LSAW steel pipe weld appearance basic requirements:
Straight seam steel pipe before NDT, weld visual inspection should meet the requirements. General requirements for straight seam steel pipe weld appearance and surface quality of welded joints are as follows:
Welding should look good shape, width of each side groove edge 2mm overshadowed appropriate. Fillet weld leg height should meet the design requirements, the shape should be smooth transition.
Welded joint surface requirements:
(1) Does not allow cracks, lack of fusion, pores, slag, spatter exist.
(2) The design temperature is below -29 degrees pipes, stainless steel and hardened alloy steel pipes tend to be larger weld surface, without undercut. Other material carbon steel pipe weld undercut depth should be greater than 0.5mm, continuous undercut length should not exceed 100mm, and both sides of the weld undercut always grow up to 10 percent of the entire length of the weld.
(3) Shall not be lower than the surface of the weld surface of the pipe. Weld reinforcement and no more than 3mm, (the maximum width of weld joints after groove).
(4) Welded joints the wrong side of the wall thickness should be less than 10% and not more than 2mm.
2017年1月3日星期二
Lamination Defect Control Measures of SSAW Steel Pipe
Lamination defect control measures of SSAW steel pipe is following below:
1, to improve the toughness of plastic tube
Improve the cleanliness of molten steel, to reduce the harmful inclusions; increase the proportion of the slab crystal axis, to reduce the center segregation and center porosity; the use of reasonable cooling system to avoid cracks occur within the slab; billet or rolling slab to be taken offline slow cooling process, reduce internal stress, thus ensuring the microstructure and mechanical properties of the finished structural steel pipe to meet the technical standards.
2, the reasonable control of the heating temperature
By measuring the thermoplastic curve, choose the best heating temperature. Note also that there is enough heating tube holding time, in order to reduce and improve plastic deformation resistance and toughness.
3, lower roll speed
Roll speed is a key parameter piercing process, the roll speed from low to high variations in the process, there is a critical stratification began the roll speed. Lower roll speed, easy to form tube bore; higher roll speed, tube and capillary easily form a layered defects. In order to eliminate delamination defects and capillary tube, roll speed should be reduced to the beginning of the critical delamination roll speed or less to control mild steel pipe.
1, to improve the toughness of plastic tube
Improve the cleanliness of molten steel, to reduce the harmful inclusions; increase the proportion of the slab crystal axis, to reduce the center segregation and center porosity; the use of reasonable cooling system to avoid cracks occur within the slab; billet or rolling slab to be taken offline slow cooling process, reduce internal stress, thus ensuring the microstructure and mechanical properties of the finished structural steel pipe to meet the technical standards.
2, the reasonable control of the heating temperature
By measuring the thermoplastic curve, choose the best heating temperature. Note also that there is enough heating tube holding time, in order to reduce and improve plastic deformation resistance and toughness.
3, lower roll speed
Roll speed is a key parameter piercing process, the roll speed from low to high variations in the process, there is a critical stratification began the roll speed. Lower roll speed, easy to form tube bore; higher roll speed, tube and capillary easily form a layered defects. In order to eliminate delamination defects and capillary tube, roll speed should be reduced to the beginning of the critical delamination roll speed or less to control mild steel pipe.
DIN30670 standard for PE Coating
DIN 30670 refers to polyethylene coatings on steel pipes and fittings –Requirements and testing.
This standard specifies requirements for factory-applied three-layer extruded polyethylene-based coatings, and one- or multi-layered sintered polyethylene-based coatings for the corrosion protection of steel pipes and fittings. The coatings are suitable for the protection of buried or submerged steel pipes at design temperatures of –40 °C up to +80 °C. The present standard specifies requirements for coatings that are applied to longitudinally or spirally welded or carbon steel pipe and fittings used for the construction of pipelines for conveying liquids or gases. Applying this standard ensures that the PE coating provides sufficient protection against the mechanical, thermal and chemical loads occurring during operation, transport, storage and installation. DIN EN ISO 21809-1 specifies requirements at international level for three-layer extruded polyethylene- and polypropylene-based coatings for steel pipes for petroleum and natural gas pipeline transportation systems. The following fields of application are not covered by DIN EN ISO 21809-1: ─ all polyethylene-based coatings for steel pipes and fittings used for the conveyance and distribution of water and wastewater, ─ all polyethylene-based coatings for steel pipes and fittings in distribution pipelines for gaseous and liquid media, ─ single- and multi-layer sintered polyethylene-based coatings for steel pipes and fittings used for transport pipelines and distribution pipelines The present standard remains valid for the above fields of application. Two-layer polyethylene-based coatings are standardized at European level in DIN EN 10288 which was published in December 2003.
Materials shall be selected at the discretion of the coater because, depending on the installation and coating procedure, various materials can be used to comply with the minimum requirements specified in this standard for the finished coating. Any deviating requirements of the purchaser regarding the materials to be used shall be subject to agreement.The surface shall be prepared by removing rust by means of blast cleaning. Blast cleaning and any necessary subsequent work shall not result in the reduction of the minimum wall thickness specified in the technical delivery standards for the steel pipe. Residual abrasive dust shall be removed prior to coating steel pipe.
This standard specifies requirements for factory-applied three-layer extruded polyethylene-based coatings, and one- or multi-layered sintered polyethylene-based coatings for the corrosion protection of steel pipes and fittings. The coatings are suitable for the protection of buried or submerged steel pipes at design temperatures of –40 °C up to +80 °C. The present standard specifies requirements for coatings that are applied to longitudinally or spirally welded or carbon steel pipe and fittings used for the construction of pipelines for conveying liquids or gases. Applying this standard ensures that the PE coating provides sufficient protection against the mechanical, thermal and chemical loads occurring during operation, transport, storage and installation. DIN EN ISO 21809-1 specifies requirements at international level for three-layer extruded polyethylene- and polypropylene-based coatings for steel pipes for petroleum and natural gas pipeline transportation systems. The following fields of application are not covered by DIN EN ISO 21809-1: ─ all polyethylene-based coatings for steel pipes and fittings used for the conveyance and distribution of water and wastewater, ─ all polyethylene-based coatings for steel pipes and fittings in distribution pipelines for gaseous and liquid media, ─ single- and multi-layer sintered polyethylene-based coatings for steel pipes and fittings used for transport pipelines and distribution pipelines The present standard remains valid for the above fields of application. Two-layer polyethylene-based coatings are standardized at European level in DIN EN 10288 which was published in December 2003.
Materials shall be selected at the discretion of the coater because, depending on the installation and coating procedure, various materials can be used to comply with the minimum requirements specified in this standard for the finished coating. Any deviating requirements of the purchaser regarding the materials to be used shall be subject to agreement.The surface shall be prepared by removing rust by means of blast cleaning. Blast cleaning and any necessary subsequent work shall not result in the reduction of the minimum wall thickness specified in the technical delivery standards for the steel pipe. Residual abrasive dust shall be removed prior to coating steel pipe.
Special Filler Metals of Welded Steel Pipe
The first one is flux-cored wires. When welding out of position on thick-walled carbon steel pipe, it is better to choose gas-shielded flux-cored wire to achieve high deposition rates. This kind of filler metal can weld out of position without a special power, and the flux coating on the wire can be considered as a dam which can hold the molten weld pool in place. Therefore, the flux –cored wires are useful for improving productivity. However, there are some disadvantages when using the flux-cored wires in the welded steel pipe. Higher levels of smoke may be produced and a slag may be generated by the wires. Then both between passes and after the cap pass, the welding operators will need to chip or grind in, which in turn leads to greater downtime for cleanup.
The other kind is metal-cored wires. When welding welded steel pipe, the metal-cored wires are accepted more and more widely. The available diameters of the metal-cored wires range from 0.035- to 1/16-inch. In order to weld out of position, the pulsing or advanced short-circuit processes, with which the metal-metal wires can be applied to weld from root to the cap, are needed by stainless steel metal-cored wire. What is more, the welded structural steel pipe with these kinds of wires can provide greater productivity. One disadvantage to metal-cored wires is their cost. Though the metal-cored wires are more expensive, the productivity and quality improvements outweigh the cost.
The third one is solid wire. When welding thicker-walled welded steel pipe, we usually choose solid wires which must use a special power source to weld out of position. If the welded steel pipe is being rotated, these filler metals can be used to weld fill and cap passes in the flat or horizontal position. In addition, solid wires are useful for welding out of position for root, fill and cap passes. However, for welded steel pipe, it is more difficult to match the chemistry. Then the availability of the filler metals may be influenced.
The last one is SMAW electrodes. SMAW (shielded metal arc welding) electrodes are of great importance for welded steel pipe because of the availability and familiarity of the filler metal. However, compared with other filler metals, the SMAW electrodes are slower and less efficient.
The other kind is metal-cored wires. When welding welded steel pipe, the metal-cored wires are accepted more and more widely. The available diameters of the metal-cored wires range from 0.035- to 1/16-inch. In order to weld out of position, the pulsing or advanced short-circuit processes, with which the metal-metal wires can be applied to weld from root to the cap, are needed by stainless steel metal-cored wire. What is more, the welded structural steel pipe with these kinds of wires can provide greater productivity. One disadvantage to metal-cored wires is their cost. Though the metal-cored wires are more expensive, the productivity and quality improvements outweigh the cost.
The third one is solid wire. When welding thicker-walled welded steel pipe, we usually choose solid wires which must use a special power source to weld out of position. If the welded steel pipe is being rotated, these filler metals can be used to weld fill and cap passes in the flat or horizontal position. In addition, solid wires are useful for welding out of position for root, fill and cap passes. However, for welded steel pipe, it is more difficult to match the chemistry. Then the availability of the filler metals may be influenced.
The last one is SMAW electrodes. SMAW (shielded metal arc welding) electrodes are of great importance for welded steel pipe because of the availability and familiarity of the filler metal. However, compared with other filler metals, the SMAW electrodes are slower and less efficient.
How to Weld Large Welded Steel Pipe?
In the welding process of large welded steel pipe, we should pay great attention to the melted region of the work piece and form a molten solder, because the melted region is the connection of cooling and solidifying the material after the pool is formed. Usually, the pressure is required by large diameter thick-walled pipe in welding process. There are many welding energy sources, for example, a gas flame, electric arc, laser, electron beam, friction and ultrasonic.
The first one is a board probe. In the process of welding welded steel pipe, after the welded steel pipe enters the production, the manufacturers use it to manufacture large diameter submerged arc welding of steel pipes. In addition, whether there are internal defects pipe can be checked by the first full-board ultrasonic test.
Then, the milling, which can ensure the width of welded steel pipe reach to target diameter when the milling machine is through the two-sided edge of the milling pipe, so the width of the welded steel pipe parallel to the edge of the pipe.
Thirdly, pre-curved edge is commonly used. When we apply the pre-bent plate edge pre-bending machine, we must ensure the welded steel pipe can meet the requirement of the edge. Therefore, the size of the carbon steel pipe can be more precise.
The next step is forming. After several multi steps, the JCO forming machine should be used. We should press the first half of the pre-bent steel into a “J” shape, and press the other half into a “C” shape, and the last, form the opening “O” shape. This process is called the origin JCOE process.
After the process of forming, the structural steel pipe enters the process of pre-welding. The pre-welding process means that seam welded steel pipe seam straightly by using carbon dioxide gas, and the welded steel pipe is forming continuously even though it has been formed.
Then the inner of the pipe must be welded. In this process, the multi-wire submerged arc column should be used on the inside of the pipe to seam welded steel pipe. After all of the process, the steel pipe must be welded outside by using multi-wire submerged arc welding.
What is more, there must be several tests to ensure the quality of the welded steel pipe, such as the ultrasonic testing and the X-ray inspection.
The first one is a board probe. In the process of welding welded steel pipe, after the welded steel pipe enters the production, the manufacturers use it to manufacture large diameter submerged arc welding of steel pipes. In addition, whether there are internal defects pipe can be checked by the first full-board ultrasonic test.
Then, the milling, which can ensure the width of welded steel pipe reach to target diameter when the milling machine is through the two-sided edge of the milling pipe, so the width of the welded steel pipe parallel to the edge of the pipe.
Thirdly, pre-curved edge is commonly used. When we apply the pre-bent plate edge pre-bending machine, we must ensure the welded steel pipe can meet the requirement of the edge. Therefore, the size of the carbon steel pipe can be more precise.
The next step is forming. After several multi steps, the JCO forming machine should be used. We should press the first half of the pre-bent steel into a “J” shape, and press the other half into a “C” shape, and the last, form the opening “O” shape. This process is called the origin JCOE process.
After the process of forming, the structural steel pipe enters the process of pre-welding. The pre-welding process means that seam welded steel pipe seam straightly by using carbon dioxide gas, and the welded steel pipe is forming continuously even though it has been formed.
Then the inner of the pipe must be welded. In this process, the multi-wire submerged arc column should be used on the inside of the pipe to seam welded steel pipe. After all of the process, the steel pipe must be welded outside by using multi-wire submerged arc welding.
What is more, there must be several tests to ensure the quality of the welded steel pipe, such as the ultrasonic testing and the X-ray inspection.
Introduction on Welded Steel Pipe Classes and Features
Classes and features of welded steel pipe
The welded steel pipe of low pressure fluid is also known as the clarinet. This kind of welded steel pipe can be used like the common welded steel pipe, for example, transporting water, gas and oil, but also it can be used to convey low pressure steam heating fluid. The wall thickness of this kind of welded steel pipe includes ordinary steel and thicker steel, and in the forming process of it, there are no steel pipes and tubes with steel. Ordinarily, we use nominal diameter which is a kind of approximate diameter to calculate the specifications of the pipe. In addition, this kind of welded steel pipe cannot only directly convey fluids, but also can weld the original steel pipe by using low pressure.
The low pressure fluid galvanized welded steel pipe, which is a kind of galvanized welded steel pipes, is commonly known as white pipe. This kind steel pipe can also transport water, gas, air and oil. What is more, the mild steel pipe can be used for other purposes, for example, conveying low pressure fluid such as steam heating and warm water and so on. The wall thickness of this kind steel pipe has two types including ordinary galvanized steel and thick galvanized steel. The form of end of the pipe includes non-threaded galvanized and threaded galvanized. In the meanwhile, this kind steel pipe also uses nominal diameter, but commonly uses inches.
The straight seam welded steel pipe, which is parallel to the longitudinal welded steel pipe, has various kinds of types, for example, metric welded steel pipe, welded tube, transformer cooling pipes and arc.
The other kind is pressurized liquid delivery LSAW steel pipe, which is mainly used for oil pipelines and natural gas. It can be used for hot-rolled steel strip coils, and often convey fluid by double-sided submerged arc welding method. There are many advantages for this kind steel pipe, for example, it can withstand strong pressure, and its welding performance is very good. This structural steel pipe passed through various rigorous scientific inspection and testing trials, so it is safe and reliable. What is more, the transmission efficiency of it is very high which can be useful for saving the laying of pipeline investments.
The Defects in Welded Steel Pipe Manufacturing
There are usually two heating products for the pipe billet of the welded steel pipe, including pre-heating and rolling tube. When manufacturing welded steel pipe, the two heating products should be heated before in a given path, and it requires the use of intermediate annealing so that the residual stress can be removed. Sometimes, the welded steel pipe is manufactured to meet special requirements, for example, improving the mechanical properties and improving organizational and process performance and heat treatment. Therefore, the defects of the welded steel pipe manufacturing are uneven heating, oxidation, decarburization, heating cracks, overheating and over-burning.
The temperature on the steel pipe usually has a great influence on the quality of it, so the manufacturers must control the temperature precisely. However, the heating temperature is too low, too high or uneven heating. The deformation resistance of the metal may be increased and the plasticity of metals may be reduced because of too low heating temperature. Generally, if the complete conversion of the structural steel pipe microstructure of austenite grains cannot be guaranteed by the heating temperature tube, the cracks will be increased. What is more, the surface of welded steel pipe may be oxidation severely, decarburization overheated or burnt when the welded steel pipe is at a high temperature.
In the meanwhile, besides the too high temperature, if the steel pipe is heated for too long time, there are also defects such as the excessive austenite grain coarsening. When the heating temperature of the carbon steel pipe reaches near the solidus temperature, the boundary may be oxidation or melted, and then a burnt will come out. If the fold is produced in the overheating perforated capillary welded steel pipe, then the burnt steel billets will be scrapped. When the welded steel pipe enters into the furnace where the temperature is too high, or the steel pipe is heated too fast in it, it is easy for the kind of steel pipe to crack. In general, the crack and the fold are easy to form both inner and outer surfaces of the pipe.
If the heat treatment is controlled improperly, the widmanstatten may be produced, which may have a bad impact on the working performance of the mild steel pipe, namely, reducing the strength of steel at room temperature and increasing brittleness.
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