Rimmed steel, generally having a low carbon content (less than 0.15 percent), have the evolved gases only partially killed or controlled by the addition of elements such as aluminium. The gases form blowholes along the outer iron of the ingot - hence the term rimmed. Blowholes are usually not objectionable unless they break throughout the outer skin of the ingot. Rimmed steels have little or no piping, and contain a ductile skin along with good surface finish. The blowholes might break throughout the skin if they are not prohibited properly. Inclusion and Impurities tend to segregate toward the centre of the ingot. Hence, products made from this steel might be defective and must be inspected.