WO2003042429A1

WO2003042429A1 - Anodes with monolithic pre-packing, novel cathodic protection system that saves electrical energy and increases the useful life of said anodes

Info

Publication number: WO2003042429A1
Application number: PCT/MX2002/000099
Authority: WO
Inventors: Hector Huerta Ceballos
Original assignee: Hector Huerta Ceballos
Priority date: 2001-10-19
Filing date: 2002-10-17
Publication date: 2003-05-22
Also published as: MXPA01012516A; AU2002349568A1

Abstract

The invention relates to a cathodic protection system based on impressed current. According to the invention, the anodes, which constitute the positive current diffusers in the system, are altered in terms of the standard structure thereof using a monolithic electroconductive material and a series of internal arrangements which cause a reduction in the electric resistance to the passage of current in an anodic device. In this way, power requirements are reduced, a considerable saving is made in relation to electrical energy and the useful life of said type of anode is increased. The configuration of the novel anode does not alter the electrochemical phenomenon intrinsic to cathodic protection. Said configuration is based primarily on the use of standard and commercial anodes in the form of an anode-core (4). The aforementioned anodes are pre-packed in a mixture of chemical compounds (2) which, through the addition of water, form a larger, heavier monolithic anode which can operate in both the vertical and horizontal positions. Moreover, said anodes can be used on sandy surfaces as well as in swamps, marshes and marine areas.

Description

MONOLITIC PRE-PREPACKED ANODES NEW CATHODIC PROTECTION SYSTEM FOR ELECTRICAL ENERGY SAVINGS

AND INCREASE OF THE USEFUL LIFE OF THE ANODES.

BACKGROUND OF THE INVENTION

It is known as "cathodic protection" to an electrochemical phenomenon that man uses to prevent corrosion of buried or submerged metal structures.

References to the above are found in the following publications:

Pipe Line Corrosion and Cathodic Protection, Third Edition, Parker - Peattie, Gulf Publishing Company;

Underground Corrosion, ASTM - Committee G-l, Technical Publication 741;

Cathodic Protection, Second Edition, John Morgan, National Association of Corrosion Engineers;

Control of Pipe Line corrosion, A. W. Peabody N.A.C.E. Houston, Tex; NACE - STANDARD RP-169-96;

Control of External Corrosion on Underground or Submerged Metallic Piping Systems. NA. CE.- INTERNATIONAL Houston, Tex.

All cathodic protection systems are based on an electrochemical cell whose main elements are the anode, the cathode, the electrolyte and a source of energy. In cathodic protection systems based on printed current, materials such as graphite, iron-silicon-chromium, titanium, platinum, niobium, some metal oxide substrates of Group IN and Group VII of the Table are currently used as anodes.

Periodic, as well as iron or steel scrap and semiconductor materials of extruded polymer type.

The functioning of the anodes is significantly affected by a range of different factors ranging from the physical and chemical properties of the anode material itself, its shape and dimension, its manufacturing process, the chemical composition of the electrolyte in which they operate, the electrical current densities to which they are subjected during their operation; as well as to positioning factors of the anodes with respect to the cathode (pipe or metal structure) that form the electrochemical cell in a cathodic protection system.

To improve the operation and service life of the anodes used in cathodic steel pipe protection systems, a carbonaceous filler or back-fill filler has been used for many years and is placed "a bulk "surrounding the anode - nucleus. This filler material or backing material electrically improves the anode-ground contact and is preferably consumed before the anode-core.

Due to the fact that it is not very often possible to use this "landfill" in sandy, swampy, lake and marine soils, the anodes - core are installed without the aforementioned filling, causing an accelerated consumption or wear of these anodes in the protection systems cathodic in operation, its immediate replacement being necessary very frequently, which results in very high costs of preventive maintenance of industrial facilities and long exposure times of pipes to attack by external corrosion.

The type of carbonaceous filling or back - fill mainly used in cathodic protection is metallurgical coke, calcined petroleum coke and bulk graphite. These are used in different granulometries. The direct current transfer in a cathodic protection system is carried out both electrolytically or ionically, and electronically.

In many electrochemical processes, such as cathodic protection, gases are produced on the surface of the electrodes.

The humidity in a group of anodes is critical for their operation. The flow of ionic current to the ground depends on the humidity in the soil - anode interface or the interface between the carbonaceous filler material and the soil.

The anode materials that are currently used in cathodic protection are consumed in different proportions, depending mainly on the direct current density to which they are subjected during their operation.

The carbonaceous back-fill provides an electronic path for the flow of current. If an anode is installed without Back - fill, the oxidation reaction occurs on the surface of the anode. On the other hand, if the anode is installed inside a carbonaceous filler, the oxidation reaction is transferred primarily to the surface of the backfill.

The transfer of the oxidation reaction to the back-fill surface consumes this material, and has the following benefits:

The electrical resistance between the anode and the ground will be reduced, since the resistance will be regulated by the dimensions of the back - fill and not by the dimensions of the anode - core.

The entrapment of the reaction gases, in the anodic area, the anode polarization and the drying tendencies of the soil, are minimized. The life of the anode - nucleus is increased. The objective of the invention is to structurally modify the current anode-fill relationship (without altering its intrinsic electrochemical phenomenon) by making it a single solid monolithic structure that can operate in all types of soils and lacustrine and marine areas; thus enabling the anode to obtain very important value-added characteristics to conventional anodes, such as significant savings in electricity consumption and anode materials among others, as well as prolonging the useful life of current cathodic protection systems.

DESCRIPTION OF THE INVENTION

The characteristic details of this new system are clearly shown in the following description and in the accompanying drawings, as well as an illustration of that and following the same reference signs to indicate the parts and figures shown.

Figure 1 is a plan view of the construction of the monolithic prepackaged anode.

Figure la is an elevation cut of the monolithic prepackage anode construction.

Figure 2 is another plan view of the monolithic prepackage anode construction, showing the installation details of the internal arrangements of the perforated tubes and their filters.

Figure 2a is another view of an elevation cut of the monolithic prepackage anode construction, showing the installation details of the internal arrangements of the perforated tubes and their filters.

Figures 3 and 3a show an illustration of the exterior finish of the monolithic prepackage anode. With reference to these figures, and once the type, material, and dimensions of the anode that will operate as a "core" (No. 4) in the construction of a monolithic prepackaged anode are selected, it is carefully inspected to reject those that have defects Important manufacturing physicists.

The type of anode - core that is recommended to be used in the construction of the monolithic prepackaged anode, are solid bars of 1 "to 4" φ with lengths of 30 to 60 inches (No. 4), which should initially be subjected to a solvent cleaning process, to remove any impurities from the surface, as well as oily residues, since on this surface a direct contact with the carbonaceous mixture (No. 2) must be established, which will solidify on the anode surface - core.

The aggregates of the carbonaceous mixture (No. 2) are the following and we will classify them into three types, according to the environment in which they will operate:

TD? OR 1.- TO OPERATE IN WET LANDS.

COMPONENT% BY WEIGHT Sprayed Graphite (Mesh - 80) 43.0

1/8 "graphite (maximum) 45.0

Portland Cement Type I (Mex) 8.0

Sodium Sulfate 3.0

Calcium Hydroxide 0.5 Surfactants for Portland Cement Type I 0.5

SUM 100.0 TTPO 2.- TO OPERATE IN FANGOSAN PANTANS

COMPONENT% BY WEIGHT

Sprayed Graphite (Mesh - 60) 42.0

Graphite 1/8 "(Maximum) 45.0

Portland Cement Type I (Mex) 10.0

Sodium Sulfate 2.0

0.5 Calcium Hydroxide

Surfactants for Portland Cement Type I 0.5

SUM 100.0

TYPE 3.- TO OPERATE IN LACUSTRES AND MARINE AREAS:

COMPONENT% BY WEIGHT Sprayed Graphite (Mesh - 60) 41.0

1/8 "Graphite (Maximum) 45.0

Portland Cement Type I (MEX) 12.0

Sodium Sulfate 1.0

Calcium Hydroxide 0.5 Surfactants for Portland Cement Type I 0.5

SUM 100.0 The approximate analysis of the graphite material to be used in the three types of mixtures above is as follows:

Fixed Carbon 95. Ó% by Weight Sulfur 4.5% by Weight

Soluble Chlorine 80.0 mg / kg

Density 1.2 kg / Lt.

Volatile Material 3.0% by Weight

Ashes 5.0% by Weight Humidity 0.3% by Weight

Resistivity 5.0 ohms - cm It is possible to use materials such as metallurgical cokes or calcined petroleum cokes in the mixture (No. 2), in proportion to their weight equivalences.

The monolithic prepackaged anode is formed by a core (No. 4), in which materials such as graphite, ferro-silicon-chromium or any commercial anodic material with dimensions between 1 and 4 inches in diameter can be used, with a length from 30 to 60 inches.

In the case of making a more detailed description of its construction, we will take as a base a commercial type graphite anode (No. 4) of a cylindrical shape of 3 "φ by 60 inches in length, it must have at one end a cable extension of 4 AWG copper, double lining, Polyethylene and P.VC. 2.5 m long, with a firm connection to the anode body either at one end or to the center of the device. A device will be installed in the cable - anode connection in the form of a cup (No. 6), of highly dielectric and heat shrinkable material, to guarantee a tight seal against the entry of some moisture towards this connection point that is one of the most important factors in the manufacturing and conditioning process of the anode A leak test should be carried out later at this connection point.

A 10 "φ monolithic prepackaged anode, manufactured with an outer shell of 30 gauge galvanized sheet (No. 3) with dimensions of 1.72 cm long by 90 cm wide. It must be passed through a cold rolling process to form a cylinder, which according to preset dimensions, can vary in diameter from 6 inches or larger than 16, 18 or 20 "inches. For the assembly of the sheet and to form a cylinder, 35 screws (No. 10) of galvanized steel with hexagonal head and V "φ x V2" nut must be used with two flat galvanized washers, to allow a good tightening. The perforations for the placement of these screws on the galvanized steel sheet must be made with a 7/64 inch diameter drill bit and a distance between them of 5 cm. Once this cylinder is assembled (No. 3), it is placed vertically on a concrete or steel mold of dimensions 35 x 35 x 15 Centimeters (No. 1), this mold has a cone inside it, a cone inverted which is precisely to give the required shape to the lower end of the monolithic anode.

Prior to the preparation of the mixture, four plain PVC pipes (No. 5) of 2.5 inches in diameter with a length of 1.77 meters, suspended inside the metal cylinder (No. 3) will be installed at a height of 15 centimeters from the bottom of the cylinder and with a distribution illustrated in Figure No. 2.

The preparation of the aggregates of the carbonaceous mixture (No. 2) is carried out in a 100 kgs capacity metal scraper, with a 12-horsepower internal or electric combustion engine with a speed reducer.

The total weight of the mixture of components that will carry each anode, is a function of the pre-designed dimensions of each of them. In the case of the 10 "" x 1.8 m length anode, approximately 100 kg of the mixture will be required.

The components are mixed first dry, until a homogeneous mixture is obtained; Once the required quality of dry mixing is obtained, pure water free of impurities, mainly organic and of a quality equivalent to drinking water, is slowly added. The proportion of water to be added to the mixture will be 19 liters.

Once the four 2.5-inch tubes (No. 5) are installed in the indicated position, the wet carbonaceous mixture (No. 2) is slowly emptied

"pasty" and not milky) inside the metal cylinder, using an electric or internal combustion vibrating device, to release air entrapment within the mixture and achieve adequate compaction.

During the setting of the carbonaceous mixture inside the cylinder, the four PVC pipes (No. 5) must be turned manually on their axis, so that they are not stick to the carbonaceous mixture. This process should be done frequently until the setting of the mixture is obtained and the four PVC pipes can be removed.

On the other hand, four sections of PVC pipe of V2 "φ by 1.63 cm in length (No. 8) are prefabricated, in which perforations of 7/64" φ will be made with a separation between them of 1 cm, both diametrically as in the entire length of this pipe. The objective of the small perforations on this pipe, is to allow the channeling and natural extraction of the gases formed within the anode as a result of the electrochemical reactions during its operation. On the upper end of this PVC pipe of V2 "φ (No. 8), an inner filter (No. 9) of 10 cm length of a Scotch-Brite plastic fiber material or the like is placed. This filter It allows the expulsion of the gases accumulated in the breast outside the body of the anode and prevents the penetration of solids from the soil into the tube, which must keep its interior free of all types of mud or solids. PVC resin between the fiber and the inside of the PVC pipe, in order to permanently fix this filter at the end of the pipe.

After the extraction of the 4 tubes (No. 5) of 2.5 inches in diameter and after the setting process is finished, 4 perforated PVC pipes of V2 "No. (No. 8) are introduced into the center of the cavities and the annular space (No. 7) that is formed is formed, with graphite of a granulometry of mesh 30 and with a 95% fixed carbon content.This material and its arrangement, are designed so that towards this annular section, channel and flow the electrochemical reaction gases that are generated within the anode, pass through the porosity of the carbonaceous material, penetrate through the multiple perforations of the PVC pipe 1/2 inch in diameter, accumulate inside, flow to the upper end, pass through the fiber filter (No. 9) and expel outwards from the anode. If the gases are not removed from the anode material, they will form blockages to the flow of direct current, (both ionic and elect form ronic), reducing the capacity or efficiency of draining current from the anode to the ground or surrounding electrolyte. On the other hand, the same carbonaceous material contained in the annular space

(No. 7) has the additional function of replenishing or complementing (make-up) the material, which due to the effect of the electrochemical reaction on the surface of the anode - core, it dissolves, that is, that this carbonaceous material placed in the annular space, in addition to using its porosity, it prolongs the efficiency and useful life of the anode - nucleus.

Claims

CLAIMS Having sufficiently described my invention, which I consider as a novelty and therefore claim as my exclusive property, the content of the following clauses:

1. A cathodic protection system based on printed current to be used preferably in sandy, swampy, lake and marine soils of the type based on an electrochemical cell formed by an anode, a cathode, an electrolyte and an energy source, characterized in that the anode is a completely solid monolithic prepackaged anode that functions as a positive current electrode; the prepackaged anode consists of a central core in the form of a solid bar made of an anodic material, which is fixedly embedded in the center of an aggregate of carbonaceous mixture; Around the central core are four cylindrical compartments, distributed at 90 ° circumferentially in the diameter of the anode, two of them in contact with the material of the core anode and the other two at the center of the monolithic solid mass formed by the mixture aggregate carbonaceous, arranged at 180 degrees each, of its circumference; Inside each of the cylindrical compartments is a PVC vent tube whose outer diameter is substantially smaller than the diameter of the compartments, each of the tubes has a plurality of small perforations throughout its length, which have as their object the to allow the channeling and natural extraction of the gases, product of the anodic reaction, towards the outside of the anode itself; PVC gas venting pipes have a filter at one end that allows the expulsion of gases, but prevents the entry of sludge or some solid material; The interior of the cylindrical compartments or annular space formed between the compartments and the vent tubes, is packed with graphite of a 30 mesh granulometry, to allow the gases of the anodic reaction to flow through this material and subsequently pass through the perforations of the PVC pipe and channeled outwards from the anode.

2. A cathodic protection system according to claim 1, characterized in that the anodic material of the central core is selected from graphite bars, ferro-silicon, ferro-silicon-chromium, Magnetite, copper bars coated with Ceramic Oxide or Platinum, Titanium and Niobium wires.

3. A cathodic protection system according to claim 1, characterized in that the anode of the central core carries at one end an extension of copper cable with a firm connection to the anode body either at one end or the center thereof, in the. Connection of the cable with the anode a cup-shaped device of highly dielectric and heat-shrinkable material is installed, to ensure a tight seal against the entry of some moisture towards this connection point.

4. A cathodic protection system according to claim 1, characterized in that the carbonaceous mixture of the anode consists of 41 to 43% by weight of powdered graphite (60 to 80 mesh); 45% by weight of graphite 1/8 ", from 8 to 12% by weight of Portland cement type I, from 1 to 3% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland Type I cement.

5. A cathodic protection system according to claim 4, characterized in that to operate in humid soils the carbonaceous mixture of the anode consists of 43% by weight of powdered graphite (80 mesh); 45% by weight of graphite 1/8 ", 8% by weight of Portland cement type I, 3% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

6. A cathodic protection system according to claim 4, characterized in that to operate in muddy swamps the carbonaceous mixture of the anode consists of 42% by weight of powdered graphite (60 mesh); 45% by weight of graphite 1/8 ", 10% by weight of Portland cement type I, 2% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

7. A cathodic protection system according to claim 4, characterized in that to operate in lacustrine and marine areas the carbonaceous mixture of the anode consists of 41% by weight of powdered graphite (60 mesh); 45% by weight of graphite 1/8 ", 12% by weight of Portland cement type I, 1% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

8. A cathodic protection system according to claim 1, characterized in that the graphite material used as packing in the anode compartments has a mesh granulometry 30 and a 95% fixed carbon content.

9. A cathodic protection system according to claim 1, characterized in that the prepackaged monolithic anode ends at a conical tip.

10. Process for the manufacture of a completely solid monolithic prepackaged anode that functions as a positive current electrode, to be used in a cathodic protection system as claimed in claims 1 to 8, characterized in that it comprises the steps of:

- cold rolling a galvanized sheet to form a cylinder that is assembled by means of a plurality of galvanized steel screws with hexagonal head and nut added with two flat galvanized washers, to allow a good tightening;

- once the cylinder is assembled, it is placed vertically on a concrete or steel mold, which has an inverted cone inside its face, which is intended to give the required shape to the lower end of the monolithic anode ; - prior to the preparation of the mixture, the central core of anodic material and four plain PVC pipes are installed, suspended inside the metal cylinder;

- the preparation of the aggregates of a carbonaceous mixture is carried out in a metal stirrer;

- the components are mixed first dry, until a homogeneous mixture is obtained; Once the required quality of dry mixing is obtained, pure water free of impurities, mainly organic and of a quality, is slowly added equivalent to drinking water;

- Once the four PVC pipes are installed in the appropriate position, the wet carbonaceous mixture is slowly emptied in a pasty and non-milky point inside the metal cylinder, using an electric or internal combustion vibrating device, to release entrapment of air inside the mixture and achieve adequate compaction;

- during the setting of the carbonaceous mixture inside the cylinder, the four PVC pipes are manually rotated on its axis, so that they do not stick to the carbonaceous mixture; - the previous step is repeated frequently until the setting of the mixture is obtained and the four PVC pipes can be extracted, thus forming four cylindrical compartments;

- separately, four sections of PVC pipe are prefabricated, in which small perforations will be made with an equidistant separation between them, both diametrically and along the entire length of this pipe;

- an inner filter of a plastic fiber material is placed at the upper end of the PVC pipe sections, using a PVC resin adhesive between the fiber and the inside of the PVC pipe, in order to permanently fix this filter at the end of the tube; - after the four tubes have been removed and the setting process is finished, the four perforated PVC pipes are introduced into the center of the cavities; Graphically pack the annular space that is formed between the compartments and perforated PVC pipes.

11. Method for the manufacture of a monolithic prepackaged anode according to claim 10, characterized in that the anodic material of the central core is selected from graphite bars, ferro-silicon, ferro-silicon-chromium, Magnetite, copper coated bars with Ceramic Oxide or Platinum, Titanium and Niobium wires.

12. Process for manufacturing a monolithic prepackaged anode according to claim 10, characterized in that the carbonaceous mixture consists of 41 to 43% by weight of powdered graphite (60 to 80 mesh); 45% by weight of graphite 1/8 ", from 8 to 12% by weight of Portland cement type I, from 1 to 3% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland Type I cement.

13. Process for the manufacture of a monolithic prepackaged anode according to claim 12, characterized in that to operate in wet soils the carbonaceous mixture consists of 43% by weight of powdered graphite (80 mesh); 45% by weight of graphite 1/8 ", 8% by weight of Portland cement type I, 3% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

14. Process for the manufacture of a monolithic prepackaged anode according to claim 12, characterized in that to operate in muddy swamps the carbonaceous mixture consists of 42% by weight of powdered graphite (60 mesh); 45% by weight of graphite 1/8 ", 10% by weight of Portland cement type I, 2% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

15. Process for the manufacture of a monolithic prepackaged anode according to claim 12, characterized in that to operate in lacustrine and marine areas the carbonaceous mixture consists of 41% by weight of powdered graphite (60 mesh); 45% by weight of graphite 1/8 ", 12% by weight of Portland cement type I, 1% by weight of sodium sulfate, 0.5% by weight of calcium oxide and 0.5% by weight of a surfactant for Portland cement Type I.

16. Process for the manufacture of a monolithic prepackaged anode according to claim 10, characterized in that the graphite material used as packing in the compartments has a mesh size 30 and a fixed carbon content of 95%.