Rod Wear Research Articles

Prediction of Sucker Rod-tubing Wear Depth in Surface Drive Screw Pump Production Wells

With the wide application of ground drive screw pump in the process of oil production, the wear problem of screw pump sucker rod-tubing is becoming more and more prominent. In order to systematically study the wear of the rod and tube of the screw pump production well and quantify the wear of the rod and tube, this paper establishes a calculation model of the contact force of the screw pump sucker rod by analyzing the force of the rod and tube string in the three-dimensional wellbore trajectory. Based on the indoor rod and tube wear simulation experiment, combined with the wear efficiency theory, a prediction model of sucker rod-tubing wear under different working conditions was established, and an example well calculation was carried out. The results show that the force of sucker rod is mainly affected by sucker rod size, submergence degree and other factors, and the wear of sucker rod and tubing is mainly affected by working time, rotational speed and wear efficiency. The research results can not only accurately carry out accurate quantitative calculation of downhole rod and tube wear, but also provide theoretical and technical basis for prediction of rod and tube wear depth.

Long-term simulation of an industrial coke breeze grinding circuit

One important application of rod milling is in size reduction of coke breeze, which is used as solid combustible in iron ore sintering plants. The work applies modeling and simulation of an industrial circuit comprised of a flip-flow screen and a rod mill to predict the circuit response in long-term operation, following the strategy used in the plant of replacing the rod charge only when it reaches the end of its life. Initially, the model for rod wear has been calibrated and the mill fillings estimated. Then the mill model has been validated with data from several industrial surveys, showing good agreement between the two. A long-term (approximately three-month) pseudo-dynamic simulation was then carried out to mimic the strategy normally used in plant operation. Additional simulations were then carried out to compare different scenarios of operation, demonstrating the benefit of increasing the rod charge and diameter, in particular when associated with operation of the mill at lower speed in the beginning of the charge life and progressive increase thereafter, besides partially replacing worn rods in their midlife. For instance, simulations showed that an increase in initial mill filling from 15 to 20 %, progressive increase in fraction of critical speed from 0.40 to 0.65 in contrast to operation at constant speed and gradual reduction of throughput from 60.0 to 40.2 t/h resulted in 56 % increase in charge lifetime, 35 % reduction in variability in product quality and 12 % reduction in cost of operation per ton of coke breeze produced.

Wear analysis and life prediction of sucker rod and tubing under ternary emulsion lubrication in Daqing oilfield: a case study in block H

Daqing Oilfield as the world’s largest application area of alkali–surfactant–polymer (ASP) flooding, in recent years, with the increase in aging wells, the eccentric wear and deformation of sucker rod and pipe during oil production has become more and more serious. In order to study the effect of emulsion lubrication in ternary composite flooding on eccentric wear of sucker rod and tubing, this paper establishes a calculation model for the depth of tubing wear under different emulsion lubrication conditions through indoor friction and wear experiments combined with White and Dawson wear efficiency theory. Based on this, the finite element method is used to predict the safe wear life of tubing under different component emulsion lubrication. The results show that compared to intact oil pipes, the residual internal pressure strength of oil pipes with defects decreases, and stress concentration occurs at the edges and middle of the defects. The wear life of oil pipes decreases with the increase in pump depth and wear coefficient under emulsion lubrication. The water content and alkali concentration have the most significant effects on the wear life of oil pipes under emulsion lubrication conditions. The safe wear life of sucker rod pipes under emulsion lubrication with a water content of 75% will be increased by 37.8% compared to those in emulsion lubrication with a water content of 95%, and under emulsion lubrication with an alkali concentration of 500 mg/l, the safe wear life will be increased by 50.6% compared to those in emulsion lubrication with a concentration of 2000 mg/l. The research results can provide theoretical and technical support for oilfield enterprises to reduce rod and pipe wear in ASP flooding oil wells, improve the pump inspection cycle of pumping wells, and ensure the safety of oil well work.

Experimental Investigation on the Penetrability Mechanism of Gel Slug During Well Completion Processes.

Reservoir formation damage is an essential problem which troubled oil and gas well production, a smart packer is a promising technology to maintain sustainable development for the oil and gas fields. Currently, the "gel valve" technology has been proved to be feasible with gel slug to seal casing and descend the completion pipe string, while the systemic performance of ideal gel is still not clear. In the underbalanced completion stage with the gel valve, the downward completion string needs to penetrate the gel slug to form an oil and gas passage in the wellbore. The penetration of rod string to gel is a dynamic process. The gel-casing structure often shows a time-dependent mechanical response, which is different from the static response. In the process of penetration, the interaction force between the rod and gel is not only related to the properties of the interface between gel and string but also affected by the moving speed, rod diameter, and thickness of the gel. The dynamic penetration experiment was carried out to determine the penetrating force varied with depth. The research showed that the force curve was mainly composed of three parts, the rising curve of elastic deformation, decline curve for the surface worn out, and another curve of the rod wear into. By changing the rod diameter, gel thickness, and penetration speed, the change rules of forces in each stage were further analyzed, which would provide a scientific basis for a well completion design with a gel valve.

Numerical simulation model of reciprocating rod seal systems with axial wear texture on rod surface

AbstractIn this paper, a simulation model of reciprocating rod seal systems when there is axial texture on the rod surface due to wear is studied. The model includes macroscopic solid mechanics analysis, microscopic contact mechanics analysis and fluid mechanics analysis, and on this basis, the change of surface pressure when the sealing ring fall into a texture is calculated by the micro‐deformation mechanics analysis of the seal surface. Then, the stiffness matrix method is used to find the film thickness when the three pressures in the sealing area are in equilibrium, completing the fluid–solid coupling calculation. Combined with the above simulation process, the performance parameters of the sealing system such as leakage and friction can be obtained. Results show that axial texture will degrade sealing performance, which increases leakage and friction. The simulation results can quantitative characterise the influence of rod wear on sealing performance and provide some theoretical basis for the study of seal failure mechanism and prediction of seal life.

Optimization of control rod travel for a small pressurized water reactor

The flexible operating conditions of small pressurized water reactors (SPWRs) demand frequent movement of control rods, causing a serious problem of control rod wear and tear. This study focused on the optimization of the control rod travel for an SPWR. Three optimization strategies were proposed to improve the reactor power control scheme by introducing proportional-derivative, lead–lag, and incomplete differential control modules in the power deviation channel, and a weighting factor in the temperature deviation channel. The parameters of the three control modules and the weighting factor were tuned using the non-smooth optimization algorithm in MATLAB. The optimization strategies were implemented in a control simulation platform of the SPWR, based on which dynamic simulations of the SPWR were performed under typical load change transients at different power levels. The results demonstrate that the optimization strategies can significantly reduce the control rod travel of the SPWR with satisfactory control performance.

A study on the wear allowance of a railway vehicle hydraulic damper

Railway vehicle hydraulic dampers are usually subject to wear-induced premature failures, so it is meaningful to evaluate the wear allowance of the hydraulic damper. Mathematical modelling of damping characteristics of a railway vehicle hydraulic damper under wear conditions is carried out, the model describes the functions of main damping characteristics indices vs. inner tube wear M1 and rod wear M2 . Simulation is then performed using the model, and indicates that increase of M1 would lead to significant drop of the maximum extension damping force, fading of the damping coefficient and significant rising of the damping force asymmetry rate, but the maximum compression damping force keeps to be constant, while increase of M2 would lead to significant drop of almost all of the indices except for the asymmetry rate. A wear allowance line for the damper is finally obtained when both of M1 and M2 work in real situations, the area enclosed by the wear allowance line and two axles is a safe area, any dot with a combination of M1 and M2 outside the safe area means the damper has exceeded its wear allowance and should be maintained or replaced. The mathematical model and the wear allowance line obtained in this work can be used for health status evaluation and design optimization of railway hydraulic dampers.

Robust design of fuel rods against potential structural damage by flow-induced vibration

We studied the flow-induced vibration (FIV) and fretting wear of fuel rod with grid relaxation. According to the flow distribution around a type of pressurized water reactor (PWR) fuel rod, the power spectral density (PSD) is obtained to characterize the turbulence excitation. By combining the correlation of PSD test parameters, the mean square value of the vibration displacement of each rod mode is found, and then the wear depth of dimple position is calculated based on the ARCHARD wear formula. The grids may relax due to inaccurate manufacturing, fuel transportation and in-core irradiation. The absence of grid clamping force would significantly influence the rod mode and thereby changes its FIV responses. Simulation results show that the failure of the leaf spring has negligible effect on the rod natural frequency whereas the dimple failure near the location with larger FIV amplitude has a much significant effect. The lateral flow velocities at the inlet and outlet of the core are larger. For the fully clamped fuel rod, the responses amplitude of turbulent excitation at the bottom and top of the fuel rod are larger. This is even more obvious with a failed dimple at these locations. Comparatively, the effect of dimple support failure in the middle is less influential. The influence of dimple support failure on the rod wear depth depicts basically the same trend as on the maximum FIV amplitude.

Research on Paraffin Deposition Law and Paraffin Removal-Prevention Technology of Rodless Lifting Wellbore

The rodless lifting technology can overcome the shortcomings of rod and tube wear, high energy consumption and heavy maintenance workload in the lifting process of rod pumps, which is gradually being developed and adopted by major oil fields around the world. However, the paraffin deposition is coming more and more serious duo to non-sucker rod disturbance in wellbore and the relatively slow flow rate of well fluid, the production and maintenance cost are increasing, the pump inspection cycle is shortened, which creates a bottleneck for the further popularization of rodless lifting technology. Therefore, the research and development of rodless lifting oil well paraffin removal-prevention technology is great significance to the application and promotion of rodless lifting technology. Based on the study of paraffin deposition in oil wells, the effects of paraffin content, fluid flow rate, gelatin, wall temperature and other factors on paraffin deposition in crude oil are analyzed, to discuss the internal relationship. By the laboratory tests, the mathematical model of paraffin deposition in rodless lifting wellbore is obtained. Field tests were carried out to verify the paraffin control effect of the developed solid paraffin inhibitor matched with the paraffin deposition law and mathematical model of rodless lifting wellbore. Field tests show that the period of heat-free washing of rodless lifting wells is more than half a year after the application of solid paraffin inhibitors, and the effect of paraffin control is obvious. The research and development of paraffin removal and prevention technology is of great significance to the popularization and application of rodless lifting technology. The research and development of paraffin removal-prevention technology is important for the popularization and application of rodless lifting technology.

Fretting wear comparison of cladding materials for reactor fuel cladding application

Relative motion between the fuel rods and fuel assembly spacer grids can lead to excessive fuel rod wear and, in some cases, to fuel rod failure. Based on industry data, such grid-to-rod-fretting is a significant cause of fuel failures in U.S. pressurized water reactor power plants. Kanthal advanced powder metallurgy technology or APMT, an FeCrAl steel alloy, and a braided SiC fiber, Chemical Vapor Infiltration SiC matrix (SiC/SiC) cladding by General Atomics are possible alternatives to conventional fuel cladding in a nuclear reactor due to their favorable performance under accident conditions. Tests were performed to examine the reliability of the cladding candidates and a conventional cladding, Zircaloy-4, under dry fretting conditions at elevated temperature. The contact was simulated with a rectangular and a cylindrical specimen over a line contact area. Confocal scanning laser microscopy was used to obtain a 3D map of the surface, which was in turn used for wear and work rate calculations on the samples. The wear rate coefficient was used as a measure of the performance and wear under fretting. Additionally, Energy Dispersive Spectroscopy was performed to qualitatively describe the microchemical changes the material undergoes during fretting. While APMT steel and SiC/SiC can perform favorably in loss of coolant accident scenarios, they also need to perform well when compared to Zircaloy-4 with respect to fretting wear. Wear coefficient measurements showed that APMT steel performs favorably in comparison to Zircaloy-4 with respect to fretting wear.

The simulation model of sucker rod string transverse vibration under the space buckling deformation excitation and rod-tubing eccentric wear in vertical wells

Considering the limitations of the static buckling theory on the eccentric wear of sucker rod and tubing, a new dynamic analysis method for the transverse vibration of sucker rod in the tubing is proposed. Taking the axial distribution load at the rod body and the dynamic load at the bottom into account, the dynamic model of transverse vibration is established based on the space buckling configuration of rod string which regarded as the deformation excitation during the down stroke. To solve the mathematical equations, the finite difference method is used to discretize the well depth, and the Newmark-beta method is used to discretize the time. Meanwhile, a restitution coefficient is introduced to depict the change of velocity and the momentum after the collision. The result shows the phenomenon of rod-tubing collision occurs mainly in the down stroke after the rod string post buckling; the collision force from the wellhead to the bottom increases gradually, of which distributed almost along the entire well depth; and the high frequency collision occurs below the neutral point where the collision force is also the biggest. Further, the collision frequency and the collision force decrease successively from the neutral point to the wellhead direction. But during the up stroke, few collisions occur, and the collision force is also very small. The simulation model is suitable for the eccentric wear analysis of rod-tubing, and provides a new theoretical basis for the optimal allocation of the centralizer.

The numerical simulation of entire sucker rod string buckling with couplings in vertical wells

A new model is built to study the buckling of a rod string with couplings in the vertical well considering two important loads: the axial distribution load along the rod and the concentrated load at the bottom. Firstly, the calculation method for the axial distribution load of the sucker rod string is established based on a wave equation of longitudinal vibration. And, the simulation results show that the axial distribution load of sucker rod string has an obvious non-uniform distribution characteristic. The friction force between the plunger and the pump barrel (FFPPB), which is an important part of the concentrated load at the bottom, is improved based on both the Newtonian fluid (NF) and the non-Newtonian power law fluid (NNPLF) by using the Flunent software. In view of the above improvement of the computational method, a simulation model of the entire rod string buckling with couplings is established. Under the assumption that the coupling is taken as a radial constraint boundary, the two-point boundary value problem (BVP) algorithm is used to solve the differential equation, and the least square method is used to establish the continuity conditions on the supporting point of coupling. The simulation results show that the eccentric state of the plunger (eccentricity ratio $$\upvarepsilon =0\sim 1$$) has a significant influence on the eccentric wear area between the rod-tubings, which should be taken into account in the practical calculation. And compared without couplings, the contact pressure between the sucker rod string and the tubing is transferred to the couplings, which fits the engineering reality. Further, the simulation result implies the centralizers should be installed firstly near the couplings in order to protect the couplings better. The new method lays the theoretical foundation for the further studying the rod wear life and the design of the eccentric wear prevention.

Fretting Wear Behavior of APMT Steel at 350°C for Reactor Fuel Cladding Application

ABSTRACTIn support of a recent surge in research to develop an accident tolerant reactor, accident tolerant fuels and cladding candidates are being investigated. Relative motion between the fuel rods and fuel assembly spacer grids can lead to excessive fuel rod wear and, in some cases, to fuel rod failure. Based on industry data, grid-to-rod-fretting (GTRF) has been the number one cause of fuel failures within the U.S. pressurized water reactor (PWR) fleet, accounting for more than 70% of all PWR leaking fuel assemblies. APMT, an Fe-Cr-Al steel alloy, is being examined for the I2S-LWR project as a possible alternative to conventional fuel cladding in a nuclear reactor due to its favorable performance under LOCA conditions. Tests were performed to examine the reliability of the cladding candidate under simulated fretting conditions of a pressurized water reactor (PWR). The contact is simulated with a rectangular and a cylindrical specimen over a line contact area. A combination of SEM analysis and wear & work rate calculations are performed on the samples to determine their performance and wear under fretting. While APMT can perform favorably in loss of coolant accident scenarios, it also needs to perform well when compared to Zircaloy-4 with respect to fretting wear.

Large-eddy simulation, fuel rod vibration and grid-to-rod fretting in pressurized water reactors

Grid-to-rod fretting (GTRF) in pressurized water reactors is a flow-induced vibration phenomenon that results in wear and fretting of the cladding material on fuel rods. GTRF is responsible for over 70% of the fuel failures in pressurized water reactors in the United States. Predicting the GTRF wear and concomitant interval between failures is important because of the large costs associated with reactor shutdown and replacement of fuel rod assemblies. The GTRF-induced wear process involves turbulent flow, mechanical vibration, tribology, and time-varying irradiated material properties in complex fuel assembly geometries. This paper presents a new approach for predicting GTRF induced fuel rod wear that uses high-resolution implicit large-eddy simulation to drive nonlinear transient dynamics computations. The GTRF fluid–structure problem is separated into the simulation of the turbulent flow field in the complex-geometry fuel-rod bundles using implicit large-eddy simulation, the calculation of statistics of the resulting fluctuating structural forces, and the nonlinear transient dynamics analysis of the fuel rod. Ultimately, the methods developed here, can be used, in conjunction with operational management, to improve reactor core designs in which fuel rod failures are minimized or potentially eliminated. Robustness of the behavior of both the structural forces computed from the turbulent flow simulations and the results from the transient dynamics analyses highlight the progress made towards achieving a predictive simulation capability for the GTRF problem.

Mechanism and Control of Eccentric Wear of Sucker Rod

The issue of eccentric wear of sucker rod is not only reduce the strength of the sucker rod that results to sucker rod breaking, but also wear out the pipe leading to leakage of tubing, which impact the regular production of the well. This paper aims at the popular issue in-site, analyze the factors such as wellbore deviation, stroke and fluid viscosity, tested the effect of water content, submergence on the eccentric wear by the laboratory experiment. The mechanism of eccentric wear of sucker rod is studied based on the factors impact the deformation under the stress and displacement constraints. An advanced technique is proposed to prevent eccentric wear based on the theory of hydraulic lubrication theory. It can make wedge form gap formed between sucker rod and tubing with the special tools, so that prolong the life of the well.

Effect of Flow Characteristics of Polymer Flooding Produced Liquid on Attrition of Sucker Rob and Tube

Because of complex flow characteristics, polymer flooding produced liquid can bring many problems such as serious eccentric wear of rod and tube, breaking and divorcing of rod, and shortened cycle of pump-check. Flow resistance experiment was carried out aimed at these problems. Experimental results show that on-way resistance that sucker rod acts on polymer flooding produced liquid mainly depends on the viscosity of liquid and its elasticity can be ignored; Local resistance caused by couplers and centralizers is mainly related to the velocity of produced liquid, while the effect brought by mass concentration can be neglected; Resistance that pump valve endued and rate of flow agree to the exponential law; Total resistance of pump valves is generated mainly by down-valve and the law of resistance that water and polymer solution act on valves are similar. The problems that eccentric wear of rods and tubes is serious and the cycle of pump-check is shortened are not completely caused by up stress increasing after polymer flooding.

Causes Analysis of Eccentric Wear of Sucker Rod in Produced Fluid with Polymer

After polymer flooding was put into effect in DaQing oilfield, eccentric wear of sucker rod and tubing has been so serious that it made the rods break. This is because production liquid produced from normal wells is pure viscous fluid while liquid produced from polymer flooding oil wells is viscoelastic fluid. The flow equation of viscoelastic fluid in eccentric annulus was established in cylinder coordinate system, and the velocity distribution was solved. Based on upper-convected Maxwell constitutive equation, the normal stress calculating model of viscoelastic fluid acting on sucker rods was established. The normal stress of viscoelastic fluid acting on inner rod in eccentric annulus was measured under different experimental conditions indoors. The result proves that normal stress is the main reason of eccentric wear.

Velocity Distribution of Viscoelastic Fluid Axial Flowing in Eccentric Annulus Based on the Upper-Convected Maxwell Model

After polymer flooding has been put into effect in Daqing oilfield, eccentric wear of sucker rod and tubing has been so serious that it made the rods break. In order to analyze the cause of eccentric wear based on the upper-convected Maxwell model, the flow equation of viscoelastic fluid in eccentric annulus was established in cylinder coordinate system. Then the equation was transformed in bipolar coordinate system and dispersed by control-volume method. The velocity distribution was solved by ADI methods and example was calculated which provides theory basis for solving eccentric wear problems.

Application and Design of Plunger Pump Lifting Viscoelastic Fluid

Daqing Oilfield has more than 10,000 million kilograms of oil through tertiary recovery every year. However, eccentric wear of sucker rod and tubing severely impede the implementation effectiveness and large-scale utilization of tertiary oil production when injecting viscoelastic fluids containing polymer. Therefore, a plunger pump lifting viscoelastic fluid is designed based on the analysis of the mechanism of eccentric wear. The principle to reduce eccentric wear is increasing hydraulic and viscoelastic friction, and expanding clearance. Due to make use of the plunger pump lifting viscoelastic, laboratory experiment and field application have demonstrated effective reduction of eccentric wear, extend the life of the sucker rod and tubing, and improve pump efficiency.

Evolution of wear, roughness, and friction of Alloy 600 superalloy surfaces in water-submersed sliding

Self-mated wear and friction of Alloy 600 superalloy was studied in a water-submersed ring-on-rod configuration, loading the side of a 6.35 mm diameter rod across the flat surface of a rotating annular ring of 100 mm outer diameter and 70 mm inner diameter producing two sliding contacts along the ring. Tests were conducted at sliding speeds of 0.178 and 0.330 m/s for sliding distances of 100 m. Normal loads of 51 and 204 N were applied, and initial R a surface roughnesses of the rings along the sliding direction were either smooth (∼0.2 μm) or rough (∼7.5 μm). Increased initial ring roughness caused a ∼20-fold increase in rod wear at the lighter load, whereas at the heavier load increased initial roughness only caused a ∼4-fold increase in wear. At lower initial ring roughness the 4-fold decrease in normal load caused a large (one order-of-magnitude) decrease in rod wear, whereas for rings of higher initial roughness the 4-fold decrease in normal load caused only minor (2-fold or less) decreases in rod wear. Wear during this 100 m sliding distance only experienced a minor effect from the 1.8-fold change in sliding speed, as did friction. In all cases friction coefficient rapidly settled into the range 0.6–0.7, except in the cases of lower load on rings of lower initial roughness where friction coefficient remained above 1 for most of this sliding duration. At this lower load the initial ∼0.2 μm rod roughnesses increased to nearly 0.8 μm by the 100 m sliding distance, whereas at the higher load this same sliding distance resulted in roughnesses returning near to the initial 0.2 μm. It was hypothesized more highly loaded cases also went through initial roughening prior to smoothening back to 0.2 μm roughness within the 100 m sliding distance, and given additional sliding the more lightly loaded cases would also experience subsequent smoothening. Increasing sliding distance to 400 m, roughnesses indicated a smoothening back to 0.2 μm level during those lightly loaded tests, with friction coefficient correspondingly dropping from 1 into the 0.6–0.7 range observed in all other cases. Extended sliding to 400 m at light loading against rings of lower initial roughness also allowed a rod wear rate which increased with increased sliding distance to be observed, approaching the same rate observed against initially rough rings within the 100 m sliding distance.