Safety precaution and emergency repair of city gas pipeline network

The urban gas pipeline network is like the “blood line” of the city, and it is essential to ensure the safe operation of the pipeline network. However, gas pipelines are affected by many external environmental intrusions and internal factors, which often cause pipeline damage and cause gas leakage accidents, which not only affects normal gas supply, but also threatens public safety. Therefore, let's explore the safety precautions of the gas pipeline network and repairs after an accident.

1. Safety precautions of urban gas pipeline network

In order to ensure the safe operation of the gas pipeline network and formulate effective preventive measures, it is necessary to analyze the causes of the pipeline accidents. According to historical data analysis of pipeline leakage accidents in various cities, the causes of accidents can be summarized into two categories: external causes and internal causes. The external factors are the main factors that constitute the leakage of the pipeline network. The main reasons are: excavation and piling of the construction site to damage the gas pipeline; road construction machinery rolling damage to the pipeline; illegal building occupation pressure caused by subsidence caused by the pipeline fracture; Pipeline damage caused by operation. The internal factors are also factors that can not be ignored in the pipeline accident. The main factors are: the foundation treatment is not dense during pipeline construction, which causes the pipeline to sink and break; the insufficient vertical crossing distance with other pipelines eventually causes local stress concentration to shear the pipeline; the quality defects of the pipeline cause leakage; Poor backfill quality of the trench caused damage to the pipeline due to dynamic load vibration. In response to the above causes of gas pipeline leakage, corresponding countermeasures must be taken to strengthen the safety precautions of the gas pipeline network, reduce the pipeline leakage rate to a minimum procedure, and eliminate major leakage accidents. 1. Make full use of the computer pipe network geographic information system to strengthen the accident prevention management of the gas pipe network.

Accident prevention management must first comprehensively grasp the comprehensive information of the pipeline network, and the use of the pipeline network geographic information system is the most effective and convenient way. The pipe network geographic information system is a tool for establishing a one-to-one correspondence between a graphic database (mainly storing topographic maps, as-built drawings and facility maps) and an attribute database (mainly storing attribute data of pipelines and facilities). Through the pipeline network geographic information system, you can quickly and accurately analyze the surrounding buildings of the pipeline network, land use, environmental indicators, infrastructure and other information as well as the operation status of the gas pipeline network itself, historical accidents, construction data, acceptance data, accident hidden danger handling and rush repair Records and other information can be called at any time, so that it is easy to repeatedly consult and compare and comprehensive analysis, which is conducive to formulating a scientific and reasonable pipe network maintenance plan and overhaul plan, so as to prevent accidents before they happen.

2. Strengthen the patrol inspection of the gas pipeline network and deal with hidden dangers in time

The main contents of the pipeline inspection are pipeline leakage, the impact of various construction projects near the pipeline, illegal construction on the pipeline, ground subsidence around the pipeline, and other abnormal conditions. Line inspections implement a responsibility contracting operation mechanism, strengthen management, and implement a responsibility system. Inspection personnel must ensure that inspections are in place, observations are in place, instruments are detected, safety considerations are in place, and treatment is in place. There is engineering construction near the gas pipeline. It is necessary to actively cooperate with the situation of providing gas pipelines, put forward safety protection measures, and conduct on-site monitoring to eliminate all kinds of hidden dangers that endanger the safety of pipelines during construction. The illegal construction of gas pipes must be discovered, stopped and corrected as soon as possible, and the illegal buildings that have been built must be dealt with according to the relevant laws and regulations of the city gas safety management.

3. Strengthen the construction quality management of the gas pipeline project, and take safety precautions from the source

The unit undertaking the construction of the gas pipeline project must possess the corresponding construction qualifications, and strengthen the quality inspection, quality supervision and quality acceptance during the construction process. According to the case analysis of gas pipeline quality accidents, there are three key points to grasp the quality of pipeline construction. First, excavate the trench and handle the foundation properly. Gas pipelines are mainly laid underground. Due to the different effects of backfill soil and external loads on the ground, the requirements for the depth of the pipeline excavation, the foundation treatment under the pipe, and the density of the backfill on the pipe are different. The following two points should be achieved: (1) Strictly control the trench depth to prevent ultra-deep excavation. According to the pipeline laying depth requirements, the excavation depth should be less than the buried pipe depth of 10cm-15cm. Before laying the pipeline, according to the depth and slope requirements, manually remove the excess soil layer. (2) Correctly handle the tube base. When the pipeline is crossed with other pipelines, in order to prevent the squeezing and fracture caused by the subsidence of all pipelines, the concrete foundation of the crossed pipelines must be built. When the pipe foundation is made of hard bricks, loose soil and corrosive soil, it is necessary to remove the 30 layers of masonry or mulch layer under the pipe foundation. Sandstone layer. Second, strictly control the selection of pipe materials and the quality of pipe materials. Regardless of the choice of gray cast iron pipes, ductile tubes, steel pipes, all qualified products and products of reputable manufacturers must be selected. The technical information such as product qualification certificates, material analysis test sheets, pressure test reports, etc. must be carefully checked before installation. Strict visual inspection to check the quality. Third, pipe trench backfilling must be tamped. The gas pipeline backfill construction includes procedures such as returning soil, leveling, tamping, and inspection. The trench backfill should be layered, backfilled and layered compacted. The first three layers of the pipe top are only suitable for manual compaction. The main roads should be backfilled with gravel and concrete to ensure the compactness of the backfill to prevent the pipeline from breaking due to ground subsidence and heavy load rolling.

2. Emergency repair of gas pipeline network accident

Accident repair is due to serious accidents such as leakage, fire, explosion, etc. of the pipeline, which have or will endanger the safety of personal property. Emergency and effective measures must be taken to eliminate the accident and ensure safety, and restore normal gas supply as soon as possible.

1. Information consultation and emergency repair decision of accident repair. When the emergency repair center receives the accident alarm or telemetry alarm signal, it should immediately search the pipeline network information and map files in the accident area through the pipeline network geographic information system and emergency repair decision system, and compile the control or close the valves and reduce the pressure of the regulator ( Stop gas) plan, provide a range of users that affect gas supply, and quickly collect and print out a complete emergency plan.

2. The emergency repair organization and major repair equipment are organized and commanded by the highest decision-making level of the transmission and distribution system. The general emergency repair is organized and commanded by the competent department. The transmission and distribution management personnel, safety firefighters and full-time emergency repair team constitute the basic lineup for the specific implementation of emergency repair. The full-time emergency repair team implements 24-hour duty, and receives the central alarm instruction and immediately dispatched to the scene.

The full-time emergency repair team must be equipped with necessary equipment and facilities, mainly including: special engineering emergency repair vehicles (equipped with alarms, car radios and handheld remote intercoms, etc.); protective and fire fighting equipment include gas masks, thermal insulation protective clothing, conventional and special fire fighting equipment , Safety fences, etc .; machinery and electrical equipment include pipe cutting and drilling equipment, welding equipment, small excavation equipment, pumps, explosion-proof lighting equipment, small generators, explosion-proof axial fans, power supply junction boxes, etc .; test instruments include gas concentration testers, Pressure tester, static tester, etc.

3. The role of the emergency repair site After the emergency repair personnel arrive at the operation site, the warning area is determined according to the degree of gas leakage. Open fire is strictly prohibited in the warning area, traffic must be controlled, and no unauthorized personnel are allowed. It was determined that the concentration of gas in the air reached or exceeded 20% of the lower explosion limit at the work site, or that the concentration of Co in the air was greater than 0.05%. It should be classified as a hazardous area, except for emergency repair personnel and firefighting under unified command in the hazardous area No personnel other than personnel and ambulance personnel shall be allowed to enter. It is strictly forbidden to use non-explosion-proof electromechanical equipment, instruments and meters during the operation, and perform forced ventilation. According to the pipeline completion plan and the emergency repair plan, the accidental pipeline will be positioned and depressurized (gas stop) on site, then excavation, gas blocking and pipe replacement will be performed, and finally the gas supply will be restored. During the depressurization operation, the low pressure reduces the gas pressure of the accident pipeline to 800Pa-1000Pa by adjusting the outlet pressure of the regulator, and the medium pressure pipeline passes through the upstream (unidirectional gas supply) or downstream (bidirectional gas supply) valves of the small accident pipeline section. Reduce the gas pressure to 800Pa-1000Pa, if necessary, the medium pressure pipe can stop the gas. The user should be notified before the medium and low pressure pipes are depressurized or stopped. During the gas-blocking operation, a closed-type eye-drilling machine is used for drilling and tapping. The operator should wear a gas mask and insert the gas-blocking bag (two) from the gas-blocking hole into the tube to inflate the gas. When changing pipes, use hydraulic or crawling pipe cutters to cut off the pipes, replace the damaged pipe sections, and then stake out and cut the pipes to connect the pipes. When restoring the gas supply, remove the choke bag, plug the choke hole with a pipe plug, check the replacement pipe section, choke hole, and the pipe joints that may be affected by the emergency repair. After the normal gas pressure is restored, perform a full leak detection again. Users must be notified in advance to restore normal gas supply. In the event of an accidental fire on the job site, the fire fighting equipment on site should be used to extinguish the fire or report "119" to assist in the rescue. It is strictly forbidden to cut off the gas suddenly to prevent the flashback and explosion.

How to ensure the safe operation of the gas pipeline network is a major issue facing the gas industry, and its discussion has great social and economic value. Therefore, in future practice, we must continue to conduct in-depth research and summary.