Seamless steel tubes are subject to mechanical performance testing. The mechanical properties test methods are mainly divided into two categories, one is the tensile test, and the other is the hardness test.
The tensile test is to make a seamless steel tube into a sample, pull the sample to break on a tensile testing machine, and then measure one or several mechanical properties, usually only the tensile strength, yield strength, elongation after fracture and rate of reduction in area. The boiler pressure component steel used in the 20G high-pressure boiler tube is generally used in boilers below 39 kg. In order to use it under higher pressure, the heating surface tube is often designed to be very thick.
In order to reduce thermal resistance and save steel, to ensure the safety of higher or high-pressure boiler steel, and to reduce the amount of steel used, 16MnG is commonly used. At the same time, there are also special steels with rare earth, magnesium and other metallic and non-metallic materials. This will improve the performance of boiler steel, reduce steel consumption, and also reduce thermal resistance. Tensile test is the most basic test method for mechanical properties of metal materials. Almost all metal materials require tensile tests as long as they have requirements for mechanical properties. Especially for those materials whose shape is not convenient for hardness test, tensile test becomes the only means of testing mechanical properties.
The hardness test is to slowly press a hard indenter into the surface of a seamless steel pipe sample under specified conditions, and then test the depth or size of the indentation to determine the hardness of the material. Hardness test is the simplest, fastest and easiest method in material mechanical property test. The hardness test is non-destructive, and there is an approximate conversion relationship between the material hardness value and the tensile strength value. The hardness value of the material can be converted into the tensile strength value, which has great practical significance.
Because the tensile test is not easy to test, and it is convenient to convert the hardness to the strength, more and more people only test the hardness of the material and less test its strength. In particular, due to the continuous progress and innovation of hardness tester manufacturing technology, it is now possible to directly test the hardness of some materials that could not be directly tested before, such as seamless steel tubes, stainless steel (stainless and acid-resistant steel) plates and stainless steel strips. Therefore, there is a tendency that the hardness test gradually replaces the tensile test.