JPS6119787A - Method for preventing corrosion of outer surface of bottom plate of outdoor tank for storing high temperature substance such as asphalt - Google Patents

Abstract

PURPOSE:To effectively prevent the outer surface of the titled bottom plate from corrosion by preventing a corrosion-proof current from dispersing to the part other than the bottom plate, by arranging a plurality of current supply electrodes by an external power source system directly under the outer surface of said bottom plate to supply the corrosion-proof current to said electrodes. CONSTITUTION:A large number of durable electrodes 5 adapted to electric corrosion-proofness by an external power source system are horizontally arranged in the foundation 7 directly under the outer surface of the bottom annular plate of an outdoor tank 1 in the circumferential direction in a properly dispersed state and lead wires 8 of the electrodes are led out of the tank 1 to be connected to the + terminal 10 of a DC power source apparatus 9. The - terminal 11 of the apparatus 9 is connected to the earth terminal 12 provided to the tank main body by an electric wire 13. After the completion of connection, the supply of a corrosion-proof current is started and the current generated from each electrode is adjusted by the output voltage tap conversion of the apparatus 9 while the corrosion-proof current of a whole of the outer surface is checked by the collimation electrode 14 arranged to the lower part of the annular plate so as to be brought to a proper value. When irregularity is generated in the protective potential in the circumferential direction of the annular plate according to a place, a resistor is inserted between each electrode and the terminal 10 to eliminate irregularity.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention is applicable to the outer surface of an annular plate on the bottom surface of a storage tank for high-temperature substances such as asphalt, which is extremely corroded, or a similar tank outer peripheral bottom plate (hereinafter referred to as an annular plate, etc.). The present invention relates to the provision of a method for preventing corrosion of

``Conventional technology'' ``The outer surface of the bottom plate of an outdoor tank for storage of high-temperature substances such as asphalt, especially the annular plate around the outer circumference of the tank, is at a high temperature, moisture can penetrate from the bottom of the foundation sand, etc. Combined with the penetration of rainwater containing corrosive substances such as salt particles, extremely severe corrosion occurs, and leakage of contents due to pitting corrosion often occurs in just a few years.
``In order to prevent such severe corrosion, attempts have been made to paint the lower part of the annular board, etc., or replace the foundation with asphalt mortar, etc., to prevent corrosion, but very effective results have not been obtained. Not yet.

In addition, when applying the cathodic protection method, as shown in Figure 2,
Corrosion prevention method in which galvanic anodes 4 are installed in a distributed manner under the bottom plate 3, or energized by installing current-carrying electrodes 5 using an external power source on the outside of the tank outer periphery 15 in a shallow or deep underground manner as shown in FIG. has also been attempted.

In the figure, 1 is a storage tank for high-temperature substances such as asphalt, 2 is the outer surface of annular plates, etc., 6 is a corrosion protection current, 7 is a foundation, 8 is an electrode lead wire and the ■ side wiring, and 9 is a DC power supply device as an external power source. , 10.11 is the O terminal of the DC power supply device 9,
The O terminal, 12 is the tank ground terminal, and 13 is the O side wiring.

"Problems to be Solved by the Invention" and "Operation" However, in the former case, the absolute amount of anti-corrosion current is insufficient, and in the latter case, the anti-corrosion current is widely dispersed, and as a result, the inflow current to the annular plate 2, etc. is insufficient or uneven. Therefore, it could not be said that it was an effective corrosion prevention method in either case. In other words, Fig. 4 shows an example of a macrocell corrosion experiment on a steel surface caused by local variations in the rust layer formed on the steel surface, heterogeneous soil, moisture differences, etc. As the temperature increases, the corrosion current density increases. In order to counteract such a large current and prevent corrosion, a large corrosion protection current greater than the corrosion current density is required. Therefore, when preventing corrosion on the external surface of an annular board, etc. of a storage tank for high-temperature materials such as asphalt whose external surface reaches approximately 100°C, conventional cathodic protection methods inevitably result in insufficient current. To compensate, a device with an extremely large current capacity that takes into account the current distributed in areas other than the annular plate is required, which ultimately increases the cost and complexity of the device.

It was unrealistic in various aspects, such as interference with other metals.

"Means for Solving the Problems" The present invention has been made in view of the above circumstances, and its gist is that in the foundation directly below the external surface of the bottom annular board, etc. of an outdoor tank for storing high-temperature substances such as asphalt, A plurality of energizing electrodes of an externally powered cathodic protection device are installed close to the annular plate, etc., and an anticorrosion current is supplied from the electrodes to the outer surface of the annular plate through the foundation sand, etc. This is achieved by preventing as much as possible the dispersion of the anti-oxidants into other areas, and by effectively flowing into the annular plates, etc., to achieve effective corrosion protection.

"Example" This will be explained in detail below based on the drawings.

Figures 1a and b are plan and side views showing the structure of the present invention. A plurality of durable electrodes 5 for corrosion protection are properly distributed horizontally in the circumferential direction, and the lead wires 8 of each electrode are drawn out of the tank and connected to the O#A terminal 10 of the DC power supply device 9. Further, the O terminal 11 of the power supply device is connected to a ground terminal 12 on the tank body by an electric wire 13.

The installation position of each electrode is
The width of the plate, etc. is in the range of 300 to 700 mm below the center of the sow, and the standard spacing between each electrode is approximately 2 m, but there may be differences in the temperature conditions, load conditions, basic corrosion environment, etc. of the material stored in the tank. The numbers may differ slightly depending on the situation.

In some cases, a conductive sheet or hack fill may be placed under the annular plate to make the distribution of the anticorrosive current more uniform and stable.

After completing the wiring, start applying the anti-corrosion current, and check the current generated by each electrode using the reference electrode 14 installed at the bottom of the annular plate to ensure that the anti-corrosive current on the entire outer surface of the annular plate is at an appropriate value. It is adjusted by output voltage tap conversion of the DC power supply device 9.

In addition, if the corrosion protection potential in the circumferential direction of the annular plate etc. varies depending on the location, insert a resistor etc. between each electrode and the power supply terminal ○ terminal to adjust the output current of each electrode and eliminate the variation. to eliminate it.

"Effects of the Invention" According to the method of the present invention, the annual
Since the electrode is placed under the plate, etc., most of the anticorrosion current generated from the electrode flows into the adjacent annular plate, etc., and the current flows to the distant bottom plate, ground rod, and piping attached to the tank. The distribution of is extremely small. Therefore, the electric capacity of the device may be such that a slight margin is added to the amount of current required for the annular plate, etc., and corrosion protection can be carried out extremely effectively and economically.

The chart shown in FIG. 5 shows the results of applying external power source cathodic protection to annular plates and the like.

Case I is the conventional construction method in which the electrode is installed on the outer periphery of the tank;
Case ■ is a construction method in which the electrode according to the present invention is installed under an annular plate, etc. From the comparison of these two methods, case
It can be seen that the corrosion protection of plates, etc. has been sufficiently achieved.

Note that the output current of each electrode can be adjusted as necessary.

The method of the present invention can also be applied to the external cathodic corrosion protection of the outer surface of underground steel structures in extremely low ground conditions.

[Brief explanation of the drawing]

Figures 1a and b are plan and side views showing the configuration of the present invention, Figures 2a and b, and Figures 3a and b are plane and side views of the conventional method, and Figure 4 is a macro cell on a steel surface. Diagrams showing examples of corrosion experiments,
FIG. 5 is a chart comparing the effects of the conventional method and the method of the present invention. Explanation of symbols ■... High-temperature substance storage tank such as asphalt, 2...
Ani 7. outer surface of color plate, etc., 3... bottom plate, 4... galvanic anode, 5... energizing electrode, 6... anti-corrosion current, 7...
Basic, 8... Electrode lead wire and O side wiring, 9... DC power supply, lO... ■ terminal, 11... O terminal, 1
2...tank ground terminal, 13...O side wiring, 14
. . . Reference electrode, 15 . . . Tank outer periphery. 29/m 0゜1ras! 2-line 2-so-so-1

Claims (1)

[Claims] A plurality of electrodes for energizing a cathodic protection device using an external power supply method are installed in the foundation immediately below the outer surface of the annular board, etc. on the bottom of an outdoor tank for storage of high-temperature substances such as asphalt, close to the annular board, etc., and the foundation sand, etc. is passed through the electrodes to the annular board, etc. A method for preventing corrosion of the outer surface of the bottom plate of an outdoor tank for storing high-temperature substances such as asphalt, characterized by supplying an anticorrosion current to the outer surface.