INTENSELY SPONTANEOUS MAGNETIZATION OF A DRILL STEM FOR OIL AND GAS FIELD

摘要

The objective of this study was a theoretical explanation of the reason causing a new phenomenon in NDT. When some drill stems for oil and gas field operated through a long period of time were maintained, NDT personnel discovered that the magnetic particle inspection could be carried out on them without magnetization, and only had to apply suspension upon them. An item analysis was conducted on this concrete condition, on the basis of geomagnetic induction effect and the unsymmetrical result of the magnetization demagnetization process of the ferromagnetic materials. The principal finding of this item analysis was that a ferromagnetic object rotating in the geomagnetic field had to be magnetized intensely. On the basis of this finding, a drill stem for oil and gas field after its operation for a long time must be magnetized intensely and spontaneously.