Drill in long-term use of corrosion and vfd speed controller wear, so that certain areas of wall thinning or presence of micro-cracks. Intensity greatly diminished, the role of external forces, most likely from the drill pipe weakest pulled off or broken.
③ processing card when drilling accident, to activities inappropriate use, when the stress exceeds the yield limit. It is deformed. Pull the drill pipe stretched thin, the stress exceeds the strength limit when. The drill will pull off.
④ resulting in the handling or use of a trauma, such as kava teeth marks, well falling matter (drill teeth, jaw) teeth caused by transverse score slips, and bruises, injured, etc. These are often traumatic stress concentration point. Thereby scaling out. And a variety of corrosion can easily start here. Cause local damage to the drill.
⑤ not tight on the buckle, the torque is not required to buckle, shoulder joints did not try to be, on the one hand shoulder losing seal. Thread likely to be drilling thorn bad. On the other hand, due to loss of shoulder support force, the male and female threads produce frequent alternating stress, fatigue thread will break.
⑥ the drilling pressure is too coil tubing drilling rig large, or the occurrence of another continuous drilling, or when a horse sticking Difficult to drill female thread swell, bursting, causing the drill off.
⑦ various connecting thread of the mating connector nipple especially for long term use and occasional breaking check that thread wear and tear caused by the drill off. You know, connecting threads are often in flux, can not check.