国产日韩欧美性爱,国产精品一二三色欲,啪啪啪国产一区二区三区,日熟女伦理一区二

Casing is usually used in the construction of the basement, used to protect the pipe or to facilitate the installation of the iron pipe. The casing is classified as rigid casing, flexible waterproof casing, steel pipe casing and metal casing. Casing is available in many areas and is generally a set of fittings that are outside the other shaft or rod parts and have a wide range of functions depending on the requirements of different environments, such as protection against shaft or rod parts Sleeves; support supporting the casing, and some casing can also be used for sliding bearings. In the mine casing is used to protect the drilling, usually used in the drill hole, to prevent the wellhead collapse and so on. Casing can also be divided into pipes, surface casing, technical casing and casing casing according to their use.