Definition Seamless steel pipe used to sustain the wall of oil or gas well, it belongs to disposable consumable material. Casing pipe consumption take up 70% of all oil well pipes. According to usage condition, casing pipe can be divided into conduit casing, skin layer casing, technical casing and oil rock layer casing. There are five grade for casing pipe, which is J55, K55, N80, L80, P110. According to casing pipe end thread and coupling form, it consist of STC, LTC and BTC. STC means short thread coupling, LTC means long thread coupling, and BTC means buttress thread coupling. Usually length consist of R1, R2 and R3. R1 is range from 4.88 to 7.62m, R2 is range from 7.621 to 10.36m and R3 is range from 10.36 to 14.63m.