Classification of J55 Casing Pipe and Drill Thread Deficiencies

The definition of imperfections in the standards for J55 casing pipe is clear: imperfections refer to discontinuities or irregularities in products that are tested in accordance with the methods given in the applicable standards; Defects are sufficiently large in size. The deficiencies of the products are the basis for product rejection in accordance with the applicable standards and their acceptance criteria and methods of determination are also stipulated in relevant standards. The following focuses on the analysis of various types of thread defects (there is no clear distinction between oil casing and drilling tools).
1. BIack crested thread
Definition: A thread without a complete crest (also called a black leather buckle).
Features: Residues of black tubes remain on the top of the threads, mostly at the large end of the thread.
Cause: Due to the fact that the original black rolled skin is not completely removed, the tube wall thickness and ovality are too large, and the tube outer diameter is too small.
Evaluation criteria: Black top thread is allowed for round thread from Lc to thread and vanishing point, not allowed within Lc, but if Lc is not within the black top thread is a point or a line, and the buckle is complete does not affect the continuity of the thread surface, the same should be done when the black top thread is on Lc;
For eccentric trapezoidal threaded sleeves, two crowns of black top threads are permitted over the Lc length, but the length of the black top thread must not exceed 25% of the circumference of the tube, and all other threads in the Lc length should be full threads.

2. Broken Thread
Definition: An entire broken thread tooth, or part of a missing tooth, with the remaining surface in a fractured appearance, also called a broken buckle.
Features: The appearance of a fractured surface metal, extending from the top of the thread or from the top to the bottom, with one or more clasps.
The shedding of the surface metal caused the thread to be discontinuous, the shedding shape was irregular, it was grayish black, and some had rust.
Causes: Due to peeling, outfolding, or inward cracking during the rolling process of the pipe, some defects may be removed when the thread is turned during these defects, causing the fracture to appear gray or gray-black, most of which belong to the quality problem of the pipe, and the thread Processing has nothing to do.
Evaluation criteria: Round threads are not allowed to break off. The trapezoidal trapezoid Lc is not allowed, and it is permissible if the depth of the flaw from Lc to the point of failure of the thread does not exceed the thread bottom cone or does not exceed 12.5% ​​of the specified wall thickness. However, it should be noted that if a defect occurs due to a defect in the surface of the pipe body, it can be regarded as acceptable, and if it is caused by a crack or fold in the pipe body extending to the surface, it is unqualified.

3. Burr
Definitions: There are serrated burrs and fly burrs at the start of the thread and at the top of the teeth (a locally occurring rough top clamp, or a very thin back or top head).
Features: Very fine hairy objects can be found on the thread surface.
Causes: Iron chips are tangled during thread processing, the workpiece material is too soft, the cutting speed is too low, the comb blade is worn and the chamfer is easy to produce.
Evaluation criteria: slight burrs can be qualified after grinding, if they can not be polished and black spots are unqualified, burrs inside and outside the edge of the pipe end is unqualified.

4. Chatter
Definition: A wavy surface (also known as a corrugation) that appears on the sides of a thread, the bottom of a tooth, the crest or the chamfer.
Features: Sharp and rasping sounds can be heard during processing. Clear water-like reflections or flash jumps can be seen on the surface of the thread. If you use a fingernail or a sharp needle to scratch, there is a throbbing sensation.
Cause: Mainly because the center of the workpiece is not concentric with the cutting center of the machine or the pipe is bent, the main pavers do not have the same mind (the depth of the knife is too great, the surplus amount of the precision car is too much, and the knife table vibrates). The installation height of the cutting tool and the center of the workpiece are not In accordance with this, the cutting tool of the tool is too sharp and the workpiece or tool is highly vibrated.
Evaluation criteria: Check with a fingernail or a sharp needle. If it feels slight, it can be considered as qualified. If you hear a clear scraping sound, see the flash jump, and use a nail or sharp needle to scrape a noticeable jump, you should be judged as unqualified.

5. Cut
Definition: Scratches or deformations of two or more crests appearing on one axis.
Features: This line is parallel or at an angle to the axis of the tube.
Cause: Iron scratches or blade chipping.
Evaluation criteria: Slight knife marks that do not produce leakage channels are acceptable; significant deformations of the crests, and more severe knife marks should be judged to be unacceptable.

6. Scratched thread
Definition: There are scratches on the surface of the thread, which is divided into the top of the tooth, the side of the tooth, and the bottom of the tooth.
Features: With the help of light, there is a straight trace in the direction of the straight thread, and it is scratched with a sharp needle, which has a sensation of jumping and resistance; it is divided into a concave shape and a protruding shape according to the shape of the thread damage. From the top to the bottom, the needle can be hung for the upper step and the lower needle can block the lower step.
Causes: Knife slicing is fluted and the blade collapses and sculpts. It has a convex edge. Iron chips adhere to the blade and form a scribe. The iron chips are swarf and the burrs are scratched and easily formed. Scratch.
Evaluation criteria: The internal thread of the effective thread is not qualified. If the groove is slightly depressed and does not affect the sealing of the thread engagement, the slight scribe of the plating off of the collar or the continuity of the thread can be accepted.


7. Dent
Definitions: Indentations without metal loss refer to dents.
Features: Occurred at the top of the thread, chamfered, deformed due to impact, damage, exhibited a groove or dimple on the surface of the thread, or flattened the top of the thread. There is a scratching feeling when touching the hand, which can block the cotton yarn.
Cause: The mechanical impact deforms the metal. It may be that when the wire is finished, the screw thread collides with the chuck when the tube is withdrawn. During the process of transporting the steel tube, the thread is not worn by the wire to cause collision and deformation. Or improper use of measurement tools.
Assessment criteria: Any slight dent within Lc that does not disrupt thread continuity or produce a leaky channel is acceptable, dents other than Lc are not more than the bottom of the tooth or 12.5% ​​of the wall thickness is acceptable, damage is detected before leaving the factory, and is repaired Grinding, without changing the thread geometry, may be considered qualified.

8.Improper thread height
Definition: Thread depth (height) is not sufficient.
Features: The metal of the thread root or tooth top is cut off. There is a flat blade left by the cutting tool. The nail or the sharp needle is scraped along the axis of the thread. It has a non-smooth, obstructing feeling.
Causes: When the taper is too large, the cutting allowance is too large, the cutting thread parameters are not adjusted properly, the cutting taper does not match the taper of the cutting thread, the tooth height of the comb cutter is poor, and the circular arc of the comb cutter bottom is incomplete.
Assessment criteria: All discarded within the Lc range.

9. Fin
Definition: Very thin metal long back, protruding from chamfered surface or threaded surface.
Features: There is a thin edge like the edge of the outer chamfer on the pipe end, and the inside chamfer has edges similar to the inside.
Causes: Excessive tool wear and machine misalignment.
Evaluation criteria: slight flash edge allows for grinding, if the blade shape is formed, the wing shape is more severe and the flash is unqualified.

10. Tear
Definition: The scaly abrasion of the threaded portion is mostly produced on the flank.
Features: Mainly flank, top (round thread) geometry (including roughness) is damaged. Early thread processing with a single knife pick deduction can easily lead to tearing, blunt tool, poor lubrication and other reasons are also easy to cause tearing, generally scaly, generally the side of the thread.
Causes: Tool wear, improper lubrication, improper adjustment of the machine tool, low cutting speed, built-up edge when cutting, impurities in the thread oil, such as sand, thread wear will cause tearing; gauge teeth The tumor, when screwed, also easily causes the surface of the pipe thread to tear.
Assessment criteria: Both failed.

11. Incomplete chamfer, chamfer failed
Evaluation criteria: In the tube end, the outer chamfer 360 degrees are all unqualified. If the starting thread disappears at the tube end instead of chamfering, obvious thin edges (featheredge, apparently thin tooth top) are also present. Failed, the circulating false starting thread on the chamfer is unqualified, the ellipticity causes the initial thread interruption to be unacceptable, and the chamfering is too large to form a knife edge (knife). It is not qualified.

12. Pitted Threads
Definition: Pungent corrosion on chamfered or threaded surfaces.
Cause: After the cutting chamfered surface and thread surface exposed inclusions or bubbles, the formation of surface pits or holes, the corrosion of the pipe in the storage.
Evaluation criteria: In the range of Lc, the rust on the thread side (non-floating rust) or small pits, or the flaking and corrosion of the coating on the thread of the coupling are all unqualified.

13. Improper thred form
Definition: The deformed buckle includes an irregular thread (drunken thread: distortion of the thread); a wave thread (wavy thrcad: the spiral angle of the thread and its radial position changes periodically); an abnormal thread (shaved thread: thread) the width is too small; the wide-tooth bottom thread: the bottom of the tooth has no observance of the arc; including other thread types that deform excessively along the axis.
Cause: With the processing tool, the machine must have a direct relationship with the NC program cutting process, it may be the tool is not standard, or the file is not timely. Twist and ripple are caused by the machine tool. Flat buckle, double top buckle is caused by the tool.
Assessment criteria: All should be rejected.

14. Other thread deficiencies
The false teeth (False Thread: Lc male thread-like scratches) are mostly caused by excessive curvature of the pipe end, uneven wall thickness, improper adjustment of the machine tool, and generally unqualified.
Drilled deep groove: The deep spiral line appears on the surface of the boring hole. This is because when the boring hole is turned, the boring tool is prematurely put into place, or the inner diameter of the collar blank is negative, and it is generally discarded.
Random buckle: thread surface irregular buckle shape. This is due to the fact that CNC lathes are misaligned and do not lift the knife during cutting. During the retracting process, chips are caught and the threads are scratched. General penalty.
Coil thread surface winding: As the coupling temperature is too high, too little fluid can cause the threads to appear blue when the thread is machined. General penalty.
Bruising: The surface of the thread has sharp pits left after the impact of foreign objects. In Lc, if a slight pit does not affect the continuity of the thread surface, the severer pit needs to be ground or discarded.
Knife edge: A thin tip portion of a thread crest formed by the disappearance of a starting thread on a round or partial trapezoidal thread, usually at the end of the pipe rather than at the chamfer. General penalty.
Edge: Because the outer chamfer angle is too small or the inner chamfer surface is too oblique, only the sharp edges of the tube ends have no end faces. General penalty.
No starting thread: The thread disappears at the end of the tube. General penalty.


Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.