Fluid Joint Nut Structure With Internal Thread Terminus for Crack Resistance
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Solution Overview
Problem
Fluid joint nuts used in high-pressure applications, such as the oil and gas industry, are prone to cracking due to fatigue and impact, limiting their service life and requiring improvements in resistance to cracking and failure.
Innovation Solution
A nut design with a varying radial thickness profile, featuring alternating reduced and increased thickness regions, with at least one thread origin or terminus located within an increased thickness region, to reduce crack sensitivity and manage stress distribution effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the nut body has uniform thickness, then the manufacturing is simple, but the resistance to cracking and fatigue is reduced
Solution Approach 1:
The nut body incorporates varying wall thickness with alternating thick and thin sections around its circumference. The thick sections provide enhanced strength and crack resistance at critical locations, while the thin sections reduce overall material usage. This local variation in thickness allows the nut to have superior cracking resistance without uniform complexity throughout the entire structure.
2Reliability
If the thread terminus is located at the end face of the nut, then the threading is easier to manufacture, but the crack sensitivity increases
Solution Approach 1:
The thread terminus is positioned within a thick section of the nut body rather than at the end face. This localized placement in a high-strength region reduces crack sensitivity at the thread endpoint, while the manufacturing process remains straightforward by simply adjusting the thread cutting depth to terminate within the thick section rather than at the extreme end.
Solution Approach 2:
The design pre-positions the thread terminus within a thick section before any loading or service conditions are applied. This preliminary placement ensures that the weakest point (thread terminus) is always located in the strongest region (thick section), preventing crack initiation regardless of the service history or loading conditions the nut encounters.
3Strength
If the radial thickness is varied with alternating regions, then the resistance to cracking is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The alternating thick and thin sections are designed with practical dimensional tolerances that can be achieved through conventional manufacturing processes. The thick sections provide the necessary fatigue resistance while the thin sections reduce material usage. The design balances the need for strength variation with manufacturability, avoiding excessively tight tolerances that would make production prohibitively difficult.
Data Source
AI summary
A nut for joining fluid conduits in a joint assembly includes a nut body having an inner body surface forming a through-bore, for supporting a first fluid conduit and a second fluid conduit. Internal threads upon the inner body surface advance in a helical path around a nut center axis between a thread origin, and a thread terminus that is located between first and second axial end faces of the nut body. At least one of the thread terminus and the thread origin is located within an increased thickness region formed by a varied radial thickness of the nut. The nut has a reduced risk of cracking in service.