Metal corrosion evaluation method for elemental sulfur deposition in high-sulfur-content gas field

Abstract

The invention discloses a metal corrosion evaluation method for elemental sulfur deposition of a high-sulfur-content gas field, and belongs to the technical field of metal corrosion testing. According to the method disclosed by the invention, the use of special devices and equipment is avoided, in the elemental sulfur deposition metal corrosion simulation working condition test, good contact between metal and deposited sulfur is kept to simulate working conditions, and the key problems that a suspension method deviates from a real working condition environment and deposited sulfur is excessively compact due to a melting coating method are avoided; according to the method, the sulfur corrosion effect is evaluated after the simulated working condition test, the evaluation process is simple and easy to control, the test evaluation result is good, a theoretical basis is laid for prevention and treatment of the elemental sulfur deposition corrosion problem of the high-sulfur-content gas field, and the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of metal corrosion testing, and in particular relates to a metal corrosion evaluation method for elemental sulfur deposition in a high-sulfur gas field. Background Art

[0002] At present, during the development of high-sulfur gas fields, elemental sulfur will be deposited in the wellbore and gathering pipelines, seriously affecting the safe development, storage and transportation of oil and gas fields. One of the key issues is the elemental sulfur corrosion problem, which causes local corrosion at the location where the elemental sulfur is deposited. Therefore, it is necessary to study the corrosion mechanism and corrosion evaluation method of elemental sulfur to lay a theoretical foundation for the corrosion protection work of elemental sulfur deposition in high-sulfur gas fields.

[0003] At present, the main elemental sulfur corrosion evaluation methods include suspension method, coating and covering method, and burial method. The corrosion rates under the evaluation methods increase in turn, but the local corrosion of metal materials under the conditions of suspended sulfur solution is the most serious. It is generally believed that elemental sulfur suspended on the surface of the liquid cannot effectively simulate on-site elemental sulfur corrosion. In the burial method, the contact between elemental sulfur and metal is not close enough, which is not applicable to the evaluation of elemental sulfur corrosion in high-sulfur gas fields. From the field production experience, it can be known that the parts with serious pipeline corrosion mainly occur at the bottom of the pipeline with low flow rate and elemental sulfur and water deposition. Therefore, the elemental sulfur coating method can better reflect the actual situation of close contact between elemental sulfur and materials and serious corrosion during the on-site production process, and can better simulate the on-site elemental sulfur corrosion conditions.

[0004] At present, the elemental sulfur coating method refers to applying the elemental sulfur on the surface of the test piece after it is melted. After the elemental sulfur is fixed on the test piece, the corrosion evaluation test is carried out according to the corrosion hanging procedure. However, this method causes the cladding sulfur to be denser, which cannot simulate the self-deposition process well, and the test evaluation results are distorted. Patent CN 104422648B briefly describes the shortcomings of the above methods, and provides a method for testing the deposition of sulfur corrosion on oil well pipe materials and a test fixture. This method is not much different from the burial method, but it requires the preparation of a mold, which is more complicated. Summary of the invention

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a metal corrosion evaluation method for elemental sulfur deposition in high-sulfur gas fields, so as to solve the technical problems of the existing evaluation methods such as distorted test evaluation results and complicated evaluation process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention discloses a metal corrosion evaluation method for elemental sulfur deposition in a high-sulfur gas field, comprising the following steps:

[0008] S1: spreading elemental sulfur powder on the surface of the hanging sheet, then dropping a binder to completely wet the elemental sulfur powder, and then drying to obtain a hanging sheet covered with elemental sulfur;

[0009] S2: The coupons covered with elemental sulfur are subjected to simulated working condition tests, and the sulfur corrosion effect is evaluated after the test;

[0010] The sulfur corrosion effect evaluation includes corrosion product characterization and corrosion rate evaluation.

[0011] Furthermore, in S1, the source of the elemental sulfur powder is a sulfur deposition mixture collected on-site or an analytically pure elemental sulfur powder medicine; the elemental sulfur powder is ground and sieved before use; the grinding and sieving is performed by grinding with an agate mortar and then sieving with a standard sieve.

[0012] Furthermore, in S1, the hanging sheet is a metal hanging sheet or a hanging sheet for on-site pipe processing; the spreading area of ​​the elemental sulfur powder on the hanging sheet surface is 0.5 to 3 cm 2 .

[0013] Furthermore, the paving area of ​​the elemental sulfur powder on the surface of the hanging piece is 1 cm 2 .

[0014] Furthermore, in S1, the binder is a PTFE solution or a Nafion solution.

[0015] Furthermore, in S1, the mass ratio of the elemental sulfur powder to the binder is (3:1) to (1:3).

[0016] Furthermore, the mass ratio of the elemental sulfur powder to the binder is 2:1.

[0017] Further, in S2, the steps of the simulated working condition test are:

[0018] Place the coupon covered with elemental sulfur on the test stand in the reactor, keep the surface of the coupon covered with deposited sulfur powder facing upward, and fill the reactor with simulated working condition corrosion solution to carry out simulated working condition test;

[0019] Or install the coupon covered with elemental sulfur on a four-point bend corrosion device to carry out stress corrosion tests under simulated working conditions.

[0020] Furthermore, in S2, the corrosion product characterization is carried out by characterizing the composition and morphology of the corrosion products produced by the simulated working condition test.

[0021] Furthermore, in S2, the corrosion rate assessment is to remove the corrosion products generated by the simulated working condition test, calculate the uniform corrosion rate using the weight loss method, calculate the maximum local corrosion rate using the ultra-depth of field microscope to test the depth of the corrosion pit, and test the corrosion cracks.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention discloses a metal corrosion evaluation method for elemental sulfur deposition in a high-sulfur gas field. The sample preparation method for obtaining a hanging piece covered with elemental sulfur is simple, and the use of special devices and equipment is avoided. When a simulated working condition test is performed, the good contact between the metal and the deposited sulfur in the actual working condition is fully simulated, and the actual problems such as the suspension method cannot truly reflect the actual conditions and the melting coating method causing the deposited sulfur to be excessively dense are avoided. The method of the invention uses the simulated working condition test to evaluate the corrosion effect, the test evaluation results are true and effective, and the evaluation process is simple and easy to control. The method disclosed by the invention provides a sample preparation method or a test evaluation method for the discussion of the mechanism of deposited sulfur and the evaluation of protective measures, lays a theoretical foundation for solving the elemental sulfur deposition corrosion problem in high-sulfur gas fields, and has broad application prospects.

[0024] Furthermore, the present invention uses Nafion solution or PTFE solution as a binder, which has good adhesion and ion permeability, ensuring that the deposited sulfur covers the metal surface, and can simulate the adhesion of elemental sulfur powder on the metal surface, and can ensure the normal intrusion and wetting of corrosion solution ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the sulfur powder adhesion on the surface of the metal coupon after the experiment in Example 1;

[0026] Figure 2 This is a schematic diagram of the corrosion condition of the metal coupon surface after the corrosion products are removed after the experiment in Example 2;

[0027] Figure 3 This is a diagram showing the maximum pitting depth on the metal coupon surface after the experiment in Example 3. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0029] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0030] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0031] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0032] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0033] The present invention provides a method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field, comprising the following steps:

[0034] Step 1: determine the source of elemental sulfur, grind and sieve it for later use, and obtain elemental sulfur powder;

[0035] Step 2: Weigh a certain amount of elemental sulfur powder and spread it on the surface of the metal coupon, add a certain amount of binder to make the elemental sulfur powder completely wet, and then dry it to obtain a coupon covered with elemental sulfur;

[0036] Step 3: Subject the coupons covered with elemental sulfur to simulated operating conditions tests, and conduct corrosion effect evaluation after the test, including corrosion product characterization and corrosion rate assessment.

[0037] Preferably, the source of elemental sulfur in step 1 can be a sulfur deposition mixture collected on-site, or can be purchased analytically pure elemental sulfur powder.

[0038] Preferably, the grinding and screening in step 1 is to fully grind the elemental sulfur through an agate mortar and then screen it with a standard sieve, preferably with a mesh size of 800.

[0039] Preferably, in step 2, the area of ​​the elemental sulfur powder spread on the surface of the metal hanging sheet is 0.5 to 3 cm 2 , preferably 1cm 2 .

[0040] Preferably, the binder in step 2 is a PTFE solution or a Nafion solution, preferably a 5 wt % Nafion ethanol solution.

[0041] Preferably, the mass / volume ratio of the elemental sulfur powder to the binder in step 2 is 3:1 to 1:3 (mg / mL), preferably 2:1 (mg / mL).

[0042] Preferably, the simulated working condition test step in step 3 refers to placing the metal coupon with deposited sulfur elements on the test frame during the high temperature and high pressure test, keeping the metal surface with deposited sulfur facing upward, and filling the reactor with simulated working condition corrosion solution to carry out the simulated working condition test, or installing the metal with deposited sulfur on a four-point bend corrosion device to carry out a stress corrosion test under simulated working conditions.

[0043] Preferably, the corrosion effect evaluation in step 3 refers to characterizing the composition and morphology of the corrosion products using instruments such as SEM and XRD, and after removing the corrosion products, calculating the uniform corrosion rate using the weight loss method, measuring the depth of the corrosion pit using an ultra-depth of field microscope to calculate the maximum local corrosion rate, and measuring the corrosion cracks using a microscope.

[0044] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0045] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0046] Example 1

[0047] A method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field comprises the following steps:

[0048] S1: The sulfur deposit mixture collected on site was fully ground with an agate mortar and sieved with a standard sieve of 800 mesh to obtain elemental sulfur powder; 6 mg of elemental sulfur powder was spread on the surface of the L245 metal hanging piece with a spreading area of ​​1 cm 2 ; Then, 2 mL of 5 wt% Nafion ethanol solution was added dropwise to completely wet the elemental sulfur powder, and then dried to obtain a hanging sheet covered with elemental sulfur;

[0049] S2: Place the coupon covered with elemental sulfur on the test stand in the reactor, keep the surface of the coupon covered with deposited sulfur powder facing up, fill the reactor with 1wt% NaCl solution to carry out simulated working condition test, set the temperature to 25 degrees and the pressure to 5Mpa, soak for 7 days, and take out the sample; use SEM to characterize the composition and morphology of the corrosion product, and characterize the corrosion product, such as Figure 1 As shown, it is a schematic diagram of the sulfur powder adhesion on the surface of the metal coupon after the experiment of Example 1. From the figure, it can be seen that the sulfur powder is still attached to the surface of the metal coupon after the experiment and has not fallen off.

[0050] Example 2

[0051] A method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field comprises the following steps:

[0052] S1: Grind the purchased analytically pure elemental sulfur powder thoroughly with an agate mortar, and sieve it with a 500-mesh standard sieve to obtain elemental sulfur powder; spread 2 mg of elemental sulfur powder on the surface of the L245 metal hanging sheet with a spreading area of ​​0.5 cm 2 ; Then, 1 mL of 5 wt% Nafion ethanol solution was added dropwise to completely wet the elemental sulfur powder, and then dried to obtain a hanging sheet covered with elemental sulfur;

[0053] S2: Place the coupon covered with elemental sulfur on the test stand in the reactor, keep the surface of the coupon covered with deposited sulfur powder facing up, fill the reactor with 1wt% NaCl solution to carry out simulated working condition test, set the temperature to 25 degrees and the pressure to 5Mpa, soak for 5 days, and take out the sample; after removing the corrosion products, calculate the uniform corrosion rate by weight loss method, and evaluate the corrosion rate. The uniform corrosion rate is 0.1473mm / y. After removing the corrosion products, the corrosion morphology is as follows: Figure 2 As shown in the figure, it can be seen that the corrosion is mainly local corrosion, and corrosion pits appear.

[0054] Example 3

[0055] A method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field comprises the following steps:

[0056] S1: Grind the purchased analytically pure elemental sulfur powder thoroughly with an agate mortar, and sieve it with a standard sieve of 800 mesh to obtain elemental sulfur powder; spread 10 mg of elemental sulfur powder on the surface of the L360 metal hanging plate, with a spreading area of ​​3 cm 2 ; Then, 4 mL of 5 wt% Nafion ethanol solution was added dropwise to completely wet the elemental sulfur powder, and then dried to obtain a hanging sheet covered with elemental sulfur;

[0057] S2: Place the coupon covered with elemental sulfur on the test stand in the reactor, keep the surface of the coupon covered with deposited sulfur powder facing upward, fill the reactor with 1wt% NaCl solution to carry out simulated working condition test, set up the depth of field microscope to test the depth of corrosion pit and calculate the maximum local corrosion rate. The results are as follows: Figure 3 As shown in the figure, it can be seen that there are obvious corrosion pits on the surface of the sample, and the maximum depth of the corrosion pits reaches 7.3μm.

[0058] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields, characterized in that: The following steps are involved: S1: spreading elemental sulfur powder on the surface of the hanging sheet, then dropping a binder to completely wet the elemental sulfur powder, and then drying to obtain a hanging sheet covered with elemental sulfur; S2: The coupons covered with elemental sulfur are subjected to simulated working condition tests, and the sulfur corrosion effect is evaluated after the test; The sulfur corrosion effect evaluation includes corrosion product characterization and corrosion rate evaluation.

2. A method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field according to claim 1, characterized in that: In S1, the source of the elemental sulfur powder is a sulfur deposition mixture collected on-site or an analytically pure elemental sulfur powder medicine; the elemental sulfur powder is ground and sieved before use; the grinding and sieving is performed by grinding with an agate mortar and then sieving with a standard sieve.

3. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 1, characterized in that: In S1, the hanging sheet is a metal hanging sheet or a processing hanging sheet of on-site pipes; the spreading area of ​​the elemental sulfur powder on the hanging sheet surface is 0.5 to 3 cm 2 .

4. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 3, characterized in that: The paving area of ​​the elemental sulfur powder on the surface of the coupon is 1 cm 2 .

5. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 1, characterized in that: In S1, the binder is a PTFE solution or a Nafion solution.

6. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 1, characterized in that: In S1, the mass ratio of the elemental sulfur powder to the binder is (3:1) to (1:3).

7. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 6, characterized in that: The mass ratio of the elemental sulfur powder to the binder is 2:

1.

8. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 1, characterized in that: In S2, the steps of the simulated operating condition test are: Place the coupon covered with elemental sulfur on the test stand in the reactor, keep the surface of the coupon covered with deposited sulfur powder facing upward, and fill the reactor with simulated working condition corrosion solution to carry out simulated working condition test; Or install the coupon covered with elemental sulfur on a four-point bend corrosion device to carry out stress corrosion tests under simulated working conditions.

9. A method for evaluating metal corrosion of elemental sulfur deposition in high-sulfur gas fields according to claim 1, characterized in that: In S2, the corrosion product characterization is to characterize the composition and morphology of the corrosion products produced by the simulated working condition test.

10. A method for evaluating metal corrosion of elemental sulfur deposition in a high-sulfur gas field according to claim 1, characterized in that: In S2, the corrosion rate assessment is to remove the corrosion products generated by the simulated working condition test, calculate the uniform corrosion rate using the weight loss method, calculate the maximum local corrosion rate by testing the corrosion pit depth using an ultra-depth of field microscope, and test the corrosion cracks.

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