Steel Pipe Threaded Connection With Smooth Make-Up Torque
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Solution Overview
Problem
In threaded connections for steel pipes used in oil wells, the make-up torque often experiences irregular changes or 'humping' during screwing, making it difficult to determine the completion of the connection, which can lead to incomplete connections and reduced sealing performance.
Innovation Solution
A threaded connection design featuring a truncated cone-shaped pin with a male thread and seal portion, and a box with a female thread and seal portion, where the root of the male thread and crest of the female thread contact after the seal portions meet, with specific diameter relationships between the tapered surfaces to prevent humping of the make-up torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional tapered thread connection is used, then the structure is simple and easy to manufacture, but the make-up torque experiences irregular changes or humping during screwing, making it difficult to determine connection completion
Solution Approach 1:
The patent uses surface finish changes (metallic luster appearance) as a visual indicator to signal connection completion. When the tapered surfaces come into contact, the metallic luster becomes visible, providing a clear visual cue that the seal portions have met and the connection is complete, eliminating the ambiguity of humping torque behavior.
2Reliability
If the seal interference amount is increased to improve sealing performance, then the sealing performance and pressure resistance are improved, but the make-up torque increases and may cause thread damage
Solution Approach 1:
The patent applies different interference amounts at different locations: a first seal interference amount at the front end seal portion and a second seal interference amount at the rear end seal portion. This local differentiation allows optimization of sealing performance at each location while distributing the mechanical loads, preventing excessive torque concentration that could damage the threads.
Solution Approach 2:
The patent uses a controlled excessive action by providing a predetermined seal interference amount that ensures reliable sealing contact. The interference amount is carefully calculated to be sufficient for sealing (slightly larger than inner diameter) but controlled to prevent excessive torque and thread damage, achieving the right balance through precise dimensional design.
3Device complexity
If a threaded connection without seal portions is used, then the structure is simpler, but the sealing performance and pressure resistance are insufficient for deep and severe oil well conditions
Solution Approach 1:
The patent merges the sealing function with the existing tapered thread structure by incorporating seal portions at the front end and rear end of the pin. This integration adds sealing capability without requiring a completely separate sealing mechanism, maintaining structural simplicity while achieving the required sealing performance for deep well conditions.
4Reliability
If the tapered surfaces are designed with specific diameter relationships, then humping of make-up torque is prevented, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise parameter relationships between the tapered surfaces: the minimum diameter of the pin's tapered surface is smaller than the maximum diameter of the box's tapered surface by a predetermined amount. This parameter control ensures smooth engagement and prevents humping, with the diameter difference carefully controlled to balance manufacturing feasibility with process stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design ensures a smooth and consistent make-up process, preventing humping of the make-up torque and enhancing the sealing performance and pressure resistance of the connection.
Implementation Method 1
the pin and the box are fitted and interfere with each other in a radial direction, and an elastic recovery force to return to the original diameter is generated between the box in which the diameter is increased and the pin in which the diameter is decreased. The elastic recovery force causes the sealing surface to tightly come into close contact with sealing surfaces.
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A threaded connection for a steel pipe includes a box which is an opening end of a second pipe and a truncated cone shaped pin which is an end of a first pipe and is inserted into the box, wherein the pin includes a male thread portion which is a tapered thread and a seal portion which includes a tapered surface, the box includes a female thread portion which is a tapered thread and a seal portion which includes a tapered surface, and in a state before make-up between the pin and the box, a minimum diameter of the tapered surface of the pin is smaller than a maximum diameter of the tapered surface of the box.