-
Drill Pipe
View Products
Heavy Weight Drill Pipe
View Products
Drill Collar
View Products
Kelly
View Products
Tool Joint
View Products
Surface Protection & Internal Coating
View Products
Specialty Drill Products
View Products
-
-
-
-
Detailed Explanation of Drill Pipe End-Thicknessing Processes: IU, EU, and IEU Thickening Types and Quality Control
Author:
WHH
Source:
LONGWAY
Published:
2026-10-09
The drill pipe body is a thin-walled seamless steel tube, while the connection section (tool joint) requires sufficient wall thickness to withstand tensile, torsional, and bending loads. To resolve the conflict between the “thin-walled pipe body” and the “thick-walled joint,” the drill pipe manufacturing process employs an upsetting operation—increasing the wall thickness at both ends of the pipe to create smoothly transitioned thickened sections.
I. Why is end thickening necessary?
Drill pipe Underground, the tubing is subjected to complex combined loads, and the joint area is where stress concentrations are most severe. If no reinforcement is applied, welding a thin-walled tubular body directly to a thick-walled tool joint will give rise to two problems:
1. Insufficient strength: The thin-walled tube cannot withstand the high torque and tensile loads transmitted through the joint, leading to failure near the weld seam.
2. Stress Concentration: Sudden changes in wall thickness can lead to stress concentration, serving as initiation sites for fatigue cracks.
The purpose of thickening the pipe ends is:
Increase the wall thickness at connection joints to enhance load-bearing capacity.
Form a smooth transition zone to reduce stress concentration.
Provide suitable end faces for friction welding to ensure weld quality.
II. Three types of thickening: IU, EU, IEU
Depending on the direction of thickening, API 5DP specifies three types of thread protection:
| Thickened type | Features | Threaded joint |
| Internally thickened IU (Internal Upset) | The inner diameter of the pipe end decreases, while the outer diameter remains unchanged. | REG (Regular Type) |
| External Upset | The outer diameter of the pipe end increases, while the inner diameter remains unchanged. | IF, NC |
| Internally and externally thickened IEU (Internal-External Upset) | Both the inner and outer diameters change simultaneously. | FH, NC |
1. Inner thickening (IU)
Internal thickening is achieved by increasing the wall thickness toward the interior of the pipe. The outer diameter at the pipe end remains unchanged, while the inner diameter decreases. Internal thickening is suitable for drill pipes that mate with REG threads, as these joints have a smaller outer diameter and a larger inner diameter.
2. Extra thick (EU)
External thickening involves increasing the wall thickness outward from the pipe. The inner diameter at the pipe end remains unchanged, while the outer diameter increases. External thickening is suitable for drill pipes with IF and NC threads and is currently the most widely used type of thickening.
3. Internally and Externally Thickened (IEU)
Double-thickened, with wall thickness increased in both the inner and outer directions. The inner diameter at the pipe end is reduced, while the outer diameter is enlarged. Suitable for drill pipes that mate with FH threads, as well as for specialized applications requiring maximum connection strength.
III. Thickened Process Flow
End thickening is a thermoforming process, with the main steps as follows:
End heating → Upsetting and forming → Transition zone forming → Cooling → Inspection
1. Pipe-end heating
Heat the end of the tube to the forging temperature (typically around 1150–1250°C). Heating methods include:
Medium-frequency induction heating: fast heating speed, precise temperature control, and minimal oxidation.
Gas furnace heating: Suitable for high-volume production, but with relatively lower temperature control accuracy.
2. Chamfering and Forming
The heated pipe end is placed into a die, and hydraulic or mechanical pressure is applied to cause the metal at the pipe end to flow and take shape. The upsetting process requires precise control:
Pressure: Ensure the metal fully fills the mold.
Speed: Avoid excessive speed to prevent unstable metal flow.
Temperature: Maintain the metal in its optimal plastic state.
3. Transition Zone Formation
The transition zone between the thickened section and the pipe body is a critical area of stress concentration. This transition zone shall be smooth, free of wrinkles and abrupt changes. Its length and geometry must comply with the requirements of API 5DP.
4. Cooling
After thickening is completed, the pipe ends must undergo controlled cooling. The cooling rate influences the microstructure and mechanical properties.
5. Inspection
After thickening, the thickened section shall undergo dimensional inspection, wall-thickness measurement, and visual inspection.
IV. Reinforced Equipment
End thickening is performed using a dedicated end‑upsetting and thickening machine. Hebei Longway employs a 1,250‑ton end‑upsetting and thickening machine manufactured by National Oilwell Varco (NOV), which features the following characteristics:
Thickened with a high compression ratio: metal flows fully, resulting in a dense microstructure.
No wrinkles: The mold is designed rationally, ensuring high-quality forming.
Transition zone smoothing over an extended length: reduces stress concentrations and enhances fatigue life.
V. Key Points for Enhanced Quality Control
| Control item | Requirements | Detection method |
| Thickened section outer diameter | Meets API 5DP tolerances | Caliper measurement |
| Thickened section inner diameter | Meets API 5DP tolerances | Inside diameter gauge / Go gauge |
| Wall thickness | The thickened section’s wall thickness meets the design requirements. | Ultrasonic thickness measurement |
| Transition zone length | Complies with API 5DP requirements. | Visual/Measurement |
| Transition zone shape | Smooth, wrinkle-free, and free of abrupt changes | Visual inspection |
| Surface quality | No cracks, no folds, no pits. | Visual + MT Inspection |
| Microstructure | Uniform, with no overheating or burnout. | Metallographic Analysis |
| Hardness | Meets API requirements | Hardness tester |
Critical Control Point:
The transition zone is a stress concentration area and must ensure a smooth transition.
The wall thickness of the thickened section must be uniform to prevent local thinning.
After thickening, nondestructive testing must be performed to ensure there are no internal defects.
VI. The Relationship Between Thickening and Friction Stir Welding
After the pipe end is thickened, the pipe body and the tool joint are joined by friction welding. The quality of the thickened section directly affects the weld quality:
The thickened end face must be flat and clean to ensure proper contact between the welding surfaces.
The wall thickness of the thickened section shall match that of the tool joint to prevent incomplete fusion during welding.
The smoothness of the thickened transition zone affects the stress distribution in the weld region.
VII. Frequently Asked Questions (FAQ)
Q1: How should I choose between IU, EU, and IEU?
Select according to the drill pipe thread type: REG threads match IU, IF, and NC threads match EU, and FH threads match IEU.
Q2: Why is the thickened transition zone important?
The transition zone is the region where the thickened section joins the pipe body, and it experiences severe stress concentration. A smooth transition can mitigate stress concentration and extend fatigue life.
Q3: Does the material require heat treatment after thickening?
It is necessary. The thickening process is carried out at high temperature, which may lead to coarse grain growth; therefore, normalizing or quenching and tempering is usually required.
Q4: How can you determine whether the thickened material meets quality standards?
A comprehensive assessment is conducted through dimensional measurements, wall-thickness measurements, visual inspection, and nondestructive testing. The transition zone must be free of wrinkles, exhibit uniform wall thickness, and show no cracks—these are the fundamental requirements.
Q5: What are the advantages of Hebei Longway’s thickened equipment?
Utilizing the U.S.-made NOV 1250‑ton upsetting and thickening machine, this process delivers a high thickening compression ratio, eliminates wrinkles, and produces an exceptionally smooth, ultra‑long transition zone, thereby ensuring consistent quality in the thickened section.
VIII. Summary
| Key points | Core content |
| Purpose of thickening | Increase the wall thickness at connection joints to reduce stress concentrations. |
| Three types | IU (internally thickened), EU (externally thickened), IEU (both internally and externally thickened) |
| Process flow | Heating → Upsetting → Transition Zone Forming → Cooling → Inspection |
| Key equipment | Pipe-end upsetting and thickening machine (e.g., NOV 1250-ton model) |
| Quality Control | Dimensions, wall thickness, transition zone geometry, nondestructive testing |
| Relationship with welding | The quality of the thickened end face directly affects the quality of friction welding. |
Thickening of the pipe ends is a critical step in drill‑pipe manufacturing, directly affecting the pipe’s load‑carrying capacity and fatigue life. Selecting an appropriate thickening method, rigorously controlling the thickening process, and ensuring a smooth transition in the transition zone are essential for producing high‑quality drill pipes.
Need to learn more about drill pipe manufacturing processes or procure API‑certified drill pipe for your project?
Contact Hebei Longway Petroleum Equipment Co., Ltd.
Get professional technical support
Hebei Longway is equipped with a 1,250-ton pipe-end upsetting and thickening machine manufactured by the U.S. company NOV, and strictly adheres to the API 5DP standard to ensure consistent and reliable quality of the thickened sections.
Leave Message
Consult Our Engineers & Get Fast Official Quotation
Give you the best solution
- Inquiries get a response within 12 hours.
- We are a professional manufacturer with competitive pricing, and we accept all DEM/ODM orders.
- Our after-sales team provides 24/7 technical support; issues are addressed within 24 hours.
- Precision quality, on-time delivery, tailored service.
We can customize high-performance drill pipe assemblies of various sizes according to customer needs.
Contact Us
Telephone
Phone/Wechat
Address
052260, East of Beikou, Yingli Town, Jinzhou County, Shijiazhuang City, Hebei Provice, China.
Get in Touch
* Fill in your phone number and email information, and we will promptly contact you within one business day to address your concerns as soon as possible.
-
-
扫一扫
微信二维码
关注我们
-
E-mail
-
WhatsApp
-
Telephone
-
Business Card