JPH09159664A - Liquid for evaluating hydrogen resistant brittleness of carbon steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid for evaluating the hydrogen resistant brittleness of carbon steel regardless of the pH region by saturating an aqueous solution containing sodium chloride and acetic acid with hydrogen sulfide and adding a specified quantity of chelating agent. SOLUTION: An aqueous solution of 5wt.% of sodium chloride and 0.5wt.% of acetic acid is saturated with hydrogen sulfide and added with a 1wt.% of chelating agent. Concentration of a typical chelating agent, i.e., EDTA.2Na, (and other chelating agents) is preferably set in the range of 1-10wt.% regardless of the pH region. Corrosion products, i.e., iron sulfides, may deposit in the acidic region when the concentration is lower than 1wt.%, and the quantity of hydrogen entering into carbon steel can not be sustained constant during the test. When the chelating agent is neutral or weak alkaline, especially when the concentration is lower than 1wt.%, no hydrogen enters into carbon steel and thereby the concentration is preferably set at 1wt.% or above. When this evaluation liquid is used, hydrogen resistant evaluation test is not limited by the pH of solution.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid for evaluating hydrogen embrittlement resistance of carbon steel that can be used in the entire pH range.

[0002]

2. Description of the Related Art In oil and natural gas well facilities, pipelines, etc., there has been a problem of hydrogen damage to carbon steel due to hydrogen embrittlement in a wet hydrogen sulfide environment. Hydrogen embrittlement is damage caused by the absorption of hydrogen produced by the electrochemical reaction of steel with a solution. Usually, this hydrogen damage is called hydrogen-induced cracking of the metal base or sulfide stress corrosion cracking near the welded portion. Although there is a difference in whether stress is applied, the pH was in the acidic region of less than 7. On the other hand, in petroleum refining-related equipment, ammonia is present together with hydrogen sulfide, so the pH range is neutral to weakly alkaline, but hydrogen-induced cracking and corrosion cracking (collectively referred to below as in the case where the pH range is acidic). This is referred to as hydrogen damage.) Conventionally,
In order to avoid problems caused by hydrogen damage in a wet hydrogen sulfide environment, the carbon steel used has been evaluated for hydrogen damage resistance. However, although there are evaluation methods in the acidic range,
There is no evaluation method that can be carried out regardless of the area, and therefore it has been conducted only in the acidic area.

As is well known, these evaluation methods are called hydrogen damage susceptibility evaluation methods, and in the acidic region, standardized test liquids shown in the following (1) and (2) and test methods using them are used. there were. (1) A method using a standard solution (hereinafter referred to as NACE solution) developed by the American Association of Corrosion Engineers (hereinafter referred to as NACE), which is a NACE Standard T
It is specified in M0284. The test solution and conditions are as follows. 5% sodium chloride + 0.5% acetic acid + 1 atm saturated aqueous hydrogen sulfide solution at a temperature of 25 ° C and a pH of about 4. (2) Standard solution developed by the British Petroleum Corporation (hereinafter,
It is called BP liquid. ), Which is defined in NACE Standard TM0284. The test solution and conditions are as follows. Blow hydrogen sulfide into artificial seawater under atmospheric pressure to a saturated state, and use this as the test solution. Temperature 25 ℃, pH
Is done at about 5.

The NACE solution described in (1) and the BP solution described in (2) are test solutions developed for hydrogen damage evaluation. The NACE liquid has stronger acidity than the BP liquid, and it is usually used properly according to the pH in the environment in which carbon steel is actually used. It is customary to also describe which method was actually selected as the evaluation method for material selection. However, the results obtained by the method for evaluating hydrogen damage by these solutions were qualitative. The reason is as follows.

The above evaluation method is based on the above (1) or (2).
The test piece is dipped in the test solution of 1), and after a certain time, the test piece is taken out and the state of cracks in the test piece is measured. However, the surface of the test piece is covered with the corrosion product during the test, and hydrogen permeation is hindered in the part covered with the corrosion product. As a result, the amount of hydrogen entering the test piece during the test greatly decreases with time. Further, both of the above two evaluation methods are evaluation methods in an acidic region, and there has been a demand for an evaluation method which can be performed in a neutral or weakly alkaline region. Conventionally, it has not been adopted as a method for evaluating hydrogen damage from neutral to weakly alkaline as a pH region, but as shown in the Corrosion Protection Association, "Corrosion Protection" 95 Proceedings, p. 36, 1995, the above A test solution was proposed in which cyan was added to the evaluation solution at about 750 ppm. However, since cyan does not have a large effect of activating the test piece, hydrogen is not introduced by simply adding cyan, and the film of the test piece is mechanically removed after the addition of cyan, or the liquid temperature is raised to 60 ° C or higher. There was a need. Under such circumstances, it is well known that the evaluation from neutral to weakly alkaline has been carried out by estimating and substituting from the data in the above acidic region environment. Further, since the conventional method is not an appropriate evaluation method in a neutral to weakly alkaline range as the pH range, there is a problem that a material with a grade higher than necessary must be used in consideration of safety. In addition, it is well known that the selected material is appropriate, but it can be obtained from accumulated experience, but since there is no accumulated experience in the new environment, trial and error is repeated in selecting the material. It was the reality.

[0006]

Therefore, the hydrogen embrittlement resistance evaluation methods for the above two carbon steels have the following problems to be improved. (1) It should not be an evaluation method that can be used regardless of the pH range. (2) The test method using the hydrogen embrittlement resistance evaluation liquid for carbon steel used in the acidic region is that the amount of hydrogen entering the carbon steel is not constant and only qualitative results can be obtained. (3) Although it has been reported that hydrogen enters carbon steel when neutral to weakly alkaline and cyanide is added,
Even if the liquid temperature is raised, it takes too long to induce hydrogen and reach the equilibrium value at the equilibrium value. Also, at room temperature, hydrogen cannot enter unless the carbon steel surface is sharpened after the addition of cyanide ions (naturally. However, it was never used in the point that hydrocyanic acid gas was generated in the acidic region). Therefore, it is an object of the present invention to provide a hydrogen embrittlement resistance evaluation liquid for carbon steel that enables evaluation regardless of the pH range, and a hydrogen embrittlement resistance evaluation method using the same.

[0007]

[Means for Solving the Problems] The present inventors have found that the NACE liquid and BP are
The reason why hydrogen is absorbed in the test piece immersed in the liquid is that the surface of the test piece is in the active region, while in the alkaline region, a passive film is formed on the surface of the test piece and does not absorb hydrogen.
I got the knowledge. Therefore, the present invention was conducted by studying an evaluation solution in which a passivation film is not formed on the surface of a test piece in an alkaline region, or even if a passivation film is formed, the passivation film is easily peeled off from the surface of the test piece. That is, the present invention
(1) An evaluation liquid for hydrogen embrittlement resistance of carbon steel, characterized in that an aqueous solution containing 5 wt% of sodium chloride and 0.5 wt% of acetic acid is saturated with hydrogen sulfide, and further contains 1 wt% or more of a chelating agent. ) 1wt of chelating agent in artificial seawater
% Or more, the rating liquid for hydrogen embrittlement resistance of carbon steel, and the chelating agent of (3) (1) or (2) is selected from chelating agents capable of forming a chelate with iron ions. It is intended to provide an evaluation liquid for hydrogen embrittlement resistance of carbon steel, which is one or more chelating agents. The present invention is an evaluation liquid for hydrogen embrittlement resistance of carbon steel obtained by saturating hydrogen sulfide in a solution containing 5% sodium chloride and 0.5% acetic acid or artificial seawater, and further containing 1 wt% or more of a chelating agent. Further, the chelating agent used in the above-mentioned evaluation liquid is an evaluation liquid for hydrogen embrittlement resistance of carbon steel, which is one or more chelating agents selected from chelating agents capable of forming a chelate with iron ions.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a hydrogen embrittlement resistance evaluation liquid for carbon steel that can be used regardless of the pH range, and a test method using the evaluation liquid. Here, “regardless of the pH range” means that the evaluation test is possible in a wide range of pH range from acidic to weakly alkaline.
Means that the hydrogen embrittlement resistance evaluation test is not restricted.

The following can be used as a chelating agent having the ability to form a chelate with iron ions. Amine such as ethylenediaminetetraacetic acid 2Na (EDTA / 2Na), 1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, glycol etherdiaminetetraacetic acid, triethylenetetramine hexaacetic acid, triethylenetetramine, tetraethylenepentamine, nitrilotriacetic acid Examples include a chelating agent, a chelating agent that forms an intramolecular complex salt such as acetylacetone and diethylthiocarbamic acid, a cationic chelating agent such as ethylenediamine and 2,2-dipyridyl, and an anionic chelating agent such as oxalic acid and tartaric acid. Further, the above chelating agents can be used alone or as a mixture as a chelating agent.

The hydrogen embrittlement resistance evaluation liquid for carbon steel of the present invention will be described in more detail. Regarding the chelating agent used in the present invention, EDTA.2 which is a typical chelating agent
An example of Na will be described. The concentration of EDTA / 2Na is pH
Regardless of the region, 1 wt% or more and 10 wt% or less, and preferably 3 wt% or more and 10 wt% or less. If it is less than 1 wt%, a film of a reaction product of iron and sulfur (hereinafter referred to as iron sulfide), which is a corrosion product, may be formed in the acidic region, and the amount of hydrogen entering the carbon steel is kept constant during the test. Can't keep on. Further, in the case of neutral or weakly alkaline, if less than 1 wt%, a passive film is likely to be formed and hydrogen cannot enter, so it is preferable to set it to 1 wt% or more. If it is 1 wt% or more, there is no particular problem except that it takes time to obtain an accurate value of hydrogen that has entered, especially in an acidic region. However, the concentration of EDTA · 2Na is preferably 3 wt% or more so that the iron sulfide film and the passive film can be immediately peeled off regardless of pH and accurate measurement can be performed in a short time. If the concentration exceeds 10 wt%, it will exceed the saturated solution of EDTA / 2Na,
Undissolved EDTA.2Na remains in the test solution, which is not preferable. The other chelating agents described above can be used alone or in combination. In that case, the concentration of the chelating agent obtained by mixing is 1 wt% or more and 10
The amount is preferably 3 wt% or more and 10 wt% or less. The reason is the same as in the case of EDTA · 2Na. Depending on the type of chelating agent, EDTA
Some of them have higher solubility than 2Na, but the effect does not change, so it is not necessary to exceed 10 wt%.

Next, a method for evaluating hydrogen embrittlement resistance of carbon steel using the evaluation liquid of the present invention will be described with reference to FIG. FIG. 1 shows an apparatus for evaluating hydrogen embrittlement resistance of carbon steel using the evaluation liquid of the present invention.
Liquid 2 for evaluating hydrogen embrittlement resistance of carbon steel in cell 2 whose bottom surface is open
Is filled, and the hydrogen sulfide gas 5 is blown in from the line 10, passes through the line 11, and is discharged to the outside of the system. The released gas is processed by a known processing method which is not shown in this figure. In addition, p of the hydrogen embrittlement resistance evaluation liquid 1 of carbon steel
H supplies the ammonia solution from the line 15 and adjusts it with the pH controller 8. The test piece 3 is sandwiched by the box 6, the packing 4 and the cell 2 of which the upper part is opened, and the airtightness is maintained. At this time, the test piece 3 is installed in a predetermined position without being pretreated.

The upper one surface of the test piece 3 installed as described above is brought into contact with the hydrogen embrittlement resistance evaluation liquid 1 of carbon steel adjusted to a predetermined pH, and hydrogen is supplied to the test piece 3 as indicated by an arrow 9. It diffuses from one surface of the upper part to one surface of the lower part of the test piece 3 and permeates into the box 6. Hydrogen 9 in the box 6 is analyzed by the analyzer 7. The analytical instrument 7 is not particularly limited, but gas chromatography is usually selected, and the gas flowing through the lines 12 and 13 to the analytical instrument 7 is nitrogen, helium, or argon when gas chromatography is selected. And the like may be used. The hydrogen passing through the above method is measured with time. In a normal test, the amount of the hydrogen embrittlement resistance evaluation liquid 1 for carbon steel is selected from 400 to 800 cc. The material of the cell may be selected from polymer materials such as acrylic and Teflon, and the shape thereof is not particularly limited, and is selected from shapes such as a rectangular parallelepiped and a cylinder. The test piece 3 is carbon steel defined by Japanese Industrial Standards (hereinafter referred to as JIS) and American Society for Testing and Materials (ASTM) standards. The material of the packing 4 may be selected from rubbers such as silicone rubber and butyl rubber, and Teflon. The material of the box 6 is not particularly limited. Regarding the diffusion of hydrogen atoms in carbon steel, it is well known that Fick's second law can be used, and the solution is represented by the following equation (1).

[0013]

[Equation 1]

Here, each symbol represents the following. C: Hydrogen content in test piece (ppm) J: Hydrogen permeation amount (ppm) L: Thickness of test piece (mm) D: Hydrogen diffusion coefficient (cm ² / sec) S: Permeation area (cm ² ) test The thickness L of the piece 3 is 0.2 mm to 0.5 mm, the area in contact with the hydrogen embrittlement resistance evaluation liquid 1 of carbon steel, that is, the permeation area S in the above formula (1) is selected to be 4 to 10 cm ^2. It The diffusion coefficient D of hydrogen varies depending on the type of carbon steel, and as an example, the first embodiment described below is used.
In the carbon steel JIS SB410 used for, the measured value is 3.6 × 10 ⁻⁵ cm ² / sec. As described above, the permeation area S, the hydrogen diffusion coefficient D, and the thickness L of the test piece are values determined by the experimenter and known values. What the experimenter measures is the hydrogen permeation amount J. From the hydrogen permeation amount J measured over time, the hydrogen content C is calculated.

[0015]

EXAMPLES The contents of the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A test was conducted using the apparatus shown in FIG. E to a 5 wt% sodium chloride and 0.5 wt% acetic acid solution
800 cc of hydrogen embrittlement resistance evaluation liquid 1 of carbon steel containing 3 wt% as DTA · 2Na was prepared. Hydrogen sulfide 5 was blown in through line 10 and discharged through line 11 under 1 bar. Ammonia water is supplied from the line 15, the pH of the evaluation liquid during the test is adjusted to 8 by the pH controller, and the analytical instrument 7
The permeated hydrogen 9 was measured by (gas chromatography). The cell 2 is made of acrylic and has a packing 4
Is made of silicone rubber. The box 6 was made of SUS material. As test piece 3, JIS SB410 was used as a representative of carbon steel. The test piece has a thickness L of 0.2 mm and a transmission area of 4.
9 cm ² was selected. Diffusion coefficient D is 3.6 × 10 ^-5 cm
² / sec. The results are shown in FIG.

Example 2 Example 1 was repeated except that the pH of Example 1 was changed from 8 to 4. The results are also shown in FIG.

Example 3 The concentration of EDTA · 2Na in Example 1 was changed from 3 wt% to 10%.
The results are also shown in FIG. 2 except that the wt% was changed.

Example 4 The concentration of EDTA · 2Na in Example 1 was changed from 3 wt% to 1 w.
It carried out like Example 1 except having changed into t%. The results are also shown in FIG.

Example 5 The procedure of Example 1 was repeated except that citric acid was used instead of EDTA.2Na. The results are also shown in FIG.

Example 6 Example 1 was repeated except that EDTA · 2Na in Example 1 was changed to 1,2-cyclohexanediaminetetraacetic acid. The results are also shown in FIG.

Example 7 The procedure of Example 1 was repeated, except that EDTA.2Na of Example 1 was changed to diethylenetriaminepentaacetic acid. The results are also shown in FIG.

Example 8 Example 8 was repeated except that EDTA.2Na in Example 1 was changed to glycol ether diamine tetraacetic acid.
The results are also shown in FIG.

Example 9 The procedure of Example 1 was repeated, except that EDTA.2Na of Example 1 was changed to triethylenetetramine hexaacetic acid. The results are also shown in FIG.

Example 10 The procedure of Example 1 was repeated, except that EDTA.2Na of Example 1 was changed to triethylenetetramine. Figure 2 shows the results.
It is described together.

Example 11 The procedure of Example 1 was repeated, except that EDTA.2Na of Example 1 was changed to tetraethylenepentamine. The results are also shown in FIG.

Example 12 Example 12 was repeated except that nitrilotriacetic acid was used instead of EDTA.2Na. The results are also shown in FIG.

Example 13 Example 13 was carried out in the same manner as in Example 1 except that EDTA.2Na in Example 1 was changed to acetylacetone. The results are also shown in FIG.

Example 14 Example 14 was carried out in the same manner as in Example 1 except that diethylthiocarbamic acid was used instead of EDTA.2Na. The results are also shown in FIG.

Example 15 The same procedure as in Example 1 was carried out except that ethylenediamine was used instead of EDTA.2Na in Example 1. The results are also shown in FIG.

Example 16 Example 16 was carried out in the same manner as in Example 1 except that EDTA · 2Na in Example 1 was changed to 2,2-dipyridyl. The results are also shown in FIG.

Example 17 The procedure of Example 1 was repeated, except that EDTA.2Na of Example 1 was replaced with oxalic acid. The results are also shown in FIG.

Example 18 Example 18 was repeated except that tartaric acid was used instead of EDTA.2Na. The results are also shown in FIG.

Comparative Example The concentration of EDTA · 2Na in Example 1 was changed from 3 wt% to 0 w.
It carried out like Example 1 except having changed into t%. As the results are also shown in FIG. 2, hydrogen did not permeate for an extremely long time.

[0035]

As described above, the liquid for evaluating hydrogen embrittlement resistance of carbon steel of the present invention contains the chelating agent and therefore has the following effects. (1) It is possible to provide a liquid for evaluating hydrogen embrittlement resistance of carbon steel regardless of pH range from acidic to weakly alkaline. (2) A quantitative test can be performed instead of the conventional qualitative test. (3) Since the evaluation can be performed regardless of the pH range, the test can be performed under more practical conditions. As a result, the materials can be selected accurately and appropriately. (4) The amount of hydrogen entering the carbon steel is kept constant during the evaluation test, and highly reliable evaluation results are obtained. (5) Further, since it is not necessary to add cyanide ions, it is not necessary to use nerves to generate hydrocyanic acid gas by adjusting the pH of the hydrogen embrittlement resistance evaluation liquid of carbon steel.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for evaluating hydrogen embrittlement resistance of carbon steel using the evaluation liquid of the present invention.

FIG. 2 is an evaluation result of carbon steel using various hydrogen embrittlement resistance evaluation liquids obtained by using the apparatus of FIG.

[Explanation of symbols]

 1 Hydrogen Steel Embrittlement Resistance Evaluation Liquid 2 Cell 3 Specimen 4 Packing 5 Hydrogen Sulfide Gas 6 Box 7 Analytical Instrument 8 pH Controller 10-15 Lines

Claims (3)

[Claims] 1. Sodium chloride 5 wt% and acetic acid 0.5 w
An evaluation liquid for hydrogen embrittlement resistance of carbon steel, characterized by saturating hydrogen sulfide in an aqueous solution containing t% and further containing a chelating agent in an amount of 1 wt% or more. 2. An evaluation liquid for hydrogen embrittlement resistance of carbon steel, characterized in that artificial seawater contains a chelating agent in an amount of 1 wt% or more. 3. The chelating agent according to claim 1 or 2, which is selected from chelating agents capable of forming a chelate with iron ions.
An evaluation liquid for hydrogen embrittlement resistance of carbon steel, which is a chelating agent of 2 or more.