US 2947680 A
Description (OCR text may contain errors)
MULTIPLE DISC ANODE Herman S. Preiser, 6904 Leesville Blvd., Springfield, Va.
Filed Dec. 2, 1957, Ser- No. 700,239
14 Claims. 01. 204-197 (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to cathodic protection of metals subjected to sea water against electrolytic corrosion and particularly to sacrificial anodes for such protection.
More particularly, this invention relates to the provision of anodes of segmented construction which can be assembled into any desired length to provide sacrificial anodic material, such as zinc, in suiiicient quantity for cathodic protection for heat exchangers and associated equipment aboard ships or the like:
Zinc or other sacrificial anodes are installed on the seawater side of heat exchangers to protect waterboxes and tube ends against electrolytic corrosion. When the zinc is coupled to other less active metals, the metals are rendered electrically passive, and therefore their corrosion tendency issuppressed. However, the zincs are naturally dissipated in service and must be replaced at regular intervals. Sometimes zincs arereplaced in certain equipment as often as once a month, but the average life is three months.
Zinc anodes cannot work properly as corrosion protection devices unless they are correctly mounted in the equipment to be protected. They must have adequate mechanical attachment and watertight electrical connections. Replacement of zincs aboard ship every three months is greatly simplified when the improved method of the instant invention is used.
Various means and methodshave been devised for supplying sacrificial anodic material for cathodic protection of heat exchangers and the like. One such method, still in wide use in naval installations, is to use a cylindrical rod or pencil anode, cut to size, machined to a shoulder at one end and threaded for attachment to a supporting plug. A slight improvement over the solid rod pencil was the use of a solid anode rod in which an axialsmaller cathodic rod was cast for purpose of supporting the surrounding anode material being expended. This latter scheme proved costly to manufacture and therefore has fallen into disuse. Another somewhat improved solid pencil type anode consisted of cylindrical rods extruded or cast to iron pipe sizes. This scheme enabled suitable lengths of rod to be cut from rod stock with a pipe cutter and threaded with the standard tapered pipe threads; all operations done manually, with the tapered thread eliminating the need of machining a shoulder stop in the old type bar stock. Another typeof anode is that described in'United States Patent No, 2,609,340. This patented anode is a segmented construction made up of circular discs, somewhat similar to the one disclosed in the instant. invention, except that each disc of the prior art patent has an axially centered and fixed core of metal tubing slightly protruding on each flat side ofthe anode disc. These discs are assembled on a partially threaded rod which is tightened into a tapped hole of a support plug. The tension pressure on the nod bearing against the 2,947,680 Patented Aug. 2., 1960 V the rod, plug, and washer assembly retained to receive a new set of anode discs. The length of the anode is changed by cutting oii a section of the threaded portion of the rod and reassembling a lesser number of discs on the shortened rod.
The disadvantages of the old methods are numerous, but the main deficiency in the solid type anode rod is the necessity of cutting them to a given size from a stock length since, the lengths used in different equipment varies in a random fashion. This means that the labor cost of installing such anode rods is excessive and many times the cost of the material used. Further, the solid type cylindrical rod has the deficiency of necking down at areas in close proximity to the metal parts under cathodic protection. Sometimes this necking down causes the anode rod to break in two before being completely expended. This reduces the useful life of the anode and in some cases endangers rotating equipment by having the anode chunk fall or be carried into the operating parts of such equipment. The segmented anode patented under U.S. Patent No. 2,609,340, overcame the two objections of the solid pencil anodes in that an adjustable anode was feasible in which a cathodic metal core support was included. But, in accomplishing this end, a plurality of added parts are necessary, namely, the anode discs, a threaded connecting rod with a swaged flattened end, a wing nut, and a pair of sealing washers. Further, with the patented anode, manual labor and tools are required to cut the connecting rod to the desired length in order to assemble a given length of anode discs.
It is therefore an object of the present invention to provide an improved anode assembly which is easily and inexpensively made and-which is not subject to the disadvantages mentioned.
Another object is to provide an anode disc with an improved core construction.
A further object is to provide an anode disc incorporating a unique core construction that afiords ready assembly of a plurality of such discs into a unitary anode without the need of special tools or skilled labor.
A further object of the invention is to provide a multiple disc anode assembly wherein mechanical rigidity, electrical continuity and tightness under vibration is assured.
In accordance with the instant invention, discs are each provided with a special fitting or core made of cathodic material and formed with a threaded, axial male tip at one end and a threaded, axial female recess at the other end and which fitting or core is secured axially in an anode segment. The outside cylindrical surface of this cathodic metal fitting or core is roughened, knurled, recessed or fluted so as to aid in gripping the anodic material cast or molded around it, while, at the same time, forming good electrical contact between the cathodic material of the core and theanodic material of the sleeve. This segmented assembly permits as many discs to be assembled as desired, simply by threading the male end of one disc into the female of another. The first segment of the anode can be screwed directly into a threaded tapped hole of the support plug. The mating of the members of each anode segment is made by close fitting threads or other locking devices so that mechanical rigidity, electrical continuity and tightness under vibration is assured. "I'hus, in accordance with this invention, the anode is assembled on the job to the desired length and is attached to a suitable threaded support plug. The plug is then screwed into an appropriatebossing 0n the heat exchanger bonnet, pump casing, or the like,. to
provide cathodic protection to the water immersed equipment surrounding the anode.
The advantages of this construction are apparent. The anode can be assembled to any length on the-job; it contains an axially centered support core of cathodic metal; contains only the required number of discs in addition to the support plug, all firmly locked together; removes the necessity of a threaded connecting rod, nut and washer; and requires no special cutting and fitting for assembly. The anode segments can be tightened in place by hand or, at most, with a pipe wrench. The discs can be stocked in the required diameters and will replace all other solid pencil and multiple disc assemblies used in the Navy up to now. The cost of such an anode is appreciably less than any of the present schemes available.
The invention, together with the above and other objects and advantages, is set forth in more technical detail in the following description and accompanying drawing in which like reference characters designate like parts throughout the several views and wherein:
Fig.1 is a side elevation of an assembled, multiple disc anode incorporating a preferred embodiment of the invention;
Fig. 2 is a top plan of the disc shown in Fig. 3; and
Fig. 3 is an enlarged side elevation, partially in axial section, of one of the discs shown in Fig. 1.
Referring now to the drawing, first to Fig. 1, in accord ance with this invention, there is shown an assembly comprising a base plug formed of brass or other cathodic material. The base plug 10 has a hexagonal head portion 14. and a body portion having external pipe threads 12 and an internal axial bore 15. The pipe threads 12 permit the base plug to be secured in a correspondingly threaded opening of a wall of a heatexchanger or other vessel. The axial bore 15 is threaded to receive the male end of the first of a plurality of anode segments 16, hereinafter referred to as anode or cathodic protector discs.
In accordance with this invention and with reference to Figs. 2 and 3, each of the anode discs 16 is of unitary construction with no relatively movable parts, and com.- prises a cylindrical core 18' formed preferably of steel or like cathodic metal and provided with a threaded axial stem or male member 20 at one end and with a threaded axial bore or female portion 22; at the opposite end. The arrangement, as described hereinafter, and as shown in Fig. 1 is that in assembling the discs, the male; end of one disc is threaded into the female of another. The spacing of the discs is somewhat exaggerated in Fig. 1.
Referring again to Fig. 3, the cylindrical outer surface of the core is roughened, knurled, recessed or fluted, as at 24, so as to aid in gripping and bonding the anodic material 26 cast or molded thereto. The anode material is preferably zinc, although magnesium or other suitable sacrificial anodic material may be used. As shown in Fig. 3, the anode material is placed on the steel core in a manner as to provide a projecting shoulder 28 exposed at the male end of the core and a slight projection or shoulder 30 at the female end. The otherwise flat surfaces of the shoulders are knurled, serrated or ratcheted, as at 32 and 34, for gripping contact of the shoulder of one disc with the shoulder of an adjacent disc, as described hereinafter. For purpose of illustration, the ratchets 32 and 34' are exaggerated in the drawing.
In assembling the multiple disc anode, shown in Fig. 1, the base plug 10 having been threaded externally as ati12 and formed with the threaded bore 15, is screw threaded onto the male end 20 of an anode disc 16, the disc, having been prefabricated as described hereinbefore. Then the male-end of a second disc is threaded into the mating tapped bore of the first disc, at third disc is threaded ,into the second, and so on until the desired lengthiofkmultiple disc anode is attained for the job at hand. The final assembly of the discs forms a line of discs, the discs being axially in substantially a straight line.
In assembling the anode, the individual discs are screwed down tightly by hand; then an additional turn is taken with a pipe wrench. It is essential that good mechanical and electrical connections be made between the base plug and the first disc and between the several discs that make up the assembly. Various thread-locking means, such as, tapered thread, upset thread, run-out on threads, or the like may also be resorted to in securing tight connections. However, it has been found in practice that excellent results, such as straight, vibrationproof and securely connectedassemblies, may be attained by using standard number two thread in the base plug and each end of the cores and by providing serrations or ratchet surfaces on the shoulder at the male end and on the projection at the female end of the core.
The cross-sectional shape of the anode discs is not critical and such shapes as polygonal, square, or triangular may be employed. However, it has been found in practice that a circular cross-section for both the core of cathodic material and the cylindrical sleeve of anodic material give excellent results. The length of the disc, relative to its diameter is likewise not critical. This relationship depends somewhat on available space as does the number of discs contained in an assembled anode. In practice, a nominal number of discs of various sizes may be stocked for convenience.
It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth in the'ap pended claims.
What is claimed is:
1. A cathodic protection device for protecting'the interior surface of a vessel having an aperture in a wall thereof, said device comprising a plug adapted for closing the aperture in the vessel, said plug having a threaded axial recess formed in the inner end thereof, an elongated multiple disc assembly fixed to the innerJendJof said plug and adapted to extend within the vessel, said multiple disc assembly comprising a plurality of discs each having a cathodic core and a sacrificial anodic sleeve firmly bonded to the core, the core being longer than the'sleeve and each of the cathodic cores having a threaded axial stem projecting from one end thereof and a threaded axial recess formed in the opposite end thereof, the construction and arrangement of the cores being such that the threaded stem of a firstdisc is screwthreaded into the threaded recess-of the plug, the. threaded stem of a second disc is, screw-threaded into the threaded recess of the first disc and so on, so that the desired number of discs are assembled on the plug, said plug and multiple disc assembly carried thereby forming a mechanically rigid, electrical conducting assembly. 7
2. A cathodic protection device as set forth in claim 1 wherein the core of each of the discs is acylindrical member of given length, wherein the sleeve is a cylindrical member of lesser length than that of the core centered on the core in a manner as to provide an exposed length of core at each end of the sleeve which exposed ends hold the sleeves in spaced relation in the assembly, and wherein each pair of screw-threaded stems and recesses has locked threads.
3. A cathodic protection device as set forth in claim 1 wherein mating surfaces of the core and of the sleeve of each of the discs are formed with means for gripping one such surface by the other.
4. .A cathodic protection device'as set forth in claim a 1 wherein the exposed ends of each of the cores are formed with means thereon for locking the endof one core to the mating end of an adjacent core. t
5. A cathodic protection device for protecting thesurface of a vessel against electrolytic corrosion,- saiddevice comprising a supporting member being provided with a means for securing the device to the vessel; a plurality of cathodic protector discs; each of said discs being of rigid unitary construction and comprising a central core of a cathodic metal and an outer sleeve of a sacrificial anodic metal around and firmly bonded to its core, with the core being longer than the sleeve, the core having an end projecting beyond the sleeve and the end comprising a stem, the other end of said core having a recess open at the corresponding end of the associated sleeve; said plurality of discs being axially fitted securely together to form a line of discs, with the stem of the core of a first disc fitting into the recess of the core of an adjacent disc along said line, and means locking the stern and recess together; said supporting member having a portion securely fitting an end of the core of an end disc of said line of discs.
6. A cathodic protection device for protecting a surface of a vessel against electrolytic corrosion, said device comprising a supporting member being provided with a means for securing the device to the vessel; a plurality of cathodic protector discs, each of said discs being of rigid unitary construction and comprising a central core of a cathodic metal and an outer sleeve of a sacrificial anodic metal around and firmly bonded to its core, the core being longer than the sleeve, the core having an end projecting beyond the sleeve and the end comprising a threaded stem, the other end of said core having a threaded recess open at the corresponding end of the associated sleeve; said plurality of discs being axially threaded together to form a line of discs, with the threaded stem of the core of a first disc screw-threaded into the threaded recess of: the core of an adjacent disc along said line; said supporting member having a threaded portion fitting a threaded end of the core of an end disc of said line of discs; an end of the core of each disc having a shoulder at the proximate surface of the associated sleeve, the shoulder extending beyond and in a direction away from the last said sleeve.
7. A cathodic portection device as defined in claim 6 wherein the other end of each core projects axially beyond its associated sleeve to form a shoulder that abuts the shoulder of the adjacent core in said line of discs.
8. A cathodic protection device for protecting a surface of a vessel against electrolytic corrosion, said device comprising a supporting member being provided with a means for securing the device to the vessel; a plurality of cathodic protector discs, each of said discs being of rigid unitary construction and comprising a central core of a cathodic metal and an outer sleeve of a sacrificial anodic metal around and firmly bonded to its core, the core being longer than the sleeve, the core having an end projecting beyond the sleeve and the end comprising a threaded stem, the other end of said core having a threaded recess open at the corresponding end of the associated sleeve; said plurality of discs being axially threaded together to form a line of discs, with the threaded stem of the core of a first disc screw-threaded into the threaded recess of the core of an adjacent disc along said line, said screw-threaded stem and recess having threadlocking threads.
9. A unitary cathodic protector disc comprising a cathodic core, a sacrificial anodic sleeve firmly bonded to said core, the core being longer than the sleeve, said core having a first end projecting beyond a first end of said sleeve, the first core end comprising a threaded stem, the other end of said core comprising a threaded recess open at the other end of said sleeve.
10. A unitary cathodic protector disc as defined in claim 9 wherein the threads on said stem and recess are slightly dissimilar for locking purposes.
L1. A unitary cathodic protector disc comprising a cathodic core, a sacrificial anodic sleeve firmly bonded to said core, the core being longer than the sleeve, said core having a first end projecting beyond a first end of said sleeve, the first core end comprising a threaded stem, the other end of said core comprising a threaded recess open at the other end of said sleeve, an end of the core having a shoulder portion at and extending beyond the associated end of the sleeve.
12. A unitary cathodic protector disc as defined in claim 11 wherein the threads on said stem and recess are slightly dissimilar for locking purposes.
13. A unitary cathodic protector disc as defined in claim 11 wherein the other end of said core also has a shoulder portion at and extending beyond the associated end of the sleeve.
\14. A unitary cathodic protector disc as defined in claim 13 wherein the threads on said stem and recess are slightly dissimilar for locking purposes.
References Cited in the file of this patent UNITED STATES PATENTS 1,008,002 Allen Nov. 7, 1911 !1,547,984 Weber July 28, 1925 1,709,523 Delavie et al. Apr. 16, 1929 2,609,340 McMahon et al. Sept. 2, 1952 2,666,027 Vallett Jan. 12, 1954 2,809,932 Abt Oct. 15, 1957 FOREIGN PATENTS 14,818 Great Britain of 1899