Casing are used to reinforce the borehole wall, both inside and outside diameter is much larger than the drill pipe; drill pipe is used to connect drill collars and drill bits, enough length to support the bit in the downhole operation.
Casing is to reinforce the wall, but also the passage of oil from the ground to the ground, is a completion tool, that is, after drilling, cementing tools. The drill pipe is a tool in the drilling process is connected to transmit power and torque, connecting the square drill, drill collars, joints and so on. Length of 9.5m, the middle of the thin, both ends of the connector. Casing thread is fine british thread 8 teeth / 25.4mm, taper 1:16. Drill pipe joints are thick buckle, more models.
