Tapered Noncontact Region in Steel Pipe Threaded Joint
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Solution Overview
Problem
Conventional threaded joints for steel pipes face challenges in maintaining sealing performance under external pressure and compressive loads due to deformation of the lip portion, leading to potential leakage and reduced resistance to compression, especially in severe environments such as horizontal or sloping wells.
Innovation Solution
The design incorporates a noncontacting region on the pin with a tapered surface having the same angle of slope as the sealing surface, which increases stiffness and resistance to deformation, allowing for improved sealing and compression resistance by distributing stress effectively and preventing damage during make-up and handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lip portion wall thickness is increased to resist external pressure, then sealing performance improves, but the joint complexity and manufacturing difficulty increase
Solution Approach 1:
The lip portion is segmented into multiple functional zones: a first portion with increased wall thickness for pressure resistance, a second portion for sealing, and a third portion for engagement. This segmentation allows each zone to be optimized for its specific function without unnecessarily increasing overall complexity.
Solution Approach 2:
The wall thickness is not uniformly increased throughout the lip portion, but only in the first portion where external pressure resistance is most critical. This localized quality change provides the necessary strength while minimizing added complexity and material usage.
2Reliability
If the lip portion is made thicker to prevent deformation under external pressure, then sealing ability improves, but ease of manufacture deteriorates
Solution Approach 1:
The lip portion is divided into distinct segments with different wall thicknesses, allowing the thicker first portion to be manufactured as a separate feature that can be integrated into standard piping processes without requiring complete redesign of the entire component.
Solution Approach 2:
The wall thickness parameter is changed only in the critical first portion of the lip, while other portions maintain standard dimensions. This selective parameter change achieves the necessary deformation resistance without making the entire component more difficult to manufacture.
3Ease of manufacture
If the lip portion is designed with uniform wall thickness, then ease of manufacture improves, but resistance to compression under external pressure deteriorates
Solution Approach 1:
The lip portion features non-uniform wall thickness with the first portion having increased thickness specifically where external pressure and compression loads are most severe. This local quality variation provides enhanced compression resistance only where needed, rather than uniformly throughout the entire lip portion.
Solution Approach 2:
The lip is segmented into portions with different wall thickness characteristics, allowing the first portion to be optimized for compression resistance while other portions maintain simpler geometry for ease of manufacture.
4Reliability
If the sealing surface is positioned closer to the end of the pin, then sealing efficiency improves, but resistance to deformation under external pressure deteriorates
Solution Approach 1:
The lip portion is segmented into a first portion with increased wall thickness for deformation resistance and a second portion containing the sealing surface. This segmentation allows the sealing surface to be positioned optimally for sealing efficiency while the first portion provides the necessary structural support against external pressure.
Solution Approach 2:
The wall thickness is locally increased in the first portion of the lip, creating a reinforced zone that protects the sealing surface area from deformation under external pressure, thereby maintaining both sealing efficiency and deformation resistance.
Data Source
Figure 1(A)~2
Figure 3(A)~3(D)
Figure 4(A)~4(D)
AI summary
A threaded joint for steel pipes comprising a pin 1 having a tapered male thread 11, a tapered sealing surface 13, and an end shoulder surface 14 and a box 2 having correspondingly a tapered female thread 21, a tapered sealing surface 23, and a shoulder surface 24 which is capable of easy tightening and has improved air tightness by the sealing surfaces is arranged such that the pin and the box each have a noncontacting region B where the peripheral surfaces of the pin and the box do not contact each other between the sealing surfaces 13, 23 and the shoulder surfaces 14 and 24. At least a portion of the noncontacting region of the pin adjoining the end of the pin is a tapered surface portion 18 having substantially the same angle of slope as the tapered sealing surface 13, and the noncontacting region of the box is a substantially cylindrical surface.