US2805198A - Cathodic protection system and anode therefor - Google Patents

Cathodic protection system and anode therefor Download PDF

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Publication number
US2805198A
US2805198A US568619A US56861956A US2805198A US 2805198 A US2805198 A US 2805198A US 568619 A US568619 A US 568619A US 56861956 A US56861956 A US 56861956A US 2805198 A US2805198 A US 2805198A
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United States
Prior art keywords
percent
anodes
anode
manganese
magnesium
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Expired - Lifetime
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US568619A
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English (en)
Inventor
Harold A Robinson
John J Newport
Osborn Oliver
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Dow Chemical Co
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Dow Chemical Co
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Priority to US568619A priority Critical patent/US2805198A/en
Priority to GB4296/57A priority patent/GB813657A/en
Priority to FR1197655D priority patent/FR1197655A/fr
Priority to DED25031A priority patent/DE1256037B/de
Application granted granted Critical
Publication of US2805198A publication Critical patent/US2805198A/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C23/00—Alloys based on magnesium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
    • C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
    • C23F13/12—Electrodes characterised by the material
    • C23F13/14—Material for sacrificial anodes

Definitions

  • This invention relates to a cathodic protection anode formed of a galvanically active metal and to a cathodic protection system wherein such a protection anode is employed.
  • Cathodic protective anodes have been used for many purposes, such as preventing corrosion of structures in sea water, pipelines buried in the soil and internal areas of hot water heaters.
  • these anodes are made of readily expendable magnesium which has been alloyed with other metals to give the anode properties which particularly adapt it for its intended use.
  • cell magnesium has a satisfactory solution potential, but a poor current eciency.
  • Certain magnesium alloys have improved current eticiencies, but lower solution potentials than cell magnesium. Consequently, more alloy anodes are required to protect a given structure, but under predetermined conditions of use these anodes will have a longer useful life. Offsetting to a certain extent some of the advantages of these anodes made from magnesium alloy is the cost of the additional process steps and alloying ingredients.
  • an improved cathodic pro tection anode is obtained by forming the anode from a magnesium base alloy containing from 0.50 to 1.3 percent by weight manganese and not more than 0.010 percent by weight aluminum.
  • a preferred method of making these anodes is to add a suitable manganese cornpound to the feed of a magnesium electrolytic cell, and the preferred composition comprises from 0.50 to .80 manganese and not over 0.005 aluminum (in weight percent), with the balance essentially magnesium.
  • the present invention is useful in providing cathodic protection for structures immersed in sea water, and can be vused under some conditions as a protective anode in hot water heaters. Yet anodes and systems comprisly fall between 200 and 300 hours per pound. Anodes at a given voltage or potential. Consequently, .an anode. metal having relatively low solution potential is desir- L able to avoid useless current generation which is in turn accompanied by rapid consumption of the anode metal.
  • Anodes comprising the present invention have the following composition in percent by weight:
  • cellmagnesium In the electrolytic production of magnesium, the molten magnesium in the electrolytic cell is referred to as cellmagnesium.
  • cell kmagnesium is pure magnesium, but certain adventitious elements are present in small amounts.
  • amounts of these adventitious elements must be controlled.
  • Iron is present in at least 0.001 percent by weight and must be limited to a maximum of 0.03 percent if an anode of the desirable characteristics of the present invention is to be obtained.
  • Nickel is restricted toy not over 0.002 .percent by weight and the tin and lead Vshould rnot exceed 0.01 percent.
  • the other metals present do not exceed 0.05 percent each. The total of all such adventitious elements does not exceed 0.2 percent in the cell magnesium.
  • Aluminum is always present in small amounts in cell magnesium and will vary from 0.0001 up to 0.02 weight percent. Although it has previously been recognized that high percentages of iron were detrimental in anodes used for cathodic protection, little if any attention was directed to the amount of aluminum in the cell magnesium.
  • the solution potential of anodes comprising the present invention is substantially uniform wheuthe manganese solutionpotentials does decrease.
  • thel amount of manganese is adjustedrelative' to the amount of aluminum ⁇ present toxobtainenhanced current efficiency and the highest solutionpotentials
  • Figure l illustratesthe. critical effectof the Mn/Al ratio on the current eiciency1ofthe anode by plot-tingxtest data from alloys comprising the present invention which* have similar aluminum content on a graph in whichfthe ordinates represent ampere hoursl per pound of'anode metal and theabscissas ⁇ represent the percentby weight of manganese.
  • the details-of thel tests and data ⁇ upon which-Figure l is-basedV are set forth in Examples ll and 2 below.
  • manganese dioxide or manganese dichloride
  • a manganese compound such as manganese dioxide or manganese dichloride
  • the constituents of the cell are analyzed at frequent intervals and the manganese added in the feed is adjusted according. to the aluminum content of the cell magnesium.
  • manganese is an, expensive alloying metal and minimum amounts useable areemploycd to' reduce the cost of these sacrificial anodes which maybe employed tothe extent of several tons foruses such as protecting pipelines.r
  • the casting of anodes from this alloy follows. the conventional procedures althoughv it is preferred to employ Arelatively cool molds. Y
  • magnesium ⁇ anodes used for laboratory investigations were cast in iron molds just slightly over C. and immediately air cooled to room temperature.
  • experimental cellsv were assembled using a 5.5 inch length of 3.5 inch. standardpipe for the cathode, and an ⁇ aqueous solution saturated with CaSOi and Mg(OH)2 interposed between the rodandthe cathode in the electrolyte. This cell was then: connected in series with other test cells and operated at an anode current densityv of 36.milliamperes per square footfor 14 days. The anodes were then removed from the cells andthe loose corrosion product was brushed or rubbed off in a stream of runningwater. This wasv followed by immersion in agitated, aqueous 20 percent chromic acid solution, containing ⁇ l percent AgNOs, to.
  • Example 2 A series of tests following the procedures above outlined weremade andthe results of these tests formed the basis for Figure 1..
  • the alloy in each case contained approximately .0005 percent Cu, less than .01 percent Ca, less'than .0005 percent Ni, less than .001 percent' Pb, ⁇ less than .001 percent Si, less than .0l percent Sn andV less than .02 percent Zn, with the balance magnesium 'Y except for aluminum, iron and manganese ⁇ as tabulated.
  • FIG. 3 is a schematic illustration of an anode field positioned about a bare ferrous metal pipeline, in this case, a bare metal 8 inch diameter pipe which is to be protected.
  • the pipeline 1 is connected through an insulated electrical conductor 2 to an insulated collector wire 3, so-called because it interconnects through lead wires 4-4 with anodes, 5-5. These anodes, which are formed from the alloy..
  • the backll 6V may be composed of 20 parts 'bentonite (dry, powdered), 75 parts gypsum (dry, powdered) and 5 parts sodium sulfate (anhydrous). This backiill isolates the anode chemically and acts as an electrolytic bridge carrying electricity from anode to earth; V
  • anodes need be used only on one side of the-,pipeline t ⁇ o be protected, lalthough exceptionally large pipes may require anodes on both sides.
  • Thespacing of the anodes-in the station shown in Figure 3, as we ll as the total numbrof stations required, is a function of the solution potential of the anode, theresistivity of the soil and the amount of current required to protect the pipeline. ⁇
  • anodes of the present invention which have higher solution potentials than thoseofthe prior iart, may be spaced farther apart, thus reducing the total number of anodes needed.
  • a cathodicprotection'anode formed of galvanically active metal having the following composition in percent by weight:
  • the amount of manganese in weight percent being at least equal to 0.5+60 (percent by Weight of aluminum).
  • Magnesium At least 99.16. Manganese 0.5 to' 0.8. Aluminum Not over 0.005. Iron Y 0.001 to 0.03.
  • the amount of manganese in weight percent being at least equal to 0.5-
  • Magnesium At least 98.5. Manganese 0.50 to 1.3. Aluminum Not over 0.01. Tin Not over 0.01. Lead Not over 0.01. Iron 0.001 to 0.03. Nickel Not over 0.002. -Other metals i(each) No't over 0.05.
  • the amount of manganese in weight percent being at least equal to 02541- (percent by weight of aluminum) when the percent by weight of aluminum exceeds .007.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Prevention Of Electric Corrosion (AREA)
US568619A 1956-02-29 1956-02-29 Cathodic protection system and anode therefor Expired - Lifetime US2805198A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US568619A US2805198A (en) 1956-02-29 1956-02-29 Cathodic protection system and anode therefor
GB4296/57A GB813657A (en) 1956-02-29 1957-02-07 Cathodic protection system and anode therefor
FR1197655D FR1197655A (fr) 1956-02-29 1957-02-27 Anode pour protection cathodique, procédé de fabrication de cette anode et système de protection cathodique comportant cette anode
DED25031A DE1256037B (de) 1956-02-29 1957-02-27 Anode fuer den kathodischen Schutz

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US568619A US2805198A (en) 1956-02-29 1956-02-29 Cathodic protection system and anode therefor

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US2805198A true US2805198A (en) 1957-09-03

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US (1) US2805198A (de)
DE (1) DE1256037B (de)
FR (1) FR1197655A (de)
GB (1) GB813657A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2834698A (en) * 1957-06-17 1958-05-13 Dow Chemical Co Superior galvanic magnesium anode
US3258682A (en) * 1966-06-28 Electrode assembly
US3549993A (en) * 1966-06-14 1970-12-22 Union Oil Co Corrosion rate measuring method by maintaining electrolytic contact and excluding any substantial oxygen contact with a test specimen
DE102019002409A1 (de) * 2019-04-02 2020-10-08 Bundesrepublik Deutschland, vertr. durch das Bundesministerium der Verteidigung, vertr. durch das Bundesamt für Ausrüstung, Informationstechnik und Nutzung der Bundeswehr Reduzierung der elektrischen Felder eines Wasserfahrzeuges

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4427517A (en) * 1982-03-01 1984-01-24 The Dow Chemical Company Underground backfill for magnesium anodes
CN101665944B (zh) * 2008-09-05 2011-06-15 淄博宏泰防腐有限公司 一种高电流效率Mg-Mn-Ca-Zn-Sr牺牲阳极

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1960700A (en) * 1930-01-10 1934-05-29 Dow Chemical Co Method of making magnesium alloys
US2431723A (en) * 1942-01-17 1947-12-02 Leland A Yerkes Electrolytic method for producing magnesium alloys
US2478479A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Cored magnesium anode in galvanic protection
US2645612A (en) * 1950-06-15 1953-07-14 American Smelting Refining Sacrificial anode
US2698230A (en) * 1950-02-21 1954-12-28 Magnesium Elektron Ltd Magnesium base alloys containing zirconium
US2742355A (en) * 1952-02-29 1956-04-17 Magnesium Elektron Ltd Method of producing magnesium base alloys

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1960700A (en) * 1930-01-10 1934-05-29 Dow Chemical Co Method of making magnesium alloys
US2431723A (en) * 1942-01-17 1947-12-02 Leland A Yerkes Electrolytic method for producing magnesium alloys
US2478479A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Cored magnesium anode in galvanic protection
US2698230A (en) * 1950-02-21 1954-12-28 Magnesium Elektron Ltd Magnesium base alloys containing zirconium
US2645612A (en) * 1950-06-15 1953-07-14 American Smelting Refining Sacrificial anode
US2742355A (en) * 1952-02-29 1956-04-17 Magnesium Elektron Ltd Method of producing magnesium base alloys

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3258682A (en) * 1966-06-28 Electrode assembly
US2834698A (en) * 1957-06-17 1958-05-13 Dow Chemical Co Superior galvanic magnesium anode
US3549993A (en) * 1966-06-14 1970-12-22 Union Oil Co Corrosion rate measuring method by maintaining electrolytic contact and excluding any substantial oxygen contact with a test specimen
DE102019002409A1 (de) * 2019-04-02 2020-10-08 Bundesrepublik Deutschland, vertr. durch das Bundesministerium der Verteidigung, vertr. durch das Bundesamt für Ausrüstung, Informationstechnik und Nutzung der Bundeswehr Reduzierung der elektrischen Felder eines Wasserfahrzeuges

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Publication number Publication date
DE1256037B (de) 1967-12-07
FR1197655A (fr) 1959-12-02
GB813657A (en) 1959-05-21

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