US3037926A

US3037926A - Galvanic protection system

Info

Publication number: US3037926A
Application number: US854719A
Authority: US
Inventors: Charles W Ambler
Original assignee: American Zinc Lead and Smelting Co
Current assignee: American Zinc Lead and Smelting Co
Priority date: 1959-11-23
Filing date: 1959-11-23
Publication date: 1962-06-05
Anticipated expiration: 1979-06-05

Description

June 5, 1962 c. w. AMBLER 3,037,926

GALVANIC PROTECTION SYSTEM Filed Nov. 25, 1959 2 Sheets-Sheet 1 177/478 4 ers,

June 5, 1962 c. w. AMBLER GALVANIC PROTECTION SYSTEM 2 Sheets-Sheet 2 Filed NOV. 23, 1959 2% w n 5 MM m, CM

3,037,926 GALVANIC PROTECTION SYSTEM Charles W. Ambler, Rock Hill, Mo., assignor to American Zinc, Lead and smelting Company, St. Louis, Mo., a corporation of Maine Filed Nov. 23, 1959, Ser. No. 854,719 4 Claims. (Cl. 204197) This invention relates to a sacrificial anode system for protecting the interior surfaces of ships, and in par ticular, tankers.

Tankers normally carry a liquid cargo in only one direction. For example, tankers bringing oil from the Middle East to the United States, return to the Middle East without oil in their tanks. In the case of oceangoing vessels, it is highly desirable that they be ballasted; in the case of oil tankers, it is desirable from a safety point of view to fill the tanks with a non-inflammable liquid. Accordingly, it has been common practice to fill the tanks, after they have been emptied of their cargo, with sea water. This has posed a severe corrosion problem in the cargo tanks.

It has been known for many years that the corrosion problem can be minimized by the use of sacrificial anodes of zinc or magnesium. In Tarr et al., Patent No. 2,444,174, it is disclosed that the suspension of zinc anodes, with a very large surface area, in the cargo tank of a seagoing tanker in which salt water is used as a ballast, provides effective protection, by coating the surfaces of the tank with a protective coating consisting of inorganic salts of zinc, magnesium and calcium. Robinson et al., No. 2,571,062, discloses a system in which magnesium electrodes, mounted on a steel wire conductor, are suspended along a steel piling in seawater.

Systems similar to Robinsons system have been suggested for tankers. For example, Jorgensen, No. 2,775,554, describes a galvanic anode installation in which a cable, with anodes strung upon it, is pulled into substantially a vertical position by means of a pulley permanently fixed to the overhead. This provides some protection for the hull plates, but, as can be seen from the drawing, requires a permanent installation of a pulley through which the cable must be threaded, requires the threading of the cable through the anodes, requires a double reach of cable to be permanently employed, and requires the use of scaffolding, at least in the initial installation of the pulleys and in the initial installation of the cables.

It has also been known heretofore to weld or otherwise permanently secure zinc or magnesium bars or plates to the inside surfaces of the tanks. The disadvantage of the permanent securing of plates or bars of anodic material to the surfaces of a tank, is that the installation of the bars or plates is diflicult initially, and doubly diflicult in replacement. The disadvantage of suspended anodes, such as those suggested by Tarr, Robinson and .lorgensen, is that they, too, are diflicult to install, and diflicult to make acceptable, safetywise, to the American Bureau of Shipping.

Still another difliculty with suspended anodes known heretofore has been that they did not provide adequate protection for the undersurface of the overhead of the tanks.

One of the objects of this invention is to provide an anodic protection system in a tank, which is simply and rapidly installed, and eifective to protect the tank.

Another object is to provide such a system which requires no staging, and permits the ready replacement of exhausted anodes.

Still another object of this invention is to provide such a system which is safe, and meets the standards of the American Bureau of Shipping.

3,037,926 Patented June 5, 1962 Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.

In .accordance with this invention, generally stated, an improved cathodic protection system is provided for tanks having a wide horizontal girder along a bulkhead defining one of two opposite walls of the tank. An electrically conductive, non-sparking cable, such, for example, as stainless steel, with anodes, such as zinc bars, mounted on and spaced along the cable, is anchored at one end to the wall opposite the horizontal girder, and is positioned and mounted at its other end by cable mounting means secured to and adjacent the horizontal girder.

The cable mounting means include a saddle, over which the cable extends and upon which it rests, a cable clamp, having a part secured to the horizontal girder and another part manipulable to admit a section of cable intermediate the ends of the cable, the cable clamp being located between the saddle and the bulkhead, and a block mounting means, spaced toward the bulkhead from the cable clamp, and aligned with the cable clamp and saddle.

In the preferred embodiment of this invention, the anodes are formed with rods extending through them, and are clamped to the non-sparking electrically conductive cable by means of cable clamps. Also, the horizontal girders are provided with upwardly extending vertical flanges, over which the saddle extends. In this embodiment, the cable clamp or clamps which receive the cable after it passes over the saddle, are provided with a base in the form of a channel or I-beam Welded to the horizontal girder at right angles to the vertical flange which extends along the edge of the girder away from the bulkhead. In practice, two cable clamps on such a base are provided, and a third cable clamp, welded directly to the web of the horizontal girder, is provided as additional security, and to hold the free end of the cable.

In installing the cathodic protection system of this invention, one end of the cable is mounted, as by a hook or eye-bolt secured to a vertical stiffener on the bulkhead opposite the horizontal girder, or to the bulkhead itself. The cable may have been equipped with anodes before the end is anchored, or the anodes may be put in place after the one end of the cable is so anchored. In either event, the anodes are preferably in position before the other end of the cable is mounted. A block and tackle is fastened to the block-mounting means. The blockmounting means may take any desired form, such as an eye bolt, a bracket or a hook, but will be referred to hereinafter as a hook, which term is used to indicate any suitable means.

The free end of the cable is then pulled into position by means of the block and tackle, making certain that the cable is drawn over and rests upon the saddle. Since the saddle, cable clamp and hook are all aligned, the cable will extend directly over the fixed part of the cable clamp. When the cable has been drawn up to the desired degree of tightness, the movable cable-receiving part of the cable clamp is put into place, and clamped down tightly on the cable. The block and tackle can then be removed, and the end of the cable, generally in the form of a loop, is secured by the cable clamp welded to the horizontal girder.

In the drawing, FIGURE 1 is a sectional view, fore and aft, of a cargo tank of a tanker, showing one string of anodes, in place, and another being brought into position; FIGURE 2 is a fragmentary topplan view of cablemounting means and a horizontal girder, a portion of the web of which is omitted to condense the view;

FIGURE 3 is a sectional view showing the mounting means and the horizontal girder of FIGURE 2, in side elevation;

FIGURE 4 is a sectional view, athwartships, showing the cathodic protection system of this invention in place with respect to a transverse web frame within a tank; and

FIGURE 5 is a fragmentary view in side elevation showing an anode mounted on a supporting cable. Referring now to the drawing for one illustrative embodiment of cathodic protective system of this invention, reference numeral 1 indicates a cargo tank or hold of a tanker. forward. side of the after bulkhead, while the forward tanks are braced on the after side of the forward bulkhead. One center tank may be double braced. In any event, each of the tanks is provided on one bulkhead with horizontal girders. In the embodiment shown in FIG- URE 1, it will be assumed that the tank 1 is a starboard, forward tank. Accordingly, a bulkhead 2 is a forward bulkhead, to the aftersurface of which

horizontal girders

3, 4, 5 and 6 are welded or otherwise secured in the cons'truction of the ship. Each of the horizontal girders has a wide web 7, and a vertical flange 8. The vertical flanges 8 extend along the edge of the web 7 away from the bulkhead 2, and each has a part extending above the upper surface of the web 7.

The tank 1 is defined by the forward bulkhead 2, plates 9 of the ship, a longitudinal bulkhead -10, a transverse after bulkhead 12, and an overhead 14. Transverse web frames are indicated in FIGURE 1, and one of them is shown in detail in FIGURE 4. Longitudinal braces are also shown in FIGURE 4, tho-ugh omitted in FIGURE 1. V

In the embodiment shown, upper and lower cable hooks 17 and 1-8 are welded to the. after bulkhead 12. If there I are. vertical stiifeners along this bulkhead, the

hooks

17 and 18 are preferably welded to them. Suspended on the

hooks

17 and 18, by means of eyes in one end, are upper and lower cables 20 and 21, respectively.

The cables 20 and 21 are made of a non-sparking, electrically conductive material such, for exarnple, as stainless steel. Anodes 25 are securely attached to and spaced along the cables 20! and 21. At their ends opposite the

hooks

17 and 18, each of the cables is provided with an eye 35. v A

On and adjacent the

horizontal girders

3 and 4,'are cable positioning and mounting means 36. In this embodiment, the cable positioning and mounting means 36 include a hook 37,'welded to the forward bulkhead 2, a saddle 38, cable clamps 40' and 41, with a base 42, andan eye clamp 45, welded to the upper surface of the web 7.. V

The saddle 38 is arcuate in elevation, and is provided with a channel 39, as shown in FIGURES 2 and 3. It is preferably welded or otherwise securely attached to the base 42 or flange 8, or both. In this embodiment, the base 42 is an I-beam of approximately the same height as the part of the flange 8 which extends upwardly from the web 7. The base 42 is welded to the upper surface of the web 7, and a lower part 43 of the cable clamps 40 and 41 is welded or otherwise secured to the base 42, in effect making the base an integral part of the cable clamps 40 and 41. Each of the cable clamps 40 and 41 is provided with a removable or loosenable upper part 44, adapted to permit the admission of a section of the cable intermediate the ends of the cable. Likewise, the eyeclamp 45 is adapted, to receive a, part of the cable manngup the eye 35.

In the embodiment shown, which is the preferred embodiment, each of the anodes 25 is provided with a rod 26, upon which the anodes are cast. The rod 26 projects from each end of the anode, and is clamped to the cable by means of cable clamps 27. This arrangement has at least two advantages over the conventional arrangement represented by FIGURE 3 of Iorgensen Patent No.

Commonly, the after tanks are braced on the p 2,775,554. First, there are no wedges, which are dependant upon frictional engagement, to work loose. Second, the anodes of this invention can be put onto the cable either before or after the cable is partly or wholly in lace.

p The cable is electrically connected to the tank, in addition tothe connections at the hook on the after bulkhead and the mounting means, by a copper 'wire 50, connected at one end to the cable, and at the other end to the bulkhead 12.

The positioning of the cable is illustrated in FIGURE 1. As shown in thatfigure, one end of the cable 21 is supported by the cable hook 18. The other end of the cable 21 is releasably supported by a hook on a lower block 52 of block and tackle 53. An upper block 54 is supported by the block hook 37. The cable 21 is drawn up by means of the block and tackle 53, until the part of the cable irnmediatelybeyond the eye 35 is drawn over and within the channel 39 of the saddle 38. As the cable is drawn toward the block 37, it is led between the movable parts 44 and the fixed parts 43 of the cable clamps 40 and 41. When the cable has been drawn to its desired tightness, the cable clamps 40 and 41 are tightened to hold the cable securely. The block and tackle 53 is removed, and the eye 35 is held down by means of eye clamp 45.

In the standard construction of tankers, the web 7 of the horizontal girders is on the order of 41 inches wide. This is ample to enable the installers of the system to work on the platform it provides. It also is sufiicient to accommodate the block and tackle between the eye 35 and the block hook 37, to permit the cable to be drawn up to the desired degree of tension.

Some of the advantages of the use of the system of this invention are, that no scaffolding is required, since a permanent or portable ladder may be used to obtain access to the hooks on the two bulkheads, and that, in spite of the ease with which the system can be installed, it provides protection to the underside of the overhead, and to the upper portions of the transverse 'web frames, since the anodes 25 of the upper cable 20- lie along and substantially parallel with the undersurface of the overhead. This is a result which has long been desired, but has not been attained heretofore.

Numerous variations within the scope of the appended claims will occur to those skilled in the art in the light of the foregoing disclosure. For example, the cable could be made of a non-metallic material, provided a separate conductor were electrically connected to the anodes and from the anodes of the hull of the ship. A nylon line, with a copper wire along it, might be used, for example. The expression electrically conductive, non-sparking cable is used in the claims to embrace such an arrangement. Mechanical equivalents of certain others of the parts can, of course, be used. For example, eye bolts, brackets or any other suitable block-supporting device may be used instead of they hooks 37, and similarly, any suitable cable anchoring means may be used instead of the hooks :17 and 1-8. As alternatives to the use of two. cable clamps on a base 42, either a single cable clamp may be used between the saddle 38 and the hook 37, or more than two cable clamps may be used. The form of cable clamp may be varied. For example, cable clamps using two bolts instead of one, with a totally removable top part, may be used instead of the clamps illustrated in the drawings, in which the cable can be inserted from one open side of the loosened clamps. The configuration of the. saddle 38 may also be W varied.

Thus it can be seen that a cathodic protective system is provided which is simple, easily installed and re placed, elfective to accomplish its purpose, and safe.

Having thus described theiinvention, what is claimed ffand desired to be securedby Letters Patent is:

1. In a tank provided witha' wide horizontal girder along'a bulkhead defining one of two opposite walls of said tank and at a substantial vertical height above the bottom of said tank, the improvement in cathodic protection systems comprising an electrically conductive, nonsparking cable, anchored at one end to the wall of said tank opposite said horizontal girder and at substantially the same vertical height above said tank bottom as said girder; anodes mounted on and spaced along said cable, and cable mounting means on said horizontal girder and anchoring the other end of said cable, said cable mounting means including a saddle, over which the cable extends and upon which it rests, and a cable clamp having a part secured to said girder and another part movable therefrom to admit a section of cable intermediate the cables ends, said cable clamp being located between the said bulkhead and the said saddle and engaging said cable whereby an end of said cable is positioned between said clamp and said bulkhead.

2, In a ships tank provided with a wide horizontal girder along a bulkhead defining one of two opposite walls of said tank and at a substantial vertical height above the bottom of said tank; said girder having, at its edge remote from said bulkhead, an upwardly extending vertical flange, the improvement in cathodic protection system comp-rising a conductive, non-sparking cable, anchored at one end to the wall of said tank opposite said horizontal girder and at substantially the same vertical height above said tank bottom as said girder; anodes mounted on and spaced along said cable, and cable mounting means on said horizontal girder and anchoring the other end of said cable, said cable mounting means including a saddle, extending over the vertical flange on said horizontal girder, and over which the cable extends and upon Which-it rests, and a cable clamp, said cable clamp having a base secured to said girder and extending at right angles to the said vertical flange, and said cable clamp having a part movable from said base to admit a section of cable intermediate the cables ends, said cable clamp being located between the said bulkhead and the said saddle, and engaging said cable whereby an end of said cable is positioned between said clamp and said bulkhead.

3. The improvement of claim 1 wherein the cable mounting means include a fixed hook, spaced from the cable clamp in a direction toward the bulkhead a distance suificient to accommodate a two-block block and tackle and aligned with said cable clamp and said saddle.

4. The improvement of claim 1 wherein the anodes are mounted on the cable by means of cable clamps, engaging the cable and a rod upon which the anodes are mounted, whereby said anodes may be mounted on and demounted from the cable intermediate the ends of said cable.

References Cited in the file of this patent UNITED STATES PATENTS 669,922 Gottlob Mar. 12, 1901 1,296,883 Van Got-t Mar. 11, 1919 2,190,824 Cook Feb. 20, 1940 2,775,554 Jorgensen Dec. 25, 1956 2,802,781 Feather-1y Aug. 13, 1957 2,838,453 Randall June 10, 1958 2,870,079 McC-all Ian. 20, 1959

Claims

1. IN A TANK PROVIDED WITH A WIDE HORIZONTAL GIRDER ALONG A BULKHEAD DEFINING ONE OF TWO OPPOSITE WALLS OF SAID TANK AND AT A SUBSTANTIAL VERTICAL HEIGHT ABOVE THE BOTTOM OF SAID TANK, THE IMPROVEMENT IN CATHODIC PROTECTION SYSTEMS, COMPRISING AN ELECTRICALLY CONDUCTIVE, NONSPARKING CABLE, ANCHORED AT ONE END TO THE WALL OF SAID TANK OPPOSITE SAID HORIZONTAL GIRDER AND AT SUBSTANTIALLY THE SAME VERTICAL HEIGHT ABOVE SAID TANK BOTTOM AS SAID GIRDER; ANODES MOUNTED ON AND SPACED ALONG SAID CABLE, AND CABLE MOUNTING MEANS ON SAID HORIZONTAL GIRDER AND ANCHORING THE OTHER END OF SAID CABLE, SAID CABLE MOUNTING MEANS INCLUDING A SADDLE, OVER WHICH THE CABLE EXTENDS AND UPON WHICH IT RESTS, AND A CABLE CLAMP HAVING A PART SECURED TO SAID GIRDER AND ANOTHER PART MOVABLE THEREFROM TO ADMIT A SECTION OF CABLE INTERMEDIATE THE CABLE''S ENDS, SAID CABLE CLAMP BEING LOCATED BETWEEN THE SAID BULKHEAD AND THE SAID SADDLE AND ENGAGING SAID CABLE WHEREBY AN END OF SAID CABLE IS POSITIONED BETWEEN SAID CLAMP AND SAID BULKHEAD.