In practical applications of steel pipes and pipelines, people often hear the term "DN". What does' DN 'represent? After checking, it was found that DN represents an average inner diameter. 

Pipes of the same size can have different inner and outer diameters depending on the material and thickness. If pipeline specs are just inner or outer diameter, it'll cause confusion. The nominal diameter provides a standard for communication and operation during the design, selection, and construction processes. The value of DN roughly corresponds to the average inner diameter of the pipeline, but it should be noted that this is only an approximate value.