Analysis of eight surface defects of seamless steel pipe

In today’s industrial landscape, where steel materials are used extensively, seamless steel pipes have become essential components in sectors such as oil and gas, chemical processing, power boilers, machinery manufacturing, automotive, and aerospace. Their advantages—high strength, excellent pressure resistance, and the absence of weld seams on both inner and outer walls—make them particularly suitable for high-performance and high-pressure applications. However, unlike ERW (Electric Resistance Welded) pipes or SSAW (Spiral Submerged Arc Welded) pipes, which may face different types of welding-related flaws, seamless pipes are particularly prone to surface defects formed during hot rolling or cold drawing processes.Surface quality plays a critical role in performance and post-processing operations. This article provides a comprehensive analysis of eight common surface defects in seamless steel pipes, their causes, and the corresponding preventive measures—insights that also offer valuable references for manufacturers of drill pipes and other tubular products.

1. Seamless steel pipe folding

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

2. Seamless steel pipe cracks

It refers to the small cracks distributed in straight lines or spirals on the inner and outer surfaces of seamless steel pipes, with a depth of 1 mm or more, and there are continuous and discontinuous cracks. According to the analysis of Shandong Jute Pipe Industry, the reasons are: there are subcutaneous bubbles and subcutaneous inclusions in the hot-rolled tube blanks, there are cracks or deep pits on the steel tube before drawing, and during the hot rolling or cold drawing operations, Longitudinal scratches or scratches have occurred. Preventing the formation of cracks also lies in improving the quality of pipe blanks and strengthening the inspection and grinding of pipe materials. At the same time, pitting, scratches and scratches on the pipe during the cold drawing production process should be avoided.

3. Seamless steel pipe scratches

The defect is characterized by longitudinal linear scratches of varying lengths on the inner and outer surfaces of the seamless pipe, mostly in the form of grooves, but they may also be raised stripes. The main reasons for scratches (scratches) are: there are internal scratches on the pipe material, which cannot be eliminated during drawing, oxide iron scale remains on the steel pipe and the mold sticks to the steel, the strength and hardness of the mold are insufficient or uneven, and the mold Chips and wear occur, the hammer head is defective, the sharp edges of the transition part of the hammer head damage the mold, etc. In order to prevent scratches and scratches, the quality of each preparation process before drawing should be improved, and molds with high strength, hardness, and good smoothness should be used.

4. Seamless steel pipe pits

This is one of the most common surface defects of seamless pipes. Local depressions of varying areas are distributed on the surface of the steel pipe. Some are periodic and some are irregular. The pits are caused by oxide scale or other hard dirt being pressed into the surface of the steel pipe during the drawing or straightening process, or the warping that originally existed on the surface of the steel pipe is peeled off. Shandong Jute Pipe Industry pointed out that the measures to prevent pits are to carefully inspect the pipe material and remove defects such as warped skin, 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 round 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 incorrect angle of the straightening roller, the steel pipe rubs the convex shoulder on the edge of the straightening roller during straightening, there are worn grooves on the straightening roller, and excessive bending at both ends of the steel pipe may appear on the outer surface of the steel pipe. Dimples.

5. Seamless steel pipe pitted surface

It is characterized by small, point-like pits appearing on the surface of the steel pipe. The main reason for pitting is pitting corrosion during pickling. After annealing, the oxide scale is too thick and straightened and then pressed into the surface of the steel pipe to form pitting. The steel pipe is stored in a humid environment, and even pitting corrosion occurs after water enters. After the rust spots are removed, Forming pockmarks.

6. Seamless steel pipe spots

Since the seamless steel pipe comes into contact with water (or water vapor) during processing or storage and is not treated in time (such as drying), the traces left after the water evaporates are called water spots. If the seamless steel pipe has been in contact with water for a long time, or the water contains corrosive substances Rust spots will form when exposed to substances. Water spots generally have no depth, while rust spots often corrode to the surface of the steel pipe, and the pitted surface will still remain after removal.

7. Seamless steel pipe warping

Its characteristic is that the inner and outer surfaces of seamless steel pipes have thin flakes that are partially separated from the metal matrix. Some of them are lumpy and discontinuous. They may or may not take root on the pipe wall, but they cannot peel off naturally. The reasons include poor steel quality and the existence of subcutaneous bubbles, which are exposed after cold drawing; the warped skin produced during hot rolling was not removed from the tube blank until cold drawing; the original deep and angular transverse pits on the steel tube were After pulling, the skin becomes warped.

8. Seamless steel pipe scarring

Defects such as folding and peeling on the inner and outer surfaces of the steel pipe were not removed in time, and thin flakes that could not be separated from the metal matrix were formed during subsequent processing. Some of them were lumpy and discontinuous. They may or may not take root on the pipe wall, but they cannot peel off naturally. , called scarring. Surface defects must be carefully checked and removed in time to eliminate scarring.

Conclusion

Surface defects in seamless steel pipes are not just cosmetic—they can compromise the mechanical integrity and corrosion resistance of the product, affecting both safety and performance in critical applications. Understanding the nature and causes of each defect type is essential for improving product quality and reducing scrap rates. By emphasizing billet selection, process control, tooling maintenance, and proper storage practices, manufacturers can significantly reduce the occurrence of surface defects and deliver higher-quality seamless steel pipes to the market.