With the rapid development of China's economic construction and the improvement of people's living standards, the requirements for residential buildings are becoming higher and higher. People pay more and more attention to the design of kitchen and bathroom, which are the indispensable parts of residential buildings. The Ministry of Construction, the Economic and Trade Commission, the Bureau of Quality and Technology Supervision and the Bureau of Building Materials jointly issued the Notice on Eliminating Backward Products in Residential Construction in December 1999. Article 4 of the Notice clearly states that "from June 1, 2000, in newly built residential buildings in cities and towns, the cast iron drainage pipes with sand mould shall be eliminated for indoor drainage pipes, and the application of rigid polyvinyl chloride (UPVC) plastic drainage pipes shall be popularized and conformed to the Notice of"Eliminating Backward Products in Residential Cast iron drain pipe with flexible joint mechanism for drainage (GB/T12772-2008). From this we can see that the new flexible interface mechanism of cast iron drainage pipe to replace the traditional pipe has become a necessity. At present, in recent years, the drainage pipes popularized by the Ministry of Construction have become the mainstream materials in newly built residential areas. In some high-grade residential areas, the cast iron drainage pipes with new flexible interface mechanism have been widely used, and the cast iron drainage pipes with new flexible interface mechanism have good prospects for development. However, due to the short history of the development of the new flexible interface mechanism cast iron drainage pipe in China, people know little about it compared with other drainage pipe materials. Now, combined with the author's experience in construction, this paper briefly introduces its performance, characteristics and application in engineering.

1. Brief introduction of cast iron drain pipe with new flexible interface mechanism

Nowadays, there are two kinds of universal straight pipes and fittings (i.e. cast iron drainage pipes and fittings with no socket hoop) in the world. According to their interface types, they are divided into two types: A-type flexible interface (flange cover connection) and W-type flexible interface (hoop connection), abbreviated as A-type and W-type flexible interface.

1.1 The new flexible joint cast iron drainage pipe adopts high-speed centrifugal casting technology. It has the advantages of compact structure, uniform wall thickness, smooth inner and outer wall, no trachoma and slag, high tensile and compressive strength, stable chemical composition, corrosion resistance, fire prevention and non-toxicity, meeting the requirements of fire safety and environmental protection, no noise, no distortion and long service life.

1.2A type pipe: A type pipe has the advantages of high strength, low noise, good fireproof performance and long service life, good flexibility and seismic performance of its connection, but in practical engineering, it is found that the installation space of socket joint is larger, the pipe body is bulky and consumes more steel, especially in high-rise buildings, which is difficult to be accepted by the constructors.

1.3W pipe: W pipe has the characteristics of high strength, low noise, good fireproofing performance and long service life, good flexibility and seismic performance of the connection, as well as synchronous construction, high utilization rate of pipe materials, easy pipeline clearance, reduced hydraulic test times, shortened construction period and improved economic benefits. In addition, this type of interface bolt is tightened on the outside, which avoids the flange of the flexible interface of socket and socket being easily damaged and the bolt against the foot of the wall being difficult to fix. It has the advantages of simple operation and so on. Therefore, it has strong competitiveness in the selection of building drainage pipes and fittings. In addition, because the length of W-shaped straight pipe is 3 m, the number of intermediate joints can be greatly reduced and arbitrary length can be intercepted according to the need, thus saving a lot of pipe materials, reducing consumption and cost. W-type Non-socket pipe hoop adopts ribbed stainless steel clamp, flexible lining rubber ring connection, high seismic performance, good sealing performance, allowing swing within a certain range and no leakage. Therefore, W-tube has been widely used both at home and abroad.

2. Material issues

Because this kind of pipe has been formally used on a large scale in recent years, and according to the requirements of the construction industry, the demand is increasing year by year. As a result, the number of manufacturers is increasing gradually. As a result, the quality of products is also uneven. How to grasp the quality of materials will have a decisive impact on the quality of the project. Therefore, the procurement of materials should be carried out in strict accordance with the relevant standards and norms, requiring that pipes, fittings and raw materials processed must be qualified products. After the raw materials enter the market, they should be stored and protected strictly according to the requirements.

3. Application in Engineering

According to the author's construction experience, in the actual installation project, the above two kinds of pipes can be used together with a better effect, not only to meet the needs of construction quality and use function, but also to save materials and reduce costs. Generally, type A pipe is suitable for horizontal drainage pipe and first-floor outlet pipe, and type W pipe is suitable for drainage riser and branch pipe. The advantage of this collocation is that because of the better mechanical performance of flange cap connection, the service life and use function of type A pipe can be guaranteed when making drainage transverse trunk pipe. At the same time, because of its good mechanical strength, it is especially suitable for high-rise drainage outlet horizontal pipe, which can withstand the impact of upper water.

W-type pipe is suitable for selection of drainage riser because of its fast installation and good flexibility of interface. Especially when it is used as the installation and construction of drainage horizontal branch pipe in toilet and bathroom, the good flexibility and tightness of its interface can be used to control the slope of drainage pipe. At the same time, due to the characteristics of W-type pipe connectors, combined with the current status of residential project completion and decoration (usually toilet and bathroom drainage risers are exposed), when the riser is concealed decoration, it is easy to decoration and layout, can save space and increase the actual use area. In addition, the combination of A-type and W-type pipes is due to the installation and construction of A-type pipes, in addition to the above reasons.