Helical welded pipes is the low-carbon structural steel or low alloy steel
strip by the helix angle (called molding angle) rolled into a tube, and then the
tube made of seam welded together, it can be used a narrow bandsteel production
of large-diameter steel pipe. Helical welded pipes for oil pipeline and gas
pipeline specifications diameter * wall thickness. Helical welded pipes side
welding and double-sided welding, the pipe should ensure that hydrostatic test,
weld tensile strength and cold performance to meet the requirements.
The process of helical welded pipes is as follows:
Open book - on volume - leveling - butt welding - Milling - molding -
welding - Weld - cut pipe - break - the follow-up welding - hydrostatic test
Uses of helical welded pipes:
Helical welded pipes are mainly used in water engineering, petrochemical
industry, chemical industry, power industry, agricultural irrigation, urban
construction in the country. For the transport of liquids: water supply,
drainage. For gas transportation: gas, steam, liquefied petroleum gas. For
structural purposes: as piling pipe for bridges; docks, roads, building
structure pipe.
2020年3月30日星期一
Groove of steel pipe
Definition: According to the design or process needs, the weldments to be
welded processed and assembled into a certain groove geometry, called
groove.
Purpose: the open groove is to get all of the weldment thickness penetration welds. Groove is primarily for welding parts, to ensure the welding degrees, with machining methods machined-surface under ordinary circumstances, can also be gas cutting when requirement is low (if it is A class of welds, ultrasonic testing required, you can only use the machine processing methods), but need to remove the oxide slag.
Common groove forms are: butt groove and angular contact groove (on the project in order to distinguish the butt corner joints and general butt welds, now divided into docking, pick bevel, fillet three categories).
Butt groove mainly: I type, V-type, X-type, U-type, Y-type, UV type, VV type, etc.
Fillet groove are: T-type, lap, J type, etc.
Welding groove criteria:
CB 1220-1993 921A, 922A steel welding groove basic types and sizes
CB / T 3190-1997 hull structure welding groove types and sizes
GB 985-88 welding, SMAW basic form and GMAW weld groove basic types and sizes
GB 986-88 submerged arc weld groove basic types and sizes
Welding groove index
1, Appearance: no cracks, delamination, inclusions and other defects
2, Size: as required examination direction drawings and WPS, angle, blunt edge, set gap
3, low-alloy steel material Rm≥540Mpa and Cr-Mo steel bevel should be in accordance with JB / T4730.4-2005 to do MT detection.
4, non-ferrous and stainless steel bevel with special requirements on the drawing should be carried out to do PT detection.
5, the slope of the base metal surface on both sides of the mouth, at least within the range of 20mm should remove the descaling, oil, slag and other harmful contaminants
Purpose: the open groove is to get all of the weldment thickness penetration welds. Groove is primarily for welding parts, to ensure the welding degrees, with machining methods machined-surface under ordinary circumstances, can also be gas cutting when requirement is low (if it is A class of welds, ultrasonic testing required, you can only use the machine processing methods), but need to remove the oxide slag.
Common groove forms are: butt groove and angular contact groove (on the project in order to distinguish the butt corner joints and general butt welds, now divided into docking, pick bevel, fillet three categories).
Butt groove mainly: I type, V-type, X-type, U-type, Y-type, UV type, VV type, etc.
Fillet groove are: T-type, lap, J type, etc.
Welding groove criteria:
CB 1220-1993 921A, 922A steel welding groove basic types and sizes
CB / T 3190-1997 hull structure welding groove types and sizes
GB 985-88 welding, SMAW basic form and GMAW weld groove basic types and sizes
GB 986-88 submerged arc weld groove basic types and sizes
Welding groove index
1, Appearance: no cracks, delamination, inclusions and other defects
2, Size: as required examination direction drawings and WPS, angle, blunt edge, set gap
3, low-alloy steel material Rm≥540Mpa and Cr-Mo steel bevel should be in accordance with JB / T4730.4-2005 to do MT detection.
4, non-ferrous and stainless steel bevel with special requirements on the drawing should be carried out to do PT detection.
5, the slope of the base metal surface on both sides of the mouth, at least within the range of 20mm should remove the descaling, oil, slag and other harmful contaminants
Inspection method for oil bushing manufacturer
What are the detection methods of oil casing pipe ? Let's take a brief look:
1. Ultrasonic testing
When ultrasonic waves are spread in the tested raw materials, the acoustic characteristics of the raw materials and the changes in the internal organization have a positive impact on the spread of the ultrasonic waves. After detecting the affected levels and conditions of the ultrasonic waves, the changes in the function and structure of the raw materials are understood .
2. Radiographic inspection
Radiographic inspection uses the difference in the amount of radiation transmitted between the normal part and the defective part to form the resolution of the blackness on the negative.
3. Penetrant test
Penetrant test is to use the capillary action of liquid to permeate the penetrant into the opening on the surface of the solid raw material, and then draw the penetrant penetrant to the surface through the developer to show the existence of the defect. Penetration testing is suitable for a variety of metal and ceramic workpieces, and the time from penetration manipulation to the appearance of defects is relatively short, usually about half an hour. It may be useful to detect surface fatigue, stress corrosion and welding cracks, and to directly measure the size of cracks.
4. Magnetic particle detection
Magnetic particle detection is to use magnetic flux leakage to absorb magnetic particles and form magnetic marks to provide defect manifestation. It can detect surface and subsurface defects. The nature of defects is easy to distinguish. Paint and electroplated surfaces do not affect the detection vividness.
5. Eddy current detection
If the eddy current detection mainly uses the eddy current induced in the workpiece by the ferromagnetic coil to analyze the internal quality of the workpiece, it can detect the shortcomings of the surface and near surface of various conductive raw materials, the usual parameter control is troublesome, and the detection results are difficult to explain. Moreover, it is required that the detection object must be a conductive crack, and the length of the fault can be measured euphemistically.
6. Magnetic flux leakage detection
Magnetic flux leakage detection of petroleum casing is based on the characteristics of high permeability of ferromagnetic materials. Basically, the quality of in-service petroleum casing is tested by measuring the permeability change caused by defects in ferromagnetic materials .
7. Magnetic impression detection
Magnetic impression detection is derived from the relationship between the physical nature of the magnetic phenomenon of metals and the dislocation process. It has many advantages such as high utilization, low cost, and no grinding. It has an important and ordinary application prospect in the industry.
In order to improve the service life of oil well pipes and reduce costs, oilfields require oil well pipes to be reused multiple times, which puts forward requirements for excellent anti-stick performance of oil pipes. If the oil pipe is stuck, the integrity of the thread connection will be damaged. Continued use may cause leakage at the thread connection and decrease the connection strength. Serious problems such as falling off the well may cause huge economic losses to the oilfield.
The API specification requires that the tubing can be shackled 6 times without sticking when in use. Although the well conditions of each oil field are different, the conditions of the buckle (the method of buckle, the torque of the buckle and the speed of the buckle) are not the same when the tubing goes down. The requirements for the number of trips on the tubing are different. It is required that the number of trips of the oil pipe can reach more than 10 times, and some oilfields require more than 30 times.
http://www.xysteelpipe.com/info/Inspection-method-for-oil-bushing-manufacturer-1641-1.htm
1. Ultrasonic testing
When ultrasonic waves are spread in the tested raw materials, the acoustic characteristics of the raw materials and the changes in the internal organization have a positive impact on the spread of the ultrasonic waves. After detecting the affected levels and conditions of the ultrasonic waves, the changes in the function and structure of the raw materials are understood .
2. Radiographic inspection
Radiographic inspection uses the difference in the amount of radiation transmitted between the normal part and the defective part to form the resolution of the blackness on the negative.
3. Penetrant test
Penetrant test is to use the capillary action of liquid to permeate the penetrant into the opening on the surface of the solid raw material, and then draw the penetrant penetrant to the surface through the developer to show the existence of the defect. Penetration testing is suitable for a variety of metal and ceramic workpieces, and the time from penetration manipulation to the appearance of defects is relatively short, usually about half an hour. It may be useful to detect surface fatigue, stress corrosion and welding cracks, and to directly measure the size of cracks.
4. Magnetic particle detection
Magnetic particle detection is to use magnetic flux leakage to absorb magnetic particles and form magnetic marks to provide defect manifestation. It can detect surface and subsurface defects. The nature of defects is easy to distinguish. Paint and electroplated surfaces do not affect the detection vividness.
5. Eddy current detection
If the eddy current detection mainly uses the eddy current induced in the workpiece by the ferromagnetic coil to analyze the internal quality of the workpiece, it can detect the shortcomings of the surface and near surface of various conductive raw materials, the usual parameter control is troublesome, and the detection results are difficult to explain. Moreover, it is required that the detection object must be a conductive crack, and the length of the fault can be measured euphemistically.
6. Magnetic flux leakage detection
Magnetic flux leakage detection of petroleum casing is based on the characteristics of high permeability of ferromagnetic materials. Basically, the quality of in-service petroleum casing is tested by measuring the permeability change caused by defects in ferromagnetic materials .
7. Magnetic impression detection
Magnetic impression detection is derived from the relationship between the physical nature of the magnetic phenomenon of metals and the dislocation process. It has many advantages such as high utilization, low cost, and no grinding. It has an important and ordinary application prospect in the industry.
In order to improve the service life of oil well pipes and reduce costs, oilfields require oil well pipes to be reused multiple times, which puts forward requirements for excellent anti-stick performance of oil pipes. If the oil pipe is stuck, the integrity of the thread connection will be damaged. Continued use may cause leakage at the thread connection and decrease the connection strength. Serious problems such as falling off the well may cause huge economic losses to the oilfield.
The API specification requires that the tubing can be shackled 6 times without sticking when in use. Although the well conditions of each oil field are different, the conditions of the buckle (the method of buckle, the torque of the buckle and the speed of the buckle) are not the same when the tubing goes down. The requirements for the number of trips on the tubing are different. It is required that the number of trips of the oil pipe can reach more than 10 times, and some oilfields require more than 30 times.
http://www.xysteelpipe.com/info/Inspection-method-for-oil-bushing-manufacturer-1641-1.htm
2020年3月29日星期日
Inspection method for oil bushing manufacturer
What are the detection methods of oil casing pipe ? Let's take a brief look:
1. Ultrasonic testing
When ultrasonic waves are spread in the tested raw materials, the acoustic characteristics of the raw materials and the changes in the internal organization have a positive impact on the spread of the ultrasonic waves. After detecting the affected levels and conditions of the ultrasonic waves, the changes in the function and structure of the raw materials are understood .
2. Radiographic inspection
Radiographic inspection uses the difference in the amount of radiation transmitted between the normal part and the defective part to form the resolution of the blackness on the negative.
3. Penetrant test
Penetrant test is to use the capillary action of liquid to permeate the penetrant into the opening on the surface of the solid raw material, and then draw the penetrant penetrant to the surface through the developer to show the existence of the defect. Penetration testing is suitable for a variety of metal and ceramic workpieces, and the time from penetration manipulation to the appearance of defects is relatively short, usually about half an hour. It may be useful to detect surface fatigue, stress corrosion and welding cracks, and to directly measure the size of cracks.
4. Magnetic particle detection
Magnetic particle detection is to use magnetic flux leakage to absorb magnetic particles and form magnetic marks to provide defect manifestation. It can detect surface and subsurface defects. The nature of defects is easy to distinguish. Paint and electroplated surfaces do not affect the detection vividness.
5. Eddy current detection
If the eddy current detection mainly uses the eddy current induced in the workpiece by the ferromagnetic coil to analyze the internal quality of the workpiece, it can detect the shortcomings of the surface and near surface of various conductive raw materials, the usual parameter control is troublesome, and the detection results are difficult to explain. Moreover, it is required that the detection object must be a conductive crack, and the length of the fault can be measured euphemistically.
6. Magnetic flux leakage detection
Magnetic flux leakage detection of petroleum casing is based on the characteristics of high permeability of ferromagnetic materials. Basically, the quality of in-service petroleum casing is tested by measuring the permeability change caused by defects in ferromagnetic materials .
7. Magnetic impression detection
Magnetic impression detection is derived from the relationship between the physical nature of the magnetic phenomenon of metals and the dislocation process. It has many advantages such as high utilization, low cost, and no grinding. It has an important and ordinary application prospect in the industry.
In order to improve the service life of oil well pipes and reduce costs, oilfields require oil well pipes to be reused multiple times, which puts forward requirements for excellent anti-stick performance of oil pipes. If the oil pipe is stuck, the integrity of the thread connection will be damaged. Continued use may cause leakage at the thread connection and decrease the connection strength. Serious problems such as falling off the well may cause huge economic losses to the oilfield.
The API specification requires that the tubing can be shackled 6 times without sticking when in use. Although the well conditions of each oil field are different, the conditions of the buckle (the method of buckle, the torque of the buckle and the speed of the buckle) are not the same when the tubing goes down. The requirements for the number of trips on the tubing are different. It is required that the number of trips of the oil pipe can reach more than 10 times, and some oilfields require more than 30 times.
1. Ultrasonic testing
When ultrasonic waves are spread in the tested raw materials, the acoustic characteristics of the raw materials and the changes in the internal organization have a positive impact on the spread of the ultrasonic waves. After detecting the affected levels and conditions of the ultrasonic waves, the changes in the function and structure of the raw materials are understood .
2. Radiographic inspection
Radiographic inspection uses the difference in the amount of radiation transmitted between the normal part and the defective part to form the resolution of the blackness on the negative.
3. Penetrant test
Penetrant test is to use the capillary action of liquid to permeate the penetrant into the opening on the surface of the solid raw material, and then draw the penetrant penetrant to the surface through the developer to show the existence of the defect. Penetration testing is suitable for a variety of metal and ceramic workpieces, and the time from penetration manipulation to the appearance of defects is relatively short, usually about half an hour. It may be useful to detect surface fatigue, stress corrosion and welding cracks, and to directly measure the size of cracks.
4. Magnetic particle detection
Magnetic particle detection is to use magnetic flux leakage to absorb magnetic particles and form magnetic marks to provide defect manifestation. It can detect surface and subsurface defects. The nature of defects is easy to distinguish. Paint and electroplated surfaces do not affect the detection vividness.
5. Eddy current detection
If the eddy current detection mainly uses the eddy current induced in the workpiece by the ferromagnetic coil to analyze the internal quality of the workpiece, it can detect the shortcomings of the surface and near surface of various conductive raw materials, the usual parameter control is troublesome, and the detection results are difficult to explain. Moreover, it is required that the detection object must be a conductive crack, and the length of the fault can be measured euphemistically.
6. Magnetic flux leakage detection
Magnetic flux leakage detection of petroleum casing is based on the characteristics of high permeability of ferromagnetic materials. Basically, the quality of in-service petroleum casing is tested by measuring the permeability change caused by defects in ferromagnetic materials .
7. Magnetic impression detection
Magnetic impression detection is derived from the relationship between the physical nature of the magnetic phenomenon of metals and the dislocation process. It has many advantages such as high utilization, low cost, and no grinding. It has an important and ordinary application prospect in the industry.
In order to improve the service life of oil well pipes and reduce costs, oilfields require oil well pipes to be reused multiple times, which puts forward requirements for excellent anti-stick performance of oil pipes. If the oil pipe is stuck, the integrity of the thread connection will be damaged. Continued use may cause leakage at the thread connection and decrease the connection strength. Serious problems such as falling off the well may cause huge economic losses to the oilfield.
The API specification requires that the tubing can be shackled 6 times without sticking when in use. Although the well conditions of each oil field are different, the conditions of the buckle (the method of buckle, the torque of the buckle and the speed of the buckle) are not the same when the tubing goes down. The requirements for the number of trips on the tubing are different. It is required that the number of trips of the oil pipe can reach more than 10 times, and some oilfields require more than 30 times.
Surface treatment method and function of stainless steel tube
The surface of the stainless steel pipe will change differently in different environments. Knowing the influence of the use environment on the stainless steel pipe can choose the right model, otherwise the stainless steel pipe will rust and corrode.
Pretreatment is an important treatment step before the surface of stainless steel pipe enters the surface treatment (including pickling, chemical polishing and electrochemical polishing, electroplating, passivation, blackening, coloring, chemical processing, etc.). During the forming process of stainless steel pipes, the surface may be stained with oil, burrs, and rough surfaces and oxides. Therefore, before surface treatment, the oil, burrs, uneven surfaces and oxides must be removed to enable subsequent processing. Get satisfactory results.
The dirt on the surface of the stainless steel pipe to be removed in the pretreatment, it can be divided into two categories: organic and inorganic. Organic pollutants: including mineral oils (such as diesel, motor oil, petroleum jelly, paraffin, etc.) and animal and vegetable oils (such as soybean oil, tea oil, rapeseed oil, lard, tallow, etc.). These oil pollution mainly come from the processing of stainless steel pipes. Used lubricants, cutting oils, quenching oils, polishing and polishing pastes, and fingerprints. Inorganic dirt: Including dirt, dust particles, and oxides generated during heat treatment.
The procedure of stainless steel pipe pretreatment is as follows:
(1) Mechanical leveling of the surface: Eliminate the rough state of the stainless steel surface, and achieve a certain surface finish after mechanical grinding and polishing.
(2) Degreasing: degreasing on the surface,
(3) Pickling: remove the oxide on the surface.
(4) Weak corrosion: Activate the surface to be treated, remove the surface passivation film, and expose the metal crystal structure.
The surface pretreatment method of stainless steel pipe is as follows:
(1) Mechanical method: Use a polisher, polisher or other machinery to remove the rough surface, and then polish and polish it.
(2) Chemical method: degreasing with alkali solution, acid washing with acid solution and organic solvent to dissolve grease and decontamination.
(3) Electrochemical method: the application of electrochemical degreasing and electrochemical etching.
(4) Rolling light, centrifugal light, centrifugal plate light decoration and rotating light decoration, suitable for small parts.
(5) Sand blasting: suitable for large area treatment, and has the functions of decontamination and oxide scale removal.
Therefore, according to the different surface conditions, the quality requirements for the subsequent treatment of stainless steel pipes, using appropriate pretreatment methods.
Pretreatment is an important treatment step before the surface of stainless steel pipe enters the surface treatment (including pickling, chemical polishing and electrochemical polishing, electroplating, passivation, blackening, coloring, chemical processing, etc.). During the forming process of stainless steel pipes, the surface may be stained with oil, burrs, and rough surfaces and oxides. Therefore, before surface treatment, the oil, burrs, uneven surfaces and oxides must be removed to enable subsequent processing. Get satisfactory results.
The dirt on the surface of the stainless steel pipe to be removed in the pretreatment, it can be divided into two categories: organic and inorganic. Organic pollutants: including mineral oils (such as diesel, motor oil, petroleum jelly, paraffin, etc.) and animal and vegetable oils (such as soybean oil, tea oil, rapeseed oil, lard, tallow, etc.). These oil pollution mainly come from the processing of stainless steel pipes. Used lubricants, cutting oils, quenching oils, polishing and polishing pastes, and fingerprints. Inorganic dirt: Including dirt, dust particles, and oxides generated during heat treatment.
The procedure of stainless steel pipe pretreatment is as follows:
(1) Mechanical leveling of the surface: Eliminate the rough state of the stainless steel surface, and achieve a certain surface finish after mechanical grinding and polishing.
(2) Degreasing: degreasing on the surface,
(3) Pickling: remove the oxide on the surface.
(4) Weak corrosion: Activate the surface to be treated, remove the surface passivation film, and expose the metal crystal structure.
The surface pretreatment method of stainless steel pipe is as follows:
(1) Mechanical method: Use a polisher, polisher or other machinery to remove the rough surface, and then polish and polish it.
(2) Chemical method: degreasing with alkali solution, acid washing with acid solution and organic solvent to dissolve grease and decontamination.
(3) Electrochemical method: the application of electrochemical degreasing and electrochemical etching.
(4) Rolling light, centrifugal light, centrifugal plate light decoration and rotating light decoration, suitable for small parts.
(5) Sand blasting: suitable for large area treatment, and has the functions of decontamination and oxide scale removal.
Therefore, according to the different surface conditions, the quality requirements for the subsequent treatment of stainless steel pipes, using appropriate pretreatment methods.
Most anticorrosive steel tubes are spiral steel tubes
In recent years, anticorrosive steel pipes have begun to be widely used in the construction of water and natural gas pipelines. Anti-corrosion steel pipes are usually selected from spiral steel pipes. The diameter of spiral steel pipes is usually relatively large, which is in line with the current requirements of water pipelines, natural gas pipelines and thermal pipelines.
1. Compared with the profile steel in the form of ordinary open section, the round pipe and square (rectangular) section have the characteristics of flat surface, no dead angle and small external surface area. Spiral steel pipe is conducive to saving anti-corrosion and fire-resistant coatings, and easy to remove dust.
a. During the forming process, the steel plate is uniformly deformed, the residual stress is small, and the surface is not scratched. The processed spiral steel pipe has greater flexibility in the size and size range of diameter and wall thickness, especially in the production of high-steel-grade thick-walled pipes, especially small and medium-caliber thick-walled pipes. More requirements for spiral steel pipe specifications.
b. Adopting advanced double-sided submerged arc welding technology, welding can be achieved in an excellent position, which is not prone to defects such as misalignment, welding deviation, and incomplete penetration, and it is easy to control the quality of welding.
c. 100% quality inspection of steel pipes makes the whole process of steel pipe production under effective inspection and monitoring, which effectively guarantees product quality.
d. All the equipment of the entire production line has the function of networking with the computer data acquisition system, real-time data transmission, and the central control room controls the technical parameters in the production process.
2. The wind resistance coefficient of the steel pipe section is small, and it has significant advantages when exposed to fluids (such as wind and water flow).
3. The internal space of the steel pipe structure is available. For example, filled concrete steel pipe can not only improve the bearing capacity of the component, but also extend the fire resistance limit of the component; water is injected into the tube, and the internal water circulation can be used for fire prevention.
4. Liquid can be transported in the pipe. At present, oil pipeline bridges and rainwater drainage pipes have been developed based on this feature.
5. Prestressing cables can also be placed in the tube to apply prestressing in the body.
http://www.xysteelpipe.com/info/Most-anticorrosive-steel-tubes-are-spiral-steel-tubes-1640-1.htm
1. Compared with the profile steel in the form of ordinary open section, the round pipe and square (rectangular) section have the characteristics of flat surface, no dead angle and small external surface area. Spiral steel pipe is conducive to saving anti-corrosion and fire-resistant coatings, and easy to remove dust.
a. During the forming process, the steel plate is uniformly deformed, the residual stress is small, and the surface is not scratched. The processed spiral steel pipe has greater flexibility in the size and size range of diameter and wall thickness, especially in the production of high-steel-grade thick-walled pipes, especially small and medium-caliber thick-walled pipes. More requirements for spiral steel pipe specifications.
b. Adopting advanced double-sided submerged arc welding technology, welding can be achieved in an excellent position, which is not prone to defects such as misalignment, welding deviation, and incomplete penetration, and it is easy to control the quality of welding.
c. 100% quality inspection of steel pipes makes the whole process of steel pipe production under effective inspection and monitoring, which effectively guarantees product quality.
d. All the equipment of the entire production line has the function of networking with the computer data acquisition system, real-time data transmission, and the central control room controls the technical parameters in the production process.
2. The wind resistance coefficient of the steel pipe section is small, and it has significant advantages when exposed to fluids (such as wind and water flow).
3. The internal space of the steel pipe structure is available. For example, filled concrete steel pipe can not only improve the bearing capacity of the component, but also extend the fire resistance limit of the component; water is injected into the tube, and the internal water circulation can be used for fire prevention.
4. Liquid can be transported in the pipe. At present, oil pipeline bridges and rainwater drainage pipes have been developed based on this feature.
5. Prestressing cables can also be placed in the tube to apply prestressing in the body.
http://www.xysteelpipe.com/info/Most-anticorrosive-steel-tubes-are-spiral-steel-tubes-1640-1.htm
2020年3月12日星期四
Advantages and disadvantages of cold rolled steel pipe
Hot-rolled seamless pipe is relative to cold-rolled seamless pipe. Cold-rolled seamless pipe is rolled below the recrystallization temperature, and hot-rolled seamless pipe is rolled above the recrystallization temperature.
Advantages: It can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate the defects of the microstructure, thereby making the steel structure dense and improving the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to a certain extent. Bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into flakes, and delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and interlayer tearing may occur when the weld seam shrinks. The local strain induced by the shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.
2. Residual stress caused by uneven cooling. Residual stress is the internal self-phase equilibrium stress without external force. Hot-rolled sections of various sections have this type of residual stress. Generally, the larger the section size of the section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain effect on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance.
3.Hot rolled steel products are difficult to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction. Since hot rolling at the beginning, even if the length and thickness are up to standard,there will still be a certain negative difference after cooling. The wider the negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large steel, the width, thickness, length, angle,and edge of the steel cannot be required to be too precise.
http://www.xysteelpipe.com/info/Advantages-and-disadvantages-of-cold-rolled-steel-pipe-1621-1.htm
Advantages: It can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate the defects of the microstructure, thereby making the steel structure dense and improving the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to a certain extent. Bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into flakes, and delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and interlayer tearing may occur when the weld seam shrinks. The local strain induced by the shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.
2. Residual stress caused by uneven cooling. Residual stress is the internal self-phase equilibrium stress without external force. Hot-rolled sections of various sections have this type of residual stress. Generally, the larger the section size of the section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain effect on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance.
3.Hot rolled steel products are difficult to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction. Since hot rolling at the beginning, even if the length and thickness are up to standard,there will still be a certain negative difference after cooling. The wider the negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large steel, the width, thickness, length, angle,and edge of the steel cannot be required to be too precise.
http://www.xysteelpipe.com/info/Advantages-and-disadvantages-of-cold-rolled-steel-pipe-1621-1.htm
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