Large Diameter Steel Reinforced Corrugated Plastic Pipe For The Buried Sewer Application in China
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Large Diameter Steel Reinforced Corrugated Plastic Pipe For The Buried Sewer Application in China The Rapid Developing of the Plastic Buried Sewage Pipe Industries And The Technical Innovation At the moment, sustainable development is the common goal of the whole world. To prevent the environment pollution, all countries have to establish the complete, reliable and economy water draining pipeline system. The buried plastic pipe is approved as the best solution after a long term practice. Different kinds of the buried plastic pipe products from the world have been applied in China. After years’ practices, only few kinds of pipes are being survived in the competition. On the small and middle diameter ranges (Dn200 to 800mm), the main products are double wall corrugated PVC, PE or PP pipe. On the large diameter ranges (over 800mm until 3000mm), the steel reinforced spiral corrugated pipe becomes the winner in the market. To make the buried plastic pipe in large diameter, the wall thickness of the pipe must be very heavy, enough to keep the pipe stiffness and against the soil weight and loading on the road. Thus the high plastic material cost is a big problem for using the large diameter plastic pipe in the project. Therefore, in the large diameter sewage pipe field, the composite & reinforced pipe becomes the priory selection. There are various reinforce and composite methods and solutions, for example, the spiral reinforced pipe with PP tube reinforcement (by Krah or Bauku technology, German), and the spiral HDPE pipe with the steel ribs (developed by Rib Loc, Australia) and the steel reinforced corrugated pipe (by Kanaflex Japan and Goldstone China). Those pipes have an intense competition from the properties, pipe cost, safety and installation. Finally, most of the Chinese pipe makers adopt the solution of Steel Reinforced Polyethylene Corrugated Pipe (hereinafter called SRPCP). Developing of the Steel Reinforced Plastic Buried Pipe Compared with the traditional steel and concrete pipe, the plastic pipe has big advantages such as anti-corrosive, less leakage, light weight and easy installation. But the serious disadvantage of the plastic pipe is the low elastic modulus, e.g. polyethylene Ep value is about 800 Mpa. This character makes the full plastic pipe can not provide a high ring stiffness easily. Or, even we can approach to the high ring stiffness by increasing the wall thickness and material grade, but the expensive pipe cost is not acceptable by most of end users. So before the developing of the reinforced structure wall pipe, the full plastic pipe is mainly used in the area of small and middle diameter ranges. Before using the steel reinforced corrugated pipe, the typical structure wall pipes are double wall spiral pipe developed by KWH, Finland and the reinforced spiral pipe from Krah, Germany. KWH’s spiral pipe is wrapped with a rectangle profile on the mandrel to form a structure wall polyethylene pipe with the flat wall. And Krah’s technology is to warp the pipe on a long drum and the pipe rib is reinforced by a small polypropylene tube. Another supplier of reinforced spiral pipe is Bauku GmbH from Germany. In principle, if the soil is in good geological condition and the pipe is installed with correct process, then under the soil-pipe interaction, even the plastic sewage pipe has low ring stiffness; it could be also used safely. The evaluations of pipe stiffness please refer to “The Design of Buried Thermoplastics Pipe (1999)” which was published by TEPPFA (European Thermoplastics Pipe and Fitting Association) and APME (Association of Plastics Manufactures in Europe). However, a number of failure evidences tell us that the main reason of pipe bulking is using the low stiffness pipe. So if the project adapts low stiffness pipes, the requirements of the soil quality, installation quality and loading of the pipe are very restrictive, any tiny mistake may bring the fatal failure risk. In another hand, the high ring stiffness buried pipe can reduce the risk of the pipe failure. Pipe deformed to ellipse, compact the soil around the pipe. The soil will support the pipe to against the pressure. In the ring stiffness classification, there are SN2, SN4, SN8 and SN16 four grades. Usually SN4 and SN8 will be selected. SN8 is preferred for some areas with worse geological condition, e.g. at the Shanghai area, the loading capacity of soil is less and the underground water level is relative higher, so in designing the SN8 plastic pipe is required. However, only few plastic structure wall pipes could offer the stiffness up to SN8 in large diameter, most of pipes can only provide the ring stiffness from SN2 to SN6, even less. The large diameter buried sewage pipe is usually installed at the downstream of main pipeline or drain water networks, so it has stricter requirement in safety, that cause many contractors and designers worry about using of plastic wrapped structure wall pipe. The elastic modulus of carbon steel is about 190,000 Mpa, while the polyethylene is only about 800Mpa; the steel EP value is almost 200 times higher than polyethylene. As well, the price of steel is half of the polyethylene. So if we can combine the advantages of two kinds of materials, steel and plastic, that will be an ideal solution to get a perfect pipe with high stiffness and less cost. The question is how to compose two kinds of materials in a good way, keep their advantages but avoid the defects, let them complement each other. There are many manufacturers are researching the answer, among them, the steel reinforced corrugated pipe (SRPCP) is a relative successful solution which proved by mass evidences. The conception of steel reinforced corrugated pipe (SRPCP) was developed by Kanaflex of Japan. In 1990’s, Kanaflex started to use the steel profile to reinforce the polyethylene pipe. There are many projects in Japan, American and Israel. In year 2005, the ASTM F 2435-05 standard was published and implemented. And in 2012, the standard was upgraded to ASTM F 2435-12. Since 2003, Goldstone Orient company in China started to develop the SRPCP with their owned technology. With the new designed powerful steel forming units and process, the pipe stiffness was raised to SN16 or higher, and the pipe diameter was enlarged to Dn2500mm from Kanaflex original Dn1000. Because of its obvious advantages on material cost and stiffness, during the last 10 years of time, SRPCP was rapidly developed in China, became the winner in competition with other kinds of structure wall pipe. About 300 SRPCP pipe production lines are installed in every province allover the China. On the drainage and sewage pipe market, if the pipe diameter is larger than Dn800, more than 50% of the projects adopt SRPCP pipe; and if the pipe is bigger than Dn1500, the SRPCP occupied 80% of the market.