The steel grade of drill pipe refers to the classification of drill pipe steel, determined by its minimum yield strength. According to API standards, drill pipe steel grades are categorized into five levels: D, E, 95(X), 105(G), and 135(S), with X, G, and S grades classified as high-strength drill pipes. Higher steel grades correspond to greater yield strength of the pipe material, resulting in enhanced overall strength properties of the drill pipe, including tensile, torsional, and external collapse resistance. In the strength design of drill strings, it is recommended to improve drill string strength by increasing steel grade rather than increasing wall thickness
| Physical properties | Drill pipe steel grade | |||||
| D | E | 95(X) | 105(G) | 135(S) | ||
| Minimum yield strength | MPa | 379.21 | 517.11 | 655.00 | 723.95 | 930.70 |
| 1b/in² | 55 000 | 75 000 | 95 000 | 105 000 | 135 000 | |
| Maximum yield strength | MPa | 586.05 | 723.95 | 861.85 | 930.79 | 1137.64 |
| 1b/in² | 85 000 | 105 000 | 125 000 | 135 000 | 165 000 | |
| Minimum tensile strength | MPa | 655.00 | 689.48 | 723.95 | 792.90 | 999.74 |
| 1b/in² | 95 000 | 100 000 | 105 000 | 115 000 | 145 000 | |
Geological drill pipe materials: D40(50 Mn), DZ50(45Mn2), R780(36Mn2V), R780(42MnMo7), DZ60(45MnMoB). The standard length is generally 9 meters or 9.2 meters, and can also be customized according to user requirements. DZ50(45Mn2)/R780(36Mn2V) offers good quality at a low price. R780(42MnMo7) adopts normalizing + tempering heat treatment process, with excellent mechanical properties, suitable for higher-level drilling requirements (mainly used for deep-hole drilling and trenchless drill pipes).
The drill pipe tool joint is a component of the drill pipe, divided into male joint and female joint, connected at both ends of the drill pipe body. Threads are machined on the joint to connect individual drill pipes. During the drilling process, the joint area is frequently disassembled, and the joint surface is subjected to considerable tong gripping force. Therefore, the drill pipe joint has a larger wall thickness and is made of higher-strength alloy steel. Domestic drill pipe joints generally use 35CrMo alloy steel.
The thread connection must meet three conditions: equal size, same thread type, and matching male and female threads. The joint dimensions of different-sized drill pipes vary. The thread types of the same-sized drill pipes are also not identical. The joint types used by different drill pipe manufacturers are difficult to be completely consistent.
