Research and development of pressure-based leak sealing technology for oil and gas pipelines

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In our country, there are approximately **tens of thousands** of oil and gas pipeline leaks each year. It is concerning that the handling of oil and gas pipeline leaks is often not much different from routine pipeline maintenance, and a lack of specialized leak-sealing techniques can frequently lead to serious accidents. Therefore, it is necessary to systematically study the pressure-based leak plugging techniques and application strategies for oil and gas pipelines. According to industry experts, the prerequisite for researching technologies for oil and gas pipeline leaks and countermeasures to stop them is to scientifically classify leakage incidents, and then develop appropriate sealing technologies and products for each type of leakage. The sealing level of the appropriate leak-sealing products, their structural design, the manner in which they protect the pipeline itself, and the methods of installation should be determined based on factors such as the pressure level of the oil and gas pipeline leakage, its location, the cause of the leakage, the medium being transported, and the temperature. To date, China has developed seven pressure-based leak sealing technologies, including steel strip tensioning technology, rapid bundling technology, low-pressure bonding technology, injection-type sealing technology, rapid theft prevention technology, plug welding technology, and pipeline repair under pressure; these technologies have been used to seal more than 30,000 leaks successfully. ——Steel strip tensioning technology. For leaks with a pressure rating below 1.6 MPa, the clamp sealing method was commonly used in the past. The disadvantage of this method is the long prefabrication time and poor adaptability on site. Products such as the composite leak-sealing device and the shaped leak-sealing steel strip, which are part of the patented steel belt tensioning technology developed by Beijing Guantong Company, can effectively overcome the shortcomings of the clamp-based leak sealing method. On August 13, 2003, a leak occurred at the weld of the elbow in the outlet pipeline of the sedimentation tank at the Xiaoji United Station of the Third Oil Production Plant in Dagang Oilfield. The fluid involved was a mixture of oil, gas, and water, with a pressure of 1.2 MPa. The leak was successfully sealed under pressure using a steel strip tensioning method over a period of 20 minutes. ——Fast bundling technology. Sealant products can be structurally divided into two parts: a holding element and a sealing element. A binding tape is a sealant product that combines these two parts together; during binding, as the tape thickens, it generates continuous compressive force, thereby enabling rapid sealing. On August 20, 2004, the outlet composite pipe at Station H106-6, Team 11, Mine 2 of Xianhe Oil Production Plant in Shengli Oilfield leaked; the fluid involved was a mixture of oil, gas, and water, with a pressure of 1.2 MPa. The leak was successfully sealed under pressure using a rapid bundling technique within 30 minutes. ——Low-pressure bonding technology is also known as chemical bonding technology. Existing adhesives are not suitable for direct repair under pressure; a flow guide device is required to enable repair under pressure. The patented product ‘Flow Guide Cap’, developed by Beijing Guantong Company and owned by its own intellectual property rights, solves this problem. On September 19, 2004, a leak occurred at the bottom of Tank No. 1 at Injection Station No. 100, Team 29, Mine 1 of Xianhe Oil Production Plant in Shengli Oilfield; the fluid involved was wastewater, and the pressure was 0.2 MPa. The leak was successfully sealed under pressure using a low-pressure sealing technique within 30 minutes. ——Injection-type sealing technology. For oil and gas leaks with a pressure of over 20–30 MPa, as well as leaks in difficult-to-reach areas such as flanges and valves, injection sealing technology is generally used; however, this method can easily cause damage to the leaking area itself. To this end, Beijing Guantong Company has developed a patented high-pressure sealing injection product that can address various types of leaks at different pressure levels below 35 MPa, in different leakage locations, and with different leaking media. On March 13, 2004, a leak occurred at the flange of the heat exchanger head on the Dongfang Platform of CNOOC Zhanjiang Branch; the medium involved was natural gas at a pressure of 6 MPa. A new repair technique was used to seal the leak while the system was still under pressure, and this approach succeeded within 20 hours. As a result, the shutdown of the entire gas field as well as the fertilizer plants downstream was avoided, saving 3 million yuan in costs. ——Rapid theft prevention technology. In recent years, criminals have installed valves on oil and gas pipelines to steal oil and gas, causing significant losses to production companies. How to safely remove the oil and gas theft valves and restore the pipeline to its original condition without shutting down production? The patented expansion-type plugging device developed by Beijing Guantong Company has solved this problem. On May 28, 2003, a spherical gas theft valve with a diameter of 20 mm was installed on the upper part of the external transmission main line at Station No. 11 of the Production and Gas Transmission Team in the Third Oil Production Plant of Zhongyuan Oilfield. The medium involved was natural gas, and the pressure was 1 MPa. An expansion-type plugging device was used to remove the valve within 20 minutes, successfully sealing the leak. ——Plug welding technology. To repair leaks in oil and gas pipelines by welding, the method of inserting wooden plugs before welding was commonly used in the past, which posed significant safety risks. The patented pipe leak-sealing pliers developed by Beijing Guantong Company, when used in combination with high-temperature sealing gaskets, allow welding to be carried out while ensuring successful leak sealing, **thereby reducing safety hazards. In July 2003, a main gas pipeline belonging to Shandong Provincial Natural Gas Pipeline Co., Ltd. suffered severe leakage in the Liaocheng section due to damage caused by an excavator; the pressure was 1.3 MPa, and the leak was successfully sealed under pressure using a plug welding technique within 90 minutes. ——Pressure-bearing pipeline repair technology. Leaks in oil and gas pipelines caused by corrosion are very common; the common technical solutions at present are emergency plugging and pipeline replacement. If it is possible to create new pipelines based on the existing ones, this approach is superior to the two methods mentioned above in terms of safe production, cost reduction, and various social benefits. The pressure-mounted pipeline repair technology developed by Beijing Guantong Company involves installing pre-made mold pipes onto the pipelines that need repair; through a pressurization process, epoxy resin is injected into the space between the mold pipes and the pipelines and solidifies there, thereby enabling repair while keeping the pipeline in operation. On the afternoon of March 14, 2006, a severe leak occurred in the butane-removal liquid discharge pipeline at the Longkou Bonan Terminal Processing Plant of China National Offshore Oil Corporation; the fluid involved was light hydrocarbons, and the pressure was 1.55 MPa. The leak was sealed using a die-casting process, and it was successfully resolved within two hours, with normal production resuming that same evening.