There are three kinds of steel pipes commonly used in long-distance pipelines
Spiral submerged arc welded steel pipe (SSAW pipe)
1. Advantages of spiral seam submerged arc welded steel pipe
(1) The weld seam is distributed in a spiral shape, so that the maximum driving cracking direction of the steel pipe is inconsistent with the direction of the minimum fracture resistance, thereby reducing the risk of pipe cracking along the weld seam direction;
(2) The vertical weld direction of the spiral welded pipe is the weak direction of strength, thus avoiding the principal stress direction of the steel pipe;
(3) The manufacturing process of spiral welded pipe is relatively simple, mature and cheap;
(4) It has a long history of use and rich experience and lessons.
2. But its spiral weld also brings its inevitable disadvantages:
(1) During the welding and forming of the spiral welded pipe, a large residual stress is formed, and after the steel pipe is subjected to internal pressure, the tensile stress increases, and the pressure bearing capacity of the steel pipe is significantly weakened;
(2) The heat-affected zone of the spiral welded pipe is relatively large and the hardness is high;
(3) The weld seam of the spiral welded pipe is long. Since the defects of the steel pipe mainly occur on the weld seam, the long weld seam means the reduction of reliability;
(4) The shape of the weld seam is not good, which brings difficulties to the coating process inside and outside the steel pipe, and often produces air pockets or leaks on both sides of the weld seam during the coating process;
(5) The accuracy of its geometric dimensions is worse than that of straight seam welded pipes;
(6) The Bauschinger effect of the spiral welded pipe is large, which reduces the yield limit of the steel pipe.
Straight seam double-sided submerged arc welded steel pipe (LSAW pipe)
On large-diameter pipelines, the excellent performance of double-sided submerged arc welding has been recognized by countries all over the world, and some countries such as Europe and the United States even regard it as the preferred product.
1. Its advantages mainly include:
(1) The cold expansion process of the full length of the pipe after welding can be used to expand the pipe, so that the forming stress and welding stress of the welded pipe can be eliminated.
(2) The straight seam double-sided submerged arc welded pipe is welded on a plane, and the weld seam is a straight line, so its welding conditions, online automatic tracking of the weld seam, online ultrasonic testing and X-ray flaw detection are relatively easy to achieve.
(3) The base material of the straight seam double-sided submerged arc welded pipe is a single controlled-rolled steel plate, which can carry out 100[wiki]%[/wiki] non-destructive flaw detection.
(4) The processing precision of straight seam double-sided submerged arc welded pipe is high, which is convenient for on-site installation and butt joint welding of pipelines.
(5) The double-sided submerged arc welding of the straight seam adopts multi-wire welding, the weld seam and the base metal have a smooth transition, and it is not easy to form air pockets or leaks on both sides of the weld seam.
(6) Short welds mean improved reliability.
2. Although straight seam submerged arc steel welding has good comprehensive performance, its popular application is limited because of its high price.
Straight seam high frequency electric resistance welded steel pipe (ERW pipe)
Due to the technological progress of the straight seam high-frequency electric resistance welded steel pipe in the past ten years, its manufacturing process has been continuously improved, so that its application range has been rapidly expanded.
1. Its main advantages are:
(1) No chemical components are added during the welding process of straight seam high-frequency resistance welded steel pipes, and its welding quality mainly depends on the quality of the base metal. In recent years, due to the continuous improvement of the quality of hot-rolled coils, the quality of the welds has also been improved in the process of pipe making. Even if the quality of the welds is slightly insufficient, it will not affect the quality of the entire steel pipe.
(2) In recent years, due to the advancement of automation technology, the main parameters of resistance welding can be optimized by computer control, which ensures a substantial improvement in welding quality.
(3) Straight seam high frequency resistance welded steel pipe has small residual stress and high strength.
(4) The geometric dimension accuracy of straight seam high-frequency resistance welded steel pipe is high, which is convenient for on-site installation, butt ring weld and anti-corrosion construction.
(5) The weld bead of the straight seam high-frequency resistance welded steel pipe is short, which means that the reliability is improved.
(6) The straight seam high-frequency resistance welded steel pipe has a price advantage, and its price is much lower than that of the straight seam double-sided submerged arc welded steel pipe. However, due to the lack of weld quality of the straight seam high-frequency resistance welded steel pipe, it is necessary to do a good job of external anti-corrosion treatment.
Spiral submerged arc welded steel pipe (SSAW pipe)
1. Advantages of spiral seam submerged arc welded steel pipe
(1) The weld seam is distributed in a spiral shape, so that the maximum driving cracking direction of the steel pipe is inconsistent with the direction of the minimum fracture resistance, thereby reducing the risk of pipe cracking along the weld seam direction;
(2) The vertical weld direction of the spiral welded pipe is the weak direction of strength, thus avoiding the principal stress direction of the steel pipe;
(3) The manufacturing process of spiral welded pipe is relatively simple, mature and cheap;
(4) It has a long history of use and rich experience and lessons.
2. But its spiral weld also brings its inevitable disadvantages:
(1) During the welding and forming of the spiral welded pipe, a large residual stress is formed, and after the steel pipe is subjected to internal pressure, the tensile stress increases, and the pressure bearing capacity of the steel pipe is significantly weakened;
(2) The heat-affected zone of the spiral welded pipe is relatively large and the hardness is high;
(3) The weld seam of the spiral welded pipe is long. Since the defects of the steel pipe mainly occur on the weld seam, the long weld seam means the reduction of reliability;
(4) The shape of the weld seam is not good, which brings difficulties to the coating process inside and outside the steel pipe, and often produces air pockets or leaks on both sides of the weld seam during the coating process;
(5) The accuracy of its geometric dimensions is worse than that of straight seam welded pipes;
(6) The Bauschinger effect of the spiral welded pipe is large, which reduces the yield limit of the steel pipe.
Straight seam double-sided submerged arc welded steel pipe (LSAW pipe)
On large-diameter pipelines, the excellent performance of double-sided submerged arc welding has been recognized by countries all over the world, and some countries such as Europe and the United States even regard it as the preferred product.
1. Its advantages mainly include:
(1) The cold expansion process of the full length of the pipe after welding can be used to expand the pipe, so that the forming stress and welding stress of the welded pipe can be eliminated.
(2) The straight seam double-sided submerged arc welded pipe is welded on a plane, and the weld seam is a straight line, so its welding conditions, online automatic tracking of the weld seam, online ultrasonic testing and X-ray flaw detection are relatively easy to achieve.
(3) The base material of the straight seam double-sided submerged arc welded pipe is a single controlled-rolled steel plate, which can carry out 100[wiki]%[/wiki] non-destructive flaw detection.
(4) The processing precision of straight seam double-sided submerged arc welded pipe is high, which is convenient for on-site installation and butt joint welding of pipelines.
(5) The double-sided submerged arc welding of the straight seam adopts multi-wire welding, the weld seam and the base metal have a smooth transition, and it is not easy to form air pockets or leaks on both sides of the weld seam.
(6) Short welds mean improved reliability.
2. Although straight seam submerged arc steel welding has good comprehensive performance, its popular application is limited because of its high price.
Straight seam high frequency electric resistance welded steel pipe (ERW pipe)
Due to the technological progress of the straight seam high-frequency electric resistance welded steel pipe in the past ten years, its manufacturing process has been continuously improved, so that its application range has been rapidly expanded.
1. Its main advantages are:
(1) No chemical components are added during the welding process of straight seam high-frequency resistance welded steel pipes, and its welding quality mainly depends on the quality of the base metal. In recent years, due to the continuous improvement of the quality of hot-rolled coils, the quality of the welds has also been improved in the process of pipe making. Even if the quality of the welds is slightly insufficient, it will not affect the quality of the entire steel pipe.
(2) In recent years, due to the advancement of automation technology, the main parameters of resistance welding can be optimized by computer control, which ensures a substantial improvement in welding quality.
(3) Straight seam high frequency resistance welded steel pipe has small residual stress and high strength.
(4) The geometric dimension accuracy of straight seam high-frequency resistance welded steel pipe is high, which is convenient for on-site installation, butt ring weld and anti-corrosion construction.
(5) The weld bead of the straight seam high-frequency resistance welded steel pipe is short, which means that the reliability is improved.
(6) The straight seam high-frequency resistance welded steel pipe has a price advantage, and its price is much lower than that of the straight seam double-sided submerged arc welded steel pipe. However, due to the lack of weld quality of the straight seam high-frequency resistance welded steel pipe, it is necessary to do a good job of external anti-corrosion treatment.
