Protective cover retainer

A protective cover comprises a substantially circular cover including a center shear disc surrounded by an annular outer portion, mounted in the fluid end of a plunger-type high pressure pump. The cover is held in place by the retainer assembly of the present invention, which is secured to the fluid end. When subjected to a compressive load by the plunger in excess of a predetermined limit, the shear disc shears from the outer portion along an arcuate boundary of reduced wall thickness between the shear disc and outer portions and the sheared disc is propelled by the pressure into the retainer assembly, striking a plug which in turn forces an impact disc into the end of the retainer, which includes a substantially circular recess therein of lesser diameter than the impact disc. The impact disc is thus sheared as the inner portion thereof enters the retainer recess, the energy from the shear disc being thereby substantially dissipated without harm to the retainer.

BACKGROUND OF THE INVENTION 
It is common practice in the petroleum industry to employ high-pressure 
plunger-type pumps in a variety of field operations relating to oil and 
gas wells, such as cementing, acidizing, fracturing, and others. An 
example of such a high pressure pump is the Halliburton Services HT-400 
horizontal triplex pump, manufactured by Halliburton Services of Duncan, 
Okla. Such pumps commonly generate pressures in excess of ten thousand 
psi, and are on occasion subject to overpressuring for a variety of 
reasons. Several common causes of overpressure are blockage of a pump 
discharge line, the erroneous closure of a valve on the discharge side of 
the pump, or the phenomenon of "sandout." 
Sandout may occur during a fracturing job, wherein the producing formation 
of the well is subjected to high pressures to crack or "fracture" the 
producing strata. It is common in such fracturing operations to include a 
proppant, such as glass or ceramic beads, walnut shells, glass 
microspheres, sintered bauxite, or sand (hereinafter collectively and 
individually referred to as "sand") in the carrier fluid, so as to provide 
a means of maintaining the cracks in the fractured producing formation 
open after the fracturing pressure is released. Present day fracturing 
operations often employ a foamed carrier fluid using nitrogen or carbon 
dioxide as the gaseous phase of the foam, in order to lower the volume and 
cost of the chemicals required and in many cases to avoid a large 
hydrostatic force on a weak formation, such as is often encountered in gas 
wells. There has also recently been a marked tendency to load up the 
carrier liquid with as much sand as possible prior to foaming, in order to 
further lower fluid volume requirements and hence job costs to the 
customer. Such concentrations may reach and exceed sixteen pounds of sand 
per gallon of carrier fluid. These high sand concentrations impose severe 
performance demands on the blender, manifold and pump systems due to the 
erosive effect of the sand and the tendency of slugs of sand to collect in 
valves, elbows, and in the fluid ends of the high pressure pumps. The 
collection of sand in these areas is dependent upon a number of 
parameters, including gravity, fluid flow rate, rheological properties of 
the carrier fluid, physical properties of the sand and the geometry of the 
system as a whole. 
However, regardless of causation, the concentration of sand associated with 
a sandout in the fluid end of a high pressure pump can result in sudden 
overpressuring of the fluid end with resulting damage to one or more of 
the plunger, connecting rod, crankshaft, or other parts of the pump 
drivetrain. The overpressuring due to sandout is particularly destructive 
as the resulting force may be eccentrically applied to the plunger and 
fluid end, as a slug of sand often collects at the bottom of the plunger, 
as has been observed. 
It has been known in the art to attempt to alleviate this sandout problem 
with ball type valves in the pumps. However, such valves are susceptible 
to clogging due to the sand content of the carrier liquid, and may also 
fail to reclose after the problem is corrected due to the presence of sand 
in the valve, or the erosive effect of the sand-laden carrier fluid. 
SUMMARY OF THE INVENTION 
The present invention comprises a retainer assembly secured to the fluid 
end of a pump behind a protective cover inserted in each cylinder of the 
fluid end. The protective cover, as disclosed and claimed in co-pending 
U.S. application Ser. No. 575,635 filed on even date herewith and assigned 
to the assignee of the present invention, is substantially circular in 
configuration, and includes a shear disc surrounded by an annular outer 
portion, with an arcuate boundary of substantially reduced wall thickness 
therebetween. When subjected to a load in excess of the shear strength of 
the arcuate boundary, the shear disc shears at its boundary with the outer 
portion of the cover and is propelled outwardly by the pressure in the 
fluid end to strike a plug which is backed by an impact disc which is 
located at the outer end of the retainer assembly of the present 
invention. The outer end of the retainer assembly includes a substantially 
circular recess therein of lesser diameter than the impact disc. The 
impact disc is sheared by the edge of the recess, the energy from the 
center portion of the cover being thereby substantially dissipated in the 
process, thereby avoiding harm to the retainer assembly. The fluid end of 
the pump, the plunger, connecting rod, crankshaft, etc. are protected from 
harm by the venting of the overpressure occurring upon shearing of the 
shear disc. After the retainer assembly, the outer portion of the cover 
and the sheared shear disc are removed from the fluid end, the sand is 
cleared from the fluid end (if sandout is the cause of the overpressure), 
a new protective cover and impact disc may be installed, the retainer 
assembly secured to the fluid end, the pump restarted and the fracturing 
operation recommenced.

DETAILED DESCRIPTION AND OPERATION OF A PREFERRED EMBODIMENT 
FIGS. 1 and 2 will be referred to in the following detailed description of 
the retainer assembly of the present invention. 
The prior art type of fluid end cover 10 is illustrated in FIG. 1, denoted 
"Prior Art." Fluid end cover 10 includes a cylindrical plug 12 secured in 
fluid end 20 by retainer 14 which is secured by threads 16 to threads 21 
of fluid end 20. Annular shoulder 18 on cover 12 is clamped between fluid 
end 20 and retainer 14, shoulder 18 actually abutting wear ring 48 
inserted in fluid end recess 46 in front of plug 12. Elastomeric seal 50, 
carried on plug 12 provides a fluid-tight seal between plug 12 and the 
periphery of fluid end recess 46. As can readily be seen, plug 12 is 
substantially coaxial with pump plunger 22 in cylinder 24. There is, of 
course, one such plug 12 at the end of each cylinder 24 of fluid end 20. 
At the bottom of FIG. 1 is suction valve assembly 26, including inlet 
valve 28 which is biased by spring 30 against valve seat 32. At the top of 
FIG. 1 is outlet valve assembly 34 including outlet valve 36 which is 
biased by spring 38 against valve seat 40. In normal pump operation, fluid 
enters cylinder 24 through suction valve assembly 26 by the withdrawal of 
plunger 22 from cylinder 24, after which the fluid in cylinder 24 is 
raised in pressure by the advance of plunger 22 toward plug 12 in cylinder 
24, the fluid then exiting from cylinder 24 into outlet passage 42 through 
outlet valve assembly 34. As this type of plunger pump and its operation 
are well known in the art, no further explanation will be given thereof, 
nor of the drive means for plunger 22, such drive means being also well 
known in the art. 
It should be noted that, in the event of an overpressure in cylinder 24 due 
to one of the aforementioned causes, the prior art plug 12 and retainer 14 
offer no means of venting the overpressure, resulting in possible damage 
to fluid end 20, plunger 22, or parts of the drivetrain to plunger 22, 
such as a connecting rod or the pump crankshaft (not shown). 
The preferred embodiment of the present invention is illustrated in FIG. 2, 
inserted in the end of cylinder 24 of fluid end 20 in lieu of cover 10 of 
the prior art. Protective cover and retainer assembly 100 includes a 
cup-shaped cover 102 having a cylindrical outer portion 104 and a circular 
inner shear disc 106 with arcuate boundary 108 of reduced wall thickness 
therebetween. The inner end of shear disc 102 has a flat circular end face 
110 surrounded by an oblique annular face 112. The exterior of outer 
portion 104 includes annular flange 114, which is of greater diameter than 
that of outer end 44 of cylinder 24, but less than that of fluid end 
recess 46 which communicates with cylinder 24. The outer end of fluid end 
recess 46 is threaded at 21, as previously noted. The inner wall 116 of 
outer portion 104 is of substantially constant diameter. 
Cover 102 is maintained in fluid end 20 by the insertion of retainer 
assembly 120 of the present invention into fluid end 20 and the making up 
of threads 124 on cover retainer 122 of retainer assembly 120 to threads 
21. Flange 114 is clamped between retainer assembly 120 and fluid end 20, 
wear ring 48 being disposed between flange 14 and fluid end 20. Cover 
retainer 122 further includes hammer lugs 126 on its exterior, by which 
cover retainer 122 may be tightly threaded to fluid end 20 by a sledge 
hammer, as is commonly used in petroleum industry field operations. The 
interior of cover retainer 122 possesses threads 128 thereon, which 
engages threads 132 on catcher 130. Catcher 130 is preferably welded to 
cover retainer 122 by an annular weld at 134. Catcher 130 is cup-shaped, 
and possesses a substantially uniform outer surface 136 contiguous to 
threads 132, surface 136 being pierced by a plurality of longitudinal 
slots 137 extending to interior wall 138, which is also of substantially 
uniform diameter. The "bottom" 140 of the cup of catcher 130 is pierced by 
axially disposed aperture 142. Shear plug 150 is disposed in the interior 
of catcher 130 on the end of hex cap screw 170, threads 172 on the body 
174 of which engage threads 153 on the interior of axially extending 
cavity 152 of shear plug 150. Inner end 154 of shear plug 150 is radially 
flat, as is outer end 156. The exterior of shear plug 150 is stepped, 
cylindrical surface 158 being of slightly lesser diameter than that of 
catcher inner wall 138, and smaller cylindrical surface 160 being of 
slightly lesser diameter than that of axially-disposed aperture 142. 
Circular impact disc 180 is disposed within catcher 130 between shear plug 
150 and the "bottom" 140 of catcher 130, hex cap screw extending through 
an axial hole (unnumbered) therein into shear plug 150. The perimeter 184 
of impact disc 180 is of slightly lesser diameter than that of inner wall 
138, while both radially extending faces of shear disc 180 are flat. The 
head 176 of hex cap screw 170 is maintained outside catcher 130 by plug 
washer 190, through which screw body 174 extends into impact disc 180 and 
shear plug 150. When hex cap screw 170 is made up tightly to shear plug 
150, the bottom 140 of catcher 130 is clamped between plug washer 190 and 
impact disc 180. 
It should be understood that protective cover and retainer assembly 100 may 
be employed at the end of each cylinder 24 in a multi-cylinder pump, such 
as the HT-400 horizontal triplex pump employed by Halliburton Services of 
Duncan, Okla., in well servicing operations, in lieu of the prior art type 
covers. The positioning of all the elements of a protective cover and 
retainer assembly 100, when installed in a fluid end 20, are as depicted 
in FIG. 2. 
When a fluid end 20 equipped with one or more protective cover and retainer 
assemblies 100 is subjected to overpressure, the pressure is vented from 
the overpressured cylinder or cylinders 24 as shown in FIG. 3. 
When the pressure in cylinder 24 exceeds the design shear load of arcuate 
boundary 108, shear disc 106 of protective cover 102 is sheared from outer 
portion 104 and is propelled outwardly as shown by arrow 200 in FIG. 3. As 
inner wall 116 of outer portion 104 and interior wall 138 of catcher 130 
are both of greater diameter than center portion 106, shear disc 106 will 
strike shear plug 150, which is backed by impact disc 180. As aperture 142 
in catcher bottom 140 is of lesser diameter than that of impact disc 180, 
the edge of aperture 142 will serve as a cutting edge on which a center 
portion 181 of impact disc 180 is sheared from an annular outer portion 
183, the outer end 156 of shear plug 150, bounded by smaller cylindrical 
surface 160, concentrating the force of shear disc 106 at the edge of 
aperture 142. As impact disc 180 shears, hex cap screw 170 with washer 190 
is moved outwardly, as shown in FIG. 3. Pressurized fluid in cylinder 24 
is safely vented upwardly and downwardly through slots 137. 
After the kinetic energy of shear disc 106 is dissipated, it will fall 
downwardly and be retained in catcher 130. 
In order to prepare the fluid end 20 of the pump for service after an 
overpressure, each retainer assembly 120 of the present invention which 
has vented is backed off from fluid end 20, shear disc 106 and outer 
portion 104 of protective cover 102 are discarded, hex cap screw is backed 
off from shear plug 150, sheared center and outer portions 181 and 183 of 
impact disc discarded. A new (unsheared) impact disc 180 is provided, new 
impact disc 180 reassembled with catcher 130, shear plug 150, hex cap 
screw 170 and washer 190 as shown in FIG. 2, a new (unsheared) protective 
cover is provided and inserted with a wear ring 48 and seal 50 into each 
cylinder 24 of fluid end 20 which was previously vented, and retainer 
assembly 120 threaded into fluid end 20 behind protective cover 102. 
If the overpressure in cylinder 24 is caused by sandout, the shearing of 
shear disc 106 may be eccentric, and center portion 106 may not strike 
shear plug 150 squarely. However, the force will still be transmitted to 
shear disc 180, and may in fact be less than in an instance of uniform 
shear, as part of the pressure may be vented to the atmosphere rather than 
acting as a propellant for shear disc 106. 
It will be understood by one of ordinary skill in the art that all of the 
protective cover and retainer assembly 100 may preferably be fabricated 
from a suitable steel such as AISI 4140, with the exception of impact disc 
180 which preferably comprises aluminum, bronze, or other suitable 
relatively soft and readily shearable material to effectively absorb the 
energy of shear disc 106. It will also be understood that the protective 
cover 102 should be designed to fail (shear disc 106 shear) at or less 
than the design plunger load, in order to prevent damage to the plunger 22 
and the pump drivetrain. 
In addition to design for failure at a certain predetermined load, the 
protective cover employed with the present invention must possess an 
adequate fatigue life at the rated pressure of the pump in which it is 
employed, in order to avoid frequent replacement of the cover and/or 
unexpected failures due to fatigue. Ideally, the maximum plunger force 
effecting cover failure (shear) would be only slightly higher than the 
maximum force generated during normal pump operations. However, such an 
approach would result in an unacceptably short fatigue life. In order to 
obtain an acceptable fatigue life of 300,000 plunger cycles, the maximum 
plunger force for cover failure is much higher. For example, in a pump 
employing a 41/2" plunger and a normal maximum operating pressure of 
approximately 11,000 psi, the plunger pressure required for failure of a 
cover having a 300,000 cycle fatigue life is about 18,000 psi. 
Accordingly, taking into account the geometry of the protective cover 102, 
including the diameter of shear disc 106, and circumferential length of 
arcuate boundary 108, as well as the hardness of the cover material 
employed, an appropriate wall thickness for arcuate boundary 108 may 
readily be selected by one of ordinary skill in the art. 
Thus, it is apparent that a novel and unobvious retainer assembly has been 
invented. While the invention has been disclosed in terms of a preferred 
embodiment, the spirit and scope of the invention is not so limited. For 
example, the present invention need not be employed in coaxial 
relationship to a pump plunger, and may be fabricated with a greater or 
fewer number of components than employed in the preferred embodiment. In 
addition, other configurations other than circular may be employed in 
impact disc 180 to absorb the kinetic energy of the shear disc 106, the 
impact disc 180 might be placed closer to the unsheared shear disc, the 
retainer assembly may be secured to the fluid end by means other than 
threads, etc. These and other additions, deletions and modifications will 
be evident to one of ordinary skill in the art. 
Furthermore, while the retainer assembly of the present invention has been 
shown to have utility in well fracturing operations, it should be 
understood that its utility is not so limited. The present invention may 
be employed in high pressure plunger-type pumps of every nature, 
whatsoever their use may be, in order to prevent damage to the pump and 
components thereof and injury to personnel from overpressures relieved by 
a protective cover.