The meaning of this sentence may be describing the structure of a kind of pipeline, the outside is used iron pipe, and the inside is paper pipe or corrugated pipe, this kind of structure is often used for the transportation of some low-pressure liquids or gases, especially in some occasions that need to change the pipeline frequently, such as the chemical industry, agriculture, medical treatment and other industries.
Corrugated pipe is a kind of pipe made of metal or plastic, which has a wave shape inside and a smooth outer surface. Due to its special wave shape, corrugated pipe has a certain degree of softness and elasticity, which can withstand a certain degree of tension and compression, and at the same time, it can also reduce the vibration and noise of pipeline conveying process.