JPS609244Y2 - Corrosion protection device for cylindrical tanks - Google Patents

Description

[Detailed description of the invention] The present invention is an anticorrosion device for preventing corrosion during filtration tests carried out during the construction of cylindrical tanks for storing petroleum, etc. This invention relates to a corrosion protection device for a cylindrical tank that allows easy attachment and removal of electrodes.

During the water filling method, which is one of the tank construction methods, and during water filling tests after construction, pitting corrosion due to ice buildup that occurs in tank welds is considered a welding defect, so corrosion prevention measures are extremely important when filling with water. For this reason, tap water has traditionally been used as water for filling water.

■Use industrial water or fresh water from lakes, swamps, etc.

■Use industrial water or seawater with anticorrosive added.

■Various measures have been taken, such as applying anti-corrosion paint to welded areas.

However, the above-mentioned countermeasure (2) cannot completely prevent the occurrence of pitting corrosion, and is also subject to restrictions on the availability of water.

■ There is a risk of pitting corrosion due to various impurities and bacteria contained in water, and ■ is accompanied by the trouble of constantly controlling the concentration of the anticorrosion agent, and the reliability of the anticorrosion effect is difficult, and furthermore, the use of If the wastewater is treated incorrectly afterwards, it may cause a public outbreak.

■If the anti-corrosive coating is damaged by construction jigs, etc., localized pitting corrosion will occur in the affected area.On the other hand, if a hard coating that is difficult to break is applied, it will take time to remove the coating after applying water. Any part of the paint film that erodes and remains is considered a welding defect, and care must be taken to ventilate the tank during painting work.In general, no measure can completely prevent the occurrence of pitting corrosion.

In addition, a large amount of iron rust occurs during water filling, and a treatment tank is required to precipitate the iron rust when draining water.

Incidentally, sacrificial electrodes made mainly of zinc or the like are installed on ships or offshore structures for corrosion protection, but in all of these cases, individual sacrificial anodes are directly welded or bolted to the ship's hull or structure. It is used permanently until the end of its life, and it is extremely inconvenient to easily install and remove it for filling a tank with water.

The present invention eliminates the above-mentioned problems and shortcomings, completely prevents the occurrence of pitting corrosion when filling a tank with water, does not have any restrictions on the availability of water for filling the tank, and can also be used with wastewater treatment equipment after filling with water. This was done in order to provide a corrosion protection device for a cylindrical tank that eliminates the need for corrosion protection electrodes and has various advantages such as the ability to easily attach and remove corrosion protection electrodes. A plurality of sets of sacrificial electrode units that can be connected to each other are provided, and each sacrificial anode unit is arranged at an appropriate height on the bottom plate of the tank so as to form an open loop along concentric circles spaced apart at approximately equal intervals on the bottom plate of the tank. By connecting both ends of each sacrificial electrode unit to the inner surface of the tank, a complete anti-corrosion effect can be achieved, and the electrodes can be easily attached and removed when the tank is filled with water. Moreover, special consideration has been taken for wastewater treatment. This relates to a pollution-free corrosion protection device for cylindrical tanks that is not required.

Embodiments of the present invention will be described below based on the drawings.

1 to 3 show a first embodiment of the present invention, in which reference numeral 1 is a cone roof tank, 2 is a bottom plate, and 3 is a side plate. A plurality of sets of sacrificial anode units 5 are formed by connecting a plurality of sacrificial anodes 4 in series at a height h, and each set of sacrificial anodes 4 is connected in series.
are arranged on the bottom plate 2 so as to form an open loop along concentric circles drawn at approximately equal intervals around the center a of the bottom plate.

Seawater is used as the dipping water. As the sacrificial anodes 4 (hereinafter referred to as anodes), commercially available rod-shaped ones with a length of about 1rrL are used, and each anode 4 is made of a simple metal such as zinc or aluminum as the main material. CV of thickness
The anodes 4 located at both ends of the open loop of each sacrificial anode unit 5 (hereinafter referred to as unit) are connected to each other via a cord 6 (vinyl coated wire) and a crimp terminal (not shown).
Tighten the electrode mounting plate 7 temporarily attached to the bottom plate 2 using nuts 8.

In addition, both ends of each anode 4 are covered with a non-conductive material approximately 15 cm square.
It is supported on the bottom plate 2 by support legs 9 made of vinyl chloride, for example.

The number of anodes 4 constituting the unit 5 is usually 3 to 4 for the innermost one and about 10 for the outermost one.
The total number of anodes 4 is determined based on the fact that when the tank is filled with water, the potential of the material that makes up the tank, that is, iron, does not exceed the lowest corrosion potential.

The method for determining the total number of anodes 4 required will be described below.

The graft resistance R of the anode is determined by the following formula.

here ρ : Specific resistance of seawater (generally 25Ωcm) L: Anode length c77 D: Anode diameter (1) shows.

The current generated from the anode is ΔE, which is the effective potential difference between the anode and iron.
(V), then the total amount of required corrosion protection current I can be determined by the following formula.

■A = SXI, Formula (3) where S: Grafting area on the inner surface of the tank (y4) ■N: Required corrosion protection current density for iron (mA/?y1''), IN is 80mA for steel plate with mill scale /
It is appropriate to set it to d.

This data was obtained by applying various anti-corrosion current densities to a steel plate with mill scale and immersing it in seawater for 20 days to investigate the minimum anti-corrosion potential that does not cause iron rust.The experimental results are shown in Figure 6. Shown below.

Figure 6 shows the initial corrosion protection current density and potential changes during zinc corrosion protection, with time on the horizontal axis and current density (on the upper half of the vertical axis).
The lower half of the vertical axis shows the potential of each part measured using a saturated Amagi electrode (generally abbreviated as SCE) as a reference potential. The value of d) is shown below.

For steel plates coated with Zr-rich primer, I
, = 10 mA/d.

The number of anodes is determined by the following equation from equations (2) and (3).

Therefore, the total number of anodes 4 can be determined by knowing the grafted area of the tank when filled with water.

After all the units 5 are mounted on the bottom plate 2 according to the above-mentioned procedure, the anticorrosion effect is confirmed by filling with water.

To confirm, use the reference electrode (SCE) from the top of the tank.
, and measure the potential of the bottom plate 2 and side plate 3 just below the water surface using a high-resistance DC voltmeter, and confirm that the potential of each part is below the corrosion potential of iron -770 mV (vsSCE).

Figure 7 shows the tank potential (vsS) in the case of zinc corrosion protection.
CE) and an example of changes in water level.

As mentioned above, since a plurality of units with necessary and sufficient capacity are arranged concentrically on the bottom plate, calculation of the potential distribution is easy and the distribution is uniform, so that the anti-corrosion effect is complete.

Further, since the anode and the bottom plate, which is the cathode, are arranged with a certain distance between them, the entire outer circumferential surface of the anode can be effectively utilized.

All you need to do is combine multiple rod-shaped electrodes with a total length of approximately 1 m into a set of units, and ground both ends of each unit to the bottom plate. Also, between each electrode, tighten a nut using a CV cord and crimp terminal. Since it has a structure that allows connection and removal, the electrodes can be attached and removed from the tank bottom plate in a short time, and after filling with water, they can be easily reused in other tanks.

Further, the deposits on the welded portion of the tank after filling with water can be removed in a short time by simply puffing with an electric brush.

Furthermore, since the anode is attached only to the bottom plate, all the corrosion products of the anode settle on the tank bottom plate.

Therefore, most of the water is clean and can be drained directly.

In addition, when a zinc electrode is used, the amount of zinc dissolved in water-filled water is approximately 1.5 my/l in experiments, and this value is below the 5 mg/l stipulated in the 1st wastewater standard. Therefore, the water can be drained as it is, making drainage extremely easy.

A second embodiment is shown in FIGS. 4 and 5.

This example shows application to a floating roof tank 10, and it is necessary to consider corrosion protection of the floating roof 11 and roof drain 12 in addition to the bottom plate 2.

In this case, one end of the unit 5' corresponding to the grafting area of the floating roof 11 is connected to the floating roof 11 using the CV cord 6', and the core metal of the anode 4 is connected to the wire 13 for the roof drain 12. Connect at.

The structure and installation procedure of the unit are the same as in the first embodiment.

Note that the present invention is not limited to the above-described embodiments, and it goes without saying that various changes may be made without departing from the gist of the present invention.

Since the anticorrosion device for a cylindrical tank of the present invention has the above-described configuration, it exhibits the following excellent effects.

(1) Since the necessary and sufficient capacity of the sacrificial anode is uniformly distributed and arranged on the tank bottom plate, the tank welds and the tank inner surface can be completely protected from corrosion.

(1) Since a plurality of sacrificial anodes are removably connected and assembled into a unit, and both ends of each unit are connected to the inner surface of the tank, attachment and detachment of the sacrificial anode is simple and easy.

Qii) Unlike conventional methods, corrosion inhibitors are not used and iron rust does not occur on the inner surface of the tank, and the corrosion products of the sacrificial electrode settle on the bottom plate, so most of the water filled with water is clean. , there is no risk of wastewater pollution, and there is no need to install wastewater treatment equipment.

(V) For the same reason as in paragraph (1), there are no restrictions on the use of seawater for water filling and the availability of water for water filling.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the layout of the corrosion protection device according to the embodiment of the present invention, Fig. 2 is a cutaway plan view taken from the direction ■-■ in Fig. FIG. 4 is an enlarged side view showing a part of the sacrificial electrode unit.
Explanatory diagram showing the layout of the corrosion protection device according to the embodiment, No. 5
The figure is a cutaway plan view from the ■-■ direction in Figure 4, and the
The figure is a chart showing changes in the initial corrosion protection current density and potential of zinc electrode corrosion protection on a steel plate with a mill scale, and FIG. 7 is a chart showing changes in the average potential at the bottom of a tank subjected to zinc corrosion protection. In the figure, 2 is a bottom plate, 4 is a sacrificial anode, 5 and 5' are sacrificial electrode units, and 6 and 6' are CV cords.

Claims (1)

[Scope of utility model registration request] A plurality of sets of sacrificial electrode units are provided in which a plurality of rod-shaped sacrificial anodes are removably connected in series, and each sacrificial anode unit is formed into an open loop along concentric circles spaced at approximately equal intervals on the tank bottom plate. A corrosion protection device for a cylindrical tank, characterized in that the sacrificial electrode units are arranged at an appropriate height on the bottom plate, and both ends of each sacrificial electrode unit are connected to the inner surface of the tank.