The historical experience of countries in the world in the process of modernization shows that the development speed of plastic pipes has exceeded the economic development speed of the same period, and the replacement of traditional pipes with plastic pipes is an irresistible trend in historical development. Large-caliber plastic-coated steel pipes, even in developed countries where dense plastic pipe networks have been built, the application of plastic pipes is still increasing year by year. The average growth rate was 5.2%, which exceeded the national economic growth rate over the same period. In the past 10 years, the average annual growth rate of China's plastic pipe market was 20%. In 2000, 2002 and 2003, the output reached 700,000-800,000 tons, 1.3 million tons and 1.5 million tons, respectively, with a growth rate of 15%. Among them, PVC pipes accounted for 55%, and PE pipes accounted for 40%. It is estimated that before 2010, the average annual growth rate of domestic plastic pipes will still exceed 20%.

Advantages of plastic pipes

Plastic buried pipes have been widely used abroad. The reason is that plastic buried pipes have many advantages over traditional buried pipes such as cast iron pipes, steel pipes, and cement pipes:

Strength and rigidity

On the surface, the strength and rigidity of plastic buried pipes are not as good as cement pipes, especially reinforced concrete pipes. In fact, plastic buried pipes are "flexible pipes". Under the conditions of correct design and laying, the plastic buried pipes and the surrounding soil can bear it together. Therefore, plastic buried pipes do not need to have the same strength and rigidity as concrete pipes and other "rigid pipes" to meet the mechanical performance requirements in buried use.

Hydraulic characteristics

The inner wall of the plastic pipe is smooth, the resistance is small, and the water flow is large. Under the same diameter, the water flow of the plastic pipe is larger than that of the concrete pipe. When the terrain has a slope, the pipe diameter of the plastic pipe can be reduced and the construction volume is smaller.

Tightness

The sealing performance of cement pipes is very poor. Domestic concrete pipes with flat joints only rely on a ring of concrete to seal the joints. It is difficult to ensure that there is no leakage during construction. In addition, the rigid pipes of the concrete pipe system can be moved slightly (such as uneven soil settlement). In addition, the cement pipe is sealed with a vulcanized rubber ring, and the plastic pipe is sealed with a thermoplastic elastomer sealing ring. The service life of the former is shorter than the latter, and there are a series of strict requirements for the connection and sealing of the plastic pipe, which can guarantee the maximum No leakage will occur. The life of cement pipe is only 15 years, and the life of plastic pipe is as long as 50-100 years. Domestic sewage, rainwater, etc. are usually corrosive, and industrial sewage is more corrosive. Metal and cement buried drainage pipes are used for transportation, and the corrosion resistance is worse than that of plastic pipes. In some areas, the outdoor natural environment is very corrosive. For example, when reclaiming land from the sea in Tanggu New District, Tianjin, the cement drainage pipes cannot be found after 3 years. They were all corroded by the salt in the seawater, so we had to lay plastic pipes a second time.

Laying construction

Plastic pipes are light in weight, large in length, few joints, low requirements for pipe trenches, convenient connection, quick construction, low construction costs, and their superiority in urban and harsh natural conditions is more prominent.

Comprehensive economy

In terms of comprehensive economy, the advantages of plastic pipes are being recognized by more and more users. Although the unit price of plastic pipes is slightly higher than that of cement pipes, the total project cost is not higher than that of cement pipes. The Tianjin Municipal Engineering Design Institute has conducted a systematic study on UPVC double-wall corrugated pipes in 1992, and the application of PE double-wall corrugated pipes in buried drainage pipes since 1998. The conclusion is: "The engineering cost of double-wall corrugated pipes and concrete The flat pipe is equivalent, 30% lower than the socket concrete pipe. The construction period is significantly shortened, and the economic benefits are significant."

Large-caliber outdoor PE buried pipe is the world's development trend

In the past 10 years, an obvious international development trend of plastic pipes is the rapid development of water supply and gas PE pipes. Since the 1998 Munich International Coal Union LGU Gas Distribution Committee meeting unanimously recommended the use of PE buried gas pipelines as distribution pipes, after more than 10 years of research and development in various countries around the world, PE pipelines have developed into multi-variety and multi-application pipes. From the beginning of gas distribution, PE pipelines have entered the fields of urban water supply and drainage, farmland irrigation, sewage discharge, mining and oil fields, floor heating, chemical and pharmaceutical industries. Statistics show that PE pipes increase at a rate of 10%-15% every year.

The main reason why the consumption of PE pipes exceeds that of UPVC pipes PE materials for pipes continue to make significant developments

At the initial stage of the development of plastic pipes, the amount of PE pipes was much smaller than that of PVC pipes, mainly because of economy. At that time, high-performance PE pipe materials had not been developed, and only PE materials with performance equivalent to PE63 could be used. Due to the low strength, the wall thickness of PE pipes is more than twice that of PVC pipes under the same conditions, not only high material costs, but also It can only be applied to lower pressure and smaller diameter pipes, otherwise the wall thickness is too large to be used. With the continuous increase in research and development efforts, a new generation of special PE materials for high-strength pipes continues to emerge, not only PE80, but also PE100 products. The upgrading of materials has significantly increased the various stresses of PE pipes, and the thickness of the pipe walls has become thinner and thinner, even lower than that of PVC pipes.

PE pipe is flexible and weldable

Although the cost of special PE materials for high-grade pipes is higher than that of PVC, they are still widely used in developed countries. One of the reasons is that PE pipes have unique flexibility, with an elongation at break of more than 500%, and the bending radius can be as small as 20 of the pipe diameter. -25 times or less, excellent scratch resistance. It is easy to move, bend and insert when laying PE pipes. PE pipes have low requirements for pipe trenches, which can not only reduce the cost of pipe trenches, but also the pipes are not easy to be damaged when the foundation has uneven settlement and dislocation. Weldability is another unique feature of PE pipes, and heat shrinkable tape can be used to connect large-diameter pipes. Novel uses of PE pipe:

(1) PE pipes with smaller diameters can be supplied in the form of long coils, which are very convenient for transportation, laying and installation;

(2) Flexible PE pipes with larger diameters can generally be connected on the ground and then laid in the trenches, which is very convenient for construction;

(3) In some occasions, pipe jacking technology can be used to lay PE pipes instead of digging trenches;

(4) Long pipe sinking method can be used to lay PE pipes at the bottom of rivers, lakes, rivers and sea water, or PE pipes can be laid on the desert without trenching:

(5) PE pipes can be used as internal repair pipes to repair old drainage pipes.

The low temperature toughness of PE pipe is better than that of PVC pipe. In North China, Northeast and Northwest China, the temperature in winter is generally 0℃-30℃. PVC pipe will become hard and brittle, even if the temperature is as low as -30℃, PE pipe still maintains good flexibility and will not become brittle.

Aging resistance now requires that the PE pipe be made blue or black, especially when 2% carbon black is added, it will prevent light and ultraviolet damage. PVC pipes are still made of yellow or white and cannot be exposed to the sun for a long time.

Environmental protection

The PE pipe has no harm to the human body and the environment. Due to the use of heavy metal salts as stabilizers, PVC pipes will pollute water and soil with heavy metals. If the incineration method is used to recycle waste PVC pipes, it will also produce harmful substances such as dioxins.

Large diameter pipe adopts structural wall pipe

Plastic buried pipes can be divided into solid wall pipes and structural wall pipes. The pressure pipes generally use solid wall pipes. The ring stiffness represents the ability of the drainage pipe to bear the external pressure load, which is proportional to the moment of inertia and elastic modulus of the pipe, and inversely proportional to the cube of the pipe diameter. Under the condition of the same ring stiffness, the use of structural wall pipes can save 50%-70% of material compared with the use of solid wall pipes. There are 6 types of structural wall pipes: PVC double-wall corrugated pipe, PVC reinforced pipe, HDPE double-wall corrugated pipe, HDPE winding pipe, carat pipe and FRP sand pipe. At present, the most used are: below Φ500mm, PVC double-wall corrugated pipe, PVC reinforced pipe and HDPE double-wall corrugated pipe; Φ500mm or more, HDPE double-wall corrugated pipe, carat pipe, winding pipe and FRP sand pipe. Large-diameter HDPE double-wall corrugated pipe is the most prominent type among the six structural wall pipes. The main reasons are low raw materials, low cost, high production efficiency, good overall performance, and convenient construction.