The riser's inner hollow core (a pipe within a pipe) is reserved for the drill string.
立管内部核心是空心的(管中管)，留给钻柱使用。
2
For every piece, the stiff, hollow pipes that connect the drill assembly with the rig at the surface have to be assembled as the drill is lowered and dismantled when it comes up again.
每一段坚实、中空的连接钻取机索导管的冰芯只能被切碎，因为钻取机再次出来时变得更低了也更细了。
3
Its upper end is drill pipe box or union, the nether end is casing pin. It is a crossover with hollow inside.