管道干线 meaning in Chinese

truck line
trunk pipe line
trunk pipe-line

Now there are thousands and thousands kilometers of pipeline in service all over the world , and in china , till the end of 1994 the longness of main pipeline in service for the transportation of petroleum and gas had been more than twenty thousands kilometers
目前全球有长达数千万公里的各类在役管道，而在我国，到一九九四年底油气管道干线已长达两万多公里。