Fiberglass Rods Research Articles

Bistatic synthetic aperture sonar images of penetrable cylinders.

Bistatic synthetic aperture sonar (SAS) and acoustic holographic images and monostatic backscattering by penetrable tilted cylinders in water were investigated. Refracted rays internally reflected from the cylinder’s backside often dominated the scattering. Ray theoretic models predict scattering enhancements for cylinders made of some isotropic and anisotropic materials. Experiments involved solid cylinders and liquid-filled cylindrical shells of polymers and fiberglass. The experiments used transient insonification and ka in the range of 9<ka<40, where ka is a product of the acoustic wave number and the cylinder radius. Bistatic measurements used a hydrophone scanned along a line. Transversely isotropic fiberglass rods produced rich features in the images and in the backscattering plotted as a function of tilt and time. The timing of some features could be explained from a ray model based on properties of quasi-shear and quasi-longitudinal waves computed from the stiffness matrix measured for the fiberglass. Bright features for solid cylinders and liquid-filled shells were typically associated with refracted waves having phase velocities less than the speed of sound in water. For some tilt angles, radiated wavefronts were relatively flat producing enhanced farfield scattering. [Work supported by ONR.]

Torsional vibrations and dispersion of torsional waves in orthotropic composite rods

The Barr’s refined theory of torsional vibrations of isotropic rods of noncircular cross section is generalized for an orthotropic material. An analysis of natural frequencies of torsional vibration of free-free orthotropic prismatic rods of rectangular cross section is carried out with the help of an exact solution of the frequency equation. For orthotropic CFRP and GFRP rods, the improved theory, which takes into account the normal stresses and inertia forces in the axial direction, in some cases, predicts a noticeable raise in the natural frequencies compared with those following from the Saint-Venant classical theory. A good agreement is obtained between the experimental and calculated values of natural frequencies of torsional vibrations of rectangular quartz and fiber glass rods. The dispersion of torsional waves in an orthotropic quasi-homogeneous rod is considered.

FRP Z-Spike Repairing of Wood Railroad Crossties

Load tests of the effect of fiber-reinforced polymer (FRP) reinforcing rods (Z-spikes) on the flexural stiffness of deteriorated railroad crossties were conducted. Reinforcement was provided by installing 13 mm (0.5 in.) diameter polyglass polyester resin fiberglass rods bonded in place using epoxy-resin. The Z-spikes were inserted into the deteriorated railroad crossties perpendicular to the primary bending axis to provide horizontal shear reinforcement and improve flexural stiffness. They were installed in pairs starting at each end of the crosstie specimen and moving inward. A total of ten rows were sequentially inserted into each crosstie specimen with load tests performed after each successive row installation. Results from load tests show an average increase in effective flexural stiffness (EI) of 58% with all ten rows of shear spikes inserted into the crossties.

Influence of interface surface conditions on indentation failure of simulated bonded ceramic onlays

This study aims to evaluate the influence of surface roughness and acid etching on interfacial failure load and fracture initiation site for simulated resin bonded ceramic restorations. Layered disks were fabricated using soda lime glass to simulate porcelain and fiberglass to represent dentin. These materials were selected due to their approximate elastic modulus to porcelain or dentin. In addition, soda lime glass allowed for visualization of crack initiation. Glass microscope slides (1.2 mm thick) were sectioned into 1-mm2 specimens. The frosted portions of the slides were used as the rough or sandblasted group and the clear areas were used as the smooth or polished group. All surfaces were either cleaned or etched. Prepared surfaces were divided into eight groups and bonded to the substrates using Optibond Solo Plus (SDS Kerr, Orange, CA) and Nexus resin cement (SDS Kerr). Support substrates were made from 5-mm slices of fiberglass rods (1/2 in. diameter). Vertical loads were applied to the layered disks with a 20-mm spherical indenter at a cross-head speed of 0.05 mm/min. Observations were made using 10x magnification with a video monitor. Load magnitudes were recorded at the time of crack initiation. Weibull parametric survival analysis and the effect likelihood ratio test were performed on the failure initiation load data to determine significant differences at the 0.05 level. Mean failure initiation loads ranged from 273.6 to 341.9N for the rough specimens and from 1056.5 to 2980.2N for the smooth samples. According to the Weibull parametric survival analysis and the effect likelihood ratio test, surface roughness and surface etch significantly influenced failure initiation loads. Smoother surfaces tolerated much greater contact loads before failure initiation. The clinical performance of all-ceramic restorations may be improved with smoother internal surfaces. Etching significantly increases survival for restorations with smooth internal surfaces.

BIOMECHANICAL COMPARISON OF EFFECTS OF SUPRASPINATUS TENDON DETACHMENTS, TENDON DEFECTS, AND MUSCLE RETRACTIONS

Rotator cuff ruptures are frequently associated with loss of strength of the shoulder. However, the characteristics of the rotator cuff tear that are responsible for the loss of force generation and transmission have not yet been identified. The purpose of this study was to compare the effects of supraspinatus tendon detachments, tendon defects, and muscle retractions on in vitro force transmission by the rotator cuff to the humerus. The rotator cuff tendons from ten cadaver shoulders were loaded proportionally to the respective cross-sectional areas of their muscles. A fiberglass rod was cemented into the medullary canal of the humerus and connected to a three-component load cell for the measurement of the forces transmitted by the rotator cuff to the humerus. This study was performed with the humerus in a hanging arm position and with various sizes of supraspinatus tendon detachments, tendon defects, and muscle retractions. Detachment or creation of a defect involving one-third or two-thirds of the supraspinatus tendon resulted in a minor reduction in the force transmitted by the rotator cuff (< or =5%), while detachment or creation of a defect involving the whole tendon resulted in a moderate reduction (11% and 17%, respectively). Simulated muscle retraction involving one-third, two-thirds, and the whole tendon resulted in losses of torque measuring 19%, 36%, and 58%, respectively. Side-to-side repair of the one-third and two-thirds defects nearly restored the force transmission capability, whereas a deficit remained after side-to-side repair following complete resection. Our results support the rotator cable concept and correspond to the clinical observation that patients with a small rupture of the rotator cuff may present without a loss of shoulder strength. Muscle retraction is potentially an important factor responsible for loss of shoulder strength following large rotator cuff ruptures. Supraspinatus muscle retraction diminishes glenohumeral abduction torque significantly more than either a defect in the tendon or a simple detachment of the tendon from the tuberosity. In cases of irreparable defects, side-to-side repair may be worthwhile to restore muscle tension and the integrity of the rotator cable.

A new type of radially cooled helices designed for a 25 T magnet

We designed a new magnet yielding a field of 25 T in a 50 mm room temperature bore for a consumed power of 11.2 MW. It consists of four coils electrically in series and hydraulically in parallel. The two outer coils are Bitter stacks which deliver together 14.7 T in a diameter of 163 mm. Two helics made of CuCrZr alloy with an elastic limit of 360 MPa and an electrical conductivity of 85% IACS constitute the inner part of the magnet. The helices are cut out of cylindrical tubes with an electrical discharge machine and produce a field of 10.4 T in 58 mm. The insulation between turns is obtained by a number of 125 /spl mu/ thick sectors of Kapton, which are maintained by two fiber glass rods. The spaces between the insulators constitute the channels for radial cooling. The high water velocity (about 21 m/s) in the channel results in a relatively low average temperature for the copper. Since July 1994 the magnet has been in operation for several hundred hours and its performance is very encouraging. Presently, it is the only magnet in our facility in which more than 10 MW is dissipated.

Managing Artificial Lift

Distinguished Author Series Summary The goal of this work is to describe an approach to produce a well for maximum profitability by managing artificial lift effectively. Achieving maximum profitability from an artificially lifted well begins with selecting the lift method and continues with selecting materials, protecting materials, monitoring production data, and monitoring equipment performance. Changes suggested by the monitoring process strive to increase the profitability on an individual well basis. Introduction Managing artificial lift is a continuous process designed to achieve maximum profitability from a producing or service well. We must keep in mind our ultimate goals.Maximum profits, not maximum hydrocarbon production; one does not always mean the other.Maximum profits, not minimum equipment failures; again, one does not always mean the other.Maximum profit within the scope of operating safely and in an environmentally sound manner. The purpose of this paper is to detail an approach to managing artificial lift. This approach is described as a series of steps. Step 1. Original selection of the artificial-lift method. Step 2. Evaluation of production factors and expected production problems. This evaluation results in the selection of the original equipment used in the well, the failure-control methods, and the monitoring deemed necessary for protecting well equipment. Step 3. Continuous monitoring of meaningful production data: rates, fluid levels, water cuts, amp charts, pressures, etc. Step 4. Continuous monitoring of equipment performance data. Step 5. Evaluation of the production equipment-failure data regularly and as needed. This monitoring/evaluation results in courses of action that may include operational changes. Changes in the lift type might be from rod pump to progressing cavity pump or vice versa, from continuous to intermittent gas lift, or from rod pump to electric submersible pump (ESP) or vice versa. Equipment changes could include moving from a bottom hold down to a top holddown rod pump, from an insert to a tubing pump, or from steel to fiberglass rods. Another possible equipment change would be to add or remove a gas separator onan ESP system. Alterations in the failure-protection method might include changing from batch to continuous downhole corrosion treatment or vice versa, starting a scale-control program, changing the pump metallurgy or the ESP cable type, or running a cable with a chemical treating string. A change in the way the well is produced could be indicated, such as increasing or decreasing the stroke speed or changing the stroke length, raising or lowering the pump, anchoring the tubing, using a variable-speed drive on an ESP to reduce water production, or changing the type of power fluid in a hydraulic pumping installation. Thus, the loop is closed; the evaluation can, and sometimes does, take us back to where we started-e. g., to artificial method selection or, in some cases, to replacement/substitution. If it is to achieve its goal of maximum profitability, the process must look at each well individually. Well-by-well economics is the basis of the process. Artificial-Lift Selection The selection of the lift method considers the following. Geographic location. An offshore and/or Arctic location can limit the viable lift methods through size/weight restrictions or environmental concerns. Capital cost. These include not only the lift equipment, but also the production facilities required to support the lift method (e.g., compression requirements for gas lift). Operating costs. These costs include the energy needed to operate the lift and the cost to repair lift-system failures. Production flexibility. This means evaluating the minimum and maximum rates available from the lift method based on normal operating conditions compared with expected production. Reliability. Reliability includes expected run time and is a function of the failure frequency and the logistics required to repair failures. P. 335^

Differential equations governing slip-induced pore-pressure fluctuations in a water-saturated granular medium

Macroscopic frictional slip in water-saturated granular media occurs commonly during landsliding, surface faulting, and intense bedload transport. A mathematical model of dynamic pore-pressure fluctuations that accompany and influence such sliding is derived here by both inductive and deductive methods'. The inductive derivation shows how the governing differential equations represent the physics of the steadily sliding array of cylindrical fiberglass rods investigated experimentally" by Iverson and LaHusen (1989). The deductive derivation shows how the same equations result from a novel application of Biot's (1956) dynamic mixture theory to macroscopic deformation. The model consists of two linear differential equations and five initial and boundary conditions that govern solid displacements and pore-water pressures. Solid displacements and water pressures are strongly coupled, in part through a boundary condition that ensures mass consereation during irreversible pore deformation that occurs along the bumpy slip surface. Feedback between this deformation and the pore-pressure field may yield complex system responses. The dual derivations of the model help explicate key assumptions. For example, the model requires that the dimensionless parameter B, defined here through normalization of Biot's equations, is much larger than one. This indicates that solid-fluid coupling forces are dominated by viscous rather than inertial effects. A tabulation of physical and kinematic variables for the rod-array experiments of lverson and LaHusen and for various geologic phenomena shows that the model assumptions commonly are satisfied. A subsequent paper will describe model tests against experimental data.

Fiberglass Sucker Rod Design Considerations

Abstract Artificial lift systems using fiberglass sucker rods were initially developed in 1973, as a means of reducing steel rod failures in sour and very corrosive pumping wells. It soon became apparent that fiberglass had other advantages over steel rods, such as:increased production due to pump overtravel;reduced surface pumping system stresses; anddecreased lifting costs. After some initial problems with rod quality control, poor string design, and misapplications. Fiber glass systems have become a reliable method of artificial lift. Fiberglass systems have become more widely used recently due to low capital cost requirements and lower operating costs, compared to other lift systems. However, a more rigorous design procedure must be used compared to steel sucker rod systems. An optimum procedure utilized by Petro-Canada is outlined in this paper. Petro-Canada's experiences with fiberglass systems are Discussed, including the use of a specially designed pumping unit made to maximize fiberglass rod benefits in a "total system" design approach. This pumping unit was the first of its type to be operated in Canada. Introduction The use of fiberglass sucker rods in pumping oil wells was pioneered in West Texas in the early 1970s(l). While the rods were initially developed to reduce corrosion related failures, the light weight and elastic properties of fiberglass were identified as a solution to increasing fluid production rates in beam pumping wells, without upgrading the surface lift equipment. The first generation of fiberglass rods were manufactured between 1975 and 1978. These rods were highly susceptible to failure and, as a result, were not widely used. The two main problems with these early rods were: rod body breaks and end fitting pinch-off of the metal pins(2). The rod body breaks resulted mainly from looping or knotting of the glass fibers during manufacturing, causing a weak point that failed under stress. Improved processes developed to maintain the glass fibers in tension during manufacturing overcame this problem. The end-fitting pinch-offs were eliminated by re-designing the pin to better distribute the load into the rod and by improved epoxy application between the metal and fiberglass. These second generation rods began to appear in 1979 and have proven to be reliable in the field. Other major problems with the installation of early fiberglass rods included poor string design and misapplication(3,2) Many premature failures were caused by the overloading of the fiberglass rods. This overloading resulted primarily from inaccuracies in the calculation of the system stresses. These inaccuracies were due to the modification of the empirical API technique, which had been developed for steel rods, to handle fiberglass systems(4). It was not until development of a computer program from first principles of Hooke's Law that system stresses could be satisfactorily estimated. Advantages of Fiberglass Over Steel Sucker Rods Reduced Corrosion Failures In pumping wells where numerous steel rod failures were attributed to corrosive conditions, it seemed logical that the use of a non-metallic material in the sucker rods could reduce the number of failures.

Test Method for Evaluation of the Resistance of Fiberglass Rods to Combined Mechanical and Chemical Stress

Test Method for Evaluation of the Resistance of Fiberglass Rods to Combined Mechanical and Chemical Stress

Test Method for Evaluation of the Resistance of Fiberglass Rods to Combined Mechanical and Chemical Stress

A flexural stress test for determining failure time of fiberglass rods in acid or other stress cracking ing agents has been developed. It differs from the CIGRE test in having two support points instead of one. This results in a 6 length of uniform stress in the rod between support points, and freedom from contact stress and concentration effects. Stress levels can be set readily and precisely over a wide range. Failure times of most rods stressed to ca. 25 ksi (ca. 20% of ultimate strength) averaged 3-5 days in lN nitric acid, including two coated rods. Another coated rod did not fail in over 30 days and is clearly superior to all the other rods from five manufacturers. Most rods failed by cracking transversely across the rod cross-section, as observed in service. The failure times at 56.7 ksi for air, water and acid on uncoated rods were as follows: over 30 days, 1 day and less than 10 minutes, respectively. While much less severe than acid, water is a stress cracking agent. The test is a simple, inexpensive means of evaluating rods for resistance to fracture under the combined effect of stress and acid.

Failure Analysis of Synthetic Insulators with Fiberglass Rod Submitted to Mechanical Loads

Failure Analysis of Synthetic Insulators with Fiberglass Rod Submitted to Mechanical Loads

Failure Analysis Of Synathetic Insulators With Fiberglass Rod Submitted To Mechanical Loads

Four end fitting designs of long rod fiberglass core suspension insulators are studied and the failure mechanisms are analyzed after UTS and creep tests. The fracture occurs in the fiberglass rod due to the stresses induced by the metal part of the endfitting that hold the insulating components.

Electrical Reliability of DC Line Insulators

Recent investigations have shown that the environment of dc lines is more damaging to insulation than that of comparable ac lines. Various mechanisms which can lead to failure of ceramic or composite insulators have been investigated. Results are reported for ceramic insulators on thermal breakdown and ionic migration. For composite insulators, we have studied ionic migration through the fiber glass rod and through the housing. The harmful effect of humidity in the fiberglass material is again evidenced. We also studied erosion due to dry band arcing. The erosion rate on the housing materials commonly used is three to five times larger than in a comparable ac test. This shows the importance of the design of the insulator on its reliability. In some cases, materials that do not track in ac, track under a dc stress.

Fiberglass Sucker Rods in Beam-Pumped Oil Wells

Fiberglass sucker rods can reduce polished rod loading and torque significantly and are virtually immune to corrosion. Sinker bars provide enough pump-plunger overtravel to compensate for increased rod stretch. These rods are strong enough for beam-pumping service; however, manufacturing defects must be eliminated before widespread application is feasible. Introduction Corrosion and stress combine in many producing wells to form a severe working environment for sucker rods. Although steel sucker rods have been the mainstay of beam-pumping systems for many years and have done an outstanding job in most beam-pumped wells, a certain percentage of producing wells develop severe failure percentage of producing wells develop severe failure frequencies. Because of this problem, many nonsteel materials have been examined recently to find a better structural material. One such material is resin-bonded fiberglass. Not only is fiberglass unaffected by corrosion, but it is lightweight and has a high inherent tensile strength compared with steel. While developing a fiberglass sucker rod, 11 separate test strings were run in eight producing wells during the past 3 1/2 years. These wells producing wells during the past 3 1/2 years. These wells ranged from 4,180 to 6,360 ft deep and were selected because of their failure histories and corrosive tendencies. The wells represented a wide range of fluid production volumes. This study discusses the design of fiberglass sucker-rod strings, inherent properties of resin-bonded fiberglass material, and field performance in eight test wells through June 1977. Description of Rod The load-carrying ability of the fiberglass rod comes from the strength of individual glass fibers. Fig. 1 is a schematic of the pultrusion process used to manufacture fiberglass sucker rods. The process entails saturating bundles of continuous glass filaments with a thermosetting resin and pulling the wet mass through a heated forming die. In the heated die, a chemical reaction cures the liquid resin and changes it to a solid. The resulting product is a solid rod composed of resin-bonded glass fibers. Because of this construction, these rods have high tensile strength and are anisotropic. These glass filaments generally are about 15 microns in diameter. Bundies of fibers (called rovings) contain thousands of fibers. As many as 150 rovings may be used in the sucker-rod construction. In fact, to process a sucker rod, more than 1.5 million individual fibers must be wetted effectively with resin and formed into a rod with good resin/fiber distribution over the whole cross-section. Why use glass fibers? Consider the properties of individual glass fibers given in Table 1. Note the high tensile strength and low modulus of elasticity compared with steel. Because the fiberglass sucker rod is a composite, the maximum amount of glass attained is about 65 percent by volume. This volume gives a theoretical ultimate strength of about 300,000 psi and a tensile modulus of elasticity of about 7 million psi. In practice, we cannot attain the theoretical strength of 300,000 psi. However, the ultimate strength of the composite rod approaches 180,000 psi. Table 2 lists the dimensions and properties of fiberglass sucker rods and compares these with 7/8-in., Grade D steel sucker rods. Fiberglass sucker rods are 37 1/2-ft long with a steel end connector at each end. JPT P. 731