What are the reasons for the damage of the drill rod?

by:Ronix Tools     2021-06-20
1. Vibration and bending wear When the drill string reaches a critical speed, the drill pipe vibrates. This vibration often leads to the drill pipe bending, excessive wear, rapid damage, and fatigue damage. Especially when two types of vibration (wave-joint vibration and spring-swing vibration) occur, it is the largest. The critical speed varies with the length of the drill bit, the size of the drill bit, the size of the drill string, and the size of the hole. 2. Tensile damage Tensile damage often occurs in the process of drill pipe. When the pulling force exceeds the yield point, the thin neck deformation occurs at the weakest or smallest part of the drill pipe wall. If the lift pull exceeds the ultimate strength, the drill pipe will pull. Tensile damage usually occurs in the upper part of the drill string. Because the upper drill bit should bear the pressure and weight of the drill string. 3. Fatigue damage Fatigue damage is drill pipe damage. There are three basic types of fatigue damage: 1. Pure fatigue damage drill pipe should withstand the cyclic stress of tension, pressure, torsion and bending. Tension and bending are the most dangerous stresses. At present, the main cause of electric drill pipe fatigue failure is the periodic stress of the drill pipe when it rotates in a curved well. Even if the drill ring has enough thickness, it may still suffer fatigue damage, and the location of the damage is not necessarily. When the drill rod is bent, every time the drill rod rotates, the corresponding position will generate periodic stress due to repeated tension and pressure. The rod above the collar is likely to be bent, because the collar is rigid and cannot be bent, which will happen above the collar. At the same time, the maximum stress of the drill pipe occurs at the end of the thickener, about 50 cm from the joint. As mentioned above, the joint cannot be bent, and the bending can only occur on the thin tube wall of the rod. The change in this part is similar to the clamping and fixing effect, making it the bending force of the fulcrum. If the entire length of the drill pipe is uniformly bent, the stress on the drill pipe will decrease and the stress cycle of fatigue failure will increase. 2. Notch fatigue failure, whether it is mechanical processing or metallurgical processing, mechanical processing or metallurgical processing, will have a great impact on the fatigue limit of the drill pipe, and its effect depends on the location, direction, shape and number of the defect. If the notch is not the main part of the drill pipe stress, it will have less influence on the fatigue damage. However, if the gap is within 50cm of the joint, since this part is the maximum bending stress of the drill pipe, it becomes the core of fatigue damage. Longitudinal can diffuse stress without causing harm. However, even a subtle but sharp mark can increase stress and cause injury. Listed below are several drill pipe surfaces that may cause notch fatigue damage: (1) Stamp mode: All marks can become stress concentrations. If an improper position is printed on the drill pipe, the horizontal imprint of the steel plate and any position mark will become the starting point of drill pipe fatigue. The drill rod body is not printed on the area with a large cross-sectional area of u200bu200bthe drill rod, and the mark can safely absorb the resulting stress. In addition, dot marks can be used instead of line marks, so that the Roman numeral steel marks are arranged vertically along the drill pipe, which can also serve as a safety mark. (2) Arc burn: If a drill pipe is used as a grounding wire, it will often cause arc burns between the rod and the rail on the circumference of the drill pipe. Although these small pits are small, they are easy to be noticed. A wide burn zone is formed on it. Due to its fragile glass it is easy to accelerate fatigue damage. (3) Rubber ferrule? The circular groove formed on the top of the rubber sheath on the drill pipe is another cause of notch fatigue failure. (4) Big pliers? Dentures are the most common and the most serious among various surface damages on drill pipes. But since it is vertical and not in the same direction as the stress, it is not harmful to fatigue. If there is a slight deviation from the vertical direction, it is easy to form a stress concentration point. Hit the pliers on the joint instead of the body of the drill, because it may damage the drill. (5) Slip scars: steering wheel slips generally do not leave destructive scars on the drill pipe. However, if the knight is not properly handled or manipulated, the knight will bite the drill. (6) The surface incision of the stratum and the metal broken drill tool in the well? The tool rotates in the well, and the surface rubs against the hard shaft wall, leaving a circular mark. This mark is usually triangular and is common in drill pipes and drill rings. 3. Corrosion fatigue damage is a common cause of early fracture of drill pipes. Corrosion can cause extremely serious damage in various forms of damage (erosion, wear, fatigue). Sometimes, several forms of corrosion occur at the same time, but in general, there is always one form of corrosion that is the main cause of damage. (1) Corrosives: The main corrosives affecting drill tool steel are: oxygen, carbon dioxide, hydrogen sulfide, dissolved salts (chloride, carbonate and sodium sulfate, calcium, magnesium), various acids (formic acid, acetic acid, etc.). (2) The pH value of the factors affecting the corrosion rate: low pH water-based mud will reduce the fatigue life of the tool. The pH value is the main factor controlling corrosion fatigue, but it is difficult to accurately determine the minimum pH value that can prevent fatigue damage. Many users believe that mud pH below 9.5 will reduce the fatigue life of the drill bit. Most of the corrosion rate increases with temperature. As the mud flow rate increases, the corrosion rate will increase. Local differences in steel composition or organization increase the corrosion rate. The high stress corrosion rate is generally faster than the low stress corrosion rate.
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