Old oil pipe grading method

Abstract

The invention provides an old oil pipe grading method, which is used for grading old oil pipes with the specification of phi 88.9 * 6.45 mm according to the depths of corrosion pits on the outer surfaces of the old oil pipes, and comprises the following steps: S1, carrying out flaw detection on the old oil pipes according to an ultrasonic flaw detection scheme for detecting new oil pipes, and taking the old oil pipes of which the depths of the corrosion pits are not detected to be 12.5% greater than the standard wall thickness as first-stage oil pipes; s2, ultrasonic flaw detection is conducted on other old oil pipes except the first-stage oil pipe, the old oil pipes with the detected corrosion pit depth larger than or equal to 30% of the standard wall thickness serve as scrapped oil pipes, and the other old oil pipes serve as second-stage oil pipes. According to the old oil pipe grading method, the old oil pipes can be graded, and the old oil pipes which can be used conditionally are prevented from being abandoned.

Description

Technical Field

[0001] The present invention relates to the field of tubing flaw detection, and particularly to a method for grading used tubing. Background Art

[0002] Tubing is a metal workpiece widely used in the petroleum industry. The technical specification for new tubing delivery is usually API Spec 5CT. API Spec 5CT requires the tubing surface to be smooth, and for manufacturing defects of the tubing, it is not allowed to have pits on the tubing surface with a depth exceeding 12.5%t, or it is not allowed that the remaining wall thickness of the tubing is less than the minimum required (87.5%t) wall thickness.

[0003] However, after being used in downhole operations for a period of time, the tubing that meets the technical requirements of API Spec 5CT will inevitably form corrosion pits on the tubing surface due to corrosion, rusting, etc. According to research, the remaining strength of used tubing with pitting corrosion pit defects (punctiform corrosion pits without cracks) is positively correlated with its effective cross-sectional area. The main reason for scrapping used tubing is corrosion defects, and the depth of the corrosion pit, that is, the degree of wall thickness loss, is the main factor affecting the remaining strength of used tubing. Through theoretical simulation analysis and verification of actual material performance tests and full-scale strength tests, the results show that even if there are pits on the tubing surface with a depth exceeding 12.5%t, it can still be used conditionally, but the tubing with too severe corrosion cannot be used anymore and can only be scrapped.

[0004] Currently, the repair of used tubing is judged according to the API SPEC 5CT standard, and the scrapping ratio is between 10% and 20%. Approximately 450,000 meters of tubing are scrapped every year. A large number of existing inventory scrapped used tubing cannot be reasonably utilized, reducing the economy of reusing used tubing. Among them, a considerable part of the used tubing that could have been used conditionally because there are pits on the surface with a depth exceeding 12.5%t is scrapped, resulting in great waste. Summary of the Invention

[0005] The present invention provides a method for grading used tubing, which can grade used tubing to prevent used tubing that could have been used conditionally from being discarded.

[0006] The method for grading used tubing of the present invention grades used tubing with a specification of Φ88.9×6.45mm according to the depth of corrosion pits on its outer surface, including:

[0007] S1, flaw detecting the used tubing according to the ultrasonic flaw detection scheme for detecting new tubing, and classifying the used tubing with the depth of the detected corrosion pit not > 12.5% of the standard wall thickness as first-grade tubing;

[0008] S2, performing ultrasonic flaw detection on other used tubing except the first-grade tubing, specifically including the following steps:

[0009] (1) Use a new oil pipe with the same diameter, wall thickness, and material as the old oil pipe to be inspected as a sample pipe, and process a vertical through-hole on the sample pipe as an artificial defect, and the axis of the vertical through-hole is perpendicular to the axis of the sample pipe;

[0010] (2) Use an ultrasonic flaw detector to test the artificial defect on the sample pipe, and take the sensitivity value displayed by the ultrasonic flaw detector when the peak value of the reflected wave intensity of the artificial defect is 80% ± 0.5% as the reference sensitivity, and increase the reference sensitivity by 5 - 7 db as the scanning sensitivity;

[0011] (3) Based on the scanning sensitivity, use an ultrasonic flaw detector to detect the old oil pipe. The old oil pipe without alarm is used as a secondary oil pipe. For the old oil pipe with an alarm, detect it again with the reference sensitivity. If it alarms again, the detected corrosion defect, that is, the defect with a depth exceeding 30% of the wall thickness of the oil pipe, is used as a scrapped oil pipe.

[0012] Preferably, in step (3), when detecting the old oil pipe based on the scanning sensitivity, record the position of the detected corrosion defect for the old oil pipe with an alarm.

[0013] Preferably, S2 further includes step (4). For the old oil pipe with an alarm when detecting based on the scanning sensitivity, if it does not alarm when detecting again with the reference sensitivity, manually review whether the depth of the corrosion defect reaches more than 30% of the wall thickness of the oil pipe. If it exceeds 30% of the wall thickness of the oil pipe, the oil pipe is used as a scrapped oil pipe. If it does not exceed 30% of the wall thickness of the oil pipe, the oil pipe is used as a secondary oil pipe.

[0014] Preferably, in step (1), process a vertical through-hole on the sample pipe as an artificial defect. In step (2), take the sensitivity value displayed by the ultrasonic flaw detector when the peak value of the reflected wave intensity of the artificial defect is 80% as the reference sensitivity, and increase the reference sensitivity by 6 db as the scanning sensitivity.

[0015] Preferably, the detectable corrosion defects include circular corrosion pits, dense small corrosion pits, longitudinal corrosion pit connections, and dense shallow pits.

[0016] Preferably, the ultrasonic flaw detector uses a 2.5 MHz focused probe and uses water as a coupling agent.

[0017] Preferably, the moving direction of the ultrasonic flaw detector is parallel to the axial direction of the old oil pipe, and the moving speed is not greater than 7.5 m / min.

[0018] The present invention has the following beneficial effects compared with the prior art: Through the method for grading used oil pipes of the present invention, used oil pipes can be divided into first-grade oil pipes, second-grade oil pipes and scrapped oil pipes. The first-grade oil pipes are equivalent to new oil pipes and are used without change according to the previous method. The corrosion depth of the second-grade oil pipes exceeds 12.5%t but does not reach 30% of the wall thickness, and they are suitable for use in rod pumping wells and electric submersible pump wells with a well depth less than 4000m and a wellhead pressure less than 15MPa. It is not recommended to use them in injection gas wells, injection water wells, acid fracturing wells and other treatment wells, gas wells and oil wells with packers. It is not recommended to use the scrapped oil pipes in the well, and they can be used for other purposes. Through the method for grading used oil pipes of the present invention, not only can the scrapped oil pipes be detected to reduce the risk of liquid leakage and gas leakage of the oil pipes, but also the second-grade oil pipes can be detected and used conditionally, which is beneficial to reducing consumables and can save huge costs for oilfield development. Specific Embodiment

[0019] The present invention provides a method for grading used oil pipes, which grades used oil pipes with a specification of Φ88.9×6.45mm according to the depth of corrosion pits on their outer surfaces, including:

[0020] S1, Detect the used oil pipes according to the ultrasonic flaw detection scheme for detecting new oil pipes. The used oil pipes with a detected corrosion pit depth > 12.5% of the standard wall thickness are used as first-grade oil pipes. During the detection process, when the detected corrosion pit depth > 12.5% of the standard wall thickness, the equipment gives an alarm, and the used oil pipes without an alarm are first-grade oil pipes. The detection in this step is carried out according to the API Spec5CT standard. A longitudinal groove with a depth of 12.5% of the wall thickness is machined on the sample pipe as an artificial defect, and an ultrasonic flaw detector is used to test the artificial defect on the sample pipe. The sensitivity value displayed by the ultrasonic flaw detector when the reflection wave intensity of the artificial defect is equal to 80% of its peak value is used as the reference sensitivity to scan the used oil pipes.

[0021] S2, Perform ultrasonic flaw detection on other used oil pipes except the first-grade oil pipes, specifically including the following steps:

[0022] (1) Use a new oil pipe with the same diameter, wall thickness and material as the used oil pipe to be detected as a sample pipe, and machine vertical through holes as artificial defects on the sample pipe, and the axis of the vertical through holes is perpendicular to the axis of the sample pipe;

[0023] (2) Use an ultrasonic flaw detector to test the artificial defect on the sample pipe. The sensitivity value displayed by the ultrasonic flaw detector when the reflection wave intensity peak of the artificial defect is 80% ± 0.5% is used as the reference sensitivity, and the reference sensitivity is increased by 5 - 7db as the scanning sensitivity;

[0024] (3) Based on the scanning sensitivity, use an ultrasonic flaw detector to detect the old oil pipes. The old oil pipes without alarm are used as secondary oil pipes. For the old oil pipes with alarm, detect them again with the reference sensitivity. If there is an alarm again, the detected corrosion defect, that is, the defect with a depth exceeding 30% of the wall thickness of the oil pipe, is used as a scrapped oil pipe.

[0025] Through the old oil pipe grading method of the present invention, the old oil pipes can be divided into first-class oil pipes, secondary oil pipes and scrapped oil pipes. The first-class oil pipes are equivalent to new oil pipes and are used without change according to the previous method. The corrosion depth of the secondary oil pipes exceeds 12.5%t but does not reach 30% of the wall thickness. They are suitable for use in rod pumping wells and electric submersible pump wells with a well depth less than 4000m and a wellhead pressure less than 15MPa. It is not recommended to use them in injection gas wells, injection water wells, acid fracturing wells and other treatment wells, gas wells and oil wells with packers. Scrapped oil pipes are not recommended for use in wells and can be used for other purposes. Through the old oil pipe grading method of the present invention, not only can the scrapped oil pipes be detected to reduce the risk of liquid leakage and gas leakage of the oil pipes, but also the secondary oil pipes can be detected and utilized conditionally, which is beneficial to reducing consumables and can save huge costs for oilfield development.

[0026] In July 2015, according to the old oil pipe grading method of this application, the applicant detected 1913 scrapped oil pipes, and determined 1500 secondary oil pipes. The secondary oil pipes can be used after repair. The repair includes items such as cleaning, gauging, appearance inspection, replacing couplings, thread repair, pressure testing, marking, inspection, and thread protection. In August 2015, 590 secondary oil pipes were run into wells in TK677 and TH12204 wells. The running-in process was smooth, and the current production is normal, saving 472,000 yuan in costs. Savings amount = (1353 yuan per new oil pipe - 553 yuan per repair cost and residual value) * 590 pipes = 472,000 yuan. Through the old oil pipe grading method of the application, the abnormal rejection rate of old oil pipe repair can be significantly reduced, and 150,000 old oil pipes previously determined to be scrapped in each oil production plant can be revitalized. According to an 80% repair rate, it is estimated that more than 120,000 secondary oil pipes can be repaired, saving 96 million yuan in procurement funds.

[0027] In step (1), process vertical through holes on the sample pipe as artificial defects. In step (2), use the sensitivity value displayed by the ultrasonic flaw detector when the peak value of the reflected wave intensity of the artificial defect is 80% as the reference sensitivity, and increase the reference sensitivity by 6db as the scanning sensitivity.

[0028] The ultrasonic flaw detector used in the old oil pipe grading method of the present invention uses a 2.5MHz focused probe and uses water as a coupling agent. The moving direction of the ultrasonic flaw detector is parallel to the axial direction of the old oil pipe, and the moving speed is not greater than 7.5m / min. The detectable corrosion defects include circular corrosion pits, dense small corrosion pits, longitudinal corrosion pit connections and dense shallow pits.

[0029] In step (3), when detecting the old oil pipes based on the scanning sensitivity, record the positions of the corrosion defects detected for the alarmed old oil pipes. S2 further includes step (4). For the old oil pipes that alarm during the detection based on the scanning sensitivity, if they do not alarm when detected again with the reference sensitivity, manually review whether the depth of the corrosion defect reaches more than 30% of the wall thickness of the oil pipe. If it exceeds 30% of the wall thickness of the oil pipe, the oil pipe is regarded as a scrapped oil pipe. If it does not exceed 30% of the wall thickness of the oil pipe, the oil pipe is regarded as a secondary oil pipe. In this way, only a small amount of manual review and review at specific positions are required to improve the detection accuracy, greatly reducing the manual review while improving the detection accuracy.

[0030] In Example 1: In step (1), process vertical through-holes as artificial defects on the sample pipe, and use an ultrasonic flaw detector to test the artificial defects on the sample pipe. In step (2), take the sensitivity value displayed by the ultrasonic flaw detector when the reflection wave intensity of the artificial defect is equal to 80% of its peak value as the reference sensitivity, and increase the reference sensitivity by 6 db as the scanning sensitivity;

[0031] In Example 2: In step (1), process vertical through-holes as artificial defects on the sample pipe, and use an ultrasonic flaw detector to test the artificial defects on the sample pipe. In step (2), take the sensitivity value displayed by the ultrasonic flaw detector when the reflection wave intensity of the artificial defect is equal to 80.5% of its peak value as the reference sensitivity, and increase the reference sensitivity by 7 db as the scanning sensitivity;

[0032] In Example 3: In step (1), process vertical through-holes as artificial defects on the sample pipe, and use an ultrasonic flaw detector to test the artificial defects on the sample pipe. In step (2), take the sensitivity value displayed by the ultrasonic flaw detector when the reflection wave intensity of the artificial defect is equal to 79.5% of its peak value as the reference sensitivity, and increase the reference sensitivity by 5 db as the scanning sensitivity.

[0033] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art make various modifications or equivalent replacements within the essence and protection scope of the present invention, which also fall within the protection scope of the present invention.

Claims

1. An old oil pipe grading method, characterized in that, grading the old oil pipes with a specification of Φ88.9×6.45mm according to the depth of the corrosion pits on their outer surfaces, including: S1, detecting the old oil pipes according to the ultrasonic flaw detection scheme for new oil pipes, and regarding the old oil pipes with the detected corrosion pit depth > 12.5% of the standard wall thickness as first-grade oil pipes; S2, performing ultrasonic flaw detection on other old oil pipes except the first-grade oil pipes, specifically including the following steps: (1) Use a new oil pipe with the same diameter, wall thickness, and material as the old oil pipe to be inspected as a sample pipe, and process vertical through holes as artificial defects on the sample pipe, and the axis of the vertical through hole is perpendicular to the axis of the sample pipe; (2) Using an ultrasonic flaw detector to test the artificial defects on the sample pipe, and taking the sensitivity value displayed by the ultrasonic flaw detector when the peak value of the reflected wave intensity of the artificial defect is 80% ± 0.5% as the reference sensitivity, and increasing the reference sensitivity by 5 - 7db as the scanning sensitivity; (3) Based on the scanning sensitivity, using an ultrasonic flaw detector to detect the old oil pipes, regarding the old oil pipes without alarm as second-grade oil pipes, and for the old oil pipes with alarm, detecting them again with the reference sensitivity. If it alarms again, the detected corrosion defect, that is, the defect with a depth exceeding 30% of the wall thickness of the oil pipe, is regarded as a scrapped oil pipe.

2. The old oil pipe grading method according to claim 1, characterized in that: In step (3), when detecting the old oil pipes based on the scanning sensitivity, record the positions of the detected corrosion defects for the old oil pipes with alarm.

3. The old oil pipe grading method according to claim 1 or 2, characterized in that: S2 further includes step (4). For the old oil pipes with alarm when detecting based on the scanning sensitivity, if they do not alarm when detecting again with the reference sensitivity, manually review whether the depth of the corrosion defect reaches more than 30% of the wall thickness of the oil pipe. If it exceeds 30% of the wall thickness of the oil pipe, the oil pipe is regarded as a scrapped oil pipe. If it does not exceed 30% of the wall thickness of the oil pipe, the oil pipe is regarded as a second-grade oil pipe.

4. The old oil pipe grading method according to claim 1, characterized in that: In step (1), a vertical through-hole is machined on the sample tube as an artificial defect. In step (2), taking the sensitivity value displayed by the ultrasonic flaw detector at 80% of the peak intensity of the reflected wave of the artificial defect as the reference sensitivity, the reference sensitivity is increased by 6 dB as the scanning sensitivity. ​ 5. The old oil pipe grading method according to any one of claims 1 - 4, characterized in that: The detectable corrosion defects include circular corrosion pits, dense small corrosion pits, longitudinal corrosion pit connections, and dense shallow pits.

6. An old oil pipe grading method according to any one of claims 1 - 4, characterized in that: The ultrasonic flaw detector uses a 2.5MHz focused probe and uses water as a coupling agent.

7. The old oil pipe grading method according to claim 6, characterized in that: The moving direction of the ultrasonic flaw detector is parallel to the axial direction of the old oil pipe, and the moving speed is not greater than 7.5m / min.