A method for improving the corrosion resistance of galvanized bolts for weathering steel profiles

Abstract

The invention discloses a weathering steel angle steel for a power transmission and transformation tower, which is connected by galvanized bolts, reduces the galvanic corrosion probability between the weathering steel and the galvanized bolts, and improves the service life of the galvanized bolts. The method comprises: firstly, the bolt connection part of the weathering steel plate is cleaned, heated in air, and then immersed in a pre-corrosion rust agent solution to oxidize it under the action of temperature and corrosive liquid, and after drying, 0.1mm steel shot is used for low-speed shot peening under 0.5MPa airflow to spray away the loose rust layer on the surface, leaving a stable rust layer, and after repeated several times, the treated part with the rust layer is put into a stable solution for boiling and soaking to improve the stability of the rust layer. The corrosion current between the bolt and the weathering steel can be reduced, and the rust layer can be continuously stable in the subsequent service process, and the resistance of the rust layer can be further improved, so that the electrochemical corrosion tendency between the weathering steel and the connection and fastening bolts can be effectively reduced, and the stability and reliability of the weathering steel angle steel tower using galvanized bolts can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal structures, and in particular relates to a method for improving the corrosion resistance of galvanized bolts for weathering steel profiles. Background Art

[0002] Weathering steel profiles are used for the installation and erection of power transmission and transformation towers. Due to the alloy elements Cu, Ni, Cr, P (a small amount of Nb, V, Ti) added to weathering steel, a dense oxide film is formed on the steel surface, which prevents the spread and development of rust and protects the substrate under the rust layer to slow down the corrosion rate. This will effectively reduce the need for anti-corrosion coatings for ordinary tower profiles, reduce unnecessary surface coating processes, significantly reduce environmental damage, and save costs. It is the direction that the erection of power transmission and transformation towers is currently paying attention to.

[0003] The anti-corrosion principle of weathering steel itself lies in the formation of a dense oxide film. However, if weathering steel profiles are connected by bolts, the difference in microstructure and composition between the connecting bolts and the weathering steel profiles will also lead to a potential difference between the bolts and the weathering steel profiles. Under service conditions, electrochemical corrosion will occur due to the difference in corrosion potential, causing electrochemical corrosion of the weathering steel profiles or connecting bolts. This phenomenon has been concluded in the applicant's early experiments. When 304 stainless steel bolts are used, a significant corrosion layer appears on Q355NH weathering steel. When ordinary galvanized bolts are used, the bolts are significantly corroded. When stainless steel bolts with higher potential are used directly for connection, the weathering steel itself will become an anode, and the weathering steel matrix will corrode at the contact point with the stainless steel bolts. When galvanized bolts are used directly for connection, the galvanized layer of the bolts will be extensively damaged during the formation of the weathering steel oxide film, resulting in significant corrosion of the bolts.

[0004] Therefore, although weathering steel itself can reduce the degree of corrosion by forming dense oxides, when it is directly connected to metal fasteners with different potentials, the electrochemical corrosion problem caused by the potential difference, namely galvanic corrosion, is difficult to avoid. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for improving the corrosion resistance of galvanized bolts for weathering steel profiles.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for improving the corrosion resistance of galvanized bolts for weathering steel profiles, characterized in that: comprising:

[0009] First, clean the bolted joints of the weather-resistant steel plates, heat them and immerse them in a pre-corrosion rust-removing solution to oxidize them under the action of temperature and corrosive liquid. After drying, sandblast them under air flow to remove the loose rust layer on the surface and leave a stable rust layer. After repeating this several times, put the treated parts with rust layer into a stable solution and boil them to improve the stability of the rust layer.

[0010] As a preferred solution of the method for improving corrosion resistance described in the present invention, the heating condition is heating to 200-300° C. in a resistance furnace and keeping the temperature for 10-30 minutes.

[0011] As a preferred solution of the method for improving corrosion resistance described in the present invention, the sandblasting conditions are: using a pneumatic sandblasting machine, a gas pressure of 0.2-0.5 MPa, and 0.1 mm stainless steel shot.

[0012] As a preferred embodiment of the method for improving corrosion resistance of the present invention, after the sandblasting is completed, the mixture is immersed in a room temperature rusting agent solution at room temperature and stirred for 2-5 minutes to continue to promote rusting. The above sandblasting and rusting process can be repeated 2-4 times.

[0013] As a preferred scheme of the method for improving corrosion resistance described in the present invention, the formula of the pre-corrosion rusting agent is CuSO4-1%~2.5%; Fe2(SO4)3-0.5~3%; NaCl-3%~5%; FeCl3-2%~3%, HCl-5%~15%.

[0014] As a preferred solution of the method for improving corrosion resistance described in the present invention, the formula of the stabilizing solution is 10-40% wt. NaOH; 5-20% wt. NaNO2 aqueous solution.

[0015] As a preferred solution of the method for improving corrosion resistance described in the present invention, wherein: the boiling in a stable solution is for 30-60 minutes, so as to complete the pretreatment of the angle steel bolt connection parts and form a preliminary pre-corrosion area.

[0016] As a preferred embodiment of the method for improving corrosion resistance of the present invention, the pretreated area will continue to form dense α-(Fe1- x Cr x)OOH oxide film.

[0017] Beneficial effects of the present invention:

[0018] It can reduce the corrosion current between the bolts and weathering steel. The rust layer can remain stable during the subsequent service process, further increasing the resistance of the rust layer, thereby effectively reducing the electrochemical corrosion tendency between the weathering steel and the connecting fastening bolts, and effectively improving the stability and reliability of the weathering steel angle steel tower using galvanized bolts. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0020] Figure 1 This is the 7-day salt spray corrosion diagram of Example 2 of the present invention and Comparative Example 1.

[0021] Figure 2 This is a 21-day salt spray corrosion diagram in Example 2 of the present invention.

[0022] Figure 3 This is a microscopic rust layer diagram in Example 2 of the present invention.

[0023] Figure 4 A comparison of the significant corrosion when using 304 stainless steel bolts (a) and ordinary galvanized bolts (b). DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0025] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0026] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0027] Example 1

[0028] Based on this, the purpose of the present invention is to target weathering steel containing Cu, Ni, Cr, and P, such as conventional Q355NH angle steel, by pre-forming a reliable high-density rust layer on its surface to reduce the efficiency of current passing through its surface, thereby effectively reducing the corrosion current between the weathering steel and the galvanized bolts when galvanized bolts are used for fastening connections, delaying the loss of the galvanized layer of the galvanized bolts, and improving the corrosion resistance of the bolts, thereby meeting the requirements for corrosion resistance of bolts in the erection of weathering steel towers.

[0029] The bolted connection area on the weathering steel is cleaned, heated to 200-300°C by a resistance furnace, kept warm for 10-30 minutes, and then immersed in a room temperature rust agent solution (1) (3-5 minutes) until cooled. After drying, a pneumatic sandblasting machine is used with a gas pressure of 0.2-0.5MPa and 0.1mm stainless steel shot to spray away part of the reddish brown rust layer formed in the higher temperature rust agent. Due to the use of a lower shot blasting intensity, the non-dense oxides in the rust layer will be impacted and dropped, and some relatively dense oxides will continue to adhere to the surface. These remaining rust areas are discontinuous point-distributed oxides, which can serve as nucleation sites for the continued formation of oxides. Subsequently, the sandblasted area is immersed in a room temperature rust agent solution at room temperature, stirred for 2-5 minutes, and rusting is continued. The above shot blasting and rusting process can be repeated 2-4 times. The bolt connection area is inserted into the stable solution (2) and boiled for 30-60 minutes, thus completing the pretreatment of the angle steel bolt connection area and forming a preliminary pre-corrosion area. The pre-treated area will continue to form dense α-(Fe1- x Cr x )OOH oxide film, and because the oxide has poor conductivity, it can effectively isolate the corrosion current between the bolt and the angle steel matrix.

[0030] The angle steel after the above treatment can be directly used with galvanized bolts during erection and connection, or nylon washers can be used between the bolts and the angle steel to form a denser oxide film before the washers age, thereby achieving a better effect of isolating current.

[0031] (1) Rust agent solution: CuSO4 - 1% ~ 2.5%; Fe2(SO4)3 - 0.5 ~ 3%; NaCl - 3% ~ 5%; FeCl3 - 2% ~ 3% in HCl - 5% ~ 15% hydrochloric acid to prepare a corrosive agent.

[0032] (2) Soaking in a 10-40% wt. NaOH or 5-20% wt. NaNO2 aqueous solution at a temperature of 50-70°C for 30-60 min to provide an initial environment for the formation of a dense oxide film.

[0033] Example 2

[0034] The bolt connection area on the weathering steel is cleaned, heated to 240°C by a resistance furnace, kept warm for 20 minutes, and then immersed in a room temperature rust agent solution (1) for 4 minutes until cooled. After drying, a pneumatic sandblasting machine is used with a gas pressure of 0.4MPa and 0.1mm stainless steel shot to spray away part of the reddish-brown rust layer formed in the higher temperature rust agent. Due to the use of a lower shot blasting intensity, the non-dense oxides in the rust layer will be impacted and dropped, and some relatively dense oxides will continue to adhere to the surface. These residual rust areas are discontinuous point-distributed oxides, which can serve as nucleation sites for continued oxide formation. Subsequently, the area after sandblasting is immersed in a room temperature rust agent solution at room temperature and stirred for 4 minutes to continue to promote rusting. The above shot blasting and rusting process can be repeated 3 times. After completion. The bolt connection area is inserted into the solution (2) and boiled for 45 minutes, completing the pretreatment of the diagonal steel bolt connection part and forming a preliminary pre-corrosion area. The pretreated area will continue to form dense α-(Fe1- x Cr x )OOH oxide film, and because the oxide has poor conductivity, it can effectively isolate the corrosion current between the bolt and the angle steel matrix.

[0035] The angle steel after the above treatment can be directly used with galvanized bolts during erection and connection, or nylon washers can be used between the bolts and the angle steel to form a denser oxide film before the washers age, thereby achieving a better effect of isolating current.

[0036] The rust-removing agent solution is prepared in the following proportions: CuSO4-1.5%, Fe2(SO4)3-2%, NaCl-4%, and FeCl3-2.5% in HCl-12% hydrochloric acid to form a corrosive agent.

[0037] (2) Soaking in a 30% wt. NaOH or 15% wt. NaNO2 aqueous solution at 60°C for 45 min to provide an initial environment for the formation of a dense oxide film.

[0038] This method can be seen Figure 1 In the 7-day salt spray corrosion chamber, the galvanized bolts and weathering steel were directly fastened to the galvanized bolts without any treatment. Sample 1#, which was made of weathering steel without any treatment, had obvious local corrosion characteristics due to galvanic corrosion. However, the galvanized bolts only had local fluid flow after the weathering steel was treated to form a suitable oxide film and then connected to the galvanized bolts. The overall integrity of the galvanized bolts was improved, and the corrosion area was about 20%.

[0039] After 21 days of salt spray corrosion, the bolts treated with weathering steel plates still have some galvanized layer ( Figure 2The rust layer on the surface of the treated weathering steel can be seen as follows: the rust layer on the surface of the treated weathering steel is directly connected to the galvanized bolt, and a large amount of galvanized layer on the surface of the galvanized bolt is missing. It can be seen from the rust layer on the surface of the treated weathering steel that after pre-corrosion treatment, a dense rust layer will appear inside after a long time. The rust layer has good bonding with the substrate, and there is no obvious interface between the rust layer and the substrate. Therefore, the rust layer formed after pre-treatment has good bonding and can form a good insulating rust layer, thereby reducing the corrosion current between the weathering steel and the bolt, and to a certain extent slowing down the accelerated corrosion of the galvanized bolt as the anode, with a corrosion area of ​​about 70%.

[0040] Microscopic rust layer Figure 3 shown.

[0041] Comparative Example 1

[0042] Compared with Example 2, the formula of the rust remover solution is: CuSO4-1%; Fe2(SO4)3-0.5%; NaCl-3%; FeCl3-2%, HCl-5%.

[0043] The formula of the stabilizing solution remains unchanged.

[0044] Comparative Example 2

[0045] Compared with Example 2, the formula of the rust agent solution is: rust agent solution CuSO4-2.5%; Fe2(SO4)3-3%; NaCl-5%; FeCl3-3%, HCl-15%.

[0046] The formula of the stabilizing solution remains unchanged.

[0047] Comparative Example 3

[0048] Compared with Example 2, the stabilizer solution formula is: 10% wt. NaOH, 5% wt. NaNO2 aqueous solution.

[0049] The rust remover solution formula remains unchanged.

[0050] Comparative Example 4

[0051] Compared with Example 2, the stabilizer solution formula is: 40% wt. NaOH; 20% wt. NaNO2 aqueous solution.

[0052] The rust remover solution formula remains unchanged.

[0053] Among them, after the pre-corrosion treatment, a dense rust layer appeared inside the comparative examples 1 and 2, and there was a relatively obvious interface between the rust layer and the substrate. Although some corrosion was reduced, it could not provide sufficient protection.

[0054] In Comparative Examples 3 and 4, the bolts formed a preliminary pre-corrosion area after being treated in the stabilizer solution, but no obvious dense α-(Fe1- x Crx )OOH oxide film provides only limited resistance to electrochemical corrosion.

[0055] Serial number Corrosion area Salt spray time (days) Comparative Example 1 48％ 7 Comparative Example 2 52％ 7 Comparative Example 3 50％ 7 Comparative Example 4 53％ 7 Serial number Corrosion area Salt spray time (days) Comparative Example 1 93％ 21 Comparative Example 2 95％ 21 Comparative Example 3 91％ 21 Comparative Example 4 92％ 21

[0056] The extent of corrosion is shown in the table above and the corroded area is an estimate.

[0057] The anti-corrosion principle of weathering steel itself lies in the formation of a dense oxide film. However, if weathering steel profiles are connected by bolts, the difference in microstructure and composition between the connecting bolts and the weathering steel profiles will also lead to a potential difference between the bolts and the weathering steel profiles. Under service conditions, electrochemical corrosion will occur due to the difference in corrosion potential, causing electrochemical corrosion of the weathering steel profiles or connecting bolts. This phenomenon has been concluded in the applicant's early experiments. Figure 4 When 304 stainless steel bolts are used, a significant corrosion layer appears on Q355NH weathering steel. Figure 4 (a) When ordinary galvanized bolts are used, the bolts show significant corrosion Figure 4 (b) When stainless steel bolts with higher potential are used directly for connection, the weathering steel itself will become the anode, and the weathering steel matrix will corrode at the contact point with the stainless steel bolts; when galvanized bolts are used directly for connection, the galvanized layer of the bolts will be damaged on a large scale during the formation of the weathering steel oxide film, resulting in significant corrosion of the bolts.

[0058] The current mature design ideas and cost control of power transmission and transformation towers have a relatively low strength grade design for the angle steel used for erection. For example, the strength grades of conventional usage are concentrated in the grades of Q235 and Q355, and their yield strengths are between 235MPa and 355MPa. In order to ensure weather resistance at the same time, the content of the main strengthening element C in its alloy elements is mostly less than 0.1%wt. The conventionally used bolts have a higher strength grade. For example, the 8.8-grade M16 bolts with a yield strength of 640MPa have an elemental composition C content and other alloying elements that are much higher than ordinary angle steels. This leads to material differences between existing traditional angle steels and bolts, which naturally leads to differences in their corrosion potentials. Therefore, the existing power transmission and transformation towers are all erected with galvanized angle steels and bolts, so their surface potentials are consistent and electrochemical corrosion will not occur. If surface-coating-free weathering steel is used, no matter what form of bolts are used, there will be problems in matching the weathering steels:

[0059] (1) Directly using traditional galvanized bolts, which will cause local corrosion of the galvanized layer of the bolts under galvanic corrosion conditions, and further cause corrosion of the bolt matrix.

[0060] (2) Using the same material as weathering steel to manufacture bolts, since the strength level of weathering steel is lower than that of bolts, this will result in the weathering steel bolts produced having insufficient strength grade.

[0061] (3) When high-strength weathering steel is used to manufacture bolts, the potential difference between the bolts and the angle steel is still caused by the difference in composition, which can also cause electrochemical corrosion of the angle steel or bolts.

[0062] This electrochemical corrosion between angle steel and bolts can be alleviated in many structures (such as bridges) by local protection of the connection parts, that is, only the bolt connection part is coated to isolate the electrolyte, so as to effectively prevent galvanic corrosion. Or the strength level design of the structural parts is consistent with that of the bolts, and similar materials can be used to manufacture them, so as to avoid potential differences.

[0063] However, the design of the power transmission tower is characterized by a truss structure, which uses multiple connection nodes to ensure high structural stability under low deadweight. Its single structural component (angle steel) does not bear much load, but it can still achieve high bearing capacity through a reasonable truss structure. This leads to a large number of bolt nodes in the power transmission tower. If local coating is used to isolate the electrolyte solution for protection, it is basically equivalent to full coating. For this reason, how to use weathering steel profiles with the characteristic of no painting in the erection of power transmission towers to reduce the efficiency of galvanic corrosion at the bolted joints is an important issue to be solved in the current application of weathering steel in power transmission towers.

[0064] The most fundamental reason for corrosion at the connection between the weathering steel angle steel and the bolts is that there is a corrosion potential difference between the angle steel and the bolts. When there is a dielectric solution in the outside world, a corrosion primary cell is spontaneously formed. If a galvanized bolt is used for direct connection, the more active, low-potential zinc layer is used as the anode, and the relatively high-potential angle steel (cathode) will lose electrons, forming a cathode current from the galvanized layer to the weathering steel, which causes the galvanized layer to gradually lose electrons and corrode. Generally, to alleviate this electrochemical corrosion, under the premise that the potential difference cannot be controlled and the presence of electrolyte solution cannot be eliminated, if the corrosion current can be blocked or the corrosion current density can be effectively reduced, the electrochemical corrosion between different metals can be effectively slowed down. If the density of the current flowing from the anode to the cathode is blocked and the resistance of the current is increased, the efficiency of electrochemical corrosion between the two metals can be effectively reduced, thereby alleviating corrosion to a certain extent. Based on this principle, the present invention performs surface pretreatment on the weathering steel angle steel to form a reliable, high-density rust layer, and utilizes the poor conductivity of the rust layer to hinder the corrosion current between the weathering angle steel and the bolt, thereby effectively improving the corrosion resistance of the galvanized bolts, and realizing the application of galvanized bolts in weathering steel angle steel profiles, thereby improving the corrosion resistance of galvanized bolts for weathering steel profiles.

[0065] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for improving the corrosion resistance of galvanized bolts for weathering steel profiles, characterized in that: include, Clean the part where the weathering steel plate is connected with the bolts, immerse it in a pre-corrosion rust-removing agent solution after heating, oxidize it under the action of heating and corrosive liquid, and sandblast it under air flow after drying to remove the loose rust layer on the surface and leave a stable rust layer. After repeating several times, put the treated part with rust layer into a stable solution and boil it to improve the stability of the rust layer, thus completing the pretreatment of the part where the weathering steel plate is connected with the bolts; This area effectively isolates the corrosion current between the bolt and the angle steel matrix, delays the loss of the zinc coating on the galvanized bolt, and improves the corrosion resistance of the bolt; The formula of the pre-corrosion rust-removing agent is CuSO4-1.5%; Fe2(SO4)3-2%; NaCl-4%; FeCl3-2.5%, HCl-12%; The formula of the stabilizing solution is 30%wt. NaOH; 15%wt. NaNO2 aqueous solution.

2. The method for improving the corrosion resistance of galvanized bolts for weathering steel profiles according to claim 1, characterized in that: The heating condition is to heat the resistance furnace to 200-300° C. and keep the temperature for 10-30 minutes.

3. The method for improving the corrosion resistance of galvanized bolts for weathering steel profiles according to claim 1, characterized in that: The sandblasting conditions are as follows: using a pneumatic sandblasting machine, a gas pressure of 0.2-0.5 MPa, and 0.1 mm stainless steel shot.

4. The method for improving the corrosion resistance of galvanized bolts for weathering steel profiles according to claim 1, characterized in that: After the sandblasting is completed, the mixture is immersed in a room temperature rusting agent solution at room temperature and stirred for 2-5 minutes to continue to promote rusting. The sandblasting and rusting process is repeated 2-4 times.

5. The method for improving the corrosion resistance of galvanized bolts for weathering steel profiles according to claim 1, characterized in that: The boiling in the stable solution is for 30-60 minutes to complete the pretreatment of the angle steel bolt connection parts and form a preliminary pre-corrosion area.

6. The method for improving the corrosion resistance of galvanized bolts for weathering steel profiles according to claim 1, characterized in that: The region will continue to form dense α-(Fe1- x Cr x ) OOH oxide film.

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