Pipe Threaded Connection With Dual Shoulders for Compressive Load
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Solution Overview
Problem
The semi-flush-type integral threaded connections with a two-step thread construction face challenges in providing sufficient strength to withstand high compressive loads due to reduced pipe-wall thickness and compromised sealability when increasing the contact width between intermediate shoulder surfaces.
Innovation Solution
The threaded connection design includes a tubular pin and box with specific axial distances between shoulder surfaces, allowing the pin and box end shoulder surfaces to contact under compressive load, thereby distributing the load and enhancing compression resistance without sacrificing sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the contact width between intermediate shoulder surfaces is increased to improve compression resistance, then compression resistance is improved, but pipe-wall thickness is reduced and sealability is compromised
Solution Approach 1:
The connection structure is divided into two functional zones: intermediate shoulder surfaces for torque transmission during make-up, and end shoulder surfaces for compression load bearing. This segmentation allows each zone to be optimized for its specific function without compromising the other, resolving the contradiction between compression resistance and sealability.
Solution Approach 2:
The load-bearing function is shifted from the radial dimension (intermediate shoulder contact width) to the axial dimension (end shoulder surfaces). By utilizing the axial space between the intermediate shoulders and pipe end, the design achieves compression resistance without increasing radial contact width, thereby preserving pipe-wall thickness and sealability.
2Strength
If the contact width between intermediate shoulder surfaces is increased to improve compression resistance, then compression resistance is improved, but pipe-wall thickness is reduced
Solution Approach 1:
The design transitions from radial load distribution (requiring increased contact width that reduces wall thickness) to axial load distribution (utilizing end shoulder surfaces). This dimensional shift allows compression resistance to be achieved without compromising the radial pipe-wall thickness.
3Strength
If the axial distance between intermediate shoulder surfaces is increased to allow end shoulder contact under compression, then compression resistance is improved, but the size restrictions for flush-type connections may be violated
Solution Approach 1:
The axial distance between intermediate shoulders is optimized locally to enable end shoulder contact under compression, while the overall box outer diameter is controlled to meet flush-type connection requirements. This localized adjustment allows compression resistance improvement without violating global size restrictions.
Data Source
AI summary
A threaded connection for pipe in which the axial distance between the box intermediate shoulder surface and the box end shoulder surface of the box before make-up, LB, is larger than the axial distance between the pin intermediate shoulder surface and the pin end shoulder surface of the pin before make-up, LP, such that, upon completion of make-up, the pin and box intermediate shoulder surfaces and are in contact and function as torque shoulders, while the pin and box end shoulder surfaces are in light (or no) contact. The difference between the axial distances, (LB−LP), is such that, when the pin and box are made up and upon application of an axial compressive load, the pin and box are slightly axially compressed by the compressive load and the pin end shoulder surface comes into pressure contact with the box end shoulder surface to bear part of the compressive load.