The steel grades of common oilfield API-5CT casing pipe include J55, K55, N80-1, N80Q, and P110. Casing pipe is mostly used for oil well drilling. In accordance with API-5CT and ISO11960 standard, pipes can be classified as STC (short thread), LTC (long thread) and BTC (buttress thread) accompanied with their couplings. Oilfield casing pipes are