316 hot rolled stainless steel pipein the process of welding or grinding of stainless steel in the air is heated to a certain temperature, lower surface of the weld, welds on both sides and chromium oxide hot temper color appears at the bottom. Hot temper thinner than oxide protective film, and clearly visible. Color determined by the thickness, you can see a rainbow - colored, blue, yellow and purple to pale brown. Thick oxide is black. It is due to stay under high temperature or at a height for a long time. When there is any such oxidation layer, metal surfaces of chromium content is reduced, resulting in reduced corrosion resistance of these regions. In this case, not only to eliminate hot temper and other oxide layer, also depleted chromium metal layers below them should be cleaned up.