Using high-density polyethylene resin as the main raw material, the buried polyethylene pipe for gas is extruded and formed, referred to as high-density polyethylene gas pipe.
How to distinguish HDPE water supply pipe and HDPE gas pipe
The materials of HDPE water supply pipe and HDPE gas pipe are high density polyethylene, so how to distinguish HDPE water supply pipe and HDPE gas pipe?
If you want to distinguish the difference between HDPE water supply pipe and HDPE gas pipe, you can directly observe from the appearance of the pipe. It can be clearly seen that there are four blue lines on the appearance of HDPE water supply pipe, and some manufacturers will produce white pipe body or other colors. The pipe body, but all have blue lines; and the HDPE gas pipe has an orange line or a yellow line on the exterior, so from the exterior, it can be distinguished which is the water supply pipe and which is the gas pipe.
Can HDPE water supply pipes and gas pipes be mixed used?
HDPE water supply pipes and HDPE gas pipes have different production standards, different pipeline pressures, and different environmental protection standards, so they cannot be universal.
Requirements for burying HDPE gas pipes
1. The minimum thickness of the top cover soil for HDPE gas pipelines shall meet the following requirements:
(1) When buried under the roadway, it should not be less than 0.8m;
(2) When buried under the non-vehicle road, it should not be less than 0.6m;
When buried under paddy fields, it should not be less than 0.8m; after taking effective protective measures, the above regulations can be appropriately reduced.
2. The foundation of the HDPE gas pipeline should be the original soil layer without sharp hard earth and stone and without salt. When the original soil layer has sharp hard earth and salt and salt, fine sand or fine soil should be laid. For the sections that may cause uneven settlement of the pipeline, the foundation should be treated or other anti-settling measures should be taken.
3. When the HDPE gas pipeline is transporting gas containing condensate, it should be buried below the soil freezing line, and a condensate tank should be set up. The slope of the pipeline slope to the condensate tank should not be less than 0.003.
HDPE gas pipe installation precautions
1. After the HDPE gas pipe is installed, it must be properly protected (especially when tiling tiles). Do not disassemble, move, touch, smash, squeeze or press the gas pipe without permission to ensure that the gas pipe is in good condition.
2. If the indoor pipeline is already carrying gas and the indoor gas leak is found, first close the gas valve in front of the meter, open the indoor doors and windows for ventilation, and prohibit opening electrical switches and other behaviors that may cause sparks. .
3. HDPE gas pipes can not be buried in the wall and not less than 10cm from the ground. Gas pipes are not allowed to pass through the wall and should not be too long, and the stove hose should not exceed 2 meters.
4. Remember not to seal the gas pipe, especially the main valve of the whole building and the gas meter in each user's home. If you need to decorate it, you can make it into a valve cabinet or leave a ventilation hole, and reserve enough space for maintenance and security inspection.
5. Do not disassemble and assemble PE gas pipelines (including pipeline fixing hooks or pipe clips) and water heaters without permission. They should be installed by professional technicians of relevant gas companies to ensure safety.
Causes of sudden leakage of HDPE gas pipelines
1 Design
From the long-term work experience, the design work has played an irreplaceable role in the gas pipeline installation process. The selection of equipment specified in the design, the quality of pipes and the choice of gas supply schemes are all related to the operation of the pipeline. Therefore, from the initial design stage, we need to conduct an in-depth survey to understand the geological data of the area, and set up the compensation device on the pipeline, and must not cut corners.
2 Construction
The level of construction quality also has an important impact on the safety of gas, which is embodied in the following aspects: First, the quality of the pipeline. In many cases, the leakage of gas is often caused by the poor pressure resistance of the pipeline, insufficient anti-corrosion and poor material quality, which cause safety hazards. The second is the welding quality of pipeline materials and pipe fittings, or the wrong welding parameters and incorrect welding methods. In 2004, during the emergency repair process of 114 high-pressure pipelines in diameter from Nanqiao to Qingxi, it was found that the cause of pipeline leakage was caused by slag inclusions in welding. Furthermore, in the process of construction, due to the change of design, the excavation depth of the pipe trench did not meet the expected requirements, which in turn led to serious damage to the pipe when subjected to external force.
3 Long-term wear and tear
The use of gas pipelines is long-term. This is a project with very high technical requirements and an important way for the production and transportation of gas products. Once it is applied to our production and life, it means that it will stick to its post for a long time. Since gas, methanol and other products are corrosive to a certain extent, in the long-term transportation process, the pipeline will inevitably react and cause corrosion. In addition, the city is densely populated, so the distribution of gas pipelines is also very dense, and it does not exist in isolation, but intersects with power supply, communication and urban water conservancy, so the destruction of gas pipelines is very likely to accompany the occurrence of underground engineering construction. . In addition, in the long-term use process, due to the complex environment, changeable weather and other reasons, a series of corrosion effects, such as: electrochemical corrosion, bacterial corrosion and chemical corrosion, etc., cause the phenomenon of thinning or even perforation of the pipeline.
4 vandalism
Because some people are selfish, they only care about their immediate interests and disregard the safety of the public—theft of gas facilities and equipment, private access to gas pipelines and other bad behaviors cause gas leakage. The use of excavators and illegal construction in cloudy and rainy days at night also caused damage to the gas pipeline.
Emergency repair and countermeasures for sudden leakage of HDPE gas pipeline
The damage of gas pipeline is also divided into serious and serious, and different measures are taken according to the degree of damage in the process of repairing. If the damage to the pipe is not very serious, such as the phenomenon of partial perforation, we choose to use the saddle repair method, which consists of 4 steps:
• ①Before repairing, it is necessary to do some preparations, such as cleaning the pipeline. Generally, there will be many oxide films on the part to be dissolved, we need to scrape it off, and sometimes it is necessary to depressurize or stop the gas according to the situation.
• ②After scraping off the oxygen layer, you can fix the repair saddle tightly on the pipe, and at the same time, the repair saddle and the pipe must be kept perpendicular.
• ③In the welding process, the adjustment of parameters is also very important, such as the voltage and time during welding. After the adjustment, the welding can be carried out.
• ④The last step is to be done here, that is, the detection after cooling. Sometimes we often encounter some very urgent situations, and the wooden wedge plays a very crucial role in comparing with the smaller funnel. After the safety issues are alleviated, the dust is removed from the pipes, and then the repair work is carried out. When the outer diameter of the PE pipe is less than or equal to 110mm, in the case of serious damage to the pipe, it is best to flatten the two ends of the pipe, that is, the method of flattening and cutting off the gas to replace the pipe, because at this time, the repair is very likely to fail. expected effect.
However, in the actual application outside, the operation process of flattening and ventilation does not take too long, because it is generally used to replace new pipes and carry out emergency repairs. Polyethylene is a thermoplastic material with excellent flexibility and strength, so when you flatten it, you don't have to worry about changing its shape. The specific implementation steps of this method are described with the branched pipeline at the end:
• ①For the sake of safety, a warning area must be demarcated, and it is forbidden for stray people to enter. Qualified explosion-proof instruments and equipment must be used.
• ②The staff must also take safety precautions, and the wearing of insulating shoes and clothing is inevitable. During the development of the work pit, it is inevitable to encounter special sections. When the depth is greater than 1.5m, it is necessary to provide supports in order to ensure the normal progress of the welding operation.
• ③It is most suitable to place the pipe gripper at a distance of about one meter from the injury. When the clamp is in the proper position, the pipe gripper will be locked.
• ④Open the vent at the end of the gas pipe.
• ⑤ Cut off the damaged pipe section and measure its length.
• ⑥ Prepare two electrofusion sleeves and one new pipe, and connect them by dead-end docking.
• ⑦While cooling down and opening the gripper, connect a new pipe and perform leak detection.
Finally, don't forget the backfilling of earthwork, the making of warning signs and informing users to use gas.
When the outer diameter is greater than or equal to 110mm, it is the most suitable choice for the plugging device to carry out the gas exchange tube method. This is a new skill, because PE pipes are widely used, so its plugging device has become a necessary equipment for maintenance and repair. The operation process is similar to "clamp flat and cut off the gas", the difference is that the previous pipe clamp is replaced with a blocking device.
Under normal circumstances, one plugging device can satisfy the gas connection at the end; when the annular pipe network requires uninterrupted gas supply, only two plugging devices are required; For air supply, then a bypass pressure hose can be added on the basis of the two devices. The specific operation steps of the device are as follows:
• ①Select the welding saddle fittings and transition joints, and then you can start the pressure leak detection and installation work after the work.
• ②Install the drilling machine and drill according to the mark.
• ③ After drilling the hole, remove the drilling machine, install and operate the plugging machine on the valve.
• ④ After the emergency repair or construction is completed, remove the plugging machine and install the plugging machine on the valve box, and install the plug at the opening.
• ⑤The last step is to unload the plug machine. Along with the removal of the valve box and the transition joint, the protective cover is installed and leak detection is carried out.
1 Preparing for emergency repairs
The old saying goes: "Know the enemy and know yourself, and you will be safe in a hundred battles." This is also true in pipeline repair work. We must know the source of gas leakage, determine the location of gas leakage, understand the pressure of the pipeline and the situation of the pipe network around it. The next step is to In the formulation of the emergency repair plan, the on-site commander and staff must also follow the procedures, clarify the division of labor, obey the command, standardize the operation, and do a good job in safety protection.
2 Treatment of leaking pipes
(1) Depressurization treatment
If the leakage of the pipeline is large and the time is short, the pipeline of the same material as the original pipeline should be used for filling. When the hole is small and the time is short, and the quality of the pipe reaches the standard, the direct welding repair method can be used. When the pipeline is damaged in a large area, a scar shall be made in advance according to the situation of the leakage surface, covering the pipeline, and monitoring shall be completed after welding.
(2) No depressurization treatment
For pipeline cracks, corrosion and perforation, emergency repair pipe hoop is the best choice. The disadvantage is that it is only suitable for leakage points in straight pipe sections. In some more urgent cases, it is necessary to repair the large leakage of the pipeline immediately, and the gas supply cannot be stopped, then we must choose the operation method with gas and pressure.
(3) Safety measures
When doing these work, we should attach great importance to safety issues, which is reflected in the formulation of emergency repair plans and protective measures by the emergency repairers; strictly abide by the safety operation procedures, and unified command and dispatch; set up safety warning areas; To dig a safe passage.
(4) Aftermath work
• ①Emergency rescue is a high-tech job, so we need to form a skilled team.
• ② Formulate emergency repair plans and drills according to the situation.
• ③ Install cathodic protection to protect pipelines and odorize high-pressure long-distance gas pipelines.
Pipeline transportation is the main way of gas transportation. There are many reasons for the leakage of pipeline gas. In the face of different reasons, we need to take corresponding measures to minimize the loss.
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