Is thicker drill pipe always better? An introduction to drill pipe steel grades and strength

Drill pipe is a basic component of the drill string. It is made of seamless steel pipe (wall thickness is generally 7~12mm). Its main function is to transmit torque and convey drilling fluid, and to deepen the wellbore by gradually lengthening the drill pipe.

Drill pipes are the basic components of a drill string. They are made of seamless steel pipes (generally 7-12mm thick). Their main function is to transmit torque and convey drilling fluid, and by gradually lengthening the drill pipe, the wellbore is continuously deepened. Therefore, drill pipes play a very important role in the exploration and drainage of water and gas in coal mines.

Drill Pipe Structure and Specifications

　　Drill pipes are composed of seamless steel pipes, generally 7-12mm thick, consisting of a drill pipe body and a drill pipe connector. The drill pipe body and connector are friction welded together, known as friction welded drill pipes.

　　Schematic Diagram of Drill Pipe Structure

Steel Grade and Strength of Drill Pipes

　

The steel grade of a drill pipe refers to the grade of the drill pipe steel, which is determined by the yield strength of the drill pipe steel. API specifies five grades of drill pipes: D, E, 95(X), 105(G), and 135(S), with X, G, and S grades being high-strength drill pipes. The higher the steel grade, the greater the yield strength of the pipe material, and the greater the various strengths of the drill pipe (tensile, torsional, and anti-extrusion). In the strength design of the drill string, it is recommended to use the method of increasing the steel grade to improve the strength of the drill string, rather than increasing the wall thickness.

Geological drill pipe specifications: 42*5/6/6.2 50*6/6.5 60*7.1 63.5*7.1/7.5 73*7*8*9.19 89*9.35 101.6*8.56 114.3*8.56 127*9.19

　　Geological drill pipe materials: D40(50 Mn ) DZ50(45Mn2)、R780(36Mn2V)、R780(42MnMo7),DZ60(45MnMoB). Generally, the standard length is 9 meters or 9.2 meters, but it can also be customized according to user needs. DZ50(45Mn2)/R780(36Mn2V) is of high quality and low price. R780(42MnMo7) uses normalizing + tempering heat treatment process, with excellent mechanical properties, suitable for drilling requirements (mainly used for deep hole drilling and non-excavation drilling).

　　Drill pipe connectors are components of drill pipes, divided into male and female connectors, connected to both ends of the drill pipe body. The connectors are threaded for connecting individual drill pipes. During drilling, the connectors are frequently disassembled, and the connector surface is subjected to considerable clamping force, so the drill pipe connector has a larger wall thickness and uses higher-strength alloy steel. Domestic drill pipe connectors generally use 35CrMo alloy steel.

　　The threaded connection meets three conditions: the dimensions are equal, the thread type is the same, and the male and female threads match. The connector dimensions of drill pipes of different sizes are different. The thread types of drill pipes of the same size are also different. The connector types used by different drill pipe manufacturers are also difficult to be completely consistent.