application

Double wall corrugated pipe is a new type of pipe, with light weight, high strength, convenient construction, material saving and other advantages.  Compared with the same strength of the light wall tube, it can save about 40% of the raw material, widely used in communication optical cable sheath, building drainage, municipal drainage, farmland low-pressure irrigation and other fields.  In recent years, the application of double-wall bellows gradually expanded, in the field of communication cable casing, has basically replaced the cement pipe.  Compared with other plastic pipe, its consumption is also the largest.  In the field of building drainage, due to its sound insulation performance is slightly poor, at the same time, the development of pipe fittings is not enough, so the amount is not very much.  However, in municipal and factory drainage, especially the use of large diameter buried double wall bellows is increasing.  The use of double wall corrugated pipe compared with the same specification of plastic light wall pipe cost is low, the construction cycle can be shortened 5~10 times.

China began to introduce the production of this type of pipe since the early 1990s, initially mainly small diameter series of φ 110 or less, the raw material is mainly PVC, mainly used as communication cable casing.  In recent years, the double-wall bellows gradually develop to the direction of large diameter. At present, the largest domestic bellows can be φ 1200.  The raw materials used are also developed from MAINLY PVC to PE, PP and so on. Bellows production line equipment has also grown from scratch. At present, many domestic equipment factories can produce bellows production line with diameter up to 1200mm.

There are three kinds of thermoplastics used in buried drainage pipes: POLYvinyl chloride, polyethylene and polypropylene.  The elastic modulus E of the three materials (according to PREN13476-1) is:

Obviously, POLYvinyl chloride is the highest, followed by polypropylene and polyethylene the lowest.  Because the elastic modulus E of POLYvinyl chloride is greater than that of polyolefin, the same ring stiffness can be achieved with a smaller moment of inertia I.  If you use the same wave design you can use a smaller wall thickness.  In a certain range of PVC double – wall bellows in the economic advantage, so in the field of buried drainage pipe PVC double – wall bellows in the earliest application is also the largest amount.  In recent years, polyolefin double-wall bellows have developed rapidly, for the following reasons:

The fluidity and thermal stability of PVC materials are relatively poor, so it is difficult to produce large diameter structure wall pipe.  (At present, the general diameter of PVC double-wall bellows in foreign markets is less than 500mm. In the information introduction, only one manufacturer is found to produce the maximum diameter of 1000mm.)  Polyolefin materials can produce double-walled bellows with large diameters (reported to be up to 1800 mm).

Because there is no technical information in this respect when the domestic development of buried drainpipe begins, it basically relies on the enterprise to grope for some detours.

For example, the initial production of polyethylene double-wall bellows has used PE80 high density polyethylene material suitable for gas pipes.  This material in order to ensure the flexibility of the gas pipe, the molecular weight is relatively low, the elastic modulus is relatively low (below 800Mpa), used in the production of double-wall bellows often can not reach the required ring stiffness, have to increase the wall thickness, obviously not economic.  In 2003, sinopec yanhua company took the lead in developing 6360M high density polyethylene HDPE double wall corrugated pipe material for buried drainage in China according to the requirements of users, drawing on the experience of foreign development for many years and according to the requirements of international advanced standards.  6360M polymerization process adopts advanced double peak production technology, so that the special material has a more special molecular chain structure, high elastic modulus and at the same time to ensure excellent cracking resistance, impact resistance and other properties.  After that, Yanhua developed special material 7000 for buried drainage pipe suitable for large-diameter polyethylene double-wall bellows.

QHE16A/B, a special resin for large-caliber HDPE double-wall bellows jointly developed by Qilu Petrochemical Research Institute and plastic factory, has been recognized by many large-caliber bellows manufacturers and has become one of the earliest and successful large-caliber HDPE double-wall bellows special resin developed in China.  This special material adopts a new formula of S-type catalyst, has a complete technical scheme, and has high melt strength, bending modulus and thermal stability.  The large-caliber double-wall corrugated pipe produced with this special material has good flaring, ring stiffness and anti-aging performance, which is comparable to the comprehensive performance of imported material, and can meet the production requirements of large-caliber double-wall corrugated pipe of different domestic production lines.