Drill pipe – Drilling Equipment – Readyzone

Drill pipe

drill - pipe

Drill pipe

The major portion of the drill string, or drill column, is ordinarily composed of drill pipe. The upper end of the drill pipe is supported by the Kelly stem during drilling operations. The drill pipe rotates with the Kelly and the drilling fluid is simultaneously conducted down through the inside of the drill pipe and subsequently returned to the surface in the annulus outside of the drill pipe. In a deep well, the top portion of the drill pipe is under considerable tension while drilling, since most of the weight of the drill string is supported from the derrick.

The drill pipe in common use is hot-rolled, pierced seamless tubing. API Grade D drill pipe has a minimum yield strength of 55,000 psi, and Grade E drill pipe has a minimum yield strength of 75,000 psi. Drill pipe made of stronger steel is also available.

The drill pipe most commonly used is Range 2 pipe, which has a average length of 30 feet per individual length (joint) of pipe. The addition of tool joints produces an average made-up length of about 31 feet per individual length of pipe.

drill pipe

Drill pipe

The individual lengths of pipe are fastened together by means of tool joints, which means that there are complete tool joints spaced at 31 foot intervals throughout the length of the drill pipe. The male half of a tool joint is fastened to one end of an individual piece of pipe and the female half is fastened to the other end. Ordinary pipe proved to be unsuitable for drill pipe, and pipe made of higher grade of steel failed in the threaded connections. Upsetting the ends of the pipe to compensate for metal removed in cutting threads proved to be a partial answer. In internal upset pipe, the pipe wall near the end of the length is made thicker by decreasing the internal diameter. In external upset pipe, the pipe wall near the end is made thicker by increasing the external diameter. In internal-external upset pipe, greater thickness at the end of the pipe is achieved by both decreasing the ID and increasing the OD. Threads of ordinary dimensions will not stand up under the repeated uncoupling and making-up which is required every time a round trip is made with the drill pipe for such purposes as replacing a worn bit. Therefore, tool-joint threads, which are large, tapered threads, were cut into short lengths of alloy steel with sufficient OD, six inches or more, to accommodate such threads. These short pieces of alloy steel were then threaded on their other end so that they in turn might be screwed on the upset ends of the drill pipe. Satisfactory performance has been achieved by shrink fitting the tool joint to the pipe and welding a bead around the end of the tool joint so that it is firmly fastened on the pipe. Before this practice became widespread, failure were common at the last exposed thread of the pipe where it fastened into the tool joint. In addition to threaded connections, tool joints are butt-welded to drill pipe and some pipe is sufficiently upset that an integral tool joint is cut on the pipe.

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Reference : Mc Cray & Cole, Oil Well drilling Technology, New India Publication.

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