Corrosion inhibitor additive for metal surface pickling and pickling solution containing the same

Abstract

This invention provides a corrosion inhibitor additive for pickling metal surfaces and a pickling agent using the same, suitable for steel pickling and rust removal processes. The corrosion inhibitor additive comprises 10 to 30 wt.% of an acid-modified nitrogen-containing polymer (A), 5 to 20 wt.% of an alkynyl alcohol compound (B), 1 to 10 wt.% of a polyether polyol (C), and an equilibrium amount of water. The acid-modified nitrogen-containing polymer (A) includes at least five nitrogen-containing functional groups located on the main chain or branches, and the polyether polyol (C) has a molecular weight of 200 to 1000. The acid-modified nitrogen-containing polymer of this invention has acidic properties, which can improve water solubility and form a stable corrosion inhibitor layer on the metal surface to achieve a corrosion inhibition effect; the alkynyl alcohol compound can densely fill the voids in the inhibitor layer, enhancing the corrosion inhibition effect; and the polyether polyol improves the whiteness and smoothness of the steel after pickling. Compared to traditional alkaline inhibitors, this invention avoids the fumes, odors, and exothermic phenomena generated by acid-base neutralization reactions, and combines high efficiency, environmental friendliness, and process economy.

Description

Technical Field

[0001] This invention relates to a corrosion inhibitor for pickling metal surfaces and a pickling agent using the same, particularly to a corrosion inhibitor for steel pickling and rust removal process design and a pickling agent using the same. Prior Technology

[0002] In the steel manufacturing process, an oxide layer (rust) forms on the surface of the produced steel after storage. Taking cold-rolled steel as an example, rust will form on the surface of the hot-rolled steel coil after high-temperature hot rolling. Rust not only affects the appearance but may also adversely affect subsequent processing, such as causing a decline in the surface quality of the metal or damage to the rolls. Therefore, rust must be removed through pickling before cold rolling.

[0003] Rust scale is composed of ferrous oxide, magnetite, and ferric oxide from the inside out. Hydrochloric acid is an effective pickling agent for dissolving these three oxides, and conventional technology allows for its recycling and reuse, offering both economic and environmental benefits. Therefore, most steel mills commonly use hydrochloric acid for pickling. However, while removing rust scale, hydrochloric acid can also cause problems such as decreased whiteness, increased roughness, hydrogen embrittlement, pitting corrosion, and even excessive corrosion of the metal substrate. To address these potential defects, pickling inhibitors need to be added. These inhibitors not only reduce the incidence of these problems but also effectively suppress acid mist formation and reduce acid consumption.

[0004] A pickling inhibitor, a metal pickling solution composition, and a pickling method have been proposed in the prior art. This technology exhibits significant anti-corrosion effects in pickling environments with high concentrations (15-30%) and high temperatures (>90°C). The formulation of the pickling inhibitor includes: imidazole tertiary amine salt, polyamine polymer, organic sulfur compound, and water.

[0005] A prior art invention also proposes an environmentally friendly carbon steel pickling inhibitor and its application in pickling and rust removal. This inhibitor is non-toxic and harmless, aligning with the trend of green and environmentally friendly development. Its formulation includes: hexamethylenetetramine, cationic surfactants (such as dodecyl dimethyl benzyl ammonium chloride, octadecyl dimethyl benzyl ammonium chloride, dodecyl dimethyl benzyl ammonium bromide, tetradecyl dimethyl benzyl ammonium chloride), and water.

[0006] However, while the aforementioned conventional technologies can provide corrosion resistance to a certain extent, they still have several limitations. First, their formulations contain alkaline amine compounds, which not only have a pungent odor but also readily neutralize acids in acidic solutions, generating fumes and exothermic reactions, adversely affecting the health of on-site operators and the working environment. Second, although the aforementioned environmentally friendly carbon steel pickling inhibitors claim to be non-toxic and harmless, their formulations still contain halogenated compounds, which may damage the ozone layer and pose potential ecotoxicity risks.

[0007] Therefore, it is necessary to provide a corrosion inhibitor for pickling metal surfaces and a pickling agent using the same, in order to solve the problems existing in conventional technology. Summary of the Invention

[0008] The main objective of this invention is to provide a corrosion inhibitor for pickling metal surfaces and a pickling agent using the same, which can effectively inhibit excessive corrosion of steel substrates during the pickling process, maintain the surface quality of the metal, and improve processing accuracy and operational safety.

[0009] A secondary objective of this invention is to provide a corrosion inhibitor for pickling metal surfaces and a pickling agent using the same. The additive utilizes a nitrogen-containing polymer to generate an acidic base nitrogen-containing polymer through an acid acidification reaction. Combined with the synergistic effect of alkynyl alcohol compounds and polyether polyols, it achieves a stable inhibition mechanism under acidic conditions, thereby avoiding the fumes, odors, and exothermic phenomena caused by acid-base neutralization reactions, significantly improving the working environment and enhancing safety.

[0010] Another objective of this invention is to provide a corrosion inhibitor additive for pickling metal surfaces and a pickling agent using the same, which can still have excellent corrosion resistance without the presence of halogen compounds, thereby reducing environmental impact and conforming to the trends of low-carbon processes and green chemistry.

[0011] Another objective of this invention is to provide a corrosion inhibitor additive for pickling metal surfaces and a pickling agent using the same, which can provide a pickling inhibitor composition with good corrosion inhibition performance, low cost and environmental friendliness.

[0012] To achieve the above objectives, the present invention provides a corrosion inhibitor for pickling metal surfaces, comprising 10 to 30 wt.% of an acid-treated nitrogen-containing polymer (A), 5 to 20 wt.% of an alkynyl alcohol compound (B), 1 to 10 wt.% of a polyether polyol (C), and an equilibrium amount of water, wherein the acid-treated nitrogen-containing polymer (A) comprises at least five nitrogen-containing functional groups located on the main chain or branches, the alkynyl alcohol compound (B) has a molecular weight of less than 1000, and the polyether polyol (C) has a molecular weight of 200 to 1000.

[0013] In one embodiment of the present invention, the alkynyl alcohol compound (B) is selected from the group consisting of: ethynyl alcohol, propynyl alcohol, butynediol, 2-pentyn-1-ol and 2,4-hexadiyn-1,6-diol.

[0014] In one embodiment of the present invention, the acidified nitrogen-containing polymer (A) is copolymerized with sulfur-containing or phosphorus-containing functional groups.

[0015] In one embodiment of the present invention, the acidified nitrogen-containing polymer (A) includes at least ten nitrogen-containing functional groups on the main chain or side chain.

[0016] In one embodiment of the invention, the acidified nitrogen-containing polymer (A) is selected from the group consisting of: polyallylamine hydrochloride, polydieneamine hydrochloride-sulfur dioxide copolymer, polydieneamine carbamate-sulfur dioxide copolymer, and polydieneamine sulfate-sulfur dioxide copolymer.

[0017] In one embodiment of the present invention, the acidified nitrogen-containing polymer (A) is acidified by organic acid or inorganic acid.

[0018] In one embodiment of the present invention, the polyether polyol (C) includes ethoxy, propoxy, or a combination thereof.

[0019] In one embodiment of the present invention, the polyether polyol (C) is polyethylene glycol.

[0020] In one embodiment of the present invention, the corrosion inhibitor further includes 0.05 wt.% to 0.5 wt.% of an acid-base conditioner.

[0021] The present invention also provides a pickling agent for pickling metal surfaces, comprising: a pickling solution; and a corrosion inhibitor as described above, wherein the concentration of the corrosion inhibitor is 0.05 to 0.2 wt.% based on a total weight of 100 wt.% of the pickling agent.

[0022] In one embodiment of the present invention, the pickling solution is 10 wt.% hydrochloric acid. Implementation

[0023] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments of the present invention will be described in detail below.

[0024] The working principle of pickling inhibitors lies in their active ingredients adsorbing onto the metal surface to form an inhibitory film, thereby blocking the electrochemical reaction between the acid and the metal, achieving corrosion inhibition. Existing inhibitors are mostly composed of compounds containing nitrogen, sulfur, or phosphorus functional groups. These compounds possess a pair of uncoordinated electrons, which can interact with the empty 3d orbitals of the metal through their excess p-orbital electrons, thus forming a corrosion-inhibiting layer on the metal surface. Common steel pickling inhibitors on the market mainly consist of hexamethylenetetramine or alkynyl alcohol compounds. While hexamethylenetetramine has the advantage of low price, it is a basic compound and easily undergoes acid-base neutralization reactions upon addition to acid, accompanied by the generation of fumes, exothermic reactions, and pungent odors. Furthermore, under acidic conditions, it easily decomposes to produce formaldehyde and ammonia, leading to increased ammonia nitrogen levels in the atmosphere and causing environmental pollution problems.

[0025] This invention provides a corrosion inhibitor for pickling metal surfaces, comprising 10 to 30 wt.% of an acid-treated nitrogen-containing polymer (A), 5 to 20 wt.% of an alkynyl alcohol compound (B), 1 to 10 wt.% of a polyether polyol (C), and an equilibrium amount of water. The alkynyl alcohol compound (B) has a molecular weight of less than 1000, and the polyether polyol (C) has a molecular weight of 200 to 1000. Optionally, the corrosion inhibitor further comprises 0.05 wt.% to 0.5 wt.% of an acid-base conditioning agent.

[0026] Although alkynyl alcohols have good corrosion inhibition properties, they are expensive and lack thermal stability. They are prone to decomposition and failure in high-temperature pickling environments, which limits their feasibility for long-term application.

[0027] The development strategy of this invention lies in selecting a nitrogen-containing polymer (A) that has undergone acid leaching treatment. Due to the high molecular weight of the polymer compound, a small amount can effectively cover the steel surface, forming the main body of the corrosion-inhibiting layer. After acid leaching, the nitrogen-containing polymer (A) transforms into an acidic compound, which not only avoids the side reaction of acid-base neutralization in acid solutions but also improves its water solubility and effective concentration, thereby enhancing the corrosion inhibition effect. Furthermore, the introduction of a small-molecule alkynyl alcohol compound (B) into the formulation can densely fill the gaps in the inhibition layer, further improving the integrity and coverage of the inhibition layer on the steel surface, thus enhancing the overall protective performance. Moreover, the polyether polyol (C) can be used as a brightening agent, effectively improving the whiteness and smoothness of the steel surface after pickling, enhancing its appearance quality and suitability for subsequent processing.

[0028] Optionally, the choice of the alkynol compound (B) is not limited by a specific number of carbon atoms or alcohol groups, and can be acetylenol (AA), propynol (PA), butynediol (BYD), 2-pentyn-1-ol (Pynol-2), 2,4-hexadiyn-1,6-diol (HDD) or a combination thereof.

[0029] Furthermore, the acid-acidified nitrogen-containing polymer (A) can be copolymerized with sulfur-containing or phosphorus-containing functional groups. The nitrogen-containing functional groups of the acid-acidified nitrogen-containing polymer (A) can be in the main chain or branches, and the number of nitrogen-containing functional groups is preferably 5 or more, more preferably 10 or more. The acid used to acidify the nitrogen-containing polymer (A) can be, for example, but not limited to, organic or inorganic acids.

[0030] Optionally, the acidified nitrogen-containing polymer (A) can be polyallylamine hydrochloride (PAA), polydieneamine hydrochloride-sulfur dioxide copolymer (PAS-1), polydieneamine formate-sulfur dioxide copolymer (PAS-2), polydieneamine sulfate-sulfur dioxide copolymer (PAS-3), or a combination thereof.

[0031] The polyether polyol (C) may include, but is not limited to, ethoxy, propoxy, or combinations thereof. Preferably, the polyether polyol (C) is polyethylene glycol with a molecular weight of 200 to 1000.

[0032] Furthermore, the present invention also provides a pickling agent for pickling metal surfaces, comprising: a pickling solution; and a corrosion inhibitor additive as described above, wherein the concentration of the corrosion inhibitor additive is 0.05 to 0.2 wt.% based on a total weight of 100 wt.% of the pickling agent. For example, the pickling solution is 10 wt.% hydrochloric acid.

[0033] Preferred embodiment

[0034] The present invention will be further described with reference to the following comparative examples and embodiments. However, it should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the present invention.

[0035] Test methods and materials

[0036] The metal test pieces used in the comparative examples and embodiments of this invention were all hot-rolled low-carbon steel produced by China Steel Corporation, with a chemical composition of: 0.15 wt.% carbon, 0.58 wt.% manganese, 0.05 wt.% phosphorus, 0.05 wt.% sulfur, and the balance being iron. The test pieces were cut to a size of 4 cm × 3 cm, and the surface rust was removed with fresh hydrochloric acid before testing to ensure consistent testing conditions.

[0037] The pickling inhibitor is prepared by mixing and stirring a nitrogen-containing polymer (A), an alkynyl alcohol compound (B), a polyether polyol (C), and an equal amount of water in a certain proportion at room temperature and pressure until completely dissolved, thus obtaining a homogeneous pickling inhibitor solution. This process has low energy consumption and requires no complicated steps, making it simple to operate.

[0038] The pickling conditions were set as follows: 10 wt.% hydrochloric acid (HCl) was used as the pickling solution, the pickling temperature was controlled at 85°C, the pickling time was 30 minutes, and 0.05 wt.% pickling inhibitor was added to the acid solution.

[0039] The efficiency of pickling corrosion inhibition is evaluated using the weight loss method, which calculates the efficiency by comparing the weight difference of the test pieces before and after pickling. The formula is as follows:

[0040] Inhibition rate (%) = (ΔW0 - ΔW1) / ΔW0 * 100%

[0041] Wherein, ΔW0 is the weight loss of the test piece after acid washing with acid solution without the addition of inhibitor, and ΔW1 is the weight loss of the test piece after acid washing with acid solution with the addition of inhibitor.

[0042] The surface quality of the pickled test pieces was assessed by measuring the roughness with a surface height tester and the whiteness with a colorimeter, which served as the basis for surface quality evaluation.

[0043] Example

[0044] This invention further verifies the influence of different components on the pickling corrosion inhibition performance through a series of experiments. Tables 1, 2, and 3 respectively explore the differences in the pickling corrosion inhibition effects of different acid-treated nitrogen-containing polymers (A), different alkynyl alcohol compounds (B), and polyether polyols with different molecular weights (C).

[0045] In the acid-modified nitrogen-containing polymer (A) section, the tested samples included polyallylamine hydrochloride (PAA), polydieneamine hydrochloride-sulfur dioxide copolymer (PAS-1), polydieneamine formate-sulfur dioxide copolymer (PAS-2), and polydieneamine sulfate-sulfur dioxide copolymer (PAS-3). The results showed that all four provided significant corrosion inhibition effects, with polyallylamine hydrochloride (PAA) showing the best performance, achieving an inhibition rate of 89.94%, indicating that it formed a denser and more stable corrosion-inhibiting layer on the metal surface. Polydieneamine hydrochloride-sulfur dioxide copolymer (PAS-1) and polydieneamine formate-sulfur dioxide copolymer (PAS-2) also showed good effects, reaching 88.78% and 87.71%, respectively, while polydieneamine sulfate-sulfur dioxide copolymer (PAS-3) was relatively lower at 81.64%. Therefore, acid-modified nitrogen-containing polymers have a significant impact on the inhibition efficiency.

[0046] In the alkynyl alcohols (B) section, the tested samples included acetylenol (AA), propynyl alcohol (PA), butynediol (BYD), 2-pentyn-1-ol (Pynol-2), and 2,4-hexadiyn-1,6-diol (HDD). The results showed that butynediol (BYD) had the highest inhibition rate, reaching 89.02%, indicating its superior stability and inhibition performance under acid washing conditions. Proynyl alcohol (PA) and 2-pentyn-1-ol (Pynol-2) also showed good results, at 85.81% and 82.57%, respectively, while acetylenol (AA) was relatively low at only 83.28%. These results indicate that alkynyl alcohols (B) have a significant impact on their adsorption capacity and thermal stability.

[0047] In the polyether polyol (C) section, the tested samples were polyethylene glycols of different molecular weights, including PEG200, PEG400, PEG600, and PEG1000. The results showed that all four (including PEG600 in Tables 1 and 2) provided good corrosion inhibition effects, with inhibition rates of 86.16%, 85.22%, and 86.68%, respectively. Among them, PEG600 (tested in the aforementioned optimal combination) exhibited better performance, not only maintaining a high inhibition rate but also effectively improving the surface whiteness and reducing roughness of the steel after pickling. This indicates that the molecular weight of the polyether polyol affects both inhibition efficiency and surface quality improvement, with PEG600, with its moderate molecular weight, achieving the best balance between performance and economy.

[0048] In summary, the experimental results show that polyallylamine hydrochloride (PAA) is the most effective acid-acidified nitrogen-containing polymer (A), butynediol (BYD) is the most advantageous among alkynyl alcohol compounds (B), and PEG600 is the most outstanding in improving surface quality among polyether polyols (C). The combination of these three compounds creates a synergistic effect, providing excellent corrosion inhibition efficiency and improved steel surface quality, making it one of the optimal formulation combinations of this invention. However, according to the results in Tables 1 to 3, other combinations also achieve significant corrosion inhibition performance in pickling processes, demonstrating the broad application flexibility and industrial value of this invention. Table 1. Differences in corrosion inhibition efficacy of different acidified nitrogen-containing polymers (A) Example 1 Example 2 Example 3 Example 4 composition PAA 30 - - - PAS-1 - 30 - - PAS-2 - - 30 - PAS-3 - - - 30 BYD 20 20 20 20 PEG600 10 10 10 10 water 40 40 40 40 Inhibition rate (%) 89.94 87.71 88.78 81.64 Unit of composition: weight percentage Table 2. Differences in corrosion inhibition efficacy of different alkynyl alcohol compounds (B) Example 5 Example 6 Example 7 Example 8 composition PAA 30 30 30 30 AA 20 - - - PA - 20 - - Pynol-2 - - 20 - HDD - - - 20 PEG600 10 10 10 10 water 40 40 40 40 Inhibition rate (%) 83.28 89.02 85.81 82.57 Unit of composition: weight percentage Table 3. Differences in corrosion inhibition efficacy of polyether polyols (C) with different molecular weights Example 9 Example 10 Example 11 composition PAA 30 30 30 BYD 20 20 20 PEG200 10 - - PEG400 - 10 - PEG1000 - - 10 water 40 40 40 Inhibition rate (%) 86.16 85.22 86.68 Unit of composition: weight percentage

[0049] Table 4 discusses the effects of different composition ratios on corrosion inhibition and the surface quality of steel after pickling. Comparative Example 1 is a commercially available pickling inhibitor currently used in the pickling and oiling line of China Steel Corporation. Its formulation includes 30 to 40 wt.% quaternary amine polymer, 20 to 30 wt.% nitrogen-containing heterocyclic compound, 5 to 10 wt.% acid-base conditioner, and a balanced amount of water. Due to the presence of the acid-base conditioner, its pH value is neutral (pH 7.6). In contrast, all embodiments proposed in this invention are acidic formulations (pH 2 to 3), which can effectively avoid the fumes, odors, and exothermic phenomena caused by acid-base neutralization reactions.

[0050] Example 1 represents the optimal formulation considering both inhibition effectiveness and cost, achieving an inhibition rate of 89.94%, a steel surface roughness of only 0.18 μm, and a whiteness improvement to 66.84, demonstrating its advantages in both corrosion inhibition and surface quality improvement. Example 11 explores the effect of varying PAA dosage. When PAA was increased to 60 wt.%, the inhibition rate only slightly decreased to 89.32%, indicating that the inhibition effect of PAA has saturation; excessive addition does not have a significant additive effect but instead increases the cost burden.

[0051] Example 12 explored adjusting the amount of BYD added. When BYD increased to 40 wt.%, the inhibition rate increased to 90.33%, the highest among all combinations. However, the improvement was limited, and the economic benefits gradually decreased with increasing addition, indicating that the amount of BYD added needs to be controlled within a reasonable range. Example 13 removed PEG600, and the results showed that the inhibition rate remained at 89.23%, similar to Example 1, but the whiteness decreased to 64.24, indicating that although PEG600 is not a key component for inhibition efficacy, it has a significant effect on improving the whiteness of the steel surface and plays an indispensable role as a brightening agent.

[0052] In contrast, the conventional commercial formulation (Comparative Example 1) has an inhibition rate of only 82.99%, a roughness as high as 0.26 μm, and a whiteness of only 62.39, showing that it is significantly inferior to the formulation of the present invention in terms of corrosion inhibition and surface quality improvement. Table 4. Composition of pickling inhibitor formulations in the embodiments and comparative examples of the present invention Example 1 Example 11 Example 12 Example 13 Comparative Example 1 composition PAA 30 60 30 30 - BYD 20 20 40 20 - PEG600 10 10 10 - - Other 1 - - - - 37 Other 2 - - - - twenty two Other 3 - - - - 6 water 40 10 20 50 35 pH value 3.1 2.7 3.0 3.2 7.6 Inhibition rate (%) 89.94 89.32 90.33 89.23 82.99 Roughness Ra (μm) 0.18 0.18 0.17 0.18 0.26 Whiteness 66.84 65.98 66.37 64.24 62.39 Unit of composition: weight percentage

[0053] The acidic pickling inhibitor composition proposed in this invention effectively overcomes the problems caused by the generation of fumes, odors, and exothermic phenomena during the acid-base neutralization reaction in conventional techniques when using basic amine compounds, thus significantly improving operational safety and environmental friendliness. Because the nitrogen-containing polymer, after acid acidification, can form a stable corrosion-inhibiting layer on the metal surface and synergistically work with alkynyl alcohol compounds to densely fill the gaps in the inhibition layer, it can significantly improve corrosion inhibition efficiency. Experimental results show that its inhibition rate can reach over 89%, which is superior to existing commercial formulations. On the other hand, the polyether polyol contained in the formulation has a brightening effect, which can improve the whiteness and smoothness of the steel surface after pickling, reduce roughness, and further improve the appearance quality and subsequent processing performance of the steel. Furthermore, the preparation method of this invention is simple, requiring only stirring and dissolving at room temperature and pressure, with low energy consumption and no complicated procedures, reducing manufacturing costs and technical barriers, and possessing feasibility for industrial application. More importantly, the formulation of this invention does not contain halogen compounds, thus avoiding potential harm to the ozone layer and the ecological environment. It aligns with the development trend of low-carbon processes and green chemistry, combining high efficiency with environmental friendliness. In summary, this invention not only overcomes the shortcomings of prior art in terms of safety and environmental impact, but also balances corrosion inhibition performance, surface quality improvement, and process economics, demonstrating significant industrial application value and promotion potential.

[0054] Although the present invention has been disclosed with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art may make various modifications and alterations without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0055] none

Claims

1. A corrosion inhibitor for pickling metal surfaces, comprising 10 to 30 wt.% of an acid-treated nitrogen-containing polymer (A), 5 to 20 wt.% of an alkynyl alcohol compound (B), 1 to 10 wt.% of a polyether polyol (C), and an equilibrium amount of water, wherein the acid-treated nitrogen-containing polymer (A) comprises at least five nitrogen-containing functional groups located on the main chain or branches, the alkynyl alcohol compound (B) has a molecular weight of less than 1000, and the polyether polyol (C) has a molecular weight of 200 to 1000.

2. The corrosion inhibitory additive as claimed in claim 1, wherein the alkynyl alcohol compound (B) is selected from the group consisting of: ethynyl alcohol, propynyl alcohol, butynediol, 2-pentyn-1-ol and 2,4-hexadiyn-1,6-diol.

3. The corrosion inhibitory additive as claimed in claim 1, wherein the acidified nitrogen-containing polymer (A) is copolymerized with a sulfur-containing functional group or a phosphorus-containing functional group.

4. The corrosion inhibitory additive as claimed in claim 1, wherein the acidified nitrogen-containing polymer (A) comprises at least ten nitrogen-containing functional groups on the main chain or side chain.

5. The corrosion inhibitory additive as claimed in claim 1, wherein the acidified nitrogen-containing polymer (A) is selected from the group consisting of: polyallylamine hydrochloride, polydieneamine hydrochloride-sulfur dioxide copolymer, polydieneamine formate-sulfur dioxide copolymer, and polydieneamine sulfate-sulfur dioxide copolymer.

6. The corrosion inhibitory additive as claimed in claim 1, wherein the acidified nitrogen-containing polymer (A) is acidified by organic or inorganic acid.

7. The corrosion inhibitory additive as claimed in claim 1, wherein the polyether polyol (C) comprises ethoxy, propoxy, or a combination thereof.

8. The corrosion inhibitory additive as described in claim 7, wherein the polyether polyol (C) is polyethylene glycol.

9. The corrosion inhibitor additive as claimed in claim 1, wherein the corrosion inhibitor additive further comprises 0.05 wt.% to 0.5 wt.% of an acid-base conditioner.

10. A pickling agent for pickling metal surfaces, comprising: A pickling solution; And the corrosion inhibitory additive as described in any one of claims 1 to 9, wherein the concentration of the corrosion inhibitory additive is 0.05 to 0.2 wt.% based on 100 wt.% of the total weight of the pickling agent.