Drill pipe, is hollow, thick-walled, steel piping that is used on drilling rigs and horizontal drilling to facilitate the drilling of a wellbore and comes in a variety of sizes, strengths, and weights but are typically 30 to 33 feet in length. They are hollow to allow drilling fluid to be pumped through them, down the hole, and back up the annulus.
Because it is designed to support its own weight for combined lengths that often exceed 1 mile down into the Earth's crust, the case-hardened steel tubes are expensive, and owners spend considerable efforts to reuse them after finishing a well, replacing the drill stems with thinner walled tubular casing, tapping the natural resources of oil reservoirs. Used drill stem is often sent to a yard for inspection, sorted, and stored until new drill sites can be explored. 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.
Drill pipe is a portion of the overall drill string. The drill string consists of both drill pipe and the drill stem which is the tubular portion closest to the bit or downhole assembly. Drill pipe and drill stems can be differentiated in that the drill pipe is quite flexible and produced in longer segments whereas the drill stem is much more rigid and manufactured in shorter task specific segments.
See Drilling rig (petroleum) for a diagram of a drilling rig.
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