Features and Causes of 8 Defects of Seamless Steel Pipe

If there are some defects in the seamless steel pipe, it will undoubtedly have a fatal impact on the quality of our products. So how to avoid these defects? Then you need to understand the reasons for these defects. Permanent Steel Manufacturing Co.,Ltd will work with you to discuss the specific reasons for the 8 defects of seamless steel pipes:

1. Seamless steel pipe-folding

It is a linear or spiral, continuous or discontinuous state that exists on the outer or inner surface of seamless steel pipe. The main reason for the folding is poor quality of the pipe material, folding itself, or inclusions, serious scratches and cracks on the surface, edges and corners in the grinding place, and folding after drawing. In order to avoid folding, the quality of the pipe material should be improved and attention should be paid to inspection and grinding.

2. Seamless steel pipe-crack

Refers to the small cracks on the inner and outer surfaces of the seamless steel pipe that are distributed in a straight line or a spiral, with a depth of 1 mm or more, continuous and discontinuous. According to the analysis of Permanent Steel Manufacturing Co., Ltd, the cause is: the hot-rolled tube blank has subcutaneous bubbles and subcutaneous inclusions, and there are cracks or deep pits on the steel pipe before drawing. During the hot rolling or cold drawing processes Longitudinal scratches or scratches occurred during the operation. Preventing the formation of cracks also lies in improving the quality of the tube blank and strengthening the inspection and grinding of the tube material. At the same time, pitting, scratches and scratches should be avoided during the cold drawing production process.

3. Seamless steel pipe-scratches

The characteristic of the defect is that there are longitudinally linear scratches of varying lengths on the inner and outer surfaces of the seamless pipe. Most of them are groove-shaped, but they may also be raised stripes. The main reason for the scratches (cutting) is: there are internal markings on the pipe material, which cannot be eliminated during drawing, the iron oxide film remains on the steel pipe and the mold sticks to the steel, and the strength and hardness of the mold are insufficient or uneven. Fragmentation and wear occur, the hammer head is defective, and the sharp edges and corners of the hammer head transition part damage the mold. In order to prevent scratches and scratches, the quality of each preparation process before drawing should be improved, and molds with high strength and hardness and good smoothness should be used.

4. Seamless steel pipe-pit

This is one of the most common surface defects of seamless pipes. Local depressions with different areas are distributed on the surface of the steel pipe. Some of them are periodic and some are irregular. The pits are caused by iron oxide scale or other hard dirt pressed into the surface of the steel pipe during the drawing or straightening process, or the peeling of the original peeling on the surface of the steel pipe. Shandong Jute Pipe Industry pointed out that the measures to prevent pits are to carefully inspect the pipe material and remove defects such as warping, keep the work site, tools and lubricants clean, and prevent oxide scale and dirt from falling on the surface of the steel pipe.

When there are smooth or sharp spiral marks on the outer surface of the seamless steel pipe, the straightening machine should be checked. Due to the incorrect position and angle of the straightening roller, the steel pipe rubbed the shoulders on the edge of the straightening roller during straightening. There are worn grooves on the straightening roller, and both ends of the steel pipe may appear on the outer surface of the steel pipe. Pits.

5. Seamless steel pipe-pitted surface

It is characterized by small pits in the form of pieces and dots on the surface of the steel pipe. The main reason for the pitting surface is pitting corrosion during pickling. After annealing, the oxide scale is too thick and straightened and pressed into the surface of the steel pipe to form a pitted surface; the steel pipe is kept in a humid environment, and even pitted rust occurs after water enters. After removing the rust spots Form pitted surface.

6. Seamless steel pipe-spots

Since seamless steel pipes are in contact with water (or water vapor) during processing or storage and are not treated in time (such as drying), the traces left by water evaporation are called water spots, such as long contact with water or corrosive water Rust spots are formed when the substance is Water spots generally have no depth, and rust spots often corrode the surface of the steel pipe, and there will still be pitted surfaces after removal.

7. Seamless steel pipe-warped skin

It is characterized in that the inner and outer surfaces of the seamless steel pipe are partially separated from the metal substrate, and the individual pieces are lumpy, discontinuous, rooted or not rooted on the pipe wall, but cannot peel off naturally. The reasons are poor steel quality, the existence of subcutaneous bubbles, which are exposed after cold drawing; the warping produced during hot rolling is not removed on the tube billet to cold drawing; the original deep and angular transverse pits on the steel tube After drawing, it forms a warped skin.

8. Seamless steel pipe-scar

The inner and outer surfaces of the steel pipe were not removed in time due to defects such as folding and warping. In the subsequent processing, thin slices that could not be separated from the metal substrate were formed. Some of them were lumpy, discontinuous, and rooted or not rooted on the pipe wall, but they could not peel off naturally. , Called scarring. Surface defects must be checked and removed in time to eliminate scars.

Other supplementary information:

9. Inclusions

It is manifested as non-metallic inclusions embedded in the surface or surface cracks of the steel pipe. The inclusions are generally brought by the smelting, casting, hot working or heat treatment process, and are pressed into the surface when the tube blank is heated or the steel tube is annealed. The inspection should be strengthened in the relevant process and dealt with in a timely manner.

10. Diameter out of tolerance

The main reasons for the out-of-tolerance diameter are improper mold matching during cold working, insufficient mold hardness, or ignoring the change in the size of the extubation mold due to wear. Excessive reduction of the straightening roller during the straightening process will also cause the diameter of the steel pipe to become smaller.

11. Wall thickness out of tolerance

The main reasons for the excessive wall thickness are improper cold working mold matching, insufficient mold hardness, insufficient wear resistance, or ignoring the change in mold size due to wear and tear. Incorrect, the position of the mandrel is not adjusted properly when the short mandrel is drawn using the curved outer die and the tapered mandrel—before or after. In order to prevent the wall thickness from being out of tolerance, the mold should be correctly matched and the position of the mandrel should be adjusted correctly. The wall thickness change of the steel pipe in the emptying pass should be estimated accurately.

12. Uneven wall thickness

The main reasons for the uneven wall thickness of the steel pipe are: the uneven wall thickness of the tube blank is too large, the drawing line and the axis of the steel pipe are inconsistent during drawing, and the die holes of the mandrel and the drawing die are elliptical. In order to reduce the uneven wall thickness of the steel pipe, the uneven wall thickness of the pipe material should be as small as possible, and at the same time, the mold should be carefully checked and the pipe pulling machine should be adjusted.

13. Ellipse

That is to say, the die section of the steel pipe is oval, and the diameters on the same section are different. The difference between the maximum outer diameter and the minimum outer diameter is called ellipticity. During the drawing process, a drawing die with an oval die hole is used, or the two ends of the steel pipe are bent too much when straightening, and the steel pipe moves up and down during the straightening process, the steel pipe is stuck when the outer diameter is too large, and the steel pipe is stuck when pushed in. Excessive tail swing and uneven distribution of reduction between pairs of straightening rolls can cause this defect. If the defect occurs due to the ellipse of the die hole, the tube film should be replaced; if it is formed during the straightening process, the cause should be found and eliminated in time.

14. Bend

When the steel pipe rolls on the plane or is close to the ruler, there is a gap, which is called bending. The thinner the steel pipe, or the lower the strength, the easier it is to bend under the action of external force. In the process of processing, due to improper hoisting or improper stacking, the positive electrode is prone to bending, and in severe cases, the steel pipe may be deformed, resulting in exceptional ovality.

15. Bevel cut

When the end of the steel pipe is processed, the processing surface is not perpendicular to the axis of the steel pipe. It may be caused by the improper installation of the tool, or the skewness of the steel pipe when it enters the processing area.

16. Welding flash

There are irregular, roughly smooth surface protrusions on the surface of the steel pipe near the weld zone, called weld flashes. Mainly due to improper protection of the welding area, the electric spark is shot to the surface of the steel pipe.

17. Glitch

After the end of the steel pipe is processed, there will be a whole circle or part of the residual jagged flakes in the circumferential direction, and this defect is called burr. Mainly due to insufficient machining tool accuracy or improper tool installation.

Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces.
ASTM A53 GR.B ERW steel pipe is a typical carbon steel pipe. It is largely used to convey fluids at low / medium pressures such as oil, gas, steam, water, air and also for mechanical applications.