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Difference between Seam Stainless Steel Pipe and Seamless Stainless Steel Pipe

Date:2017-10-06    keywords:seam stainless steel pipe, seamless stainless steel pipe
Stainless steel tube is a hollow long circular steel, mainly used in petroleum, chemical, medical, food, light industry, mechanical instruments and other industrial pipelines and mechanical structural components. So what are the main differences between seam stainless steel pipes and seamless stainless steel pipes?

1, Concentricity
The manufacturing process of the seamless steel pipe is to punch out a hole in the stainless steel billet at a temperature of 2200 ° f, at which the tool steel is softened and spirally formed from the hole by pressing and drawing. So that the wall thickness of the pipe is not uniform and the eccentricity is high. Thus astm allows the wall thickness difference of the seamless pipe to be larger than the wall thickness of the grooved pipe. The seam pipe is made by means of an accurate cold rolled plate (each roll width of 4-5 feet). These cold rolled plates typically have a maximum wall thickness difference of 0.002 inches. The steel plate is cut into the width of πd, where d is the outer diameter of the pipe. The tolerances of the wall thickness are small and the wall thickness of the entire circumference is very uniform.

2, Welding performance
Generally there are some differences in the chemical composition of the seam and the seamless tube. Production of seamless steel composition of steel is only to meet the basic requirements of astm. While the production of sewn steel is suitable for welding the chemical composition. Such as silicon, sulfur, manganese, oxygen and triangular ferrite and other elements in a certain proportion of mixing can be produced in the welding process is easy to pass a heat of the weld, so that the entire weld penetration. The lack of the above chemical composition of the steel pipe, such as seamless pipe, in the welding process will produce a variety of unstable factors, not easy to weld and welding thoroughly.

3, Grain size
The grain size of the metal is related to the heat treatment temperature and the time at which the same temperature is maintained. The annealed seamed stainless steel pipe and seamless stainless steel tube have the same grain size. If the seam is machined with minimal cooling, the grain size of the weld is smaller than the grain size of the metal being welded, otherwise the grain size is the same.

4, Pipeline strength
The strength of the pipe depends on the composition of the alloy, and thus the same alloy and the same heat treatment of seam stainless steel pipe and seamless stainless steel tube is essentially the same intensity. After tension testing and three-dimensional vibration test, the tearing of the sewn stainless steel pipe occurs almost far away from the welding point or the heated area. This is because the weld less impurities and nitrogen content is slightly higher, so the strength of the weld better than other parts. However, the ASME (American Society of Mechanical Engineers) believes that sewn stainless steel tubes can only withstand 85% of the allowable pressure, mainly due to the data collected earlier than the use of improved welding equipment.

ASME stipulates that 100% of the sewn stainless steel tubes tested by ultrasonic tests are fully tolerated. Similarly, Europe and Asia also require the use of eddy current test of seamless stainless steel pipe to ensure the quality of its welding performance, eddy current testing is subject to legal procedures and holders of the permit institutions. TRENT's eddy current test passed the permission of the Swedish power department. ASME believes that the small current loss is based on the quality of the seam pipe.

5, Corrosion resistance
The corrosion resistance is also dependent on the composition of the alloy. The same chemical composition of seamless stainless steel tube and completely heat-treated seamless steel pipe corrosion resistance is consistent. ASTM's supplemental test proves that the corrosion resistance at the weld is equivalent or better than the metal being welded. In the acidic chloride environment, the corrosion of the welded joints of the incomplete heat treatment is accelerated, but this is only the need for corrosion testing. In fact, the environment is not so bad.

6, Bending and extensibility
The extension of the weld can be verified by the following tests specified by ASTM: bending 45 °and bending to 90 °and flattening along the weld; then turn the stainless steel seam to repeat the above steps to make the weld bend to 180 °. The quality of the weld passes through the standard is 40 times the magnification of the case does not allow tear or intergranular separation. Pipeline bending radius is controlled by the composition of the alloy, the general minimum bending radius of 2d. The ideal welding condition is that the weld is in a neutral or pressurized state. Moreover, the pipe should be annealed to reduce its hardness, thereby improving the bending performance.

7, The price
The price of sewn stainless steel pipe is usually only half of the stainless steel seamless pipe.

8, Wall thickness / diameter
Thickness / diameter of small thin-walled stainless steel pipe is best to use welding production; thickness / diameter of the thick-walled tube is best made of stamping method.

9, Integrated quality
In general, the quality of the sewn stainless steel pipe is superior to that of a seamless stainless steel tube because the sewn stainless steel pipe is made of an accurate cold rolled plate which is tested so that any defects are limited to the weld. The seamless pipe is made of stainless steel billet punching, resulting in a lot of tearing in the wall formed by extrusion. The vortex test shows that the defective rate of the sewn stainless steel pipe is usually lower than that of the seamless stainless steel tube. With ultrasonic testing, the background noise of seamless stainless steel tubes is so large that it is difficult to find defects. While the background noise of the sewn stainless steel tube is very low, easy to find defects.

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