The causes of external defects and indentation of hot-rolled seamless steel pipes

As one of the important basic materials in modern industry,hot-rolled seamless steel pipes are widely used in fields such as petroleum,chemical,and mechanical manufacturing.However,during the production process,various defects often appear on the surface of seamless steel pipes,among which external defects and indentation are the two most common ones.These two defects not only affect the aesthetics of steel pipes,but more importantly,they will reduce their mechanical properties and service life,posing safety hazards to production and application.This article will explore in detail the causes of external defects and indentation of hot-rolled seamless steel pipes,in order to provide reference for relevant production enterprises and technical personnel.

1、Reasons for the occurrence of external defects of hot-rolled seamless steel pipes

External folding refers to the continuous or discontinuous spiral or linear folding defects on the outer surface of seamless steel pipes.This defect is usually closely related to the production process,raw material quality,and equipment status of the steel pipe.

Raw material quality factors

The quality of raw materials is one of the important factors affecting the folding of seamless steel pipes.If the internal structure of the billet is poor,with problems such as looseness,segregation,and excessive non-metallic inclusions,these defects will further expand and form external folds during the hot rolling process.In addition,the quality of the surface of the pipe blank cannot be ignored.If there are defects such as cracks and ears on the surface of the billet,these defects are also prone to expand during hot rolling,leading to the occurrence of external folding.

Process operation factors

The production process of hot-rolled seamless steel pipes is complex,and improper operation is also an important reason for external folding.During the perforation process,if the pressing amount in front of the top is too large,the top is severely worn,or the parameters of the perforating machine are not adjusted properly,it will cause strong alternating stress on the metal in the central part of the pipe blank,resulting in internal bending of the inner wall of the blank pipe during rolling.These internal folds will further expand to the outer surface during the subsequent rolling process,forming external folds.

In addition,uneven heating temperature can also lead to the occurrence of external folding.If the temperature of the heating furnace is uneven or the heating time is too long,it will cause a significant temperature difference between the surface and interior of the billet,resulting in thermal stress during the hot rolling process and causing the surface of the steel pipe to fold.

Equipment factors

The condition of the equipment directly affects the production quality of seamless steel pipes.If there is damage to the rolls of the perforating machine or pipe rolling machine,the surface of the steel pipe will be subjected to uneven stress distribution during the rolling process,leading to the occurrence of external folding.In addition,if the roll angle of the straightening machine,pipe rolling machine or sizing machine is not adjusted properly,the pressing amount is too large,or the roll wear is severe,similar problems can also be occurred.

Causes of indentation on hot-rolled seamless steel pipes

Indentation refers to the local depression or protrusion formed on the surface of hot-rolled seamless steel pipes,usually caused by improper cooling of rolling or pinch rollers,surface cracks,or chipping.Indentation not only affects the aesthetics of steel pipes,but also reduces their mechanical properties and corrosion resistance.

Factors of rolling mill and pinch roller

Rollers and pinch rollers are key equipment in the production process of hot-rolled seamless steel pipes.If the cooling of these devices is not uniform,it can cause cracks or nodules on the surface of the rollers or pinch rollers,resulting in indentation during the rolling process.In addition,if the surface hardness of the roller or pinch roller is insufficient,or if it is severely worn,it can also cause indentation on the surface of the steel pipe.

Surface defects on steel billets

The quality of the steel billet surface also has a significant impact on the indentation of hot-rolled seamless steel pipes.If there are defects such as cracks,inclusions,pores,and weld marks on the surface of the steel billet,these defects will propagate during the hot rolling process,forming hot rolling indentations.Therefore,when selecting raw materials,the surface quality of the steel billet should be strictly controlled to avoid using defective raw materials.

Uneven heating

Uneven heating is another important cause of indentation in hot-rolled seamless steel pipes.If the temperature of the heating furnace is uneven or the heating time is too long,it will cause a significant temperature difference between the surface and interior of the steel billet,resulting in thermal stress during hot rolling and causing indentation on the surface of the steel pipe.Therefore,during the heating process,the heating temperature and heating time should be strictly controlled to ensure uniform heating of the steel billet.

Unreasonable hole pattern of roughing mill unit

The design of the pass of the roughing mill also has a certain impact on the indentation of hot-rolled seamless steel pipes.If the hole design is unreasonable,it will cause uneven stress distribution on the surface of the rolled piece,resulting in indentation during the rolling process.Therefore,in the design and adjustment process of the roughing mill,the rationality of the pass should be fully considered to ensure that the rolled piece is subjected to uniform stress distribution during the rolling process.

Measures to reduce external folding and indentation of hot-rolled seamless steel pipes

In order to reduce the external folding and indentation of hot-rolled seamless steel pipes and improve product quality,the following measures can be taken:

Strictly control the quality of raw materials

The quality of raw materials is the foundation that affects the production quality of seamless steel pipes.Therefore,when selecting raw materials,the internal structure and surface quality of the steel billet should be strictly controlled to avoid using defective raw materials.At the same time,it is necessary to strengthen the inspection and testing of raw materials to ensure that their quality meets production requirements.

Optimize production process

The optimization of production process is the key to improving the quality of seamless steel pipe production.During the perforation process,the pressing amount in front of the top and the parameters of the perforating machine should be adjusted reasonably to avoid strong alternating stress on the metal in the central part of the billet.During the heating process,the heating temperature and time should be strictly controlled to ensure uniform heating of the steel billet.In addition,it is necessary to strengthen the monitoring and management of the production process,timely discover and solve problems in the production process.

Strengthen equipment maintenance and management

The status of the equipment directly affects the production quality of seamless steel pipes.Therefore,it is necessary to strengthen the maintenance and management of equipment,regularly inspect and maintain the equipment,and ensure that the equipment is in good working condition.At the same time,it is necessary to strengthen the inspection and testing of equipment,timely discover and solve problems that exist in the equipment.

Improve employee quality

The quality of employees is one of the important factors affecting the production quality of seamless steel pipes.Therefore,it is necessary to strengthen training and education for employees,improve their operational skills and quality awareness.At the same time,a sound quality management system and incentive mechanism should be established to stimulate employees'work enthusiasm and creativity.

conclusion

The external folding and indentation of hot-rolled seamless steel pipes are important factors affecting product quality and service life.The occurrence of these defects is closely related to the quality of raw materials,process operation,equipment status,and employee quality.In order to reduce the occurrence of these defects and improve product quality,it is necessary to strictly control the quality of raw materials,optimize production processes,strengthen equipment maintenance and management,and improve employee quality.Only in this way can high-quality hot-rolled seamless steel pipes be produced to meet market demand and customer expectations.

With the development of modern industry,the application scope of hot-rolled seamless steel pipes is becoming increasingly wide.Therefore,higher requirements have been put forward for the production quality of seamless steel pipes.Hopefully this article can provide reference and inspiration for relevant production enterprises and technical personnel,and jointly promote the progress and development of hot-rolled seamless steel pipe production technology.