The imperfect surface of oil drill pipe, whether formed by mechanical process or formed in metallurgical process, will greatly affect the fatigue limit of drill pipe, and the extent of its influence depends on the location, direction, shape and quantity of defects. If the notch is not the part of the main stress on the drill pipe, it has a slight effect on the fatigue failure. However, if the notch is in the range of 50 cm away from the joint, it will become the core of fatigue failure because this part is the biggest bending stress of drill pipe. The longitudinal notch can diffuse stress without harm. However, even a slight but with sharp bottom notch, will make the stress increase, and lead to failure. The surface of several drilling rods which can cause the damage of the concave fatigue is listed as follows:

Stamp patterns of all prints can be horizontal stress concentration. If not at the appropriate position of the drill pipe stamped, mark seal font pattern and transverse arbitrary position will become the starting position of drill rod fatigue.

It is not allowed to print on the body of the drill rod. It can safely absorb the stress produced by marking the disappearing part of the drill rod thickened with a larger cross section. In addition, the point mark to replace the line mark, and the Rome digital seal along the drill pipe vertically, can also play a security label effect.

If the drill pipe is used as the grounding wire for arcing, the arcing between the tie rod and the rail will often cause the burn on the circumference of the drill pipe. These small pits, though not noticeable, are very tiny, but they form a wide burn band on the drill pipe. It has hard brittle glass and is very easy to accelerate fatigue damage.

The circumferential groove formed on the top of the rubber band on the drill rod is another reason for the fatigue failure of the concave mouth.

The teeth mark of the tongs is the most common and most serious of the various surface marks of the tongs in the drill rod. But because it is longitudinal, not in the same direction as the action stress, so it has little harm to fatigue damage. If it is slightly deviated from the vertical direction, it is very easy to form a stress concentration point. Put the pliers on the joint rather than on the drill rod because it may damage the drill rod.

Kava scar disc kava generally does not leave a damaged scar on the drill rod. But if the kava teeth are poorly processed or poorly operated, the kava teeth will bite the drill rod.

The broken metal in the formation and the well will rotate the drill hole on the surface of the drill tool in the well, and the surface will be rubbed with the hard shaft lining, leaving the circumferential notch. The marks are often triangular, common on drill rods and drill collars.