Double cantilever beam specimen stress corrosion test processing device and method

Abstract

The invention relates to a double cantilever beam sample stress corrosion test processing device, the processing device comprises a container, a high-pressure gas source, a gas distribution pipe, and a separator, the separator is provided with a plurality of sample placement holes, the separator is installed in the container, the gas distribution pipe is an annular structure, and is installed around the separator in the container, the gas distribution pipe is provided with a plurality of gas outlet holes, the high-pressure gas source is connected to the gas distribution pipe through a gas transmission pipe, the high-pressure gas source can transport inert gas to the gas distribution pipe, and the inert gas can diffuse from the gas outlet holes into the container; and a method for performing a double cantilever beam sample stress corrosion test processing using the above device is provided; the invention solves the problem of sample non-cracking, so that batch tests can also meet the test standard requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of test processing methods, and in particular relates to a double cantilever beam sample stress corrosion test processing method. Background Art

[0002] With the rapid development of the global economy, the demand for energy in countries around the world has further increased, and the consumption of oil and natural gas as the main energy sources has also risen sharply. The exploitation of oil and gas fields around the world is becoming more and more difficult, and more and more complex geological blocks such as high-sulfur and ultra-deep wells are being developed. The demand for high-strength oil well pipes that are resistant to hydrogen sulfide corrosion and cracking is growing rapidly. In order to adapt to the development and competition of the international market, our company has developed a series of H2S corrosion-resistant products, such as duplex steel, nickel-based alloys, titanium alloys, etc., as well as high-grade (105ksi steel grade and above) hydrogen sulfide stress corrosion cracking resistant oil well pipe products; H2S corrosion inspection tests for oil casing products generally use A method (uniaxial tensile test method).

[0003] In recent years, the hydrogen sulfide stress corrosion DCB double cantilever beam test (hereinafter referred to as D method test) has received more and more attention. Foreign major oil companies such as Shell, Mobil, Chevron and others have explicitly required that the D method test results be included in the quality assurance book for purchased oil casing; domestic laboratories are also actively carrying out D method test comparison work; compared with the A method uniaxial tensile test, the D method test has the following two advantages: first, the test cycle for carbon steel or low alloy steel can be shortened (the D method test cycle is 14 days, and the A method test cycle is 30 days); second, the D method test can derive a quantitative stress corrosion intensity factor (KISSC) value, while the A method test result is only a qualitative pass or fail; third, the D method test does not require a special loading device, which is convenient for carrying out autoclave tests.

[0004] However, in the process of implementing the D method test in recent years, a series of unexpected problems have occurred, such as sample processing problems, loading displacement control problems, and sample failure to crack or cracking that does not meet requirements.

[0005] In order to solve the problem of failure of D method test, many measures have been taken. They have been entangled in H2S concentration, sample placement direction during test, sample processing, etc., but this thorny problem has not been solved, which not only leads to a large waste of test resources, but also fails to report correct test results. From the structure and stress analysis of the double cantilever beam sample, it is found that the EDM notch and the side V-groove are the main origin guides of the cracking of the DCB sample. After a large number of tests and observations, it is found that due to the particularity of the DCB sample: 1) The width of the prefabricated crack of the electrospark machining (ie, the EDM notch) is only 0.25mm, which is extremely easy to be blocked by dirt, and because the material of the sample is mostly ferromagnetic, iron filings are adsorbed here and cannot be removed, resulting in the test corrosion solution cannot enter this area, resulting in the problem of no cracking. 2) The side V-groove is used as a guide for corrosion cracking. If it is not thoroughly cleaned, a large number of unacceptable shark tooth morphologies will appear on the edge of the cracking morphology, affecting the test results.

[0006] Therefore, based on these problems, a double cantilever beam specimen stress corrosion test processing method is provided, which is environmentally friendly and energy-saving, and improves the effectiveness of batch EDM notched double cantilever beam specimen stress corrosion test, which has important practical significance. Summary of the invention

[0007] According to the NACE TM 0177:2016 standard, after the test is finished, the loading wedge is pulled out to obtain the peeling load P value, the sample is extremely cold and brittle, the sample is split, and the surface characteristics of the cracked fracture are checked to determine the stress intensity factor Kissc. The fracture surface should meet the eight characteristics described in Chapter 11. At present, the cracked D method sample basically meets the four characteristics of a, b, d, and g. The cases that do not meet the characteristics include: no cracking, non-planar fracture surface beyond the V groove that does not meet item c, severe shark teeth that do not meet item e, cracks that do not meet item f bifurcation to one side of the side arm, etc., resulting in test failure; the present invention mainly conducts research and exploration on the problem that the sample does not crack and causes the test to be invalid.

[0008] The present invention solves the technical problem by adopting the following technical solutions:

[0009] A double cantilever beam specimen stress corrosion test processing device, the processing device comprises a container, a high-pressure gas source, a gas distribution pipe, and a separator, the separator is provided with a plurality of sample placement holes, the separator is installed in the container, the gas distribution pipe is an annular structure, and is installed around the separator in the container, the gas distribution pipe is provided with a plurality of gas outlets, the high-pressure gas source is connected to the gas distribution pipe through a gas transmission pipe, the high-pressure gas source can transport inert gas to the gas distribution pipe, and the inert gas can diffuse from the gas outlets into the container.

[0010] Furthermore, a stop valve is installed on the side wall of the container.

[0011] The method for performing a stress corrosion test on a double cantilever beam specimen using the above-mentioned device comprises the following steps:

[0012] Place the double cantilever beam specimens with their open ends facing downward into the specimen placement holes of the separators;

[0013] Prepare a cleaning solvent, pour the prepared cleaning solvent into a container, and make sure that the double cantilever beam specimen is completely immersed;

[0014] Open the high-pressure gas source, so that the inert gas is divided into several gas streams through the gas distribution pipe, forming a circulating liquid flow in the container, which impacts the EDM notch and the side V-groove on the double cantilever beam specimen. After multiple flushing, the residual dirt on the specimen is removed;

[0015] Take out the double cantilever beam sample, clean it, rinse it in anhydrous ethanol, dry it with hot air, and load the sample immediately;

[0016] The magnetic iron chips of the loaded specimens were eliminated and purged, and then immediately placed in the test solution for stress corrosion testing.

[0017] Furthermore, the lateral dimension of the sample placement hole is larger than that of the cantilever beam sample, so that the sample can be placed vertically.

[0018] Furthermore, the cleaning solvent is prepared by mixing household detergent with water in a volume ratio of 1:500.

[0019] The advantages and positive effects of the present invention are:

[0020] 1. The present invention can thoroughly clean the EDM notch in the special structure of the sample, without covering the part due to ferromagnetism and processing emulsion, so that the metal in the narrow EDM notch with a width of only 0.25 mm is completely in contact with the test solution, thereby solving the problem of the sample not cracking;

[0021] 2. The present invention can be adapted to batch sample testing and can quickly process 30 to 100 samples within 1 hour, solving the problem that when there are many samples, the test deoxygenation and H2S saturation concentration cannot be completed within one day due to the long processing time, so that the batch test can also meet the test standard requirements;

[0022] 3. The present invention enables the side V-grooves to be thoroughly cleaned, so that there are no obvious shark teeth on the cracked surface of the sample, and the cracked morphology of the sample meets the requirements of Chapter 11 of NACE TM0177:2016, and the test results are more accurate and stable;

[0023] 4. The present invention uses household cleaning agents as solvents, which can realize green treatment and achieve the same effect as industrial chemical solvent treatment, thus solving the problem that industrial chemical solvents harm the health of testers and surrounding personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0025] Figure 1 A top view of the structure of a double cantilever beam specimen provided by an embodiment of the present invention;

[0026] Figure 2 for Figure 1 A magnified view of the structure at center;

[0027] Figure 3 A schematic diagram of the structure of a double cantilever beam specimen stress corrosion test processing device provided by an embodiment of the present invention;

[0028] Figure 4 A top view of the structure of a container of a double cantilever beam specimen stress corrosion test processing device provided by an embodiment of the present invention;

[0029] Figure 5 A structural front view of a separator of a double cantilever beam specimen stress corrosion test processing device provided by an embodiment of the present invention;

[0030] Figure 6 A top view of the structure of a separator of a double cantilever beam specimen stress corrosion test processing device provided by an embodiment of the present invention; DETAILED DESCRIPTION

[0031] First, it should be noted that the specific structure, features and advantages of the present invention will be specifically described below by way of example, but all descriptions are only for illustration and should not be understood as limiting the present invention in any way. In addition, any single technical feature described or implied in the embodiments mentioned herein can still be combined or deleted between these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned herein.

[0032] The present invention provides a double cantilever beam specimen stress corrosion test processing device, the processing device comprises a container 3, a high-pressure gas source 5, a gas distribution pipe 7, and a separator 8, the separator is provided with a plurality of sample placement holes 9, the separator is installed in the container, the gas distribution pipe 7 is an annular structure, and is installed around the separator in the container, the gas distribution pipe is provided with a plurality of gas outlets, the high-pressure gas source 5 is connected to the gas distribution pipe through a gas transmission pipe, the high-pressure gas source 5 can transport inert gas to the gas distribution pipe, and the inert gas can diffuse from the gas outlets into the container.

[0033] It should be noted that the high-pressure gas source 5 adopts a high-pressure gas cylinder, on which a high-pressure gas regulating valve 6 is installed, through which the flow rate and pressure of the gas can be adjusted; and a stop valve 4 is installed on the side wall of the container.

[0034] like Figure 3 As shown, the separator is a flat plate structure with a supporting leg structure, and a plurality of transparent sample placement holes 9 are formed on the surface of the flat plate structure; wherein, the design height of the separator is 60% to 70% of the sample length, and the width and length of the sample placement hole are approximately 4 mm larger than the corresponding dimensions of the cantilever beam sample, so that the sample can be placed vertically.

[0035] The method for performing a stress corrosion test on a double cantilever beam specimen using the above-mentioned device comprises the following steps:

[0036] Place the double cantilever beam specimens with their open ends facing downward into the specimen placement holes of the separators; wherein the open end of the double cantilever beam specimen is one end of the loading wedge;

[0037] Prepare a cleaning solvent, pour the prepared cleaning solvent into a container, and immerse the double cantilever beam sample completely; wherein the cleaning solvent is prepared by using a daily detergent and water in a volume ratio of 1:500;

[0038] Open the high-pressure gas source 5, so that the inert gas is divided into several gas streams through the gas distribution pipe 7, forming a circulating liquid flow in the container, and the flow impacts the EDM notch 1 and the side V-shaped groove 2 (such as Figure 1 , 2 ), after multiple flushing, remove the remaining dirt on the sample;

[0039] Take out the double cantilever beam sample, clean it, then rinse it in anhydrous ethanol, blow dry it with hot air, and make sure to make sure the EDM notch is completely dry. After checking the cleanliness of the EDM notch under a fluorescent lamp, load the sample immediately;

[0040] Since steel is ferromagnetic, it may absorb iron filings during the loading process. This small amount of iron filings will also prevent the test solution from entering the 0.25mm narrow EDM gap, causing the sample to not crack and the test to be invalid. Therefore, the magnetic iron filings are eliminated from the loaded sample with a copper coil and purged. The EDM gap of each sample is carefully checked under a fluorescent lamp, and then immediately placed in the test solution for stress corrosion testing.

[0041] By using the treatment method of this embodiment, the sample can be in a reasonable surface state before entering the test solution, ensuring the effectiveness of the D method test. According to test statistics, since the use of this treatment method, 100% of the 420 DCB samples were cracked during the 100% H2S stress corrosion test, achieving the expected effect.

[0042] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. Double cantilever beam specimen stress corrosion test processing device, characterized by: The processing device includes a container, a high-pressure gas source, a gas distribution pipe, and a separator. The separator is provided with a plurality of sample placement holes. The separator is installed in the container. The gas distribution pipe is an annular structure and is installed around the separator in the container. The gas distribution pipe is provided with a plurality of gas outlet holes. The high-pressure gas source is connected to the gas distribution pipe through a gas transmission pipe. The high-pressure gas source can transport inert gas to the gas distribution pipe, and the inert gas can diffuse from the gas outlet holes into the container.

2. The double cantilever beam specimen stress corrosion test processing device according to claim 1, characterized in that: A stop valve is installed on the side wall of the container.

3. A method for performing a stress corrosion test on a double cantilever beam specimen using the device of claim 1 or 2, characterized in that: The steps include: Place the double cantilever beam specimens with their open ends facing downward into the specimen placement holes of the separators; Prepare a cleaning solvent, pour the prepared cleaning solvent into a container, and make sure that the double cantilever beam specimen is completely immersed; The high-pressure gas source is turned on, so that the inert gas is divided into several gas streams through the gas distribution pipe, forming a circulating liquid flow in the container, which impacts the EDM notch and the side V-groove on the double cantilever beam specimen. After multiple flushing, the residual dirt on the specimen is removed; Take out the double cantilever beam sample, clean it, rinse it in anhydrous ethanol, dry it with hot air, and load the sample immediately; The magnetic iron chips of the loaded specimens were eliminated and purged, and then immediately placed in the test solution for stress corrosion testing.

4. The double cantilever beam specimen stress corrosion test processing method according to claim 3, characterized in that: The lateral dimension of the sample placement hole is larger than that of the cantilever beam sample, so that the sample can be placed vertically.

5. The double cantilever beam specimen stress corrosion test processing method according to claim 3, characterized in that: The cleaning solvent is prepared by mixing household detergent and water in a volume ratio of 1:500.

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