The defects of pipe threads are as follows:


1. Tear (rupture): mainly damage to the tooth side, top (round thread) geometry (including roughness). Early single-knife picks used in thread processing are easy to cause tearing, blunt tools, poor lubrication and other reasons are also easy to cause tearing, generally scaly, ubiquitous thread surface; impurities in thread oil, such as sand, can also cause tearing; instrument side has tumors, rules are easy to cause pipe thread surface tearing.


2. Scratch (tremor): The top and side of teeth are caused by feeding, tool knocking or blunt tool wear.


3. Wear marks: the top of the teeth is grinded very smoothly into a flat top. After grinding, there are cracks, pits and other defects on the surface of the pipe (wall thickness allowed to grind 12.5%), which are caused by processing threads.


4. Shoulder: There are two forms: (1) the outer thread disappears after the buckle, due to the tube is not round, eccentricity and other causes, some are called "white neck". Some trapezoids disappear freely along the direction of the tube because there is no L4 regulation, so there is no shoulder. (2) Appeared at the top of the teeth, mainly due to the lack of a tool wear.


5. Black buckle: Round buckle outside LC thread is not allowed; local buckle outside LC thread is allowed 2 buckles, not more than 1/4 circumference.


6. Incision: formerly referred to as breaking, the line is discontinuous. Processing generally does not occur, usually caused by external forces (such as chisel bit) is sometimes caused by insufficient body tube, FRP thread occluded a lot, may be caused by foam.


7. Damage: Many shapes appear on the top and side of the teeth. The general principle is that geometric shape is damaged. Vertical, flat traces. Mechanical damage, protection line by external impact, removal can be seen, some are in the process of handling, transportation caused by the collision. Before the damage of the top of the teeth is found in the factory, the geometric shape can be regarded as qualified after grinding. On-site inspection of the teeth with obvious protrusions on the top plane of the thread will scratch the thread coating, and the result will be found to be unqualified.


8. Magic Poster: Very few discoveries were found, due to excessive torque, wrong buckle, poor lubrication, high-speed buckle. The material is soft and sticky, and should not appear in 5B regulation of pipe material after four buckles of buckle ring; 5C5 regulation has nine buckles of buckle ring anti-skid buckle on pipe, and the second buckle on casing.


9. Deformation buckle: Strange buckle, inspection found relatively small, such as skew, ripple, flat buckle, double buckle and other defects. Bending and ripple are caused by machines. Flat button and double top button are caused by tools.


10, rust: Mainly after applying oil, the water pressure is not treated.


11. Blade: The thin tip of the top of the thread, usually formed by the initial thread disappearing on the round or even trapezoidal thread rather than on the chamfer at the end of the tube.


12. Cutting: The oblique tube is not only a sharp edge, because the outer chamfer is too small or the surface of the chamfer is too small.