Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Metal or metal alloy
Reexamination Certificate
2001-06-06
2003-01-14
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Metal or metal alloy
C205S726000, C205S729000, C205S740000, C204S196020, C204S196060, C204S196070, C204S196110
Reexamination Certificate
active
06506295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cathodic protection method and apparatus for protecting a metal structure exposed in the atmosphere such as exterior wall of a building, roof, and bridge from being corroded by oxidation, and to as an application thereof, a cathodic protection method and apparatus of a steel member contacted with water in water piping or tanks.
DESCRIPTION OF BACKGROUND ART
A metal structure exposed in the atmosphere, even when its metal surface is painted, with the passage of time, is oxidation corroded by electrolytic water and dissolved oxygen in that water formed on the surface by rain water or moisture in the air or pollution substances in the atmosphere or the like.
As protective anode and cathodic protection system for performing corrosion protection of the coated surface of such a metal structure, there is an apparatus developed and commercialized by C. L. I. Systems Inc. (U.S.A.) (U.S. Pat. No. 2,579,259 (Japanese Patent Laid-open Publication No. 4-318183).
This electrical corrosion protection apparatus has an effect for corrosion protection of a metal structure having a surface protected by surface coating which is exposed in the atmosphere, however, has the following two unavoidable problems. These problems are
(1) Current control means as a subject matter has a function to apply a current proportional to the environmental humidity detected by a humidity sensitive device. However, in practice, depending on the amount of sea salt particles or atmospheric pollution substances dissolved in the water film, even with the same humidity and the same thickness of the water film, it is evident that electrical resistance per unit length of the water film itself is greatly varied. Therefore, since the current necessary for corrosion protection is changed with the quality of the water film, even when the same magnitude of current is applied, reaching range of corrosion protection current is changed according to the environmental water quality at that time.
Further, the surface coating film of the metal structure is partly degraded by sand dust or other environmental affecting factors, generating a defect in part thereof. If this defective part expands, even with the same environmental humidity, the current amount necessary for extensive surface corrosion protection of the metal structure containing the defective part is greatly increased. For example, assuming a case where a large amount of sea salt particle is dissolved in the water film and the defect of the coating film is generated around the protective anode of the apparatus, at a humidity of 60 to 70% and a low temperature, and if only a small amount of current is supplied, since the supplied current flows into the above-described defective part, the current is consumed in a small area in the vicinity of the protective anode, thus reducing the reaching range of the corrosion protection current.
(2) To prevent over-corrosion protection of the metal structure in the vicinity of the protective anode, the anode output voltage is set to a maximum of 12V. However, as described above, when the area of the defective part of coating film is increased, to achieve the desired corrosion protection range, it is necessary to further increase the voltage to increase the current. For this requirement, current application by a maximum output voltage of 12V cannot meet.
With the above prior art circumstances, it is therefore an object of the present invention to provide a cathodic protection method and apparatus for a metal structure in which the area of corrosion protection obtainable by a single anode can be increased to a maximum without causing over-corrosion protection.
DISCLOSURE OF THE INVENTION
With the aim of solving the above problems, the inventors have conducted the following experiments and investigations and accomplished the present invention.
In the experiments, various systems have been constructed, trial and error has been repeated to confirm whether or not the desired function can be achieved, and initially the system as shown in
FIG. 1
has been completed.
In the figure, numeral
1
indicates a terminal of a 100 to 200V power supply,
2
is a fuse,
3
is a surge current absorption varistor.
4
is a transformer which steps the output down to 18 to 20V. Further,
5
is a rectifier circuit which converts AC to DC.
6
and
7
are capacitors.
8
is a regulator which controls the voltage applied to a main anode
15
.
9
and
10
are capacitors, and
21
is also a capacitor.
22
is a regulator which controls the voltage applied to a pilot anode
20
to a constant value.
23
and
24
are capacitors.
The above-described power supply terminal
1
to capacitor
10
, capacitor
21
, regulator
22
, and capacitors
23
and
24
are incorporated in a controller
30
.
A transistor
11
, resistors
12
and
14
, and a Zener diode
13
constitute a first current limitation means
100
for limiting the current supplied to the main anode
15
to a predetermined value. Further, a capacitor
25
, an operational amplifier
26
, resistors
27
,
28
and
29
constitute a second current limitation means
101
which detects the current from the pilot anode
20
to a coated steel plate (metal structure)
16
to be corrosion protected, and according to the detected current value, controls the output voltage of the regulator
8
through the ground of the regulator
8
, whereby flowing a predetermined optimum current from the main anode
15
to the coated steel plate
16
. Between the main anode
15
and the coated steel plate
16
, a special medium
70
having an electrical resistance is disposed.
The first current limitation means
100
is integrated with the main anode
15
, and the second current limitation means
101
is integrated with the pilot anode
20
. In the figure, numeral
17
indicates a coating film provided on the coated steel plate
16
to be corrosion protected.
18
is a defective part of the coating film
17
, and
19
denotes a water film formed on the surface of the coated steel plate
16
.
In the apparatus of the above construction, when the output voltage of the regulator
22
is a constant value of 8V to 12V, and the current is increased by an increase in electrical conductivity of the water film
19
and expansion of the defective part
18
, accordingly the output voltage of the regulator
8
is increased from 10V to, for example, 15V to supply the desired optimum corrosion protection current to the coated steel plate
16
.
FIG. 2
shows an outline of a test apparatus for confirming the corrosion protection function of the protection apparatus of the construction shown in FIG.
1
. The main anode
15
and the pilot anode
20
are stuck to the coated steel plate
16
through an insulating two-sided bonding material. Anode wires
30
a
from the controller
30
are connected to the corresponding main anode
15
and pilot anode
20
, and further, a cathode wire
30
b
connected to a base material
32
of the coated steel plate
17
.
Part of the coating film at a position away from the anode connection position of the coated steel plate
16
is peeled out to form an artificial coating film defective part 18 of 10 mm in diameter. The coating film defective part
18
is provided with an Ag/AgCl microelectrode (&phgr;=0.1 mm)
31
coated with agar agar containing saturated KCl. Potential of the steel plate base material
17
to the electrode
31
is outputted to a computer through a buffer to collect data.
The controller
30
is connected with AC 100V power supply, after confirming that the voltage of the pilot anode
20
is constant at the setting value 10V, the coated steel plate
16
is subjected to an exposure test for about 30 days. As a result, in the state of a humidity of less than 60%, the voltage applied to the main anode
15
exhibits the minimum value 10V, the potential increases with increasing humidity, reaching about 13V in rainfall.
Further, in addition to the above-described position, a coating film defective parts are also formed between the coating film de
Takahashi Masahiro
Takahashi Yasuhiko
Wada Eisuke
Bell Bruce F.
Jonan Co., Ltd.
Workman & Nydegger & Seeley
LandOfFree
Cathodic protection method and device for metal structure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cathodic protection method and device for metal structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cathodic protection method and device for metal structure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3004262