Stainless steel seamless pipe is a kind of hollow long round steel, which is mainly used for industrial pipelines and mechanical structural parts such as petroleum, chemical industry, medical treatment, food, light industry, mechanical instrument and so on. It is widely used due to its good corrosion resistance.
Seamless steel pipe means a pipeline with a hollow section, which is used in large quantities as a pipeline for conveying fluids, such as pipelines for conveying oil, natural gas, gas, water and certain solid materials
Types of surface defects of stainless steel seamless pipes
1. Rolled into iron oxide scale, pits
Scratches on rolled surfaces vary in shape, depth and incidence. Roll-in scale is caused by insufficient scale removal before or during hot rolling and processing.
2. Indentation and rolling marks
Indentations (depressions) and rolling marks (protrusions) can be distributed at a certain distance or irregularly over the entire length and width of the steel pipe. Periodic rolling marks are caused by broken rolls or clamping bars. Indentations are caused by sticking foreign objects on the rolls or other rolls.
3. Scratches and grooves
Mechanical damage of varying width, depth and length on the surface, which is substantially parallel or perpendicular to the rolling direction, may have slight rollover and contains little scale. This damage is caused by the relative motion friction between the steel pipe and the equipment, or the movement between the pipes.
Use sand skin to identify its extent. When identifying, choose abrasive paper from high to low, and grind the scratched area back and forth along the scratch direction, 25-50 times, and count back and forth once. 25 times for new sandpaper. If it can be beaten, it can be used for surface processing.
4. Heavy leather
An irregular "tongue-like" or "fish-scale-like" raised flake on the surface of the steel pipe. is a surface defect. The heavy skin extends in the rolling direction. The extent depends on the magnitude of the deformation. In some places they are still connected to the base metal. Appears as fine scarring particles.
The heavy skin is due to the heavy skin on the surface of the steel pipe and the scarring is not cleaned or the cleaning depth is not enough. The blank surface is uneven. Rolled to form. It is a major type of surface defect, which seriously affects the use of cold-rolled sheets.
5. Bubbles
The bubbles are located below the tight skin, their shape and size are different, and they appear during hot rolling. The bubbles are caused by poor degassing during the casting process during the smelting process.
6. Thermal cracking
Surface-wide, variable orientation defects, which may vary in length, width and depth, may occur in preferential directions or be distributed over a limited range. Thermal cracking occurs during the processing of steel pipes, blooms and continuous casting billets, and is related to steel bells, internal stresses in billets or unfavorable forming conditions.
7. Inclusions
The non-metallic inclusions on the surface are different in size and shape, the inclusions extend along the rolling direction, are randomly distributed, and their color is significantly different from the matrix.
Inclusions are mainly due to the non-metallic inclusions on the surface of the steel pipe, which do not fall off during rolling. It may also be smelting, and the inclusions brought in during the pouring process are exposed after rolling. The difference between inclusions and scratches is that there are non-metallic oxides on the surface of the steel pipe, while the scratches are mainly metal substrates, which can be distinguished by scanning electron microscopy.
8. Cracks
The reasons are more complicated. The characteristics of steel grades, the control of composition and the heating system of hot rolling are mainly caused by the stress generated by the steel pipe during the cooling process. The intermittent linear cracks of different shapes on the surface of the steel pipe in the longitudinal and transverse directions are parallel or perpendicular to the rolling direction, and rarely appear in the form of network micro-cracks. It can be repaired according to the standard, if the quantity is large, it can be judged scrap
9. Scarring and Scars
Overlapping substances, surface overlaps of varying shapes and degrees, are irregularly distributed throughout the steel tube and bonded to the base metal. There are more non-metallic inclusions or iron oxide scale in the scar.
Scarring can occur during ingot casting or as a result of material surface displacement or slippage during rolling. Scarring is mainly due to defects in the parallel rolling direction on the semi-finished product, such as flame cutting burrs. caused by overlapping during rolling.
10, warped skin
Irregular and scaly surface defects. The heavy skin extends in the rolling direction and remains connected to the base metal. There are pits after removal. It is a major type of surface defect, which seriously affects the use of cold-rolled sheets.
11. Folding
Folding is divided into folded with touch and without touch. It can be seen from the surface and has a back feeling. The touchless folded print cannot be seen from the front, but can only be seen from a certain angle on the side. Folding is generally produced by steel mills during the rolling process.
12. Orange peel
Generally, the surface of the steel pipe has a lot of fine, no-feel, small folds, which cannot be seen from the front and side, but can be seen from a certain angle on the top.
13. Pattern defects
Due to the poor pickling section of cold rolling, a large area of white or yellow cloud pattern appears on the surface of the strip, or because the surface of the strip is exposed to water vapor and mist, etc., a large pattern appears on the plate surface. The surface of the strip can be touched with hands (gloves) to see if it can be wiped off. The pattern that cannot be removed can be judged as a brushed surface processing board. The surface of the strip can also be cleaned with a weak acid solution. The disadvantage is that the surface of the strip will have a dull white color difference, but it will not affect the material.
Seamless steel pipe means a pipeline with a hollow section, which is used in large quantities as a pipeline for conveying fluids, such as pipelines for conveying oil, natural gas, gas, water and certain solid materials
Types of surface defects of stainless steel seamless pipes
1. Rolled into iron oxide scale, pits
Scratches on rolled surfaces vary in shape, depth and incidence. Roll-in scale is caused by insufficient scale removal before or during hot rolling and processing.
2. Indentation and rolling marks
Indentations (depressions) and rolling marks (protrusions) can be distributed at a certain distance or irregularly over the entire length and width of the steel pipe. Periodic rolling marks are caused by broken rolls or clamping bars. Indentations are caused by sticking foreign objects on the rolls or other rolls.
3. Scratches and grooves
Mechanical damage of varying width, depth and length on the surface, which is substantially parallel or perpendicular to the rolling direction, may have slight rollover and contains little scale. This damage is caused by the relative motion friction between the steel pipe and the equipment, or the movement between the pipes.
Use sand skin to identify its extent. When identifying, choose abrasive paper from high to low, and grind the scratched area back and forth along the scratch direction, 25-50 times, and count back and forth once. 25 times for new sandpaper. If it can be beaten, it can be used for surface processing.
4. Heavy leather
An irregular "tongue-like" or "fish-scale-like" raised flake on the surface of the steel pipe. is a surface defect. The heavy skin extends in the rolling direction. The extent depends on the magnitude of the deformation. In some places they are still connected to the base metal. Appears as fine scarring particles.
The heavy skin is due to the heavy skin on the surface of the steel pipe and the scarring is not cleaned or the cleaning depth is not enough. The blank surface is uneven. Rolled to form. It is a major type of surface defect, which seriously affects the use of cold-rolled sheets.
5. Bubbles
The bubbles are located below the tight skin, their shape and size are different, and they appear during hot rolling. The bubbles are caused by poor degassing during the casting process during the smelting process.
6. Thermal cracking
Surface-wide, variable orientation defects, which may vary in length, width and depth, may occur in preferential directions or be distributed over a limited range. Thermal cracking occurs during the processing of steel pipes, blooms and continuous casting billets, and is related to steel bells, internal stresses in billets or unfavorable forming conditions.
7. Inclusions
The non-metallic inclusions on the surface are different in size and shape, the inclusions extend along the rolling direction, are randomly distributed, and their color is significantly different from the matrix.
Inclusions are mainly due to the non-metallic inclusions on the surface of the steel pipe, which do not fall off during rolling. It may also be smelting, and the inclusions brought in during the pouring process are exposed after rolling. The difference between inclusions and scratches is that there are non-metallic oxides on the surface of the steel pipe, while the scratches are mainly metal substrates, which can be distinguished by scanning electron microscopy.
8. Cracks
The reasons are more complicated. The characteristics of steel grades, the control of composition and the heating system of hot rolling are mainly caused by the stress generated by the steel pipe during the cooling process. The intermittent linear cracks of different shapes on the surface of the steel pipe in the longitudinal and transverse directions are parallel or perpendicular to the rolling direction, and rarely appear in the form of network micro-cracks. It can be repaired according to the standard, if the quantity is large, it can be judged scrap
9. Scarring and Scars
Overlapping substances, surface overlaps of varying shapes and degrees, are irregularly distributed throughout the steel tube and bonded to the base metal. There are more non-metallic inclusions or iron oxide scale in the scar.
Scarring can occur during ingot casting or as a result of material surface displacement or slippage during rolling. Scarring is mainly due to defects in the parallel rolling direction on the semi-finished product, such as flame cutting burrs. caused by overlapping during rolling.
10, warped skin
Irregular and scaly surface defects. The heavy skin extends in the rolling direction and remains connected to the base metal. There are pits after removal. It is a major type of surface defect, which seriously affects the use of cold-rolled sheets.
11. Folding
Folding is divided into folded with touch and without touch. It can be seen from the surface and has a back feeling. The touchless folded print cannot be seen from the front, but can only be seen from a certain angle on the side. Folding is generally produced by steel mills during the rolling process.
12. Orange peel
Generally, the surface of the steel pipe has a lot of fine, no-feel, small folds, which cannot be seen from the front and side, but can be seen from a certain angle on the top.
13. Pattern defects
Due to the poor pickling section of cold rolling, a large area of white or yellow cloud pattern appears on the surface of the strip, or because the surface of the strip is exposed to water vapor and mist, etc., a large pattern appears on the plate surface. The surface of the strip can be touched with hands (gloves) to see if it can be wiped off. The pattern that cannot be removed can be judged as a brushed surface processing board. The surface of the strip can also be cleaned with a weak acid solution. The disadvantage is that the surface of the strip will have a dull white color difference, but it will not affect the material.
