Mining Pipe is the pipe that a Mining Well uses to replace the blocks beneath it. When broken, it drops itself. The Mining Pipe is a pipe only in name, as it cannot be used as a normal pipe - nothing will flow through it, and its orientation will not change depending on the pipes next to it.
They are effectively useless - they can only be used by a Mining well. You can, however, recycle them using a Recycler. Mining pipe cannot be crafted.
This is Build Craft's Mining pipe, which is different from Industrial Craft's Mining Pipe. Tips:
Do not break mining pipes downward, as they break faster than you fall, so you can take fall damage.
There is always the chance that lava is at the bottom if you DO dig down, so be careful.