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API 5CT N80 fault
(1) the well depth and the well pressure not appropriate to meet;
(2) lax to thread inspection of each API 5CT N80 or on-site repair;
(3) in the factory, transportation and on-site handling API 5CT N80 improper operation;
(4) on API 5CT N80 did not abide by the rules of correct;
(5) the scene when repairing threads of improper;
(6) replace and add the collar of inferior quality;
(7) when stored properly maintained;
(8) for the API 5CT N80 through the wellbore narrow site and the torque is too high;
(9) pulling string too fierce, may make the column top collar loose. Before this case column in the end, using tongs retighten;
(10) in the API 5CT N80 in rotary drilling. After cementing, the adjustment of API 5CT N80 the force does not properly is one of the most main reason for the failure;
(11) in the end under the directional hole API 5CT N80 continues to drill, drill wear on the API 5CT N80 is particularly obvious. Dogleg bend over in inclined shaft, or occasionally in straight wells corrective measures dogleg bending will cause API 5CT N80 bending, and the bending in turn leads to internal API 5CT N80 excessive wear. When the borehole dogleg bend is large, this wear is more serious;
(12) joint top large release tension, the slurry erosion without cementing well section of API 5CT N80 bend;
(13) API 5CT N80 column suddenly falling, even very short distance will make API 5CT N80 damage;
(14) pressure acting on the external pressure or under, joint leakage is a common fault, the reason may be:
① thread compound improper selection.
Improper use of the tongs.
The thread of a foreign body.
Because of dirt or accidentally to buckle, or screw bumps, or rotates too quickly, or is too tight, or thread abrasion.
The on-site repair improper thread.
The pulling string too hard.
The sudden drop column.
The shackle of excessive.
The clamp position is too high, especially when the bending shackle, because such causes the thread abrasion.
The joint in the factory is improper. API 5CT N80 is not round. United top the improper operation, so that the threaded joints generated stress exceeds the yield point.
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