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Hydraulic calculation of the ductile iron pipe background

by:XEX     2021-03-11
Hydraulic calculation of the ductile iron pipe background before the 1990 s, most of the water supply pipe is grey cast iron pipe, on the basis of the investigation of 27 large and medium-sized cities in our country's water supply pipe data, the proportion of grey cast iron tube for 84. 72%. In the process of long-term use, grey cast iron tube has a very mature design specifications, design standard atlas and construction specifications. These are for pipe manufacturers, design unit, construction unit has brought great convenience. Ductile iron pipe is on the basis of grey cast iron pipe of a new revolution. It not only inherits the advantages of grey cast pipe corrosion resistance, wear resistance, and its mechanical properties than grey cast pipe, more close to the steel pipe. With nodular cast iron pipe to enter the Chinese market, more and more water companies and construction units to understand and master the performance of ductile iron pipes, ductile iron pipes the water supply pipe has become the dominant products, and gradually replace the grey cast iron pipe, it has become an indisputable fact. But unfortunately, many in China about the design, construction and acceptance of the ductile iron pipe specification are not timely, bring to the construction of the pipeline could not be in accordance with the situation. Due to the lack of standards, the current approach is only to use the specification of grey cast iron pipe. We know that the ductile iron pipe compared with grey cast iron pipe, pipe itself, interface coating, pipeline design, installation and acceptance are very different, ready-made of error is quite large, for the normal operation of the pipeline, the economic benefits are brought a significant impact. The main problem is as follows: - The design of the pipeline, because of nodular cast iron pipe coating a layer of smooth cement lining, roughness k is about 0. 03. And grey cast iron pipe is not lining protection in pipeline operation after a period of time, there will be a layer of corrosion, roughness k is about 0. 2 to 0. 3. As a result, two kinds of pipeline hydraulic resistance coefficient will be very different. Because this kind of problem is very outstanding, the paper has carried on the detailed elaboration, and on the technical and economic comparison. - Pipeline installation, ductile iron pipes generally adopted T slip type flexible interface, grey cast iron pipe interface is more, such as, lead interfaces, expansive cement, asbestos cement interface, etc. , these all belong to the rigid interface. Ductile iron pipe installation is relatively simple, the manufacturers to provide technical installation manual or technical personnel to visit guidance, it is easy to grasp, so the installation problem does not give the construction unit how difficult. Should note, however, is to nodular cast iron pipe installation standards, including some special connector installation, in most of the current design and construction in the specification are not reflect, this situation is not satisfactory. - Concrete piers, the water supply and drainage standard atlas S3, a definition of concrete piers, its design is based on the three regions in 1965, Beijing, guangzhou, chengdu test made of grey cast iron tube. Due to different, such as tubing, the interface form atlas of piers size is not suitable for ductile iron pipes. If we can launch a series of ductile cast iron pipe with cement block the installation of atlas, will bring a lot of to pipeline design, construction is convenient. - Engineering hydraulic pressure test, the current GB50268 - 97 'construction and acceptance of water supply and drainage pipeline engineering of some of water pressure test method and the value of some parameters are not reasonable, and has not adapted to the acceptance of the ductile iron pipe. At present, zhengzhou running water company accumulated a lot of test data in engineering construction, the revision of the hydrostatic test provides many valuable Suggestions, these are for ductile iron pipes in China's development has a positive role in promoting. - Product standard of the old and wrong, GB13295 - And GB13294-91 91 not updated after more than ten years, already can't keep up with the development of ductile cast iron pipe. In addition, GB13295 - 91 still contain some mistakes, for example, DN700 (the weight of the pipe K9 grade, standard working length is 6 m) Is 1126 kg, if according to the weight of the socket part, combined with the weight of the straight part of the calculation, the result is 1123 kg. Both are the result of the 3 kg, obviously it is not reasonable. The new national standard GB/T13295 - 200 x has issued approval, then the new version will be officially launched, it certainly is a cause for celebration of the good news. In a word, on the one hand, the use of nodular cast iron pipe has been overwhelming majority of technical experts of the water supply industry identity; On the other hand, because of the nodular cast iron pipe specification does not keep up with, make the construction of the ductile iron pipes appeared a kind of uncertain predicament, hindered the development of ductile cast iron pipe. Therefore, update the design, construction and acceptance standard for our country and the requirements of product standard is very urgent, also is inevitable.
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