PIPE AND RECOVERING BORONIZING POWDER

FIELD OF THE INVENTION

[001] The invention relates to the post-boriding 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 boriding. However, while nitriding 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 boriding techniques can be employed, where electrolytic or electro-less baths are employed to deposit layers of borides. Gas boriding or plasma boriding can also be used. However, these methods, while having certain advantages, are unsuitable for environmental reasons or are impractical for long tubing. Paste-boriding is a particular type of selective boriding, where the boronizing composition is applied as a paste to the metal surface, and then heated. This technique, while being useful for localized spot boriding, 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 (B ₄ C), calcium hexaboride (CaB ₆ ), or borax react with a halide-based activator upon heating to form gaseous boron tri-halides, such as BF ₃ or BC1 ₃ , 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 boriding powder compositions are also prone to sintering to a solid cake inside of a pipe that is difficult to break apart and remove after boriding. 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- sintering agent for the powder, to prevent sintering and caking of powder inside the tubing making it easier to remove after boriding.

[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, CI 10, PI 10, 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 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 HOOF 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 boriding. 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 boriding. 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 boriding process. The development of a boriding 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 boriding 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 boriding.

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 borided 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 a boriding temperature, thereby forming a borided 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 borided 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 borided 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 borided 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 boriding temperature, thereby forming a borided 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. [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 boriding temperature, thereby forming a borided layer on the inside surface, and spent boriding powder; and removing the spent boriding 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 boriding temperature, thereby forming a borided layer on the inside surface, and spent boriding powder; and removing the spent boriding 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 boriding temperature, thereby forming a borided 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 borided 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 second end, an inside surface and an outside surface; heating the pipe to form a borided 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 borided layer on the inside surface, and generating spent reaction gases and spent boriding 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 borided layer on the inside surface, and generating spent reaction gases and spent boriding 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 borided layer on the inside surface, and spent boronizing powder; heating the pipe with the borided 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. 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.

[0027] 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 "boriding;" and "boronized" and "borided" 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 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 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. [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 boriding 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 boriding 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 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, BF ₃ , BC1 ₃ , 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. [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 BF ₃ or BC1 ₃ . 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 B ₄ C, amorphous boron, calcium hexaboride, borax or mixtures thereof. More preferably, the boron source is B ₄ C. 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 Fe ₂ B which has inferior performance characteristics when compared to a single -phase boride layer comprised of only Fe ₂ B 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 BF ₃ or BC1 ₃ . The boron atoms are then inserted by a gas diffusion process into the metal structure. Preferably, the activator is selected from KBF ₄ , ammonia chloride, cryolite, sodium fluoride, ammonium bifluoride, potassium fluoride, calcium fluoride, or mixtures thereof. More preferably, the activator is KBF ₄ . 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. [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 boriding 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 boriding powder having greatly reduced thermal conductivity making it take longer to heat and cool the boriding 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 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 boriding vapors (BF ₃ , BC1 ₃ ) 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 boriding 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 B ₄ C, amorphous boron, calcium hexaboride, borax or mixtures thereof; 1.0 to 25.0 wt% of an activator selected from KBF ₄ , ammonia chloride, cryolite, sodium 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 Fe ₂ B 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 B ₄ C, 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 KBF ₄ , 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 B ₄ C, amorphous boron, calcium hexaboride, borax or mixtures thereof; 1.0 to 25.0 wt% of an activator selected from KBF ₄ , 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 B ₄ C, amorphous boron, calcium hexaboride, borax or mixtures thereof; 1.0 to 15.0 wt% of an activator selected from KBF ₄ , ammonia chloride, cryolite, sodium fluoride, ammonium bifluoride, potassium fluoride, calcium fluoride, or mixtures thereof; and 82.0 to 98.5 wt% of a stream 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 60.0. 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 11.0.

[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 Fe ₂ B. 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 Fe ₂ B which has inferior performance characteristics when compared to a single-phase boride layer comprised of only Fe ₂ B 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 boriding 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 boriding powder having greatly reduced thermal conductivity, making it take longer to heat and cool the boriding 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 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 boriding 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 Fe ₂ B 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 boriding 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. [0070] The formation of the boride layer can include two phases: Fe ₂ B and FeB. Of these two phases, Fe ₂ B 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 Fe ₂ B/FeB interface of a dual-phase layer. The cracks can result in spalling or flaking, or even failure when subjected to mechanical stress. Thus, the percentage of Fe ₂ B in the borided layer should be as high as possible. Preferably, the boride layer comprises 90.0 to 100.0 vol% Fe ₂ B and 0 to 10.0 vol% FeB, where the fractions of Fe ₂ B and FeB are measured by comparing the depth of the Fe ₂ B 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 Fe ₂ B 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 Fe ₂ B, based on the total amount of the FeB and Fe ₂ B). Such analysis is normally conducted using measurements of both FeB and Fe ₂ B 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% Fe ₂ B and 0 to 5.0 vol% FeB. Even more preferably, the boride layer comprises 98.0 to 100.0 vol% Fe ₂ B and 0 to 2.0 vol% FeB. Most preferably, the boride layer should be a single phase Fe ₂ B layer, where for the purpose of this specification, the term "single-phase Fe ₂ B 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 micro structure. 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 borided layer is from 1100 to 2900 HV. More preferably, the hardness of the borided layer in ferrous materials is from 1100 to 2000 HV.

[0073] Heat Treatment of Borided Pipe [0074] It has been unexpectedly found possible to produce borided 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 borided. Until now, borided 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 boriding process involves heating pipe to an austenitizing temperature in order to form the boride layer, and boriding suppliers will typically remove the tubing from the furnace at the boriding temperature, and air cool the pipe from the boriding temperature down to ambient room temperature. This austenitizing that occurs during boriding 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 borided pipe is emptied of borided 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 boriding temperature followed by tempering in order to transform the austenite structure present at the boriding temperature to a martensite core structure, as described below. Attempting to quench pipes filled with boriding powders could contaminate the liquid quenching bath if liquids come into contact with the boriding powder. If the boriding powder were to mix with quenchants it would also turn the boriding 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 boriding 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 boriding furnace at the end of the boriding 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 length. It is critically important to keep these pipes as straight as possible during boriding 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 boriding in order to create a stress-free tube that is straight prior to boriding, 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 boriding cycle, the pipes are then borided on straight fixtures and then cooled to ambient. After all spent boriding powder is removed, the borided 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 boriding enables treatment of borided 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 borided 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 boriding 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 borided and unbonded 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 borided pipes, can be alternatively adjusted to meet the requirements of other desirable high strength rated piping such as C90, T95, CI 10, PI 10, 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 borided pipes means that the boride layers are not oxidized, cracked or flaked. An internal borescope may be used to inspect 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 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 boriding 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 boriding 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, borided 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. [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 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] Borided, 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 boriding such that the tubing should not warp upon heating during boriding 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 boriding. Boriding powder of composition 71% SiC, 3% B ₄ C, 5% KBF ₄ , 20% Carbon Black was charged into the tubing and endcaps were secured onto both ends of the tubing to seal the boriding powder inside the tube. Tubing was then fixtured to heat resistant supports that will help maintain straightness during boriding and prevent any creep distortion or bending due to non-uniform heating/cooling and placed into the boriding furnace. Tubes were then heated to 1750F for 8 hours, slow cooled in the furnace and removed from the boriding furnace. The boriding powder was removed from the tubes after boriding. 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 borided 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 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 boriding, 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 boriding powder compositions were prepared to evaluate sintering performance and evaluation of the boriding layer deposited. The compositions included a boron source (B ₄ C), activator (KBF ₄ ), 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 ½" 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 boriding 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 boriding 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 boriding, 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 layer microstructures were photographed and the boride layer analyzed. The boriding compositions and results are shown in Table 1.

Table 1

(1) incomplete layer at surface

(2) single-phase Fe ₂ B solid layer

(3) mostly single-phase Fe ₂ B 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 borided 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 KBF ₄ present. The term "single-phase Fe ₂ B solid layer," means a complete layer having a single phase of Fe ₂ B with no FeB or ferrite present. [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 Fe ₂ B. Sample 10, corresponding to a boron source concentration of 5.0 wt%, produces a boride layer having a mostly single-phase Fe ₂ B solid layer, with some FeB at the surface.

[00105] Examples 11-18

[00106] A series of boriding powder compositions were prepared and tested as with

Examples 2-10 above. The boriding compositions and results are shown in Table 2, where the activator KBF ₄ is varied between 0.5 to 25.0 wt%, while the boron source and carbon black concentrations are held constant.

Table 2.

(1) incomplete layer at surface

(2) single-phase Fe ₂ B solid layer

(3) mostly single-phase Fe ₂ B solid layer, some FeB at surface

(4) highly porous and incomplete layer 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 Fe ₂ B solid layers.

[00107] Examples 19-26

[00108] A series of boriding powder compositions were prepared and tested as with

Examples 2-10 above. The boriding 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.

(1) incomplete at surface

(2) single-phase Fe ₂ B solid layer

(3) mostly single-phase Fe ₂ B solid layer, some FeB at surface

(4) highly porous and incomplete layer [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, Fe ₂ B 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 boriding temperature during the test, and started boriding 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 KBF ₄ 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.