Hardness unit of Structural pipe

　　With a certain diameter of the ball or carbide ball, ASME Structural ERW Pipes with a specified test force (F) pressed into the surface of the sample, after a specified time to remove the test force to measure the surface indentation diameter (L). The Brinell hardness value is the quotient of the test force divided by the indentation spherical surface area. In HBS (steel ball), said unit is N / mm2 (MPa).