First, differences in production processes
ERW straight seam resistance welded steel pipe is rolled continuously by hot rolled coil. By using skin effect and proximity effect of high frequency current, the edge of coil is hot melted, and the extrusion roll force is pressed and welded under pressure. Realize production. Therefore ERW straight seam resistance welded steel


The residual stress of the pipe is small. The residual stress can be further released and reduced by heat treatment, sizing, straightening and hydraulic pressure. Practice has proved that the residual stress of ERW straight seam welded steel pipe during storage and use will not affect the steel pipe. In the absence of any wire, the weld is physically and chemically identical to the sheet metal. The quality of ERW straight seam resistance welded steel pipe depends on the quality of sheet metal.


The spiral steel pipe is welded together with steel plates through the spiral revolving line of the unit. The spiral rotation of steel plate makes the geometric stress more complex, and some even reach the yield limit of steel plate. After the spiral tube is formed, there are large residual stresses, and the residual stresses are tensile stresses. When the steel pipe is subjected to internal pressure, the circumferential tension stress also occurs on the pipe wall, and the bearing capacity of the steel pipe is weakened by superimposing the two stresses. It is more insecure in use. The steel plate is welded together by welding wires containing chemical composition, and it is easy to produce bubbles and weld cracks in the welding process. The physical properties and chemical composition of weld metal and base metal are obviously different. It is very easy to generate large concentrated stress at the joint between the weld and the base metal. In the welding process, the heat effect is great and the hardness is high.


Second, the difference of raw materials
The raw material used in ERW steel pipe is hot rolled coil produced in large-scale factories. Its chemical composition and physical properties are relatively stable.


Most of the raw materials used in spiral tube mill are low-grade hot-rolled strips. Their chemical composition and physical properties are unstable, and they have many internal defects and impurities.


Third, procurement cost and procurement difficulty
The spiral steel pipes produced by large-scale steel pipe plants in petrochemical systems are mainly concentrated in the manufacture of large-caliber steel pipes with low manufacturing costs. However, for medium and small caliber (114 mm 355.6 mm), the manufacturing cost is higher, which is 8%~15% higher than that of ERW steel on average.


Large spiral pipe mills usually do not produce small and medium diameter spiral pipe, so it is difficult to buy. Due to the large number of manufacturers, small and medium ERW steel pipe is very easy to buy.


Fourth, the geometric dimensions of steel tubes
1. The geometric accuracy of ERW steel pipe is high, while the geometric accuracy of spiral welded pipe is low, which makes it difficult to butt the weld to the spot.


2. The welding coefficient of ERW pipe is 100% and that of spiral welded pipe is 130% - 200%. The welding length of spiral pipe is much longer than that of ERW pipe, and the incidence of defects increases at the same time.


3. The internal weld height of ERW steel pipe is almost zero and invisible to the naked eye; the internal and external surface of spiral steel pipe must have a residual height of about 0.3 mm (determined by the production process). The weld seam is very high, and there is a gap between the anti-corrosion layer (3PE) and the pipe body, which greatly reduces the corrosion resistance of the steel pipe.


4. Because of the high weld height of spiral steel pipe, the high-speed fluid transported will be greatly disturbed, which increases the flow resistance and reduces the pipeline transporting efficiency. The inner wall of ERW steel pipe is smooth, so there is no such problem.


Fifth, other differences
The extrusion resistance of ERW steel pipe is higher than that of spiral steel pipe.


Sixth, application comparison
The general design code for long-distance oil and gas pipelines stipulates that spiral submerged arc welded pipe can only be used in Grade 1 and 2 areas. The United States, Japan and Germany generally reject SSAW, and believe that SSAW should not be used on the main line; SSAW for Canada and Italy, SSAW for Russia, SSAW for a small amount. For historical reasons, most domestic trunk lines still use SSAW.