Causes of Damage to Oil Drill Pipe

1. Oil well drill pipe vibration, bending damage

When the drill pipe string reaches the critical speed ratio, it will cause the drill pipe to vibrate. This vibration usually causes the drill pipe to bend, excessively damage, quickly damage and fatigue damage. Especially when the drill pipe produces two kinds of vibrations (both node vibration and spring pendulum type vibration) overlapping. The critical speed ratio changes with the length of the drilling tool, the specifications of the drilling tool, the specifications of the drill collar and the borehole size.

2. Tensile failure of oil well drill pipe

Tensile failure often occurs during the whole process of pulling and tightening the stuck drill pipe. When the tensile force exceeds the yield limit, a "fine neck" deformation will occur at the weaker part of the drill pipe wall or at a small cross section. If the pull-up resistance exceeds the limit compressive strength just now, the drill pipe will be torn off. Tensile failure generally occurs at the upper end of the drill string. Because the upper drilling tool has to bear the force and the net weight of the drill string.

3. Fatigue damage of oil well drill pipe

Fatigue damage is the most common type of drill pipe damage. There are three basic types of fatigue damage:

3.1 Pure fatigue destruction

At this stage, the key reason for the fatigue failure of the oil well drill pipe is caused by the regular stress generated when the drill pipe rotates in the curved borehole. In a curved well hole, even if the drill collar has sufficient thickness, fatigue damage is still likely to occur, and the damage location is not necessarily. When the drill rod is bent, every time the drill rod rotates, its matching part will cause regular stress due to repeatable tension and force. The drill pipe close to the drill collar is likely to be bent. Because the drill collar has great rigidity and can resist bending, the bending will occur on the drill pipe above the drill collar.

3.2 Notch fatigue damage

Defects on the surface of the drill pipe, whether it is produced by mechanical processing or the whole process of the metallurgical industry, will greatly harm the fatigue strength of the drill pipe. The degree of damage lies in the location, orientation, appearance, and a total number of the defect. If the notch is located on a part of the drill pipe that is not a critical stress function, the damage to fatigue damage is minor. However, if the notch is located in the range of 50 cm from the connector, because this part is where the drill pipe causes greater bending stress, it will become the key to fatigue failure.

3.3 Erosion fatigue damage

This type of damage is due to extensive damage to the drill pipe at this stage. Erosion is likely to cause more serious damage in various or multiple comprehensive damage methods (corrosion, wear, fatigue). Sometimes, several types of etching methods will be produced separately, but generally speaking, there has always been one type of etching method that has become a critical damage.