How many types of oil casing pipe threads are there

1.Oil casing joint thread

 

Oil casing is a deep machining product with high requirements and large consumption in oil drilling and production engineering.The thread is used to connect a single oil casing pipe into a long string tubular high-pressure vessel that can accept hundreds of atmospheres for several kilometers.In 1924,API formulated the specification for oil well tubing.The joint threads of oil and casing are 10 threads per inch and 8 threads per inch,which are V-shaped threads.However,they were later replaced by API 8 round threads and partial ladder threads,and are still used today.API SPEC 5B specifies that common casing threads are round threads(CSG for short)and trapezoidal threads(BCSG for short).These two types of threaded joints are commonly used in oil and gas fields in China.With the exploration and development of oil and gas in China,especially the increase of deep wells,ultra deep wells,high-pressure gas wells,directional wells,hydrogen sulfide containing wells and other wells,higher requirements have been put forward for the application performance of oil casing joints.The airtightness,joint strength and corrosion resistance of API round threads and eccentric ladder threads have become unaccustomed,and special threaded joints have emerged as the times require.

 

1)API round thread

 

Casing round thread includes casing short round thread(CSG/STC)and casing long round thread(LCSG/LTC).

 

The round thread of oil pipe includes non thickening oil pipe thread(TBG/NUE)and external thickening oil pipe thread(UPTBG/UEE).

 

API round thread pipe joint

 

2)API trapezoidal thread

 

This kind of thread is planned to improve the ability to resist axial tension or compression load and provide anti leakage.It is abbreviated as BCSG/BTC.There is no shoulder taper pipe thread,and it needs to be connected with a coupling.The thread type is trapezoidal,flat top and flat bottom.See the following figure for its tooth type:

 

API trapezoidal threaded pipe joint

 

2.Drilling tool thread

 

The thread of drill tool joint is used to connect drill collars,drill pipes,drill tool stabilizers,conversion joints and drill string components.The current specification for production and inspection is API SPEC 7,which calls the drilling tool joint thread"rotary shoulder connection"and is the mechanical organization for connecting drill string components in the petroleum drilling industry.The tapered thread has the feature of compensating the diameter error of the connecting part through axial displacement,so it has high interchangeability,tight combination and simple assembly and disassembly.Its technical features are inch taper pipe thread,shoulder joint and triangle thread,which are widely used in pipe joint.The thread type is shown in the table below:

 

1)Numerical thread(NC)

 

The digital thread is the preferred thread recommended by API,and V-0.038R flat top round bottom triangular thread is selected as the standard.The feature of this thread is that the radius of the round bottom is 0.038"(0.965mm),and the taper is 1:8,1:6 and 1:4.It is applied to the east and west drilling of kelly,drill pipe,drill collar,drill tool stabilizer,etc.

 

2)Normal thread(REG)

 

This type of drill pipe joint thread was originally used to connect the inner thickened drill pipe,forming a drill pipe joint with an inner diameter smaller than the thickened inner diameter,while the drill pipe

 

The inner diameter of the thick end is smaller than the drift diameter of the inner diameter of the pipe body.The purpose of API planning for normal thread is to apply it to bit jointing,

 

Since the drill bit is located at the end of the drill string,it does not matter whether there is stress concentration at the bottom of the thread,so API

 

Keep all their standards.V-0.050 and V-0.040 tooth forms are used for this type,which is in the 40th edition of API SPEC 7

 

Zhongxin added 1REG and 1-1/2REG using V-0.055(flat bottom,0.055 inch top width,1397 mm)tooth form

 

Two standard threads.

 

3)Internal flat thread(IF)

 

The thread of this type of drill tool joint is connected with the external thickened drill pipe or the surface thickened drill pipe to form the inner diameter of the drill pipe joint,the thickened inner diameter of the pipe body and the pipe

 

Equal or approximate internal diameter.V-0.065 flat top and flat bottom triangular tooth form is selected for standard threads,which is

 

The width of the flat bottom of the tooth was 0.065 inches(1.65 1mm).Except for 5 1/2IF,it is interchangeable with NC thread.However,because the thread structure of this type is easy to cause stress concentration,API has replaced it by NC series.

 

4)Through hole thread(FH)

 

Although there are few standards for this type of thread,it was once widely used for taps,kellies,drill pipes,drill collars and drill bits.Now,except for 5-1/2 FH and 6-5/8FH,which use V-0.050 thread type and 1:6 taper,other threads are eliminated by API.The 4FH with V-0.065 thread is replaced by the NC40 digital thread just like the internal flat thread.