API 5CT N80 casing pipe covers N80-1 and N80Q types. N80-1 and N80Q steel have same chemical composition and mechanical attributes, and their difference lies in the heat treatment. N80-1 steel is normalized and tempered, while N80Q steel is quenched and tempered. So N80Q steel has higher collapsing strength and internal pressure strength than N80-1 steel. When API 5CT N80 casing pipe is selected, the designer should clearly show N80-1 or N80Q.