US3660249A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for determining both the average corrosion rate, and the pitting tendency, substantially independently of the resistance of the electrolyte
Assignee: Magna Corp
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Filing: 1970-02-05
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Granted: 1972-05-02
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Expires: 1990-02-05
Abstract
Abstract The method makes use of three electrodes which are exposed to the corrosive environment, the electrodes being the corroding or test electrode, the reference electrode, and the auxiliary electrode. The corroding electrode is made 10 millivolts positive relative to the reference electrode, and is then made 10 millivolts negative relative thereto. The anodic and cathodic currents which flow through a circuit including the corroding electrode and the auxiliary electrode are then averaged to produce an indication of the general or average corrosion rate, there being no substantial error due to the resistance of the electrolyte. The difference between such anodic and cathodic currents is determined in order to provide the pitting tendency or pitting index of the system. In accordance with a second embodiment of the method, the corroding electrode is forced to be at the same potential as that of the reference electrode. The current which then flows through a circuit including the corroding electrode and the auxiliary electrode is measured by a microammeter and is the pitting tendency of the system. Thereafter, the microammeter is caused to read zero despite the fact that current is passing therethrough, and the corroding electrode is forced to be at a 10 millivolt potential difference from the reference electrode. The reading of such microammeter is then directly proportional to the general or average corrosion rate.
Inventors
- 👤 Clarence R Townsend
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 23:57
CPC Classifications
G; G01; G01N; G01N17/00; G01N17/02
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
16 words
The invention as claimed in claim 1, in which said number is less than about 20.
Claim 2
Dependent Claim
100 words
The invention as claimed in claim 1, in which said first-mentioned polarization current is applied before application of said second-mentioned polarization current, in which a microammeter is employed to read said first-mentioned polarization current, and in which said method further comprises compensating said microammeter to zero while said first-mentioned polarization current is passing therethrough, and thereafter passing through said microammeter said second-mentioned polarization current, said first-mentioned polarization current being the pitting tendency, the current reading of the scale of said compensated microammeter while said second-mentioned polarization current is passing therethrough being directly proportional to the general or average corrosion rate.
Claim 3
Independent Claim
266 words
A method of determining the instantaneous general or average rate of corrosion of a metal exposed to an electrolyte, and also determining the pitting tendency of said metal exposed to said electrolyte, which comprises: providing a corroding electrode formed of said metal the corrosion rate and pitting tendency of which are to be determined, providing a reference electrode also formed of said metal, providing an auxiliary electrode, exposing said three electrodes to a body of said electrolyte, providing external circuit means to connect said corroding electrode to said auxiliary electrode wherebY a current may flow therebetween through a circuit including said electrolyte and said external circuit means, determining the amount of pitting current which flows through said circuit as the result of only the open circuit potential difference between said corroding electrode and said reference electrode, said current being the pitting tendency of said metal exposed to said electrolyte, impressing sufficient polarization voltage between said corroding electrode and said auxiliary electrode to cause the potential of said corroding electrode to be a predetermined small amount positive or negative relative to said reference electrode, and determining the amount of general or average corrosion current which flows through said circuit as the result of said impressed polarization voltage only, and not the result of said open circuit potential difference, said last-named amount of current being directly proportional to the instantaneous general or average corrosion rate of said metal exposed to said electrolyte, said steps of impressing said polarization voltage, and of determining the amounts of said currents, being performed by means of a differential amplifier and an ammeter.
Claim 4
Independent Claim
89 words
A method of determining the corrosion characteristics of a metal exposed to an electrolyte, which comprises: providing a corroding electrode and a reference electrode both formed of said metal, providing an auxiliary electrode, immersing said electrodes in a body of said electrolyte, passing sufficient polarizing current between said corroding and auxiliary electrodes to force the potential of said corroding electrode to be the same as the potential of said reference electrode, and measuring said polarizing current to thus determine the pitting tendency of said metal exposed to said electrolyte.
Claim 5
Dependent Claim
86 words
The invention as claimed in claim 5, in which said method further comprises passing between said corroding electrode and said auxiliary electrode sufficient polarizing current to cause the potential of said corroding electrode to be a predetermined small amount different from the potential of said reference electrode, determining the magnitude of said last-mentioned polarizing current, and subtracting from said last-mentioned polarizing current said first-mentioned polarizing current, the difference thus obtained being proportional to the general or average corrosion rate of said metal exposed to said electrolyte.
Claim 6
Dependent Claim
24 words
The invention as claimed in claim 6, in which said predetermined small amount is substantially greater than zero but less than about 20 millivolts.
Claim 7
Dependent Claim
137 words
The invention as claimed in claim 5, in which said polarizing current also flows through external circuit means which connects said auxiliary electrode to said corroding electrode, in which said measuring step is performed by an ammeter connected in said external circuit means, and in which said method further comprises compensating said ammeter to cause it to read zero despite the passage of said polarizing current therethrough, thereafter discontinuing said forcing step and passing through said external circuit means and through said electrolyte between said corroding electrode and said auxiliary electrode sufficient polarizing current to cause the potential of said corroding electrode to be a predetermined small amount different from that of said reference electrode, and thereafter reading said compensated ammeter to thus determine the general or average corrosion rate of said metal exposed to said electrolyte.
Claim 8
Dependent Claim
23 words
The invention as claimed in claim 8, in which said method further comprises passing said polarizing currents by means of a differential amplifier.
Claim 9
Dependent Claim
154 words
The invention as claimed in claim 9, in which said method further comprises connecting one input of said differential amplifier to a voltage source calibrated to produce said predetermined small potential difference between said corroding electrode and said reference electrode, connecting the oTher input of said differential amplifier to said reference electrode, connecting one output of said differential amplifier to said auxiliary electrode, connecting the other output of said differential amplifier to said corroding electrode, connecting said one input to said corroding electrode in order to effect said forcing step whereby the potential of said corroding electrode is caused to be the same as that of said reference electrode, thereafter reading said ammeter to determine the pitting tendency, thereafter causing said ammeter to read zero despite the passage of current therethrough, thereafter disconnecting said one input from said corroding electrode, and thereafter again reading said ammeter to determine the general or average corrosion rate.
Claim 10
Independent Claim
366 words
A method of determining the instantaneous general or average rate of corrosion of a metal exposed to an electrolyte, and also determining the pitting tendency of said metal exposed to said electrolyte, which comprises: providing a corroding electrode formed of said metal the corrosion rate and pitting tendency of which are to be determined, providing a reference electrode also formed of said metal, providing an auxiliary electrode, exposing said three electrodes to a body of said electrolyte, providing external circuit means to connect said corroding electrode to said auxiliary electrode whereby a current may flow therebetween through a circuit including said electrolyte and said external circuit means, determining the amount of pitting current which flows through said circuit as the result of only the open circuit potential difference between said corroding electrode and said reference electrode, said current being the pitting tendency of said metal exposed to said electrolyte, impressing sufficient polarization voltage between said corroding electrode and said auxiliary electrode to cause the potential of said corroding electrode to be a predetermined small amount positive or negative relative to said reference electrode, and determining the amount of general or average corrosion current which flows through said circuit as the result of said impressed polarization voltage only, and not the result of said open circuit potential difference, said last-named amount of current being directly proportional to the instantaneous general or average corrosion rate of said metal exposed to said electrolyte, said method further comprising effecting said determinations of the amounts of said pitting current and said general or average corrosion current by a. forcing said corroding electrode to be at the same potential as that of said reference electrode, b. determining the current which flows through said circuit when said corroding and reference electrodes are thus at the same potential, said current being said pitting current, and c. determining the amount of said general or average corrosion current by subtracting said pitting current from the current which flows through said circuit due to said impressing of sufficient polarization voltage between said corroding electrode and said auxiliary electrode to cause said corroding electrode to be said predetermined small amount positive or negative relative to said reference electrode.
Claim 11
Dependent Claim
55 words
The invention as claimed in claim 11, in which said subtracting is effected by reading said pitting current with an ammeter, thereafter causing said ammeter to read zero despite the passage of said pitting current therethrough, thereafter impressing said sufficient polarization voltage, and thereafter reading said ammeter to determine said general or average corrosion current.
Claim 12
Dependent Claim
165 words
Apparatus for determining the general or average corrosion rate, and the pitting tendency, of a metal exposed to an electrolyte, and without the necessity of correcting for the resistance of such electrolyte, which comprises: means to mount a corroding electrode formed of said metal the corrosion rate and pitting tendency of which arE to be determined, a reference electrode also formed of said metal, an auxiliary electrode, a differential amplifier, a source of D.C. voltage calibrated to produce a predetermined small potential difference between said corroding electrode and said reference electrode, means to connect one output of said source to one input terminal of said amplifier, means to connect the other input terminal of said amplifier to said reference electrode, means to connect one output terminal of said amplifier to said auxiliary electrode, means to connect the other output terminal of said amplifier to said corroding electrode, and means to determine the current flowing through said electrolyte between said auxiliary electrode and said corroding electrode.
Claim 13
Dependent Claim
27 words
The invention as claimed in claim 13, in which means are provided to connect said corroding electrode to the other output of said source of D.C. voltage.
Claim 14
Dependent Claim
54 words
The invention as claimed in claim 14, in which said auxiliary electrode is a metal sleeve, and in which said corroding electrode and said reference electrode are elongated electrodes the inner end portions of which are mounted in said sleeve in spaced and insulated relationship relative to each other and relative to said sleeve.
Claim 15
Dependent Claim
32 words
The invention as claimed in claim 14, in which means are provided to reverse the polarity of the D.C. voltage supplied to the input terminals of said amplifier by said voltage source.
Claim 16
Dependent Claim
27 words
The invention as claimed in claim 14, in which said current-determining means is an ammeter connected in circuit with either said auxiliary electrode or said corroding electrode.
Claim 17
Dependent Claim
39 words
The invention as claimed in claim 14, in which said current-determining means includes a resistor connected in circuit with either said auxiliary electrode or said corroding electrode, and in which storage and compute means are connected across said resistor.
Claim 18
Dependent Claim
71 words
The invention as claimed in claim 14, in which said current-determining means is an ammeter connected in circuit with either said auxiliary electrode or said corroding electrode, in which means are provided to cause said ammeter to read zero despite the flow of current therethrough, and in which circuit means are provided to connect said one input of said amplifier to said corroding electrode, said last-named circuit means incorporating a switch.
Claim 19
Dependent Claim
21 words
The invention as claimed in claim 14, in which said differential amplifier has a high gain and a high input impedance.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-05-02 | 1975-11-01 | 1976-05-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-05-02 | 1979-11-01 | 1980-05-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-05-02 | 1983-11-01 | 1984-05-02 | $7700.00 | Window Closed / Lapsed |