U.S. patent number 3,882,665 [Application Number 05/443,930] was granted by the patent office on 1975-05-13 for flexible pumping strand and method of making.
This patent grant is currently assigned to Bethlehem Steel Corporation. Invention is credited to James M. Doll, Charles R. Hughes.
United States Patent |
3,882,665 |
Hughes , et al. |
May 13, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Flexible pumping strand and method of making
Abstract
A flexible pumping strand is formed from a plurality of steel
wires stranded or held together within an abrasion resistant
flexible outer plastic jacket perforated at intervals along its
length, each of the plurality of steel wires being coated with an
imperforate corrosion resistant plastic bonded to the surface of
the wire. A method of forming the flexible pumping strand and the
perforations in the outer coating of the strand involving the use
of steam induced perforation during extrusion of the plastic jacket
over the strand is also disclosed.
Inventors: |
Hughes; Charles R. (Hellertown,
PA), Doll; James M. (Allentown, PA) |
Assignee: |
Bethlehem Steel Corporation
(Bethlehem, PA)
|
Family
ID: |
23762763 |
Appl.
No.: |
05/443,930 |
Filed: |
February 19, 1974 |
Current U.S.
Class: |
57/217; 57/7 |
Current CPC
Class: |
D07B
7/145 (20130101); D07B 1/0693 (20130101); D07B
1/162 (20130101); D07B 2205/2046 (20130101); D07B
2201/2012 (20130101); D07B 2201/2084 (20130101); D07B
2201/2044 (20130101); D07B 2205/2046 (20130101); D07B
2801/18 (20130101) |
Current International
Class: |
D07B
5/00 (20060101); D07B 7/14 (20060101); D07B
7/00 (20060101); D07B 1/00 (20060101); D07B
1/16 (20060101); D07b 001/16 (); D07b 007/14 () |
Field of
Search: |
;57/149,153,162,164,144
;64/2 ;138/125,129 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Watkins; Donald E.
Attorney, Agent or Firm: O'Keefe; Joseph J. Wilkinson;
Charles A.
Claims
We claim:
1. A flexible pumping strand comprising:
a. a plurality of wires collected together into a linear
member,
b. a polymeric coating on the exterior of each of said wires, said
polymer being substantially inert to an oil well fluid,
substantially impermeable to the water and gaseous corrodants and
being resistant to fretting and abrasion between said wires,
c. said polymeric coating being closely bonded to the surface of
said wires through a thin film of an intermediate primer,
d. an outer plastic jacket coating the outside of said strand,
e. said outer plastic jacket having perforations throughout its
length such that free passage of an oil well fluid through the
plastic jacket is assured.
2. A flexible pumping strand according to claim 1 wherein the
polymeric coating on the wires is comprised of a fluoropolymer.
3. A flexible pumping strand according to claim 2 wherein the
flexible pumping strand is a helical strand.
4. A flexible pumping strand according to claim 3 wherein the
flexible pumping strand has opposite rotations in different lays
and the outside of the outer jacket has a smooth cylindrical
surface.
5. A flexible pumping strand according to claim 3 wherein the
polymeric coating on the wires is comprised essentially of a
polymer selected from the group consisting of polyvinylidene
fluoride, polychlorotrifluoroethylene, a copolymer of
tetrafluoroethylene and hexafluoropropylene,
polyethylenechlorotrifluoroethylene and
polyethylenetetrafluoroethylene.
6. A flexible pumping strand according to claim 5 wherein the
fluoropolymer is bonded to the surface of the underlying wire at
least in part through an intermediate film of a fused coating of a
polymer having a similar fluoropolymer composition applied
initially in a dispersed condition in an organic solvent.
7. A flexible pumping strand according to claim 6 wherein the
fluoropolymer is bonded to the surface of the underlying wire
through an intermediate film comprised of two primary coats one of
which is an epoxy base primer.
8. A flexible pumping strand according to claim 7 wherein the
perforations in said outer plastic jacket are from one-eighth inch
in diameter to one-half inch in diameter.
9. A flexible pumping strand according to claim 8 wherein the
perforations in said outer strand jacket are spaced apart along the
longitudinal extent of the strand at intervals no greater than 30
feet.
10. A flexible pumping strand according to claim 3 wherein the
flexible pumping strand has opposite rotations in different layers
of wires in the strand and the outside of the outer plastic jacket
has a substantially smooth outer surface.
11. A flexible pumping strand comprising:
a. a plurality of wires collected together to form an extended
linear member,
b. a polymeric coating on the exterior surface of said wires which
is substantially inert to oil well fluid, substantially impermeable
to water and corrosion inducing gases and resistant to fretting and
abrasion between the wires,
c. an outer abrasion resistant plastic jacket covering the outside
of said strand,
d. said outer abrasion resistant plastic jacket having perforations
throughout its length such that the free passage of an oil well
fluid through said plastic jacket is assured.
12. A flexible pumping strand according to claim 11 wherein said
polymeric coating of (b) is a fluoropolymer.
13. A flexible pumping strand according to claim 12 wherein said
fluoropolymer is comprised of polyvinylidene fluoride.
14. A flexible pumping strand according to claim 12 wherein said
fluoropolymer is comprised of polychlorotrifluoroethylene.
15. A flexible pumping strand according to claim 12 wherein said
fluoropolymer is comprised of a copolymer of tetrafluoroethylene
and hexafluoropropylene.
16. A flexible pumping strand according to claim 12 wherein said
fluoropolymer is comprised of
polyethylenechlorotrifluoroethylene.
17. A flexible pumping strand according to claim 12 wherein said
fluoropolymer is comprised of polyethylenetetrafluoroethylene.
18. A flexible pumping strand according to claim 12 wherein the
fluoropolymer is tightly bonded to said wire surface by an
intermediate film of polymer.
19. A flexible pumping strand according to claim 18 wherein the
primer constitutes at least in part a fused film of a polymer
similar in composition to the polymeric protective coating applied
to the surface of the wire.
20. A flexible pumping strand according to claim 19 wherein the
polymer is bonded to the surface of the wire through an
intermediate film comprised of two primary coats one of which is an
epoxy base primer.
21. A flexible pumping strand according to claim 20 wherein the
perforations in said outer plastic jacket are from one-eighth inch
in diameter to one-half inch in diameter and the said perforations
are spaced apart on said longitudinal extent of said strand at
intervals no greater than about thirty feet.
22. A method of making flexible pumping strand comprising:
a. coating a plurality of wires with a fluoropolymer,
b. stranding said plurality of wires into a wire strand,
c. contacting the wires of said strand with a vaporizable liquid,
and
d. pressure extruding an outer jacket of polymer about said strand
under a pressure such that the coatings on the wires are
temporarily compressed during said extrusion step and the heat of
the extrusion causes vaporization of said liquid and perforation of
said soft jacket prior to hardening.
23. A method of making flexible pumping strand according to claim
22 additionally comprising initially applying a primer to the
surfaces of the wires by contacting the surfaces of the wires with
a dispersion of a polymer similar in composition to the
fluoropolymer with which the wires are to be coated and fusing said
polymer.
24. A method of making flexible pumping strand according to claim
23 where the primer is applied in a two step operation comprising
initially contact the wire surface with a film of an epoxy base
composition, heat curing the epoxy composition, applying a film of
a dispersion in an organic solvent of a polymer having a
composition similar to the composition of the protective
fluoropolymer coating which is to be applied to the wire and fusing
said film of polymer to the surface of the wire.
Description
BACKGROUND OF THE INVENTION
The present invention relates to oil well pumping and more
particularly to corrosion resistant flexible pumping strands.
In U.S. Pat. No. 3,234,723 issued Feb. 15, 1966 to K. D. Brown
there is disclosed in FIGS. 6 and 7 a type of flexible pumping
strand wherein a plurality of longitudinal tension wires are
disposed in a so-called "bundled" arrangement within a plastic
tubing. Each of the wires is preferably also individually jacketed
with a plastic composition so that each wire is protected from
corrosion by two jackets, an individual plastic jacket for each
wire and an overall plastic jacket surrounding the entire flexible
pumping strand. Thus if some corrosive substances or liquids gain
entrance to the pumping strand through the outer jacket it is
supposed that the inner jackets will provide a second line of
defense against corrosion of the wires of the strand by the
corrosive substances. The outer jacket of the U.S. Pat. No.
3,234,723 patent jacket also serves to "bundle" or confine the
plurality of wires which comprise the strand together since
according to the disclosure of the patent the individual wires are
disposed in a somewhat loose bundle within the jacket and are
substantially straight or parallel to each other in order to attain
the maximum strength in the strand per metal cross section. The
individual plastic jacketing of the wires not only provides a
secondary line of defense against corrosive substances, but also
serves to facilitate movement and adjustment between the individual
wires with a minimum friction and abrasion between the wires. The
invention of the U.S. Pat. No. 3,234,723 has been tried
experimentally in strands having an overall outer plastic jacket
extruded over the strand and individual plastic jackets extruded
over the wires as disclosed in the patent, but in which the
individual wires, rather than being bundled together loosely within
the jacket to facilitate individual movement and adjustment of the
wires, are instead stranded together into a helical wire strand
having a fairly long helix or lay, the length of which falls
somewhere between the customary lay which is provided in most
helical wire strands both to hold the strands together and to
facilitate bending of the strands about a radius, and the parallel
wire arrangement of a conventional parallel wire strand in which
the wires are not stranded together in a helix. Since a flexible
pumping strand conventionally operates while disposed in a straight
vertical condition such strand requires only sufficient helix or
twist to facilitate bending of the strand during transportation and
withdrawal of the strand from the well and if the strand is
additionally jacketed with an outer plastic jacket, the plastic
jacket will aid somewhat in maintaining the individual wires
together. The previous experimental strands were jacketed and the
wires were individually coated with various types and grades of
nylon. In the experimental strands referred to it was found that
the strands did not successfully withstand corrosive conditions in
oil wells and particularly in so-called "sour brine" oil wells
containing hydrogen sulfide. The outer nylon jackets were found to
suffer damage due to perforation and the like and the individual
nylon jacketed wires suffered intermittent corrosion which caused
failure of the strands after uneconomically short periods.
Sometimes the failure of the strands was devastatingly sudden.
Various other coating substances were tried to discourage corrosion
on laboratory specimens held in simulated corrosive oil well
environments including Teflon, or polytetrafluorethylene, suggested
as an alternative coating composition in the specification of the
U.S. Pat. No. 3,234,732, but no really satisfactory solution to
corrosion and damage to such strands has been found heretofore
where the strand is to have the individual wires coated within an
outer plastic jacket to withstand corrosion and the strand is to
have a substantially static interior environment, i.e., as
contrasted to the strands disclosed in U.S. Pat. No. 3,637,341
where an internal corrosion inhibitor is periodically renewed or
renewable within the strand to prevent or inhibit internal
corrosion of the component wires as external corrodants slowly gain
entrance to the interior of the strand through the natural slight
permeability of many nominally impermeable plastic resins.
SUMMARY OF THE INVENTION
The foregoing problems associated with previous double jacketed
flexible pumping strands have now been obviated by the flexible
pumping strand made in accordance with the present invention.
In accordance with this invention a flexible pumping strand is
constructed of a plurality of wires coated with a chemically
resistant plastic coating which is inert to oil well fluid, has a
low permeability to water and corrosive gases and is sufficiently
tough to survive stranding and interwire fretting or abrasion
during service. Preferably the plastic coating is formed of a
polyvinylidene fluoride composition which has been found by the
inventors to be the most suitable composition for corrosive oil
well environments and substantially essential along with several
other similar fluoropolymers for use in severely corrosive
environments in oil wells. The plastic coating is bonded to the
individual wires to prevent propagation of corrosion due to
migration of corrosive elements between the coating and the
underlying wire starting at restricted minor defects in the
coating. Over the individually coated wires there is extruded an
overall outer plastic jacket formed of an abrasion resistant
plastic such as nylon and particularly so-called Nylon 11. This
outer plastic jacket is provided with holes or perforations through
the coating at periodic intervals which are spaced with sufficient
frequency with respect to the size of the perforations to allow
free passage of well fluid back and forth through the perforations
from the interior to the exterior of the strand and back again.
The invention also includes a method of forming the strand
including the formation of perforations in the strand by means of
vapor generated in the interior of the strand by vaporization of a
vaporizable liquid in the core during extrusion of the plastic
jacket over the body of the strand.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic elevation of an oil well using a flexible
pumping strand fabricated according to the present invention.
FIG. 2 is a partially broken away longitudinal cross-section of the
flexible pumping strand of the invention.
FIG. 3 is a transverse cross-section of the flexible pumping strand
shown in FIG. 2 at 3--3.
FIGS. 4a and 4b respectively are elevations of a wire coating line
and a strand fabricating and coating line with which the wire
coating line is associated for making the flexible pumping strand
of the invention.
DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
In FIG. 1 there is shown a schematic view of an oil well 11
including a well casing 13, a differential pressure or other
suitable pump 15 positioned at the bottom of said casing to pump
the oil up to the surface through the casing or through a well
tubing not shown, disposed within the casing, a flexible pumping
strand 17 comprised of individual steel wires 19 each of which is
coated with an individual plastic jacket 21 of polyvinylidene
fluoride or other suitable corrosion resistant plastic and which
wires are stranded together into a long lay strand having an outer
abrasion and corrosion resistant jacket 23 covering the exterior of
the strand, all as shown in greater detail in FIGS. 2 and 3. The
flexible pumping strand 17 passes at the well head 25 through the
usual packing 27 preferably being protected as it passes through
the packing by being enclosed in a so-called hollow polished rod 29
which is secured to the strand and reciprocates in the packing 27
as the flexible pumping strand 17 is reciprocated by the movements
of a horsehead 31 operated at the surface of a motor 33 through a
connecting rod 35 connected to a flyweight arm 37. The
reciprocation of the flexible pumping strand 17 serves to operate
the pump 15 to which the flexible pumping strand is attached
through a swaged fitting 39 or other suitable fitting, a shear
release fitting 41 and a connecting pony rod or pumping rod 43. The
hollow polished rod 29 and strand may preferably be supported from
the horsehead 31 by a carrier bar 45 through bridles 47. Excess
flexible pumping strand 17 is reeled as shown on a reel 49 secured
to the supporting framework 51 upon which the horsehead 31 is
pivotally mounted, or is coiled on the surface.
It will be readily understood that the oil well, which is for
convenience of illustration shown in FIG. 1 broken in the center,
may be several thousand feet deep and will be filled with crude oil
which is in many cases saturated with highly corrosive substances
which may be predominantly acid or alkali and may otherwise vary
depending upon the nature of the surrounding geological strata and
environment. Not only is the well 11 likely to be filled with
highly corrosive substances, but it is also often subjected to very
high pressures particularly in the lower portions of the well. The
well may also be very hot in its lower reaches due to the usual
approximate temperature increase of about 1.degree. centigrade for
every 100 feet or so of depth. The high pressures and high
temperatures encountered in the lower reaches of the oil well quite
naturally tend to aggravate the corrosive effects of corrosive
substances in the well upon the metallic components of the flexible
pumping strand 17 and the degradative effects of the surrounding
environment upon the plastic components of the flexible pumping
strand. Changes in pressure occur in the well both from time to
time within any given portion of the well and also as the flexible
pumping strand is lowered into and withdrawn from the oil well for
inspection, repair or replacement of the pump 15 or other
components of the pumping string. Such pressure changes not only
tend to aggravate whatever corrosion and degradation may already be
present due to a naturally detrimental deep oil well environment,
but may in themselves tend to burst, rupture or otherwise damage
the strand coating or jacket. In short the usual deep oil well
environment is often a very rigorous environment which rather
quickly damages most exposed surfaces which are subjected to
it.
The flexible pumping strand of the present invention is designed to
withstand the rigors of corrosive oil well environments. Durability
of the strand under adverse corrosive conditions is attained by
coating the individual wires with an adherent plastic resin
composition which is simultaneously extremely resistant to
penetration of the corrosive substances found in oil wells,
resistant to degradation of the plastic by these same substances or
other destructive substances found in an oil well and which is
resistant to fretting and abrasion between the individual wires.
The plastic coating is applied in a manner which makes the plastics
very adherent to the underlying surface of the individual wires of
the strand in order to discourage propagation of corrosion by any
corrosive agent which may somehow gain access through the coating
to a limited portion of the wire surface underneath. Such
propagation of corrosion along the wires between the plastic
coating and the surface of the metal wires is not only detrimental
in itself, but seems to precipitously increase the rate of
corrosion at the point of access through the coating as well. The
wire coating will be composed of polyvinylidene fluoride which is
available on the market under the name of KYNAR, a proprietary
tradename of the Pennwalt Company. While polyvinylidene fluoride
has been found to be the preeminent coating material for protection
of the individual wires of the strand and this polymer or a
comparable fluoropolymer is substantially a necessity for use in
very corrosive oil well environments and particularly those which
contain significant quantities of hydrogen sulfide as one of the
corrodents, such as for example sour brine type wells, other
corrosion resistant plastics such as nylon and polypropylene could
be used in wells which are not severely corrosive and particularly
those wells which are not acid in composition and do not contain
hydrogen sulfide or similar compounds as a corrodent. Various
fluoropolymers are in general better for corrosion protection of
the individual wires in oil well environments, but all
fluoropolymers, for example polytetrafluoroethylene or Teflon, are
not suitable because of difficulties in application to the wire and
particularly difficulties in obtaining a secure bond of the plastic
to the surface of the wire.
After being individually coated with the corrosion resistant
plastic and preferably a polyvinylidene fluoride composition, the
wires are stranded, laid or formed into the strand 17 and an outer
abrasion resistant plastic jacket is extruded over the surface of
the strand. The plastic jacket is preferably composed of a nylon
composition such as Nylon 11. The nylon coating is also preferably
applied by a pressure type extrusion operation rather than a vacuum
type extrusion operation in order to provide a thick plastic jacket
with a smooth cylindrical exterior plastic surface. At frequent
intervals along the strand, which intervals should normally not be
greater than 30 feet and preferably considerably less, the nylon
coating on the strand is perforated with small perforations about
one-eighth to one-half of an inch in diameter. The perforations
must extend completely through the plastic jacket in order to
provide free access for well fluids from the interior of the strand
to the exterior of the strand or from the exterior well environment
to the interior of the strand. The perforation may be positioned on
various sides of the strand or may be placed along only one side.
The size of the perforations or orifices does not seem to be
critical, but the orifices should be large enough and frequent
enough to provide free and unimpeded passage of well fluid back and
forth through the orifices yet not so large as to allow large
abrasive particles to gain access to the interior of the strand,
particularly before it is placed in the well or to substantially
weaken the plastic jacket due to the removal of an excessive amount
of plastic from the circumference of the jacket. It has been found
that much of the failure of the plastic jackets on previous
experimental strands has been due to repeated and occasionally
extreme pressure variations on the exterior of the strand as
compared to the interior as the strand works in the well or is
removed from or replaced in the well. These pressure variations are
accentuated by the fact that the interior of the strand is
essentially empty, or, more correctly, filled only with atmospheric
gases. Even a thick plastic jacket on the exterior of the strand
does not appear to be able to withstand the differential pressure
between the exterior of the strand and the substantially empty
center of the strand in the interstices between the component wires
for long continued periods. Likewise, if well fluid should gain
entrance to the strand and the strand is then removed from the well
for inspection, the strand jacket may be damaged by the excess
fluid in the strand. Strangely, much of this damage to the strand
occasioned by pressure differentials is not evident as mechanical
damage to the strand but may initially appear to be due to
corrosive effects of the environment. It may be that a synergistic
effect between the pressure and the corrosive or degradative
substances in the well causes the damage to the strand jacket. In
any event it has been found that damage to the plastic strand
jacket and associated damage to the underlying wires of the strand
can be avoided by providing perforations in the strand jacket which
allow free access to the interior of the strand for the well fluid
and free interchange of the well fluid back and forth through the
outer plastic jacket.
In FIGS. 2 and 3 there is shown an enlarged partially cut away
longitudinal cross section and a transverse cross section
respectively of a preferred construction of the flexible pumping
strand 17 shown in use in an oil-well in FIG. 1. As shown in FIG. 3
the strand 17 is a 1 .times. 37 wire construction composed of 0.100
inch improved plow share steel grade wires having a tensile
strength of 120 to 135 tons per square inch (240,000 to 270,000
psi.) composed of three separate operations or layers of wires, the
lay of the wires in each operation being opposite to the lay of the
adjacent wire operation or operations. Each wire has an outer
jacket composed of polyvinylidene fluoride coated to a final coated
wire diameter of 0.110 inches overall. There is about 13 percent
void space in the interior of the finished strand. The opposite
lays of the various operations provide a strand with minimal
rotational properties. Various different lay lengths can be used in
the various operations or layers to attain the particular
rotational properties desired or all of the lays of the strand can
be the same. It will be evident to those skilled in the art that
other wire sizes and types and alternative strand constructions
could be used. Other types of commercially available plastic resins
such as other fluoropolymers or other compositions of plastics
which (a) are inert to the particular well fluid and corrosive
elements in the well fluid (b) have low permeability in water and
corrosive gas and (c) are sufficiently tough to survive stranding
operations and interwire fretting and abrasion during service can
be used.
Over the outer circumference of the strand 17 there is applied an
outer jacket 23 formed of an abrasion resistant polyamide such as
Nylon 11 approximately 0.050 inches thick over the tops of the
outer wires of the strand and having a smooth outer surface. The
polyamide jacket has perforations 24 about three-sixteenths of an
inch in diameter spaced at intervals of not greater than about
thirty feet along the longitudinal extent of the strand and
preferably at more frequent intervals of a few feet or less. In
FIG. 3 two such perforations or orifices are shown spaced
transversely from each other on the same circumference of the
strand for purposes of illustration, but it will be understood that
such perforations will more usually be spaced longitudinally along
the length of the strand. The perforations are effective to allow
free passage of well fluid back and through the strand and to allow
the strand to be quickly filled with well fluid as it is being
passed downwardly into the well and to allow the well fluid to
drain quickly from the strand as it is being withdrawn from the
well. It will be understood that other types of abrasion resistant
plastics which are substantially inert to the well fluid and other
thicknesses of plastic than those illustrated could be used for the
outer jacket. Various types of perforations or shapes of orifices
in the jacket can, furthermore, be used so long as the orifices
provide free flow of well fluid back and forth through the plastic
jacket, but are not so extensive that they interfere with the
substantial continuity of the strand covering provided by the
plastic outer jacket. The outer jacket is preferably applied to the
strand by a pressure extrusion operation so that the plastic forms
a fairly thick layer on the surface of the strand and has a smooth
outer surface rather than an outer surface conforming generally to
the contours of the individual wires which comprise the outer
surface of the metallic portion of the flexible pumping strand. The
plastic strand jacket may desirably have a thickness of about 0.050
inches for a polyamide or particularly a Nylon 11 jacket, but may
also have other thicknesses depending upon the plastic composition
used and the environment in which it is to be used.
The flexible pumping strand of the invention may be made as shown
in FIGS. 4a and 4b which illlustrate an integrated production line
for the initial coating of the component wires, the stranding of
the coated wires together to form the body of the flexible pumping
strand and the jacketing of the pumping strand with a perforated
outer plastic jacket.
In FIG. 4a a wire 61 is initially unreeled from a pay-off reel 63
and passed constructively through an alkaline cleaning bath 65 and
a pickling bath 67 to remove drawing soaps and scale in a
conventional manner. The wire is then passed through a rinse bath
69 to remove residues remaining from the preceding treating baths.
The wire 61 then passes into a phosphate activator bath 71 where
the surface of the wire is activated prior to passage into a
phosphating bath 73 which applies a phosphate coating to the wire
surface by treatment in a proprietary phosphate composition in a
known manner of producing an iron phosphate conversion coating on a
steel surface. The proprietary phosphating compound may be
Granodine 1100, produced by Amchem Products Incorporated. However,
other types or brands of commercial phosphate coatings can also be
used. After passing through the phosphate tank or bath 73 the
phosphated wire passes through a rinse tank 75 where the phosphated
wire is rinsed in water and then passes into a post treatment bath
76 where the phosphated wire is treated in an acid rinse to fix the
phosphate coating and activate the surface of the wire in
preparation for the next treatment. The wire then passes into a
spray application chamber 77 where an epoxy type primer is applied
to the surface of the wire. The epoxy primer, which serves
primarily as an adhesive to aid in obtaining a tightly bonded
plastic coating on the wire, may be any one of a number of
commercially available primers suitable for use with the
subsequently applied plastic. As an example, NUBLAR epoxy primer
No. 67431 made by the Glidden Company suitably thinned by a solvent
was applied to the wire in the spray chamber 77 as the wire moved
through the chamber at 130 feet per minute. Overspray from the
sprays 79 falls into the trough 81 within the chamber 77 and is
recycled by the pump 83 back to the sprays 79 through pipe 85.
From the spray chamber 77 the primer coated wire passes into an
induction furnace 87 where the primer is baked onto the surface of
the wire. The furnace 87 serves to expel the solvent from the
primer as well as activate and cure the primer, and solvent vapors
are caught in a hood 89 and returned to a mixing and makeup tank 91
via the suction engendered by centrifugal pump 93. From the
induction furnace 87 the wire passes to a second spray chamber 95
where a second primer coating is applied over the surface of the
first primer. The second primer is comprised of a suspension of the
same polymer which is to be applied by extrusion to the outer
surface of wire dispersed or dissolved in a suitable organic
solvent such as, for example, xylene, isopherone or diacetone
alcohol. For example polyvinylidene fluoride may be dispersed in
isopherone and sprayed by the sprays 97 onto the wire as the wire
passes through the chamber 95. The overspray is caught in the
trough 99 and recycled via pump 101 and pipe 103 back to the sprays
97. The second primer may consist of a proprietary primer known as
Kynar dispersion No. 202 sold by the Pennwalt Corporation if the
final coating on the wires is to be composed of polyvinylidene
fluoride. The wire then passes through a second induction furnace
105 where the solvent is evaporated from the primer and the
remaining plastic resin of the primer is fused upon the wire over
the first primer. The solvent vapor escaping from the furnace 105
is caught or collected by the hood 107 and returned to make-up and
mixing tank 109 via the suction induced by the centrifugal pump
111. The wire may suitably leave the induction furnace 105 at a
temperature of about 500.degree. F. and with a total coating
thickness comprised of the two primer coatings of about 0.0005
inch. From the induction furnace 105 the wire next passes through a
water cooling weir 113 and then through a pressure extruder 115
where a coating of polyvinylidene plastic is extruded onto the
surface of the moving wire. The polyvinylidene fluoride bonds very
securely to the thin film of the second primer, which is comprised
after it is fused on the surface of the wire of a very thin film of
polyvinylidene fluoride, to form an overall protective plastic
coating or plastic jacket which is extremely adherent to the
surface of the underlying wire. The thickness of the final
protective polyvinylidene fluoride protective coating may be about
0.005 inches or a total of 0.010 inches of plastic added to the
diameter of the wire. After extrusion of the coating onto the wire,
the wire passes through a second weir 117 where the wire with its
overlying coating is thoroughly cooled before passing the wire
about a pulling capstan 119 and then onto a take-up reel or spool
121, and when that reel or spool 121 is full onto additional reels
or spools designated as 123.
The polyvinylidene fluoride plastic resin or PVF.sub.2 may be
so-called Kynar, a proprietary composition of the Pennwalt Company.
However, polyvinylidene fluoride resins supplied by other sources
or companies may also be used. While PVF.sub.2 is preferred because
of price and handling characteristics as the wire coating
composition for sour brine type wells, i.e., oil wells having a
large amount of brine and hydrogen sulfide in them, other types of
fluoropolymers have also been found satisfactory though somewhat
less convenient. One example of such fluoropolymers is
polychlorotrifluoroethylene, often designated as PCTFE. This
polymer can be purchased from the 3M Company under the brand name
of Kel F. Another suitable fluoropolymer is a copolymer of
tetrafluoroethylene and hexafluoropropylene sometimes designated as
FEP polymer. This resin is sold by the DuPont deNemours Company
under the brand name of Teflon FEP. A third suitable fluoropolymer
in addition to the preferred polyvinylidene fluoride is
polyethylenechlorotrifluoroethylene often designated as PECTFE. The
polyethylenechlorotrifluoroethylene copolymer is sold by the Allied
Chemical Corporation under the brand name of Halar. A further
polymer which has been found to be suitable in a simulated sour
brine oil well environment is polyethylenetetrafluoroethylene or
PETFE which copolymer is sold by The DuPont deNemours Company under
the brand name Tefzel. All of these fluropolymers have been found
to have the required characteristics of inertness to the well
fluid, low permeability to water and corrosive gases and sufficient
toughness to withstand stranding and handling of the coated wires
and interwire fretting and abrasion of the wires during service in
an oil well. Other fluoropolymers may possibly also be suitable in
sour brine or acid type oil wells and other types of polymer
coatings in addition to the fluoropolymers may be suitable for
sweet brine wells, i.e., brine wells which do not contain hydrogen
sulfide, and alkaline type oil wells. Each polymer used should, of
course, be tightly bonded to the underlying wire surface by the use
of an appropriate primer or primers during the coating operations.
Plastic compositions which may themselves have suitable properties,
such as inertness and impermeability to corrosive substances found
in oil wells, to act as protective shields against corrosion will
not be suitable for use in jacketing the individual wires of the
strand in a corrosive oil well environment if there is no practical
manner known to securely bond the plastic to the underlying
metallic surface of the wire.
After the wire or wires 61 are suitably coated and stored on the
reels 121 and 123, the spools are either transferred to the
stranding line shown in FIG. 4b or the coated wire is removed from
the reels and wound on suitable spools for use in the stranding
line.
In the stranding and jacketing line shown in FIG. 4b, which may be
a separate line or may be a continuation of the wire coating line
shown in FIG. 4a, the spools 121 containing the coated wires 61a
and 61b are placed in position with respect to or on the flyers or
rotatable stranding cages 131a, 131b and 131c. The flexible pumping
strand shown in FIGS. 2 and 3 is a 37 wire oppositely stranded wire
strand and in order to make this strand as shown in FIG. 4b there
are required three stranding operations or stranding machines each
of which will form or lay one operation or layer of wires 61b about
the center wire 61a of the strand. It will be understood that the
flyer 131a will during the stranding operate in one direction, the
flyer 131b will operate in the opposite direction and the flyer
131c will operate in the direction of the first flyer to form a
cross layed strand, or a strand having opposite rotations or lays
in each operation or lay of wires. If a cross layed, or opposite
lay, strand is not desired the flyers would, of course, be operated
in the same direction. The rotational speeds of the flyers may be
varied with relation to the speed of passage of the wires or the
formation of the strand to vary the lay of the various operations
of wires and thus vary the characteristics and particularly the
rotational characteristics of the strand as is familiar to those
skilled in the art of stranding. If desired the strand could, of
course, be formed by three passes through one flyer or rotatable
stranding cage rather than one continuous pass through three
consecutive flyers. The flyers 131 are rotatably journaled on
suitable supporting and drive means 133 at their leading ends and
rotatably supported on bearing roller means 135 at their opposite
ends. Associated with each flyer 131 there are stranding dies 137a,
137b, and 137c respectively to which the wires 61b from the spools
131 on each flyer are directed as illustrated to strand the wires
about either the center wire 61a or the previous operation of
wires. Leading to each stranding die is a tube 139 shown for
convenience as an arrow which conveys a small stream of a water
base stranding lubricant to each respective stranding die, which
lubricant prevents detrimental abrasion and damage to the wires or
their coatings as they are forcibly drawn through the stationary
stranding dies from the rotating flyers. The water base lubricant
is obtained from a reservoir 141 of lubricant. The lubricant is
forced through the tubing 139 by the action of the pump 143. The
stranded wires leaving the last stranding die 137c then pass to a
pressure type extruder 145, preferably by way of a looping tower
arrangement 147 which serves to accommodate adjustments in the
operating speeds of the extruder 145 and the stranders during
stopping and starting of the stranding line. The stranding
operation tends to require starting and stopping more frequently
than the extruding operation and this starting and stopping may
cause imperfect extrusion unless the speed of the extrusion line
can be maintained fairly constant. Alternatively, of course, the
extrusion and stranding may be done on separate lines with a
separate reeling and unreeling operation between the stranding and
extrusion lines. The wires of the strand will in either case retain
a fair amount of the stranding lubricant clinging to the surfaces
of the wires within the interstices between the wires. The
particular lubricant is not critical so long as it contains a high
percentage of water or other vaporizable liquid component. It is
very desirable that the lubricant be a water base lubricant,
however, because the lubricant, which is essentially a light
lubricant having just enough lubricity to allow the wires to slip
past each other in the stranding die without damage to either the
wires or the coating on the wires, also serves as a coolant for the
stranding operation. If there is not sufficient lubricity to the
lubricant the coating on the wires may be nicked, while if the
stranding operation is not cooled sufficiently the coating may
again be damaged. One very suitable lubricant to use is composed of
about one part of Cimperial oil, which is a soluble cutting fluid
or oil combined with a corrosion inhibitor. Cimperial oil is made
and distributed by the Cincinnati Milling Products Division of
Cincinnati Milacron in Cincinnati, Ohio. The soluble cutting oil is
diluted or combined prior to use with about 9 or 10 parts of water.
Cimperial Oil is a cutting lubricant made for use primarily in
thread cutting operations which is also widely used as a stranding
lubricant. Other types of soluble lubricants could also be used as
the stranding lubricant as well as emulsions of oil and water and
the like.
As the strand passes through the pressure extruder 145 the
fluoropolymer coating on the individual wires will be temporarily
or momentarily compressed by the combined effects of the pressure
in the extruder and the heat of the extruder. The extruder is, of
course, hot enough to render the material being extruded, i.e., a
polyamide such as Nylon 11 or the like, soft and plastic to
facilitate its extrusion. The normal 13 percent void space between
the individual wires of the strand thus drops momentarily to a very
low level due to compression of the fluoropolymer wire coatings
together as the strand passes through the extruder. As the outer
jacket of Nylon 11 is extruded onto the outer surface of the strand
the heat of the extruding operation causes the water in the water
base lubricant to vaporize and since the space between the wires is
momentarily very constricted the vapor has nowhere to go and cannot
escape from the strand toward the entrance of the extruding die.
Thus the vapor as the strand passes from the extruding die is
released instead into the interior of the newly jacketed portion of
the strand and, it has been discovered, quite unexpectedly, that
the vapor pressure induced in the strand causes periodic
perforation of the outer plastic jacket of the strand while the
plastic jacket is still in a somewhat plastic condition. The amount
of the water base lubricant which clings to the individual wires
when a 10 to 1 water to lubricant solution is used is just
sufficient to provide a perforation pattern for the finished strand
which is suitable to provide free access from the interior to the
exterior and vice versa in the finished strand when the strand is
used in an oil well. If necessary, of course, some water or other
vaporizable liquid can be placed on the wires of the strand just
before the strand passes into the extruding die to provide either
all of the vapor or an effective amount of additional vapor to
cause proper perforation of the strand.
As an alternative to vapor perforation the strand perforations may
be made by mechanical perforation with a metal die. For example, in
one case a 3/16 inch cylindrical steel rod with a flat end was
warmed, pressed into the soft jacket immediately after the strand
exited from the extrusion die 145 and held against the strand until
the rod was carried into the subsequent cooling means where the
plastic hardened. After removal of the rod from the hardened jacket
a suitable perforation of the strand jacket remained. Suitable
perforations may also be formed in the hardened jacket by means of
small cutting dies and the like or by drilling a hole through the
jacket. Such operations however, require extreme care to avoid
cutting into and damaging the plastic coatings on the individual
wires of the flexible pumping strand.
After the now jacketed strand leaves the extruder 145 and
perforation of the still soft jacket material takes place, the
strand is passed into a cooling weir 149 where a water bath cools
and hardens the plastic jacket. From the weir 149 the strand passes
to and about a pulling capstan 151 which serves to pull the strand
through the preceding apparatus and then passes onto a take-up reel
153 for storage or shipment.
Any type of strong abrasion resistant plastic material which is
substantially inert to or not substantially degraded by the well
fluid will be satisfactory as the outer jacket of the strand. It is
not necessary for the material of this jacket to be impermeable to
water or corrosive gas so long as it is not itself seriously
degraded by such substances since the outer jacket is perforated in
any event specifically to allow free passage of the well fluids
through the outer jacket. Various other types of nylon in addition
to the preferred Nylon 1, i.e., a nylon having 11 carbon atoms on
the principal di-acid, di-amine or amino-acid monomers from which
the nylon polymer is polymerized, can be used if such other types
are tough and abrasion resistant. Another very suitable outer
jacket material is ultra-high molecular weight polyethylene or
so-called UHMW polyethylene.
When the flexible pumping strand of the invention is placed in a
corrosive oil-well environment the well fluid has free access to
the interior of the strand through the perforations in the plastic
jacket of the strand. This prevents damage of the jacket arising
from pressure variations encountered in all portions of the well
and particularly from the high pressures encountered in the lower
portions of a deep well. The plastic outer jacket, on the other
hand, effectively protects the inner components of the strand from
abrasion and wear. It is important that the fluoropolymer coatings
on the individual wires of the strand be protected from physical
contact with the structures of the inside of the well and the
general well environment and the outer jacket serves very
effectively to package or protect all the individual wires from
mechanical damage both in the well and during storage and
transportation prior to use in the well. In the case of a pumping
strand which has substantially parallel wires, furthermore, such as
are shown in U.S. Pat. Nos. 3,212,582 or 3,234,723 to K. D. Brown
and where individually coated wires are used as shown in U.S. Pat.
No. 3,234,723, the outer plastic jacket serves effectively to
maintain the wires of the strand together in a compact bundle.
However, with the preferred strand shown in FIGS. 1, 2 and 3 in
which the flexible pumping strand 17 has a fairly long lay to
maintain the wires of the strand together and to facilitate bending
of the strand while still maintaining a minimum overall diameter of
the strand, the outer plastic jacket has only a minimum effect in
keeping the wires together. However, if a strand such as described
and claimed in U.S. Pat. No. 3,234,723 is made in the approved
manner of the present invention, that is with a fluoropolymer
bonded securely to the wire surface to inhibit migration of
corrosion along the wire surface under the plastic coating and
having an outer perforated abrasion resistant plastic jacket, then
the perforated plastic jacket of the invention would serve, in
addition to protecting the inner wire from damage, to, of course,
also maintain the individual wires together in a compact bundled
arrangement.
It has been found very important to have the fluoropolymer or other
plastic covering the individual wires tightly bonded to the
surfaces of the wires. The bonding blocks migration of corrosion
inducing agents such as hydrogen sulfide and the like along the
surface of the wire under the plastic coating and thus prevents
corrosion of the wire surface. Surprisingly, when the plastic is
tightly bonded to the surface of the wire in the manner of the
invention, it has been found that even when the fluoropolymer has
occasional pinholes or tiny holidays extending through it to the
metal surface below no significant corrosion of the metal surface
of the wire occurs even directly under the pinholes. Thus the
bonding of the plastic to the underlying metal surface not only
prevents the propagation of corrosion along the metal surface under
the plastic, but actually also inhibits corrosion in an oil well
environment of the metal surface in the immediate vicinity of the
pinhole or tiny holiday itself. This is quite contrary to the
experience with prior plastic coated wires in oil well environments
in which the plastic is not tightly bonded to the surface of the
wire but is instead loosely extruded over the wire perhaps with a
corrosion inhibiting substance or the like deposited as an
undercoating on the surface as disclosed for example in U.S. Pat.
No. 3,443,982 to Kjellmark. In such cases corrosion tends to occur
quickly at pinholes in the coating and spreads rapidly in spite of
the corrosion inhibitor deposited between the plastic coating and
the metal surface often resulting in very accelerated failure of
the wire in the vicinity of the pinhole.
* * * * *