Method for hydrostatic testing of steel pipes

Abstract

To provide a water pressure test method for a steel pipe capable of suppressing generation of corrosion of a steel pipe after a water pressure test while using hydraulic water that does not affect an environment even when discharged through general wastewater treatment.SOLUTION: A water pressure test method for a steel pipe (10) includes a preparation step (#5) and a test step (#10). In the preparation step (#5), hydraulic water (20) used for a water pressure test is prepared. In the preparation step (#5), the content of a rust preventive agent in the hydraulic water (20) is adjusted to 0.5 to 2.0 mass% by adding the rust preventive agent, and pH of the hydraulic water (20) is adjusted to over 7.0 to 8.6. In the test step (#10), the water pressure test is performed on the steel pipe (10) using the hydraulic water (20) after the preparation step (#5).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a hydraulic test method for steel pipes.

Background Art

[0002] Steel pipes used for oil well pipes, piping, etc., and steel pipes including pipe fittings such as couplings usually undergo quality inspection tests. One of the quality inspection tests is a hydraulic test. Techniques related to hydraulic tests are described in, for example, Patent Documents 1 to 3. In the hydraulic test of a steel pipe, for example, hydraulic heads are attached to both ends of the steel pipe. The hydraulic heads are sealed to the steel pipe with seal packing. Pressurized water (hereinafter also referred to as hydraulic water) is supplied into this steel pipe through the hydraulic heads. Then, the quality of the steel pipe is evaluated by checking for damage and water leakage of the steel pipe.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Steel pipes are shipped after passing quality inspection tests such as hydraulic tests. The shipped steel pipes are stored indoors or outdoors. Here, there is a risk that the steel pipes may corrode due to components contained in the hydraulic water used in the hydraulic test during the period from shipment to storage and until the customer uses them.

[0005] In light of these problems, in order to suppress corrosion in steel pipes, pressurized water containing rust inhibitors is sometimes used in hydrostatic tests. Rust inhibitors are described, for example, in Table 1 of Patent Document 1. Rust inhibitors generally contain oils, sulfonates, amines, and surfactants. If pressurized water containing such rust inhibitors is discharged to the outside without any treatment, it may affect the water quality of the external environment (e.g., pH, chemical oxygen demand (COD), and nitrogen content).

[0006] Typically, in factory premises such as steel mills, the pressurized water used for hydrostatic testing is mixed with wastewater from other factory facilities, and then treated with purification processes such as neutralization and dilution as needed before being discharged. Because such purification treatment is performed before discharge, factory wastewater containing the pressurized water used for hydrostatic testing does not actually have an impact on the environment. Nevertheless, it is preferable that the pressurized water used for hydrostatic testing does not have an impact on the environment even if it is discharged as is.

[0007] As described above, the hydrostatic testing method for steel pipes requires that the pressurized water used does not affect the environment even when discharged without special treatment beyond normal wastewater treatment, and that corrosion of the steel pipes after the hydrostatic testing is suppressed.

[0008] The purpose of this disclosure is to provide a method for testing steel pipes using hydrostatic water that does not affect the environment even when discharged in general wastewater treatment, while suppressing corrosion of steel pipes after hydrostatic testing. [Means for solving the problem]

[0009] The method for testing the hydrostatic pressure of a steel pipe according to this disclosure comprises a preparation step and a testing step. In the preparation step, hydrostatic water to be used for the hydrostatic pressure test is prepared. In the preparation step, the content of the rust inhibitor in the hydrostatic water is adjusted to 0.5 to 2.0 mass% by adding a rust inhibitor, and the pH of the hydrostatic water is adjusted to greater than 7.0 to 8.6. In the testing step, the hydrostatic pressure test of the steel pipe to be tested is performed using the hydrostatic water prepared in the preparation step. [Effects of the Invention]

[0010] According to the water pressure testing method for steel pipes of the present invention, it is possible to suppress corrosion of steel pipes after the water pressure test while using pressurized water that does not affect the environment even when discharged in general wastewater treatment. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a flowchart illustrating a water pressure test method for steel pipes according to an embodiment. [Figure 2] Figure 2 is a cross-sectional view showing the hydrostatic pressure test. [Modes for carrying out the invention]

[0012] The hydrostatic pressure test method for steel pipes according to this embodiment comprises a preparation step and a test step. In the preparation step, hydrostatic water to be used for the hydrostatic pressure test is prepared. In the preparation step, the content of rust inhibitor in the hydrostatic water is adjusted to 0.5 to 2.0 mass% by adding a rust inhibitor, and the pH of the hydrostatic water is adjusted to greater than 7.0 to 8.6. In the test step, the hydrostatic pressure test of the steel pipe to be tested is performed using the hydrostatic water prepared in the preparation step.

[0013] In the hydrostatic testing method according to this embodiment, the hydrostatic testing of steel pipes is performed using the hydrostatic water prepared in the preparation step. In the preparation step, the hydrostatic water to be used for the hydrostatic testing is prepared. Specifically, in the preparation step, the content of the rust inhibitor in the hydrostatic water is adjusted to 0.5 to 2.0 mass%. This suppresses the occurrence of corrosion in the steel pipes after the hydrostatic testing. In addition, in the preparation step, the pH of the hydrostatic water is adjusted to greater than 7.0 to 8.6. This ensures that even if this hydrostatic water is discharged through general wastewater treatment, it will not have an impact on the environment.

[0014] The following describes the hydrostatic testing method for steel pipes according to the embodiment, with reference to the drawings. In each drawing, the same or equivalent components are denoted by the same reference numerals, and the same explanation is not repeated.

[0015] Figure 1 is a flowchart showing the hydrostatic testing method for steel pipes according to this embodiment. As shown in Figure 1, the hydrostatic testing method of this embodiment comprises a preparation step (#5) and a testing step (#10). In this embodiment, the steel pipe 10 shown in Figure 2, which will be described later, is the object of the test. The steps shown in Figure 1 will be described in detail below.

[0016] Figure 2 is a cross-sectional view showing a hydrostatic pressure test. In the hydrostatic pressure test method according to this embodiment, a steel pipe 10 as shown in Figure 2 is prepared. In this example, the steel pipe 10 is a steel pipe used for oil well tubular construction. The steel pipe 10 includes a coupling 11. That is, the coupling 11 is attached to one end of the steel pipe 10.

[0017] Both ends of the steel pipe 10 are threaded. In short, the steel pipe 10 has male threaded portions 10a and 10b. Male threaded portion 10a corresponds to one end of the steel pipe 10, and male threaded portion 10b corresponds to the end opposite to male threaded portion 10a. Both ends of the coupling 11 are threaded. In short, the coupling 11 has female threaded portions 11a and 11b. Female threaded portion 11a corresponds to the end on the steel pipe 10 side, and female threaded portion 11b corresponds to the end opposite to female threaded portion 11a. The female threaded portion 11a of the coupling 11 is fastened to the male threaded portion 10a of the steel pipe 10. During the hydrostatic test, pressurized water 20 is injected into the steel pipe 10.

[0018] 〔Preparation Process (#5)〕 In the preparation process (#5), the hydraulic pressure water 20 used for the hydraulic pressure test is prepared. In the preparation process (#5), by adding a rust inhibitor, the content of the rust inhibitor in the hydraulic pressure water 20 is adjusted to an appropriate amount, and the pH of the hydraulic pressure water 20 is adjusted to an appropriate amount. In the preparation process (#5), for example, a rust inhibitor having the following composition may be added to the hydraulic pressure water 20. Refined mineral oil: 70 - 80% by mass Petroleum sulfonate: 5 - 10% by mass Emulsifier: 1 - 10% by mass Triethanolamine: 1 - 5% by mass Oiliness improver: 1 - 5% by mass Defoamer: trace amount

[0019] When the content of the rust inhibitor in the hydraulic pressure water 20 is too low, the rust prevention property of the hydraulic pressure water 20 is insufficient, and the occurrence of corrosion in the steel pipe 10 after the hydraulic pressure test is not sufficiently suppressed. On the other hand, when the content of the rust inhibitor in the hydraulic pressure water 20 is too high, an increase in the amount of organic substances in the hydraulic pressure water 20 and fluctuations in the pH of the hydraulic pressure water 20 occur. In this case, there is a risk of affecting the environment when the hydraulic pressure water 20 is discharged. Therefore, in the preparation process (#5), the content of the rust inhibitor in the hydraulic pressure water 20 is adjusted to 0.5 - 2.0% by mass.

[0020] When the pH of the hydraulic water 20 tends to be acidic, that is, when the pH of the hydraulic water 20 is less than 7.0, sufficient rust prevention performance may not be ensured. On the other hand, when the pH of the hydraulic water 20 is inclined to the alkaline side to a certain extent, that is, when the pH of the hydraulic water 20 is greater than 7.0 to a certain extent, sufficient rust prevention performance is ensured. However, when the hydraulic water 20 is closer to neutral, the impact on the environment when the hydraulic water 20 is discharged is smaller compared to when the hydraulic water 20 is far from neutral. For example, in the general wastewater standards (https: / / www.env.go.jp / water / impure / haisui.html) listed on the homepage of the Ministry of the Environment, the allowable limit of pH (for those discharged into public water areas other than the sea area) is described as 5.8 - 8.6. Therefore, in the preparation process (#5), the pH of the hydraulic water 20 is adjusted to exceed 7.0 and up to 8.6 within its allowable limit.

[0021] The preparation of the hydraulic water 20 is carried out, for example, in the following manner. The hydraulic water 20 is injected into a hydraulic pit (water tank) and is periodically stirred inside the hydraulic pit. Also, the pH of the hydraulic water 20 inside the hydraulic pit is measured at any time. According to this measurement result, for example, by adding a rust inhibitor to the hydraulic water 20, the content of the rust inhibitor and the pH of the hydraulic water 20 are adjusted so as to be within the above-mentioned range. The hydraulic pit is connected to the hydraulic test device by piping. Therefore, the hydraulic water 20 can circulate between the hydraulic test device and the hydraulic pit.

[0022] 〔Testing process (#10)〕 In the testing process (#10), a hydraulic test of the steel pipe 10 is performed using the hydraulic water 20 after the preparation process (#5). The testing process (#10) is carried out by a hydraulic test device. Referring to FIG. 2, also, a pin thread protector 12 is fitted into the open male thread portion 10b of the steel pipe 10. The pin thread protector 12 prevents the hydraulic water 20 from coming into contact with the male thread portion 10b during the hydraulic test.

[0023] Hydraulic heads 13 and 14 are attached to both ends of the steel pipe 10, respectively. At the end of the steel pipe 10 on the male threaded portion 10a side, the hydraulic head 13 is attached to the coupling 11. The space between the hydraulic head 13 and the coupling 11 is sealed with a seal packing 15. At the end of the steel pipe 10 on the male threaded portion 10b side, the hydraulic head 14 is attached to the steel pipe 10. The space between the hydraulic head 14 and the steel pipe 10 is sealed with a seal packing 16.

[0024] In the test process (#10), hydraulic water 20 at a predetermined pressure is injected into the steel pipe 10. After holding it in this state for a certain period of time, the presence or absence of damage to the steel pipe 10 or leakage of hydraulic water 20 is checked. This allows for the evaluation of the quality of the steel pipe 10.

[0025] When the hydrostatic pressure test (#10) is performed on multiple steel pipes 10, the preparation of the hydrostatic water 20 in the preparation step (#5) does not need to be performed each time a hydrostatic pressure test is performed on each steel pipe 10. In short, as long as the content of the rust inhibitor in the hydrostatic water 20 and the pH of the hydrostatic water 20 are within the specified range described above, the hydrostatic water 20 may be used repeatedly for hydrostatic pressure tests on multiple steel pipes 10 without preparation each time. However, the preparation of the hydrostatic water 20 may be performed each time a hydrostatic pressure test is performed on each steel pipe 10.

[0026] [effect] In the hydrostatic testing method according to this embodiment, in the test step (#10), a hydrostatic test of the steel pipe 10 is performed using the hydrostatic water 20 prepared in the preparation step (#5). In the preparation step (#5), the hydrostatic water 20 to be used for the hydrostatic test is prepared. Specifically, in the preparation step (#5), the content of the rust inhibitor in the hydrostatic water 20 is adjusted to 0.5 to 2.0 mass%. This suppresses the occurrence of corrosion in the steel pipe 10 after the hydrostatic test. In addition, in the preparation step (#5), the pH of the hydrostatic water 20 is adjusted to greater than 7.0 to 8.6. This ensures that even if the hydrostatic water 20 used for the hydrostatic test is discharged through general wastewater treatment, it will not have an impact on the environment.

[0027] Embodiments of the present disclosure have been described above. However, the embodiments described above are merely examples for carrying out the present disclosure. Therefore, the present disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of the disclosure. For example, the steel pipe under test may be a single steel pipe without a coupling. [Examples]

[0028] [First Embodiment] To confirm the rust inhibitor content in pressurized water and the rust prevention performance based on the pH of the pressurized water, a salt spray test was conducted based on JIS Z2371 (2015). In this example, a rectangular steel block measuring 40 mm wide x 24 mm long x 3 mm thick was prepared as a test specimen. The steel block was equivalent to API (American Petroleum Institute) standard P110. Specifically, the material of the steel block was 0.23%C-1.3%Mn-0.2%Cr. A recess with a diameter of 16 mm and a depth of 1.0 mm was made in this steel block. Test specimens No. 1 to 17 were prepared using this procedure.

[0029] A portion of each test specimen was doped onto the bottom surface of the recess. When doping was applied, the dope was applied to half of the bottom surface of the recess. The amount of dope applied was approximately 0.14 ± 0.10 g. Test specimens No. 1, 4, and 7 were not doped. The other test specimens were doped with API dope or yellow dope.

[0030] After applying dope to some of the test specimens, solvent was dropped into the recesses of each specimen. In the doped specimens, the solvent and dope were present together both inside the recesses and near the edges of the recesses on the surface of the specimen. The solvent used was water or a 0.17% NaCl aqueous solution with a chloride ion concentration of 10 ppm or less. However, the solvent in the 0.17% NaCl aqueous solution was water with a chloride ion concentration of 10 ppm or less. The amount of solvent dropped into the recesses of each specimen was approximately 2 ml, corresponding to the volume of the recess. The rust inhibitor content in the solvent dropped into each specimen was adjusted to 0-2.0% by mass. Hereafter, the solvent after the rust inhibitor content has been adjusted will also be referred to as simulated hydrostatic water.

[0031] Each test specimen was then placed in a plastic case and kept in a constant temperature and humidity chamber at 98% RH and 50°C for 7 days. After 7 days, the recesses of each test specimen were visually observed and the corrosion state was evaluated. The results of this example are shown in Table 1. The "Corrosion Status" column in Table 1 shows the results of evaluating the corrosion state of the bottom surface of the recesses of each test specimen according to the following criteria. No corrosion: No corrosion was observed. Localized corrosion: Corrosion was observed in less than half the area of ​​the bottom surface of the recess. Total corrosion: Corrosion was observed over more than half of the bottom surface area of ​​the recess.

[0032] [Table 1]

[0033] As shown in Table 1, no corrosion occurred in test specimens No. 7 to 17, which were dropped with simulated hydraulic water containing 0.5 to 2.0% by mass of rust inhibitor, regardless of the type of solvent or whether dope was applied. Furthermore, among these test specimens, no corrosion occurred regardless of the type of dope applied. The pH of the simulated hydraulic water in these test specimens was 7.2 to 8.7. From these results, it can be seen that hydraulic water with a rust inhibitor content of 0.5 to 2.0% by mass and a pH greater than 7.0 has sufficient rust-preventive properties.

[0034] [Second Example] In this example, hydrostatic pressure tests were conducted on approximately 50 oil well pipes using actual hydrostatic testing equipment. After the hydrostatic pressure tests, each pipe was stored for a long period, and the corrosion status of each pipe was observed. For the hydrostatic pressure tests, industrial water with a chloride ion concentration of 10 ppm or less, to which a rust inhibitor had been added, was used as the pressurized water. Based on the evaluation results of the first example, the rust inhibitor content in the pressurized water used in the hydrostatic pressure tests was 1.2 to 1.4% by mass. The pH of the pressurized water was greater than 7.0 to 7.8.

[0035] The steel pipes, after the hydrostatic pressure test described above, were stored for several months to one year under conditions similar to those used for normal product storage. The corrosion status of each test specimen was then observed. As a result, no corrosion was observed in any of the steel pipes. [Explanation of Symbols]

[0036] 10: Steel pipe 20: Pressurized water

Claims

[Claim 1] A method for testing the hydrostatic pressure of an oil well pipe, A preparation step for preparing hydraulic water to be used in a hydrostatic test, comprising: adjusting the content of a rust inhibitor in the hydraulic water to 0.5 to 2.0% by mass by adding a rust inhibitor, and adjusting the pH of the hydraulic water to greater than 7.0 to 8.6; The system includes a test step of performing a hydrostatic pressure test on the oil well pipe under test using the hydrostatic water after the preparation step, The oil well pipe has a male threaded portion corresponding to one end of the oil well pipe, A hydrostatic pressure test method, wherein the test step involves performing a hydrostatic pressure test with the coupling fastened to the male screw portion, or with a pin screw protector fitted to the male screw portion.

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