In the drilling industry, "three types of drill pipe joints" are typically categorized by their thread/connection design or their upset method (pipe end thickening).
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Classification by Thread Type (API Rotary Shouldered Connections)
This is the most common classification used on rig sites, focusing on the relationship between the internal diameter (ID) of the joint and the ID of the pipe body.
IF (Internal Flush):
Features: The ID of the tool joint is consistent with the ID of the pipe upset and the pipe body.
Advantages: It offers the least resistance to drilling fluid, resulting in minimal hydraulic power loss.
Application: The most widely used type. Modern NC (Numbered Connection) series like NC38 and NC50 are mostly interchangeable with IF.
REG (Regular):
Features: The internal diameter of the joint is significantly smaller than the ID of the pipe body.
Advantages: It has the thickest wall section, providing maximum structural strength.
Application: Primarily used for drill bits, crossover subs, and fishing tools; it is rarely used for the main drill pipe string.
FH (Full Hole):
Features: The joint ID is between IF and REG, creating a stepped internal profile.
Application: An older standard that has largely been replaced by the modern NC series in current drilling operations.
API Drill Pipe Connection Types (RSC)
This table refers to the thread design of the Tool Joints welded to the ends of the drill pipe.
| Connection Type | Equivalent NC | TPI (Threads Per Inch) | Taper | Design Features (ID vs. Pipe ID) | Primary Applications |
| IF (Internal Flush) | NC26, NC31, NC38, NC50 | 4 | 1:6 | Flush Bore: Joint ID = Upset ID = Pipe Body ID | Industry Standard. Lowest flow resistance; max hydraulic power. |
| REG (Regular) | - | 4 or 5 | 1:4 or 1:6 | Contracted Bore: Joint ID is significantly smaller than Pipe ID | Drill Bits, Crossover Subs, and fishing tools (Thickest wall). |
| FH (Full Hole) | NC40, NC46 | 4 | 1:4 | Stepped Bore: ID is between IF and REG types | Legacy drilling rigs; largely replaced by the NC series. |
Classification by Upset Type
This refers to how the ends of the pipe body are thickened before the tool joints are welded on:
IU (Internal Upset):
The pipe's outside diameter (OD) remains constant while the wall thickness increases internally. This causes higher fluid turbulence but keeps a smooth exterior.
EU (External Upset):
The pipe's internal diameter (ID) remains constant while the wall thickness increases externally. This provides high connection strength but results in a larger exterior profile at the joints.
IEU (Internal & External Upset):
Both the ID and OD are thickened. This is the most common modern method, as it provides the best balance between connection strength and efficient fluid flow.
Drill Pipe Upset Types (API 5DP)
This table refers to the physical thickening of the Pipe Body ends before welding the tool joints.
| Upset Code | Full Name | Internal Diameter (ID) Change | Outside Diameter (OD) Change | Core Advantages |
| IU | Internal Upset | Becomes smaller (Internal wall thickened) | Remains constant | Smooth exterior; ideal for tight-clearance operations. |
| EU | External Upset | Remains constant | Becomes larger (External wall thickened) | High connection strength; zero internal fluid obstruction. |
| IEU | Internal & External Upset | Becomes smaller | Becomes larger | Most common type. Best balance of tensile strength and flow efficiency. |
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FAQ
What is class 2 drill pipe?
Class 2 drill pipe refers to used drill pipe with a remaining wall thickness of at least 65% of the original wall thickness. Unilateral wear is permissible; however, the overall cross-sectional area must be equivalent to that of Premium grade, corresponding to a uniform wall thickness reduction of no more than 20%.
How long is one joint of drill pipe?
The standard length of a single drill pipe joint is typically around 9 meters; this is the most common specification in oil drilling operations and falls within the 9–10 meter range recommended by API standards.
In actual field operations, drill pipes are connected one by one-in units referred to as "joints"-and lowered into the well. The three predominant lengths are 6 meters, 9 meters, and 12 meters; among these, the 9-meter length is the most widely adopted standard, as it strikes an optimal balance between operational efficiency and connection stability at the wellhead.
