Flexible Shear Coupling for Downhole Bending and Torque Loads
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Solution Overview
Problem
Conventional shear couplings fail to withstand axial, torsional, and bending stresses in downhole applications, particularly in deviated wellbores, leading to premature failure and interruptions in wellbore production, and are not designed for use with both rotary and reciprocating downhole pumps.
Innovation Solution
A flexible shear coupling using a shear nut and connecting member as the shear element, with a polygonal shaft and hub profile for torque transmission, and pretensioning to isolate the shear nut from alternating stresses, providing increased resistance to bending and torsional stresses while protecting from corrosive environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional shear couplings use shear pins or shear necks as shear elements, then the coupling can transmit axial forces, but the shear element acts as a stress concentrator causing premature fatigue failure under combined axial, torsional, and bending stresses
Solution Approach 1:
The patent removes the traditional shear element (shear pin or shear neck) from the coupling structure. Instead of having a shear element that extends into both coupling members, the invention uses a shear plate that is received within a recess of one coupling member, eliminating the stress concentrator effect of protruding shear elements while maintaining axial force transmission capability
Solution Approach 2:
The patent divides the coupling into distinct functional components: driving engagement members for torque transmission, a shear plate for axial force transmission, and a recess that isolates the shear plate from corrosive environments. This segmentation allows each component to be optimized for its specific function without compromising the others
2Force
If conventional shear couplings are designed for axial force transmission, then they can break at pre-set axial load, but they cannot adequately transmit torque in rotary applications
Solution Approach 1:
The patent designs the coupling members with driving engagement members (such as splines, keys, or interlocking surfaces) that enable the coupling to function in both reciprocating and rotary applications. The coupling members are configured to transmit both axial forces and torque, making the shear coupling universal for different pump types without requiring separate designs
3Device complexity
If shear elements are exposed to the wellbore environment, then the coupling can be simple in structure, but the shear element is vulnerable to corrosion from corrosive wellbore elements
Solution Approach 1:
The patent places the shear plate within a recess of one coupling member, creating a nested structure where the shear plate is protected from the external corrosive wellbore environment. The recess acts as a protective enclosure, isolating the shear plate while maintaining the overall simplicity of the coupling structure
Data Source
AI summary
A shear coupling can be used with reciprocating and rotary pumps. The shear coupling uses a shear nut and connecting member as the shear element. The connecting member and shear nut are located inside the axial bore of the shear coupling to protect from corrosive wellbore elements. The coupling members may be connected by matching polygonal shaft and hub profiles on the coupling members to transmit torque. The shaft and hub may have octagonal profiles for better torque transmission capacity. The shear nut may be isolated from large alternating stresses due to pretensioning of the connecting member. The length of the connecting member, especially when pretensioned, and a reduced cross-section that may be formed on the outer surface of the shear coupling increase the overall flexibility of the shear coupling, thereby increasing the resistance to bending stress.