The major portion of drill string is composed of drill pipe. Drill pipe consists of three components: a tube with a pin tool joint welded to one end and a box tool joint welded to the other.
Before the tool joints are welded to the tube, the tube is upset, or forged, on each end to increase the wall thickness.
After upsetting, the tube is heat treated to the proper grade strength. All tool joints are heat treated to the same material yield strength (120,000 psi), regardless of the grade of pipe to which they are attached. Most drill pipe is made from material similar to AISI 4125/30 steel seamless tube. Most tool joints are made from material similar to AISI 4140 steel forgings, tubing, or bars stock.
- Drilling Pipes
Drill pipe dimensional and metallurgical specifications are defined by the American Petroleum Institute (API) and published in API Spec 7 Specifications for Drill Stem Elements and API Spec 5D Specifications for Drill Pipe.
Performance characteristics, guidelines for drill pipe use and inspection standards are in API RP7G Recommended Practice for Drill Stem Design and Operating Limits. Drill pipe specifications and performance characteristics can also be found in ISO 10407-1, ISO 10407-2, ISO 10424-1, ISO 10424-2, and ISO 11961.
This list is not all inclusive; it contains drill pipe assemblies with various tool joints but not all OD and ID combinations of tool joints.
The following items are required to completely identify a length of drilling pipe:
– Pipe size is the pipe OD (in., mm). The API specification for the drill pipe tube is API 5D.
– Pipe weight (lb/ft, kg/m) is for the tube only exclusive of tool joints and upset ends and is used to specify wall thickness. Except in a few cases, the tabulated pipe weight is not the calculated pipe weight.
– Pipe grade is the pipe yield strength. Drill pipe manufacturers may offer higher strength grades or grades designed for specific applications such as drilling in H2S environments. Pipe upset The drill pipe tubes are upset on each end to increase the wall thickness. The thicker wall is needed to compensate for loss of material
strength during the welding process. There are three configurations of upsets:
• Internal upset (IU), inwhich the wall thickness is increased by decreasing the ID. This allows smaller OD tool joints to be welded to the pipe. This pipe is sometimes referred to as a slim hole pipe and is used in smaller diameter holes.
• External upset (EU), inwhich the wall thickness is increased by increasing the OD. This allows larger tool joints to be welded to the pipe. The larger tool joints provide more torsional strength and create a lower pressure drop than those used on IU pipe.
• Internal external upset (IEU), in which the wall thickness is increased by increasing the OD and decreasing the ID. This is the most common upset type on pipe larger than 4 in.
Tool joint type. The API tool joint types are printed in bold. These include API Reg (used mostly for drill collars, bits, subs and other bottom-hole assembly components), NC numbered connections, and 512 and 658 full hole (FH). Before the NC-type connections were established,
tool joint manufacturers often produced interchangeable tool joints with different names. The NC connections were established to reduce the number of tool joint types. Tool joints with the same thread form and pitch diameter at the gage point are usually interchangeable. Drill pipe manufacturers may also offer proprietary tool joints, such as different variations of double shoulder tool joints for increased torsional strength and tool joints with special threads.
Tool joint OD and ID.
The OD and ID (in., mm) of the tool joint dictates its strength. Generally, the torsional strength of the box is dictated by the tool joint OD and that of the pin is dictated by the ID. Because the box strength does not depend on its ID, the box ID of most drill pipe assemblies is the maximum available regardless of the pin ID. The tool joint OD affects
the fish ability of the length and the equivalent circulation density (ECD). The tool joint ID affects the drilling fluid pressure losses in the string.
Tool joint tong length.
The tong length (in, mm) is the length of the cylindrical portion of the tool joint where the tongs grip. API specifies tong lengths for API connections. Drill pipe is often produced with tong lengths greater than the API-specified tong length, usually in 1-inch increments, to allow more thread recuts. Each time a damaged thread is recut, about 3- 4 in. of tong space is lost.
Drill pipe length.
API-defined drill pipe is available in three standard lengths: range 1, range 2, and range 3, which are approximately 22, 3112 , and 45 ft long, respectively.
Drill pipe is often producedwith hardbanding on the box. The hardbanding reduces the wear rate of the tool joints, reduces casing wear, and reduces the frictional drag of the pipe rotating and sliding in the hole. Sometimes, hardbanding is applied to the pin as well as the box.
1. Drilling Equipment and Operation.
2. drilling Operation.