JP5459035B2 - Durability judgment method for coated steel - Google Patents

Description

  The present invention relates to a method for determining the durability of a coated steel material that easily determines deterioration of coating or linening in a steel member that has been anticorrosive by painting or linening.

  Typical steel members used in the atmosphere, ocean / river environment, and soil include steel sheet piles, steel pipe piles, steel pipe sheet piles, H-shaped steel, steel pipes, etc., foundation structures, bridges, buildings, harbors, airports Widely used for road and other infrastructure.

  These structures are designed and constructed on the assumption that they will be used for 50 to 100 years, and most of them are protected by organic coating layers such as paint. Although anti-corrosion coatings with excellent performance are currently in widespread use, no anti-corrosion performance that has synchronized with the service life of steel structures has been developed yet. It is important not to increase the maintenance and management costs of steel structures by repairing the anticorrosive layer.

  Currently, the method standardized to ASTM D610-68 is used to determine the life of anticorrosion coating, but the rust generated on the coated steel surface gradually spreads and the rust generation area ratio is a constant value, in the case of a bridge If it becomes 5 to 10%, it is a method for judging rust of a coated steel material that is judged to be a life, and does not estimate the life of the coated steel material.

  In addition, Patent Document 1 describes, as a method for predicting the life of a coated metal, the time until a hole in which a rust under the coating can pass is formed in the coating film, and the lifetime is predicted at an early stage after use. Propose that. Applying a voltage to the coated steel, pre-determining the current value when holes occur in the coating film, extrapolating the time until the current value at the initial stage of coating becomes the current value, and calculating the life of the coated metal It is characterized by predicting.

Japanese Patent Publication No. 6-100570

  By the way, the following knowledge about the deterioration of the organic coating layer has been obtained.

  1. First, the deterioration of the organic coating layer starts from the edge of the organic coating layer or a portion where the coating layer is poorly glued (such as an edge portion of a steel member) or a portion damaged by external force. Although these measures are taken for the time being, they are inevitably or accidentally generated and are difficult to avoid.

  2. When the steel surface is exposed around the edges and scratches, corrosion of the steel material starts from that part. These corrosion reactions not only occur only in the exposed part, but also affect the healthy part of the surrounding organic coating layer.

3. In the exposed part of the steel material, an iron dissolution reaction (anode reaction) and a cathodic reaction related to corrosion occur. Since part of the cathode reaction occurs on the steel surface under the surrounding organic coating layer, the cathode reaction product causes adhesion degradation. (Although this reaction takes place under the organic coating layer other than around the wound, the rate is very slow and the deterioration rate at the wound and the edge is several times greater.)
4). In order to prevent such a phenomenon, it is effective to suppress the cathode reaction under the organic coating layer. The cathodic reaction under the organic coating layer is a phenomenon that occurs because the potential shows a relatively noble potential compared to the exposed part of the steel at the edges and scratches. The organic coating layer deteriorates, and the larger the potential difference, the faster the deterioration.

  However, a method for estimating the life of the coated steel material based on such knowledge has not yet been proposed. The method described in Patent Document 1 must be obtained by extrapolating the current value when a hole is generated from the change in the current value when a voltage is applied to the coated steel material, and the correlation between the change in the current value and the coating film deterioration is obtained. It is necessary to analyze and obtain various data relating to the coating film and corrosion.

  In addition, although an exposure test is often used as a method for estimating the life of a coating or an organic lining, it takes a long time to obtain a result, and a certain time is required even in an accelerated exposure test.

  Then, an object of this invention is to provide the method of determining the superiority or inferiority of the performance in the coating and lining used for corrosion prevention of a steel structure in a short time.

The object of the present invention can be achieved by the following means.
1. A durability evaluation method of coating steel, in moist environment, for the test material and the reference material obtains the corrosion potential of the corrosion potential and the bare steel as coated steel respectively, when satisfying the formula (1), the test material test and excellent durability as compared to the reference material, if it meets the expression (2), the test material by determining a poor durability in comparison with the reference material, and compares these corrosion potential A method for judging the durability of a coated steel material, comprising: judging whether the durability of coating with respect to a reference material is good or bad.
ΔE ≦ ΔE ′ (1)
ΔE> ΔE ′ (2)
In these equations, ΔE = E1−E2, ΔE ′ = E1′−E2 ′ (where ΔE ′> 0), E1: Corrosion potential of the test material to be evaluated as a coated steel material, E2: Test to be evaluated E1 ': Corrosion potential of the reference material with known durability of the coating layer as a coated steel material, E2': Corrosion potential of the bare steel material with reference material of which the durability of the coating layer is known E1 < In the case of E2, it is not limited to this and it is judged that the durability is excellent.
2. The wet environment has a chlorine ion concentration of 0. In 0 1 mol / L or more aqueous solutions, for coating steel of the test material according to claim 1, wherein the Oh Rukoto coated steel material to form an organic coating layer of 10~100μm steel surface was cleaned A method for judging the durability of coated steel.

  According to the present invention, it is possible to determine the superiority or inferiority of an organic coated steel material in a short period of time, which is extremely useful industrially.

The schematic diagram explaining the measuring method of a corrosion potential. The figure which shows the relationship between corrosion potential difference (DELTA) E and the peeling width | variety from a crosscut part.

  The present invention judges the superiority or inferiority of the covering performance of the test material compared to the reference material whose durability of the covering performance is already known. In a humid environment, the test material and the reference material are coated steel materials. The corrosion potential of the steel and the corrosion potential of the bare steel material are obtained, and these corrosion potentials are compared and judged. In the following description, it is assumed that the coated steel material is a painted steel material, and the bare steel material is a painted steel material.

  In the present invention, the corrosion potential of the test material as a coated steel material is E1, the corrosion potential of the bare steel material of the test material is E2, and the corrosion potential of the reference material to be compared with the test material is E1 ′. When the corrosion potential of the bare steel material of the reference material is E2 ′ and these relationships satisfy the equation (1), it is determined that the covering performance of the test material is superior to that of the reference material. When the formula (2) is satisfied, it is determined that the covering performance of the test material is inferior to the reference material in terms of durability.

ΔE ≦ ΔE ′ (1)
ΔE> ΔE ′ (2)
In these equations, ΔE = E1−E2, ΔE ′ = E1′−E2 ′ (where ΔE ′> 0),
When the organic coating layer is applied to the test material, the potential is lower (E1 <E2) than the potential of the bare steel material, and the polarity due to the potential difference basically deteriorates when the polarity of the steel coating portion and the organic coating layer is reversed. Since it is determined that it is difficult to occur, it is absolutely superior in durability rather than in comparison with the reference material. For example, this is a case where the coating layer contains a material that has a sacrificial anticorrosive action such as Zn or aluminum.

  In general coating, most of them show ΔE> 0, and it is preferable to select a reference coating system from those showing this value.

  In addition, when the steel material is coated and the electric corrosion prevention is used in combination, the electric potential of the bare steel material due to the electric corrosion prevention or the like is used as the corrosion potential E2 of the bare steel material.

  Usually, for the anticorrosion of steel, 1. By external power supply method There is a galvanic anode method using a sacrificial anode such as Zn, Al, Mg, etc. In any case, the potential reached by the bare steel material by these may be adopted as E2. Normally, steel is corrosion-protected at a potential lower than -850 mV, so E2 takes a value much lower than the corrosion potential of steel. When practicing the present invention, the corrosion potential is preferably measured by the method described below.

  FIG. 1 shows an example of a method for measuring the corrosion potential of an organic coated steel material. A test piece 2 and a test solution are put in a container 1a, and a reference bridge 3 and a container 1b containing a saturated KCl solution are connected by a salt bridge 4 to which a cock 10 is attached, and the corrosion potential of the test piece 2 is measured by a potentiometer. 5 (FIG. 1 (a)).

  For the corrosion potential, test piece 2 is 2. Test material for evaluating the durability of coating (coated steel material), 2.1 Bare steel material (uncoated steel material) of the test material of 2.1 Measurement is made for each of the reference materials (coated steel materials) for comparing the durability of the coating with the test materials as bare steel materials (non-coated steel materials) of 4.3.

  Whether the test piece 2 is a coated steel material or an uncoated steel material, cover the test material other than the target area (measurement surface 9) with a sealant 6 (in the case of a coated steel material, thicker than the coating film), The lead wire 7 covered with the protective tube 8 is pulled out from the measurement surface 9 and connected to the potentiometer 5.

  In the case where the test piece 2 is a coated steel material as a test material or a reference material, if the thickness of the organic coating layer is thick, the insulation becomes high and the measurement of the corrosion potential becomes difficult. The thickness of the organic coating layer is 10 to 100 μm from the first layer and the second layer on the steel material side so that the corrosion potential can be measured in a short period.

  If it is less than 10 μm, pinholes are likely to occur in the coating layer, and the corrosion potential of steel cannot be measured. On the other hand, if it exceeds 100 μm, it is difficult to measure the corrosion potential. Depending on the surface roughness of the steel material, pinholes are likely to be formed. Therefore, it is necessary to select an appropriate film thickness within a range of 10 to 100 μm. The thickness of the coating layer can be easily measured with an electromagnetic film thickness meter or the like.

  The measurement solution for immersing the test piece 2 in the container 1a uses a solution containing 0.01 mol / L or more of chlorine ions because the measurement of the corrosion potential becomes difficult if the chlorine ions are less than 0.01 mol / L. . Here, 1 mol / L indicates that 1 mol of chlorine ions is contained in the solution in 1 L.

  The upper limit of the chlorine ion concentration in the solution is not particularly defined, but is preferably selected in consideration of the environment in which it is used. The cation paired with the chlorine ion is not particularly limited, but monovalent ions (sodium, lithium, potassium) are preferable. This is because the hydration radius of ions is large for divalent ions and is difficult to diffuse into the organic coating layer.

  When the test piece 2 is a bare steel material in the test material or the reference material, the steel material surface is cleaned. Sites to be coated with coated steel or steel structures are pre-cleaned (blasting, pickling, polishing, etc.), and the measured value of the corrosion potential varies depending on the state of deposits and oxide scale. Because. Further, the present invention will be described in detail with reference to examples.

(Manufacture of bare steel)
Steel materials (steel materials Nos. 1 to 7) having the composition shown in Table 1 were subjected to shot blasting using 0.5 mmφ steel balls to remove the surface oxide layer and contamination layer, and further emery polished paper (# 500, The surface was polished and cleaned by # 800, # 1200). The size of the steel material was 50 mm × 70 mm × plate thickness.
(Manufacture of coated steel)
On one side of these steel materials (steel materials Nos. 1 to 7), an epoxy-based primer coating (trade name: Million Prime manufactured by Kansai Paint Co., Ltd.) and a modified epoxy primer coating (trade name: ESCO manufactured by Kansai Paint Co., Ltd.) as the first layer. NB) and a zinc rich primer (trade name: SD zinc manufactured by Kansai Paint Co., Ltd.) were applied. The coating thickness is 60 μm for each paint, and the upper layer (second layer) is coated with a phthalic acid paint at a thickness of 100 μm to form a coated steel material. Put a wound to reach.

The surface of the test material cut into a size of 20 mm × 20 mm was coated with any of the above-mentioned undercoat paints with a thickness of 10 μm to 100 μm. A 1 mmφ copper wire was fixed to the test material with solder, and the back and painted surfaces were left 10 mm × 10 mm, and the periphery was sealed with a silicon-based sealant. The bare steel material was treated in the same manner as a test material for measuring the corrosion potential. Of the above-described coated steel materials, the steel material No. 4 is a reference material (a combination of a known steel material and a paint type used as a reference when judging coating performance), and other steel materials (No. 1, 2, 3, 5, 6, 7) was used as a test material.
(Measurement method of corrosion potential)
With respect to the above-described coated steel material and bare steel material, the corrosion potential after 2 hours was measured in the case of the bare steel material, and the corrosion potential after 72 hours was measured in the case of having the coating layer. A 0.01 mol / L to 0.5 mol / L NaCl solution was used. All the reference materials satisfy ΔE ′> 0.
(Exposure test method)
In order to verify the effect of the present invention, a salt spray test was conducted as an exposure test. Put the test material for the corrosion test in a salt spray tester (5% NaCl solution, 35 ° C) for 30 days, measure the peel width from the defective part after collecting the test material, and define the maximum peel width as the peel width did.
(Test results)
Table 2 shows the measurement result of the corrosion potential of the test material and the measurement result of the peel width from the crosscut portion in the salt spray test. In Table 2, series 1 is the case where epoxy base coat is used for various steel materials, series 2 is when modified epoxy base coat is used for various steel materials, and series 3 is a zinc rich primer used for various steel materials. Is the case.

  Table 3 shows the measurement result of the corrosion potential of the reference material and the measurement result of the peel width from the crosscut portion in the salt spray test. The reference material was a combination of epoxy base coating (same as series 1) and steel 4 (reference 1), or a combination of modified epoxy base coating (similar to series 2) and steel 4 (standard 2).

  FIG. 2 illustrates the results of Tables 2 and 3, and shows the relationship between ΔE and the width of separation from the crosscut. Of the three types of test materials, in the case of series 3 (zinc rich primer), ΔE is ΔE <0, that is, E1 <E2. Since E1 ≦ E2 is satisfied, it is determined that the durability is better than the standards 1 and 2 of the reference material.

  In the salt spray test, it was confirmed that the peel width from the cross cut was remarkably small compared to other series, and the coating corrosion resistance was good.

  In the case of the series 1 and the series 2, the coating durability is determined to be poor in the range of ΔE> ΔE ′ with the reference material (references 1 and 2) as a boundary. In the salt spray test, it was confirmed that the peeling width from the cross cut was large and the coating corrosion resistance was poor. As described above, the effectiveness of the determination result according to the present invention was proved by the salt spray test result.

DESCRIPTION OF SYMBOLS 1a, 1b Container 2 Test piece 3 Reference electrode 4 Salt bridge 5 Potentiometer 6 Sealing agent 7 Lead wire 8 Protective tube 9 Measuring surface 10 Cock

Claims (2)

A durability evaluation method of coating steel, in moist environment, for the test material and the reference material obtains the corrosion potential of the corrosion potential and the bare steel as coated steel respectively, when satisfying the formula (1), the test material test and excellent durability as compared to the reference material, if it meets the expression (2), the test material by determining a poor durability in comparison with the reference material, and compares these corrosion potential A method for judging the durability of a coated steel material, comprising: judging whether the durability of coating with respect to a reference material is good or bad.
ΔE ≦ ΔE ′ (1)
ΔE> ΔE ′ (2)
In these equations, ΔE = E1−E2, ΔE ′ = E1′−E2 ′ (where ΔE ′> 0), E1: Corrosion potential of the test material to be evaluated as a coated steel material, E2: Test to be evaluated E1 ': Corrosion potential of the reference material with known durability of the coating layer as a coated steel material, E2': Corrosion potential of the bare steel material with reference material of which the durability of the coating layer is known E1 < In the case of E2, it is not limited to this and it is judged that the durability is excellent. The wet environment has a chlorine ion concentration of 0. In 0 1 mol / L or more aqueous solutions, for coating steel of the test material according to claim 1, wherein the Oh Rukoto coated steel material to form an organic coating layer of 10~100μm steel surface was cleaned A method for judging the durability of coated steel .