Drill pipe

Drill pipe, is hollow, thin-walled, steel or aluminium alloy piping that is used on drilling rigs to facilitate the drilling of a wellbore which comes in a variety of sizes, strengths, and weights but are typically 27 to 32 feet in length (Range 2). Longer lengths, up to 45 feet, exist (Range 3). They are hollow to allow drilling fluid to be pumped through them, down the hole, and back up the annuls.

Because it is designed to transfer drilling torque for combined lengths that often exceed 1 mile down into the Earth's crust, the tempered steel tubes are expensive, and owners spend considerable efforts to reuse them after finishing a well. A used drill stem is inspected on site, or off location. Modified instruments similar to the spherometer are used at inspection sites to identify defects in the metallurgy, in order to prevent fracture of the drill stem during future wellboring. New drill pipe is classed as new (N class), becoming premium (P-class) and finally down to C (C 1 to 3) as the body outside diameter is worn down by usage. Eventually the drill pipe will be graded a scrap and marked with a red band.