Steel Pipe Threaded Connection With Nose for Pressure Seal Balance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Threaded connections for steel pipes with large diameters and wall thicknesses face challenges in maintaining high external-pressure sealability while improving internal-pressure sealability, as high external pressures can lead to radial warping of the pin lip, reducing seal contact forces and external-pressure sealability, and insufficient wall thickness of the box can diminish internal-pressure seal contact forces.
Innovation Solution
A threaded connection design with a tubular pin and box, where the clearance between the pin and box surfaces is set within specific limits to prevent radial warping under high external pressure and optimize the wall thickness ratio to enhance seal contact forces, including a nose with a pin shoulder, taper, and sealing surfaces, and applying surface treatments to improve sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wall thickness of the box is increased to improve internal-pressure sealability, then the seal contact force increases, but the production cost increases
Solution Approach 1:
The patent applies parameter changes by optimizing the wall thickness of the box within a specific range (0.08D to 0.15D, where D is the nominal outer diameter of the steel pipe). This optimization ensures the box has sufficient strength to provide adequate seal contact force for internal-pressure sealability, while avoiding excessive wall thickness that would unnecessarily increase production costs, thus resolving the contradiction between reliability and manufacturing cost.
2Reliability
If a nose is added to improve external-pressure sealability, then the seal contact force under external pressure increases, but the structure becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the pin into functionally distinct segments: the nose portion (with outer diameter smaller than the box inner diameter) and the main body portion (with male threads). This segmentation allows the nose to specifically provide external-pressure sealability while the main body provides threading and assembly functionality, thereby improving external-pressure sealability without unnecessarily complicating the overall structure.
Solution Approach 2:
The patent applies inversion by making the nose portion of the pin have an outer diameter that is smaller than the inner diameter of the box, which is opposite to the conventional design where the pin diameter equals the box inner diameter. This inverted design allows the nose to fit within the box without filling it completely, creating space that prevents radial deformation under external pressure while still providing seal contact, thus improving external-pressure sealability without excessive structural complexity.
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
The solution maintains high external-pressure sealability and improves internal-pressure sealability by setting a lower limit on clearance to prevent nose deformation and optimizing the wall thickness ratio, resulting in enhanced seal contact forces and reduced production costs.
Implementation Method 1
the amount of interference causes the diameter of the pin sealing surface to decrease and the diameter of the box sealing surface to increase and each of the sealing surfaces tries to recover their original diameters and thus generates elastic recovery forces, which produce contact pressures on the sealing surfaces to cause them to adhere to each other along the entire periphery, thereby providing sealability
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A threaded connection for steel pipe is provided that improves its internal-pressure sealability while maintaining the high external-pressure sealability of a threaded connection having a nose used in a steel pipe with large diameter and large wall thickness. In a threaded connection for connecting steel pipe bodies each having an outer diameter equal to or larger than 7 inches and a wall thickness equal to or larger than 0.7 inches, Expression (1) in the description is satisfied and tB/tL>1.4, where δ [mm] is the clearance between the outer surface of the pin and the inner surface of the box upon make-up as measured at the borderline between the pin taper surface and the pin round surface, D [inch] is the outer diameter of the steel pipe body, t [inch] is the wall thickness of the steel pipe body, L [mm] is the distance between a pivot point, which is a position, in the region of contact between the pin sealing surface and the box sealing surface, which is closest to the tip of the pin, and the tip of the pin upon make-up as measured along the pipe-axis direction, tL [mm] is the wall thickness of the pin as measured at the pivot point, and tB [mm] is the wall thickness of the box as measured at the pivot point.