Wing Nut Thread Geometry for Crack-Resistant Hammer Unions
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Solution Overview
Problem
Threaded wing nuts in hammer unions used in oil and gas exploration are prone to cracking under high stress, leading to failure in hydraulic fracturing systems.
Innovation Solution
A full-radius-threaded wing nut with variable wall thickness and circumferentially-spaced lugs is designed, where the wall thickness at the internal shoulder is greater than at the end surface, and the internal threaded connection has a full-root radius, enhancing rigidity and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the wall thickness is increased at the internal shoulder, then the rigidity and stress resistance are improved, but the manufacturing complexity increases
Solution Approach 1:
The wing nut features variable wall thickness where the wall at the internal shoulder is thicker than the wall at the end surface. This local quality variation concentrates material where stress is highest (at the internal shoulder near the threaded connection) while maintaining thinner walls elsewhere, thereby improving stress resistance without proportionally increasing overall manufacturing complexity.
Solution Approach 2:
The patent changes the geometric parameter of wall thickness along the axial length of the body. By transitioning from a uniform wall thickness to a variable wall thickness profile, the design optimizes the distribution of material to match the stress distribution, with thicker walls at high-stress regions and thinner walls at low-stress regions.
2Reliability
If the wall thickness is increased to prevent cracking, then the reliability is improved, but the weight increases
Solution Approach 1:
Instead of uniformly increasing wall thickness throughout the entire wing nut body, the invention applies increased wall thickness specifically at the internal shoulder region where cracking is most likely to occur under high stress. This localized approach improves reliability at the critical stress point while minimizing the overall weight increase compared to a uniform thickening approach.
3Strength
If a full-root radius threaded connection is used, then the stress concentration is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The threaded connection features a full-root radius, meaning the root of the threads has a continuous curved profile rather than sharp corners or flat bottoms. This curvature eliminates stress concentration points at the thread roots, significantly improving the strength and fatigue resistance of the threaded connection. The smooth transition reduces stress peaks that would otherwise initiate cracks.
Data Source
AI summary
According to one aspect, a hammer union includes a female sub; a male sub; and a wing nut that is concentrically disposed about the female and male subs. The wing nut includes a body having first and second end surfaces, and an exterior surface extending therebetween; a passage extending through the body from the first to second end surface that defines an interior surface of the body; an internal shoulder formed by the interior surface; an internal threaded connection that extends from the first end surface and towards the internal shoulder; and lugs extending radially from the exterior surface. In one aspect, the body has a wall thickness defined between the interior and exterior surfaces, with a greater wall thickness at the internal shoulder than at the first end surface; the internal threaded connection has a full-root radius; and a lug that extends along the axial length of the body.