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Analysis of welded stainless steel pipe and seamless stainless steel pipe difference

Jul 17, 2017

Stainless steel pipe is a kind of hollow long strip round steel, mainly used in petroleum, chemical, medical, food, light industry, machinery, instrument and other industrial pipeline and mechanical structure parts. In addition, the bending and torsional strength of the same weight is lighter, so it is also widely used in the manufacture of mechanical parts and engineering structures. It is also used to produce all kinds of conventional weapons, guns, shells and so on.

1 concentricity

The seamless tube is made by pressing a hole in a stainless steel billet at a temperature of 2200 degrees F. At this high temperature, the tool steel is made soft and spirally shaped from the hole by stamping and drawing. Thus, the wall thickness of the pipeline is uneven and the eccentricity is high. Thus ASTM allows seamless pipe wall thickness ratio of the wall thickness difference of seamed tube. Through the seamed tube cold rolling plate precision (per roll width is 4-5 feet) made. These cold rolled plates usually have a maximum wall thickness of 0.002 inches. The steel plate is cut into a width of PI D, in which D is the outer diameter of the pipe. Tube wall thickness tolerance is very small, and the entire circumference of the wall thickness is very uniform.

2. Welding performance

Chemical composition of seamed pipe and seamless pipe are different. The production of seamless steel components only meets the basic requirements of astm. The production of seamed tube steel containing suitable for chemical composition of welding. For example, the mixing of silicon, sulfur, manganese, oxygen, and a certain proportion of elements such as the triangle ferrite can produce a welding flux which is easy to transfer heat during welding, so as to make the whole weld be welded well. The lack of steel pipe above the chemical components, such as seamless tube, can produce all kinds of unstable factors in the process of welding, welding and welding penetration is not easy.

3. Grain size

The grain size of the metal is related to the temperature of heat treatment and the time of keeping the same temperature. The welded stainless steel pipe and seamless stainless steel tube as the annealed grain size. If the minimum tube cold treatment, the grain size of the weld metal is smaller than the grain size, welding or grain size is the same.

4, pipe strength

The strength of the pipeline depends on the alloy composition, which contains the same alloy and the same heat treatment of stainless steel seamless pipe and welded stainless steel pipes essentially consistent strength.

After the tensile test and three-dimensional vibration test, welded stainless steel pipes tearing almost all occurred in the region far away from the welding point or local heating. This is because there is little impurity in the weld and the nitrogen content is slightly higher, so the strength of the welded joint is better than that of other parts. However, ASME (American Society of Mechanical Engineers) that welded stainless steel pipes can withstand 85% of the allowable pressure, which is mainly due to improved welding equipment data collection prior to today.

The provisions of ASME 100% completely under permit pressure through ultrasonic testing of welded stainless steel pipe. Similarly, Europe and Asia also stipulates that can ensure the quality of welding performance by eddy current testing of welded stainless steel tube for eddy current testing is subject to legal procedures and licensed institutions. TRENT's eddy current test was approved by the Swedish power division. ASME believes the current loss is relatively small, high-quality performance based on the seamed tube.

5, corrosion resistance

The quality of corrosion resistance also depends on the composition of the alloy. Seamless stainless steel pipe of the same chemical composition and heat treatment of fully welded stainless steel pipes for corrosion resistance is consistent. Additional tests provided by ASTM show that the corrosion resistance at the weld is equivalent to or better than that of the metal being welded. In acidic chloride environment, the tube with incomplete heat treatment of weld corrosion will accelerate, but this is only the corrosion test, in fact the environment is not so bad.

6, bending and extensibility

The extension of the welding can be verified by the following provisions: bending test ASTM 45 degrees, and then bent to 90 degrees, and then along the weld flattening; stainless steel pipe joints and turned the repeat the steps to make the weld bending diameter reaches 180 degrees. The standard adopted for weld quality is that there is no tearing or intergranular separation in case of magnification of 40. The bending radius of the pipe is controlled by the composition of the alloy, and the minimum bending radius is 2D. The ideal welding condition is that the weld is in neutral or compression state. Also, the pipe shall be annealed to reduce its hardness and thereby improve its flexural properties.

7, the price

Welded stainless steel pipe price is only half of the stainless steel seamless pipe.

8 wall thickness / diameter

Thin wall stainless steel tubes with small thickness / diameter should be produced by welding. Thick or big diameter thick walled tubes should be made by stamping.

9, comprehensive quality

In general, the quality is better than that of welded stainless steel pipes seamless stainless steel pipes, welded stainless steel tube is made for precise cold rolled plate after inspection by, so any defect in the welding position limit. Seamless tubes are made from stainless steel billets punched by punches, resulting in many tear in the tube walls formed by extrusion. The eddy current test shows that the welded stainless steel pipes of the defective rate is usually lower than the rate of defective seamless stainless steel tube. Ultrasonic testing makes seamless stainless steel tubes so noisy that it is difficult to detect defects. The background noise of welded stainless steel tube is very low, easy to find defects.