US2775554A

US2775554A - Galvanic anode installation

Info

Publication number: US2775554A
Application number: US426518A
Authority: US
Inventors: Roy C Jorgensen
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1954-04-29
Filing date: 1954-04-29
Publication date: 1956-12-25
Anticipated expiration: 1973-12-25

Description

Dec. 25, 1956 R. c. JORGENSEN 2,775,554

' GALVANIC ANODE INSTALLATION Filed April 29, 1954 1N VENTOR Ray C. Jorge/wen BY 5 z 3 g ATTORNEYS.

United States Patent() GALVANIC ANODE INSTALLATION Roy C. Jorgensen, Lake Jackson, Tex., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application April 29, 1954, Serial No. 426,518

4 Claims. (Cl. 204-197) This invention relates to the cathodic protection of metallic surfaces against electrolytic corrosion, and particularly to means for protecting corrodible metal structures such as the interior surfaces of tanks.

The cathodic protection of tanks and compartments of ships, particularly ballast tanks which are filled with sea water, has been accomplished in the past with some degree of success. In such cathodic protection systems the galvanic anodes are usually bolted to special anode hangers which project from the hull of the hip. Such installations require scaffolding to attach each anode hanger to the hull and to attach anodes to the hangers. Repeated scaffolding in the tanks is not only expensive but often times cannot be conveniently installed due to the maze of cross bracing in the tank. Thus, the expense of achieving cathodic protection in this manner often proves prohibitive.

Further, when the anodesare mounted on hangers attached to the hull, uneven protection often occurs due to the large current between the anode and that part of the hull which is closest thereto.

Another difficulty in connection with the installation of anodes on hangers is that the hangers are usually welded to the hull, and if the steel adjacent to the weld crystallizes, and loosens the hanger, the anodes which are exposed to air may rub against steel and cause sparking.

Accordingly, a principal object of this invention is to provide an improved means for providing cathodic protection to the interior portion of tanks or compartments.

Other objects of this invention are to provide means for effecting more uniform, safer, and more economical cathodic protection to the interior portion of tanks or compartments.

The above and related objects are achieved in accordance with this invention by mechanically and electrically conductively securing at least one galvanic anode to an electrically conductive cable or wire which is electrically and mechanically secured to the lower portion of the hull. The other end of the cable is passed over a pulley which is secured underneath the deck supporting structure or top of the tank and then is pulled taut and electrically and mechanically secured to the hull or tank wall. Guy wires may be connected between the hull and the part of the cable carrying the anodes if needed. Since both ends of the cable are electrically connected to the hull, sparking between the anode and hull is eliminated in case of a break in the cable to which the anodes are attached. Anodes may be replaced without the erection of any scaffolding, since by loosening the end of the cable which is passed over the pulley, the portion of the cable bearing the consumed anodes may be lowered to the bottom part of the hull where it is easily reached.

Because the anodes may be centrally mounted or spaced in the tank or compartment, more even cathodic protection is provided.

The invention as well as additional objects and advantages thereof will best be understood when the following detailed description is read in connection with the accompanying drawings, in which:

Fig. 1 is. a partial transverse section through a tanker showing, in elevation, the arrangement of galvanic anodes in accordance with this invention;

Fig. 2 is a partial sectional view taken along the lines 22 of Fig. 1;

Fig. 3 is an enlarged isometric'view showing the mean of attaching an anode to a cable, and

Fig. 4 is an enlarged view showing the means of attaching the anode carrying cables to the walls of a ship tan or compartment.

Referring to Figs. 1 and 2, there is shown a compartment 10 in a ship 12. A cable 14 having a plurality of galvanic anodes 16, such as magnesium anodes, for example, attached thereto has one end anchored to a channel iron 18 in the lower part of the hull 20. The other end of the cable 14 is passed over a pulley 22 secured to the bottom of the deck supporting structure 24 and then is fastened to the lower portion of the tank bulkhead 26. Protection against side sway of the part of the cable 14 carrying the anodes 16 is provided by guy wires 28 which extend between the cable 14 and the bulkhead 26 and hull 20 of the ship 12. Turn buckles 30 are provided along each brace line 28 to permit small adjustments in the tension on the braces. Another turnbuckle 32 is provided at the end of the cable 14 and is attached to the channel iron 18 to permit a similar adjustment in tension on thecable 14. The cable 14, as well as the wire braces 28 and sheave 22 may advantageously be made of some corrosion resistive substance such as Monel metal or other nickel-copper alloy.

As is shown more clearly in Fig. 3, each anode 16 comprises a hollow steel core 34 through which the cable 14 passes. The consumable metal portion 36 of the anode, usually magnesium, is cast around the core 34. The anode 16 is held in place on the cable 14 by wedges 38 which are driven between the cable 14 and the core 34. Each wedge 38, which has a serrated edge 40which' makes contact with the core 34, provides the means for making electrical contact between the anode 16 and the cable 14. The number of anodes 16 which are attached along the cable 14 depends on the current density and anode life requirements of the installation.

Fig. 4 shows, in detail, a suitable means for mechanically and electrically securing the cable 14 to the bulkhead 26 of the ship. The other end of the cable may be fastened to the hull in a similar manner. The end of the cable 14 is mechanically secured to the bulkhead 26, for example, by being looped through the steel eye 42 and clamped back on itself by a cable clamp 44. A loop 46 in the cable 14 provides a convenient way for attaching a block and tackle (not shown) to the cable 14 when the anodes are to be lowered or raised. Other mechanical means of securing the cable 14 could, of course, be used. The mechanical connection between the cable 14 and the bulkhead 26 is not relied upon to provide the electrical connection therebetween. between the cable 14 and the bulkhead 26 is made by a bonding cable 48, usually made of copper, which is held in metallic contact with the cable 14 by the clamp 50 and has one end 52 brazed to the bulkhead 26. As mentioned previously, the cable 14 is electrically connected to the hull or bulkhead at each point where it is mechanically secured thereto, thus avoiding the danger of sparks occurring between the magnesium anodes and steel parts of the ship or tank in event the cable 14 breaks or comes unfastened. This arrangement is of considerable importance since an explosive mixture of gas fumes may be present in the tank or compartment 10. A loop 46 in the cable 14 provides means for connecting another line to the cable when the anodes are raised or lowered into position.

The anodes 16 are installed by threading the anodes 16 onto the cable 14 in the proper number and with the The electrical connection proper spacing between anodes and electrically and mechanically. connecting the cable 14. and the anodes. 16 together, by means of the wedges 38, for example. One end of the cable 14 is secured to the lower portion of the hull 20 and; theothei: end thereof is threaded through a sheave. 22= and is drawn towards its anchoring position on the bulkhead 26, raising the anodes 16 into position. The guy. wires 2& may be attached before the anodes 16 are raised, if desired. To replace anodes, the end of the cable which is anchored to the bulkhead 26 is unfastened and allowed to rise (being paid out by. a block and tackle, for example), loweringthe. anodes to the lower part of the hull 20.. The. other end of the cable is disconnected from its clamp allowing the consumed anodes to be removed. and fresh ones attached to the cable, which is raised into position again. No scaffolding is required to install anodes once. the cable 14 is threaded through the pulley 22. There. may be as many cables 14. carrying the galvanic anodes 16 as are required to provide adequate protection. For. the sake of simplicity in the drawings only a single. anode carryingcable 14 has been shown.

An installation of galvanic anodes in accordance with this invention is economical in that it requires but little scafiolding to make the initial installation and no scaffolding to replace anodes. Because the anodes, in accordance with the method of the invention, may be secured between any two points between which a cable may be strung, the anodes may be advantageously spaced with respect to. the surfaces they are to protect. Thus, more even cathodic protection is provided and this, too, efiects an economy in the installation and maintenance of a cathodic protection system. And, as previously mentioned, since each end of the cables 14 is electrically connected to the hull 20 or bulkhead 26, the danger of sparking is eliminated even if the cable 14 breaks and permits the anodes 16 to bump against the steel in the tank or compartment.

Thus, the present invention provides an efficient, economical and safe method. of cathodically protecting the interior surfaces of a tank or. compartment from corrosion due to. electrolytic action.

That which is claimed is:

l. A cathodic protection system for protecting. the interior surfaces of a tank from electrolytic colrosion, said system comprising, within a tank having a supporting member and an anchoring member, a pulley secured to said supporting member, a metallic cable having its end portions detachably secured. to said anchoring member and its intermediate portion passing through said pulley, a plurality of galvanic anodes, said anodes beingmechani- @1 13 a d, electr ll e ur d to Sa a l etw en n of said end portions thereof and said pulley, and means adjacent to each end of said cable for making positive electrical contact between said cable and said anchoring member.

2. A cathodic protection system for metallic tanker compartments comprising a metallic cable, a plurality of galvanic anodes disposed along a part of said cable and mechanically and electrically secured thereto, the end of said cable which is closest to said anodes being anchored to a surface of said compartment, a pulley, said pulley being spaced from the anchored end of said cable and secured to a surface of said compartment, the part of said cable which does not have anodes secured thereto passing through saidpulley and being secured to a surface of said compartment, and means for electrically connecting said cable to said compartment adjacent to where said cable is anchored and secured thereto.

3. A cathodic protection system in accordance with claim 2, wherein each compartment contains a plurality References Cited in the file of this patent UNITED STATES PATENTS Taylor Feb. 17, 1948 Tarr et al. June 29, 1948 Robinson et al Oct. 9, 1951

Claims

1. A CATHODIC PROTECTION SYSTEM FOR PROTECTING THE INTERIOR SURFACES OF A TANK FROM ELECTROLYTIC CORROSION, SAID SYSTEM COMPRISING, WITHIN A TANK HAVING A SUPPORTING MEMBER AND AN ANCHORING MEMBER, A PULLEY SECURED TO SAID SUPPORTING MEMBER, A METALLIC CABLE HAVING ITS END PORTIONS DETACHABLY SECURED TO SAID ANCHORING MEMBER AND ITS INTERMEDIATE PORTION PASSING THROUGH SAID PULLEY, A PLURALITY OF GALVANIC ANODES, SAID ANODES BEING MECHANICALLY AND ELECTRICALLY SECURED TO SAID CABLE BETWEEN ONE OF SAID END PORTIONS THEREOF AND SAID PULLEY, AND MEANS ADJACENT TO EACH END OF SAID CABLE FOR MAKING POSITIVE ELECTRICAL CONTACT BETWEEN AND CABLE AND SAID ANCHORING MEMBER.