Casing thread gauge is a deep machining product with high requirement and large amount in oil drilling and production engineering.A single oil casing is connected by thread into a long string thousands of meters long and able to withstand a pressure of hundreds of atmospheres — a tubular high-pressure vessel.In 1924, the API established the first standard for oil well pipes. The casing joint thread was 10 teeth per inch and 8 teeth per inch V-thread, but it was later replaced by API8 round thread and offset ladder thread, and is still in use today.API SPEC 5B provides that the common casing threads are round thread (CSG) and offset trapezoidal thread (BCSG).
These two kinds of threaded joints are generally used in oil and gas fields .With the oil and gas exploration and development, especially in deep wells and ultra deep wells and high pressure gas well and directional well, hydrogen sulfide-bearing wells such as the increase of oil casing joint performance put forward higher requirements, the use of API round thread and partial ladder model of air tightness, bonding strength and corrosion resistance can meet requirements, for countries to have a special development and application of the nipple.API round thread, partial ladder thread and some special thread are described in the following.
API round thread gauge: API Round Thread Gauge is divided into Casing Short Round Thread Gauge (CSG) and Casing Long Round Thread Gauge (LCSG).Tubing Thread Gauge is abbreviated as TBG and is subdivided into Non-Thickness Tubing Thread Gauge (TBG) and External Thickness Tubing Thread Gauge (UP TBG).
The thread form of the circular thread gauge is a tapered pipe thread without shoulder, which needs to be connected with a collar. The tooth type is triangular, the bottom of the dome is round, the tooth angle is 60°, the thread taper is 1:16, the bisector of the tooth angle is perpendicular to the axis. When the thread is tightened, the tooth side of the internal and external thread is sealed.
Gauges for offset trapezoidal thread:BCSG, non-shoulder tapered pipe thread with collar connection, offset trapezoidal, flat top, flat bottom, tooth type.