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 positioned into well bore and cemented in place to secure both subsurface formations and the wellbore from collapsing, also to enable drilling mud to circulate and extraction to take place. Casing pipes are normally manufactured using outside dimension sizes from 114.3 mm to 508.0 mm.
The strict quality requirement for steel is due to the harsh working conditions of casing. The steel product should be produced and checked in accordance with special standards or specifications. ISO 11960 and API Spec 5CT have specified the steel product standards of casing.
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