6 major defect characteristics and causes of ASTM A53 seamless pipes

　　ASTM A53 GR.B Seamless steel pipes (SMLS pipe) as an indispensable material in the modern industrial field, have a vital impact on the safety and stability of various engineering projects due to their quality and performance. However, various defects often occur during the production and use of seamless steel pipes. These defects not only affect the performance of the steel pipes, but may also threaten the safety of engineering projects. Therefore, understanding the defect characteristics and causes of seamless steel pipes is of great significance for improving the quality and use of seamless steel pipes.

　　Main defect characteristics of seamless steel pipes:

　　1. Folding

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

　　2. Cracks

　　Refers to fine cracks distributed in straight lines or spiral lines on the inner and outer surfaces of seamless steel pipes, with a depth of 1 mm or more, which can be continuous or discontinuous. According to the analysis of Shandong Jute Pipe Industry, the causes are: subcutaneous bubbles and subcutaneous inclusions in the hot-rolled tube billet, cracks or deep pitting on the steel pipe before drawing, and longitudinal scratches or abrasions during hot rolling or cold drawing. Preventing the formation of cracks also lies in improving the quality of the tube billet and strengthening the inspection and grinding of the tube material. At the same time, pitting, scratching and abrasions should be avoided during the cold drawing process.

　　3. Scratches

　　The defect is characterized by longitudinal straight scratches of varying lengths on the inner and outer surfaces of the seamless pipe, mostly in the shape of grooves, but 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, iron oxide scale remains on the steel pipe, the mold sticks to the steel, the mold strength and hardness are insufficient or uneven, the mold is broken and worn, the hammer head is bad, and 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 a mold with high strength, hardness and good finish should be used.

　　4. Pits

　　This is one of the most common surface defects of seamless pipes. It is a local depression of varying areas distributed on the surface of the steel pipe. Some of the distribution is periodic, and some are irregular. The pits are caused by the iron oxide scale or other hard dirt pressed into the surface of the steel pipe during drawing or straightening, or the peeling of the peeling that originally existed on the surface of the steel pipe. Hunan Standard Steel Co., Ltd pointed out that the measures to prevent pits are to carefully check the pipe material and remove defects such as warping, keep the workplace, tools and lubricants clean, and prevent iron oxide and dirt from falling on the surface of the steel pipe.

　　5. Pockmarks

　　It is characterized by small pits in sheets and dots on the surface of the steel pipe. The main reason for the pitting is pitting during pickling. After annealing, the iron 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 occurs after water enters, and pitting is formed after the rust is removed.

　　6. Spots

　　Since the seamless steel pipe is not treated in time (such as drying) when it comes into contact with water (or water vapor) during processing or storage, the traces left after the water evaporates are called water spots. If the contact time with water is long, or there are corrosive substances in the water, rust spots will be formed. Water spots generally have no depth, while rust spots often corrode the surface of the steel pipe, and pitting will still exist after removal.

　　Causes of seamless steel pipe defects:

　　1. Raw materials

　　Poor internal structure and poor surface quality of raw materials are important causes of seamless steel pipe defects. Poor internal structure may cause defects such as internal folding, internal cracks in the tube wall, and delamination; poor surface quality may cause defects such as external folding.

　　2. Process operation

　　Improper process operation such as improper heating, excessive deformation pressure, and incomplete surface cleaning of the tube blank are also important causes of seamless steel pipe defects. Improper heating may cause defects such as internal folding, external folding, and internal cracks in the tube wall; excessive deformation pressure may cause defects such as cracks.

　　3. Equipment

　　Poor equipment performance, looseness, scratches, etc. may also cause seamless steel pipe defects. For example, damage to the piercing machine roll or the tube rolling mill roll may cause defects such as rolling folding.

　　ASTM A53 GR.B Seamless steel pipes the defect characteristics and causes are multifaceted, and comprehensive analysis and control are required from the aspects of raw materials, process operations, equipment, etc. By strengthening raw material quality control, optimizing process operations, strengthening equipment maintenance and management, and strengthening quality inspection and monitoring, the occurrence of seamless steel pipe defects can be effectively reduced and the quality and use effect of seamless steel pipes can be improved.