立管内部核心是空心的(管中管)，留给钻柱使用。

The riser's inner hollow core (a pipe within a pipe) is reserved for the drill string.

youdao

立管内部核心是空心的(管中管)，留给钻柱使用。

The riser's inner hollow core (a pipe within a pipe) is reserved for the drill string.

youdao