US 2743227 A
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Description (OCR text may contain errors)
April 1956 w. G. WAlTE, ET AL 2,743,227
PROTECTION OF METALLIC STRUCTURES 4 Sheets-Sheet 1 A E H. 0 w /w H m r W N. r/w 1.2 3. 0M0. H A Q 1 NF m m v M 0 L [/6 L a Q W o Q W W/ I 0 u Q 1 o a o 7 Lun "nun" O Q 6 o 0 Q H 1 0 6 1 1 o April 1956 w. G. WAlTE ET AL 2,743,227
PROTECTION OF METALLIC STRUCTURES Filed Aug. 4, 1953 4 Sheets-Sheet 2 4 Z 46 L -37 2 M l Q g i ll y I 7 Z 42 If Z Z -40 4 FIG. 2.
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WILLIAM G: WA/f' A? WILL/AM H/es-nvs' April 1956 w- G. WAlTE ET AL 2,743,227
PROTECTION OF METALLIC STRUCTURES Filed Aug. 4, 1953 4 Sheets-Sheet 3 April 1955 w. G. WAITE ET AL PROTECTION OF METALLIC STRUCTURES 4 Sheets-Sheet 4 Filed Aug. 4, 1953 mm QQQQ 8 2 q 7 a W (HUI d u U a X n V H B V0 Q E 2/ N m g a U. U a V. U E q u 7? a $9009 4 8 2 FIG. 7
lriverffzr W/LL/AM 6. Man; If 37 h/lLL/AM F H/G-auvs flf/onneya United States Patent PROTECTION or METALLIC STRUCTURES William Godfrey Waite and William Frederick Higgins, London, England, assignors to- F. A. Hughes & Co. Limited, London, England, a British company Application August 4, 1953 Serial No. 372,336 Claims priority, application Great Britain August 5, 1952 3 Claims. (Cl. 204-197) This invention relates to the protection of metallic structures against corrosion by the provision in electrical communication therewith of consumable anodes made of a metal or alloy anodic to the metal of the structure.
The object of the present invention is to provide eflicient cathodic protection of ferrous metal tanks of an oil tanker. These tanks are commonly filled with sea water as ballast for the voyages in one direction and at other times may be empty or filled with oil. Under these conditions there is a considerable tendency to corrosive attack on the tank. In providing these tanks with consumable anodes it is found desirable that they develop a fairly high current initially but when the tank structure becomes polarised much less current is needed. It is accordingly desirable to provide main anodes of large vol urne to surface area ratio and subsidiary anodes of small volume to surface area ratio which provide the required initial high current and become consumed in an initial period of use.
According to the present invention the means for the protection against corrosion of ferrous metal tanks of oil tanker ships comprises main anodes within the tank and electrically connected therewith, and subsidiary anodes of less volume to surface-area ratio than the main anodes and consisting of plates mounted on ferrous rod devices which extend over a major part of the height of the tank and are disposed at intervals around and in proximity to the side walls of the tank, each device carrying a plurality of said plates at different levels.
The anodes may be made of magnesium or a magnesiurn base alloy, e. g. a magnesium alloy containing 2 to 7 per cent aluminium and/or 1 to 4 per cent zinc, with or Without 0.01 to 0.4 per cent manganese. The subsidiary anodes may each be in the form of a cast plate to 30 inches in diameter and three-eighths to threequarters of an inch thick with a central cast boss Where it is apertured to receive a ferrous metal split sleeve which slides on the rod and is fixed in position on the rod by a clamp engaging the split part. Alternatively we may use a sleeve which it not split and is welded to the rod. The subsidiary anodes may have from 0.13 to 0.88 square feet surface area per lb. of metal (preferably 0.30 to 0.60 square feet per 1b.), and may be spaced near (e. g. at less than six inches) the wall of the tank. The main anodes may be made with cast-in iron rods which extend into the anode metal and are clamped to the floor girders of the tank. The main anodes may have less than 0.1 square feet of surface area per lb. of anode metal e. g. 0.033 to 0.071 square feet per lb., or preferably 0.045 to 0.63 square feet per lb.
The invention will be further described by way of example with reference to the accompanying diagrammatic drawings wherein:
Figure l is a perspective view of a tank of a tanker, broken to show the interior;
Figures 2 to 6 are enlarged views of parts shown in Figure 1; and
Figure 7 is a plan view of the interior of the tank.
The tank of which the interior is shown in Figure 1 has walls or bulkheads 10 provided with vertical stifliening members or stringers 11 and horizontal stiffening members or stringers 12. A cover plate 13 has strengthening girders 18 and an inspection manhole 14 leading to iron steps 15. A floor 16 has strengthening girders 17.
Main anodes 20 are attached to the floor girders 17. These anodes are distributed at intervals over the floor area as shown in Figure 7 and are each in the form of a hemi-spherical block of metal having an iron rod 21 (Figure 4) cast in it which has an anchor plate 22 embedded in the anode metal, a ring 23 on the upper end of the rod to facilitate handling, a projecting threaded lower end 24, and nuts 25, 26, which attach the anode to a girder 17.
Subsidiary anode plates 28 are mounted in vertical sets 7 and 8 which are distributed around the tank or tank compartments. As shown in Figure 7 two or three sets are disposed at intervals along each wall.
The sets disposed along a wall having stringers 12 I have the upper plates 28 mounted on an iron rod 30 (Figures 5 and 6) which is hooked at its upper end and engages in a hole 31 in one of the roof girders 18. The rod passes through a split sleeve 34 which in turn passes a boss 32 provided centrally of the plate. The sleeve is secured to the plate by nuts 33 and the sleeve is sccured to the rod by means of clamps 35. The other plates are attached in the same way. The lower end of the rod is clamped by a clamp 37 to a fixed rod 36 that 'is welded to a stringer 12; The next lower plates of the for supporting the plates and the lowermost rod is clamped by clamp 44 to a short rod 43 (Figure 3) welded to the floor girder 17.
The sets provided along the other walls may be similarly mounted with the aid of brackets 46 welded to the walls 10 and serving in'place of the stringers 12 to carry the rod device.
1. Means for the protection against corrosion of ferrous metal tanks of oil tanker ships having horizontally extending strengthening stringers and floor strengthening girders, comprising main anodes attached to said girders within the tank and electrically connected therewith, and subsidiary anodes of less volume to surface-area ratio than the main anodes and consisting of plates mounted on ferrous rod devices having hooked portions engaging about said stringers and rigidly secured thereto, said rod devices extending over a major portion of the height of the tank, disposed at intervals around and in proximity to the side walls of the tank, each rod device carrying a plurality of said plates at different levels and secured at its upper and lower ends rigidly to portions of the tank; each anode plate having a central apertured boss, a split sleeve mounted within said boss and rigidly attached thereto, and means for clamping said split sleeve on the ferrous roddevice.
2. Means for the protection against corrosion of ferrous metal tanks of oil tanker ships, comprising main anodes within the tank and electrically connected therewith, and subsidiary anodes of less volume to surfacearea ratio than the main anodes and consisting of plates mounted on'ferrous rod devices having hooked portions, brackets rigidly secured to the Walls of the tank, said hooked portions engaging about said brackets and rigidly secured thereto, and said rod devices extending over a major portion of the height of the tank, disposed at intervals around and in proximity to the side walls of the same, each rod device carrying a plurality of said plates Patented Apr. 24, 1956 I at difierent levels, and rigidly secured at its upper and lower ends to portions of the tank; eachanode plate having a central apertured boss, a split sleeve mounted within said boss and rigidly attached thereto, and means for clamping saidsplit sleeve on the ferrous rod device.
3. Means as claimed in claim 2 wherein the subsidiary anodes are cast plates of magnesium base alloy having a diameter of 1-5 to 30'inc hes, a thickness of three eighths to three quarters of an inch, 21 surface area of 0.13 to 0.88 square feet per 1b. of metal plate, and a central cast boss apertured to receive a ferrous metal split sleeve through which the rod device passes, nuts securing the sleeve to the boss, and a clamp being provided to clamp the sleeve to the rod device, and themain anodes have less than 0.1 square feet of surface area per lb. of anode meta-1*.
References Cited in the file of this patent UNITED STATES PATENTS 1,900,011 Durham Mar. 7, 1933 2,200,469 Cox Nov. 8; 1939 2,571,062 Robinson et a1. Oct. 9, 195] FOREIGN, PATENTS 491,168 Canada Mar. 10, 1953 3,205 Great. Br;itain 1885 11,025 Great Britain 1886