Trial use of water plugging in water supply pipeline construction
In order to reduce the scope and time of water cut-off as much as possible during the cutting and repair of new and old pipelines, Ningbo Water Engineering Construction Co., Ltd. established a research group on the application of water plugging method in the construction of water supply pipelines, and demonstrated the possibility and applicability of water plugging method in the application of water supply pipelines by comparing experiments with traditional operation methods.
The safe and stable operation of urban water supply network is an important purpose of modern water supply enterprises. However, the cutting of new and old pipelines and the rush repair of pipelines often require a large area of water cut off, which affects the safe and stable operation of the entire water supply network. It is an urgent problem to reduce the scope and time of water cut off as much as possible when cutting new and old pipelines and repairing pipelines. When the pipe network bursts, according to the current technical conditions, the method of regional water cut-off maintenance is mainly adopted. After the water supply is cut off in the pipe burst area, drain the water in the pipe network, and then repair the damaged pipe. However, with the extension of service time, many valves can not be completely closed due to the influence of impurities in the pipeline or aging of valves (such as: foreign matters appear in the valve groove, the valve screw rod can not completely drop the valve plate to the valve groove position due to corrosion, etc.), resulting in increased water stop time or incomplete water stop in the leak repair section, which directly leads to difficult construction. Since the leakage repair section mostly adopts the operation mode of steel pipe emergency repair or cement tapping, the excessive residual water pressure or discontinuous water flow will have a great impact on the emergency repair, and the normal stop of construction can only be ensured by expanding the scope of water cut-off. In recent years, the extension of water cut-off time due to incomplete water stop has occurred frequently, which has brought many adverse social impacts to the enterprise. Based on this phenomenon, construction enterprises at home and abroad have used new technologies to overcome this difficulty, and water plugging is one of them. In China, some municipal companies and water supply companies have used this technology and received certain results. In view of the application of water blocking method in water supply pipeline construction, we specially set up a research group to demonstrate the possibility and applicability of water blocking method in water supply pipeline by comparing it with traditional operation methods through experiments.
2 Working principle of water plugging The working principle of water plugging is to use high-quality air inflation method to make it shrink, when the internal gas pressure reaches the rule request, fill the entire pipe section, and use the friction force between the wall and the pipe to plug the water leakage, so as to achieve the goal of no water seepage in the target pipe section. This experiment adopted the German consumption introduced by a company in Shanxi. There are two models for each caliber, with and without diversion holes. When the pressure in the pipeline is small, the one without diversion hole shall be used, while when the pressure in the pipeline is large, the one with diversion hole shall be used. The purpose of the diversion hole is to reduce the unsafe factors caused by the high pressure in the sealed pipe section caused by water leakage.
3 Experiment steps and contents
3.1 Preparations before water plugging
(1) Understand the water flow condition of the working pipe section, the upstream water flow source and the distribution of the pipe network, the source and water flow condition of each branch pipeline, and the size of the operation port.
(2) Coordinate with the pipeline dispatching department, discuss and schedule the plan of water cut-off, water plugging and water transfer. Including water flow plan, relevant pump station water pressure control, branch pipe plugging method. Use the list of tools and formulate safety protection measures.
(3) According to the pipe diameter of the construction pipe section, make the corresponding steel flange tee (the tee is used for the outlet after construction), and prepare the flange blank plate of the corresponding diameter.
3.2 As we have purchased a diversion hole and a non diversion hole for the water shutoff operation, the first experiment was carried out in the DN600mm diameter pipe section, and the non diversion hole was used. The second experiment was carried out in the DN200mm diameter pipe section with diversion holes. The staff shall wear protective masks and safety maintenance equipment, and special personnel shall be assigned to monitor in the air.
3.2.1 DN600 pipe test
(1) Measure the diameter of the incoming pipe to ensure that the size is within the application range.
(2) Before inserting, clean the outside of the pipe and the inside of the pipe into which the line will enter.
(3) Pull the end of (with air nozzle) with a traction rope, and gradually put it into the pipeline. Pay attention to the nozzle during the process of putting it into the pipeline to prevent damage. Before inflation, it shall be completely inserted into the pipeline, inserted into the gas pipe, and connected with the barometer and the air pump.
(4) Start the air pump, start inflation, slowly open the air valve of the pressure control meter, and control the inflation pressure in the safe area outside the red area of the pressure indicator. Check the inflation condition and confirm the start of inflation state before the staff evacuate. Ensure that no one is near the pipe during inflation.
(5) Tighten the traction rope and bind the rope firmly on the sleeper
(6) Check the air pressure data through the pressure control table. When the air pressure reaches the technical rule data, close the air pressure control valve, and the inflation is completed.
(7) After inflation, the pressure control table shall be connected with the gas pipe within 20 minutes, and the pressure data change shall be checked. If everything is normal, the pipeline construction can be started.
(8) During pipeline plugging and other operations, special personnel shall be assigned to monitor and check the air pressure, maintain good and stable communication with the personnel at the operation site, and report any abnormal situation in a timely manner to ensure the safety of the operators.
(9) So far, the normal water plugging operation experiment has been completed, and the destructive operation experiment has entered. Before the experiment, check again whether there are people near the operation section; As the valve of the pipe section in this experiment is closed well, there is only a small amount of residual water. In order to imitate the discontinuous flow in the future construction, we opened the valve in the future water direction a little, and water began to enter the pipeline.
(10) After 5 minutes, the sliding phenomenon appeared, and the water inlet valve was immediately closed, and the destructive experiment was completed.
3.2.2 DN200 pipe test
(1) Measure the diameter of the incoming pipe to ensure that the size is within the application range.
(2) Before inserting, clean the outside of the pipe and the inside of the pipe into which the line will enter.
(3) Pull the end of (with air nozzle) with a traction rope, and gradually put it into the pipeline. Pay attention to the nozzle during the process of putting it into the pipeline to prevent damage. Before inflation, it shall be completely inserted into the pipeline, inserted into the gas pipe, and connected with the barometer and the air pump. Connect the DN50mm hose to the diversion hole, and connect the other end of the hose to the drainage well. The following experiment steps are the same as the first experiment, and the first part of the experiment is completed normally
(4) After entering the destructive experiment, although the inlet valve was opened, due to the existence of the diversion hole, the flowing water was smoothly discharged to the drainage well through the drainage hose, without slipping.
3.3.3 Removal
(1) Before removal, confirm that no other personnel are working in the pipeline. Check the hauling rope and tighten it.
(2) Open the valve to vent.
(3) Pay attention to the water level change and the condition of the hauling rope during the deflation process. If necessary, pump the water in the pipeline to reduce the rear pressure of. Otherwise, it may slip due to the pressure of water.
(4) Check the barometer, confirm the restoration and remove it.
(5) The pre manufactured tee shall be pulled out with a traction rope, and attention shall be paid to maintenance to prevent scratching the appearance.
4. Analysis of experimental results
4.1 Analysis of normal water plugging operation During normal water plugging operation, the operation procedures provided by the manufacturer shall be followed. Since the two experiments were all stopped without water, the operation procedure was successfully completed, and no unexpected situation occurred. The time from the beginning of water plugging to the completion of normal water plugging was controlled within 45 minutes. Since the water shutoff application is stopped when there is running water, the operation in this case only verifies the operability of the water shutoff operation procedure and the time required for the water shutoff operation, which cannot prove whether it can work normally under complex practical conditions.
4.2 Destructive experiment analysis
In order to imitate the practical situation of discontinuous water leakage on site, we opened the water inlet valve in two experiments respectively to test the possibility that there is no diversion hole and there is no diversion hole in the continuous water leakage. From the experimental results, we can see that when the pressure in the pipe without diversion hole is lower than 0.1MPa, it can not move, and the plugging condition is good, and no water leakage is found. But when the pressure in the pipe is greater than 0.1MPa, as the pressure gradually increases to the free water pressure, it starts to move under the pressure, that is to say, the effect of water plugging is lost. Because the water supply pipeline is a pressurized pipeline, when water leakage occurs, the pressure in the sealed pipe section will inevitably be the same as the free pressure over time, and the pipeline maintenance construction often lasts for several hours. During this period, the pressure in the sealed pipe section has already exceeded 0.1MPa, so in order to ensure the safety and operability of the construction, It is difficult to use the non diversion hole in the water supply pipeline. In the experiment with diversion holes, due to the existence of the diversion holes, the drainage effect of the diversion holes effectively reduces the pressure of the pipe between the water stop valve and the pipe from time to time, ensures the maintenance time of the maintenance pipe section, and enables the operation task to be completed effectively. In practical construction, after the pressure reduction of the drain outlet and the fire valve, the water leakage generally does not exceed the flow of DN50 mm diameter, while the diameter of the diversion hole is DN50 mm, which can just offset the increasing water pressure from time to time, so the one with the diversion hole is applicable to the water supply pipeline.
5 Conclusions and suggestions According to the results of normal water plugging operations and destructive experiments, under the normal operating procedures, those with diversion holes can play a proper role in the water supply pipeline (pressurized pipeline) through corresponding decompression measures, and provide effective operation methods for water supply areas where the water stop valve cannot be completely closed, It has the value of promoting in the practical application of water supply pipeline. Those without diversion holes cannot comply with the increasing pressure in the sealed pipe section from time to time, so they are not suitable for use in water supply pipelines. However, in non pressure pipelines (such as water pipes and rainwater pipes), they can be used because there is no possibility of increasing pressure in the sealed pipes from time to time. Looking at the whole process of application, compared with the traditional water plugging operation, the added data include a steel tee, a flange blind plate, corresponding screws and other auxiliary materials. For water supply enterprises, the increased cost is negligible compared with the economic and social benefits brought by significantly reducing the water stop time. Moreover, if it is used and maintained properly and can be used repeatedly, its cost can be allocated to each cutover and rush repair accordingly, so from an economic perspective, it is also within the range of affordability. Through experiments, we have the following proposals for the application of water supply pipeline construction:
(1) The capital we have thought about is of great economic significance for us to take care of ourselves. During construction, sharp objects such as stones and protrusions in the pipeline must be removed. The interface and interior of the prefabricated tee as the outlet must be smooth to ensure that it will not be scratched during construction, so as to facilitate repeated use.
(2) In order to ensure that it can play its due role, during the water plugging operation, pay attention to the pressure reduction of the sealing pipe section between the sealing valve and the water stop valve, such as turning over the drain valve, fire valve, etc., to ensure that the pressure in the sealed pipe section can pass through the diversion hole without increasing.
(3) In order to ensure the safety of construction, it is strictly forbidden to stand on the back and front to prevent accidents.