JP5413292B2 - Corrosion accelerated test method for heavy anti-corrosion coated steel - Google Patents

Description

  The present invention relates to a corrosion acceleration test method for heavy anticorrosion coated steel materials used in severe corrosive environments such as the ocean and rivers.

Corrosion protection of harbor steel structures exposed to severe corrosive environments such as rivers and oceans varies depending on the environment in which the harbor structures are arranged. The parts arranged in the sea part of the harbor structure are subjected to anticorrosion, and the parts arranged in the tidal and splash zones are subjected to heavy corrosion prevention such as polyurethane and polyethylene.
Since such harbor steel structures are required to have a durability of 20 to 50 years, it is necessary to evaluate the durability based on corrosion prediction. In particular, in recent years, there has been a demand for design and maintenance methods for harbor structures that take into account life cycle costs (LCC), and it is necessary to establish a method for evaluating the durability of heavy anticorrosion coated steel materials based on corrosion prediction.

As a method for predicting the life of steel materials for evaluating the durability of steel structures, environmental factor values are measured at one or more sites in the target actual structure or a structure simulating the actual structure. Based on the relationship between the amount of corrosion and the amount of corrosion and the measured values of the environmental factors, data showing the relationship between the amount of corrosion and the exposure time is obtained, and the progress of corrosion is predicted based on that data. A life prediction method has been proposed (see, for example, Patent Document 1).
In addition, based on the corrosion rates of two or more metals with known corrosion rates that have been used for a long time in the actual structure, the metal (plating, diffusion layer, coating, organic It is possible to accurately estimate the corrosion rate and anti-corrosion time of unknown metals in real environments and real structures by short-term corrosion acceleration tests for coatings, inorganic coatings, organic-inorganic composite coatings, etc. A method for predicting the corrosion resistance of a metal and a coated metal plate has been proposed (see, for example, Patent Document 2).

JP 2002-318227 A JP 2006-234802 A

The form of corrosion development for heavy anti-corrosion coated steel is a special corrosion in which the corrosion gradually progresses from the edge of the coating to the bottom of the coating layer, and does not occur in the remaining coating, but only in the coating peeling area. Indicates the form of progress.
However, what was disclosed in Patent Document 1 is based on the premise that corrosion occurs on the entire surface of the steel material, and cannot be applied to the case where the corrosion progresses from the end portion of the coating as in the heavy anticorrosion coated steel material.
In addition, what is disclosed in Patent Document 2 is based on the premise that the steel material corrodes on the entire surface after the coating disappears, and no corrosion occurs in the coating remaining portion as in the heavy anticorrosion coated steel material, and only in the coating peeling portion. Not applicable when corrosion occurs.

As described above, there is no conventional technique capable of accurately predicting corrosion or predicting the life of a steel having a special corrosion growth form such as a heavy anti-corrosion coated steel material in consideration of a special corrosion mechanism.
The reason why it is not possible to accurately predict the corrosion of heavy anti-corrosion coated steel is due to the fact that there is no established corrosion acceleration test method that reproduces the form of corrosion development in which corrosion proceeds from the end of the coating like heavy anti-corrosion coated steel. Therefore, development of a corrosion acceleration test method for such heavy anticorrosion coated steel materials is desired.

  The present invention has been made in order to solve such problems, and an object of the present invention is to provide a technique for accurately predicting corrosion in a short period of time in consideration of the corrosion mechanism of a heavy anticorrosion coated steel material.

In order to solve the above-mentioned problems, the present inventors have studied a corrosion acceleration test method for reproducing the corrosion form of the heavy anticorrosion coated steel material.
FIG. 1 is a schematic view showing a state of progress of corrosion in a cross section near a joint of a steel sheet pile subjected to a heavy anticorrosion coating that is an example of a heavy anticorrosion coated steel material.
As shown in FIG. 1, the heavy-duty coated steel material has a coated end portion 5 of the heavy-duty coated coating 3 in the vicinity of the joint 1, and an uncoated steel material exposed portion 7 exists from the coated end portion 5 to the joint side. Furthermore, the tip side is the inside 9 of the joint.
The joint interior 9 where the joint 1 and the joint 1 are combined is difficult for water and oxygen to enter, and corrosion is suppressed. Therefore, the corrosion of the heavy anticorrosion coated steel material occurs under the coating layer with the peeling of the coating from the steel material exposed portion 7 and the coated end portion 5. In the example of FIG. 1, rust has entered the distance S from the coating end 5 under the coating layer.

The inventor investigated the relationship between the corrosion amount of the steel material exposed portion 7 and the coating layer and the corrosion time for the heavy anticorrosion coated steel material as described above. As the coating layer, the investigation was performed at three locations of 5 mm, 10 mm, and 15 mm from the coated end portion 5.
The results of the investigation are shown in the graph of FIG. In the graph of FIG. 2, the vertical axis represents the corrosion amount (mm), and the horizontal axis represents the elapsed time (day) from the start of corrosion at each position (test period—corrosion start time). In addition, about a period, it converts as 365day = 1y.
As shown in FIG. 2, the corrosion immediately proceeds in the steel exposed portion 7, but gradually begins to corrode under the coating layer, and the corrosion rate is greatest at the steel exposed portion 7, and three locations under the coating layer. Both were found to be about 1/2 of the exposed steel.

From the above results, the inventor used (1) the corrosion rate of the steel exposed portion of the heavy anticorrosion coated steel material, and (2) the rust penetration rate under the coating layer as a representative index of corrosion degradation. It was found that an accurate corrosion acceleration test can be performed by setting test conditions for accelerating each while maintaining the speed ratio of (2).
In the actual environment, the corrosion rate of the exposed steel part is amm / y, the rust penetration rate under the coating layer is bmm / y, the corrosion rate of the exposed steel part in the corrosion acceleration test is a'mm / y, and the rust under the coating layer The penetration speed is b'mm / y. Focusing on the corrosion rate of the exposed steel part, a ′ / a becomes the acceleration factor, and focusing on the rust penetration rate, b ′ / b becomes the acceleration factor. When a ′ / a = b ′ / b, that is, b ′ × a / (b × a ′) = 1.0, the ratio of the corrosion rate of the exposed steel part and the rust penetration rate in the actual environment is maintained, respectively. In this way, it is possible to perform a test in accordance with the actual environment by performing a corrosion acceleration test.

However, it is rare that b ′ × a / (b × a ′) = 1.0, and in general, the value of b ′ × a / (b × a ′) is in the direction from 1.0 to ±. Sneak away. Therefore, in an actual corrosion acceleration test, the extent of deviation of the value of b ′ × a / (b × a ′) from 1.0 was examined as to whether it was useful as a corrosion acceleration test.
FIG. 3 is a model of a post-corrosion cross section in the vicinity of the end portion of the heavy anticorrosion coated steel material used in this study.

The model conditions were a steel material exposed portion corrosion rate of 0.2 mm / y, a rust intrusion rate of 5 mm / y, and a sublayer corrosion rate of 0.1 mm / y after 10 years. Although the length of the steel exposed portion in the vicinity of the joint of the heavy anticorrosion coated steel material is about 3 to 10 mm, it is 5 mm in this model.
In this cross-sectional model after 10 years, the corrosion amount of the steel exposed portion is 0.2 mm × 10 = 2 mm, and the corrosion cross-sectional area of the steel exposed portion is 2 mm × 5 mm = 10 mm ² . Further, the amount of corrosion at the end of the coating layer is 0.1 × 10 = 1 mm, and the portion where corrosion has occurred after 10 years is 5 mm × 10 = 50 mm from the end of the coating layer. The lower corrosion cross-sectional area is obtained as a triangular area and is 1 mm × 50 mm × 1/2 = 25 mm ² . Therefore, the corrosion cross-sectional area in the steel material exposed portion and the entire area under the coating layer is 10 mm ² +25 mm ² = 35 mm ² .

When b ′ × a / (b × a ′) deviates from 1.0, it was determined how much error occurred in the corrosion cross section in the post-corrosion cross section model after 10 years shown in FIG. Specifically, when the corrosion amount of the exposed steel material is fixed to 2 mm and b ′ × a / (b × a ′) is 1.1, the rust penetration distance is multiplied by 1.1, and b ′ × a / ( When b × a ′) is 0.9, the rust penetration distance is multiplied by 0.9.
FIG. 4 is a graph showing the relationship between the deviation of b ′ × a / (b × a ′) from 1.0 and the relative error, the vertical axis is the relative error (%), and the horizontal axis is b ′. It is a value of * a / (b * a ').
Durability evaluation of harbor steel structures is obtained from the secondary moment of section of heavy corrosion-resistant coated steel, not directly from the corrosion cross section, but it is possible to predict the corrosion cross section with a relative error of 30% or less. Useful.
Therefore, when the value of b ′ × a / (b × a ′) that can predict the corrosion cross section with a relative error of 30% or less is read from the graph of FIG. 4, 0.6 ≦ b ′ × a / (b × a ′). ) ≦ 1.4. Conversely, when 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4, it can be seen that the relative error of the corrosion cross section is 30% or less.

  The present invention has been obtained based on the above-described experiments and based on knowledge, and specifically comprises the following configuration.

(1) The corrosion promotion test method for heavy anticorrosion coated steel materials according to the present invention is a corrosion acceleration test method for heavy anticorrosion coated steel materials having a coating end, and is an exposure test in a real environment for heavy anticorrosion coated steel material test pieces. Using test specimens with the same specifications as those used in the actual environment exposure test process and the actual environment exposure test process to determine the corrosion rate amm / y of the exposed steel part and the rust penetration speed under the coating layer bmm / y Pre-corrosion with a preliminary corrosion-acceleration test step for performing corrosion acceleration tests under multiple types of test conditions to determine the steel corrosion rate a'mm / y and the rust penetration rate b'mm / y under the coating layer B ′ × a / (b × a ′) is obtained for the steel material corrosion rate a ′ mm / y and the rust penetration rate b ′ mm / y in each test condition obtained in the accelerated test process, and this value is closest to 1. The test conditions for the corrosion acceleration test are determined as the corrosion acceleration test conditions, and the determined test conditions are determined. It is characterized in carrying out the accelerated corrosion test with.

(2) Further, in the above (1), the value of b ′ × a / (b × a ′) under the test conditions determined as the corrosion promotion condition is 0.6 ≦ b ′ × a / (B × a ′) ≦ 1.4 is satisfied.

(3) Further, in the above (1) or (2), the test conditions in the corrosion acceleration test are characterized by repeating a series of processes including a salt spray, drying and wetting processes. is there.

  In the present invention, a corrosion promotion test method for heavy corrosion-resistant coated steel material having a coated end portion, wherein the corrosion rate of the exposed steel material is amm / y by performing an exposure test in a real environment of the heavy corrosion-resistant coated steel specimen. A steel material that has been subjected to a corrosion acceleration test under multiple types of test conditions using a test piece with the same specifications as that used in the actual environment exposure test process and the actual environment exposure test process to determine the rust penetration speed under the layer bmm / y Steel corrosion under each test condition obtained in the preliminary corrosion acceleration test step, which has a corrosion rate a'mm / y and a preliminary corrosion acceleration test step for determining the rust penetration rate b'mm / y under the coating layer B ′ × a / (b × a ′) is obtained for the speed a ′ mm / y and the rust intrusion speed b ′ mm / y, and the test condition of the corrosion acceleration test whose value is closest to 1 is determined as the corrosion acceleration test condition. In order to perform a corrosion promotion test using the determined test conditions Since, it is possible to more accurate corrosion prediction of heavy duty coated steel in a short period of time, it is possible to correct the durability evaluation.

It is a schematic diagram which shows the mode of corrosion progress of the cross section of the joint vicinity of the steel sheet pile which performed the heavy anti-corrosion coating which is an example of a heavy anti-corrosion coating steel material. It is a graph which shows the corrosion rate of the steel-material exposed part of a heavy-duty protection coating steel material, and a coating layer. It is a model of the post-corrosion cross section after 10 years near the end of the heavy-duty coated steel material. It is a graph which shows the relationship between the value of b'xa / (bxa ') which is a parameter | index which determines a corrosion acceleration test condition in this invention, and the relative error of the corrosion cross section in a cross-section model after corrosion. It is a flowchart which shows a flow from the corrosion test condition extraction in the corrosion acceleration test method of the heavy corrosion-resistant coating steel material in this Embodiment to this test implementation. It is a graph which shows the corrosion rate of the steel material exposure part in the corrosion acceleration test of the heavy-duty protection coating steel material in this Embodiment, and a marine exposure test. It is a graph which shows the rust penetration | invasion speed | rate under the coating layer in the corrosion acceleration test of the heavy-duty protection coating steel materials in this Embodiment, and a marine exposure test. It is a schematic diagram of the heavy corrosion-resistant coated steel material small test piece used in the examples of the present invention. It is explanatory drawing of the test conditions used in the preliminary | backup corrosion acceleration | stimulation test of the Example of this invention.

The corrosion promotion test for heavy corrosion-coated steel materials according to the present embodiment is a representative evaluation index of the corrosion rate of the steel material exposed portion and the rust penetration rate under the coating layer as a deterioration mode of the heavy corrosion-coated steel material occurring in the marine environment. did. The flow from the extraction of corrosion accelerated test conditions for the heavy anticorrosion coated steel material of the present invention to the implementation of this test will be described with reference to FIG.
As shown in the flowchart of FIG. 5, the corrosion promotion test method according to the present embodiment includes a marine exposure test step (S1) in which an exposure test is performed in the marine environment, which is the actual environment of the heavy anticorrosion-coated steel material test piece, Preliminary corrosion acceleration test step (S2) for performing corrosion acceleration test under multiple types of test conditions using the same heavy anticorrosion coated steel specimen as used in the exposure test step, and marine exposure test and preliminary Preliminary corrosion evaluation process (S3) to measure the amount of corrosion and rust intrusion of the exposed steel part in the corrosion test, and calculate the corrosion rate and rust infiltration rate of the exposed steel part in the marine exposure test and preliminary corrosion test Corrosion rate / rust intrusion rate calculation step (S4), corrosion rate amm / y of exposed steel in marine exposure test, rust intrusion rate bmm / y under coating layer, and multiple types of tests in preliminary corrosion acceleration test On condition A corrosion acceleration test is performed, and the steel material corrosion rate a ′ mm / y and the rust penetration rate b ′ mm / y below the coating layer are 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4. The accelerated test condition extraction step (S5) for extracting the test conditions and the corrosion accelerated test is performed under the test conditions in which the value of b ′ × a / (b × a ′) is closest to 1 among the extracted test conditions. A corrosion acceleration test step (S6) and an evaluation step (S7) for evaluation are provided.
Hereinafter, the meaning of each term and each process will be described in detail.

  Heavy anti-corrosion coated steel materials are steel sheet piles, steel pipe sheet piles, steel pipe piles, etc. that have been coated with organic coatings such as polyurethane and polyethylene in harbors exposed to severe corrosive environments such as the ocean and rivers. These heavy anticorrosion coatings are thick films of 2 mm or more, and the corrosion of steel materials does not occur in the healthy part of the coating. Corrosion occurs under the coating as the exposed steel part near the coating edge and the coating peel off.

<Real environment exposure test process (S1)>
The actual environment exposure test process (S1) is a process of conducting an ocean exposure test using multiple types of small specimens of heavy anticorrosion coating, and the corrosion rate and rust penetration rate of the exposed steel parts of the heavy anticorrosion coating steel in the marine environment. Do to figure out.
In order to confirm the versatility of the test, it is preferable to perform a plurality of types of coating on the heavy anticorrosion-coated small test piece, and it is more preferable to perform the coating with three or more types to improve the versatility of the test. It is more preferable to use a plurality of test pieces for each type.
As the shape of the heavy corrosion-resistant coated small test piece, one having a heavy corrosion-resistant coated end portion and a steel exposed portion is used. For example, when a 100 mm square test piece is used, a steel material exposed portion having a width of about 20 mm is provided at the center portion and the other portion is covered with a predetermined organic coating layer.
Such a corrosion-proof coated small test piece is exposed to the sea, tidal zone, splash zone, etc., and the corrosion progressing form is observed. The exposure test needs to be conducted over multiple periods to determine the corrosion rate. About a period, the period of the grade which can confirm peeling from a coating edge part and corrosion under a coating layer is required, for example, is about 1 to 3 years.

<Preliminary corrosion acceleration test step (S2)>
Preliminary corrosion acceleration test step (S2) is a step in which a corrosion acceleration test is preliminarily performed using the same heavy anticorrosion coated small test piece as in (S1), and the steel exposed portion of the heavy anticorrosion coated steel material in the marine environment. This is a preliminary test to extract test conditions that are accelerated at a ratio equal to the corrosion rate and rust penetration rate.
The method of the corrosion acceleration test is not particularly limited, but a cycle test in which salt water and wet / dry cycles are given is preferable in that it simulates the actual environment. In order to determine the corrosion acceleration test conditions, it is desirable to carry out under a plurality of conditions such as changing the cycle pattern and the ratio of each process, and it is desirable to carry out at least three types for comparison.
The accelerated corrosion test needs to be performed in multiple periods to determine the corrosion rate. The test period is not particularly limited, but a period of time is required so that peeling from the edge and corrosion under the coating layer can be confirmed, for example, about 1 to 6 months.

<Preliminary corrosion evaluation process (S3)>
The preliminary corrosion evaluation step (S3) is a step of measuring the steel material exposed portion corrosion amount and the rust penetration distance in the marine exposure test and the preliminary corrosion acceleration test.
The amount of corrosion of steel is determined by removing the heavy protection coating and corrosion products after the test, measuring the thickness using a caliper, laser displacement meter, etc., and the thickness before applying the heavy corrosion protection coating before the test. It can be obtained from the difference between
Also, the rust penetration distance is the distance from the edge position of the coating measured before the test to the rust penetration position after measuring the distance from the edge of the test piece to the coating edge before the test, removing the heavy anti-corrosion coating after the test. Can be measured directly or after taking a photograph using a caliper.
In any measurement of the corrosion amount and the rust penetration distance, it is preferable to measure at a plurality of locations.

<Corrosion rate / rust intrusion rate calculation step (S4)>
The corrosion rate / rust intrusion rate calculating step (S4) is a step of calculating the corrosion rate and the rust intrusion rate at the exposed steel part in the marine exposure test and the corrosion acceleration test from the measurement result of (S3). The marine exposure test results and corrosion acceleration test results are evaluated in the same way.
FIG. 6 shows an example of how to obtain the corrosion rate of the exposed steel part, and FIG. 7 shows an example of how to obtain the rust penetration rate under the coating layer. The vertical axis of the graph shown in FIG. 6 represents the corrosion amount (mm) of the exposed steel material, and the horizontal axis represents the test period (day). Moreover, the vertical axis | shaft of the graph shown in FIG. 7 shows the rust penetration distance (mm), and the horizontal axis has shown the test period (day).
The steel exposed portion corrosion rate is the average value of the exposed amount of steel exposed portion corrosion over a plurality of periods measured in (S3) (average of multiple test pieces with the same specification, average of measured values at multiple locations) on the graph of FIG. The regression line passing through the origin is obtained by the least square method, and the slope is taken as the corrosion rate.
Similarly, for the rust intrusion rate, the average value of the rust intrusion distances measured in (S3) over a plurality of periods is plotted on the graph of FIG. 7, and a regression line passing through the origin is obtained by the least square method, and the slope is determined. Rust penetration speed.

<Accelerated test condition extraction step (S5)>
The accelerated test condition extraction step (S5) is a step of extracting the corrosion accelerated test conditions by comparing the corrosion rate and rust penetration rate of the exposed steel parts in the marine exposure test and the accelerated corrosion test obtained in (S4). is there. Specifically, it is performed as follows.
Corrosion rate a'mm / y in the exposed steel part in the marine exposure test, rust penetration speed under the coating layer bmm / y, and the corrosion rate test a ' b ′ × a / (b × a ′) is calculated for mm / y and the rust penetration speed b ′ mm / y under the coating layer.
When b ′ × a / (b × a ′) = 1.0, it indicates that the ratio between the corrosion rate of the steel exposed portion and the rust penetration rate in the corrosion acceleration test is equal to that in the marine exposure test. Therefore, the test condition to be extracted is such that the value of b ′ × a / (b × a ′) is closest to 1.

In addition to the condition that the value of b ′ × a / (b × a ′) is closest to 1 as the test condition to be extracted, the value of b ′ × a / (b × a ′) is 0.6. It is preferable that ≦ b ′ × a / (b × a ′) ≦ 1.4.
In the corrosion acceleration test with 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4, the corrosion amount of the steel exposed portion is the same as that in the ocean exposure test. The relative error from the result of the exposure test is 30% or less, which is useful for evaluating the durability of heavy anticorrosion coated steel materials.
On the other hand, in the case of the corrosion acceleration test in which the value of 0.6 ≦ b ′ × a / (b × a ′) is less than 0.6 or greater than 1.4, the corrosion cross section is the same as that in the marine exposure test. The result and the relative error are larger than 30%, which is not necessarily appropriate as a corrosion acceleration test for evaluating the durability in the marine environment.

In addition, in any of the heavy anticorrosion coating species used in (S1) and (S2), by extracting those satisfying the condition of 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4, It can increase the versatility of the test and can be used as a useful evaluation method for new materials.
In addition, the acceleration magnification in the obtained corrosion acceleration test is an average value of the acceleration magnification of the steel material exposed portion corrosion rate in the plurality of types of test pieces. Here, when none of the plurality of heavy anti-corrosion coating types satisfy the condition of 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4, the preliminary corrosion promotion test step (S2) Return, change the test conditions, and then perform the condition extraction step in the same way.

<Corrosion promotion test process (S6)>
The corrosion acceleration test step (S6) is a step of performing a corrosion acceleration test on the heavy corrosion-resistant coated small test piece to be evaluated. As the heavy corrosion-resistant coated small test piece, the same test piece as used in (S1) and (S2) is used. The test conditions are the test conditions extracted in (S5).
The test period needs to be performed in multiple periods in order to obtain the corrosion rate and the rust penetration rate, and a period in which peeling from the coating end and corrosion under the coating layer can be confirmed is required. For example, about 1 to 6 months It is.

<Corrosion evaluation process (S7)>
The corrosion evaluation step (S7) is a step of performing corrosion evaluation of the heavy-duty anticorrosion coated small test piece. Corrosion is evaluated from the corrosion rate of the exposed steel material, the rust penetration rate under the coating layer, and the corrosion rate under the coating layer.
The corrosion rate of the exposed steel material and the rust penetration rate under the coating layer are determined in the same manner as (S3) and (S4). Moreover, the corrosion rate under the coating layer is plotted in the same way as shown in FIG. 6 for the average corrosion amount for each distance from the coating end in a plurality of periods, and the regression through the origin by the least square method. Find the straight line and use the slope as the corrosion rate.

  As described above, according to the corrosion acceleration test method of the present embodiment, the corrosion form of the heavy anti-corrosion coated steel material that occurs in an actual environment such as the ocean is accurately reproduced, thereby making it possible to more accurately detect the heavy anti-corrosion coated steel material. This makes it possible to evaluate the durability.

  Examples of the present invention will be described below.

<Steel plate used for specimen>
In both the marine exposure test and the corrosion acceleration test, a hot rolled steel sheet (base steel material) (JIS SS400) of size 100 mm × 100 mm × 6 mm whose surface was made approximately 50 μm in 10-point average roughness by steel grid blasting was used as a test piece.

<Thickness measurement method>
The thickness of the steel sheet was measured using a laser displacement meter. The entire surface was measured at 1 mm intervals with the coated surface facing up. In the measurement, a special jig was attached to the stage of the laser displacement meter so that the position (each measurement point) of the test piece did not shift before and after the test, so that the plate thickness could always be measured at the same position in the horizontal direction. . After the test, pickling was performed after the coating was peeled off, and the rust was completely removed.

<Heavy anti-corrosion coating>
The following three types of heavy anticorrosion coatings were applied to the steel plate. Before applying the heavy anti-corrosion coating, a 20 mm wide vinyl tape was stretched from the upper end to the lower end of the steel plate at the center of the steel plate to make a portion to be the exposed portion of the steel plate. The heavy anticorrosion coating was made of two types of polyurethane coating and one type of polyethylene coating.
The polyurethane-coated steel sheet (hereinafter referred to as “PU-A”) is spray-coated with a polyurethane resin two-component curing type primer (“Permguard 331” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to an average film thickness of 50 μm. After drying at room temperature for 24 hours, 3.0 mm of polyurethane resin (“Permguard 137” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was applied. After coating, it was cured at room temperature for 7 days.

  Another polyurethane-coated steel sheet (hereinafter referred to as “PU-B”) was coated with an epoxy resin two-component curing primer (Nippon Paint U-1001 primer) by airless spraying with an average film thickness of 50 μm for 24 hours at room temperature. And dried. Thereafter, polyurethane (U-1001-S1 manufactured by Nippon Paint Co., Ltd.) was applied by 3.0 mm with an airless spray and cured for 7 days.

  A polyethylene-coated steel sheet (hereinafter referred to as “PE”) was coated with 50 μm of epoxy resin two-component curing type primer (Japan Epoxy Resin JER828: B002 = 10: 5) using a glass rod, 120 ° C. × 8 Pre-cured in 5 minutes. Next, 0.3 mm adhesive polyethylene (manufactured by Mitsui Chemicals, NE060) and 1.9 mm polyethylene (manufactured by Nippon Polychem) were laminated, pressed with a hot press at 180 ° C. for 10 minutes under a pressure of 0.1 Mpa, and then air-cooled. .

  After the heavy anticorrosion coating is applied, in order to peel off the vinyl tape stretched at the center of the steel plate surface 20 mm wide from the steel surface, the heavy anticorrosion coating on the end of the 20 mm wide vinyl tape is cut with a cutter, and the heavy anticorrosion coating is removed. A steel exposed part and a coated end part were prepared. A schematic diagram of the prepared test piece is shown in FIG. After the steel exposed portion was created, the distance from the steel plate end face of the heavy anticorrosion coating end was measured with a caliper and used for rust penetration distance measurement described later.

<Marine exposure test>
As a marine exposure test, the heavy-duty anti-corrosion coated steel sheet small test piece was exposed to an exposure test site in Tokyo Bay, Chiba Prefecture. Collected after 1 year, 2 years and 3 years.

<Preliminary corrosion acceleration test>
As a corrosion acceleration test, a salt spray test and a wet and dry test were performed. The test conditions were 6 conditions shown in Table 1 below. The test flow of each test is shown in FIGS.

Test condition 1 was a normal salt spray test as shown in FIG. 9 (a), and was performed at an ambient temperature of 35 ° C. using a 5% NaCl aqueous solution in accordance with JIS Z2371.
As shown in FIG. 9 (b), the test condition 2 is a salt spray process for 2 hours according to JASO M609-91, followed by a drying process for 4 hours, and then a wetting process for 2 hours, for a total of 8 hours. This was repeated for a plurality of cycles during the test period described later. In the salt spray process, a 5% NaCl aqueous solution was used and the test was performed at an ambient temperature of 35 ° C. In the drying process, the inside of the test tank was maintained at an atmospheric temperature of 60 ° C. and a relative humidity of 40% or lower, and similarly in the wet process, the atmospheric temperature was maintained at 50 ° C. and the relative humidity of 65% or higher.

Test conditions 3 to 5 are the same in the conditions of each process of test condition 2 and the cycle time is changed. In test condition 3, as shown in FIG. 9 (c), the salt spray process was performed for 3 hours, then the drying process was performed for 4 hours, and then the wetting process was performed for 1 hour, for a total of 8 hours as one cycle.
As shown in FIG. 9 (d), the test condition 4 is that the salt spray process is performed for 2.5 hours, then the drying process is performed for 3 hours, and then the wet process is performed for 2.5 hours, for a total of 8 hours for one cycle. It was.
As shown in FIG. 9 (e), the test condition 5 is a salt spray process for 1.5 hours, then a drying process for 3 hours, and then a wet process for 1.5 hours, for a total of 6 hours for one cycle. It was. This was repeated for a plurality of cycles during the test period described later.
As shown in FIG. 9F, the test condition 6 is the same as the test condition 2 in each process, and the cycle pattern was changed. That is, the salt spray process was performed for 2 hours, then the drying process was performed for 2 hours, then the wetting process was performed for 2 hours, and then the drying process was performed for 2 hours, for a total of 8 hours as one cycle.
The above test conditions 1 to 6 were repeated a plurality of cycles for the following test period.
The test period was three periods of 60 days, 90 days, and 120 days.

<Measurement of corrosion amount and rust penetration distance>
Remove the heavy anticorrosion coating layer for each of the three types of collected heavy anticorrosion coated steel small test pieces, measure the distance from the steel plate end surface to the rust intrusion position with calipers, and rust intrusion from the coating end measured before the test. The average value of distance was calculated | required. Then, after pickling and removing rust completely, the plate | board thickness of steel materials was measured with the laser displacement meter, and the amount of corrosion was calculated | required.

<Calculation of corrosion rate and rust penetration rate>
Based on the average value for each period of corrosion amount of exposed steel part measured for each of the three types of heavy corrosion-resistant coated steel small test pieces, the steel material for each of the marine exposure test and the corrosion acceleration test was performed according to the method shown in FIG. The exposed portion corrosion rate was determined.
Similarly, for each of the marine exposure test and the corrosion acceleration test by the method shown in FIG. 7 based on the average value of the rust intrusion distance for each period measured for each of the three types of small anti-corrosion coated steel materials. The rust penetration rate was determined.

<Extracting test conditions for corrosion acceleration test>
Steel exposure part corrosion rate, rust intrusion rate, b '× a / (b × a ′) value in the marine exposure test of three types of heavy anti-corrosion coated steel small test pieces and six types of corrosion acceleration tests, and Table 2 shows the acceleration magnification.

３種類の重防食被覆ＰＵ−Ａ、ＰＵ−Ｂ、ＰＥ全てにおいて、０．６≦ｂ’×ａ/（ｂ×ａ’）≦１．４を満たした試験条件は、試験条件３であった。この試験条件の促進倍率に関しては、鋼材露出部腐食速度に関する促進倍率の平均値が、９．３であることから、促進倍率としては９．３とした。この理由は、この試験条件における錆浸入速度に関する促進倍率の平均値が９．７となり、鋼材露出部腐食速度と異なる値となっているため、どちらの促進倍率を採用するかが問題となるが、鋼材の断面欠損を生ずる鋼材断面方向の腐食の方が断面性能への影響の大きいことから、鋼材断面方向への腐食に直接関連する鋼材露出部腐食速度に関する促進倍率を採用したものである。

The test condition that satisfied 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4 in all three types of heavy anticorrosion coatings PU-A, PU-B, and PE was Test Condition 3. . Regarding the acceleration factor under this test condition, since the average value of the acceleration factors related to the corrosion rate of the exposed steel portion is 9.3, the acceleration factor is set to 9.3. The reason for this is that the average value of the accelerating magnification related to the rust infiltration rate under this test condition is 9.7, which is different from the corrosion rate of the exposed steel part. Since the corrosion in the cross-section direction of the steel material that causes the cross-sectional defect of the steel material has a larger influence on the cross-sectional performance, an acceleration factor relating to the corrosion rate of the exposed steel portion directly related to the corrosion in the cross-section direction of the steel material is employed.

<Corrosion acceleration test>
The test of test condition 3 was conducted as a corrosion acceleration test of the present invention using a polyurethane coating thickness of 1.0 mm as the PU-A heavy anticorrosion coated steel material as an example of a material with an unknown deterioration rate.
As a comparative example, the test under Test Condition 2 was performed. In the comparative example, only the corrosion amount of the exposed steel part was compared with the exposure test, and the acceleration factor was obtained. The test period was 60 days, 90 days, and 120 days, respectively.
In addition, the same marine exposure test was conducted as for the extraction of conditions to confirm the validity of the accelerated corrosion test. The test period was 1, 2, and 3 years. The validity evaluation of the corrosion acceleration test is a comparison of the corrosion amount of the exposed steel part and the rust penetration distance in the exposure test after three years, and the corrosion amount of the steel exposed part and the rust penetration distance after three years predicted from the results of the respective corrosion acceleration tests. I went there.

<Calculation of corrosion rate and rust penetration rate>
Similar to the preliminary corrosion acceleration test, the steel exposed portion corrosion rate and the rust penetration rate were calculated. The results are shown in Table 3.

<Prediction of corrosion rate and rust penetration rate>
Table 4 shows a comparison between the results of 3 years predicted from the test of test condition 3 set by the method of the present invention and the test of test condition 2 performed as a comparative example, and the results after 3 years in the marine exposure test. Show.

In the test of test condition 3, since the accelerating magnification was 9.3 times, both the steel exposed portion corrosion rate and the rust penetration rate were multiplied by 1 / 9.3, and the value after 3 years was determined. The predicted value of the corrosion amount of the exposed steel material was obtained from the following formula (1).
y = (a ′ / k) t (1)
Where y: corrosion amount of exposed steel part (mm), a ': corrosion rate of exposed steel part (mm / y) of corrosion accelerated test (test condition 3), k: accelerated magnification (9.3 times), t: elapsed time Time (year)

Moreover, the predicted value of the rust penetration distance l was obtained from the following equation (2).
l = (b ′ / k) t (2)
Where l: rust penetration distance (mm), b ': rust penetration speed (mm / y) of corrosion acceleration test (condition 3), k: acceleration magnification (9.3 times), t: elapsed time (years)

On the other hand, in the test of test condition 2 performed as a comparative example, the rust penetration distance when the steel material exposed portion corrosion amount became the same value as the marine exposure test after 3 years was obtained. The rust penetration distance l ₂ was obtained from the following formula (3).
l ₂ = (b ₂ '/ a ₂ ') y _3y (3)
Where l ₂ : rust penetration distance (mm), b ₂ ': rust penetration rate (mm / y) of corrosion acceleration test (condition 2), y _3y : corrosion amount (mm) after 3 years of marine exposure test, a ₂ ': Corrosion rate (mm / y) of exposed steel in corrosion accelerated test (Condition 2)

As shown in Table 4, the relative error of the predicted value after 3 years obtained from the test result of the test condition 3 is 8% for the corrosion amount of the exposed steel part and 3% for the rust penetration distance, and the predicted value is appropriate. It was confirmed that.
On the other hand, in the predicted value after 3 years obtained from Comparative Example Condition 2, there is a relative error of 51% in the rust penetration distance even if the steel exposed portion is assumed to be the same value. Could not be reproduced.

  The corrosion acceleration test for heavy corrosion-resistant coated steel materials according to the present invention enables accurate prediction in a short period of time for corrosion amount prediction for predicting the life of heavy corrosion-resistant coated steel materials currently used and for developing new coating materials. It can be used for effective port facility design and maintenance planning.

1 Coupling 3 Heavy corrosion protection coating 5 Coated end 7 Steel exposed part 9 Inside of joint

Claims (3)

A corrosion acceleration test method for heavy anti-corrosion coated steel with a coated end,
Real environment exposure test process to determine the corrosion rate amm / y of the steel material exposed part and the rust penetration speed bmm / y under the coating layer by conducting an exposure test of the heavy corrosion protection coated steel material test piece in the actual environment Using a test piece having the same specifications as that used in the process, a corrosion acceleration test is performed under a plurality of test conditions to obtain a steel corrosion rate a'mm / y and a rust penetration rate b'mm / y under the coating layer. A steel corrosion rate a ′ mm / y and a rust penetration rate b ′ mm / y in each test condition obtained in the preliminary corrosion promotion test step. B ′ × a / (b Xa ′) is determined, the test condition of the corrosion acceleration test whose value is closest to 1 is determined as the corrosion acceleration test condition, and the corrosion acceleration test is performed using the determined test condition. Test method for accelerated corrosion of coated steel.   The value of b ′ × a / (b × a ′) under the test conditions determined as the corrosion promotion condition satisfies 0.6 ≦ b ′ × a / (b × a ′) ≦ 1.4. The corrosion acceleration test method for heavy anticorrosion coated steel material according to claim 1.   The test method of the corrosion-promoted coated steel material according to claim 1 or 2, wherein the test conditions in the corrosion-accelerated test are a series of processes including salt spray, drying and wetting processes.

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