Hardness : Stainless steel tubes are commonly used to measure the hardness of Brinell, Rockwell and Vickers. Brinell hardness Among the stainless steel pipe standards, Brinell hardness is the most widely used, and the hardness of the material is often expressed by the indentation diameter, which is both intuitive and convenient. However, it is not suitable for steel pipes of harder or thinner steel.