JPH0548310B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for preventing corrosion of underwater steel structures using an underwater paint or an underwater curing putty. The present invention relates to pretreatment performed when anticorrosive construction is performed using putty. [Prior art] In recent years, steel structures such as oil drilling rigs or oil stockpile purging, offshore plants, ships, etc. accompanying offshore development,
The number of structures and constructions such as steel sheet piles and other steel structures used for seawall construction, piers of huge bridges built on the sea, and underwater structures at seaports continues to increase. It is almost impossible to move steel structures from the installation area for maintenance purposes. Therefore, problems such as cleaning and maintenance of anticorrosion coatings in the underwater parts or splash zones of these marine steel structures arise, and the need for maintenance at sea has become a major issue. Therefore, it would be of great benefit if there were a coating method that could be applied under water as efficiently as on land, and that could provide a coating film with excellent corrosion resistance. Conventionally, the method of painting submerged parts and splash zone parts of ships and underwater structures is to use a type 2 scouring method, which involves simply scraping away floating rust, etc. as a surface treatment, and then spraying a high-speed stream of water to further clean the surface. There are methods such as mixing sand in a high-speed stream of water and spraying it on the steel surface to remove rust and scale even better. Alternatively, it is common practice to apply putty using a brush, spatula, or the like. However, when applying underwater curable paint or putty with a brush or spatula after applying the above-mentioned surface treatment and adjusting the steel surface, the submerged parts of underwater structures, especially the splash zone, are exposed to a severe corrosive environment. Therefore, it is virtually impossible to paint. Moreover, even if it can be painted, the coating efficiency will be extremely poor, so it is almost useless. [Problems to be Solved by the Invention] The problems to be solved by the present invention are to solve the above-mentioned difficulties of the conventional underwater coating method. It is an object of the present invention to develop a coating method that can perform coating with considerable coating efficiency even in submerged water or in a splash zone. [Means for Solving] The above problem is solved when painting objects such as ships and underwater structures with underwater curing paint, preferably by spraying a high-speed water jet onto the surface of the object or by spraying sand with a high-speed water jet. During the period from when conventional pretreatment such as spraying is applied to when the underwater curing paint or underwater curing putty is applied to the object to be coated, the surface of the object to be coated is kept in a substantially wet state, and cathodic protection treatment is applied. This is achieved by applying. [Structure and operation of the invention] In the present invention, before painting the object with an underwater curing paint or an underwater curing putty, the object is cleaned or the surface of the object is brought into a substantially wet state. After cleaning while performing electrolytic protection treatment on the surface, electrolytic protection is performed in a wet state until an underwater curing paint or underwater curing putty is applied. The "wet state" used in the present invention includes not only a state in which the object to be coated is in water, but also a state in which water is substantially present on the surface of the object to be coated, such as spraying water. It can also be applied to water-retentive cloth, paper, etc. by passing water through a pipe with countless holes and applying countless water gun-like streams of water to the surface of the object to be coated. A condition in which the surface of the object to be coated becomes substantially wet, including a state that can be achieved by applying the object to the object in a wet state or by combining the above methods. say. Furthermore, an important point in the present invention is to uniformly moisten the entire coating area on the surface of the object to be coated, and if the object itself is not submerged in water, to apply a wet film of water on the water surface. It is to make it continuous. If this wet water film is not connected to the water surface, the effect of the cathodic protection treatment, which is important in the present invention, will be difficult to fully exhibit, and the effects of the present invention may not be fully expected. As is clear from the above, the "underwater steel structure" of the present invention refers not only to those existing underwater, but also to steel structures existing in the splash zone, on water, and on land. The cathodic protection treatment of the present invention refers to applying a cathodic protection method to a steel structure and applying a corrosion protection current to the steel structure. The cathodic protection method can be applied with either an external power supply method or a galvanic anode method. The external power supply method refers to a method in which a counter electrode is connected to the positive electrode of an external DC power source, and a steel structure is connected to the negative electrode, and a corrosion protection current is flowed from the counter electrode toward the steel structure. Lead-silver alloy electrodes, magnetic iron oxide electrodes, silicon iron electrodes, platinum electrodes, carbon electrodes, etc. are used. The galvanic anode method uses aluminum, magnesium,
This is a method in which an anode made of zinc, aluminum alloy, magnesium alloy, zinc alloy, etc. is connected to a steel structure, and the current generated by the potential difference between the two metals is used as a corrosion protection current. The anticorrosion current density is generally ^about 100 mA/m2 as a standard, and is used in the range of ^about 50 to 500 mA/m2. In the present invention, the period of wet treatment and cathodic protection treatment is carried out, but both are substantially submerged from the point of performing known pretreatment such as high-speed water jets or spraying high-speed water jets containing sand onto the surface of the object to be coated. Refers to the time of application of hardening paint. Of course, the same effect as the present invention can be obtained even if the electrolytic protection treatment is continued after the coating operation or if the electrolytic protection treatment is stopped immediately before the coating operation and is not performed thereafter. In the present invention, by performing the above electrolytic corrosion treatment, it is possible to apply an underwater curable paint or an underwater curable putty extremely easily. The reason for this is assumed to be as follows. That is, when a steel material to be coated is treated according to the present invention, the surface of the steel material to be coated, which has been cleaned by a high-speed water stream or a high-speed water stream containing sand, is in a wet state, so that due to the action of cathodic protection, an underwater-curable paint or an underwater It is kept clean during the period until the hardening putty is applied, and the steel is kept clean due to seawater, which would form on the surface of the workpiece if no cathodic protection treatment was applied. Since inhibitory substances are suppressed by the cathodic protection treatment, the underwater curing paint reliably adheres to the surface of the object to be coated. Therefore, it is presumed that even in the splash zone of the water surface where corrosion is severe, the paint will reliably adhere to the surface of the object to be coated, making it possible to easily apply the coating by ordinary means. As the underwater curable paint or underwater curable putty used in the present invention, any of those that have been conventionally used in this field can be used.For example, epoxy resin as the main ingredient, polyamide resin, modified aromatic Underwater-curable paints or putty that use hardening agents such as group polyamines, modified aliphatic polyamines, heterocyclic polyamines, alicyclic polyamines, etc., and underwater-curable paints or underwater-curable putties that use unsaturated polyester resin as a base material. A typical example is putty. Further, as a means for applying this paint or putty, the usual means for painting on land can be widely adopted, and typical examples include means for applying with a spatula or a lever. The effects of the present invention will be illustrated in more detail with reference to Examples below. Example 1 and Comparative Examples 1 to 3 Shot blasted 9mm x 300mm x 300
Immediately after immersing a mm steel plate in 3% saline solution, lift it out of the water, expose 2/3 of the total surface area above the water surface, and immediately cover the steel surface above the water surface evenly with a dampened case. Soak in 3% saline solution. At the same time, an Al alloy anode is connected to this steel plate,
Leave it for one day. Peel off the gauze from this steel plate and use a commercially available brush to apply the underwater curing paint to a dry film thickness of approximately 1.
The above water area was painted in a wet state to a thickness of mm. The underwater curable paint used here is a commonly used epoxy resin based underwater curable paint, and its composition is shown in Table 1. Further, the anticorrosion current during immersion in 3% saline solution in Example 1 was 400 mA/m ² .

[Table] Various physical properties were measured for the obtained coated objects. The results are shown in Table 2 below. The Examples and Comparative Examples shown in Table 2 were visually observed for coating workability, adhesion after a 6-month immersion test in 3% saline, and the presence or absence of rust. <Painting workability> The standards for painting workability are shown below. ○...The paint adheres to the steel surface just by touching it, allowing good brush movement. △...It will stick if you rub it a few times, but the brush handling is very poor. ×...Almost no adhesion even if rubbed several times. <Adhesion> After being immersed in 3% saline for 6 months, the sample was taken out and the tensile adhesive strength was measured using an adhesion tester (manufactured by Elcometer). In addition, visually observe the coating film cohesive failure rate and the presence or absence of rust in the adhesion measurement area. The above results are shown in Table 2.

[Table] Comparative Example 1 is the same as Example 1 except that the water-wetted gauze and the Al alloy anode were not used (other conditions were the same as Example 1). Comparative Example 2 is a case where the Al alloy anode was not used in Example 1 (the other conditions were the same as Example 1). Comparative Example 3 is the same as Example 1 except that the gauze soaked in water was not used (the rest was the same as Example 1). Example 2 and Comparative Example 4 Immediately after shot blasting, 1%
9mm x 300mm connected with Al alloy anode soaked for days
× 300mm steel plate (current density is 100mA/m ² ) using a commercially available brush to apply underwater curing paint to a dry film thickness of approximately 1.
It was painted underwater to a thickness of mm. The underwater curable paint used here was the same as in Example 1.
Various physical properties of the coated product were measured in the same manner as in Example 1. The results are shown in Table 3.

[Table] However, in Comparative Example 4, the Al alloy anode was not connected and the other processes were the same as in Example 2. Example 3 and Comparative Example 5 Painting was carried out in the same manner as in Example 1 and Comparative Example 2 using the compositions shown in Table 4 below. The results are shown in Table 5.

【table】

[Table] Example 4 and Comparative Example 6 Using the compositions shown in Table 6 below, a current density of 50
Everything is the same as Example 2 except that mA/m ² and dry film thickness are 3 mm.
And painting was carried out in the same manner as in Comparative Example 4. The results are shown in Table 7.

【table】

【table】

Claims (1)

[Claims] 1. When applying an anti-corrosion coating with an underwater curing paint or an underwater curing putty after cleaning the steel surface of an underwater steel structure, the feature is that electrolytic protection treatment is applied under humidity during the anti-corrosion coating after cleaning. Corrosion prevention method for steel structures underwater.