Joints and connections – Molded joint – Socket or open cup for bonding material
Reexamination Certificate
1999-05-24
2001-02-27
Silbermann, Joanne (Department: 3628)
Joints and connections
Molded joint
Socket or open cup for bonding material
C403S265000, C403S269000
Reexamination Certificate
active
06193431
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an end fitting or connector for connecting rods end-to-end, and particularly fiberglass or composite sucker rods for use in an oil well.
BACKGROUND OF THE INVENTION
In many oil wells, the pressure in the well reservoir is often insufficient to lift the oil to the surface. In such cases, it is conventional to use a sub-surface pump to force the oil out of the well. The sub-surface pump is driven by a pumping unit located at the surface. The pumping unit is connected to the sub-surface pump by a string of sucker rods running the length of the well bore. The pumping unit moves the sucker rod string up and down in the well bore to drive the sub-surface pump.
For many years sucker rods were generally made of steel. Due to the heavy weight of the steel rods, large pumping units were required and pumping depths were limited. It is now preferable to use sucker rods made of fiberglass or composite material with steel connectors joining the rods together to make a string of the required length. Fiberglass rods provide sufficient strength to tolerate the mechanical stresses of pumping, and yet weigh substantially less than steel rods. Another advantage of fiberglass or composite sucker rods (“FSR”) over steel is their improved resistance to the chemical stresses encountered in corrosive environments. Fiberglass rods have been used successfully in the field since 1973, and have proven to be of particular value in corrosive environments where steel rods have an unacceptable failure rate due to weakening of the steel from corrosion and high load levels.
Fiberglass sucker rods (“FSR”) are usually about 37½ feet long and approximately ⅞ inches in diameter. Each rod is composed of bundles of glass filaments (rovings) approximately 15 microns in diameter that have been wetted with a resin and formed into a rod. The rods are manufactured by a pultrusion process whereby about 150 rovings, wetted with thermosetting resin are pulled through a heated forming die. The heat catalyzes a chemical reaction causing the resin to harden and bonding the rovings and the resin together into a composite solid which is formed into a rod by the die. It is critical that the rods be manufactured so as to prevent looping of the rovings or other imperfections which introduce flaws in the rod body greatly increasing the odds of rod failure in the field.
Sucker rods are connected together in a string by steel connectors attached to the ends of each rod. With the solving of rod manufacturing problems such as looping, the steel connectors or end fittings between rods have proven to be the source of most composite rod failures or end fitting pullouts. Therefore, the sucker rod connectors have been the focus of recent efforts to improve the reliability of fiberglass or composite sucker rod construction.
The end fittings comprise a rod receptacle at one end to receive the rod end, and a threaded coupling at the other end to threadedly connect to the end fitting of the next successive rod. The space between the interior wall of the rod receptacle and the external surface of the rod defines a space or annulus which is filled with epoxy or some other initially flowable adhesive such as epoxy. The epoxy cures into a solid which bonds to the rod. Typically, the adhesive is heat activated and heat is applied to the rod as a curing agent. Early experiments with such connectors resulted in rod pullouts, where the rod is pulled out of the connector rod receptacle causing failure of the string. Such string failure can be catastrophic, requiring expensive repairs or even well closure.
Current end fittings are formed such that the epoxy cures into a series of wedges that cooperatively engage complimentary surfaces in the rod receptacle to prevent rod pullouts.
FSRs were developed to improve the operation characteristics of artificial lift rod pumping systems in crude oil production.
The use of FSR in rod pumping systems is indicated when analysis of the down hole pumping system(s) reveals a need for the particular performance characteristics offered by FSRs, which characteristics comprise resistance to corrosion, light rod string weight, lower pumping unit gearbox loads, and the “rubber band” effect due to the elastic properties and geometric shape memory after elongation of the fiberglass (or composite) component of the system. Fiberglass sucker rod pumping systems have become an accepted ingredient in artificial lift design, and are used extensively throughout the range of crude oil production.
Among the mechanical forces acting on the rod/adhesive/metal interface, are compressive forces, such as during a stroke of the pump either up or down, and negative load forces. Negative load refers to forces acting on the side of the wedge opposite from the gripping side of the wedge. Negative load is very destructive to the wedges of prior art designs, causing catastrophic shear failure of the wedge. In the present invention, however, when a shock load occurs that creates a negative load, the wedge has the ability to absorb the negative load forces and to thereby resist failure of the rod connection.
Early rod designs were plagued with early time to first failure. Failure analysis of early FSR designs revealed the following:
A. Failure, while exhibiting itself catastrophically, is rarely a result of a catastrophic evens. The exhibition of catastrophic failure is usually a result of improper maintenance and materials handling procedures.
B. Failure, regardless of its manifestation, can be linked to the interface between the fiberglass rod and the metal end fitting.
C. End fitting designs that distribute applied stresses more fully along the length of the interface are more successful in reducing failure.
The design of the metal end fitting has consistently comprised a wedge shaped pocket (receptacle) to accept the fiberglass rod. The following procedure applies to various diameters of rod sizes, and the principles and practices remain the same regardless of rod size. Current production practices involve the preheating of an end fitting, filling the end fitting with a one part heat activated adhesive, installing an end fitting onto both ends of a fiberglass rod of some length, and heating the area(s) to include all of the interface between the metal and fiberglass. It is important that in such a system, the adhesive layer serves to adhere to the fiberglass only, and not the end fitting pocket. The adhesive layer thus acts as a plug being wedged by force to the end fitting pocket socket. After proper time intervals and heat application, the assembly is then tested by application of force directed coaxially in opposing directions to test the wedge strength and to “set” the end fitting wedge receptacle with the hardened adhesive. The pocket or pockets in the end fitting serve as both the mold to form the wedge or wedges from the fluid adhesive, and as receptacles to capture the hardened adhesive wedges.
Wedges transmit the compressive and tensing forces of pumping from the steel connector to the fiberglass rod and vice-versa. The metal end fitting is harder than the hardened adhesive, and deforms the shape of the hardened adhesive wedge. Essentially, the metal end fitting squeezes the deformations in the adhesive when compressive and back travel forces are applied to the construction. Ideally, the deformations are squeezed by the end fitting out toward the end of the rod, transmitting the forces, at least to some extent, into the metal end fitting for optimum dispersal of destructive forces.
Axial forces applied to a rod cause deformations of the rod material. The deformations are transmitted throughout the rod body and vary depending on the magnitude of the force and the cross-sectional area of the rod. Abrupt changes in the cross-sectional area of the rod concentrate stress forces in certain areas of the rod. The wedges of sucker rod connections change the cross-sectional area of the rod in comparison to the rod body in such a way as to concentrate stress forces on the rod. The c
Silbermann Joanne
The Fiber Composite Company, Inc.
The Matthews Firm
LandOfFree
Fiberglass sucker rod end fitting does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fiberglass sucker rod end fitting, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fiberglass sucker rod end fitting will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2595620