Method for cleaning steel structure

Abstract

To provide a method for cleaning a steel structure in which corrosion or the like present on a surface layer of a steel structure including a pitting-corrosion part can be removed more securely, and whose treatment is relatively easy.SOLUTION: A method for cleaning corrosion and / or corrosive component present on a surface layer of a steel structure comprises: a member installing step of installing a cleaning member surrounding and / or coating a part to be cleaned on which corrosion and / or corrosive component are present; a cleaning liquid contacting step including a treatment of supplying cleaning liquid into the cleaning member to bring the part to be cleaned in contact with the cleaning liquid; and a cleaning liquid removal step including a treatment of removing the contacted cleaning liquid together with the corrosion and / or corrosive component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for cleaning a steel structure. [Background technology]

[0002] Traditionally, when the entire or partial section of an existing steel structure is severely deteriorated, it has been repainted, but there is usually a lot of rust on the steel surface, and simply repainting such a surface will gradually cause the paint film to peel and not provide long-term protection. For this reason, before repainting, it was necessary to carry out physical rust removal treatment (surface preparation) such as blasting with type 3 scraping or more, and then paint the surface. However, this type of physical surface preparation generates a lot of dust and noise during the work, which creates a very poor working environment and poor work efficiency. Also, even if type 2 or type 3 scraping is carried out on the steel surface, it is difficult to remove rust from recesses and narrow parts of the steel structure, and Cl is present at the interface between the rust layer and the steel base in those areas. - or SO4 2- Therefore, even if the area is repainted, the corrosion resistance of the area is significantly reduced.

[0003] In order to solve such problems, several methods have been proposed for removing rust and corrosive components remaining on steel materials. For example, Patent Document 1 discloses a method in which a viscous aqueous solution containing a film-forming resin is applied to the surface of a steel structure, and then dried to form a film, which then absorbs chloride ions and removes them.

[0004] Furthermore, Patent Document 2 discloses a method for removing rust and anions from the surface of steel material by applying a rust decomposer to the surface of the steel material as a surface preparation for the steel material, then applying an anion adsorbent thereto, and finally removing the rust decomposer and anion adsorbent.

[0005] Furthermore, Patent Document 3 discloses a method in which an aqueous wetting agent containing water and a water-soluble polymer is applied to chlorides present on the surface of a steel structure after base preparation, thereby dissolving chloride ions generated from the chlorides into the aqueous wetting agent and removing the chloride ions.

[0006] Furthermore, Patent Document 4 and Non-Patent Document 1 disclose a method of efficiently removing rust by performing an abrasive water jet treatment on a steel material having rust on its surface. The abrasive water jet treatment is an operation in which water and an abrasive are sprayed at high speed and pressure through a small opening onto an object and collided with it, and is considered to be a method capable of efficiently removing corrosive substances such as rust and salt present not only on the surface but also inside the object. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2022-95558 [Patent Document 2] Patent No. 6727019 [Patent Document 3] JP 2023-25447 A [Patent Document 4] International Publication No. WO2022 / 176278 [Patent Document 5] JP 2013-19163 A [Non-patent literature]

[0008] [Non-Patent Document 1] Weathering steel material: Extremely removes abnormal rust and salt "AWT method" in final stages of practical use, Bridge Communications (Bridge Communications Co., Ltd.), October 1, 2022 Summary of the Invention [Problem to be solved by the invention]

[0009] The methods disclosed in Patent Documents 1 to 3 are all said to be effective in removing rust, chlorides, salts, etc. present on the surface of the target steel material or steel structure, but it is difficult to completely remove corrosive components such as rust and salts contained in rust present in deep corroded areas such as pitting corrosion using the methods described in these documents. This is because simply applying a liquid or a resin containing a liquid does not allow the liquid to penetrate into the pitting corrosion or react with the rust sufficiently due to the effects of drying and the limit of the amount of application. Therefore, rust and salts remain in the pitting corrosion, which may lead to early rusting.

[0010] In addition, the methods disclosed in Patent Document 4 and Non-Patent Document 1 are considered to be capable of removing almost all rust, salt, and the like, but there are problems with the scattering of the sprayed water and abrasive material into the surrounding area and with post-spray treatment, and therefore their application is limited to locations where sufficient measures to prevent scattering and treatment of waste liquid can be taken.

[0011] In view of the problems with the conventional technology, the inventors of the present application have conducted intensive research into both the removability of corrosive components such as rust and salt (hereinafter sometimes simply referred to as "rust, etc.") remaining in the pitted corrosion parts and the ease of processing (for example, measures to prevent scattering, processing of waste liquid, etc.). As a result, they have found that performing the following steps is particularly effective in order to ensure that the cleaning liquid can be sufficiently supplied to the pitted corrosion parts, that the cleaning liquid can be in contact with the rust, etc. for a certain period of time, and that the cleaning liquid can be removed together with the rust, etc.

[0012] In other words, by comprising at least the steps of surrounding and / or covering the part of the steel structure to be cleaned with a cleaning component, supplying a cleaning liquid into the inside of this cleaning component to bring it into contact with the part to be cleaned, and dissolving rust and the like in this cleaning liquid and removing it together with the cleaning liquid, it has been discovered that the cleaning liquid can be sufficiently supplied to and brought into contact with the pitted corrosion parts, so that remaining rust and the like can be more reliably removed, and that this is also effective in terms of ease of processing, and thus the present invention has been completed.

[0013] Therefore, an object of the present invention is to provide a cleaning method for steel structures that can more reliably remove rust and the like present on the surface of a steel structure, including pitted portions, and that is relatively easy to process.

[0014] In addition, a method has been proposed for repairing corrosion that has occurred in a portion of a steel member of a structure that is in contact with concrete, which involves injecting a neutral rust remover between the steel member and the concrete to bring the rust remover into contact with the steel member, and removing the rust remover together with the rust (Patent Document 5). According to one example of Patent Document 5, when the concrete is a lining concrete, a method is taught in which, in order to allow the rust remover to penetrate between the lining concrete and a steel column, a wall is formed at the top end of the lining concrete to surround the column, and the rust remover is injected inside the wall to form a rust remover tank. However, the method of Patent Document 5 only includes the surface that is in contact with the concrete as an application area, and the rust remover used is limited to a neutral one, and is not suitable for one that penetrates concrete. Therefore, even if the method of Patent Document 5 is taken into consideration, it is difficult to use it as a method for more reliably washing and removing rust and corrosive components for all steel members. [Means for solving the problem]

[0015] That is, the gist of the present invention is as follows. (1) A method for cleaning rust and / or corrosive components present on the surface of a steel structure, comprising the steps of: a member installation step of installing a cleaning member that surrounds and / or covers the part to be cleaned in which rust and / or corrosive components are present; a cleaning liquid contacting step including a process of supplying a cleaning liquid to the inside of the cleaning member and bringing the cleaning liquid into contact with the part to be cleaned; and a cleaning liquid removal step including a process of removing the contacted cleaning liquid together with rust and / or corrosive components. (2) The cleaning method for steel structures described in (1) is characterized in that the cleaning liquid contact step includes a holding treatment for keeping the cleaning liquid in contact with the part to be cleaned, and the holding treatment and the subsequent removal treatment in the cleaning liquid removal step constitute one cycle, which is repeated one or more times. (3) A method for cleaning a steel structure according to (1), characterized in that the contacting treatment of the cleaning liquid with the part to be cleaned in the cleaning liquid contacting step and the removal treatment of the cleaning liquid in the cleaning liquid removal step are carried out in a single liquid passing process. (4) The cleaning member has a supply part for supplying a cleaning liquid to the inside and a discharge part for discharging the supplied cleaning liquid, The method for cleaning a steel structure according to (3), characterized in that the series of liquid passing treatments is carried out by supplying the cleaning liquid from the supply section and discharging the cleaning liquid from the discharge section. (5) The method for cleaning steel structures according to (3), further comprising a circulation step of circulating the discharged cleaning liquid and subjecting it to the cleaning liquid contact step again. (6) The method for cleaning a steel structure according to any one of (1) to (3), wherein the cleaning liquid contains a cleaning promoter made of a rust remover and / or an anion adsorbent. (7) The method for cleaning a steel structure according to any one of (1) to (3), further comprising a rough scraping step of roughly scraping a surface of the steel structure prior to the member installation step. (8) The method for cleaning a steel structure according to any one of (1) to (3), characterized in that the cleaning member is a sealed cleaning member that seals the part to be cleaned. (9) A method for cleaning a steel structure according to any one of (1) to (3), characterized in that it further comprises a cleaning liquid cleaning step for removing rust and / or corrosive components from the cleaning liquid removed in the cleaning liquid removal step, and the cleaning liquid after the cleaning liquid cleaning step is subjected again to a cleaning liquid contact step. (10) The method for cleaning a steel structure according to any one of (1) to (3), characterized in that the cleaning liquid contact step includes a cleaning promotion step of performing at least one treatment selected from vibration, ultrasonic waves, stirring, light irradiation, and heating. (11) A method for cleaning a steel structure according to any one of (1) to (3), characterized in that after the cleaning liquid removal step, it comprises a post-treatment step of subjecting the surface of the steel structure to at least one post-treatment selected from cleaning treatment, drying treatment and blasting treatment. Effect of the Invention

[0016] According to the method of the present invention, rust and corrosive components present on the surface of a steel structure, including pitted parts, can be removed more reliably. In addition, the method of the present invention is relatively easy to handle, including measures to prevent scattering and waste liquid treatment. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the cleaning method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The following describes the details of the embodiments of the present invention, but the scope of the present invention is not limited to the following embodiments, and various modifications and combinations of the following embodiments are possible without departing from the gist of the present invention.

[0019] An example of the method for cleaning a steel structure according to the present invention is shown simply in Fig. 1. However, the embodiment of the present invention is not limited to the example shown in Fig. 1. The present invention is a method for cleaning rust and / or corrosive components present on the surface of a steel structure (reference numeral 1. Hereinafter, only the numeral may be used. The same applies to other reference numerals), and includes a member installation step of installing a cleaning member 3 that surrounds and / or covers a part to be cleaned 2 where rust and / or corrosive components are present. The method also includes a cleaning liquid contact step including a process of supplying a cleaning liquid 4 to the inside of the cleaning member 3 to bring the cleaning liquid into contact with the part to be cleaned 2. The method further includes a cleaning liquid removal step including a process of removing the contacted cleaning liquid together with the rust and / or corrosive components. Here, reference numeral 5 in FIG. 1 indicates the inlet direction of the cleaning liquid, and reference numeral 6 indicates the outlet direction of the cleaning liquid. The inlet and outlet directions are not limited to this example, and may be any configuration that allows the liquid to pass through, as described below.

[0020] <Steel structures> In the present invention, the steel structure to be cleaned includes steel materials as the main base material, processed into plates, bars, pipes, etc., and structures, and examples thereof include, but are not limited to, roads, steel towers for power transmission and communication, bridges, various plants, etc. Also, metal elements other than iron may be included.

[0021] The steel structure to be cleaned has rust and / or corrosive components on its surface. The term "surface" is not limited to, but includes not only the surface of the steel structure but also a certain range from the surface in the depth direction, including the above-mentioned pitted corrosion part. In other words, in the present invention, the rust and corrosive components contained in the pitted corrosion part of the steel structure (part to be cleaned) are also included. "Rust" refers to corrosion products generated by corrosion of the steel structure, and includes oxides derived from the constituent elements of the steel structure, usually iron oxides (e.g., red rust, black rust, etc.). The term "corrosive components" is not limited to, but refers to components that corrode steel members, and includes corrosion factors such as water, oxygen, chloride ions, and sulfate ions.

[0022] In the present invention, the part of the surface layer of the steel structure that has rust or corrosive components is called the part to be cleaned, and it is necessary to bring the cleaning liquid into contact with at least the part to be cleaned. The part to be cleaned may be a part or the entire surface of the steel structure, depending on the condition of the steel structure to be cleaned.

[0023] In addition, for steel structures, the surface layer may be roughly scraped as a pretreatment. That is, in the present invention, a rough scraping process for roughly scraping the surface layer of the steel structure may be provided before the member installation process described later. By rough scraping the surface layer of the steel structure in advance, relatively large rust and corrosive components present on the surface layer of the steel structure can be reduced in advance, which is preferable because it improves the efficiency of cleaning using a cleaning liquid. Here, the "rough scraping" is not limited, but may be, for example, surface preparation such as cleaning or four-type scraping (removing powdered matter, dirt, etc. using a combination of power tools and hand tools). Note that in the present invention, it is not limited to rough scraping, and normal pretreatment (for example, diamond tool treatment, hammer scraping, high-pressure water washing, etc.) performed when cleaning steel members may be performed, and it is not limited to four-type scraping, and pretreatment using one to three types of scraping is not excluded.

[0024] <Component installation process> In the present invention, as described above, it is necessary to carry out the cleaning process by bringing the cleaning liquid into contact with the part to be cleaned of the steel structure having rust and / or corrosive components on the surface. Here, in general, if the cleaning liquid is simply supplied or applied to the part to be cleaned, in some cases the cleaning liquid may flow out of the part to be cleaned quickly, and the cleaning liquid may not remain in the part to be cleaned, and sufficient cleaning may not be performed. In addition, if the cleaning liquid is exposed to the outside, it may scatter or volatilize during the process, which may reduce the effect of using the cleaning liquid. Therefore, in the present invention, for example, a cleaning member that surrounds and / or covers the part to be cleaned, as shown by reference number 3 in FIG. 1, is installed (member installation process). By installing such a cleaning member that surrounds and / or covers the part to be cleaned and supplying the cleaning liquid into the space formed inside it, it is possible to prevent the cleaning liquid from flowing out quickly, scattering, volatilizing, etc., and it becomes possible to effectively keep the cleaning liquid in the part to be cleaned for a certain period of time or for a long period of time. The method of supplying and contacting the cleaning liquid to the part to be cleaned will be described later.

[0025] Here, the cleaning member is not limited as long as it can at least surround and / or cover the part of the steel structure to be cleaned, and a suitable example is a cover such as that shown in Fig. 1. In Fig. 1, not only the part to be cleaned 2 but also the entire surface of the steel structure 1 is illustrated as being covered with the cleaning member 3, but the cleaning member may be one that covers the entire surface of the steel structure in this way, or one that extends from the back side or side side of the steel structure to the front side and covers it as a single unit, and as mentioned above, there is no limitation as long as it surrounds and / or covers at least the part to be cleaned.

[0026] "Encirclement" by the cleaning member means that at least the part to be cleaned is surrounded by the cleaning member, and does not necessarily have to cover the entire top or side. The cleaning member may be in a state where the entire steel structure is surrounded. In other words, the cleaning member is installed so that at least the part to be cleaned is surrounded, and the cleaning liquid is held inside the cleaning member up to the height of the installed cleaning member, so that the cleaning liquid comes into contact with and is held on the part to be cleaned. However, the contact and liquid-tightness of the surface where the cleaning member and the steel structure come into contact must be ensured so that the cleaning liquid does not flow out from the lower side or side side of the cleaning member. For example, when the cleaning member is installed on the surface of the steel structure, it is preferable that the lower part of the cleaning member and the upper surface (surface) of the steel structure are in close contact. On the other hand, when the cleaning member is installed so as to surround the side of the steel structure, it is preferable that the side of the cleaning member and the side of the steel structure are in close contact. In order to improve the adhesion between the cleaning member and the steel structure, it is preferable to use an auxiliary tool or implement that fills the gap between the two. An example of such a tool or implement is a resin sealant.

[0027] As for such a cleaning member and its embodiment by "enclosing", depending on the material, for example, an embodiment in which the part to be cleaned is surrounded by a relatively hard material (for example, a corrosion-resistant metal plate, a plastic molded body, or a composite material thereof, etc.) having a certain rigidity can be mentioned. Other materials can be used without restriction even if they do not have rigidity, so long as they can surround the part to be cleaned and hold the cleaning liquid in the part to be cleaned inside. Such other materials include, but are not limited to, for example, a corrosion-resistant metal foil, a resin sheet, a rubber sheet, a water-resistant cloth, a water-resistant paper, etc. It is preferable that the surface is covered with a material that is not corroded, dissolved, altered, or significantly reduced in rigidity by the cleaning liquid, and more preferably, the wall is made of a resin and / or rubber member.

[0028] In addition, "covering" by the cleaning member refers not only to the above-mentioned surrounding, but also to a state in which the upper side of the part to be cleaned is covered by the cleaning member, but it does not have to be sealed. In other words, as long as the cleaning liquid contacts and is retained on the part to be cleaned inside the "covering" and does not scatter or volatilize to the outside, it is not necessary for the part to be completely covered. In a more preferred embodiment, it is preferable to use a sealed cleaning member that seals the part to be cleaned with the cleaning member. By covering the part to be cleaned with a sealed cleaning member, a sealed space can be created inside, and the scattering and volatilization of the cleaning liquid can be more reliably suppressed. Furthermore, by using a sealed cleaning member, a relatively large amount of cleaning liquid can be supplied and retained in the sealed space generated between the cleaning member and the part to be cleaned, so that the contact efficiency between the cleaning liquid and the part to be cleaned is increased and the cleaning effect is also improved, which is preferable. There is no restriction on the degree to which the sealed space is created, and it can be appropriately adjusted taking into consideration the shape and size of the steel structure to be used and the shape and size of the sealed cleaning member to be used. In addition, the required level of sealed space can be determined in advance, taking into consideration the amount of rust and corrosive components present in the parts to be cleaned, including pitted corrosion parts, and the type and amount of cleaning liquid to be supplied thereto.

[0029] As for such a cleaning member and its embodiment by "covering", depending on the material, for example, an embodiment in which a relatively hard material with a certain rigidity (for example, a corrosion-resistant metal plate, a plastic molded body, or a composite material thereof, etc.) is used to cover the part to be cleaned like a lid can be mentioned. Other materials can be used without restriction even if they do not have rigidity, so long as they can cover the part to be cleaned and hold the cleaning liquid inside the part to be cleaned. Such other materials include, but are not limited to, for example, a corrosion-resistant metal foil, a resin sheet, a water-resistant cloth, a rubber sheet, etc. As with the above-mentioned "enclosure", it is preferable that the surface is covered with a material that is not corroded, dissolved, altered, or significantly reduced in rigidity by the cleaning liquid, and more preferably, it is a lid or sheet made of a resin and / or rubber member.

[0030] The cleaning member is preferably provided with a supply part for the cleaning liquid to supply the cleaning liquid to the inside thereof, and also with a discharge part for discharging the supplied cleaning liquid. There are no limitations on the embodiment of the supply part and the discharge part, but for example, as shown in Fig. 1, holes for supplying or discharging the cleaning liquid may be provided on the top or side of the cleaning member, and a supply pipe or a discharge pipe made of, for example, a hose or a tube may be connected to the holes to form the supply part and the discharge part. The shapes and installation positions of the supply part and the discharge part and the holes connected thereto may be appropriately changed depending on the shape of the cleaning member and the way in which the cleaning liquid is supplied and discharged.

[0031] <Cleaning solution contact process, cleaning solution removal process> In the present invention, after the member installation process in which the above-mentioned cleaning member is installed on the steel structure (part to be cleaned), a cleaning liquid contact process is then carried out, which includes a process of contacting the part to be cleaned with the cleaning liquid by supplying the cleaning liquid to the inside of the cleaning member. Then, a cleaning liquid removal process is carried out in which the cleaning liquid that has been supplied to and contacted the part to be cleaned for a certain period of time is removed together with the rust and corrosive components dissolved therein. As described later, these processes may be performed in a series, so they will be explained in the order of the process and procedure.

[0032] (Cleaning solution) Here, the cleaning liquid may be any liquid containing known cleaning liquid components that partially or entirely decompose, dissolve, adsorb, or replace rust and corrosive components present on the part to be cleaned. Although an embodiment using only water, an alcohol-based solvent, or a mixture thereof as the cleaning liquid is not excluded, it is preferable that the cleaning liquid contains a cleaning promoter consisting of a rust remover and / or an anion adsorbent. By containing a cleaning promoter, the above action is performed more efficiently, so that the action of decomposing and dissolving rust and corrosive components on the part to be cleaned can be performed efficiently.

[0033] The rust remover as a cleaning promoter is preferably a component having the action of decomposing already generated rust, that is, the action of changing iron oxide to iron ions by chemical reaction. More preferably, it is preferable that the rust remover has a dissolving action in addition to the decomposition action, that is, the action of dissolving iron ions in a solvent by changing them into a chelating (complexing) action or a soluble substance. Such rust removers can be widely used from acidic to alkaline, and can be used according to the type of rust, the location of occurrence (base material), the amount of rust, and the like. Examples of the rust remover having the action of decomposing rust include organic acids or inorganic acids such as citric acid, phosphoric acid, oxalic acid, ascorbic acid, and hydrochloric acid. Examples of the rust remover having both the action of decomposing and dissolving rust include salts of organic acids or inorganic acids such as diammonium hydrogen citrate and ammonium thioglycolate. Among these, it is more preferable to use diammonium hydrogen citrate.

[0034] In addition, as an anion adsorbent for cleaning promotion, Cl - or SO4 2- It is preferable that the anion adsorbent contains a corrosive ion fixing agent for capturing the corrosive components (ions) such as ammonium nitrate, etc., and at the same time chemically reacting with the corrosive components (ions) to fix and inactivate them as water-insoluble double salts. As the corrosive ion fixing agent as such an anion adsorbent, a known one can be used, and representative examples include hydrocalumite, hydrotalcite, ion exchange resin beads, etc.

[0035] Hydrocalumite is a hydrous crystalline powder with a layered structure represented by the formula: 3CaO·Al2O3·CaX2 / m·nH2O (wherein X is a monovalent or divalent anion, m is the valence of the anion, and n is 20 or less). The anion (X) is NO3 - Or NO2 - , O.H. - , CH3COO - , CO3 2- When these anions come into contact with chloride ions, sulfate ions, etc., they undergo anion exchange, forming NO3 -, NO2 - etc., and the corrosive ion substances are immobilized (supported) in the hydrocalumite, making them inactive. The liberated anions also form a passive film on the surface of the steel material, further improving corrosion resistance.

[0036] Hydrotalcite is typically represented by the formula: Mg 4.5 Al2(OH) 13 It is a hydrous crystalline powder with a layered structure represented by the formula CO3·nH2O (wherein n is 4 or less, preferably 3.5). Like hydrocalumite, it undergoes anion exchange when it comes into contact with corrosive ionic substances, fixing the corrosive ions within the hydrotalcite and preventing them from being released from the crystal structure.

[0037] Ion exchange resin beads that are known in the art can be used. Usually, beads in which polystyrene is crosslinked with divinylbenzene are used as a base resin, and the base resin has a structure that ionizes as an ion exchange group. For example, the base resin beads include strongly acidic cation exchange resin beads having sulfonic acid groups, weakly acidic cation exchange resin beads having carboxyl groups, strongly basic anion exchange resin beads having quaternary ammonium groups, and weakly basic anion exchange resin beads having primary amino groups to tertiary amino groups. Such ion exchange resin beads can be produced by a known method, or can be obtained as a commercially available product.

[0038] The cleaning solution used in the present invention preferably contains both the rust remover and the anion adsorbent, which are the cleaning promoters. The concentration when used is not limited, but the rust remover in the cleaning solution is usually about 1 to 50 mass%, and it is more preferable to use about 5 to 20 mass% in terms of dissolving corrosive components. The anion adsorbent is usually about 1 to 40 mass% in the cleaning solution, and it is more preferable to use about 5 to 30 mass% in terms of the viscosity, dispersion stability, and cleaning promotion performance of the cleaning solution. As components other than the cleaning promoter in the cleaning solution, solvents such as water and alcohol-based solvents (methanol, ethanol, etc.) are used. In addition, other components other than these can also be used. As other components, known components such as viscosity adjusters, dispersants, surfactants, pH adjusters, antioxidants, rust inhibitors, and chelating agents that adjust the viscosity of the cleaning solution can be appropriately used.

[0039] The temperature of the cleaning liquid can be adjusted as appropriate depending on the ingredients to be mixed and the condition of the part to be cleaned. Although it depends on the ingredients to be mixed, it can usually be preferably used in the range of room temperature to about 50°C. The amount of cleaning liquid to be used can be adjusted as appropriate depending on the size of the part to be cleaned, the amount of remaining rust, and the cleaning method (intermittent, continuous) described below. It is a preferred embodiment that the amount of cleaning liquid to be used is prepared and stored in advance using a cleaning liquid tank or the like. By using a cleaning liquid tank (tank), it can be suitably used when discharging or circulating the cleaning liquid described below. A plurality of cleaning liquid tanks (tanks) may be used.

[0040] (Intermittent Method) The method of contacting the cleaning liquid with the part to be cleaned after the cleaning member is placed is not particularly limited, but may be such that the cleaning member is provided with the above-mentioned supply part or hole in advance, and the cleaning liquid is supplied through the supply part or hole to contact the part to be cleaned. Specifically, the cleaning liquid may be supplied / contacted and removed / discharged intermittently or continuously, including the subsequent "cleaning liquid removal step". Each of these methods will be explained below.

[0041] First, a method of intermittently contacting the cleaning liquid with the part to be cleaned will be described. In the method of intermittently contacting the cleaning liquid, a certain amount of the cleaning liquid is contacted with the part to be cleaned and the state is maintained for a certain time (retention treatment). During that time, the rust remover and anion adsorbent contained in the cleaning liquid sufficiently penetrate the part to be cleaned including the pitted corrosion part, and rust and corrosive components present in the part to be cleaned including the pitted corrosion part are decomposed and dissolved in the cleaning liquid by the action of each component. In order to ensure sufficient penetration of the cleaning liquid and the action of decomposing and dissolving the rust and corrosive components, the retention treatment is preferably performed within a range of 1 hour to 24 hours, and more preferably, from the viewpoint of ensuring cleanability and preventing corrosion of the steel structure (base material) having the part to be cleaned, it is preferable to perform the retention treatment within a range of 6 to 12 hours. The retention treatment time can be estimated by prior consideration from the known amounts of rust and corrosive components.

[0042] In addition, while the cleaning liquid is in contact with the part to be cleaned, a cleaning promotion process may be separately performed to promote the decomposition or dissolution of rust, etc. (cleaning promotion step). The cleaning promotion process is not limited, but is preferably at least one process selected from vibration, ultrasonic waves, stirring, light irradiation, and heating. These processes can be performed using known devices and equipment.

[0043] After such a retention process or cleaning promotion process (step), a process is performed to remove the cleaning liquid that is in contact (retained) from the cleaned part (cleaning liquid removal process). By performing the cleaning liquid removal process, rust and corrosive components dissolved in the cleaning liquid are removed from the cleaned part together with the cleaning liquid. When this cleaning liquid removal process is performed, the rust and corrosive components are removed from the cleaned part, completing a series (one cycle) of cleaning processes using an intermittent method.

[0044] There is no limitation on the method of the cleaning liquid removal process, as long as the cleaning liquid after contact is removed from the cleaned part. For example, the cleaning liquid may be absorbed into an absorbent cloth or the like and wiped off, or the cleaning liquid may be discharged through a discharge part. There is no limitation on the use of a discharge part, either, and the cleaning liquid may be forcibly discharged from the discharge part by tilting the upper side of the steel structure so that it faces downward, or the cleaning liquid may be pushed into the discharge part by sending air from the supply part side and discharged. In addition, the cleaning liquid may be pumped out using a pump or the like and discharged to the outside, or the cleaning liquid may be discharged to the outside using the siphon principle, which is a particularly preferred discharge method when a relatively large steel structure is the target.

[0045] After the cleaning liquid removal step has been carried out, a holding process can be carried out again in the same manner, in which a fixed amount of cleaning liquid is brought into contact with the part to be cleaned and this state is held for a fixed period of time. That is, in this intermittent method, when the process of bringing the cleaning liquid into contact with the part to be cleaned and holding the cleaning liquid, and the subsequent removal process in the cleaning liquid removal step are considered as one cycle, this cycle may be carried out only once, or it is also possible to carry out multiple cycles repeatedly. It is preferable that this cycle is carried out until it can be confirmed that no rust or corrosive components remain in the pitted parts of the part to be cleaned, and this can be appropriately determined depending on the steel structure (part to be cleaned) used.

[0046] In addition, the used cleaning liquid after contacting the part to be cleaned and removing the rust and corrosive components can be used as it is as the cleaning liquid in the next cycle. However, since the cleaning performance may be deteriorated as the amount of rust and corrosive components in the used cleaning liquid increases, when the used cleaning liquid is reused, it is preferable to carry out a cleaning process to remove the rust and corrosive components contained in the used cleaning liquid (cleaning liquid cleaning process). That is, when the used cleaning liquid is used, it is preferable to carry out a cleaning liquid cleaning process to purify the cleaning liquid. The method of purifying the cleaning liquid is not limited, but examples of the method include known processes such as a process using a filtering device or device such as a filter, an adsorption process to an ion exchanger, and an anion exchange process using hydrocalumite. Among these, in order to remove the corrosive components, it is preferable to carry out an adsorption process to an ion exchanger, an anion exchange process using hydrocalumite, and a precipitation process of the corrosive components by a chemical reaction. The cleanliness of the cleaning liquid after the cleaning process can be confirmed, for example, by a change in the hue of the cleaning liquid or a method using a detector tube.

[0047] (Continuous Method) Next, a method of continuously contacting the cleaning liquid with the part to be cleaned will be described. A method of continuously contacting the cleaning liquid with the part to be cleaned can be performed by a series of liquid passing processes, namely, a contact process of the cleaning liquid with the part to be cleaned and a removal process of the cleaning liquid in the cleaning liquid removal process. Specifically, a series of liquid passing processes is performed by supplying the cleaning liquid from a supply part provided in the cleaning member and continuously contacting the part to be cleaned, and continuously discharging the supplied and contacted cleaning liquid from the discharge part, thereby making it possible to continuously supply and contact the part to be cleaned with the cleaning liquid. In other words, this is a method in which the cleaning liquid is supplied from the supply part of the cleaning member and contacted with the part to be cleaned, while the contacted cleaning liquid is continuously discharged from the discharge part.

[0048] By such continuous liquid passing treatment, the rust remover and anion adsorbent contained in the cleaning liquid, which is continuously supplied to and contacted with the part to be cleaned, penetrate sufficiently into the part to be cleaned, including the pitted part, and the action of each component of the rust remover and anion adsorbent decomposes and dissolves the rust and corrosive components present in the part to be cleaned, including the pitted part, into the cleaning liquid. In this continuous method, unlike the above-mentioned intermittent method, the cleaning liquid is constantly discharged, so that the rust and corrosive components are continuously removed (discharged) from the part to be cleaned, and therefore the cleaning efficiency is relatively high. In order to ensure sufficient penetration of the cleaning liquid and the action of decomposing and dissolving the rust and corrosive components, it is preferable to appropriately adjust the liquid passing speed, and it is more preferable not to make the liquid passing speed too fast. It can be appropriately adjusted depending on the equipment used (supply part, discharge part, tube hole size, etc.), the range of the part to be cleaned in the steel structure, and the amount of remaining rust and corrosive components. Although not limited, for example, a liquid passing speed that makes the flow rate in the part to be cleaned 0.01 to 2 cm / sec is a practical embodiment. The liquid passing treatment is preferably carried out for a period of 1 to 24 hours, and more preferably for a period of 6 to 12 hours from the viewpoints of ensuring cleanability and preventing corrosion of the steel structure (base material) having the part to be cleaned. Even in this continuous method, the treatment time can be estimated in advance based on the amount of known rust and corrosive components.

[0049] In this continuous method, similarly to the above-mentioned intermittent method, a cleaning promotion process may be separately carried out when the cleaning liquid is brought into contact with the part to be cleaned (cleaning promotion step).

[0050] Here, in the series of liquid passing processes, the cleaning liquid after contacting the cleaned part may be simply discharged (discarded) from the discharge part, or new cleaning liquid may be constantly supplied from the supply part and continuously discharged (discarded) from the discharge part to clean the cleaned part. According to such a method, new cleaning liquid is constantly supplied to the cleaned part, so that the efficiency of cleaning the cleaned part can be relatively high, and this is a preferred embodiment for such a purpose.

[0051] On the other hand, in the series of liquid passing processes, the cleaning liquid after contacting the part to be cleaned may not only be discharged but also reused. As a method of reuse, a circulation line for circulating the used cleaning liquid discharged from the discharge part is provided, and the used cleaning liquid discharged through the circulation line is again subjected to the cleaning liquid contact step and poured in from the supply part side (circulation step). The circulation line may be installed so that the discharge part of the cleaning liquid is directly or indirectly connected to the supply part using a commonly used pipe or the like. When this circulation line is installed, it is preferable that the above-mentioned cleaning liquid tank (tank) is installed in the circulation line, and it is also preferable that a circulation pump is installed. In this case, the used cleaning liquid discharged from the discharge part is supplied to the cleaning liquid tank (tank) through the circulation line, so that the used cleaning liquid can be circulated from the cleaning liquid tank (tank) to the supply part and reused. However, the supply line and discharge line of the cleaning liquid may be installed separately from the circulation line.

[0052] In the continuous method, when the cleaning liquid is used by circulating it, in order to prevent the cleaning property of the cleaning liquid after use from decreasing, it is preferable to perform a cleaning process to remove rust and corrosive components contained in the cleaning liquid after use, as in the case of the intermittent method described above (cleaning liquid cleaning step). The method of purifying the cleaning liquid includes the same method as described above. In this case, the cleaning liquid cleaning step can be provided separately from the circulation line (step), but it is more preferable to incorporate it into the circulation line (step). That is, by directly subjecting the used cleaning liquid discharged from the discharge part to the cleaning liquid cleaning step, the used cleaning liquid can be continuously purified while the cleaned cleaning liquid can be directly supplied from the supply part to the cleaning liquid contact step again, thereby improving the cleaning efficiency. In addition, by providing the cleaning liquid cleaning step in the circulation step, the amount of cleaning liquid discharged can be reduced while maintaining high cleaning efficiency, which is advantageous in terms of cost and is preferable because it is a method that can achieve both of these.

[0053] After such a series of liquid passing processes and cleaning promotion processes (steps), a process is carried out to remove the cleaning liquid that has been in contact (passed) from the cleaned part, as described above (cleaning liquid removal process). By carrying out the cleaning liquid removal process, rust and corrosive components dissolved in the cleaning liquid are removed from the cleaned part together with the cleaning liquid. In the case of this method, the cleaning liquid removal process is carried out, for example, by stopping the supply of cleaning liquid from the supply part while feeding only gas such as air, while discharging the used cleaning liquid from the discharge part, with the circulation line stopped. Once this cleaning liquid removal process is carried out, the cleaning process by a series of liquid passing processes using this continuous method is completed.

[0054] <Post-processing process> After all of the above intermittent or continuous treatments have been performed and all of the cleaning liquid removal processes have been completed, it is preferable to perform post-treatment on the surface of the steel structure (post-treatment process). As the post-treatment, it is preferable to perform one or more of the following treatments: a cleaning treatment for cleaning the surface using water, an organic solvent, gas, etc., a drying treatment for drying the surface, and a blasting treatment for polishing the surface. It is more preferable that all of these treatments are performed in order. By performing one or more of these treatments, the surface of the cleaned steel structure can be maintained in a cleaner state and the occurrence of rust reversion when repainting can be suppressed. All of these treatments can be performed using known methods.

[0055] In a preferred embodiment, the steel structure that has undergone any post-treatment process is repainted with paint from the viewpoint of improving corrosion resistance and preventing rusting. In a preferred embodiment, this repainting is performed by, for example, applying a base coat as an anti-rust paint, a middle coat to protect the base coat, and a top coat as a final finish paint in layers multiple times. These paintings can be performed using known paints and following known painting procedures. EXAMPLES

[0056] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples and comparative examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0057] <Preparation of test steel plate> As steel structures having areas to be cleaned, three types of corrosion test steel plates were prepared using the following procedure.

[0058] (Corrosion test steel plate 1 (CCT)) A test steel plate of 150 mm x 70 mm (SS400 structural steel plate (JIS G 3101, sandblasted) manufactured by TP Giken Co., Ltd., thickness: 3.2 mm) was prepared, and a combined cycle test (CCT) was performed on this plate as specified in JIS K5600-7-9, Appendix 1, Cycle D. A combined cycle test machine (CYP-90L manufactured by Suga Test Instruments Co., Ltd.) was used to perform the CCT. Specifically, 56 cycles (total 336 hours) were performed, with one cycle consisting of a first stage (5% salt water spray at 30°C for 0.5 hours), a second stage (humidification at 30°C and 95RH% for 1.5 hours), a third stage (hot air drying at 50°C for 2 hours), and a fourth stage (hot air drying at 30°C for 2 hours), each of which lasted a total of 6 hours. This resulted in the preparation of a corrosion test steel plate 1 with rust on the entire surface. The salt content of the surface and rust was approximately 10 to 30 g / m 2 And brittle rust had formed.

[0059] (Corrosion test steel plate 2 (exposed on Miyako Island)) A test steel plate similar to corrosion test steel plate 1 was prepared and exposed outdoors for 9 months in Miyakojima, Okinawa Prefecture, to prepare corrosion test steel plate 2, which had rust on the entire surface. The salt content of the surface and rust was about 2 to 4 g / m 2 A hard layer of rust had formed.

[0060] (Corrosion test steel plate 3 (promoted localized corrosion (pitting corrosion))) A test steel plate similar to the corrosion test steel plate 1 was prepared, and a silicone sealant (Bond Silicone Coke manufactured by Konishi Co., Ltd.) was placed (height 5 mm) on the outer peripheral edge (width about 5 mm) of the test steel plate. 8.4 g of 20 mass% NaCl aqueous solution was placed on the surface of the test steel plate inside the sealant, and the test plate was tilted to spread the NaCl aqueous solution evenly on the surface of the test steel plate inside the sealant, and dried at room temperature for 18 hours or more. Next, the test steel plate with NaCl attached was placed on a 60°C hot plate. Ion-exchanged water was sprayed onto the surface of the test steel plate for 40 to 60 seconds from a location about 140 cm vertically above the surface of the test steel plate (spraying treatment). Then, it was left for 900 seconds. During this time, the test steel plate was heated from the back side by the hot plate, and the ion-exchanged water evaporated (drying treatment). This spraying treatment and drying treatment constitute one cycle, and 1280 cycles were performed to prepare a corrosion test steel plate 3 in which the inside of the sealant had rusted. The salt content on the surface and in the rust is 160g / m 2 The amount of rust was less than that of corrosion test steel plates 1 and 2. Note that even after grid blasting (vacuum blasting equipment: Suction Bijin III (FDO-G3-KA) manufactured by Chiba Giko Co., Ltd., abrasive: alumina, finishing grade (ISO8501-1): Sa2.5), salt remained on corrosion test steel plate 3, and the amount of remaining salt was approximately 100 mg / m 2 That is, it was confirmed that localized corrosion (pitting corrosion) had progressed in the corrosion test steel plate 3, and that salt had penetrated into the pitted areas.

[0061] <Cleaning and evaluation of corrodible steel plates> (Cleaning process) [Example 1] First, the surface of the corrosion test steel plate 1 prepared above was polished with a disk sander (PDA-100C(S) manufactured by Hitachi Koki Co., Ltd.) and roughly scraped until 40 to 60% of the surface was covered with rust. In other words, the remaining 40 to 60% was roughly scraped until it had a metallic luster.

[0062] Next, a cleaning member was installed on the corrosion test steel plate 1 that had been roughly scraped. Specifically, a silicone sealant (Bond Silicone Coke manufactured by Konishi Co., Ltd.) was installed on the outer peripheral end (width: about 5 mm) of the corrosion test steel plate 1, and a silicone rubber sheet (thickness: 5 mm) of the same dimensions as the test steel plate was placed on top of it to cover the part of the corrosion test steel plate 1 to be cleaned. It was confirmed that the gap between the silicone rubber sheet and the part to be cleaned was about 2 mm, and a flow path was secured. In order to improve the sealing between the placed silicone rubber sheet and the corrosion test steel plate 1, the entire outer peripheral part was clamped and fixed using clips. The silicone rubber sheet had two holes with a diameter of 6 mm at the ends of its upper surface, and a thermoplastic elastomer tube (inner diameter 3.18 mm, outer diameter 6.35 mm) was inserted into each hole from the outside to serve as the supply and discharge points for the cleaning liquid, respectively.

[0063] Next, a liquid pump (TP-1973D manufactured by AS ONE Corporation) was installed on the tube connected to the supply unit, and the tip of the other end of the tube connected to the supply unit was placed in a cleaning liquid tank (total amount: 100 g). By turning on the liquid pump, the cleaning liquid was supplied to the surface (cleaned part) of the corrosion test steel plate 1 on which the cleaning member (silicon rubber sheet) was installed through the supply unit and contacted (continuous method, liquid passing speed: 10 g / min, flow rate in the cleaned part: about 0.14 cm / sec). By continuing the liquid passing, it was confirmed that the used cleaning liquid was discharged from the discharge part. The discharged used cleaning liquid was circulated by putting the tip of the tube from the discharge part into the cleaning tank. Then, the passage and circulation of the cleaning liquid was continued in this manner for 6 hours. The cleaning solution used was 5% by mass diammonium hydrogen citrate.

[0064] After the six hours of liquid passage and circulation, the tip of the tube connected to the supply part in the cleaning tank was removed, and the liquid pump was continued to operate to send air into the tube and drain all of the cleaning liquid from the part to be cleaned. After the drainage of the cleaning liquid was completed, the liquid pump was stopped and the tip of the tube on the drain side was removed from the cleaning liquid tank.

[0065] Next, the cleaning solution tank was filled with ion-exchanged water, and the tubes were set up again to circulate as described above, and each end of the tube was placed in the tank containing ion-exchanged water. By restarting the liquid supply pump, the ion-exchanged water was supplied to the part to be cleaned and brought into contact with it, and then circulated to clean the part to be cleaned. The ion-exchanged water was circulated for about 10 to 15 minutes.

[0066] After the cleaning process using the ion-exchanged water was performed, the ion-exchanged water was discharged from the cleaned area by sending air from the supply side in the same manner as after the end of the liquid passage. After the discharge operation was completed, the cleaning member (silicon rubber sheet) was removed from the corrosion test steel plate 1. The cleaned area was then subjected to a drying process (left at room temperature for about 1 hour). For the cleaned test steel plate 1 after all of the cleaning processes had been completed, the salt removal ability was evaluated from the amount of salt in the cleaning liquid according to the following procedure, and the cleanability was evaluated. The results are shown in Table 1.

[0067] (evaluation) [Salt removal] The salt removal ability was evaluated by calculating the salt removal rate from the following formula (1) using the amount of salt (amount of salt removed) a in the cleaning liquid (used cleaning liquid) after passing and circulating the cleaning liquid for 6 hours, and the amount of salt (amount of salt remaining) b remaining on the test steel plate 1 after the cleaning process was fully completed. The salt removal rate was then evaluated with the following codes according to its value. Salt removal rate = 100 × a / (b + a) (1) (standard) ◎: Salt removal rate is 80% or more ○: Salt removal rate is between 60% and 80% △: Salt removal rate is between 30% and 60% ×: Salt removal rate is less than 30%

[0068] The above amount of salt removal a was measured by the following procedure. That is, 15 mL of the cleaning solution after use was collected with a micropipette, and 15 g of pure water was added to it to dilute it 2-fold. An excess amount (3.6 g to 5.6 g) of calcium hydroxide was added to the diluted solution, which was greater than the solubility, and the solution was stirred with a stirrer for 2 to 4 hours. The addition of calcium hydroxide removed the iron ions contained in the cleaning solution after rust removal. The solution after stirring was centrifuged at 17,500 rpm, 30 minutes, and 20°C, and the supernatant was collected. The obtained supernatant was diluted 5-fold. Next, the chloride ion concentration of the diluted supernatant was measured using an electrophoresis capillary (Agilent 7100 manufactured by Agilent Technologies, Inc.), and this was calculated as the amount of removed salt a.

[0069] On the other hand, the residual salt content b was measured by the following procedure. That is, the post-cleaning test steel sheet 1 after the cleaning treatment was immersed in a 20 mass % aqueous solution of diammonium hydrogen citrate for 18 hours or more. The chloride ion concentration of the obtained immersion liquid was measured in the same manner as in the measurement for the amount of removed salt a, and calculated as the amount of remaining salt b.

[0070] [Example 2] The corrosion test steel plate 1 used in Example 1 was used, and the same cleaning treatment as in Example 1 was carried out without passing any liquid through it. That is, the cleaning liquid supplied from the supply part of the cleaning member (silicon rubber sheet) was not immediately discharged, but was left in contact with the part to be cleaned and left to stand for 6 hours (intermittent method). After leaving it to stand for 6 hours, the cleaning liquid was discharged as in Example 1. In addition, the part to be cleaned was subjected to cleaning treatment, drying treatment, etc. in the same manner, and the cleaning treatment was completed. The amount of removed salt a and the amount of remaining salt b were determined in the same manner as in Example 1 to determine the salt removal rate, and the salt removal ability was evaluated according to the criteria. The results are shown in Table 1.

[0071] [Comparative Example 1] The corrosion test steel plate 1 used in Example 1 was used, and a polyethylene porous sheet (Piolas PE sheet manufactured by AION Co., Ltd.) impregnated with about 32 g of the cleaning solution used in Example 1 was placed on the surface having the part to be cleaned, and the cleaning solution was brought into contact with the part to be cleaned. To prevent drying, the test steel plate and the porous sheet were covered with food wrap film. The vertical and horizontal dimensions of the porous sheet were the same as those of the corrosion test steel plate 1, and the thickness was 5 mm. After the porous sheet was in contact for 6 hours, it was removed. After removing the porous sheet, the area to be cleaned was thoroughly cleaned with ion-exchanged water. After that, it was dried (left at room temperature for about 1 hour) to complete the cleaning. Thereafter, the remaining salt content b was measured using the test steel plate 1 after completion of cleaning. Here, the amount of removed salt a was calculated by measuring the total salt content a+b from another test steel plate 1 prepared in the same manner, and subtracting the obtained remaining salt content b from it. Using the thus obtained a and b, the salt removal rate was calculated in the same manner as in Example 1. As in Example 1, the salt removal ability was evaluated according to the criteria. The results are shown in Table 1.

[0072] [Examples 3 to 6] In place of the corrosion test steel plate 1 used in Example 1, the corrosion test steel plate 2 exposed to Miyakojima was used, and rough scraping was carried out to the same extent as in Example 1. Next, the cleaning operations (installation of the cleaning member, contact and circulation of the cleaning solution, and purification treatment) were carried out in the same manner as in Example 1, except that the concentration of the cleaning solution and the flow rate of the solution were changed as shown in Table 1, and then the salt removal ability was evaluated in the same manner according to the criteria. Note that, when the flow rate of the solution is 50 g / min, the flow rate at the part to be cleaned is calculated to be about 0.69 cm / sec. The results are shown in Table 1.

[0073] [Example 7] Instead of the corrosion test steel plate 1 used in Example 2, the corrosion test steel plate 2 exposed to Miyakojima was used, and a cleaning test was carried out under stationary conditions in the same manner as in Example 2. After the cleaning treatment was completed, the salt removal rate was determined in the same manner as in Example 2, and the salt removal ability was evaluated according to the criteria. The results are shown in Table 1.

[0074] [Example 8] Instead of the corrosion test steel plate 1 used in Example 1, a corrosion test steel plate 3 in which localized corrosion (pitting corrosion) had been promoted was used, and rough scraping was carried out to the same extent as in Example 1. Next, except for changing the concentration of the cleaning solution and the flow rate as shown in Table 1, the cleaning operations (installation of the cleaning components, contact and circulation of the cleaning solution, and purification treatment) were carried out in the same manner as in Example 1, and then the salt removal ability was evaluated in the same manner according to the criteria. The results are shown in Table 1.

[0075] [Table 1] [Explanation of symbols]

[0076] 1...steel structure, 2...part to be cleaned, 3...cleaning member, 4...cleaning liquid, 5...direction of inlet of cleaning liquid, 6...direction of outlet of cleaning liquid

Claims

1. A method for cleaning rust and / or corrosive components present on the surface of a steel structure, comprising the steps of: a member installation step of installing a cleaning member that surrounds and / or covers the part to be cleaned in which rust and / or corrosive components are present; a cleaning liquid contacting step including a process of supplying a cleaning liquid to the inside of the cleaning member and bringing the cleaning liquid into contact with the part to be cleaned; and a cleaning liquid removal step including a treatment for removing the contacted cleaning liquid together with rust and / or corrosive components.

2. The cleaning method for steel structures according to claim 1, characterized in that the cleaning liquid contact step includes a holding treatment for keeping the cleaning liquid in contact with the part to be cleaned, and the holding treatment and the subsequent removal treatment in the cleaning liquid removal step constitute one cycle, which is repeated one or more times.

3. 2. The method for cleaning a steel structure according to claim 1, wherein the contacting treatment of the cleaning liquid with the part to be cleaned in the cleaning liquid contacting step and the removal treatment of the cleaning liquid in the cleaning liquid removal step are carried out in a single liquid passing process.

4. the cleaning member has a supply part for supplying a cleaning liquid to the inside and a discharge part for discharging the supplied cleaning liquid, 4. The method for cleaning a steel structure according to claim 3, wherein the series of liquid passing processes is carried out by supplying the cleaning liquid from the supply section and discharging the cleaning liquid from the discharge section.

5. 4. The method for cleaning a steel structure according to claim 3, further comprising a circulation step of circulating the discharged cleaning liquid and subjecting it to the cleaning liquid contact step again.

6. 4. The method for cleaning a steel structure according to claim 1, wherein the cleaning liquid contains a cleaning promoter made of a rust remover and / or an anion adsorbent.

7. 4. The method for cleaning a steel structure according to claim 1, further comprising a rough scraping step of roughly scraping a surface of the steel structure prior to the member installation step.

8. 4. The method for cleaning a steel structure according to claim 1, wherein the cleaning member is a sealed cleaning member that seals the part to be cleaned.

9. The method for cleaning a steel structure according to any one of claims 1 to 3, characterized in that it further comprises a cleaning liquid cleaning step of removing rust and / or corrosive components from the cleaning liquid removed in the cleaning liquid removing step, and the cleaning liquid after the cleaning liquid cleaning step is subjected again to a cleaning liquid contacting step.

10. 4. The method for cleaning a steel structure according to claim 1, wherein the cleaning liquid contact step includes a cleaning promotion step of performing at least one treatment selected from vibration, ultrasonic waves, stirring, light irradiation, and heating.

11. 4. The method for cleaning a steel structure according to any one of claims 1 to 3, further comprising a post-treatment step of performing at least one post-treatment selected from cleaning treatment, drying treatment and blasting treatment on the surface of the steel structure after the cleaning liquid removing step.

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