4. Pipe strength
The strength of the pipeline depends on the alloy composition, so the seamless stainless steel pipe and the seamed stainless steel pipe containing the same alloy and the same heat treatment are essentially the same in strength.
After the tensile test and three-dimensional vibration test, the tears of seamed stainless steel pipes almost all occur far away from welding points or heated areas. This is because the weld has fewer impurities and slightly higher nitrogen content, so the strength of the weld is better than other parts. However, ASME (American Society of Mechanical Engineers) believes that seamed stainless steel pipes can only withstand 85% of the allowable pressure. This is mainly due to the collection of data earlier than the improved welding equipment used today.
5. Corrosion resistance
The corrosion resistance also depends on the composition of the alloy. The corrosion resistance of seamless stainless steel pipes with the same chemical composition and fully heat-treated seamed stainless steel pipes is the same. The supplementary test provided by ASTM proves that the corrosion resistance of the weld is equal to or better than the metal being welded. In the acid chloride environment, the corrosion of the welded joints of incompletely heat-treated seam steel pipes will accelerate, but this is only the need for corrosion testing, and the environment is not so harsh.
6. Flexibility and extensibility
The extensibility of the weld can be verified by the following test specified by ASTM: bend 45°, then bend to 90°, and then flatten along the weld; then turn the stainless steel seam pipe and repeat the above steps to make the weld bend inner diameter to 180°. The standard for welding seam quality is that no tearing or intergranular separation is allowed under the condition of 40 times magnification. The bending radius of the pipeline is controlled by the composition of the alloy, and the minimum bending radius is generally 2d. The ideal welding condition is that the weld is in a neutral or compressed state. Moreover, the pipeline should be annealed to reduce its hardness, thereby improving bending performance.
7. Price
The price of a seamed stainless steel pipe is usually only half of that of stainless steel seamless pipe.
8. Wall thickness/diameter
Thin-walled stainless steel pipes with small thickness/diameter values are best produced by welding; thick-walled pipes with large thickness/diameter values are best produced by stamping.
9. Comprehensive quality
Generally, the quality of seamed stainless steel pipes is better than seamless stainless steel pipes, because the seamed stainless steel pipes are made of accurate cold-rolled plates that have passed inspections, so any defects are limited to the weld. Seamless pipes are stamped from stainless steel blanks by punches, resulting in many tearing phenomena in the pipe wall formed by extrusion. The eddy current test shows that the defective rate of seamed stainless steel pipes is generally lower than that of seamless stainless steel pipes. Using ultrasonic testing, the background noise of seamless stainless steel pipes is so great that it is difficult to find defects. The background noise of seamed stainless steel pipes is very low, and it is easy to find defects.
Post time: Nov-29-2023