Drill pipe, is hollow, thick-walled, steel piping

Pipe (material)

A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

 that is used on drilling rigs

Drilling rig (petroleum)

This article lists the main components of a petroleum onshore drilling rig.Offshore drilling rigs have similar elements, but are configured with a number of different drilling systems to suit drilling in the marine environment....

 to facilitate the drilling of a wellbore

Wellbore

A wellbore is any hole drilled for the purpose of exploration or extraction of natural resources such as water, gas or oil where a well may be produced and a resource is extracted for a protracted period of time....

 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

Drilling fluid

In geotechnical engineering, drilling fluid is a fluid used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. Liquid drilling fluid...

 to be pumped through them, down the hole, and back up the annulus

Annulus (oil well)

The annulus of an oil well refers to any void between any piping, tubing or casing and the piping, tubing, or casing immediately surrounding it. It is named after the corresponding geometric concept...

.

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

Spherometer

A spherometer is an instrument for the precise measurement of the radius of a sphere. Originally, these instruments were primarily used by opticians to measure the curvature of the surface of a lens....

 are used at inspection sites to identify defects in the metallurgy

Metallurgy

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

, in order to prevent fracture

Fracture

A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...

 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)

Drilling rig (petroleum)

This article lists the main components of a petroleum onshore drilling rig.Offshore drilling rigs have similar elements, but are configured with a number of different drilling systems to suit drilling in the marine environment....

for a diagram of a drilling rig.