Shear Coupling Pin Isolation for Predictable Downhole Failure
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Solution Overview
Problem
Existing shear couplings in downhole systems are prone to premature fatigue and unpredictable failure due to cyclic compressive stress, leading to fragments lodging between the pump and wellbore, making pump retrieval difficult and costly, and requiring expensive equipment.
Innovation Solution
A shear coupling design that isolates the shear pin from torsional, bending, and compression forces, allowing it to fail predictably into two pieces upon a tension force above a threshold, with a shear groove for controlled separation, and a retention assembly to prevent unintentional disengagement, ensuring the fragments remain connected to the coupling halves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional shear pins are used to connect coupling members, then the shear coupling can transfer tension forces, but the shear pins are prone to premature fatigue from cyclic compressive stress and unpredictable failure
Solution Approach 1:
The shear pin is segmented into two functional zones: an isolated shaft portion that bears only tensile loads and a grooved portion that experiences compressive loads. This segmentation allows each portion to be optimized for its specific function, with the shaft portion designed for predictable tensile failure and the grooved portion designed to prevent fragment dropout.
Solution Approach 2:
The grooved portion acts as an intermediary element between the shaft portion and the coupling members. It receives compressive loads from the coupling members while transmitting only tensile loads to the shaft portion, thereby isolating the shaft portion from cyclic compressive stress and preventing fragment dropout.
2Ease of operation
If shear pins break under compressive stress, then the coupling fails, but fragments fall downhole and become lodged between the pump and wellbore, making pump retrieval difficult
Solution Approach 1:
The grooved portion is pre-designed with a specific geometry that prevents fragment dropout before failure occurs. The grooves are formed in advance to accommodate and retain any fragments that may form, ensuring that when failure occurs, the fragments remain contained within the coupling assembly rather than falling into the wellbore.
Solution Approach 2:
The design converts the potentially harmful effect of fragment formation into a beneficial outcome by using the grooved portion to capture and retain fragments. What would normally be a problem (fragment dropout) is transformed into a controlled feature where fragments are contained and do not interfere with pump retrieval operations.
3Strength
If the shear pin is subjected to both compression and tension forces, then it can handle reciprocating pump loads, but it experiences premature fatigue from cyclic compressive stress
Solution Approach 1:
The shear pin is divided into functional segments: the shaft portion handles tensile loads and the grooved portion handles compressive loads. This segmentation allows the shaft portion to be optimized for strength under tension while being protected from the fatigue-causing cyclic compressive stresses, thereby extending service life.
Solution Approach 2:
The grooved portion serves as a mediator that absorbs and isolates cyclic compressive stresses from the shaft portion. It acts as a buffer zone that experiences the full range of compressive loading while transmitting only tensile forces to the shaft portion, protecting it from fatigue damage.
Data Source
AI summary
A shear coupling includes a first half, a second half, and a shear pin connected therebetween. The connections between the shear pin and the first half and the second half substantially isolate the shear pin from torsional, bending, and compression forces experienced by the first half or the second half. The connections between the shear pin and the first half and the second half transfer tension forces experienced by the first half and the second half to the shear pin from. A tension force above a predetermined threshold causes the shear pin to separate into two pieces that remain connected to the first and second halves.