Some insights into the use of U-PVC water supply pipes

I. Introduction

With the development of urban construction, the improvement of people’s living standards has put forward higher requirements for drinking water quality. At the same time, in order to ensure the water quality of the water supply pipe network, the Ministry of Construction, the Ministry of Chemical Industry, the China Light Industry Federation, the National Building Materials Administration, and the Sinopec Corporation jointly issued a document and the Shaanxi Provincial Department of Construction, the Shaanxi Provincial Bureau of Quality and Technical Supervision, and the Shaanxi Provincial Administration for Industry and Commerce The bureau jointly issued a document Shaanxi Jianchengfa [2001] No. 247 that strictly prohibits the use of galvanized steel pipes and eliminates gray cast iron pipes in water supply pipelines. ​

Through investigation and analysis of the water supply quality, our company found that gray cast iron parts, especially galvanized steel pipes, are one of the main reasons affecting the quality of water supply. The water capacity is reduced and the resistance to water transportation is increased, seriously threatening the safety and reliability of water transportation. ​

2. Promote the application of U-PVC pipes

There are many types of plastic pipes used for water supply on the market. Each type of plastic pipe has its own advantages and disadvantages. Therefore, appropriate plastic pipes must be selected based on actual conditions. To this end, our company has established a special leadership group for the selection of new pipes. After research and repeated demonstrations, we have formulated the basic principles for the selection of new pipes:

1. Technical regulations are complete, product standards and design, construction and acceptance specifications are complete;

2. The pipes have complete specifications and the supporting pipe fittings have complete specifications and categories;

3. Easy to construct and operate, no special tools required, fast and reliable;

4. It is convenient to connect branch pipes. If there is no water, you can open a tee to connect the branch pipes.

5. Easy maintenance, simple maintenance methods, complete maintenance pipe fittings;

6. The pipes are not corroded by sewage, industrial wastewater and various harmful gases;

Combining the above basic principles, carefully analyze the products of many manufacturers on the market, and refer to the successful experiences and problems in use of other water companies, and based on the actual situation of the company, it is determined that U-PVC pipes will be used as gray cast pipes and galvanized pipes. As a substitute for pipes, U-PVC pipes are light in weight, do not rust, do not scale, have smooth inner walls, have superior hydraulic conditions, and will not cause secondary pollution of the pipes. Compared with other plastic pipes, U-PVC pipes have mature technology. , pipes and pipe fittings have complete specifications, are easy to repair, etc., and have successful use practices. Our company has determined to promote the use of U-PVC pipes and issued “About stopping the use of galvanized pipes and gray cast iron pipes in the water supply pipeline process, promoting the use of Notice of new pipe materials”. Considering that there are currently many manufacturers of U-PVC pipes, pipe fittings are not very versatile. Our company has identified products from three manufacturers as trial pipes. ​

In addition, combined with various U-PVC connection methods and the actual operating habits of construction workers, it is clear that DN200 and DN100 pipes should be connected with U-PVC socket rubber rings. DN50 and DN25 adopt U-PVC pipe flexible joint connection and socket-type glue connection.

3. Some experiences in application

U-PVC pipes, as buried water supply pipes, have been used across the country for several years. In comparison, our company used them relatively late. After a period of use, here are some experiences in application:

1. Trench excavation and backfilling. ​

Compared with ductile iron pipes and steel pipes, U-PVC pipes are light in weight, easy to install, require less labor, and do not require high construction machinery and tools. Based on the above characteristics, during construction, in order to save costs, the construction unit sometimes does not meet the specification requirements for trench excavation width. For example, sometimes the trench width for DN200 pipes is 0.6-0.7M. Although it will not affect the pipeline installation, the quality of the backfill is difficult to guarantee, and the soil compaction cannot be guaranteed. Especially when it is constructed at the same time as the road construction project, the trench is usually excavated for the pipeline project only after the road construction unit has prepared the soil layer. Generally, the designed burial depth of the pipeline is about 1.7M. In fact, only about 1M is needed to dig the trench. Narrow and shallow, it is difficult to meet the backfill requirements. Immediate pavement lamination will threaten the safety of the pipeline and affect the quality of the road project.

In addition, the thickness of the sand cushion should be no less than 100MM at the cnc machining gas stove bottom joint of the ditch. Especially in old urban areas, there is a lot of construction waste at the bottom of the ditch. The specifications must be strictly implemented to ensure the quality of backfill so that the pipeline can operate safely. ​

2. Pipeline installation

U-PVC pipes have a smaller specific weight than metal pipes. The installation requires less labor and the installation cost is low. The connection method adopts a rubber ring interface, which greatly improves the installation efficiency. The larger the pipe diameter, the more obvious the superiority. The only shortcoming is that there is no jacking depth marking line at the pipe port, which makes it difficult to know the jacking depth during installation, especially when installing at night. The impact is greater. In addition, pipes often need to be cut during pipe installation. The end face of the cut must be carefully beveled, especially when crossing other underground facilities, because most U-PVC elbows have double sockets, which are different from straight-line installation. If the groove is not in place, it will be difficult to install, and it is easy to damage the rubber ring or cause the rubber ring to be misplaced. For example, in a pipeline project, the pipe needs to go over an electric ditch. Because the groove on the end face of the cut pipe is not in place and uneven, it is difficult to use It took nearly two hours to push in, but after re-beveling, the installation was successful.

3. Pipeline pressure test

During pipeline pressure testing, the specification stipulates that the hydrostatic pressure of the hydraulic pressure test shall not be less than the design internal water pressure, and shall not be less than 0.8Mpa. Our company follows the metal pipe village test standard, and the test pressure is 1. OMPa, voltage stabilization 0.5h, the axial linear expansion coefficient of U-PVC pipe is larger than that of metal pipes. Our pressure test standard is higher than the standard. During the pressure test, the interface will generally come out by 2-5MM, so the backfill earthwork must reach At the required degree of compaction, the pipe buttresses must reach the design strength and the backs must be safe and stable. At the same time, observe each interface during compression to ensure the smooth progress of the pressure test and the quality of the project. ​

4. Pipe piers

As water supply pipes, U-PVC pipes have been used for some time, but the relevant standards are not very complete. For example, there are relatively complete standard atlases for pipe buttress methods and metal pipe village buttress methods, and construction workers are already familiar with metal pipe methods. , in practice, construction workers often build U-PVC pipe piers according to the method of metal pipe piers. However, the material characteristics of U-PVC pipes and metal pipes are very different, and they should be analyzed separately. The specification clearly stipulates that “U-PVC pipes and metal pipes have very different material characteristics.” PVC pipes must not use 360° “full-pack concrete for foundation treatment or to enhance the load-bearing capacity of the pipe”. To avoid damage to the pipe due to local stress concentration due to expansion and contraction of the pipe, affecting the safe operation of the pipe, our company combines the specifications and regional soil characteristics to design the buttresses. The masonry was standardized, construction standards were formulated, construction was regulated, and project quality was ensured.

5. User management installation

When installing user pipes, since there is no corresponding installation standard for water meter wells made of U-PVC, most installations refer to the national standard atlas for existing metal pipes. Due to the different materials of U-PVC and metal pipes, some problems are prone to occur:

5.1 There are many pipe fittings in the water meter well, especially in the bypass meter. When the pipe diameter is DN>100 during construction, the pipe fittings connections are generally rubber ring connections and flange connections. When using an apron interface, there is a certain distance from the surface wall in both vertical and horizontal directions. During the water test, the pipe fittings sometimes come off (the average pressure of the Xi’an water supply pipe network is about 0.24MPa), and the flange connection is used. This phenomenon has not occurred. Based on construction practices, flange connections for pipe fittings in water meter wells are safer than rubber ring connections. ​

5.2 The price of U-PVC pipe fittings is higher than that of other metal pipe fittings. Taking the installation of a water meter with a main pipe diameter of DN200 and a bypass pipe diameter of DN100 as an example, the main cost of U-PVC pipe fittings is more than 2 times higher than that of ductile graphite pipe fittings. It affects the enthusiasm of construction units for application, thus reducing the price of pipe fittings and enabling U-PVC pipes to be better promoted. ​

5.3 When installing according to the existing water meter and standard atlas, most of the pipes and fittings in the water meter are in a suspended state. Buttresses are built at the gates and water meters. Whether buttresses are built at the tees and elbows. Currently, U —There are no clear specification requirements for water meters for PVC pipes. During actual operation, maintenance and inspection are sometimes required. Failure to build buttresses will affect pipeline maintenance and installation. The original water meter and standard atlas were formulated based on the characteristics of metal materials, and U-PVC pipes are very different from 3d printing engine outlet pipe. Corresponding modifications should be made based on the characteristics of U-PVC materials, and the water meter should be built with tees and elbows. Buttresses or reinforcement measures are effective measures to ensure the safe operation of pipelines. ​

Combined with the experience in construction practice, it is necessary to promote and implement the use of U-PVC pipes. The company’s design regulations, construction standards, and acceptance standards must be formulated according to national standards and specifications and combined with the characteristics of the company. At the same time, we should do a good job in training and better promote U-PVC pipes. ​

4. Conclusion

As a new pipe material for urban water supply pipes, U-PVC pipes are increasingly used in water supply projects due to their advantages. In production practice, it is necessary to continuously summarize and further improve technical specifications and related standards. U-PVC pipes are Make greater contributions to the application and promotion of water supply pipes. The above is the author’s experience in construction practice. If there are any deficiencies, I hope my colleagues will correct me.