Patent Grant
8029875
This disclosure relates to an apparatus and methods for coating interior surfaces of hollow substrates which may have relatively high aspect ratios (L/D) via plasma ion processing which may then provide a relatively high hardness wear-resistant coating.
Crude oil is a naturally occurring substance including a complex mixture of hydrocarbons of various lengths. Crude oil may be found in porous rock formations or mixed in sand in the upper strata of the earth's crust. The crude oil may pool into reservoirs into which from which the oil may be extracted. Once extracted, the crude oil may be transported to various destinations by pipelines. The pipelines, however, may be subject to material build-up and wear. For example, waxes contained in the crude oil and hydrates formed at a water/oil interface may build-up in the pipelines resulting in occlusions which may necessitate cleaning and may possibly even halt production. In addition, wear may occur due to, for example, friction generated by the flow of the crude oil in the pipeline or particulate matter that may be present in the crude oil.
The same may be true for other transportation pipelines as well. For example, relatively large scale pipelines may carry water, brine or sewage over relatively long distances. Smaller scale pipelines may carry materials throughout a plant, such as polymer pellets, grains or chemical compounds, etc. Depending on the materials carried, many of these pipelines may experience similar problems with respect to wear and material build-up.
In a first exemplary embodiment, the present disclosure relates to a method for plasma ion deposition and coating formation. The method includes providing a vacuum chamber from a hollow substrate having a length, diameter and interior surface and reducing the pressure in the chamber and introducing a precursor gas. This may then be followed by generating a plasma within the chamber and applying a negative bias to the hollow substrate to draw ions from the plasma to the interior surface of the hollow substrate to form a coating. The coating may have a Vickers Hardness Number (Hv) of at least 500.
In another exemplary embodiment, the present disclosure may again amount to a method for plasma ion deposition and coating formation by initially providing a vacuum chamber from a hollow substrate having a length, diameter and interior surface including an electrode extending along all or a portion of the hollow substrate length. This may then be followed by reducing the pressure in the chamber and introducing a precursor gas and generating a plasma within the chamber. One may then again apply a negative bias to the hollow substrate to draw ions from the plasma to the interior surface of the hollow substrate to form a coating.
In an exemplary apparatus form, the present disclosure relates to an apparatus for plasma ion coating including an electrically conductive hollow substrate having a length, a diameter and interior surface capable of enclosing volume. A gas inlet may then be provided which is capable of supplying one or more precursor gases to the enclosed volume wherein the one or more precursor gases is capable of forming a plasma. The apparatus may also include a device for evacuating the volume to a selected pressure level along with a power supply device capable of providing a pulsed voltage to negatively bias the hollow substrate to form plasma ions and to draw the ions to the interior surface of the hollow substrate.
The detailed description below may be better understood with reference to the accompanying figures which are provided for illustrative purposes and are not to be considered as limiting any aspect of the invention.
a-d illustrates exemplary hollow substrates.
The present disclosure relates to a coating and the application thereof, wherein the coating may be resistant to material build-up and wear. The coatings may amount to what may be termed a diamond like carbon (DLC) coating (i.e. a coating formed from amorphous carbon) which may be applied by a plasma coating process onto the surfaces of hollow substrates, and in particular, an interior surface. Such coatings may be utilized in pipelines and other applications which may then prevent or reduce material build-up or wear.
A hollow substrate may be understood herein as a substrate initially having exposed exterior and interior surfaces which may define some amount of interior volume and which may also have a relatively high aspect ratio (AR). The aspect ratio may be understood as the ratio of length (L) to the diameter (D) of the substrate, or L/D. Objects having a relatively high aspect ratio herein may have a length to cross-sectional area ratio of two or more, including all values and increments in the range of about 2 to about 3,000. For example, objects herein may have an aspect ratio of greater than or equal to 10. As may therefore be appreciated, such aspect ratios may define a structure such as a section of pipe which may have, e.g., lengths up to 25 feet (7.62 meters) including all values and increments therein, at diameters of about 3-10 inches (7.6 cm to 25.4 cm). It may therefore be appreciated that one may conveniently utilize a pipe having a length of about 20 feet (6.10 meters) at about a 4 inch diameter (10.2 cm) which therefore defines an exemplary aspect ratio of at least 60 or higher.
The hollow substrates herein, as explained more fully below, may also be those which may define all or a portion of a vacuum chamber, which vacuum chamber may then contain the formed plasma (ionized gas) for coating purposes. The hollow substrate defining the vacuum chamber may then itself become electrically biased in an amount suitable to attract plasma ions (e.g. positive ions or I+) for a coating formation.
Exemplary views of hollow substrates suitable for plasma coating herein are illustrated in
To evacuate the tubular substrate 202 the vacuum system 208 may be provided in fluid communication with the interior portion of the tubular object 202. The vacuum system 208 may include, for example a momentum transfer pump 212 and a positive displacement, i.e., mechanical pump 214. Exemplary momentum transfer pumps may include diffusion pumps or turbomolecular pumps. One or more valves may be positioned between the vacuum system 208 and the tubular object. As presently illustrated the valves may include a throttle valve 216 and a gate valve 218. It should be appreciated that a number of other valves may be utilized as may be necessary by system requirements.
As noted above, gasses may be supplied to the tubular object 202 via a gas supply system 210, which may also be present at both ends of the hollow substrate, or at one end thereof, and which may include a gas inlet port 222. Gasses may therefore be fed from one or more storage devices 224 to the gas inlet port 222. One or more valves and/or regulators 226 may be supplied between the storage device 224 and the gas inlet port 222 aiding in the control of gas flow and pressure in the system 200. Furthermore, a pressure gauge 228 may be positioned on the multiport fitting/couplings 206 at one or both ends of the tubular substrate. The pressure gauge 228 may allow for the measurement of system pressure, which measurements may then be used to adjust or maintain the system pressure in a desired range or at a desired value. Accordingly, the control of pressure and/or gas flow may be provided manually or by an automated feed back system.
A relatively high voltage pulsating DC power supply 230 may be connected to the hollow substrate 202 as illustrated which may then provide that the hollow substrate becomes biased with a negative voltage so that it may draw ions from the plasma to the substrate inner surface, wherein the ions may then simultaneously impinge on the inner surface to form a coating as explained more fully below. The voltage pulses may be less than or equal to about 10 kV. The pulse frequency may be about 100 Hz to about 20 kHz, including all values and increments therein, at a pulse width from about 5 microseconds to about 40 microseconds, including all values and increments therein.
Furthermore, with attention to
An exemplary method of forming a wear and resistant coating on a hollow substrate is next illustrated in
The interior surface of the hollow substrate may also be optionally provided with a precursor bond coat which may be applied as an amorphous (non-crystalline) coupling layer as between the metallic surface and outer coating layers. Reference to coupling layer is reference to the feature that the precursor bond coat may improve the bonding strength as between the coating layer and the substrate surface. Suitable silicon containing precursors include, e.g. silane compounds, which may be understood as the silicon analogue of an alkane hydrocarbon, of the formula SinH2n+2 wherein n is an integer and may have a value of 1-10. For example, a suitable silane compound may therefore include silicon tetrahydride (SiH4). The silane compound may also include substituted aliphatic and/or aromatic functionality, e.g. trimethylsilane [SiH(CH3)3]. Similar to the above, the bond layer may be applied at pulse frequency of from about 100 Hz to about 20 kHz may be applied, at a pulse width of about 5 microseconds to about 40 microseconds, to negatively bias the tube up to about 10 kV with respect to ground, for a period of up to about 60 minutes, including all values and increments therein. For example, it has been found useful to negatively bias the tube at about 4 kV for a period of about 15 minutes
Whether or not the above two steps are applied, the inner surface of the hollow substrate, i.e. an inner surface without sputter cleaning and/or a precursor bond coating, may then be exposed to a plasma containing one or more inorganic or organic gaseous precursors, which may be understood as any gas capable of forming an ion plasma, and which may then provide an inner surface wear-resistant coating of a desired thickness and hardness. The coatings may be applied on all or a portion of the inner surface of the hollow substrate, and may be relatively uniform in thickness, i.e. where such coating does not vary in thickness by more than about +/−20% along the length of a given hollow substrate.
The coatings may also exhibit a Vickers Hardness Number (Hv) of 500 or greater, including all values and increments in the range of 500 to 3000 (Hv). As alluded to above, the coatings herein may therefore be understood to include, but not be limited to, those coatings which are termed diamond like carbon (DLC) coatings which may be understood herein as coating that contain some amount of amorphous carbon. In addition, such coatings may include those which may exhibit a dry sliding (kinetic) coefficient of friction (μk) in the range of 0.01 to 0.2, including all values and increments therein. Furthermore, the coatings may exhibit an electrical resistivity in the range of about 10×106 to 10×1014 ohm/cm, including all values and increments therein. The coatings may be applied at thicknesses in the range of about 0.1 to 15 microns, including all values and increments therein. The coatings also may exhibit a water contact angle (CA) in the range of 60° to 110°, including all values and increments therein. The contact angle may be understood as the shape of a liquid water droplet as it rests on a solid surface. The contact angle is the measured angle between a tangent line at the drop boundary and the solid surface. Such contact angles indicate that the coating layers herein are relatively hydrophobic (i.e. they provide a relatively non-polar surface that does not interact well with polar molecules such as water).
Exemplary precursor gasses suitable for formation of the above referenced coating on the interior surface of the hollow substrate may include hydrocarbon compounds (i.e. compounds containing carbon and hydrogen which may be provided as a gas) such as acetylene (C2H2), ethylene (C2H4) and/or methane (CH4) etc., which may be used alone or in combination with precursor gases containing an inorganic element such as the silane compounds noted above (SinH2n+2), silicon carbide (SiC), silane compounds including substituted aliphatic and/or aromatic functionality hexamethyldisiloxane (HMDSO or (CH3)3—Si—(CH3)3), trimethyl silane (3 MS or SiH(CH3)3), or other types of organic (carbon containing) gases such as perfluoropropane (CF3—CF2—CF3) and/or hexafluoroethane (CF3—CF3) and combinations thereof. Still further, other exemplary precursor gases may include Cr-containing organic gases such as hexacarbonyl chromium (Cr(CO)6) and/or Ti-containing gases such as Tetrakis titanium (Ti[N(CH3)2]4).
The coatings noted above may be formed on all of a portion of the interior surface of a hollow part such as hollow part 202 illustrated in
In addition, the coatings herein may be further characterized with respect to the presence of surface chemistry functionality via a technique such as X-ray photoelectron spectroscopy (XPS). XPS may be understood as a quantitative spectroscopic technique that may measure the empirical formula, chemical state and/or electronic state of the elements that exist at the surface of a sample. The XPS measurements may be performed by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy (KE) and number of electrons that may be excited in the top 1 to 10 nm of the material being analyzed. The chemical bonding states that have been observed herein include one or more of the following: C—H bonds, C═O bonds, C—O—O— bonds, C—F bonds, and/or C—Si bonds, which as noted above may depend on the various precursor gases used to provide a given plasma.
The tubular substrate with internal surfaces coated as discussed above may be specifically incorporated into a pipeline system for the transportation of materials such as crude oil. In such a manner, a system is provided herein which incorporates at least a portion of pipeline having pipe sections that include plasma coatings on the interior surface. In addition, as noted earlier, it may be appreciated that as crude oil may contain various waxes and hydrates. The application of the coatings herein on the inside surfaces of piping that may be employed for crude oil transport may therefore provide a reduction in wax and/or hydrate build-up which may otherwise restrict oil flow.
The above various features of the present disclosure may now be illustrated by the following non-limiting examples.
A number of coatings were initially produced on stainless steel and silicon wafer test coupons mounted on the inside surface of exemplary hollow substrate structures. The general deposition procedure generally included mounting the tubular structures inside of a vacuum chamber and evacuating the chamber to a pressure 1×10−5 Torr. The samples were cleaned using an inert gas (argon) plasma to remove residual hydrocarbon and/or metal oxide layers. On a number of the samples a bond coat including silicon was deposited using silane (SH4) gas plasma. Coating layers were then deposited using different precursor gases and various deposition parameters. In some cases a top coating layer was deposited using a different precursor gas mixture. Tables 1-4 summarize the various coating processes carried out for the above reference sputter cleaning process, bond layer formation, and first and second layer formation.
The water contact angle of a number of the above samples was then examined. Table 5 summarizes the results of such contact angle measurements.
In addition, the primary bonding chemical states were examined for various coatings utilizing X-ray photoelectron spectroscopy (XPS). Table 6 summarizes the results of the analysis.
Coatings were also applied to pipe (10 foot in length at about 4.0 inch diameter). The plasma coatings were applied in accordance with the above protocols and again, to evaluate coating efficiency, silicon coupons were positioned on the interior surface of the pipe to evaluate coating performance.
In addition, to the above, coatings were applied to 20 foot long pipe (6.10 meters) at about 4.0 inch diameter (10.2 cm) with similar results to therefore provide useful coatings on a hollow substrate which may therefore be employed, as noted above, in applications such as crude oil transport. Persons of ordinary skill in the art will therefore recognize that various modifications that may be made to the disclosure herein and should not be considered limiting with respect to the invention defined by the following claims.
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