In the process of high-frequency welding steel pipe, the welding process and the control of process parameters, the placement of the induction coil and the position of the resistor have a great influence on the welding quality of the steel pipe weld.
1) Control of weld gap of steel pipe The steel strip enters into the welded pipe unit, which is formed by the forming roll, after the orientation of the guide roll, the round steel pipe blank with open gap is formed, and the squeezing amount of the squeezing roller is adjusted, ~ 3mm, and to keep the weld ends flush. Weld gap control is too large, will weld the weld caused by poor fusion or cracking; weld gap control is too small, due to excessive heat, resulting in weld burning, melting metal splash, welding quality of the weld . In this case,
2) The position of the induction coil should be placed on the same center line as the steel tube. The distance between the front end of the induction coil and the center line of the squeeze roller should not be burned. As close as possible. If the induction coil is farther away from the squeeze roller, the effective heating time is longer and the heat-affected zone is wider, so that the strength of the steel pipe weld is decreased or not penetrated; otherwise, the induction coil is easy to burn the squeeze roller. In this case,
3) The control of the impedance of the impedance of the resistor is a pipe or a group of special magnetic bar, the cross-sectional area of the impedance should normally not be less than 70% of the cross-sectional area of the tube diameter, its role is to induction coil, pipe welding edge and magnetic The rods form an electromagnetic induction loop, producing proximity effects, with vortex heat concentrated near the edge of the tube weld, which heats the edge of the tube to the welding temperature. The resistor should be placed in the V-zone heating section with the front end at the center of the squeeze roll so that the centerline coincides with the tube centerline. Such as the placement of the bad resistor, affecting the welding speed of welding and welding quality, so that steel pipe cracks.
2018年4月24日星期二
Seamlessly Resistance Welded Pipe Production Knowledge
Electric Resistance Welding (ERW) and seamless steel pipe is the biggest difference lies in the ERW if has a weld, which is the key to the quality of ERW steel pipe.
Modern ERW steel pipe production process and equipment, as the international community, especially the United States and other years of unremitting efforts, making the ERW seamless steel pipe has been a more satisfactory solution. It was the ERW seamless steel pipe is divided into geometric seamless and physical seamless. Geometric seamless ERW steel pipe is to remove the internal and external glitches. Due to the structure and tool of the inner burr removal system, the burr removal of large and medium-sized steel pipes has been well handled. The burr can be controlled in -0.2mm ~ +0.5 mm or so. Physical seamless means that there is a difference between the microstructure of the weld metal and the base metal, which leads to the decrease of the mechanical properties of the weld area, and needs to take measures to make it uniform and uniform. The high-frequency welding heat process of ERW steel tube caused the temperature gradient in the vicinity of the edge of the tube, and formed characteristic regions such as melting zone, semi-melting zone, superheating structure, normalizing zone, incomplete normalizing zone and tempering zone. In the superheat zone, the austenite grain grows abruptly under the condition that the welding temperature is above 1000 ℃, and the hard and brittle coarse crystal phase is formed under the cooling condition. Besides, the existence of the temperature gradient will produce welding stress. In this way, the formation of the mechanical properties of the weld zone lower than the base metal case, the physical seamless steel pipe is through the local conventional heat treatment process that is to use the medium frequency induction heating device will weld area heated to AC3 (927 ℃), and then 60m length, the speed of 20m / min in the air-cooled process, when necessary, then water cooling. The use of this method to eliminate stress, soften and refine the organization, improve the comprehensive heat-affected zone mechanical properties of the purpose. At present, the world's most advanced ERW unit has been widely used this method to deal with the weld, has achieved good results. High-quality ERW steel pipe not only can not argue out the weld, and the weld coefficient of 1, to achieve the weld area of the organization and the base material match.
Modern ERW steel pipe production process and equipment, as the international community, especially the United States and other years of unremitting efforts, making the ERW seamless steel pipe has been a more satisfactory solution. It was the ERW seamless steel pipe is divided into geometric seamless and physical seamless. Geometric seamless ERW steel pipe is to remove the internal and external glitches. Due to the structure and tool of the inner burr removal system, the burr removal of large and medium-sized steel pipes has been well handled. The burr can be controlled in -0.2mm ~ +0.5 mm or so. Physical seamless means that there is a difference between the microstructure of the weld metal and the base metal, which leads to the decrease of the mechanical properties of the weld area, and needs to take measures to make it uniform and uniform. The high-frequency welding heat process of ERW steel tube caused the temperature gradient in the vicinity of the edge of the tube, and formed characteristic regions such as melting zone, semi-melting zone, superheating structure, normalizing zone, incomplete normalizing zone and tempering zone. In the superheat zone, the austenite grain grows abruptly under the condition that the welding temperature is above 1000 ℃, and the hard and brittle coarse crystal phase is formed under the cooling condition. Besides, the existence of the temperature gradient will produce welding stress. In this way, the formation of the mechanical properties of the weld zone lower than the base metal case, the physical seamless steel pipe is through the local conventional heat treatment process that is to use the medium frequency induction heating device will weld area heated to AC3 (927 ℃), and then 60m length, the speed of 20m / min in the air-cooled process, when necessary, then water cooling. The use of this method to eliminate stress, soften and refine the organization, improve the comprehensive heat-affected zone mechanical properties of the purpose. At present, the world's most advanced ERW unit has been widely used this method to deal with the weld, has achieved good results. High-quality ERW steel pipe not only can not argue out the weld, and the weld coefficient of 1, to achieve the weld area of the organization and the base material match.
What is 304 Stainless Steel
A grade of stainless steel, 304 steel is the most widely used steel because it's easy to weld and work. It is available in a wider range of stock forms and finishes than any other steel product.
The 304 stainless steel is classified as a T 300 series austenitic stainless steel alloy, containing a minimum of 8 percent nickel and 18 percent chromium with a maximum of 0.08 percent carbon. This grade of steel also has excellent drawing properties and can be formed into bar, rod or sheet stock.
It comes in a low-carbon version, commonly used in heavy-gauge equipment because it does not require annealing. There is also a high-carbon version, suited to applications in which the steel may be exposed to high temperatures. The heat resistance of 304 steel is good in ranges up to 925 degrees C for continuous use, and it also can withstand extreme cryogenic temperatures. It is very corrosion-resistant and can be exposed to a variety of atmospheric conditions and a wide range of corrosive agents.
Applications for which 304 steel is suited include food and beverage processing equipment, kitchen equipment and utensils, chemical containers, springs and fasteners. This stainless steel can be used in architectural applications such as wall paneling, railings and trim.
Possible alternatives to 304 steel are 301L, 302HQ, 303, 316, 321, 3CR12 and 430 steel, depending on the application and cost requirements.
http://www.xysteelpipe.com/info/What-is-304-Stainless-Steel-1024-1.htm
The 304 stainless steel is classified as a T 300 series austenitic stainless steel alloy, containing a minimum of 8 percent nickel and 18 percent chromium with a maximum of 0.08 percent carbon. This grade of steel also has excellent drawing properties and can be formed into bar, rod or sheet stock.
It comes in a low-carbon version, commonly used in heavy-gauge equipment because it does not require annealing. There is also a high-carbon version, suited to applications in which the steel may be exposed to high temperatures. The heat resistance of 304 steel is good in ranges up to 925 degrees C for continuous use, and it also can withstand extreme cryogenic temperatures. It is very corrosion-resistant and can be exposed to a variety of atmospheric conditions and a wide range of corrosive agents.
Applications for which 304 steel is suited include food and beverage processing equipment, kitchen equipment and utensils, chemical containers, springs and fasteners. This stainless steel can be used in architectural applications such as wall paneling, railings and trim.
Possible alternatives to 304 steel are 301L, 302HQ, 303, 316, 321, 3CR12 and 430 steel, depending on the application and cost requirements.
http://www.xysteelpipe.com/info/What-is-304-Stainless-Steel-1024-1.htm
Different types of Annealing process
Annealing is a heat treatment process for metal, slowly heated the metal to a certain temperature and maintain a sufficient time, and then cooling at an appropriate rate. The purpose for annealing is to improve or eliminate defects in various tissues and prevent deformation of the work piece or cracking. Also, annealing can be used for softening the metal for machining. Besides, it helps to grain refinement to improve the organization in order to improve the mechanical properties of the work piece. It is the preparation process for the final heat treatment (quenching and tempering).
There are different types of annealing process, these process are:
1. Fully Annealing (for refinement and low carbon steel). During the steel casing, forging and welding, the steel appreas poor mechanical properties. During fully annealing, the steel work piece is heated to a temperature above 30~50 degree, and then all the ferrite turn into austenite. Holding for some time, and then slowly cooled with the furnace. In the cooling process, austenite transformed again which make the steel organization thinner.
2. Ball Annealing. In order to reduce the high hardness of the steel after forging. The work piece is heated to a temperature between 20 to 40 degrees which the steel of austenite begins to form, and then slowly cooling after incubation. During the cooling, the lamellarpearlite cementite becomes spherical which will reduces the hardness of the steel.
3. Isothermal Annealing. In order to reduce the high hardness, high chromium content and some nickel content alloy structural steel before cutting, Isothermal Annealing is necessary. First, cooled the steel at a faster rate to the most unstable austenite temperature, and then hold the temperature for a appropriate time. In the last, the austenite turned into sorbite prop’s body which can reduce the hardness of the steel.
4. Re-crystalization Annealing. The purpose for re-crystalization annealing is to eliminate metal wire and sheet metal hardness during the cold drawing or cold rolling process (hardness increased plasticity decrease) . The heating temperature is generally between 50~150 degree which the austenitic begins to form. This is the only way to eliminate the effect of hardening and make the steel softened.
5. Diffusion Annealing. It is applied on alloy castings fro the chemical composition uniformity and improves its performance. The method is applied when the meting does not occure under the premise, the casting is heated to a temperature as high as possible, and prolonged heat until alloy of various elements diffusion after slow cooling more uniform distribution.
6. Graphitization Annealing. To make the cast iron contains a lot of cementite into plastic good malleable iron. The casting process operation is heated to about 950 degree. Before cooling needed to hold to a certain temperature for a certain time. In the end, the cementite decomposes to form group flocculent graphite.
7. Stress Relief Annealing. The purpose of Stress Relief Annealing is to eliminate the stress of steel castings and weldments. After the start of heating for the formation of austenite steel prodcuts below the temperature 100 to 200 degree and after holding cooling in the air for a certain time, you can eliminate stress of the steel.
http://www.xysteelpipe.com/info/Different-types-of-Annealing-process-1025-1.htm
There are different types of annealing process, these process are:
1. Fully Annealing (for refinement and low carbon steel). During the steel casing, forging and welding, the steel appreas poor mechanical properties. During fully annealing, the steel work piece is heated to a temperature above 30~50 degree, and then all the ferrite turn into austenite. Holding for some time, and then slowly cooled with the furnace. In the cooling process, austenite transformed again which make the steel organization thinner.
2. Ball Annealing. In order to reduce the high hardness of the steel after forging. The work piece is heated to a temperature between 20 to 40 degrees which the steel of austenite begins to form, and then slowly cooling after incubation. During the cooling, the lamellarpearlite cementite becomes spherical which will reduces the hardness of the steel.
3. Isothermal Annealing. In order to reduce the high hardness, high chromium content and some nickel content alloy structural steel before cutting, Isothermal Annealing is necessary. First, cooled the steel at a faster rate to the most unstable austenite temperature, and then hold the temperature for a appropriate time. In the last, the austenite turned into sorbite prop’s body which can reduce the hardness of the steel.
4. Re-crystalization Annealing. The purpose for re-crystalization annealing is to eliminate metal wire and sheet metal hardness during the cold drawing or cold rolling process (hardness increased plasticity decrease) . The heating temperature is generally between 50~150 degree which the austenitic begins to form. This is the only way to eliminate the effect of hardening and make the steel softened.
5. Diffusion Annealing. It is applied on alloy castings fro the chemical composition uniformity and improves its performance. The method is applied when the meting does not occure under the premise, the casting is heated to a temperature as high as possible, and prolonged heat until alloy of various elements diffusion after slow cooling more uniform distribution.
6. Graphitization Annealing. To make the cast iron contains a lot of cementite into plastic good malleable iron. The casting process operation is heated to about 950 degree. Before cooling needed to hold to a certain temperature for a certain time. In the end, the cementite decomposes to form group flocculent graphite.
7. Stress Relief Annealing. The purpose of Stress Relief Annealing is to eliminate the stress of steel castings and weldments. After the start of heating for the formation of austenite steel prodcuts below the temperature 100 to 200 degree and after holding cooling in the air for a certain time, you can eliminate stress of the steel.
http://www.xysteelpipe.com/info/Different-types-of-Annealing-process-1025-1.htm
Precautions for steel pipe production
R&D center and production center would have discussion for the precautions measures during the steel pipe’s production, so that they would supply high quality steel pipe from seamless steel pipe to welded steel pipe like ERW steel pipe for customers.
First of all, suppliers should pay high attention to joint. In order to make no wrong side or less than a range like the general error is less than or equal to 8%, we should make strategies before production.
What’s more, rightful penetration depth is another parameter for manufacturers. It is important to make insure there is no cracking, no burning phenomenon after welding.
Additionally, for final external welding quality, we should get the continuous weld and good shape.
http://www.xysteelpipe.com/info/Precautions-for-steel-pipe-production-1026-1.htm
First of all, suppliers should pay high attention to joint. In order to make no wrong side or less than a range like the general error is less than or equal to 8%, we should make strategies before production.
What’s more, rightful penetration depth is another parameter for manufacturers. It is important to make insure there is no cracking, no burning phenomenon after welding.
Additionally, for final external welding quality, we should get the continuous weld and good shape.
http://www.xysteelpipe.com/info/Precautions-for-steel-pipe-production-1026-1.htm
2018年4月15日星期日
Welding requirements for large diameter straight pipe steel pipe
Large diameter straight seam steel pipe welding, including pre-welding, welding and welding outside the three processes. The so-called pre-welding that is, after the steel pipe forming, the use of continuous high-speed gas shielded welding (MAG) method of forming steel pipe positioning welding. After the pre-welding, respectively, within the steel pipe, multi-wire submerged arc welding.
In the case of high-speed gas-shielded pre-welding, there are currently two methods. One is the use of single-wire dual-power high-current high-speed gas protection pre-welding, such as the United States, Germany that is used in this way; the other is double-wire high-speed gas protection pre-welding, Japan is the use of this method. At present, more applications are monofilament high-speed gas protection pre-welding method, in a reasonable welding process conditions, can achieve not less than 7m / min high speed, and straight bead forming beautiful. As the pre-welding of the first step of welding, the quality is ensured. Pre-welding quality, not only its own quality problems, but also affect the follow-up, the quality of welding. Its quality requirements, targeted mainly as follows:
1, The weld should be continuous, and the appearance of shape to avoid uneven, in order to facilitate the final quality assurance of welding.
2, To ensure the penetration depth and the appropriate amount of welding, it is necessary to ensure that after welding does not crack, but also to make the phenomenon of burn-through when not produced.
3, To have a higher welding speed, in order to improve production efficiency.
In the case of high-speed gas-shielded pre-welding, there are currently two methods. One is the use of single-wire dual-power high-current high-speed gas protection pre-welding, such as the United States, Germany that is used in this way; the other is double-wire high-speed gas protection pre-welding, Japan is the use of this method. At present, more applications are monofilament high-speed gas protection pre-welding method, in a reasonable welding process conditions, can achieve not less than 7m / min high speed, and straight bead forming beautiful. As the pre-welding of the first step of welding, the quality is ensured. Pre-welding quality, not only its own quality problems, but also affect the follow-up, the quality of welding. Its quality requirements, targeted mainly as follows:
1, The weld should be continuous, and the appearance of shape to avoid uneven, in order to facilitate the final quality assurance of welding.
2, To ensure the penetration depth and the appropriate amount of welding, it is necessary to ensure that after welding does not crack, but also to make the phenomenon of burn-through when not produced.
3, To have a higher welding speed, in order to improve production efficiency.
Weld treatment of LSAW steel pipe
LSAW steel pipe is the strip into the pipe unit, the multi-roll rolling, strip gradually rolled up to form a circular gap open billet, adjust the squeeze roll reduction, so that weld gap control In the 1 ~ 3mm, and make both ends of the welding flush. If the gap is too large, it will reduce the proximity effect, eddy current heat shortage, weld intergranular bonding caused by poor fusion or cracking. Such as between
If the gap is too small, the proximity effect will be increased, the welding heat will be too large, and the weld will be burned; or the weld will be crushed and crushed to form the pit, which will affect the weld surface quality.
Welding process example:
Weld φ32 × 2mm longitudinal welded pipe, for example, briefly describes the process parameters:
Strip specifications: 2 × 98mm bandwidth by medium diameter expansion plus a small amount of molding margin.
Steel material: Q235A
Input excitation voltage: 150V Excitation current: 1.5A Frequency: 50Hz.
Output DC voltage: 11.5kV DC current: 4A Frequency: 120000Hz.
Welding speed: 50 m / min.
Parameter adjustment: according to the welding line energy changes in time to adjust the output voltage and welding speed. Fixed parameters generally do not have to adjust.
If the gap is too small, the proximity effect will be increased, the welding heat will be too large, and the weld will be burned; or the weld will be crushed and crushed to form the pit, which will affect the weld surface quality.
Welding process example:
Weld φ32 × 2mm longitudinal welded pipe, for example, briefly describes the process parameters:
Strip specifications: 2 × 98mm bandwidth by medium diameter expansion plus a small amount of molding margin.
Steel material: Q235A
Input excitation voltage: 150V Excitation current: 1.5A Frequency: 50Hz.
Output DC voltage: 11.5kV DC current: 4A Frequency: 120000Hz.
Welding speed: 50 m / min.
Parameter adjustment: according to the welding line energy changes in time to adjust the output voltage and welding speed. Fixed parameters generally do not have to adjust.
Characteristics of Welded Steel Tube Slag
Welded steel pipe slag is residual slag inside the weld. From the theoretical analysis, submerged arc welding seam slag generated mainly due to the following three reasons: ① raw materials (including base metal, wire, flux) in the inclusion of more; ② multi-layer welding clean up when the inter-layer; ③ improper selection of welding process parameters is not conducive to the emergence of slag.
According to the production characteristics of straight seam submerged arc welded steel pipe, it can be ruled out that the interlayer cleaning is not clean when the multi-layer welding is done and the slag is generated.
For the inclusions in raw materials and make the weld slag, straight seam steel pipe company to take the pre-test test base metal, replacement of new welding wire and flux and other measures, weld fusion line slag generated only a slight reduction in the proportion, Indicating that inclusions in the raw materials are not the main causes of slag formation.
Therefore, thick-walled LSAW steel pipe welding line slag generated mainly due to improper selection of welding process parameters. The welding parameters of thick-walled submerged arc welded pipe are: line energy, welding current, welding voltage, welding speed, wire spacing, groove size.
According to the production characteristics of straight seam submerged arc welded steel pipe, it can be ruled out that the interlayer cleaning is not clean when the multi-layer welding is done and the slag is generated.
For the inclusions in raw materials and make the weld slag, straight seam steel pipe company to take the pre-test test base metal, replacement of new welding wire and flux and other measures, weld fusion line slag generated only a slight reduction in the proportion, Indicating that inclusions in the raw materials are not the main causes of slag formation.
Therefore, thick-walled LSAW steel pipe welding line slag generated mainly due to improper selection of welding process parameters. The welding parameters of thick-walled submerged arc welded pipe are: line energy, welding current, welding voltage, welding speed, wire spacing, groove size.
AWWA C200 Steel Water Pipe
Water pipeline AWWA C200 steel water pipe is widely used in the following fields/industries:
Hydraulic power station, potable
Water supply industry, irrigation penstock, Sewage disposal pipe line
AWWA C200 standards covers butt-welded, straight-seam or spiral-seam steel pipe, 6 in. (150 mm) and larger, for transmission and distribution of water, including fabrication of pipe, requirements of welding operations, permissible variations of weight and dimensions, preparation of ends, fabrication of specials, inspection, and test procedures.
Inspection
All work performed and material furnished under this standard may be inspected by the purchaser, but such inspection shall not relieve the manufacturer of responsibility to furnish material and perform work in accordance with this standard.
Quality assurance
The manufacturer shall maintain a quality-assurance program to ensure that minimum standards are met. It shall include a certified welding inspector (AWS QC1) to verify that welders and welding procedures are qualified, procedures are being followed with limitation of testing, and quality-assurance functions are being implemented.
Defects
The finished pipe shall be free from unacceptable defects. Defects in seamless pipe or in the parent metal of welded pipe will be considered unacceptable when the depth of the defect is greater than 12.5% of the nominal wall thickness.
The repair of defects will not be permitted if the depth of the defect exceeds 1/3 of the nominal wall thickness of the pipe and if the length of that portion of the defect in which the depth exceeds 12.5% is greater than 25% of the outside diameter of the pipe. Each length of repaired pipe shall be tested hydrostatically in accordance with standard requirements.
Hydraulic power station, potable
Water supply industry, irrigation penstock, Sewage disposal pipe line
AWWA C200 standards covers butt-welded, straight-seam or spiral-seam steel pipe, 6 in. (150 mm) and larger, for transmission and distribution of water, including fabrication of pipe, requirements of welding operations, permissible variations of weight and dimensions, preparation of ends, fabrication of specials, inspection, and test procedures.
Inspection
All work performed and material furnished under this standard may be inspected by the purchaser, but such inspection shall not relieve the manufacturer of responsibility to furnish material and perform work in accordance with this standard.
Quality assurance
The manufacturer shall maintain a quality-assurance program to ensure that minimum standards are met. It shall include a certified welding inspector (AWS QC1) to verify that welders and welding procedures are qualified, procedures are being followed with limitation of testing, and quality-assurance functions are being implemented.
Defects
The finished pipe shall be free from unacceptable defects. Defects in seamless pipe or in the parent metal of welded pipe will be considered unacceptable when the depth of the defect is greater than 12.5% of the nominal wall thickness.
The repair of defects will not be permitted if the depth of the defect exceeds 1/3 of the nominal wall thickness of the pipe and if the length of that portion of the defect in which the depth exceeds 12.5% is greater than 25% of the outside diameter of the pipe. Each length of repaired pipe shall be tested hydrostatically in accordance with standard requirements.
Manufacturing Loss Rate of Spiral Steel Pipe
Spiral steel pipe manufacturing loss rate refers to the spiral pipe in the manufacturing process, the proportion of raw materials, waste, according to professional and technical personnel for many years statistical analysis spiral tube manufacturing loss rate of between 2% -3%.
During the manufacture of spiral steel pipe, the main components of waste are: the first piece of spiral pipe forming the first piece, the tail to tail, the raw material milling, spiral pipe production process necessary steps, if the production can not be normal spiral pipe milling edge, truncated , To the end, the production of steel pipe pass rate is very low.
When spiral steel pipe manufacturing, there are some losses can be avoided, such as spiral pipe weld quality unqualified, can not be repaired, then the spiral pipe quality unqualified, can not be used, resulting in a waste of material. In the manufacturing process, we must strictly control each process, handle the details, so as to improve the spiral tube yield and pass rate, to avoid unnecessary losses, so that can avoid unnecessary cost.
During the manufacture of spiral steel pipe, the main components of waste are: the first piece of spiral pipe forming the first piece, the tail to tail, the raw material milling, spiral pipe production process necessary steps, if the production can not be normal spiral pipe milling edge, truncated , To the end, the production of steel pipe pass rate is very low.
When spiral steel pipe manufacturing, there are some losses can be avoided, such as spiral pipe weld quality unqualified, can not be repaired, then the spiral pipe quality unqualified, can not be used, resulting in a waste of material. In the manufacturing process, we must strictly control each process, handle the details, so as to improve the spiral tube yield and pass rate, to avoid unnecessary losses, so that can avoid unnecessary cost.
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