Standard drill pipes are long tubular sections of pipe that make up the majority of the drill string. They are typically a 31-foot-long section of tubular pipe but may be anywhere from 18 to 45 feet in length.
Heavy-weight drill pipe (HWDP) is a tubular pipe that adds weight or acts as a transitional piece in the drill string. As a transitional section of the drill string, it is placed between the drill collar and the standard drill pipe to reduce fatigue failures. In other applications, the HWDP is used as an additional weight to weigh down the drill string.
Drill collars are a component of the drill string that makes up part of the BHA. They are thicker-walled, heavier, and more rigid than drill pipes and are primarily used to weigh down the drill bit while dampening vibration and impact forces.