Tensile failure often occurs during the drilled collars of the drilled oil. When the pull force exceeds the yield point, the "thin neck" deformation will occur at the weakest or the smallest section of the drill pipe wall. If the pull force is more than the limit strength, the drill rod will be broken. Tensile failure usually occurs at the upper part of the drill string. Because the upper drill is not only to bear the pressure, but also to bear the weight of the drill string.

This damage is a common cause of early damage to the drill pipe. Corrosion may be severely damaged by various or several forms of comprehensive destruction (erosion, abrasion, and fatigue). Sometimes several forms of corrosion occur at the same time, but generally, there is always a form of corrosion that is the main cause of destruction.

The main corrosive agents that affect the drilling tool steel include oxygen, carbon dioxide, hydrogen sulfide, dissolved salts (chloride, carbonate and sodium sulfate, calcium and magnesium), various acids (formic acid, acetic acid and so on).

Factors affecting the corrosion rate

Water based mud with low pH value will reduce the fatigue life of the drill. PH is the main factor to control corrosion fatigue, but it is difficult to accurately determine the minimum pH value that is sufficient to prevent fatigue damage. Many users believe that the mud pH value is less than 9.5, which will reduce the fatigue life of the drill. The corrosion rate of most of the temperature will be accelerated with the increase of temperature. The velocity of flow speeds up the rate of corrosion as the velocity of mud increases. The local difference in the component or microstructure of non-uniform steel will increase the corrosion rate. The corrosion rate of high stress is generally faster than that of low stress parts.