Evaluation method for floating roof coating of large oil product storage tank

Abstract

A method for evaluating a floating roof coating of a large oil product storage tank comprises the following steps: measuring the ponding corrosion characteristics of a floating roof, grading the natural corrosion environment of the floating roof according to the ponding corrosion characteristics, and establishing a corrosion simulation environment in a laboratory according to the grading result of the natural corrosion environment. And preparing a coating sample, testing the performance of the coating sample in a corrosion simulation environment in a laboratory, and evaluating whether the coating meets the environmental requirements of the floating roof or not according to a test result. According to the method, short-period evaluation of the coating for the ponding floating roof can be achieved, reference for coating matching selection is provided for design, construction and operation and maintenance units, and long-period stable operation of the storage tank is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical anticorrosion, in particular to a method for evaluating a floating roof coating of a large oil storage tank. Background Art

[0002] The corrosion protection of petrochemical steel equipment has always been a key issue in petrochemical production. Storage tanks are required for the transportation, storage, and transit of crude oil and other petrochemical products. The harsh corrosive environment has caused serious damage to facilities and equipment such as petroleum and chemical industries. Especially for oil tanks in coastal areas, the salt content of land or surface water is high, and there are a large number of salt compounds mixed in the atmosphere; under natural conditions with high air humidity such as the rainy season, an electrolyte film is easily formed on the outside of the floating roof; it is highly corrosive to the anti-corrosion coating; at the same time, the chlorine-containing marine atmosphere and the reaction of oxygen and water with high humidity will accelerate corrosion.

[0003] At present, the selection of external floating roof coatings for domestic oil tanks is mainly based on meeting the requirements of atmospheric corrosion environment; special environments of water immersion are not considered. Primers are mostly epoxy zinc-rich and inorganic zinc-rich, and intermediate paints are mostly epoxy iron oxide; topcoats are mostly polyurethane and acrylic; in recent years, functional coatings such as solar heat reflective topcoats have also begun to be used more. Under the working conditions of water accumulation and ultraviolet coupling on the floating roof, the coatings used for the outer wall of ordinary storage tanks are difficult to reach their service life and fail prematurely. The external floating roof coatings of large oil storage tanks are mostly due to the corrosive environment caused by deformation and water accumulation, and premature failure occurs, such as bubbling and peeling, resulting in failure of metal substrates such as welds exposed to the corrosive environment. In addition, there are problems such as poor surface treatment effect, lack of dust inspection, poor coating effect, resulting in dry spraying and sagging in the construction of external floating roof coatings, which reduces the actual shielding effect of the coating. Against the background of the increasingly serious corrosion problems mentioned above, the industry lacks an evaluation method to determine whether the coating meets the floating roof corrosion environment in a short period of time. It requires a long period of natural environment exposure test, which is not conducive to ensuring the long-term stable operation of the storage tank. Summary of the invention

[0004] The present invention aims to provide a method for evaluating the floating roof coating of a large oil storage tank, so as to realize the short-term evaluation of the coating for the water-logged floating roof, provide a reference for the selection of coatings for the design, construction and operation and maintenance units, and ensure the long-term stable operation of the storage tank.

[0005] In order to solve the above technical problems, the specific scheme adopted by the present invention is: a method for evaluating the floating roof coating of a large oil storage tank, determining the water corrosion characteristics of the floating roof, grading the natural corrosion environment of the floating roof according to the water corrosion characteristics, establishing a corrosion simulation environment in the laboratory according to the natural corrosion environment grading results, preparing coating samples and conducting performance tests of the coating samples in the corrosion simulation environment in the laboratory, and evaluating whether the coating meets the environmental requirements of the floating roof based on the test results.

[0006] Preferably, the water corrosion characteristics include the corrosive ion content, the soluble salt content and the local summer radiation average value:

[0007] Ion chromatography was used to measure the corrosive ion content, and the corrosive ion was SO4. 2- , CL - 、CO3 2- 、NO3 - PO4 3- ;

[0008] According to GBT18570.9-2005 "Surface cleanliness assessment test for steel surface treatment before coating Part 9: Field conductivity determination method for water-soluble salts", the salt content of the water accumulation area, dry area, and dry-wet alternating area of ​​the floating roof of the storage tank is tested respectively, and the highest value is taken as the soluble salt content of the floating roof surface;

[0009] A portable UV intensity meter was used to measure the average local summer radiation.

[0010] Preferably, the corrosive ion content, soluble salt content and ultraviolet intensity of the floating roof are scored respectively, and the scores of the corrosive ion content, soluble salt content and ultraviolet intensity of the floating roof are added together to obtain a natural corrosion environment score, and the higher the natural corrosion environment score, the higher the environmental corrosion rating;

[0011] In the corrosive ion content scoring, the higher the corrosive ion content, the higher the score; in the soluble salt content scoring, the higher the soluble salt content, the higher the score; in the ultraviolet intensity scoring, the higher the local summer radiation average value, the higher the score.

[0012] Preferably, a corrosion simulation environment in the laboratory is established according to the environmental corrosion rating results, and the corrosion simulation environment in the laboratory includes an acid resistance index, a water resistance index, a UV aging resistance index and a salt spray resistance index; the higher the environmental corrosion rating of the floating roof, the higher its acid resistance index, water resistance index, UV aging resistance index and salt spray resistance index.

[0013] Preferably, a coating sample is prepared and subjected to a long-term performance test based on the acid resistance index, water resistance index, UV aging resistance index and salt spray resistance index.

[0014] Preferably, before the long-term performance test, the coating sample is first subjected to a preliminary performance test, the preliminary performance test including flexibility test, coating adhesion performance test, oil resistance test, freeze-thaw cycle test and impact resistance test.

[0015] Preferably, the performance test results of the coating samples satisfy that the coating protection system has no failure phenomena such as blistering, rusting, cracking, peeling, etc.; and the level of powdering, discoloration and gloss loss is ≤ level 1, then the coating is evaluated to meet the environmental requirements of the floating roof.

[0016] Preferably, after the performance test of the coating sample is carried out in a corrosion simulation environment in the laboratory, the same coating sample is prepared and placed in a floating roof water accumulation condition for a long period of field testing.

[0017] The present invention provides a coating performance evaluation method for the floating roof of a large storage tank. The method analyzes the characteristics of the corrosive medium of water accumulation, conducts classification of the natural corrosion environment of the floating roof, establishes a laboratory simulated corrosion environment, prepares coating samples and conducts physical and chemical performance evaluation, and verifies the coating exposure test results in the natural environment. The method can make up for the lack of a floating roof coating performance evaluation method under water accumulation conditions in large storage tanks at home and abroad. The method can avoid the human and material resources consumption caused by long-term natural environment exposure tests, greatly shorten the evaluation time of coatings for water accumulation floating roofs, and provide a reference for the selection of coatings for design, construction and operation and maintenance units, ensuring the long-term stable operation of storage tanks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a technical roadmap for a method for evaluating a floating roof coating of a large oil storage tank. DETAILED DESCRIPTION

[0019] The specific implementation content of the large oil storage tank floating roof coating evaluation method of the present invention is as follows:

[0020] (1) Analysis of characteristics of water corrosion media

[0021] 1) Take samples of the accumulated water on the floating roof of large storage tanks and use ion chromatography to measure the content of corrosive ions, such as SO4 2- , CL - 、CO3 2- 、NO3 - PO4 3- wait.

[0022] 2) Refer to GBT18570.9-2005 "Surface cleanliness assessment test for steel surface treatment before coating Part 9: Field conductivity determination method for water-soluble salts" to test the salt content in the water accumulation area, dry area, and dry-wet alternating area of ​​the floating roof of the tank, and take the highest value as the soluble salt content of the floating roof surface.

[0023] 3) Use a portable UV intensity meter to measure the average local summer radiation.

[0024] (2) Classification of natural corrosion environment of floating roof

[0025] 1) Water corrosivity rating

[0026] Based on the analysis results of the corrosive ion content of the floating roof water in large storage tanks, targeted scoring is performed, see Table 1 for details. Table 1 Corrosive ion content of water

[0027] 2) Grading and scoring of soluble salt content

[0028] Based on the analysis results of the soluble salt content of the floating roof of large storage tanks, targeted scoring is performed, see Table 2 for details. Table 2 Soluble salt content classification Points <![CDATA[Soluble salt content (μg / cm 2- )]]> 10 ＞5 8 2～5 4 1～2

[0029] 3) UV intensity scoring

[0030] Points are assigned based on the strongest local UV intensity. The UV intensity directly affects the service life of the coating. See Table 3 for details. Table 3 UV intensity scoring Points UV intensity 10 ≥10 8 8～10 4 3～7 1 ＜3

[0031] 4) Comprehensive score of corrosion environment in floating roof working conditions

[0032] The above-mentioned corrosive ion content scores, soluble salt content graded scores, and ultraviolet intensity scores are summed up, and scores between 65 and 80 are classified as extremely severe corrosion environments, scores between 40 and 65 are classified as severe corrosion environments, scores between 10 and 40 are classified as moderate corrosion environments, and scores below 10 are classified as slightly corrosive environments. Table 4 Corrosive ion content of accumulated water Rating Total score Very severe corrosion 65～80 Severe corrosion 40～65 Moderate corrosion 10～40 Slight corrosion ＜10

[0033] (3) Establishing a corrosion simulation environment in the laboratory

[0034] 1) Acid resistance index

[0035] According to the floating roof corrosion environment rating results, the acid resistance test conditions and indicators in the laboratory are clarified, see Table 5 for details. Table 5 Acid resistance simulation test indicators Rating <![CDATA[H2SO4 concentration (wt%)]]> Test temperature (℃) Test time (d) Very severe corrosion 10％ 60 45 Severe corrosion 10％ 60 30 Moderate corrosion 5％ Room temperature 30 Slight corrosion 5％ Room temperature 30

[0036] 2) Water resistance index

[0037] According to the floating roof corrosion environment rating results, the water resistance test conditions and indicators in the laboratory are clarified, see Table 6 for details. Table 6 Water resistance simulation test indicators Rating NaCl concentration (wt%) Test temperature (℃) Test time (d) Very severe corrosion 5％ 60 45 Severe corrosion 5％ 60 30 Moderate corrosion 3％ Room temperature 30 Slight corrosion 1％ Room temperature 30

[0038] 3) UV aging test

[0039] According to the floating roof corrosion environment rating results, the UV aging resistance test conditions and indicators in the laboratory are clarified, see Table 7 for details. Table 7 UV aging resistance simulation test indicators

[0040] 4) Salt spray resistance test

[0041] According to the floating roof corrosion environment rating results, the UV aging resistance test conditions and indicators in the laboratory are clarified, see Table 8 for details. Table 8 Salt spray resistance simulation test indicators

[0042] (4) Preparation of coating samples and evaluation of physical and chemical properties

[0043] 1) Prepare coating samples. See the following table for relevant requirements: Table 9 Coating sample preparation

[0044] 2) Conduct preliminary performance testing

[0045] a. Conduct flexibility test: simulate the deformation condition of the floating roof of a large storage tank, and use flexibility test to examine the flexibility index of the coating, which should not be less than 1mm, and there should be no cracking or peeling.

[0046] b. Conduct coating adhesion performance test: Considering that adhesion is an important indicator affecting the long-term anti-corrosion performance of the coating, the adhesion is required to be no less than 5MPa.

[0047] c. Carry out oil resistance test: simulate the oil overflow condition caused by the poor sealing of the floating roof of the storage tank, and require to soak in diesel at room temperature for 30 days. There should be no rust, cracking and peeling.

[0048] d. Carry out freeze-thaw cycle test: simulate the freezing condition in winter after water accumulates on the floating roof. The test is required to be carried out in accordance with SY / T 0319, and the number of cycles should be more than 5 times.

[0049] e. Carry out impact resistance test to simulate the working condition where the tank coating is damaged by external force collision, and require that there should be no cracking, peeling, etc. at a length of no less than 50cm.

[0050] 3) Carry out long-term performance testing

[0051] Carry out water resistance, acid resistance, UV aging resistance and salt spray resistance tests on the coating. The specific test conditions are determined based on the corrosion environment rating results.

[0052] After completing the accelerated test specified above, the corresponding coating samples should meet the following requirements: the coating protection system has no failure phenomena such as blistering, rusting, cracking, peeling, etc.; the level of powdering, discoloration and gloss loss is ≤ Level 1.

[0053] (5) Verification of coating exposure test results against natural environment

[0054] Based on the test data, the results of the on-site exposure and immersion test of the floating roof of large storage tanks were compared and analyzed, and the feasibility of the above laboratory evaluation method was verified based on the comparative analysis results. The basis for subsequent accelerated tests was continuously revised based on the results of the on-site exposure and immersion test.

[0055] The requirements for on-site exposure and immersion tests are as follows: prepare the same type of coating specimens, place them in floating roof water accumulation conditions for long-term field tests, and regularly check the coating appearance.

[0056] Based on the above implementation method, the technical solution of the present invention is further described using two embodiments as follows:

[0057] Example 1

[0058] The floating roof coating of a crude oil storage tank of a domestic coastal refinery company has cracking and peeling, and it is necessary to select an external floating roof coating suitable for the corrosive environment. - The content is 1.26ppm, SO4 2- The content is 26.0ppm, CL - The content is 5.37ppm, CO3 2- The content is 4.59ppm, NO3 - The content is 1.93ppm, PO4 3- The content is 0.88ppm, and the comprehensive score of corrosive ions is 33 points; the surface soluble salts in various areas of the floating roof are tested and the content is 8μg / cm 2 , with a score of 10 points; the average summer UV intensity on site is level 10, with a score of 10 points; in summary, the comprehensive score is 53 points, which is rated as severe corrosion. The acid resistance test conditions are determined to be 10% H2SO4, water bath 60℃, and the test time is not less than 30d; the water resistance test conditions are 5% NaCl, water bath 60℃, and the test time is not less than 30d; the UV aging resistance test conditions are irradiation intensity 0.51 (w / m 2 / nm), test temperature 65℃, test time not less than 3000h, dry-wet cycle 120min:18min; salt spray resistance test conditions are NaCl 5wt%, test temperature 35℃, test time 1200h, and the final scratch corrosion expansion on both sides is 2mm.

[0059] Tests were conducted on a coating supporting system with application potential. The test system is as follows: environmentally friendly graphene rust-resistant primer 80μm~100μm + environmentally friendly fiber-modified epoxy micaceous iron intermediate paint 150μm~180μm + environmentally friendly fluorine-modified composite coating 80μm~100μm.

[0060] Conduct flexibility test: the index is 1mm, and there is no cracking or peeling. Conduct coating adhesion performance test: the adhesion is 10MPa. Conduct oil resistance test by immersing in diesel at room temperature for 30 days, and no rust, cracking, peeling and other phenomena occur. Conduct freeze-thaw cycle test, and no failure phenomena such as cracking and peeling occur after 5 cycles. Conduct water resistance, acid resistance, UV aging resistance, and salt spray resistance tests based on the determined long-cycle test indicators, and conduct appearance inspection after the test. The coating protection system has no failure phenomena such as blistering, rust, cracking, peeling, etc.; the level of powdering, discoloration and loss of gloss is ≤1.

[0061] Three samples with a size of 150*70*1mm and a material of Q235 were prepared and placed in the floating roof technology of the storage tank for a long-term exposure and immersion test. After one year, the samples were taken out for testing. The adhesion was 10MPa, and the coating protection system had no failure phenomena such as blistering, rusting, cracking, and peeling; the level of powdering, discoloration, and gloss loss was ≤1.

[0062] Maintenance construction was carried out on the floating roof of the storage tank and an anti-corrosion coating matching system was used. After three years of actual operation on site, adhesion testing and appearance inspection were carried out. The test results showed that the adhesion was greater than 10Mpa.

[0063] The coating protection system has no failure phenomena such as blistering, rusting, cracking, peeling, etc. The level of powdering, discoloration and gloss loss is ≤ level 1. It meets the use requirements and verifies the scientificity and practicality of the method.

[0064] Example 2

[0065] The floating roof coating of a crude oil storage tank of an inland petrochemical enterprise in China was cracked and peeled off, and it was necessary to select an external floating roof coating suitable for the corrosive environment. - Content is 0.5ppm, SO4 2- Content is 15ppm, CL - The content is 2.5ppm, CO3 2- The content is 2.5ppm, NO3 - The content is 0.8ppm, PO4 3- The content is 0.5ppm, and the comprehensive score of corrosive ions is 15 points; the surface soluble salts in each area of ​​the floating roof are tested, and the content is 1.5μg / cm 2, with a score of 4 points; the average summer UV intensity on site is level 5, with a score of 4 points; in summary, the comprehensive score is 23 points, which is rated as moderate corrosion. The acid resistance test conditions are determined to be 5% H2SO4, room temperature, and the test time is not less than 30 days; the water resistance test conditions are 3% NaCl, room temperature, and the test time is not less than 30 days; the UV aging resistance test conditions are irradiation intensity 0.28 (w / m 2 / nm), test temperature 35℃, test time not less than 2000h, dry-wet cycle 240min:240min; salt spray resistance test conditions are NaCl 5wt%, test temperature 35℃, test time 1000h, and the final scratch corrosion expansion on both sides is 2mm.

[0066] Tests were conducted on a coating supporting system with application potential. The test supporting system is: environmentally friendly graphene rust-resistant primer 60μm~80μm + environmentally friendly fiber-modified epoxy micaceous iron intermediate paint 100μm~120μm + environmentally friendly fluorine-modified composite coating 40μm~80μm.

[0067] Conduct flexibility test: the index is 1mm, and there is no cracking or peeling. Conduct coating adhesion performance test: the adhesion is 11MPa. Conduct oil resistance test by immersing in diesel at room temperature for 30 days, and no rust, cracking, peeling and other phenomena occur. Conduct freeze-thaw cycle test, and no failure phenomena such as cracking and peeling occur after 5 cycles. Conduct water resistance, acid resistance, UV aging resistance, and salt spray resistance tests based on the determined long-cycle test indicators, and conduct appearance inspection after the test. The coating protection system has no failure phenomena such as blistering, rust, cracking, peeling, etc.; the level of powdering, discoloration and loss of gloss is ≤1.

[0068] Three samples with a size of 150*70*1mm and a material of Q235 were prepared and placed in the floating roof technology of the storage tank for a long-term exposure and immersion test. The samples were taken out for testing after 2 years. The adhesion was 11MPa, and the coating protection system had no failure phenomena such as blistering, rusting, cracking, and peeling; the level of powdering, discoloration, and gloss loss was ≤1.

[0069] The floating roof of the storage tank was maintained and constructed with the anti-corrosion coating system tested and tested. After five years of actual operation on site, adhesion testing and appearance inspection were carried out. The test results showed that the adhesion was greater than 10MPa, and the coating protection system had no failure phenomena such as blistering, rusting, cracking, and peeling; the level of powdering, discoloration, and gloss loss was ≤ Level 1. It met the use requirements and verified the scientificity and practicality of the method.

Claims

1. A method for evaluating the floating roof coating of a large oil storage tank, characterized in that: Determine the water corrosion characteristics of the floating roof, classify the natural corrosion environment of the floating roof according to the water corrosion characteristics, establish a corrosion simulation environment in the laboratory based on the natural corrosion environment classification results, prepare coating samples and test the performance of the coating samples in the corrosion simulation environment in the laboratory, and evaluate whether the coating meets the environmental requirements of the floating roof based on the test results.

2. A method for evaluating a large oil storage tank floating roof coating as claimed in claim 1, characterized in that: The corrosion characteristics of the water accumulation include the content of corrosive ions, the content of soluble salts and the average local summer radiation. The content of corrosive ions was measured by ion chromatography, and the corrosive ions were SO4 2- , CL - 、CO3 2- 、NO3 - PO4 3- ; According to GBT18570.9-2005 "Surface cleanliness assessment test for steel surface treatment before coating Part 9: Field conductivity determination method for water-soluble salts", the salt content of the water accumulation area, dry area, and dry-wet alternating area of ​​the floating roof of the storage tank is tested respectively, and the highest value is taken as the soluble salt content of the floating roof surface; A portable UV intensity meter was used to measure the average local summer radiation.

3. A method for evaluating a large oil storage tank floating roof coating as claimed in claim 2, characterized in that: The corrosive ion content, soluble salt content and ultraviolet intensity of the floating roof are scored respectively, and the scores of the corrosive ion content, soluble salt content and ultraviolet intensity of the floating roof are added together to obtain the natural corrosion environment score. The higher the natural corrosion environment score, the higher the environmental corrosion rating; In the corrosive ion content scoring, the higher the corrosive ion content, the higher the score; in the soluble salt content scoring, the higher the soluble salt content, the higher the score; in the ultraviolet intensity scoring, the higher the local summer radiation average value, the higher the score.

4. A method for evaluating a large oil storage tank floating roof coating as claimed in claim 3, characterized in that: A corrosion simulation environment is established in the laboratory according to the environmental corrosion rating results. The corrosion simulation environment in the laboratory includes acid resistance index, water resistance index, UV aging resistance index and salt spray resistance index. The higher the environmental corrosion rating of the floating roof, the higher its acid resistance index, water resistance index, UV aging resistance index and salt spray resistance index.

5. A method for evaluating a large oil storage tank floating roof coating as claimed in claim 4, characterized in that: Prepare coating samples and conduct long-term performance tests based on the acid resistance index, water resistance index, UV aging resistance index and salt spray resistance index.

6. A method for evaluating a large oil storage tank floating roof coating as claimed in claim 5, characterized in that: Before the long-term performance test, the coating samples are first subjected to preliminary performance tests, including flexibility test, coating adhesion performance test, oil resistance test, freeze-thaw cycle test and impact resistance test.

7. A method for evaluating a large oil storage tank floating roof coating according to claim 1, characterized in that: The performance test results of the coating samples satisfy that the coating protection system has no failure phenomena such as blistering, rusting, cracking, peeling, etc.; if the level of powdering, discoloration and gloss loss is ≤ Level 1, the coating is evaluated to meet the environmental requirements of the floating roof.

8. A method for evaluating a large oil storage tank floating roof coating according to claim 1, characterized in that: After the performance test of the coating samples was carried out under the corrosion simulation environment in the laboratory, the same coating samples were prepared and placed in the floating roof water accumulation condition for long-term field testing.

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