an X80 steel pipeline at corrosion defect under bending moment

This work investigated the resistance of a corroded X80 steel pipe to local buckling at a corrosion defect under bending moment. A nonlinear finite element model was developed to study buckling behavior of the pipe and determine critical bending moment. Parametric effects, including geometry of the corrosion defect (shape, depth, length and width), pipe geometry (pipe outer diameter and wall thickness) and operating pressure, were determined. Results show that pipeline buckling at the corrosion defect depends on the defect geometry. A rectangular corrosion feature results in a lower buckling resistance than a semispherical corrosion pit or a cylindrical grooved corrosion. The depth and width of the corrosion defect are primarily factors affecting the buckling resistance, while the effect of defect length is negligible. The critical bending moment to cause buckling of the pipe, i.e., the critical buckling moment, decreases as the defect depth and width increase. The buckling resistance of the corroded pipe can be improved by increasing the pipe outer diameter and wall thickness. The role of internal pressure in buckling resistance depends on whether a constraint condition is applied at both ends of the pipe. For buried pipelines without sealing ends, the critical buckling moment decreases as the internal pressure increases.