Blowout preventer hydraulic cylinder repairing process method

Abstract

The invention discloses a technological method for repairing a hydraulic cylinder of a blowout preventer, and relates to the technical field of oil well blowout preventer repairing. According to the process, corrosives on the inner wall are removed through pulse type high-pressure water jet and ultrasonic cleaning, a stress atlas is subjected to rotary sand blasting coarsening and laser surveying and mapping, a stress concentration area and a main body area of a hydraulic cylinder are preheated section by section based on the atlas, and a tungsten carbide-based coating is deposited by adopting a high velocity oxy-fuel spraying combined pulse powder feeding technology. A pressure stress layer is formed through subarea temperature control gradient cooling, sealing surface grinding and ultrasonic impact strengthening; and finally, eddy current flaw detection, thickness measurement and high-temperature and high-pressure cyclic fatigue testing are performed. The process solves the problems that a traditional repairing coating is low in bonding strength and high in porosity, the corrosion resistance and the fatigue resistance of the repairing layer are improved through stress regulation and control, and the process is suitable for hydraulic cylinder repairing under the high-pressure corrosion working condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil well blowout preventer repair, in particular to a blowout preventer liquid cylinder repair process. BACKGROUND

[0002] In oil drilling operations, the blowout preventer liquid cylinder is a key component for controlling wellhead pressure and preventing blowout. It is subjected to complex working conditions such as high pressure, corrosion and friction for a long time. Defects such as wear and corrosion easily occur on the inner wall, leading to sealing failure or abnormal function. Therefore, efficient repair of the liquid cylinder is crucial to ensure the safety of oil exploitation and reduce equipment costs.

[0003] Traditional blowout preventer liquid cylinder repair processes mainly include manual roller brush coating, air spraying and electroplating hard chromium methods. However, such processes have insufficient coating performance, and the coating formed by manual roller brushing or air spraying has low bonding strength and high porosity, which makes it difficult to effectively block corrosive media, resulting in easy peeling of the repaired layer and poor corrosion resistance. SUMMARY

[0004] To solve the technical problems existing in the prior art, the present application provides a blowout preventer liquid cylinder repair process.

[0005] The technical solution adopted by the present application is as follows:

[0006] A blowout preventer liquid cylinder repair process, comprising the following steps:

[0007] Step 1: sequentially performing pulse high-pressure water jet descaling and ultrasonic cleaning on the inner wall of the liquid cylinder to be repaired,

[0008] Step 2: using a rotating diamond sand blasting device to sand blast and roughen the inner wall of the cleaned liquid cylinder to form a rough surface with Ra3.2-6.3μm, and using a 532nm pulse laser to map the residual stress pattern of the rough surface to generate a stress pattern, wherein the stress pattern includes a stress concentration area and a cylinder body area;

[0009] Step 3: controlling the temperature of different areas of the liquid cylinder according to the stress pattern, preheating the stress concentration area to 400℃ and maintaining for 30min, and preheating the cylinder body area to 280℃ to form a preheated substrate;

[0010] Step 4: using supersonic flame spraying technology combined with 50Hz frequency intermittent powder feeding pulse powder feeding technology to spray tungsten carbide-based composite powder to the surface of the preheated substrate, controlling the particle velocity to be greater than or equal to 1200m / s, spraying in pulse mode, the thickness of each layer being less than or equal to 0.1mm, and the cumulative spraying thickness being 0.3-0.5mm, using the preheating temperature to reduce the temperature difference between the coating and the preheated substrate, allowing the coating to relax stress at the pulse powder feeding gap, and forming a repaired layer with a porosity of less than 0.5%;

[0011] Step 5, gradient cooling of the repair layer under infrared temperature control, semiconductor cooling fins are arranged at the stress concentration area marked in step 2, the cooling rate of the area is controlled at 3-5℃ / min, the cooling rate of the main body area of the cylinder is kept at 6-8℃ / min, and pure argon with a purity of 99.99% is passed through the whole cooling process to prevent oxidation;

[0012] Step 6, grinding the repaired layer after cooling, and then using a high-frequency impact device to perform ultrasonic impact strengthening treatment on the surface of the repaired layer, so that a 15-20μm compressive stress layer is generated on the surface layer of the repaired layer;

[0013] Step 7, defect detection of the repaired layer is performed using a micro eddy current flaw detector, ultrasonic thickness gauge is used to verify the uniformity of the coating thickness, and high temperature and high pressure cycle fatigue test of multiple pressure cycles is performed to verify the reliability of the repaired layer, and the repaired cylinder that passes the detection is obtained.

[0014] Preferably, the pressure of the pulse high-pressure water jet cleaning in step 1 is 80-120MPa, and the pulse frequency is 20-30Hz; the frequency of the ultrasonic cleaning is 40-60kHz, and the cleaning time is 15-30min.

[0015] Preferably, the rotation speed of the spray gun of the rotary sand blasting device in step 2 is 10-15r / min, the sand blasting angle is 75-90°, the grit size is 0.2-0.3mm, and the air pressure is 0.5-0.7MPa.

[0016] Preferably, the particle size of the tungsten carbide-based composite powder in step 4 is 15-45μm, the content of tungsten carbide in the powder is 85-90wt%, and the content of cobalt is 8-12wt%.

[0017] Preferably, the oxygen flow rate of the high-velocity oxygen flame spraying is 1200-1500L / min, the fuel flow rate is 40-60L / min, and the particle velocity is 1200-1400m / s.

[0018] Preferably, the refrigerating capacity of the semiconductor cooling fin in step 5 is 150-200W, the final temperature of the gradient cooling is 50-80℃, and the temperature gradient of the surface of the repaired layer during the cooling process is ≤20℃ / mm

[0019] Preferably, the impact frequency of the high-frequency impact device in step 6 is 20-30kHz, the impact amplitude is 10-20μm, the impact pressure is 0.3-0.5MPa, and the residual compressive stress value of the compressive stress layer is -350 to -500MPa

[0020] Preferably, the pressure fluctuation range of the high-temperature and high-pressure cyclic fatigue test in step 7 is 0-160 MPa, the temperature fluctuation range is 20-150 DEG C, and the cycle number is greater than or equal to 5000 times, and each cycle period is 5-10 min.

[0021] The beneficial effects of the present application are at least one of the following:

[0022] Through the combination of pulse high-pressure water jet and ultrasonic cleaning pretreatment, the sulfide corrosion layer and drilling fluid crystallization in the inner wall of the liquid cylinder are effectively removed, a clean substrate surface is provided for subsequent coating preparation, and the coating bonding failure caused by pollutants is avoided.

[0023] The rotary sandblasting roughening process forms a surface structure with a specific roughness, and cooperates with laser stress mapping to increase the mechanical interlocking area of the coating and provide a data basis for subsequent thermal stress regulation, thereby reducing stress concentration hazards from the pretreatment stage.

[0024] Based on the segmented gradient preheating of the stress map, the temperature of different regions is accurately controlled, the original stress of the substrate is released, the thermal stress difference caused by temperature difference in the spraying process is reduced, and temperature matching conditions are created for high-quality repair layer deposition.

[0025] High-velocity oxy-fuel spraying combined with pulse powder feeding technology realizes dense deposition of the coating through high particle velocity, and the pulse powder feeding gap promotes stress relaxation of the coating, effectively reducing the internal porosity and residual thermal stress of the repair layer, and improving the coating bonding strength and uniformity.

[0026] The zoned temperature control gradient cooling process differentiates the cooling rate according to the characteristics of the stress concentration area, cooperates with inert gas protection, reduces the accumulation of thermal stress and the risk of oxidation during the cooling process, and further optimizes the internal stress state of the repair layer.

[0027] The ultrasonic impact strengthening treatment forms a compressive stress layer on the surface of the repair layer, which offsets the internal tensile stress through plastic deformation, improves the fatigue resistance of the repair layer, and especially ensures the sealing precision and wear resistance of the key parts through precise grinding of the sealing surface.

[0028] The multi-dimensional joint detection system covers defect, thickness and fatigue performance test, and focuses on monitoring the failure-prone areas based on the stress map, to ensure the quality controllability of the repair process throughout the whole process, and to provide protection for the long-term reliable service of the liquid cylinder under high pressure and corrosive conditions. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The present application is a method flowchart. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0031] EMBODIMENT

[0032] A blowout preventer hydraulic cylinder repair process method, as shown in the figure, comprising the following steps: Figure 1

[0033] Step 1, the inner wall of the hydraulic cylinder to be repaired is sequentially subjected to pulse high-pressure water jet cleaning and ultrasonic cleaning.

[0034] Considering that manual roller brushing, air spraying and other processes are not complete in surface pretreatment and have poor roughening effect, resulting in insufficient mechanical interlocking of the coating and the substrate, in a possible implementation, the pressure of pulse high-pressure water jet cleaning in step 1 is 80-120 MPa, and the pulse frequency is 20-30 Hz; the frequency of ultrasonic cleaning is 40-60 kHz, and the cleaning time is 15-30 min.

[0035] For example, when the pressure is 80 MPa (lower limit value), the pulse frequency is 30 Hz (upper limit value) for water jet cleaning, and the frequency is 40 kHz (lower limit value), the time is 30 min (upper limit value) for ultrasonic cleaning, a 0.3 mm deep sulfide corrosion layer is effectively removed in the blowout preventer hydraulic cylinder repair;

[0036] If water jet with a pressure of 100 MPa (intermediate value) and a pulse frequency of 25 Hz (intermediate value) is combined with ultrasonic cleaning with a frequency of 50 kHz (intermediate value) and a time of 22.5 min (intermediate value), the surface cleanliness reaches Sa2.5 level in the hydraulic cylinder repair.

[0037] When water jet with a pressure of 120 MPa (upper limit value) and a pulse frequency of 20 Hz (lower limit value) is combined with ultrasonic cleaning with a frequency of 60 kHz (upper limit value) and a time of 15 min (lower limit value), the cleaning is completed within 5 min and the surface residual impurity particle size is ≤3 μm in the hydraulic cylinder repair.

[0038] This embodiment solves the problems of surface contaminant residue and roughening precision by combining pulse high-pressure water jet + ultrasonic cleaning pretreatment with rotary sandblasting roughening to Ra3.2-6.3 μm, laying a foundation for high-strength bonding.

[0039] Step 2, a rotary diamond sandblasting device is used to sandblast and roughen the inner wall of the cleaned hydraulic cylinder to form a rough surface with Ra3.2-6.3 μm, and a residual stress map of the rough surface is measured using a 532 nm pulse laser to generate a stress map, wherein the stress map includes a stress concentration area and a cylinder body area.

[0040] In a possible implementation, the rotation speed of the spray gun of the rotary sandblasting device in step 2 is 10-15 r / min, the sandblasting angle is 75-90°, the diamond grit size is 0.2-0.3 mm, and the air pressure is 0.5-0.7 MPa.​

[0041] For example, when a spray gun rotation speed of 10 r / min (lower limit), a sandblasting angle of 90° (upper limit), a diamond abrasive particle size of 0.2 mm (lower limit), and an air pressure of 0.7 MPa (upper limit) are used, a rough surface with Ra3.2 μm is formed in the repair of the blowout preventer cylinder.

[0042] Using a rotation speed of 12.5 r / min (intermediate value), a sandblasting angle of 82.5° (intermediate value), a particle size of 0.25 mm (intermediate value), and an air pressure of 0.6 MPa (intermediate value), a surface roughness of Ra4.8 μm was obtained in the repair of a φ300 mm hydraulic cylinder in Shengli Oilfield.

[0043] Using a rotation speed of 15 r / min (upper limit), a sandblasting angle of 75° (lower limit), a particle size of 0.3 mm (upper limit), and an air pressure of 0.5 MPa (lower limit), a rough surface with Ra 6.3 μm was formed during the hydraulic cylinder repair. The three parameter combinations respectively cover the endpoints and the middle regions of the numerical range of rotation speed, sandblasting angle, diamond particle size, and air pressure, and can all generate a rough surface that meets the requirements of Ra 3.2-6.3 μm, providing suitable substrate conditions for subsequent 532 nm pulsed laser stress mapping.

[0044] Step 3: Control the temperature of different areas of the liquid cylinder according to the stress spectrum. Preheat the stress concentration area to 400℃ and maintain it for 30 minutes. Preheat the main body area of ​​the cylinder to 280℃ to form a preheated substrate.

[0045] Step 4: Using supersonic flame spraying technology combined with pulse powder feeding technology with intermittent powder feeding at a frequency of 50Hz, tungsten carbide-based composite powder is sprayed onto the surface of a preheated substrate. The particle velocity is controlled to be ≥1200m / s. The powder is sprayed in layers in a pulse manner, with each layer having a thickness of ≤0.1mm, and the total thickness is 0.3-0.5mm. The preheating temperature is used to reduce the temperature difference between the coating and the preheated substrate. During the intervals between pulse powder feeding, the coating is stress-relaxed, forming a repair layer with a porosity of <0.5%.

[0046] Considering the insufficient density of coatings formed by traditional electroplating hard chrome or ordinary spraying processes, this embodiment uses supersonic flame spraying (particle velocity ≥1200m / s) combined with pulse powder feeding technology to control the porosity to <0.5%. At the same time, the high corrosion-resistant component (85-90wt% tungsten carbide) of the tungsten carbide-based composite powder effectively blocks corrosive media.

[0047] In one possible implementation, the tungsten carbide-based composite powder in step 4 has a particle size of 15-45 μm, a tungsten carbide content of 85-90 wt%, and a cobalt content of 8-12 wt%. The oxygen flow rate for the supersonic flame spraying is 1200-1500 L / min, the fuel flow rate is 40-60 L / min, and the particle velocity is 1200-1400 m / s.

[0048] For example, the supersonic flame spraying and pulse powder feeding in step 4 can use the following parameter combination: when using tungsten carbide-based powder with a particle size of 15μm (lower limit) (tungsten carbide 85wt% lower limit, cobalt 12wt% upper limit), combined with an oxygen flow rate of 1200L / min (lower limit), a fuel flow rate of 60L / min (upper limit) and a particle velocity of 1200m / s (lower limit), a coating with a thickness of 0.3mm and a porosity of 0.45% is formed in the hydraulic cylinder repair.

[0049] If 30μm (intermediate value) particle size powder (87.5wt% tungsten carbide, 10wt% cobalt), combined with 1350L / min (intermediate value) oxygen flow rate, 50L / min (intermediate value) fuel flow rate and 1300m / s (intermediate value) particle velocity, a coating with a cumulative thickness of 0.4mm and a porosity of 0.38% can be sprayed in the hydraulic cylinder repair.

[0050] Using 45μm (upper limit) powder (90wt% tungsten carbide, lower limit 8wt% cobalt), combined with an oxygen flow rate of 1500L / min (upper limit), a fuel flow rate of 40L / min (lower limit), and a particle velocity of 1400m / s (upper limit), a 0.5mm thick coating with a porosity of 0.42% was deposited in the hydraulic cylinder repair process. The three parameter combinations covered the extremes and intermediate regions of the numerical ranges for powder particle size, composition ratio, and spray flow rate, respectively, and all formed a dense repair layer with a porosity of <0.5%. Furthermore, the pulse powder feeding gap (50Hz frequency) effectively achieved stress relaxation of the coating.

[0051] Step 5: Perform gradient cooling of the repair layer under infrared temperature control. Arrange semiconductor cooling pads in the stress concentration area marked in step 2 to control the cooling rate of this area at 3-5℃ / min. Maintain the cooling rate of the cylinder body area at 6-8℃ / min. Introduce 99.99% pure argon gas throughout the cooling process to prevent oxidation.

[0052] In one possible implementation, the cooling capacity of the semiconductor cooling pad in step 5 is 150-200W, the termination temperature of gradient cooling is 50-80℃, and the temperature gradient on the surface of the repair layer during the cooling process is ≤20℃ / mm.

[0053] For example, the gradient cooling in step 5 can use the following parameter combination: when a semiconductor cooling pad with a cooling capacity of 150W (lower limit) and a termination temperature of 80℃ (upper limit) is used for cooling, in the liquid cylinder repair, the cooling rate of the stress concentration area is stable at 3℃ / min, the cooling rate of the main cylinder area is 8℃ / min, and the surface temperature gradient of the repair layer is controlled at 18℃ / mm.

[0054] If a 175W (intermediate value) cooling fin and a 65℃ (intermediate value) termination temperature are used, the cooling rate in the stress concentration area during cylinder repair is 4℃ / min, and in the main body area it is 7℃ / min, with a temperature gradient of 15℃ / mm.

[0055] When using a 200W (upper limit) cooling fin and a 50℃ (lower limit) termination temperature, the cooling rate in the stress concentration area during cylinder repair is 5℃ / min, and in the main body area it is 6℃ / min, with a temperature gradient of 12℃ / mm. These three parameter combinations cover the extremes and middle ranges of the cooling capacity and termination temperature, respectively. All of them can achieve oxidation-free cooling through 99.99% argon protection, and the surface temperature gradient of the repair layer is ≤20℃ / mm, meeting the requirements of the gradient cooling process.

[0056] Step 6: Grind the cooled repair layer, and then use a high-frequency impact device to perform ultrasonic impact strengthening treatment on the surface of the repair layer, so that a 15-20μm compressive stress layer is generated on the surface of the repair layer.

[0057] In one possible implementation, the impact frequency of the high-frequency impact device in step 6 is 20-30 kHz, the impact amplitude is 10-20 μm, the impact pressure is 0.3-0.5 MPa, and the residual compressive stress value of the compressive stress layer is -350 to -500 MPa.

[0058] For example, when using an impact frequency of 20kHz (lower limit), an impact amplitude of 10μm (lower limit), and an impact pressure of 0.3MPa (lower limit), a 15μm compressive stress layer with a residual compressive stress of -350MPa (lower limit) is formed during cylinder repair.

[0059] If a frequency of 25kHz (intermediate value), an amplitude of 15μm (intermediate value), and a pressure of 0.4MPa (intermediate value) are used, an 18μm compressive stress layer with a residual compressive stress of -425MPa (intermediate value) is generated during the repair of the hydraulic cylinder.

[0060] When using a frequency of 30kHz (upper limit), an amplitude of 20μm (upper limit), and a pressure of 0.5MPa (upper limit), a 20μm compressive stress layer with a residual compressive stress of -500MPa (upper limit) is formed in the hydraulic cylinder repair. The three parameter combinations cover the endpoints and middle regions of the numerical range of impact frequency, amplitude, pressure, and compressive stress value, respectively, and can form a compressive stress reinforcement layer that meets the requirements on the repair layer surface, effectively offsetting the internal tensile stress.

[0061] Considering that traditional processes do not control stress distribution and residual tensile stress is easily generated during spraying and cooling, this embodiment constructs a full-process stress control system through laser stress mapping, dynamic preheating, zoned gradient cooling and ultrasonic impact strengthening, which transforms surface tensile stress into compressive stress (-350 to -500 MPa) and solves the problem of microcrack propagation under alternating pressure.

[0062] Step 7: Use a miniature eddy current flaw detector to detect defects in the repair layer, use an ultrasonic thickness gauge to verify the uniformity of the coating thickness, and conduct high-temperature and high-pressure cyclic fatigue tests with multiple pressure cycles to verify the reliability of the repair layer, and obtain a repair cylinder that passes the test.

[0063] In one possible implementation, the pressure fluctuation range of the high-temperature and high-pressure cyclic fatigue test in step 7 is 0-160MPa, the temperature fluctuation range is 20-150℃, the number of cycles is ≥5000, and the cycle period is 5-10min.

[0064] For example, the high temperature and high pressure cyclic fatigue test in step 7 can use the following parameter combination: when the pressure fluctuation of 0-160MPa (full range), the temperature fluctuation of 20-150℃ (full range), and the cycle period of 5min (lower limit) are selected to perform 5000 cycles (lower limit), the reliability of the repair layer is verified in the hydraulic cylinder repair.

[0065] If a pressure fluctuation of 0-80MPa (intermediate value), a temperature fluctuation of 20-85℃ (intermediate value), and a cycle of 7.5min (intermediate value) are used to conduct 5000 cycle tests, the reliability verification will be completed in the hydraulic cylinder repair.

[0066] When subjected to 5000 cycles of testing with pressure fluctuations of 0-160MPa, temperature fluctuations of 20-150℃, and a cycle period of 10min (upper limit), the test results in the hydraulic cylinder repair showed that the three parameter combinations covered the extremes and middle regions of the numerical ranges of pressure, temperature, and cycle, respectively. The reliability of the repair layer could be verified by a combination of micro eddy current testing and ultrasonic thickness measurement.

[0067] Considering that traditional testing does not cover high-temperature and high-pressure cyclic fatigue scenarios, this embodiment uses 5000 pressure cycles at 150℃ and 160MPa, combined with eddy current testing and ultrasonic thickness measurement, to ensure the long-term reliability of the repair layer under extreme oil drilling conditions.

[0068] In summary, this embodiment utilizes a combination of pulsed high-pressure water jet (80-120MPa) and ultrasonic cleaning (40-60kHz) to remove a sulfide corrosion layer 0.3mm deep, achieving a surface cleanliness level of Sa2.5, thus providing a clean substrate for sandblasting roughening. The tungsten carbide-based coating formed by supersonic flame spraying combined with pulsed powder feeding technology (50Hz frequency) has a porosity of <0.5%, and its bonding strength is more than twice that of traditional processes. The 15-45μm particle size powder and 85-90wt% tungsten carbide content ensure the coating's wear resistance and corrosion resistance.

[0069] Based on the stress spectrum, segmented preheating (400℃ / 280℃) and zoned cooling (cooling rate of 3-5℃ / min in stress concentration area), combined with the 15-20μm compressive stress layer formed by ultrasonic impact, the residual stress concentration factor inside the repair layer is reduced by more than 60%, effectively inhibiting the initiation of fatigue cracks.

[0070] High-temperature and high-pressure cyclic fatigue tests (0-160MPa pressure fluctuation, 20-150℃ temperature fluctuation) verify the stability of the repair layer under extreme working conditions.

[0071] Through parameter gradient design (such as high-pressure water jet 80-120MPa, sandblasting air pressure 0.5-0.7MPa, etc.), this process can be adapted to different specifications of liquid cylinders (φ200-350mm) and complex working conditions (deep sea, ultra-deep well), and has a wide range of engineering application value.

[0072] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A repair process for a blowout preventer cylinder, characterized in that, Includes the following steps: Step 1: Perform pulsed high-pressure water jet descaling and ultrasonic cleaning sequentially on the inner wall of the cylinder to be repaired. Step 2: The inner wall of the cleaned liquid cylinder is roughened by sandblasting using a rotating diamond sandblasting device to form a rough surface with Ra 3.2-6.3μm. The rough surface is then mapped by residual stress using a 532nm pulsed laser to generate a stress spectrum, which includes stress concentration areas and the main body area of ​​the cylinder. Step 3: Control the temperature of different areas of the liquid cylinder according to the stress spectrum. Preheat the stress concentration area to 400℃ and hold for 30 minutes, and preheat the main body of the cylinder to 280℃ to form a preheated substrate. Step 4: Using supersonic flame spraying technology combined with pulse powder feeding technology with intermittent powder feeding at a frequency of 50Hz, tungsten carbide-based composite powder is sprayed onto the surface of a preheated substrate. The particle velocity is controlled to be ≥1200m / s. The powder is sprayed in layers in a pulse manner, with each layer having a thickness of ≤0.1mm, and the total thickness is 0.3-0.5mm. The preheating temperature is used to reduce the temperature difference between the coating and the preheated substrate. During the pulse powder feeding interval, the coating is stress-relaxed, forming a repair layer with a porosity of <0.5%. Step 5: Perform gradient cooling of the repair layer under infrared temperature control. Arrange semiconductor cooling pads in the stress concentration area marked in step 2 to control the cooling rate of this area at 3-5℃ / min. Maintain the cooling rate of the cylinder body area at 6-8℃ / min. Introduce 99.99% pure argon gas throughout the cooling process to prevent oxidation. Step 6: Grind the cooled repair layer, and then use a high-frequency impact device to perform ultrasonic impact strengthening treatment on the surface of the repair layer, so that a 15-20μm compressive stress layer is generated on the surface of the repair layer. Step 7: Use a miniature eddy current flaw detector to detect defects in the repair layer, use an ultrasonic thickness gauge to verify the uniformity of the coating thickness, and conduct high-temperature and high-pressure cyclic fatigue tests with multiple pressure cycles to verify the reliability of the repair layer, and obtain a repair cylinder that passes the test.

2. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, In step 1, the pressure of the pulsed high-pressure water jet descaling is 80-120MPa, and the pulse frequency is 20-30Hz; the frequency of the ultrasonic cleaning is 40-60kHz, and the cleaning time is 15-30min.

3. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, In step 2, the rotation speed of the spray gun of the rotary sandblasting device is 10-15 r / min, the sandblasting angle is 75-90°, the diamond particle size is 0.2-0.3 mm, and the air pressure is 0.5-0.7 MPa.

4. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, In step 4, the particle size of the tungsten carbide-based composite powder is 15-45 μm, the tungsten carbide content in the powder is 85-90 wt%, and the cobalt content is 8-12 wt%.

5. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, The oxygen flow rate of the supersonic flame spraying is 1200-1500 L / min, the fuel flow rate is 40-60 L / min, and the particle velocity is 1200-1400 m / s.

6. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, In step 5, the cooling capacity of the semiconductor cooling pad is 150-200W, the termination temperature of gradient cooling is 50-80℃, and the temperature gradient on the surface of the repair layer during the cooling process is ≤20℃ / mm.

7. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, In step 6, the impact frequency of the high-frequency impact device is 20-30kHz, the impact amplitude is 10-20μm, the impact pressure is 0.3-0.5MPa, and the residual compressive stress value of the compressive stress layer is -350 to -500MPa.

8. The method for repairing a blowout preventer cylinder according to claim 1, characterized in that, The pressure fluctuation range of the high temperature and high pressure cyclic fatigue test in step 7 is 0-160MPa, the temperature fluctuation range is 20-150℃, the number of cycles is ≥5000, and the cycle period is 5-10min.

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