Patent Application
20190382898
This disclosure relates to protective coatings useful in corrosive and scale forming environments. In particular, this disclosure relates to equipment comprising such scale and corrosion resistant coatings and methods of producing such equipment.
Fluid conduits and other equipment used in the oil and gas industry are frequently subjected to harsh conditions under which the conduits and equipment may undergo significant operational degradation as a result of corrosion and scaling of surfaces in contact with a production fluid. In oil and gas wells in which the production fluid is rich in hydrogen sulfide, corrosive scaling can be particularly severe. For example, production tubing may become rapidly clogged with iron sulfide scale under sour gas conditions wherein moderate to high concentrations of hydrogen sulfide and carbon dioxide are in contact with production tubing surfaces at temperatures and pressures prevailing in the downhole environment. Such clogging due to scale formation limits the productivity of the well and, in some instances, forces the well to be shut down. Preventing the formation of scale extends the useful life and productivity of the well.
Despite significant enhancements in the scaling and corrosion resistance of fluid conduits and equipment used in the oil and gas industry, further improvements are needed. This disclosure provides details of novel and robust coating systems having outstanding scale and corrosion resistance, and which are suitable for use in a wide variety of applications in which corrosion and scale formation present operational challenges.
In a first set of embodiments, the present invention provides a fluid conduit, the fluid conduit defining an interior volume and comprising (a) a fluid conduit exterior surface; (b) a fluid conduit interior surface; (c) an electroless nickel protective coating disposed upon at least one of the fluid conduit interior surface and the fluid conduit exterior surface; and (d) a layer of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating.
In a second set of embodiments the present invention provides a hydrocarbon production tube defining a flow channel and comprising (a) a tube exterior surface; (b) a tube interior surface; (c) an electroless nickel protective coating disposed upon at least one of the tube interior surface and the tube exterior surface; and (d) a layer of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating.
In a third set of embodiments the present invention provides a method of producing a fluid conduit comprising a nickel sulfide protective layer, the method comprising: (a) heating a fluid conduit comprising an electroless nickel protective coating disposed upon a surface of the fluid conduit in contact with a fluid comprising hydrogen sulfide; and (b) depositing a protective layer of Ni3S2 upon and substantially covering the electroless nickel protective coating.
In a fourth set of embodiments, the present invention provides a machine component comprising at least one surface having a protective outer layer, the protective outer layer comprising: (a) an inner electroless nickel coating; and (b) a layer of Ni3S2 disposed upon and substantially covering the electroless nickel coating.
Various features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters may represent like parts throughout the drawings. Unless otherwise indicated, the drawings provided herein are meant to illustrate key inventive features of the invention. These key inventive features are believed to be applicable in a wide variety of systems which comprising one or more embodiments of the invention. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the invention.
In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.
The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
As noted, in one or more embodiments the present invention provides a corrosion and scale resistant fluid conduit comprising at least one surface having an electroless nickel (EN) protective coating disposed thereon. A layer of Ni3S2, at times herein referred to as Heazlewoodite, is disposed upon and substantially covers the electroless nickel protective coating. The inventors have discovered that nearly all EN protective coatings surprisingly undergo reaction with hydrogen sulfide at moderate temperature and high pressure to form a layer of scale resistant Heazlewoodite on the surface of the EN protective coating initially in contact with a fluid containing hydrogen sulfide. Upon exposure of the EN protective coating to hydrogen sulfide at moderate temperature and high pressure, nickel within the EN protective coating is converted to Ni3S2 at or near the surface of the EN coating. The EN coating is thus consumed to some degree during the formation of the Ni3S2 layer. As more nickel reacts with hydrogen sulfide to form Ni3S2, the EN coating becomes substantially covered with Ni3S2 and, as a result, encounters between hydrogen sulfide and nickel atoms present in the EN coating are reduced over time and growth of the Ni3S2 layer slows and eventually ceases. Provided the EN coating is of sufficient thickness at the outset of exposure to hydrogen sulfide, the product resulting from such exposure at moderate temperature and pressure will be a layer of Heazlewoodite disposed upon and substantially covering the unconsumed portion of the underlying EN protective layer. Under such circumstances, the unconsumed portion of the underlying EN protective layer is hermetically isolated from contact with the environment provided the structural integrity of the layer of Heazlewoodite is maintained. Example 1b (coupon 1b) in the Experimental Section of this disclosure is illustrative. Of the initial 1 mil (25.4 microns) thick high phosphorous EN protective coating, 25 microns of the original nickel-phosphorous coating remain following reaction with hydrogen sulfide in the presence of brine at 160° C. at a pressure of 2000-3000 psi and deposition of a 10-micron thick Ni3S2 overlayer. The Ni3S2 overlayer was determined to cover 100% of the outer surface of the unconsumed portion of the underlying EN protective coating and hermetically isolates it from further contact with brine and hydrogen sulfide.
The Ni3S2 overlayer so produced exhibits outstanding scale resistance as is demonstrated experimentally herein. For example, iron sulfide scale FeS (Mackinawite), formed by corrosion of an iron source in the presence of hydrogen sulfide, does not adhere to the Ni3S2 overlayer. Moreover, the Ni3S2 overlayer is shown to be structurally robust and survives both continuous rotation through brine solution at 300 rpm at 160° C. and high pressure, and explosive decompression test conditions. It is believed that the Ni3S2 overlayer will likewise be resistant to other types of scale formation, for example for example the formation of scales comprising calcium carbonate (calcite), barium sulfate, (barite), magnesium carbonate, magnesium sulfate, calcium minerals, iron minerals, silica, dolomite, calcium sulfate, iron carbonate, Fe2O3, Fe3O4 (magnetite), FeS2 (iron pyrite), Fe7S8 (pyrrhotite), alpha FeOOH, Fe2(OH)3Cl, beta-FeOOH, and the like.
In one or more embodiments, the Ni3S2 overlayer is characterized by an average thickness in a range from about 0.5 to about 100 microns. In one or more alternate embodiments, the Ni3S2 overlayer is characterized by an average thickness in a range from about 1 to about 20 microns. In yet another set of embodiments, the Ni3S2 overlayer is characterized by an average thickness in a range from about 1 to about 10 microns.
The Ni3S2 overlayer has been observed by the inventors to form in various morphologies depending on the nature of the initial EN protective coating and/or the conditions under which the Ni3S2 overlayer is formed. Thus, the Ni3S2 overlayer formed by reaction of a portion of a 1 micron thick high phosphorous electroless nickel coating exhibits a blocky crystalline morphology after prolonged exposure to hydrogen sulfide and brine at moderate temperature and high pressure (See Coupons 1a and 1b, Tables 1 and 2). Contrast this with the rod shaped crystalline morphology of the Ni3S2 overlayer observed when an initial 2-micron thick high phosphorous electroless nickel coating is exposed to hydrogen sulfide for a shorter period of time (16 hours) at moderate temperature and pressure (See Coupons 2a and 2b, Tables 1 and 2). The inventors have observed experimentally the formation of Ni3S2 overlayers having nanowire morphologies, rod-like morphologies and block-like morphologies; and believe that other Heazlewoodite morphologies such as nanosheet morphologies may be formed as well. In addition, combinations of two or more of such morphologies may be present in a given Ni3S2 overlayer. Further, it is believed that higher energy Ni3S2 morphologies may be converted to more stable forms upon prolonged heating, for example. Thus, in one or more embodiments, the overlayer of Ni3S2 is characterized by one or more morphologies selected from the group consisting of one or more nanosheet morphologies, one or more nanowire morphologies, one or more rod-like morphologies, one or more block-like morphologies, and combinations of two or more of the foregoing morphologies. Ni3S2 overlayer morphologies were determined by x-ray diffraction (XRD) and scanning electron microscopy. In one or more embodiments, the Ni3S2 layer is initially formed with a nanowire morphology which is transformed under the reaction conditions first to a rod-like morphology and finally to a block-like morphology
The EN protective coating may contain one or more of a high phosphorous electroless nickel coating, defined as containing from 10 to 20 percent by weight phosphorous based on the total weight of the coating; a mid phosphorous electroless nickel coating, defined as containing from 8 to 9 percent by weight phosphorous based on the total weight of the coating; and a low phosphorous electroless nickel coating, defined as containing less than 8 percent by weight phosphorous based on the total weight of the coating. In one or more embodiments, the EN protective coating is a multilayer coating comprising one or more high phosphorous electroless nickel coatings, one or more mid phosphorous electroless nickel coatings, one or more low phosphorous electroless nickel coatings, or a combination of two or more of the foregoing high, mid and low phosphorous EN coatings. In one or more embodiments, the EN protective coating comprises at least one EN coating devoid of phosphorous (See for example, coupon 3a of Table 1 in which the EN protective coating is a bi-layer comprising an outer electroless nickel boron outer layer essentially free of phosphorous and a high phosphorous electroless nickel inner layer in direct contact with the T95 steel substrate. It should be noted that the heat treatment referred to in Example 3 (coupon 3a), 350° C. for 1 hour, may have resulted in migration of phosphorous into the electroless nickel boron outer layer, and conversely migration of boron into the electroless nickel phosphorous inner layer. Such heat treatment may also result in a metallurgical bond being formed between an EN inner layer and the substrate. Such a metallurgically bound layer is at times herein referred to as a bond layer. Multilayer EN protective coatings may be prepared stepwise, for example by coating the substrate first with a phosphorous-containing EN coating and subsequently subjecting the EN coated substrate to a second electroless nickel coating step. Those of ordinary skill in the art will understand that phosphorous-containing EN protective coatings may be prepared by reduction of dissolved nickel ions with a phosphorous-containing reducing agent such as sodium hypophosphite (NaPO2H2) in the presence of a substrate immersed in a medium comprising the dissolved nickel ions and the phosphorous-containing reducing agent. By substituting a boron-containing reducing agent, for example diborane (B2H6), for the phosphorous-containing reducing agent an EN protective coating containing boron instead of phosphorous may be obtained.
In one or more embodiments, the EN protective coating comprises solid particles enhancing one or more performance characteristics of such EN coating. For example, the EN protective coating may contain hard particles (nanoparticulate and larger) such as diamond, silicon carbide, cubic boron nitride, talc silica, alumina, and combinations thereof which enhance abrasion resistance. Alternatively, the EN protective coating may contain soft particles such as polytetrafluoroethylene (PTFE) particles and carbon black particles which enhance resistance to damage caused by movement of a coated surface of a first machine component such as an impeller blade in close proximity to a surface of a second machine component such as a housing. In multi-layer EN protective coatings the particles; hard, soft or a combination thereof, are advantageously present in the outermost EN coating, for example as shown in
Fluid conduits provided by the present invention and comprising (a) a fluid conduit exterior surface; (b) a fluid conduit interior surface; (c) an electroless nickel protective coating disposed upon at least one of the fluid conduit interior surface and the fluid conduit exterior surface; and (d) a layer of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating, include useful items such as conduits for transporting fluids in the oil and gas industry, for example tubing used in downhole tubular applications in hydrocarbon production wells. In addition to downhole tubing used in hydrocarbon production, conduits provided by the present invention include any sort of structure though which a fluid may be caused to pass, including without limitation, valves, manifolds, blowout preventers, Christmas trees, wellheads, surface pipelines, subsea pipelines, exhaust gas flow lines, cyclonic separators, liquid-liquid separators, and the like. In some embodiments, the fluid conduit is a storage vessel. Storage vessels qualify as fluid conduits in the sense that fluids flow into and out of storage vessels. In another embodiment, the fluid conduit is a continuous reactor.
In one embodiment, the present invention provides a method of producing a fluid conduit comprising a corrosion and scale resistant nickel sulfide protective layer, the method comprising: (a) heating a fluid conduit comprising an electroless nickel protective coating disposed upon a surface of the fluid conduit in contact with a fluid comprising hydrogen sulfide; and (b) depositing a protective layer of Ni3S2 upon and substantially covering the electroless nickel protective coating. Contact between the electroless nickel protective coating and hydrogen sulfide is carried out at moderate temperatures and moderate to high pressures; the temperature being in one or more embodiments, temperatures in a range from about 100° C. to about 400° C., and the pressure being one or more pressures in a range from about 500 to about 3000 psi. In one or more embodiments, contact between the electroless nickel protective coating and hydrogen sulfide is carried out in the presence of an aqueous solution comprising one or more dissolved salts such as sodium chloride, potassium bromide, lithium iodide, calcium chloride, calcium bromide, and combinations of two or more of the foregoing salts. In one or more embodiments, contact between the electroless nickel protective coating and hydrogen sulfide may advantageously be carried out in the presence of one or more protic acids, such as hydrogen chloride, hydrogen bromide, hydrogen iodide, formic acid, and acetic acid. In one or more embodiments, an exogenous protic acid is employed.
Turning now to the figures,
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Test coupons had dimensions of 2.87 inches by 0.87 inches by 0.125 inches and were made of T95 steel. Electroless nickel coatings were applied by a commercial vendor, Surface Technology, Inc. Robbinsville N.J. 08691.
Representative coated test coupons are illustrated by entries 1a-7a, 11a-12a, 15a and 26a of Table 1. The test coupons were characterized and shown to be uniformly coated.
(1)Electroless nickel phosphorous.
(2)Electroless nickel boron.
(3)High phosphorous ENP contains 10 to 20% by weight P.
(4)Low phosphorous ENP contains less than 8% by weight P
(5)Mid phosphorous ENP contains 8 to 9% by weight P.
(6)Sub-micron nanoparticulate diamond available from Surface Technology, Inc.
(7)Micron scale diamond particles present in Composite Diamond Coating ™ available from Surface Technology, Inc.
(8)Silicon carbide.
In model scaling experiments test coupons were mounted on a rotating cage apparatus and rotated at 300 rpm while in contact with a brine solution within a heated autoclave pressurized with hydrogen sulfide and nitrogen gas. An uncoated T95 steel test coupon was placed in close proximity to the electroless nickel-coated test coupons in order to model corrosive scale formation conditions in which the uncoated T-95 steel test coupon serves as the iron source for FeS scale. Test coupons were weighed before and after being subjected to hours-long exposure to hydrogen sulfide and brine. All electroless nickel-coated test coupons (2a-7a, 11a, 12a and 26a) were observed to increase in weight or remain unchanged in weight (test coupons 1a and 15a) following the model scaling experiments, and all uncoated T95 steel control coupons were observed to decrease in weight following the model scaling experiments. Further, the surface appearance of the electroless nickel-coated test coupons was transformed from a lustrous reflective surface appearance characteristic of electroless nickel coatings, to a dull gray-green surface appearance. The uncoated T-95 steel test coupons turned black under the test conditions.
Preparation of Heazlewoodite (Ni3S2) Coatings on Electroless Nickel-Coated Substrate
Heazlewoodite (Ni3S2) coatings were unexpectedly formed on electroless nickel coated substrates during corrosive scaling tests. The tests were carried out in a one-liter C276 steel autoclave equipped with a purge tube and rotating cage apparatus on which were secured five electroless nickel-coated test coupons (See Table 1) and an uncoated control coupon made of T95 steel. A 1 molar sodium chloride solution (500 mL), an amount sufficient to completely submerge all six coupons, was purged continuously in a premixing unit with oxygen free nitrogen gas (99.9999%) over several hours at ambient temperature. The oxygen level in the brine solution was monitored with CHEMetrics ULR CHEMets kit capable of determining the concentration of dissolved oxygen in the brine in a range from about 0 to about 20 parts per billion (ppb). In representative experiments the brine was considered strictly anoxic when the concentration of dissolved oxygen was less than 4 ppb. Once the brine was judged to be strictly anoxic it was transferred to the autoclave under a nitrogen atmosphere. A mixture of hydrogen sulfide and nitrogen gas at atmospheric pressure and ambient temperature (4% H2S in N2) (2.0 liters, approximately 100 milligrams of H2S) was introduced into the autoclave bringing the initial pressure in the autoclave to 55 psi. The pressure inside the autoclave was boosted to 1450-1500 psi using a high pressure pump to introduce additional nitrogen gas. The autoclave was then heated at 160° C. at a pressure of 2250-2370 psi for approximately 16 hours while rotating the rotating cage at 300 rpm. The autoclave was allowed to cool to ambient temperature and was vented through a H2S scrubber and purged with nitrogen. The test coupons were rinsed with deionized water, dried and characterized variously by weight gain, explosive decompression testing, X-ray powder diffraction (XRD) and electron microscopy. Representative Ni3S2 coated test coupons are illustrated by entries 1b-7b, 11b-12b, 15b and 26b of Table 2.
(1)Single 16 hour cycle as described above but with higher initial H2S pressure (100 psi versus 55 psi).
(2)Ni3S2 layer passed explosive decompression test.
(3)Not Ascertained
(4)Two 16 hour cycles with initial H2S pressure of 55 psi.
(5)Prolonged exposure to hydrogen sulfide-brine protocol.
(6)Single 16 hour cycle as described above but with higher initial H2S pressure (100 psi versus 55 psi), higher brine concentration (3 molar) and the addition of a source of soluble Fe2+ ions.
The electroless nickel-Ni3S2 coated coupons were observed to have excellent resistance to scale adhesion on the outer Ni3S2 layer which in nearly all instances covered essentially 100% of the outer surface test coupon. In one instance, test coupon 26a was observed to provide a Ni3S2 coating covering only about 50% of the surface of the test coupon. This was thought to be due to the relatively high concentration of diamond particles in the original electroless nickel mono-layer. Notwithstanding the partial covering observed for test coupon 26b, the Ni3S2 outer layer exhibited very good resistance to scale accretion. The exposed diamond particle surfaces at the outer surface of the Ni3S2 layer were apparently non-stick with respect to FeS scale as well.
The experimental results indicate that the thickness of the Heazlewoodite layer may be limited to about 10 microns. Thus, coupon 1b having an initial layer of Ni3S2 having a thickness between about 0.5 and 1.0 microns thick, was subjected to extended exposure to hydrogen sulfide and brine over a twenty-one day period during which the Ni3S2 layer grew in thickness to about 10 microns. Of the initial 1 mil (25.4 microns) thick high phosphorous ENP layer, 25 microns of a nickel-phosphorous layer remained following deposition of the Ni3S2 overlayer. Coupons 12b, 15b, and 26b comprised Ni3S2 layers about 10 microns thick. Thus it appears that longer reaction times and/or higher concentrations of hydrogen sulfide did not result in Ni3S2 coatings having thicknesses greater than 10 microns.
Method 1: Preparation of Heazlewoodite (Ni3S2) Coating on an Electroless Nickel-Coated Hydrocarbon Production Tube
A hydrocarbon production tube approximately 30 feet in length, threaded at both ends, having an outer diameter of approximately 4.5 inches and having inner and outer surfaces is first coated with the electroless nickel coating composition of Example 1a of Table 1 of this disclosure on the inner surface of the tube to a thickness of approximately 2 mil. As noted, such electroless nickel coatings may be applied by commercial applicators such as Surface Technology, Inc. of Robbinsville, N.J. A first end of the tube is sealed with a first threaded steel cap likewise coated with 2 mil of the high phosphorous ENP coating of Example 1a. The tube is then moved into a vertical position open end up. Sufficient 1 molar sodium chloride brine solution to fill approximately three quarters of the length of the tube is added to the tube through the open end. The open end of the tube is then sealed with a second threaded steel cap, likewise coated with 2 mil of the high phosphorous ENP coating of Example 1a. The second threaded steel cap is equipped with gas inlet and gas outlet ports. The headspace within the tube is purged with nitrogen at atmospheric pressure and then pressurized with 4% hydrogen sulfide in nitrogen gas mixture to 1400 psi. The tube is then inserted horizontally into an oven equipped with roller bearings which allow the tube to be rotated at approximately 60 rpm. The oven is sized such that the entire length of the tube may be heated during a single heating cycle without moving the tube horizontally through the oven at any point during the heating cycle. The oven temperature is raised to approximately 160° C. and heated at that temperature for 24 hours while rotating the tube at 60 rpm. The tube is allowed to cool and is vented through a hydrogen sulfide scrubber while purging with nitrogen gas. The brine solution is recovered for reuse and the tube is rinsed inside and out with fresh water and allowed to dry. The product hydrocarbon production tube comprises an electroless nickel protective coating disposed upon the interior surface of the tube and a layer of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating.
Method 2: Preparation of Heazlewoodite (Ni3S2) Coating on an Electroless Nickel-Coated Hydrocarbon Production Tube Under Strictly Anoxic Conditions
The method is essentially the same as Method 1 herein with the exception that the brine solution is thoroughly deoxygenated prior to addition of the brine to the tube, and such addition is carried out under a strictly anoxic atmosphere. A source of ferrous ions (ferrous chloride) is added, again under strictly anoxic conditions. The open end of the tube is then sealed with a second threaded steel cap, likewise coated with 2 mil of the high phosphorous ENP coating of Example 1a. The second threaded steel cap is equipped with gas inlet and gas outlet ports. The headspace within the tube is purged with nitrogen at atmospheric pressure and then pressurized with 4% hydrogen sulfide in nitrogen gas mixture to 1400 psi. The tube is then inserted horizontally into an oven equipped with roller bearings which allow the tube to be rotated at approximately 60 rpm. The oven is sized such that the entire length of the tube may be heated during a single heating cycle without moving the tube horizontally through the oven at any point during the heating cycle. The oven temperature is raised to approximately 160° C. and heated at that temperature for 24 hours while rotating the tube at 60 rpm. The tube is allowed to cool and is vented through a hydrogen sulfide scrubber while purging with nitrogen gas. The brine solution is recovered for reuse and the tube is rinsed inside and out with fresh water and allowed to dry. The product hydrocarbon production tube comprises an electroless nickel protective coating disposed upon the interior surface of the tube and a layer of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating.
The foregoing examples are merely illustrative, serving to illustrate only some of the features of the invention. The appended claims are intended to claim the invention as broadly as it has been conceived and the examples herein presented are illustrative of selected embodiments from a manifold of all possible embodiments. Accordingly, it is Applicants' intention that the appended claims are not to be limited by the choice of examples utilized to illustrate features of the present invention. As used in the claims, the word “comprises” and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, “consisting essentially of” and “consisting of” Where necessary, ranges have been supplied, those ranges are inclusive of all sub-ranges there between. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and where not already dedicated to the public, those variations should where possible be construed to be covered by the appended claims. It is also anticipated that advances in science and technology will make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language and these variations should also be construed where possible to be covered by the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2016/107912 | 11/30/2016 | WO | 00 |
