Patent Application
20200248319
Embodiments relate in general to cathodic protection and specifically to internal cathodic protection of a fluid-containing vessel.
Corrosion protection is required for steel structures that are exposed to corrosive fluids. The steel structures can be any structure exposed to corrosive fluids including, for example, a vessel that contains or is exposed to water or corrosive fluids. A protective coating on the steel or cathodic protection can be used to protect steel from corroding.
Cathodic protection for vessels is typically done with galvanic anodes in a technique known as galvanic anode corrosion protection (“GACP”). There are three types of galvanic anodes that are typically used for corrosion protection, namely, magnesium, aluminum and zinc anodes. The magnesium anodes often demonstrate high potential and, thus, corrode in less than one year in vessel protection. The aluminum anodes are also consumed rapidly, particularly when the temperature is more than 50° C. in the vessel. The normal zinc anodes are not consumed as quickly, but may reverse polarity at higher temperatures, meaning instead of acting as anodes, they may become the cathode at high temperature. That is why high temperature zinc (“HTZ”) anodes are often used in vessels at temperatures above 50° C. and up to 70° C. These GACP conventional anodes demonstrate undesirable properties when used in severe conditions. What is meant by severe here is a combination of low resistivity, high temperature and/or high H2S. The consumption rate of HTZ anodes, for example, is increased from 12 Kg/A-Y in normal conditions to 16 Kg/A-Y in severe conditions. That is 30% more, reflecting into 30% shorter anode life.
Another problematic issue in traditional cathodic protection systems is known as erosion corrosion. Where fluids are flowing past an exposed anode, the anode can deteriorate due to erosion from such flowing fluid.
Embodiments of an apparatus and method for protecting vessels from corrosion is disclosed. In embodiments, a dimensionally stable impressed current precious anode, such as Mixed Metal Oxide (“MMO”), platinized niobium (“PtNb”) and platinized titanium (“PtTi”) anode is encapsulated in a wax-repellent layer and then installed inside wet crude handling facilities such as, for example, High Pressure Production Traps (“HPPT”), Low Pressure Production Traps (“LPPT), Water and Oil Separation Plants (“WOSEP”), Desalters and/or Dehydrators.
Precious anodes such as MMO, PtNb, or PtTi have been tested in real conditions but failed when a layer of paraffin wax developed on their surfaces, which prevented them from further corrosion. Embodiments use a dimensionally stable impressed current anode encapsulated in a wax-repellent layer. In embodiments, one or more conductive, cementitious layers are used to coat each CP anode. When cement was used around conventional anodes (galvanic or impressed current), the cement layer tends to crack as the anode corrodes away. In embodiments, dimensionally stable anodes are used. Dimensionally stable means that the consumption (corrosion/dissolution) rate is so small that the anodes do not change in size or the change in size is so negligible.
One example embodiment is a cathodic protection system including a vessel for containing a fluid or a mixture of fluids, a plurality of anodes positioned inside the vessel, an encapsulant encapsulating the plurality of anodes, and an impressed current source electrically connected to each of the anodes and the vessel. The impressed current source produces a continuous high current output (>1 Amp from each anode), and the vessel acts as a cathode when current is applied from the impressed current source. The encapsulant can be a wax repellant material that is sufficiently porous to allow ions to pass therethrough. Each of the anodes are individually monitored and controlled from outside of the vessel using one or more adjustable resistors, which may be installed in a junction box located either inside or outside the vessel. The resistors are configured to adjust the individual anode current output based upon a predetermined cathodic protection criteria, including a threshold current output.
Another example embodiment is an anode system including a vessel having an interior surface, a first phase fluid and a second phase fluid contained within the vessel, a plurality of anodes spaced apart from each other, each of the plurality of anodes being connected to the interior surface of the vessel and at least a portion of the anodes being positioned within the second phase fluid, and an impressed current source electrically connected to each of the anodes and the vessel. The impressed current source produces a continuous high current output (>1 Amp from each anode), and the vessel acts as a cathode when current is applied from the impressed current source. An encapsulant encapsulates the anodes, the encapsulant being a wax repellant material operable to transmit ions therethrough. Each of the anodes are individually monitored and controlled from outside of the vessel using one or more adjustable resistors, which may be installed in a junction box located either inside or outside the vessel. The resistors are configured to adjust the individual anode current output based upon a predetermined cathodic protection criteria, including a threshold current output.
Another example embodiment is a method of providing corrosion protection to a vessel. The method includes positioning a plurality of anodes inside the vessel, wherein the plurality of anodes are encapsulated with a wax repellant material that is sufficiently porous to allow ions to pass therethrough. The method further includes electrically connecting an impressed current source to each of the anodes and the vessel, wherein the impressed current source produces a continuous high current output (>1 Amp from each anode), the vessel being a cathode when current is applied from the impressed current source. The method further includes electrically connecting one or more adjustable resistors to each of the anodes for monitoring and controlling the anodes from outside of the vessel. The method also includes installing the one or more adjustable resistors in a junction box located either inside or outside the vessel, wherein the resistors are configured to adjust the individual anode current output based upon a predetermined cathodic protection criteria, including a threshold current output.
The foregoing aspects, features, and advantages of embodiments of the present disclosure will further be appreciated when considered with reference to the following description of embodiments and accompanying drawings. In describing embodiments of the disclosure illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments disclosed. Like reference numerals refer to like elements throughout the specification.
The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments.
Cathodic protection (“CP”) systems are used to protect steel components from corrosion. One particular type of CP system is known as a galvanic anode cathodic protection (“GACP”) system. In GACP systems, steel structures can be protected from corrosion (“a protected metal”) by being positioned as a cathode in an electrochemical cell that includes an anode composed of a more highly reactive metal than the cathode. The anodes can be composed of, for example, highly reactive metals such as aluminum, zinc, or magnesium. The electrochemical cell includes an electrolyte (e.g., water or moist soil), and the anode and the cathode are positioned in the same electrolyte to provide an ion pathway between the anode and the cathode. In the electrochemical cell, the anode and the cathode are also electrically connected to provide an electron pathway between the anode and the cathode.
When the protected metal and the anode are positioned in the electrochemical cell accordingly, the more reactive anode corrodes in preference to the protected metal structure, thereby preventing corrosion of the protected metal. Due to the difference in the natural potentials between the anode and the protected metal, by their relative positions in the electro-chemical cell, when the anode corrodes, high-energy electrons flow from the anode to the cathode through the electrical connection, thereby preventing an oxidation reaction at the protected metal structure. Thus, the anode corrodes instead of the protected metal (the cathode), until the anode material is depleted. The anode in a GACP system is known as a “sacrificial anode,” and likewise, GACP systems are also known as “sacrificial anode systems.”
A galvanic cathodic protection system 100 is shown in
Anode assembly 108 is a galvanic anode assembly for providing corrosion protection to vessel 102. One or more anode assemblies 108 are spaced apart around the interior surfaces of vessel 102. A large storage vessel, for example, can have 50 anode assemblies 108, although more or fewer anode assemblies 108 can be used. Anode assembly 108 includes anode 110 mounted on and electrically connected to anode mount 112. Anode mount 112 is mechanically and/or electrically connected to the interior surface of vessel 102 so that electric current can flow between anode mount 112 and vessel 102. As one of skill in the art will appreciate, anode 110 has more negative electrochemical potential than vessel 102, so that electric current flows from vessel 102 to anode 110. Ions 114 flow from anode 110 to vessel 102. The anode provides corrosion protection to vessel 102. In embodiments, test cable 116 is electrically connected to anode 110 and can be used to monitor the condition of anode 110 and determine, for example, if the anode 110 is failing. Test cable 116 is connected a nozzle 118, which may be used to monitor and control the anode 110 from outside of the vessel 102. Test cable 116 may terminate on the inside or extend to outside of the vessel 102 to ease monitoring and control of the anode 110 from outside of the vessel 102.
Another type of CP system is known as an impressed-current cathodic protection (“ICCP”) system. ICCP systems use anode metals connected to an external power source to provide greater current output. Impressed-current cathodic protection systems employ D/C power (e.g., rectified A/C power) to impress a current between one or more anodes and the cathode.
An impressed current cathodic protection system 120 is shown in
Anode assembly 128 is an ICCP anode assembly for providing corrosion protection to vessel 122. One or more anode assemblies 128 are spaced apart around the interior surfaces of vessel 122. A large storage vessel, for example, can have 50 anode assemblies 128, although more or fewer anode assemblies 128 can be used. At least a portion of the anode assemblies 128 are positioned to be in contact with the second phase 126. Anode assembly 128 includes anode 130 mounted on anode mount 132. Encapsulant 134 encapsulates all or a portion of anode 130. Anode assembly 128 is positioned through orifice 136 of vessel 122. Flange 138 is a flange on an outer surface of vessel 122, surrounding orifice 136. Anode mount 132 is mechanically connected to flange 138 of vessel 122. Anode 130 is electrically isolated from vessel 122, by, for example, using a non-conductive mount 132 or having an insulator such as insulated spacer 139 positioned between mount 132 and vessel 122.
Power supply 140 is a direct current (“DC”) power supply having a negative line 142 electrically connected to vessel 122 and a positive line 144 electrically connected to anode 130. Power supply 140 can be connected to an alternating current (“AC”) power source, and can include a rectifier for converting the AC electricity into DC electricity. When electric current is applied by power supply 140, electric current flows from vessel 122 to anode 130. Ions 146 flow from anode 130 to vessel 122. The anode provides corrosion protection to vessel 122.
Referring now to
An encapsulant 134 is used to encapsulate, or coat, anode 130. Encapsulant 134 can be applied to anode 130 in a generally liquid state. After curing to a hardened, cured state, encapsulant 134 is generally rigid. Alternatively, encapsulant 134 can be applied as a powder before being fired and cured. After being applied and when in the cured state, encapsulant 134 covers and is in contact with all or at least a portion of exterior surface 148. In embodiments, encapsulant 134 can be used with ICCP systems. In embodiments, encapsulant 134 is applied to anode 130 before anode 130 is connected to vessel 122. In embodiments, encapsulant 134 is spaced apart from vessel 122, meaning that it is not connected directly to and is not a part of the structure being protected, such as vessel 122, except by way of anode 130.
Encapsulant 134 is a hydrophilic cementitous coating material that permits anode 130 to discharge a current through encapsulant 134. In embodiments, encapsulant 134 is a cementitious material that is permeable, has high mechanical strength, and has the ability to repel waxy materials. Encapsulant 134 can also protect anode 130 from erosion corrosion. In embodiments, grains of encapsulant 134 can be in the general form of spheres with a diameter in a range of 350 μm to 1,500 μm and can have, for example, a diameter of about 950 μm. The grains can have a resin coating. In embodiments, the grains can include crystalline compounds such as mullite and corundum. For example, more than 50% of the crystalline compounds can be mullite or corundum, or a combination of mullite and corundum. Lesser amounts of quartz, bayrite, and microline can also be included in the cement. The composition of an example material is shown in Table 1.
In other embodiments, encapsulant 134 can comprise 40% to 60% cement and 40% to 60% carbon, and for example, can comprise 50% cement and 50% carbon and can be, for example, the SAE Inc. product known as Conducrete™.
In embodiments, encapsulant 134 can be electrically conductive. In embodiments, encapsulant 134 can be sufficiently porous to permit ions or electrons to pass therethrough. For example, the encapsulant 134 can have pores with a diameter in a range of 100 μm to 650 μm and can have, for example a diameter of about 200 μm to 250 μm. Ions 146, thus, can pass from anode 130, through encapsulant 134 and second phase fluid 126 to vessel 122.
In embodiments, encapsulant 134 repels oil droplets and, thus, prevents the oil droplets from collecting on encapsulant 134 and anode 130. Encapsulant 134 is a wax repellent material, meaning that it repels wax, such as paraffin wax, and resists wax deposition. Wax that is present in first phase 124 and second phase 126 does not adhere to encapsulant 134. Furthermore, wax is not able to pass through the pores of encapsulant 134 so encapsulant 134 prevents wax from adhering to and building up on anode 130. In embodiments, encapsulant 134 is acid resistant. More specifically, in embodiments, encapsulant 134 is resistant to H2S. In embodiments, anode 130 is used in a conductive media, such as water, so it is not necessary for encapsulant 134 to have properties that cause it to decrease the contact resistance between anode 130 and the conductive media. In contrast, conventional anodes used in, for example, concrete may need to overcome the high resistivity of that concrete by decreasing the contact resistance in the immediate vicinity of the anode by way of encapsulating the anode in a conductive media.
In embodiments, anode 130 is dimensionally stable so that it does not change shape during operation for at least a predetermined amount of time. Therefore, the outer surface of anode 130 remains in contact with the inner surface of encapsulant 134 for at least the predetermined amount of time. If anode 130 was not dimensionally stable, it could corrode during operation resulting in gaps between the outer surface of anode 130 and the inner surface of encapsulant 134. If such gaps existed, wax could migrate into the gap and have an insulating effect on the anode. By operating for at least the predetermined amount of time without any gaps forming, encapsulant 134 prevents wax from contacting anode 130 for at least the predetermined amount of time. In embodiments, the predetermined amount of time can be between 1 and 20 years. In embodiments, the predetermined amount of time can be between 3 and 15 years. In embodiments, the predetermined amount of time can be between 5 and 10 years. In embodiments, the predetermined amount of time can be greater than 5 years. In embodiments, the predetermined amount of time can be greater than 7 years. In embodiments, the predetermined amount of time can be greater than 10 years.
Referring now to
In step 206, insert the anode 130 and fill the container with the wax-repellent material. This could be done by, for example, placing a nozzle of a cement gun into the container, almost to the bottom of the container, and then slowly squeezing the trigger while the anode is inside. Then filling the container with wax-repellent material by applying steady pressure to the trigger of the cement gun. The container is considered to be filled when the wax-repellent material is flush with an opening of the container.
In step 208, the encapsulant is cured. In embodiments, the encapsulant adheres to the anode as it cures. The curing time is sufficient to cure the encapsulant to a solid state. The curing time can be any amount of time sufficient to cure the encapsulant. In embodiments, the curing time can be, for example, from 1 to 48 hours. In embodiments, the curing time can be 5 to 15 hours. In embodiments, the curing time can be about 12 hours. To cure the encapsulant, the contents of the container are pressurized. This can be accomplished by, for example, placing the entire container in a pressure chamber, or by sealing the container and applying pressure to the interior of the chamber. In embodiments, the contents of the container can be pressurized to about 2500-3500 psi. In embodiments, the contents of the container can be pressurized to about 2900-3100 psi. In embodiments, the contents of the container are pressurized to about 3000 psi. The container can also be heated during the curing time. The temperature can be heated to, for example, between about 50 and 300 degrees C. In embodiments, the temperature can be heated to, for example, between about 100 and 200 degrees C. In embodiments, the temperature can be heated to, for example, between about 140 and 160 degrees C. In embodiments, the temperature can be heated to, for example, about 150 degrees C. In embodiments, the temperature and pressure can be maintained at a constant level, or can be varied in a controlled manner during the curing process. In step 210, the anode and encapsulant assembly is removed from the container. The anode and encapsulant, together, define a mounting and have a high quality, uniform size and shape.
In step 212, the mounting (encapsulant 134 and anode 130) is connected to mount 132 to define anode assembly 128. In step 214, anode 130 and encapsulant 134 are inserted through orifice 136 into vessel 122, and mount 132 is connected to flange 138. In step 216, power supply 140 is connected to anode 130 by way of positive line 142 and negative line 144. In step 218, a fluid is introduced into vessel 122, the fluid contacting encapsulant 134. In step 220, corrosion protection is provided by activating power supply 140 to create a circuit that includes power supply 140, negative line 144, anode 130, either or both of first phase 124 and second phase 126, vessel 122, and positive line 142. First phase 124 and second phase 126 can be initially mixed when introduced into vessel 122, and then separate to form distinct layers. A plurality of anode assemblies can be spaced apart around the interior surfaces of vessel 122, with a portion of the anode assemblies being in contact with first phase 124 and a portion of the anode assemblies being in contact with second phase 126.
Another example embodiment is a cathodic protection system 300 as illustrated in
The system 300 further includes an impressed current source 310 electrically connected to each of the anodes 306 via electrical cables 308, and the vessel 302. The impressed current source 310, which may be installed in a junction box, is configured to produce a continuous high current output (>1 Amp from each anode). The vessel 302 acts as a cathode when current is applied from the impressed current source 310. Each of the anodes can be individually monitored and controlled from outside of the vessel using one or more adjustable resistors 318. The adjustable resistors 318 may be installed in a junction box 310, which may be located either inside or outside the vessel 302. The adjustable resistors 318 are configured to adjust the individual anode current output of anodes 306 based upon a predetermined cathodic protection criteria, which may include a threshold current output or a range for the current output.
In one example embodiment, the system 300 may include a plurality of anodes 306 connected to a DC power source, for example, a transformer-rectifier 320 connected to AC power. In the absence of an AC supply, alternative power sources may be used, such as solar panels, wind power or gas powered thermoelectric generators. Anodes 306 for the system 300 may be available in a variety of shapes and sizes, such as those described in the previous embodiments. Common anodes are tubular and solid rod shapes or continuous ribbons of various materials.
Cathodic protection transformer-rectifier units 320 may be custom manufactured and equipped with a variety of features, including remote monitoring and control, integral current interrupters and various type of electrical enclosures. The output DC negative terminal 314 is connected to the vessel 302 to be protected by the cathodic protection system 300. The rectifier 320 output DC positive cable 312 is connected to the anodes 306 via junction box 310. The AC power cable is connected to the rectifier 320 input terminals. In other words, a positive terminal 312 connects the transformer-rectifier 320 to the impressed current source 310, and a negative terminal 314 connects the transformer-rectifier 320 to the vessel 302. The system 300 may include one or more nozzles, similar to nozzle 118 illustrated in
The output of the system 300 can be optimized to provide enough current to provide protection to the vessel 302. The cathodic protection transformer-rectifier units 320 may be designed with taps on the transformer windings and jumper terminals to select the voltage output of the system 300. Cathodic protection transformer-rectifier 320 may be made with solid state circuit to automatically adjust the operating voltage to maintain the optimum current output or structure-to-electrolyte potential. Analog or digital meters may be installed to show the operating voltage (DC and sometimes AC) and current output. The system 300 may also be designed with multiple independent zones of anodes 306 with separate cathodic protection transformer-rectifier circuits.
As illustrated in
Conventional coalescers begin to lose efficiency when the IFT gets below 20 dyne/cm. In addition, efficient separation is a function of the compatibility of the liquids with the coalescer medium. A good coalescing medium is not necessarily compatible with the liquids and a compatible medium is not necessarily a good coalescing medium. The coalescers in the present embodiments provide for the deficiencies of conventional coalescers, and do not lose efficiency when the IFT gets below 20 dyne/cm.
System 300 may further include a plurality of cables 322 that may be coupled to the coalescers 304, and terminated outside the vessel 302. The cables 322 are used to monitor and control the corresponding coalescers 304 from outside the vessel 302. The system 300 may also include a galvanic anode monitoring system (not shown) that may be configured to monitor the vessel potential when the anodes 306 are disconnected from the vessel 302. The galvanic anode monitoring system is coupled to the transformer-rectifier 320 to adjust the individual anode current output based upon a predetermined cathodic protection criteria, which may include a threshold current output or a range for the current output.
Anodes 306 may include at least one material selected from the group consisting of mixed metal oxide (“MMO”), platinized nickel (“PtNi”), platinized cobalt (“PtCo”), platinized niobium (“PtNb”), platinized titanium (“PtTi”), high temperature zinc, and high silicon cast iron. In one example embodiment, system 400 may include a plurality of MMO anodes 306 and a plurality of high silicon cast iron anodes 316, as illustrated in
Another example embodiment is a method 500 of providing corrosion protection to a vessel, as illustrated in
The Specification, which includes the Summary, Brief Description of the Drawings and the Detailed Description, and the appended Claims refer to particular features (including process or method steps) of the disclosure. Those of skill in the art understand that the disclosure includes all possible combinations and uses of particular features described in the Specification. Those of skill in the art understand that the disclosure is not limited to or by the description of embodiments given in the Specification.
Those of skill in the art also understand that the terminology used for describing particular embodiments does not limit the scope or breadth of the disclosure. In interpreting the Specification and appended Claims, all terms should be interpreted in the broadest possible manner consistent with the context of each term. All technical and scientific terms used in the Specification and appended Claims have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs unless defined otherwise.
As used in the Specification and appended Claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly indicates otherwise. The verb “comprises” and its conjugated forms should be interpreted as referring to elements, components or steps in a non-exclusive manner. The referenced elements, components or steps may be present, utilized or combined with other elements, components or steps not expressly referenced.
Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain implementations could include, while other implementations do not include, certain features, elements, and/or operations. Thus, such conditional language generally is not intended to imply that features, elements, and/or operations are in any way required for one or more implementations or that one or more implementations necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and/or operations are included or are to be performed in any particular implementation.
The systems and methods described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While example embodiments of the system and method have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications may readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the system and method disclosed herein and the scope of the appended claims.
