Note: Descriptions are shown in the official language in which they were submitted.
t.
POST-BORIDING PROCESSES FOR TREATING
PIPE AND RECOVERING BORONIZING POWDER
FIELD OF THE INVENTION
[001] The invention relates to the post-bonding processing of pipes. More
particularly, the
invention relates to a method for hardening pipes after boronizing to improve
core mechanical
properties, the use of unthreaded end caps during boronizing to allow for
threading of pipe ends
after boronizing, and for recovery of boronizing powder.
BACKGROUND OF THE INVENTION
[002] Treating metal surfaces is sometimes necessary when the targeted
application for the metal
workpiece subjects the metal to high wear, erosion or corrosion. For example,
metal parts in
agricultural equipment are sometimes treated to successfully withstand the
erosive demands
required during their normal use. Even more demanding applications involve
both erosion and
corrosion. Such an application is embodied in the oil and gas industry where
oil wells are involved.
In oil and gas production, a sucker rod pump can be used to pump desired
products to the surface
for recovery. The pump functions from the surface by oscillating a rod up and
down inside a pipe
that drives a pump located at the bottom of the well. Each upward stroke of
the pump transports
liquid containing the targeted product up through a tube towards the surface.
But such
environments can be very harsh, with temperatures of 250 C and pressures of 70
MPa or higher
not being uncommon. The presence of sour crude in the well also means
corrosive compounds
such as hydrogen sulfide, carbon dioxide, methane, produced water, produced
crude and acidic
conditions will be present. Under the best of circumstances, these conditions
alone would
represent a challenge to a pipe operating in such a service, however, the
action of the sucker-rod
pump complicates it still further, since the rod can wear against the inside
surface of the pipe as it
moves up and down. This mechanism of wear removes a portion of the metal
tubing's surface
layer, exposing the underlying layer to corrosion. However, the newly corroded
layer cannot
protect the pipe from further corrosion since it is swiftly worn away by the
continued action of the
pump rod. Thus, an undesirable, repetitive cycle of erosion/corrosion/erosion
takes place that can
rapidly cause the pipe to fail. Since environmental concerns in recent years
have pushed drilling
rigs into deep water, further away from coastlines, the implications of pipe
failure are very serious.
Thus, oil producers have preferred treated pipe for pumping applications,
particularly, the
diffusion-based treatments such as nitriding, carburizing and bonding.
However, while nitriding
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and carburizing can produce hard metal surfaces, they do not harden as well as
boronizing, which
creates a wear layer with higher hardness than many wear resistant thermal
spray coatings, such
as tungsten carbide and chrome carbide. The boron is not mechanically bonded
to the surface, but
instead is diffused below the surface of the metal, making it less prone to
delamination, peeling
and breaking off treated parts. Just as importantly, these other methods
cannot provide the
corrosion resistance that boronizing offers.
[003] Several methods for boronizing metal articles are available. For
example, liquid bonding
techniques can be employed, where electrolytic or electro-less baths are
employed to deposit layers
of borides. Gas bonding or plasma bonding can also be used. However, these
methods, while
having certain advantages, are unsuitable for environmental reasons or are
impractical for long
tubing. Paste-bonding is a particular type of selective bonding, where the
boronizing composition
is applied as a paste to the metal surface, and then heated. This technique,
while being useful for
localized spot bonding, is completely unsuitable for pipes because there is no
practical way of
applying the paste through the length of the pipe. Powder pack boronizing,
typically referred to
as "pack cementation" boronizing, involves placing a metal part in physical
contact with the boron
source as part of the boronizing powder composition. For example, a metal part
can be buried in
a quantity of powder, or a pipe can be filled with powder so it contacts the
pipe's interior surface,
and the pipe is heated.
[004] Powder boronizing compositions typically contain a boron source, an
activator, and often
a diluent, where reactive boron-containing compounds such as amorphous boron,
crystalline ferro-
boron, boron carbide (134C), calcium hexaboride (CaB6), or borax react with a
halide-based
activator upon heating to form gaseous boron tri-halides, such as BF3 or BC13,
which react with
the metal surface to deposit boron on the surface, which is then able to
diffuse into the metal
structure. Diluents are included to provide bulk and reduce cost.
[005] Conventional boronizing of pipes typically involves manual pipe
handling, where there is
an excess of exposure to powder compositions and boronizing gas by operations
personnel during
the loading and off-loading process. Many bonding powder compositions are also
prone to
sintering to a solid cake inside of a pipe that is difficult to break apart
and remove after bonding.
It has unexpectedly been found that it is possible to minimize operator
exposure to powder and
boronizing gases through a closed system of powder movement, as well as the
use of an anti-
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_
,
sintering agent for the powder, to prevent sintering and caking of powder
inside the tubing making
it easier to remove after bonding.
[006] Conventional pipe boronizing for oil field applications has been
performed where the pipes
are boronized and treated to conform to the American Petroleum Institute's API
5CT
specification's grade J55. The requirements for J55 grade tubing listed in API
5CT Table E.5 are
55-80 KSI yield strength, 75 KSI minimum tensile strength and no hardness
requirement. The
J55 tubing does not have as high of yield strength or as high of burst
pressure as what many
petroleum companies desire; however, to date boronized tubing has only been
offered in the J55
grade. The yield strength and burst pressure of the J55 tubing is considered
marginal in many
wells and oil producers would prefer to have a higher grade of boronizing
tubing with higher levels
of yield strength and burst pressure for a greater safety factor when
operating at high pressures and
high temperatures. Higher strength grades such as L80, N80, R95, M65, C90,
T95, C110, P110,
and Q125 are all produced by performing a heat treatment involving
austenitizing, quenching and
tempering, and all have higher strength properties than J55 grade tubing. L80
is a commonly used
grade of tubing in oil producing wells. The core mechanical properties of L80
grade are 80-95
KSI yield strength, 95 KSI minimum tensile strength, and 23 HRC maximum
hardness. In many
wells, the entire string of tubing/piping used will be L80 grade tubing for
its higher strength and
burst pressure properties, but boronized tubing that only meets J55 grade
requirements is often
used at the bottom of the wells as it has improved wear and corrosion
resistance. However, as
discussed above, the J55 grade tubing does not have the same high strength and
burst pressure
ratings compared to L80 grade tubing, and this reduces the pressures that oil
producers may operate
at within the wells, and further reduces the safety factors available to oil
producers. It has
unexpectedly been found that boronizing and post-boride hardening of pipe is
possible if reheating
is performed using processing parameters that do not adversely affect the
integrity of the boride
layer. This allows the tubes to be heat treated to meet the API 5CT L80
specification for yield
strength and burst pressure while also having a boride layer present on the
inner bore to increase
wear and corrosion resistance.
[007] Oil field production tubing typically consists of a long pipe with
flared ends that have
external threaded connections at each end such that they can be joined
together using short
internally threaded couplings into long tubing strings. To date, boronizing of
tubing for oil wells
has been performed by screwing a closed cap onto one threaded end connection
of a pipe, filling
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that pipe with boronizing powder until full, and then screwing a second closed
cap onto the other
threaded connection end of the pipe to contain the boronizing powder inside
the pipe during the
process. One issue with this practice is that the boronizing process involves
heating pipe to high
temperatures such as 1400F to 1750F for many hours and the threads are soft
and have little
strength at these temperatures. Any forces or stresses placed onto these
threads by the screwed on
end cap can cause the threads to bend and warp during high temperature
bonding. High
temperature creep strength is also very low in these threads and they can warp
and distort from the
heating and cooling process alone as the metal expands during heating,
contracts during cooling
and may warp under any stresses present. Threads are also prone to damage as
they can be easily
nicked, dinged and damaged during installation of the caps, removal of the
caps, handling and
transport of the pipes and subsequent cleaning and straightening operations
after bonding. For
these reasons, many oil producers have encountered problems with making good
threaded
connections and thread leakage on boronized pipes produced with threads
present on the tubing
during the bonding process. The development of a bonding process that can be
performed on an
unthreaded pipe using new cap designs that can attach to the ends of a pipe
without requiring a
threaded connection would allow for the threading operation to be performed
after bonding which
would yield higher quality threads that would not be subject to high
temperature distortion and
warpage and could not be damaged during the processing if not present during
bonding.
SUMMARY OF THE INVENTION
[008] In one embodiment, the subject matter of the present disclosure relates
to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
second end, an inside surface and an outside surface; heating the pipe to a
temperature to form a
bonded layer on the inside surface, and spent boronizing powder; removing the
spent boronizing
powder from the pipe, thereby forming an empty boronized pipe; heating the
empty boronized pipe
to above its austenitizing temperature, thereby forming an austenitized pipe;
quenching the
austenitized pipe, thereby forming a quenched pipe; and tempering the quenched
pipe, thereby
forming a tempered pipe.
[009] In another embodiment, the subject matter of the present disclosure
relates to a pipe
produced by a process comprising placing a boronizing powder composition in a
metal pipe
comprising a first end, a second end, an inside surface and an outside
surface; heating the pipe to
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a bonding temperature, thereby forming a bonded layer on the inside surface,
and spent boronizing
powder; removing the spent boronizing powder from the pipe, thereby forming an
empty
boronized pipe; heating the empty boronized pipe to above its austenitizing
temperature, thereby
forming an austenitized pipe; quenching the austenitized pipe, thereby forming
a quenched pipe;
and tempering the quenched pipe, thereby forming a tempered pipe.
[0010] In still another embodiment, the subject matter of the present
disclosure relates to a
boronized pipe meeting the specification of API 5CT specification Grade L80.
[0011] In an embodiment, the subject matter of the present disclosure relates
to a process for
treating a boronized pipe comprising a bonded layer on its interior surface,
the process comprising:
heating the boronized pipe to above its austenitizing temperature, thereby
forming an austenitized
pipe; quenching the austenitized pipe, thereby forming a quenched pipe; and
tempering the
quenched pipe, thereby forming a tempered pipe.
[0012] In another embodiment, the subject matter of the present disclosure
relates to a pipe
produced using a process for treating a boronized pipe comprising a bonded
layer on its interior
surface, the process comprising: heating the boronized pipe to above its
austenitizing temperature,
thereby forming an austenitized pipe; quenching the austenitized pipe, thereby
forming a quenched
pipe; and tempering the quenched pipe, thereby forming a tempered pipe.
[0013] In another embodiment, the subject matter of the present disclosure
relates to a process
comprising heating a boronized pipe to above its austenitizing temperature,
thereby forming an
austenitized pipe; and quenching the austenitized pipe, thereby forming a
bonded and quenched
pipe.
[0014] In still another embodiment, the subject matter of the present
disclosure relates to a pipe
produced by a process comprising heating a boronized pipe to above its
austenitizing temperature,
thereby forming an austenitized pipe; and quenching the austenitized pipe,
thereby forming a
quenched pipe.
[0015] In another embodiment, the subject matter of the present disclosure
relates to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
second end, an inside surface and an outside surface; heating the pipe to a
bonding temperature,
thereby forming a bonded layer on the inside surface, and spent boronizing
powder; and removing
the spent boronizing powder from the pipe, wherein the spent boronizing powder
is removed from
the metal pipe with a closed transport system.
CA 2998056 2018-03-13
[0016] In an embodiment, the subject matter of the present disclosure relates
to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
second end, an inside surface and an outside surface; heating the pipe to a
bonding temperature,
thereby forming a bonded layer on the inside surface, and spent bonding
powder; and removing
the spent bonding powder from the pipe, wherein the boronizing powder is
placed in the metal
pipe by conveying the powder to the pipe using a closed transport system
selected from pneumatic
conveying, rotary valve, screw conveyer or combinations thereof
[0017] In still another embodiment, the subject matter of the present
disclosure relates to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
second end, an inside surface and an outside surface; heating the pipe to a
bonding temperature,
thereby forming a bonded layer on the inside surface, and spent bonding
powder; and removing
the spent bonding powder from the pipe, wherein the boronizing powder is
placed in the metal
pipe by conveying the powder to the pipe using a closed transport system, and
the spent boronizing
powder is removed from the metal pipe by a closed transport system.
[0018] In an embodiment, the subject matter of the present disclosure relates
to a process
comprising transporting oil or gas in an oil well with a pipe produced by a
process comprising
placing a boronizing powder composition in a metal pipe comprising a first
end, a second end, an
inside surface and an outside surface; heating the pipe to a bonding
temperature, thereby forming
a bonded layer on the inside surface, and spent boronizing powder; removing
the spent boronizing
powder from the pipe, thereby forming an empty boronized pipe; heating the
empty boronized pipe
to above its austenitizing temperature, thereby forming an austenitized pipe;
quenching the
austenitized pipe, thereby forming a quenched pipe; and tempering the quenched
pipe, thereby
forming a tempered pipe.
[0019] In an embodiment, the subject matter of the present disclosure relates
to a process
comprising transporting oil or gas in an oil well with a pipe produced by a
process comprising
treating a boronized pipe comprising a bonded layer on its interior surface,
the process comprising:
heating the boronized pipe to above its austenitizing temperature, thereby
forming an austenitized
pipe; quenching the austenitized pipe, thereby forming a quenched pipe; and
tempering the
quenched pipe, thereby forming a tempered pipe.
[0020] In still another embodiment, the subject matter of the present
disclosure relates to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
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second end, an inside surface and an outside surface; heating the pipe to form
a bonded layer on
the inside surface, and spent boronizing powder; removing the spent boronizing
powder from the
pipe, thereby forming an empty boronized pipe; heating the empty boronized
pipe to above its
austenitizing temperature, thereby forming an austenitized pipe; quenching the
austenitized pipe,
thereby forming a quenched pipe; tempering the quenched pipe, thereby forming
a tempered pipe;
and threading the tempered pipe.
[0021] In another embodiment, the subject matter of the present disclosure
relates to a process
comprising boronizing an unthreaded pipe, thereby forming an unthreaded
boronized pipe; and
threading the unthreaded boronized pipe.
[0022] In an embodiment, the subject matter of the present disclosure relates
to a process for
boronizing a metal pipe comprising a flared first end, a second end, an inside
surface and an outside
surface, the process comprising: fastening a first split-bushing end cap on
the flared first end;
depositing boronizing powder in the pipe; fastening a plate or second split
bushing end cap on the
second end; and heating the pipe to a temperature from 1400 F to 1900 F,
thereby forming a
bonded layer on the inside surface, and generating spent reaction gases and
spent bonding powder.
[0023] In another embodiment, the subject matter of the present disclosure
relates to a process for
boronizing a metal pipe comprising an unthreaded first end, an unthreaded
second end, an interior,
an inside surface and an outside surface; fastening a first plate to the first
end of the pipe; placing
boronizing powder in the interior of the pipe; fastening a second plate to the
second end of the
pipe; and heating the pipe to a temperature from 1400 F to 1900 F, thereby
forming a bonded
layer on the inside surface, and generating spent reaction gases and spent
bonding powder.
Typically, the first plate and second plate are fastened onto the ends of the
pipe by welding or
joining.
[0024] In still another embodiment, the subject matter of the present
disclosure relates to a process
comprising placing a boronizing powder composition in a metal pipe comprising
a first end, a
second end, an inside surface and an outside surface; heating the pipe to form
a bonded layer on
the inside surface, and spent boronizing powder; heating the pipe with the
bonded layer to above
its austenitizing temperature, thereby forming an austenitized pipe; quenching
the austenitized
pipe, thereby forming a quenched pipe; and tempering the quenched pipe,
thereby forming a
tempered pipe.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The subject matter of the present disclosure will be more fully
understood from the
following detailed description, taken in connection with the accompanying
drawings, in which:
[0026] Figure 1 illustrates a flow diagram for the boronizing of pipes
including the loading and
unloading of boronizing powder compositions.
100271 Figure 2 illustrates split-bushing end caps and an unthreaded flared
tube end.
[0028] Figure 3 illustrates a split-bushing end cap for an unthreaded flared
tube being mounted on
flared section of tube where the split bushing diameter fits around the main
body of the tube but
will not be able to slip over the larger diameter of the flared end of the
pipe.
[0029] Figure 4 illustrates the installation of a split-bushing endcap for
boronizing unthreaded
tubes with the two split bushing pieces surrounding the main body diameter of
the pipe. The two
split bushing pieces are about to be screwed into the end cap where the split
bushings will be pulled
up into the end cap during until inner diameter of the split bushings catches
on the tapered section
of the larger flared end diameter and secures the end cap and split bushing
assembly tight against
the end of the pipe.
[0030] Figure 5 illustrates a split-bushing end cap installed on the end of a
flared tube.
[0031] Figure 6 illustrates a split-bushing from various angles.
[0032] Figure 7 illustrates an end cap from various angles.
[0033] Figure 8 illustrate a plate end cap.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The subject matter of the present disclosure provides a process for
treating boronized
piping having a particularly designed boride layer that is physically uniform,
i.e., not oxidized,
cracked, flaked or pitted. The resulting treated pipe is capable of meeting
the stringent
requirements of high strength pipe such as API specification 5CT Grade L80.
The subject matter
of the present disclosure also provides a process for boronizing a metal pipe
in an environmentally
safe and efficient manner by loading and unloading pipes in a closed transport
system.
[0035] For the purpose of this specification, the terms "boronizing" and
"bonding;" and
"boronized" and "bonded" will be used interchangeably to designate the
boronizing process and
pipes resulting from the process of the present subject matter. Also, the
terms "pipe" and "tubing"
will be used interchangeably to designate a cylindrical or round-shaped
conduit for carrying fluids
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such as gases, liquids, slurries or powdered solids. When reference is made to
the diameter of a
tube or pipe, unless it is designated differently, it will mean the inside
diameter of the tube or pipe.
Finally, the term "powder" means a dry, bulk solid composed of a large number
of very fine
particles.
[0036] Metal Pipes
[0037] The metal pipes or tubes to be boronized preferably have an inner
diameter (ID) of 1.0 to
12.0 inches. More preferably, the pipe has an ID of 1.5 to 6.0 inches. Most
preferably, the pipe
has an ID of 1.5 to 3.0 inches. The outside diameter of the pipe can vary
depending on the pressure
rating of the pipe that can require different wall thicknesses. The burst
pressure rating of the pipe
to be boronized can range from atmospheric to 10,000 psig. The length of the
pipe can vary.
Preferably, the length of pipe can range from 1.0 to 36.0 feet. More
preferably, the length of the
pipe can range from 10.0 to 36.0 feet. Even more preferably, the length of the
pipe can range from
31.0 to 36.0 feet. Alternately, the length of the pipe can range from 14.0 to
18.0 feet.
[0038] Normally, the pipe or tube ID is the same along this entire length.
However, in some
applications, as discussed below, the end(s) of the pipe can be worked in the
forging process to
upset and enlarge (flare) the ends of the pipe. In this case, the ID of the
pipe refers to the ID of
the pipe/tube prior to any enlargement of the ends, i.e., the term ID refers
to the ID of the pipe
except at the flared ends. The ends of the tube or pipe to be boronized can be
threaded or non-
threaded. When the pipe is threaded, it is possible to cap the pipe end with a
corresponding
threaded end cap. Typically, such an end cap is also spot-welded in place to
maintain the cap's
position in preventing loss of boronizing powder, while not imposing a tight
seal on the pipe. Were
such a seal imposed on the pipe, the buildup of boronizing gases during
boronizing would
overpressure the pipe and result in pipe failure. Preferably, the pipe is non-
threaded
[0039] Preferably, the ends of the pipe to be boronized are processed in an
operation known as
upset ending, which is a forging process where the end of the pipe or tubing
is flared and thickened
by heating and forcing it through a die and over a mandrel. By processing the
tube or pipe in this
manner, the tensile strength of the pipe is enhanced, in anticipation of the
expected tensile strength
loss when the tube or pipe is threaded. Thus, the flared ends of the pipe or
tube have a larger
outside diameter than the predominant outside diameter of the tube or pipe, as
shown in FIG 4 and
5. The difference in outside diameter between the flared and non-flared
sections of the pipe is
typically 0.25 to 0.50 inch. Typically, the length of pipe that is flared is 4
to 6 inches. More
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preferably, the ends of the pipe to be boronized are first processed to be
flared as discussed above,
and are then threaded after boronizing.
[0040] When the pipe ends are flared but not yet threaded, they may be capped
in a number of
ways identical to non-flared pipes. One or both ends may be flared. When the
pipe ends are flared,
preferably, both ends are flared. A tight seal of the pipe during boronizing
where gas cannot escape
is not desired, as it would result in over-pressure of the pipe and pipe
damage or failure. For
example, a cylindrical cap may be fitted over the pipe end and spot-welded in
place. Alternately,
the end of the pipe can be filled with high temperature ceramic cloth or
metallic wiring to maintain
the stability of the boronizing powder and keep it within the tube or pipe,
but still allow the
boronizing gas produced during the boronizing process to escape the pipe. A
split-bushing endcap
can be used when the tube or pipe has a flared end. The split bushing endcap
is composed of an
end cap portion and a split-bushing portion, as shown in FIG 4 and 5. The end
cap portion, is
typically cylindrical and capped at one end, and has an interior surface that
is threaded as shown
in FIG 5. The split-bushing portion is threaded to accommodate the threading
of the corresponding
end cap, and is present as at least one curved section as shown in FIG 6.
Preferably, the split-
bushing portion is present as at least two curved sections. Optionally, the
curved section(s) can
also have at one end a portion of a metal flange, such that when all the
sections are in place on the
flared section of the tube end or pipe they form a hexagonal nut section. More
preferably, the
split-bushing portion is present as two curved sections. To cap the flared
section of the tube or
pipe, the split-bushing portion is placed over the outer diameter of central
portion of the tube or
pipe just inside the tapered flared end, and the end cap portion is fitted
over the end of the tube or
pipe so that the threaded interior of the end cap portion engages the threads
of the split-bushing
portion. FIG 4 and 5. The end cap portion is then tightened over the split-
bushing portion,
fastening it to the flared section of the tube or pipe. The split-bushing
endcap can be constructed
from any metal compatible with the temperatures of the boronizing process.
Metals
[0041] The metals to be boronized according to the process of the current
subject matter are
generally any that can be boronized. Preferably, the metal article is selected
from plain carbon
steel, alloy steel, tool steel, stainless steel, nickel-based alloys, cobalt-
based alloys, cast iron,
ductile iron, molybdenum, or stellite. More preferably, the metal to be
boronized are ferrous
materials such as plain carbon steels, alloy steels, tool steels, and
stainless steel.
CA 2998056 2018-03-13
[0042] Boronizing Process
[0043] The boronizing process of the present subject matter is particularly
designed to provide an
excellent boride layer on a metal pipe while also ensuring minimal powder
exposure to operations
personnel. This can be accomplished not only by the use of a particular
boronizing composition,
but by loading and unloading of the powder from the metal pipe in a closed
system. At the start
of the boronizing process, the metal pipe must be filled with boronizing
powder, since the bonding
reactions adequately take place only where there is contact of the powder and
the inner surface of
the pipe. The boronized powder is transferred from a storage drum, hopper or
sack that houses
powder of the appropriate composition. Because a known amount of powder will
be necessary to
fill the pipe of a particular inner diameter and length, the metal pipe can be
filled using a closed
transport system employing solids metering systems such as loss-in-weight
feeders, screw feeders,
rotary valves or a pneumatic conveyance system. Weigh cells may also be used.
When a
pneumatic conveyance system is used, air or inert gases may be used to convey
the powder.
Ancillary lines including closed screw conveyers, piping or hoses can be used
to transport the
metered boronizing powder to the pipe in the closed transport system as
described above. Such
transport piping is vented to particle separators such as a cyclone or
baghouse. A vacuum pump
or ejector can be included in the powder fill system to prevent outside
exposure of powder.
[0044] After the metal pipe is filled with boronizing powder the pipe is
heated in a furnace to
achieve a boronizing layer, i.e., a bonding temperature. Preferably, the pipes
are heated to 1400
to 1900 F. More preferably, the pipes are heated to 1500 to 1750 F.
Preferably, the pipes are
typically heated for 1.0 to 24.0 hours. More preferably, the pipes are heated
from 4.0 to 16.0 hours.
The types of furnaces typically used include either open fire or atmosphere
controlled furnaces
that are generally either batch, continuous roller hearth, car-bottom, or
pusher-type furnaces.
[0045] After the pipe is boronized, the boronized pipe is typically cooled.
Then the spent
boronizing powder is removed from the metal pipe by removing end caps,
aligning the pipes over
a closed spent boronizing powder collection container, sealing the powder
discharge to prevent
exposure, and the pipes are then vibrated to shake the boronizing powder out
of the tubes and into
the closed collection container. The removed spent powder can be transported
to a storage vessel
for spent powders by a closed transport system as described above.
[0046] For filling and emptying, the pipe can be equipped with end fittings,
as described above.
The ends of the pipe, whether flared or non-flared, can be threaded or non-
threaded prior to
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boronizing. Preferably, the ends of the pipe are non-threaded prior to
boronizing. For the purposes
of this specification, the term "threading" or "threads" on a pipe, whether
flared or non-flared,
refer to the groves cut into the pipe at its ends, whether on the inside or
outside surface of the pipe
to allow pipes to be connected, all performed in accordance with API Standard
5B "Specification
for Threading, Gaging, and Thread Inspection of Casing, Tubing, and Line Pipe
Threads," the
disclosure of which is hereby incorporated by reference.
[0047] In addition to the fittings discussed above, the end fittings can be
slip on, flanged or
screwed fittings, partially or fully welded, and can be configured to allow
free flow of solids
through the pipe end opening to facilitate powder filling or emptying, as well
as permitting venting
of boronizing reaction gases for downstream processing during the boronizing
process, while
minimizing solids movement. The end fittings can optionally be configured to
incorporate valving
or manifolding for isolation of powder flow or reaction gas venting.
Alternately, if a manual
loading/unloading operation is used, the end fittings can be metal plates as
shown in Figure 8 that
are welded to the ends of the pipe to hold the boronizing powder within the
pipe during the
boronizing process. Preferably, the metal plates would be tack-welded to the
pipe to ease removal
when the boronizing process is completed.
[0048] From time to time it may be necessary to change the formulation of the
boronizing powder
due to a depletion of active components over time, accumulation of large
sintered particles, or
because of contamination. A powder recycling system can thus be configured to
facilitate the
addition of new powder to that being reused, or individual components of the
powder
compensation that have become depleted.
[0049] Boronizing reaction gases result from the boronizing process. Depending
on the type of
activator that is used, these gases can include hydrofluoric acid, fluorine,
hydrochloric acid,
chlorine, BF3, BC13, KF, NaF, or mixtures thereof. The volume of gases will
also depend on the
amount of activator used in the boronizing composition, where higher levels of
activator
correspond to higher levels of reaction gases.
[0050] Various boronizing compositions can be used in the process of the
present subject matter.
These compositions typically contain a boron source, an activator, and
optionally a diluent or
sintering reduction agent.
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[0051] Boron Source
[0052] The boron source for use in the powder boronizing composition can
generally be any
reactive boron solid capable of reacting with an activator to form gaseous
boron trihalides, such as
BF3 or BC13. These gaseous compounds react with the surface of the metal to
deposit boron on
the surface of the workpiece which may then diffuse into the metallic
structure and form an iron-
boride compound layer. Preferably, the boron source is selected from B4C,
amorphous boron,
calcium hexaboride, borax or mixtures thereof. More preferably, the boron
source is B4C.
Preferably, the boron source is present in the powder boronizing composition
in an amount of 0.5
to 4.5 wt%, based on the total weight of the powder boronizing composition.
More preferably, the
boron source is present in the powder boronizing composition in an amount of
2.0 to 4.0 wt%.
Most preferably, the boron source is present in the powder boronizing
composition in an amount
of 2.0 to 3.0 wt%. Levels of the boron source less than those recited can
result in a poorer quality
boride layer due to thinner boride layers and larger gaps and spacing between
the teeth in the boride
layer that would be occupied by lower hardness substrate material. Levels of
the boron source
greater than those recited can result in poorer boride layer quality due to
formation of a dual-phase
boride layer comprised of both FeB and Fe2B which has inferior performance
characteristics when
compared to a single-phase boride layer comprised of only Fe2B iron boride.
[0053] Activator
[0054] The activator for use in the powder boronizing composition can
generally be any halide-
containing compound that is capable of reacting with the boron source after
heating as described
above to form gaseous boron trihalides, such as BF3 or BC13. The boron atoms
are then inserted
by a gas diffusion process into the metal structure. Preferably, the activator
is selected from KBF4,
ammonia chloride, cryolite, sodium fluoride, ammonium bifluoride, potassium
fluoride, calcium
fluoride, or mixtures thereof. More preferably, the activator is KBF4.
Preferably, the activator is
present in the powder boronizing composition in an amount of 1.0 to 20.0 wt%,
based on the total
weight of the powder boronizing composition. More preferably, the activator is
present in the
powder boronizing composition in an amount of 3.5 to 10.0 wt%. Most
preferably, the boron
source is present in the powder boronizing composition in an amount of 4.0 to
6.0 wt%. Levels of
activator less than those recited can result in a poorer quality boride layer
due to formation of voids
and porosity in the boride layer. Levels of activator greater than those
recited can result in excess
quantities of spent reaction gas, as described below, which can present
environmental challenges.
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[0055] Sintering Reduction Agent
[0056] The sintering reduction agent facilitates the operation and ease of
performing the
boronizing process by preventing sintering of the powder composition. This is
an important
consideration in process optimization, particularly in those situations where
long, small diameter
tubes must be boronized, because sintered materials cling to themselves and to
the surfaces of the
metal part. It can be a time-consuming process to remove the sintered
material, especially in the
case when the interior of long pipes is being boronized. Even in the case of
simple geometry parts
being boronized, it can be very challenging to remove parts from a sintered
block of boronizing
powder after the process is complete, which forms if the boronizing powder
does not contain a
sintering reduction agent. Very small parts can also be lost in the sintered
boronizing powder
which is not readily ground or crushed back down to loose powder that can be
sifted and sieved to
retrieve small parts. Without wishing to be bound by theory, it is believed
that the sintering
reduction agent functions by scavenging oxygen from the atmosphere of the
boronizing process.
Preferably, the sintering reduction agent is selected from carbon black,
graphite, activated carbon,
charcoal, or mixtures thereof More preferably, the sintering reduction agent
is carbon black.
Preferably, the sintering reduction agent is present in the powder boronizing
composition in an
amount of 10.0 to 30.0 wt%, based on the total weight of the powder boronizing
composition.
More preferably, the sintering reduction agent is present in the powder
boronizing composition in
an amount of 12.0 to 25.0 wt%. Most preferably, the sintering reduction agent
is present in the
powder boronizing composition in an amount of 18.0 to 22.0 wt%. Levels of
sintering reduction
agent less than those recited can result in the bonding powder pack becoming
sintered into a solid
block of caked powder that is extremely difficult to break apart and remove
parts from after
processing. Levels of sintering reduction agent greater than those recited can
result in the bonding
powder having greatly reduced thermal conductivity making it take longer to
heat and cool the
bonding powder packs. With lower thermal conductivity, it is difficult to
uniformly boride parts
in larger size powder packs as the center portion of large packs are much
slower to heat and cool
than the outside edges of the same pack. The density of carbon black is also
lower than the bulk
powder, and it has been observed that the iron-boride compound layers are not
as compact and
dense below the surface when excessive amounts of carbon black are used
instead of filling with
more dense diluent materials such as SiC powder. This is mainly due to a
specific mass of carbon
black occupying more volume than the same mass of SiC powder, thus making the
same weight
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percentages of boron source and activator become more dilutely spread out
across a larger volume
of powder.
[0057] Diluent
[0058] The diluent is included in the boronizing powder composition to provide
bulk to the
composition. The diluent must have good heat conductivity, must not sinter
together during the
process, and have high density making it more difficult for outside atmosphere
gases to permeate
into the pack and also making it more difficult for the bonding vapors (BF3,
BC13) to quickly exit
the pack, and preferably, should be inert to the activator, boron source and
sintering reduction
agent. Preferably, the diluent is selected from SiC, alumina, zirconia or
mixtures thereof More
preferably, the diluent is SiC. Preferably, the diluent is present in the
powder boronizing
composition in an amount of 45.5 to 88.5 wt%, based on the total weight of the
powder boronizing
composition. More preferably, the diluent is present in the powder boronizing
composition in an
amount of 61.0 to 82.5 wt%. Most preferably, the diluent is present in the
powder boronizing
composition in an amount of 69.0 to 76.0 wt%. Levels of diluent less than
those recited can result
in the inclusion of active components at higher levels than are desirable from
an economic
standpoint. Levels of diluent less than those recited could also lead to dual-
phase iron-boride
compound layers if the bonding pack becomes too potent with not enough diluent
present. Levels
of diluent greater than those recited can result in levels of active
components that are too low to
provide adequate boride layer properties.
[0059] Boronizing Compositions
[0060] In one embodiment, the boronizing powder composition comprises: 0.5 to
25.0 wt% of a
boron source; 1.0 to 25.0 wt% of an activator; and 50.0 to 98.5 wt% of a
diluent, based on the total
weight of the boron source, activator and diluent. Preferably, the boronizing
powder composition
comprises 2.0 to 20.0 wt% of the boron source; 2.0 to 20.0 wt% of the
activator; and 60.0 to 96.0
wt% of the diluent, based on the total weight of the boron source, activator
and diluent. More
preferably, the boronizing powder composition comprises 2.0 to 6.0 wt% of the
boron source; 2.0
to 8.0 wt% of the activator; and 86.0 wt% to 96.0 wt% of the diluent, based on
the total weight of
the boron source, activator and diluent.
[0061] In another embodiment, the boronizing powder composition comprises 0.5
to 25.0 wt% of
a boron source selected from B4C, amorphous boron, calcium hexaboride, borax
or mixtures
thereof; 1.0 to 25.0 wt% of an activator selected from KBF4, ammonia chloride,
cryolite, sodium
CA 2998056 2018-03-13
fluoride, ammonium bifluoride, potassium fluoride, calcium fluoride, or
mixtures thereof; and 50.0
to 98.5 wt% of a sintering reduction agent selected from carbon black,
graphite, activated carbon,
charcoal or mixtures thereof, based on the total weight of the boron source,
activator and sintering
reduction agent.
[0062] In still another embodiment, a particularly effective powder boronizing
composition of the
present subject matter has been particularly designed to provide a boride
layer of exceptionally
high Fe2B level, high hardness, low porosity with good thickness levels, as
well as an excellent
uniformity of the boride layer. The boride layer also displays excellent
resistance to cracking,
flaking or oxidation in subsequent heat treatment steps as described below.
Preferably, the powder
boronizing composition contains: (a) 0.5 to 4.5 wt% of a boron source selected
from B4C,
amorphous boron, calcium hexaboride, borax or mixtures thereof; (b) 45.5 to
88.5 wt% of a diluent
selected from SiC, alumina, zirconia, or mixtures thereof; (c) 1.0 to 20.0 wt%
of an activator
selected from KBF4, ammonia chloride, cryolite, sodium fluoride, ammonium
bifluoride,
potassium fluoride, calcium fluoride, or mixtures thereof; and (d) 10.0 to
30.0 wt% of a sintering
reduction agent selected from carbon black, graphite, activated carbon or
mixtures thereof. More
preferably, the powder boronizing powder composition contains (a) 2.0 to 4.0
wt% of the boron
source; (b) 61.0 to 82.5 wt% of the diluent; (c) 3.5 to 10.0 wt% of the
activator; and (d) 12.0 to
25.0 wt% of the sintering reduction agent. Even more preferably, the powder
boronizing
compositions contains: (a) 2.0 to 3.0 wt% of the boron source; (b) 69.0 to
76.0 wt% of the diluent;
(c) 4.0 to 6.0 wt% of the activator; and (d) 18.0 to 22.0 wt% of the sintering
reduction agent.
[0063] In another embodiment, the boronizing powder composition comprises:
boronizing powder
composition comprises: 0.5 to 25.0 wt% of a boron source selected from B4C,
amorphous boron,
calcium hexaboride, borax or mixtures thereof; 1.0 to 25.0 wt% of an activator
selected from KBE4,
ammonia chloride, cryolite, sodium fluoride, ammonium bifluoride, potassium
fluoride, calcium
fluoride, or mixtures thereof; and 50.0 to 98.5 wt% of a diluent, based on the
total weight of the
boron source, activator and diluent.
[0064] In still another embodiment, the subject matter of the present
disclosure relates to a
boronizing powder composition comprising: 0.5 to 3.0 wt% of a boron source
selected from B4C,
amorphous boron, calcium hexaboride, borax or mixtures thereof; 1.0 to 15.0
wt% of an activator
selected from KBE4, ammonia chloride, cryolite, sodium fluoride, ammonium
bifluoride,
potassium fluoride, calcium fluoride, or mixtures thereof; and 82.0 to 98.5
wt% of a stream
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selected from sintering reduction agents, diluents or mixtures thereof, the
sintering reduction
agents being selected from carbon black, graphite, activated carbon, charcoal
or mixtures thereof,
and the diluents being selected from SiC, alumina, zirconia or mixtures
thereof
[0065] Preferably, the powder boronizing composition has a ratio of sintering
reduction
agent/boron source, i.e., of component (d)/component (a) of 2.2 to 60Ø More
preferably the
powder boronizing composition has a ratio of component (d)/component (a) of
3.0 to 12.5. Even
more preferably, the powder boronizing composition has a ratio of component
(d)/component (a)
of 6.0 to 11Ø
[0066] Levels of the boron source less than those recited can result in a
poorer quality boride layer
due to thinner boride layers and larger gaps and spacing between the teeth in
the boride layer that
would be occupied by lower hardness substrate material. The boride layer may
also be inferior,
because the surface structure is composed of both ferrite plus single phase
Fe2B. Levels of the
boron source greater than those recited can result in poorer boride layer
quality due to formation
of a dual-phase boride layer comprised of both FeB and Fe2B which has inferior
performance
characteristics when compared to a single-phase boride layer comprised of only
Fe2B iron boride.
Levels of activator less than those recited can result in sintering of the
boronizing powder, a highly
porous boride layer, or a poorer quality boride layer due to incomplete layers
or the formation of
voids and porosity in the boride layer. Levels of activator greater than those
recited can also result
in sintering of the boronizing powder, as well as excessive unnecessary
quantities of spent reaction
gas, which can present environmental challenges. Levels of sintering reduction
agent less than
those recited can result in the bonding powder pack becoming sintered into a
solid block of caked
powder that is extremely difficult to break apart and remove parts from after
processing. Levels
of sintering reduction agent greater than those recited can result in
shallower boride layers and the
bonding powder having greatly reduced thermal conductivity, making it take
longer to heat and
cool the bonding powder packs. With lower thermal conductivity, it is more
difficult to uniformly
boride parts in larger size powder packs as the center portion of large packs
are much slower to
heat and cool than the outside edges of the same pack. The density of the
sintering reduction agent
is also lower than the bulk powder, and it has been observed that the iron-
boride compound layers
are not as compact and dense below the surface when excessive amounts of
sintering reduction
agent are used instead of filling with more dense diluent materials such as
SiC powder. This is
mainly due to a specific mass of the sintering reduction agent occupying more
volume than the
17
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same mass of SiC powder, thus making the same weight percentages of boron
source and activator
become more dilutely spread out across a larger volume of powder. Levels of
diluent less than
those recited can result in the inclusion of active components at higher
levels than are desirable
from an economic standpoint. Levels of diluent less than those recited could
also lead to dual-
phase iron-boride compound layers if the bonding pack becomes too potent with
not enough
diluent present. Levels of diluent greater than those recited can result in
levels of active
components that are too low to provide adequate boride layer properties.
[0067] Properties of Boronized Metals
[0068] The properties of the boride layer affected by the powder boronizing
process include
thickness, thickness variability, relative concentrations of Fe2B and FeB,
hardness and porosity.
The thickness of the layer can vary depending on the boronizing powder
composition, the metal
being boronized, the length of time for the boronizing and the temperature of
the boronizing. The
thickness of the boride layer is typically from 0.0005 to 0.020 inches.
Preferably, the boride layer
is 0.002 to 0.015 inches. More preferably, the boride layer is 0.005 to 0.015
inches. The thickness
of the boride layer is calculated as the maximum distance from surface of the
workpiece to the
deepest tips of the boride layer observed in the cross-sectioned
microstructure, where the boride
layer depth is measured by examining a cross-section of a treated surface
using an optical
microscope.
[0069] The variability of the thickness of the boride layer is a measure of
the consistency of the
boronizing process. Optimally, the variability should be as low as possible,
since the degree of
protection the pipe enjoys from the bonding is dependent on its thickness, and
portions of the pipe
having a lower thickness are obviously less protected. For the purpose of this
specification, the
variability of the thickness of the layer is defined as the range of boride
layer depth results observed
in at least 5 randomly selected locations of the surfaces being examined,
i.e., the distance in inches
between the highest value and the lowest value. For example, if the analysis
of five locations
results in a layer thickness ranging from 0.008" to 0.014", the variability is
the difference between
the highest and lowest values, 0.006". The reported thickness of the layer is
the midpoint of that
range, or 0.011". Preferably, the variability of the thickness of the layer
produced by the process
of the present subject matter is no greater than 0.005". More preferably, the
variability of the
thickness of the layer is no greater than .003". However, in no event will the
variability be greater
than 50.0% of the boride layer thickness.
18
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[0070] The formation of the boride layer can include two phases: Fe2B and FeB.
Of these two
phases, Fe2B is preferred because it is less brittle than a FeB phase and
exists under a state of
compressive residual stress instead of tensile residual stress. Moreover,
because the two phases
have different coefficients of thermal expansion, mixtures of the two phases
are subject to crack
formation at the Fe2B/FeB interface of a dual-phase layer. The cracks can
result in spatting or
flaking, or even failure when subjected to mechanical stress. Thus, the
percentage of Fe2B in the
bonded layer should be as high as possible. Preferably, the boride layer
comprises 90.0 to 100.0
vol% Fe2B and 0 to 10.0 vol% FeB, where the fractions of Fe2B and FeB are
measured by
comparing the depth of the Fe2B boride layer teeth to the depth of the FeB
boride layer teeth in the
cross-sections examined; (e.g., if the total boride depth is 0.010", with the
Fe2B depth being 0.008"
and the FeB depth being 0.002", then the boride layer would be said to contain
20 vol% of the FeB
and 80 vol% of the Fe2B, based on the total amount of the FeB and Fe2B). Such
analysis is
normally conducted using measurements of both FeB and Fe2B boride layer depths
in a mounted
and polished cross-section of the boride layer using an optical microscope
with image analysis
measurement tools or a measuring reticle. More preferably, the boride layer
boride layer comprises
95.0 to 100.0 vol% Fe2B and 0 to 5.0 vol% FeB. Even more preferably, the
boride layer comprises
98.0 to 100.0 vol% Fe2B and 0 to 2.0 vol% FeB. Most preferably, the boride
layer should be a
single phase Fe2B layer, where for the purpose of this specification, the term
"single-phase Fe2B
layer" means the layer contains no FeB.
[0071] Porosity is also a measure of the quality of the boride layer whereby
voids or discontinuities
can exist in the layer. Inspection for porosity is performed by microscopic
examination of a
mounted and polished cross-section of the boride layer. Preferably, the
porosity of the boride layer
should be less than 10%, where the porosity is measured by visual estimate or
image analysis of
the boride layer microstructure. More preferably, the porosity of the boride
layer should be less
than 5%.
[0072] Hardness of the boride layer can be measured according to the Vickers
Hardness test,
ASTM E384 where hardness measurements may be made directly on the treated
surface or may
be made on a mounted and polished cross-section of the boride layer.
Preferably, the hardness of
the bonded layer is from 1100 to 2900 HV. More preferably, the hardness of the
bonded layer in
ferrous materials is from 1100 to 2000 HV.
[0073] Heat Treatment of Bonded Pipe
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[0074] It has been unexpectedly found possible to produce bonded pipes for
deep well applications
that comply with the associated stringent specifications for L80 grade pipe
according to the
American Petroleum Institute's, "Specification for Casing and Tubing," API
Specification 5CT,
Ninth Edition, July 2011, the disclosure of which is hereby incorporated by
reference. This process
involves austenitizing, quenching and tempering a pipe after it has been
bonded. Until now,
bonded pipe that meets any API 5CT grade with yield strengths and burst
pressures higher than
J55 grade has not been mass produced and made available to oil producers. The
bonding process
involves heating pipe to an austenitizing temperature in order to form the
boride layer, and bonding
suppliers will typically remove the tubing from the furnace at the bonding
temperature, and air
cool the pipe from the bonding temperature down to ambient room temperature.
This
austenitizing that occurs during bonding followed by air cooling is a
normalizing process, and the
resultant core properties of the boronizing process will typically be 55-60
ksi yield strength which
will marginally meet the API 5CT J55 grade requirements of 55-80 ksi yield
strength.
[0075] Preferably, the bonded pipe is emptied of bonded powder and cooled
prior to further
treating to achieve a higher L80 grade yield strength requirement of 80-95 ksi
yield strength,
requiring rapid liquid quenching of the pipes from the bonding temperature
followed by tempering
in order to transform the austenite structure present at the bonding
temperature to a martensite core
structure, as described below. Attempting to quench pipes filled with bonding
powders could
contaminate the liquid quenching bath if liquids come into contact with the
bonding powder. If
the bonding powder were to mix with quenchants it would also turn the bonding
powder into a
messy sludge or slurry that couldn't be dried and re-used again and it would
be difficult to properly
clean the bonding media out of the tubing after the process. Another potential
pitfall of full-body
quenching the tubes with powder still present in them is that the tubes may
distort and warp if not
cooled uniformly, resulting in severe warpage and bending that would then
require post-boride
straightening with high deflections which could then crack the boride layers.
If pipes are removed
from the bonding furnace at the end of the bonding cycle and are not
individually quenched with
uniform agitation from all angles, such as quenching multiple pipes at once
together or quenching
pipes resting on a support or pipe holding device that can retain heat, they
can cool non-uniformly,
causing one side of the pipe to contract more rapidly than the other side of
the pipe during cooling
and cause the entire pipe to become badly bowed. Pipe straightening is
typically required for long
pieces of pipe after such high temperature heating because the piping tends to
bow or sag along its
CA 2998056 2018-03-13
length. It is critically important to keep these pipes as straight as possible
during bonding and
hardening such that either no straightening or straightening with only minimal
deflections is
required in order to prevent and minimize any cracking of the boride layer. A
new processing
scheme has been developed where pipes are stress relieved and optionally
straightened prior to
bonding in order to create a stress-free tube that is straight prior to
bonding, the pipes are then
fixtured onto heat resistant supports in such a manner that it will prevent
them from sagging or
creep-distorting during the high temperature bonding cycle, the pipes are then
bonded on straight
fixtures and then cooled to ambient. After all spent bonding powder is
removed, the bonded pipes
can be straightened prior to hardening with minimal deflections required, such
that the boride layer
will not crack or spall off during straightening. In order to harden the pipes
using a quench and
temper type of heat treatment, the pipes are induction hardened, quenched and
tempered. Induction
hardening and tempering of individual pipes with uniform heating and cooling
rates allows for
pipe surfaces to be quickly heated to an austenitizing temperature in a manner
of just minutes.
The short heating time allows for the process to be performed in air
atmosphere without any
excessive scaling or oxidation of the boride layer surface or oxidation of
untreated pipe surfaces.
The induction hardening process is also performed on individual tubes passing
on cross-rollers
through induction coils such that the tubes are spinning on a straight track
of rollers that helps
maintain pipe straightness along with performing uniform heating as the
rotating pipe is passed
through heating coils. After the pipe has passed through all the induction
heating coils, it has
reached the desired austenitizing temperature and the core material has
completely transformed to
austenite. The austenitic heated pipe then passes on rollers as it is rotating
through a quenching
coil or quench nozzles that direct liquid quenchant, typically water or
polymer, from all radial
angles onto the pipe surface such that the pipe is uniformly quenched radially
and maintains
acceptable limits of straightness during the heating and quenching steps.
After quenching, the
pipe will pass through another set of induction heating coils that heats the
tubing to a desired
tempering temperature. If performed correctly, the pipes may still meet the
requirements for
straightness after induction hardening and tempering and may not need any
additional
straightening operations to be performed which further mitigates any risk of
cracking the boride
layer by avoiding an additional straightening operation. Different grades of
API 5CT tubing can
be met by altering the tempering temperature to produce a specific set of
tensile and yield strength
properties. The induction hardening and tempering process after bonding
enables treatment of
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bonded pipes to reach the required specifications for L80 and other grades of
API 5CT pipe,
without oxidation, cracking or flaking of the boride layer after pipe
straightening. Such
specifications for API 5CT Grade L80 include, e.g., a KSI yield strength (80-
95 KSI); KSI
minimum tensile strength (95 KSI); and HRC maximum hardness (23 HRC). This is
possible
because the induction hardening process allows for reheating, quenching and
tempering of a
bonded part with minimal times at heat where oxidation is not a concern and
creep distortion is
minimal along with induction hardening allowing for uniform radial heating and
cooling to prevent
pipes from bowing or distorting during heating or quenching due to uneven heat
distribution.
[0076] Induction hardening is one option for post-boride treatment that is
possible. Another
option for austenitizing, quenching and tempering after bonding would be
furnace hardening.
Furnace hardening is also possible and may be performed in lieu of induction
hardening. The
main difference is a longer exposure time to heat is required to soak the
pipes out and fully
austentize the material. The longer heat exposure times will usually
necessitate the use of heating
pipe in an inert atmosphere, such as nitrogen, argon, helium, endothermic gas,
exothermic gas or
similar, to prevent oxidation of bonded and unborided pipe surfaces. The
longer heat exposure
also allows more time for pipes to sag and warp out of straight if not
properly supported during
the entire cycle and typically a walking beam or tube processing furnace will
be used where pipes
are rotating during heating and supported over their entire length. After the
pipes are fully
austentized, they may be removed from the furnace and liquid quenched in
water, salt, oil, brine
or polymer to transform the core material to martensite similar to the
induction hardening process
followed by tempering at different temperatures in order to meet various
different API 5CT grade
requirements for tensile strength, yield strength, and hardness.
[0077] While L80 is the most popular choice for grade, the treatment of the
bonded pipes, can be
alternatively adjusted to meet the requirements of other desirable high
strength rated piping such
as C90, T95, C110, P110, Q125, N80, and R95 grades by adjusting the tempering
temperature
after quenching.
[0078] Pipes produced by the process of the present subject matter have boride
layers that are
physically uniform. For the purposes of this specification, the term
"physically uniform" when
applied to boride layers produced by the described process to harden bonded
pipes means that the
boride layers are not oxidized, cracked or flaked. An internal borescope may
be used to inspect
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CA 2998056 2018-03-13
tubing bores after all processes are complete to ensure no visible cracking or
spalled areas are
present.
[0079] Heating Step
[0080] The first step of the treatment is a heating step where the pipe is
austenitized, i.e., where
the pipe is heated above its critical austenitizing temperature for a time
period long enough for the
metal to be transformed into an austenite structure. The heating can either be
an induction heating
step or a furnace heating step. Preferably, the heating is an induction
heating step. Austenite is an
intermediate crystal structure that is stable at high temperatures in steel
and is capable of
transforming into different crystal structures during later processing or heat
treatment depending
on cooling rates and schedules to a variety of different microstructures that
may be desired. The
required temperature for heating is preferably from 1400 to 2000 F. More
preferably, the
temperature is from 1400 to 1900 F, and even more preferably from 1500 to 1800
F. Preferably,
the heating is conducted using induction heating coils in an induction machine
using air
atmosphere. Alternative, the heating may be performed in high temperature
furnaces using a
protective inert atmosphere.
[0081] Quenching Step
[0082] Following the heating step is a quenching step. In the quenching step,
the metal is cooled
from the temperatures of the heating step, and becomes hardened as the
austenite is transformed
into martensite. The quenching is preferably performed with water, oil,
polymer, brine, salt or
combinations thereof. Preferably, the quenching media is at a temperature that
may range from
40 to 200 F. The quenched metal pipe is reduced to a temperature range of 40
to 200 F during
immersion into the quenchant and then allowed to cool to ambient room
temperature before
tempering
[0083] Tempering Step
[0084] Following the quenching step is a tempering step. In the tempering
step, the pipe is
reheated from the quenched temperature or ambient to reduce the hardness and
strength to the
desirable level while increasing the toughness and ductility of the hardened
steel, while removing
the tensions in the structure to improve ductility, leaving the steel with the
required hardness and
strength levels. The tempering temperature is preferably from 250 to 1375 F,
more preferably,
from 1250 to 1375 F, and even more preferably, from 1300 to 1375 F for L80
grade. The
23
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,
tempering step can be conducted either by induction heating or furnace
heating. Preferably, the
tempering step is conducted by induction heating.
[0085] In each of the furnace heating, quenching, and tempering steps, a
protective atmosphere,
such as vacuum, neutral salt, nitrogen, argon, helium, endothermic gas, or
exothermic gas, can
optionally be used for protection of the boride layer that does not cause any
oxidation, degradation
or reaction of the boride layer during heating. In induction heating, the
atmosphere surrounding
the tubing during all steps may be air atmosphere due to the short time
exposures required that is
typically less than a minute.
[0086] Preferably, the tempered pipe produced in the tempering step is non-
threaded. Threading
the ends of the pipes facilitates connecting the pipe to adjacent pieces of
pipe, eventually forming
a series of connected pieces of pipe that constitutes the well pipe. Threading
the pipe after
boronizing and heat treating in this manner advantageously avoids distorting
the grooves of the
threads during the heating and the cooling steps. Threads are also prone to
damage as they can be
easily nicked, dinged and damaged during installation of end caps, removal of
end caps, handling
and transport of the pipes and subsequent cleaning and straightening
operations after bonding
and/or hardening and tempering. In either of these situations the pipe would
either have to be
mechanically modified in an additional step or discarded as there would be a
risk of thread leakage
or poor quality connections due to poor quality threads. Thus, it is
advantageous to boride and
harden unthreaded tubing and then perform the threading after all of the other
operations which
could compromise the thread integrity have been completed.
[0087] The heating, quenching and tempering steps can alternately be conducted
when bonding
powder has not been removed from the pipe, following the boronizing step.
Preferably, the powder
is removed prior to the heating, quenching and tempering steps.
[0088] The treated, bonded steel produced by the treatment step according to
the present subject
matter meets the specification of API 5CT specification L-80.
[0089] The boronized pipes produced according to the present subject matter
are especially useful
in processes of the oil producing industry where the pipes are employed in
deep wells. Preferably,
the boronized pipes are used in a process wherein a sucker rod pump is
employed within the pipe.
The boronized pipes produced according to the present subject matter are
especially useful in the
oil and gas, refining, concrete, mining and chemical industries where the
pipes are used to transport
abrasive slurries within the pipe.
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[0090] Referring now to FIG. 1, shown is a loading and unloading process for
filling and emptying
boronizing powder from metal tubes. A hydraulic powered tilting station (1)
has pipes to be
boronized (2) loaded on the the bed. Prior to lifting, a bottom end cap (3) is
fitted to the lower end
of the tube. The pipe is tilted up into the air and positioned underneath a
powder conveyance
system (4) that uses either pneumatic conveyance, screw conveyor, rotary valve
feeder, loss in
weight feeder or any combination thereof to pull boronizing powder out of a
storage container (5)
and into the pipe to be boronized (2). A vibration unit (6) will be attached
to either the tubes or
the tilting station (1) and will vibrate the tubes during loading to
facilitate with settling of powder
to ensure tubes are completely filled and powder is packed tightly in the
interior bore of the tube.
After the tubes are filled, the top end cap (7) is installed on the top of the
tube to seal powder inside
the tube. The tubes are then lowered back to horizontal after filling and
transferred to the racking
station for boronizing. After boronizing, the boronized tubes (8) are loaded
back onto the tilting
station (1) and tilted upwards placed above a spent boronizing powder
collection container (9) and
the bottom end cap (3) is removed. The tubes are vibrated during emptying
using a vibration
device (6) attached to either the tubes directly or the tilting station. After
all powder has emptied
out of each tube, the tubes are tilted back down to horizontal, the top end
cap (7) is removed and
the finished tubes are moved out of the processing area. Filling and unloading
of the powder is
conducted in a closed system with venting to baghouse or cyclones as well.
[0091] Referring now to FIG. 2, shown is a pipe with a flared end and a split-
bushing end cap
composed of an end cap portion and a split-bushing portion. The interior
surface of the cylindrical
portion of the end cap portion is threaded and the other end is sealed. The
split-bushing portion is
shown as being in 2 curved sections, where the curved sections at one end are
fitted with a solid
flange portion
[0092] Referring now to FIG. 3, shown is a split-bushing end cap for an
unthreaded flared tube
being mounted on flared section of tube where the split bushing diameter fits
around the main body
of the tube but will not be able to slip over the larger diameter of the
flared end of the pipe.
[0093] Referring now to FIG 4, shown is the installation of a split-bushing
endcap for boronizing
unthreaded tubes with the two split bushing pieces surrounding the main body
diameter of the pipe.
The two split bushing pieces are about to be screwed into the end cap where
the split bushings will
be pulled up into the end cap during until inner diameter of the split
bushings catches on the tapered
CA 2998056 2018-03-13
section of the larger flared end diameter and secures the end cap and split
bushing assembly tight
against the end of the pipe.
[0094] Referring now to FIG 5, shown is a split-bushing endcap installed on
the end of a flared
tube.
[0095] Referring now to FIG 6, shown is a split-bushing along with the
hexagonal flange from a
variety of angles.
[0096] Referring now to FIG 7, shown is an end cap for use along with the
split-bushing from a
variety of angles.
[0097] Referring now to FIG 8, shown is a plate end cap.
[0098] The following Examples further detail and explain the preparation and
performance of the
powder boronizing compositions. Those skilled in the art will recognize many
variations that are
within the spirit of the invention and scope of the claims.
EXAMPLES
[0099] Example 1
[00100]
Bonded, hardened and tempered tubing meeting the requirements of API 5CT
Grade L80 2-7/8" tubing has been produced using the following method. Tubing
was initially
stress relieved at 900F in order to remove any residual stresses present from
the tube making
process prior to bonding such that the tubing should not warp upon heating
during bonding as
residual stresses are relieved. After stress relieving, the tubing is
inspected for straightness and
straightened to a total indicated runout (TIR) of 0.2% of the pipe length
prior to bonding. Bonding
powder of composition 71% SiC, 3% B4C, 5% KBEI, 20% Carbon Black was charged
into the
tubing and endcaps were secured onto both ends of the tubing to seal the
bonding powder inside
the tube. Tubing was then fixtured to heat resistant supports that will help
maintain straightness
during bonding and prevent any creep distortion or bending due to non-uniform
heating/cooling
and placed into the bonding furnace. Tubes were then heated to 1750F for 8
hours, slow cooled
in the furnace and removed from the bonding furnace. The bonding powder was
removed from
the tubes after bonding. Straightening was then performed where tubing was
straightened to meet
a TIR less than 0.1% of tube length prior to post-boride hardening. Post-
boride hardening
consisted of heating the bonded tubing using an induction machine to a
temperature of 1750F for
the austenitizing step, water quenching to ambient temperature and then
tempering at 1320F using
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an induction tempering machine. Both the austenitizing and tempering times for
any point along
the tubing was less than 5 minutes. After hardening and tempering, the pipes
were inspected for
straightness and were all found to meet API 5CT requirements for total
indicated runout and did
not require straightening after induction hardening. After bonding, hardening
and tempering, the
tubing was inspected for core mechanical properties which were observed to be
103.5 ksi tensile
strength, 93.7 ksi yield strength, and 15.8-18.3 HRC hardness. Microstructure
was also inspected
and the boride layer was observed to be physically uniform and free of any
oxidation, cracks and
spalling. The boride layer depth was measured to be .008" total depth with 20%
FeB present. The
boride layer hardness measured 1500-1800 HV. The boride layer had no porosity
or voids
observed. The inside bores of the tube were inspected using a borescope and no
visual signs of
boride layer cracking or spalled areas were observed. All requirements for API
5CT Grade 80
were met along with having a physically uniform .008" deep boride layer
containing 20% FeB.
[00101] Examples 2-10
[00102] A series of bonding powder compositions were prepared to evaluate
sintering
performance and evaluation of the bonding layer deposited. The compositions
included a boron
source (B4C), activator (KBF4), sintering reduction agent (carbon black), and
diluent (silicon
carbide). The level of boron source was varied, while maintaining the
activator and carbon black
levels constant. Pieces of precision ground AISI 1018 steel (1/8" thick x IA"
long) were cut from
a single bar all having the same steel chemistry. Each bar was notched on the
end of bar to identify
it. Each of the bonding powder compositions was then placed inside a small
sealed pipe
constructed from a standard black iron threaded pipe nipple (3/4" pipe size x
4" long) with two
3/4" cast iron threaded pipe caps screwed onto both ends. The steel test bars
were suspended in
the center of the sealed pipes completely submerged in the bonding powder
composition. All the
sealed capped pipes holding the test bars suspended in powder inside the
capped pipes were placed
inside a large container and loaded into a furnace. The furnace was ramped up
to heat at 500 F
per hour to 1750 F and held at 1750 F for 12 hours at heat followed by slow
cooling. The
atmosphere in the furnace was air. At the end of the bonding, each pipe was
opened and its
contents removed. The powder was examined for evidence of sintering, and each
test bar was
sectioned, mounted, ground and polished. The cross-sections were then etched
with a 2% nital
acid solution to reveal the boride layer microstructure present in the cross-
section. The boride
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layer microstructures were photographed and the boride layer analyzed. The
bonding
compositions and results are shown in Table 1.
Table 1
Example 2 3 4 5 6 7 8 9 10
B4C, we/0 0.3 0.5 1.0 2.0 2.5 3.0 4.0 4.5 5.0
KBE4, wt% 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
Carbon 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0
20.0
Black, wt%
Silicon 74.7 74.5 74.0 73.0 72.5 72.0 71.0 70.5
70.0
Carbide,
wt%
Sintering no no no no no no no no no
Boride Layer 0.004 0.004 0.005 0.0075 0.008 0.008
0.010 0.009 0.010
Thickness,
inch
Boride Layer (1) (1) (1) (2) (2) (2) (2) (2) (3)
Quality*
* (1) incomplete layer at surface
(2) single-phase Fe2B solid layer
(3) mostly single-phase Fe2B solid layer, some FeB at surface
(4) highly porous and incomplete layer
[00103] For the purposes of this specification, the term "incomplete layer
at surface" means
the presence of iron-boride compound, but not a continuous layer. This surface
structure is ferrite
which is a steel structure where there is not any iron-boride layer
precipitating out right at the
surface of the part. The term "shallow or shallower" boride layer means that
the layer is not as
deep, and refers to how deep below the surface of the bonded part where an
iron-boride compound
is present. The term "highly porous and incomplete layer" means layers with
empty pores (voids)
present in the boride layer that have poor mechanical properties. It's just
literally bubbles of gas
or vacuum beneath the surface that form when we don't have enough KBF4
present. The term
"single-phase Fe2B solid layer," means a complete layer having a single phase
of Fe2B with no
FeB or ferrite present.
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[00104] The results of Table 1 indicate that none of the Examples
exhibited sintering.
Samples 2-4, corresponding to boron source concentrations 0.3 to 1.0 wt%
exhibit incomplete
boride layers at the surface. Samples 5-9, corresponding to boron source
concentrations of 2.0 to
4.5 wt% exhibit a solid, single-phase layer of Fe2B. Sample 10, corresponding
to a boron source
concentration of 5.0 wt%, produces a boride layer having a mostly single-phase
Fe2B solid layer,
with some FeB at the surface.
[00105] Examples 11-18
[00106] A series of bonding powder compositions were prepared and tested
as with
Examples 2-10 above. The bonding compositions and results are shown in Table
2, where the
activator KBF4 is varied between 0.5 to 25.0 wt%, while the boron source and
carbon black
concentrations are held constant.
Table 2.
Example 11 12 13 14 15 16 17 18
B4C, wt% 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5
KBE4, wt% 0.5 1.0 3.5 4.0 6.0 10.0 20.0 25.0
Carbon 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0
Black, wt%
Silicon 77.0 76.5 74.0 73.5 71.5 67.5 57.5 52.5
Carbide,
wt%
Sintering yes yes no no no no no yes
Boride 0.004 0.006 0.008 0.008 0.010 0.010 0.010 0.010
Layer
Thickness,
inch
Boride (4) (4) (2) (2) (2) (2) (2) (2)
Layer
Quality*
* (1) incomplete layer at surface
(2) single-phase Fe2B solid layer
(3) mostly single-phase Fe2B solid layer, some FeB at surface
(4) highly porous and incomplete layer
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The results of Table 2 indicate that samples having the lowest levels of
activator (Examples 11
and 12 with activator levels of 0.5 and 1.0 wt%, respectively), and at the
highest level of activator
(Example 18, activator level of 25.0 wt%) exhibit sintering. Examples 11 and
12 also exhibit
highly porous and incomplete boride layers, with the rest of the samples
having single-phase Fe2B
solid layers.
1001071 Examples 19-26
[00108] A series of bonding powder compositions were prepared and tested
as with
Examples 2-10 above. The bonding compositions and results are shown in Table
3, where the
sintering reduction agent (carbon black) is varied between 5.0 to 35.0 wt%,
while the boron source
and activator concentrations are held constant.
Table 3.
Example 19 20 21 22 23 24 25 26
B4C, wt% 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5
KBF4, wt% 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
Carbon 5.0 10.0 12.0 18.0 22.0 25.0 30.0 35.0
Black, wt%
Silicon 87.5 82.5 80.5 74.5 70.5 67.5 62.5 57.5
Carbide,
wt%
Sintering yes no no no no no no no
Boride 0.010 0.010 0.010 0.009 0.010 0.006 0.006 0.005
Layer
Thickness,
inch
Boride (2) (2) (2) (2) (2) (2) (2) (2)
Layer
Quality*
* (1) incomplete at surface
(2) single-phase Fe2B solid layer
(3) mostly single-phase Fe2B solid layer, some FeB at surface
(4) highly porous and incomplete layer
CA 2998056 2018-03-13
[00109] The results of Table 3 indicate that Example 19, containing the
lowest level of
sintering reduction agent (5.0 wt%) results in sintering. All of the samples
provided boride layers
having single-phase, Fe2B layers. However, Examples 24 ¨ 26, corresponding to
levels of anti-
sintering agent of 25.0 to 35.0 wt% result in lower boride layer thickness.
Without wishing to be
bound by theory, Applicants believe that one possible explanation is that the
lower thermal
conductivity (higher carbon black content) powders took a longer time to reach
the 1750 F
bonding temperature during the test, and started bonding later than the lower
carbon black
concentration examples. Another possible explanation is that the low density
of the carbon black
causes a fixed mass of carbon to take up significantly more volume than
silicon carbide, and that
this resulted in diluting the boron carbide and KBF4 concentrations.
[00110] Other features, advantages and embodiments of the invention
disclosed herein will
be readily apparent to those exercising ordinary skill after reading the
foregoing disclosure. In this
regard, while specific embodiments of the invention have been described in
considerable detail,
variations and modifications of these embodiments can be effected without
departing from the
spirit and scope of the invention as described and claimed.
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