Elliptical Transition Section for Drill String Rod Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional drill string rods experience high stress concentrations and fatigue at the transition region between the threaded male spigot and the main length section, leading to premature breakage and reduced operational lifetime due to bending moments and tensile loads during percussion drilling.
Innovation Solution
A drill string rod design featuring a transition section with an elliptical cross-sectional profile, characterized by a specific ratio of semi-major to semi-minor axes and an exponential factor, which reduces stress concentrations and enhances stiffness to withstand large bending moments and tensile forces, thereby minimizing the risk of breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional threaded male spigot with a single radius curvature transition is used, then the structure is simple and easy to manufacture, but high stress concentrations occur at the transition region leading to fatigue and breakage
Solution Approach 1:
The patent applies a curved transition section profile with double radius curvature (first radius R1 and second radius R2) instead of a straight or single-radius transition. This curved geometry distributes stress more evenly across the transition region between the threaded section and the main rod body, reducing stress concentrations that lead to fatigue and breakage, thereby extending operational lifetime.
Solution Approach 2:
The patent specifies precise geometric parameters for the transition section including the first radius of curvature R1 ranging from 0.05D to 0.15D and the second radius of curvature R2 ranging from 0.02D to 0.08D (where D is the nominal diameter). By optimizing these curvature parameters, the design achieves reduced stress concentrations while maintaining manufacturability, resolving the contradiction between reliability and complexity.
2Stress or pressure
If the transition region is designed with larger radius curvature to reduce stress, then stress concentrations are reduced, but the space available for threading and shoulder contact is reduced
Solution Approach 1:
The double radius curvature design allows for optimized stress distribution within a compact axial space. The first radius R1 provides a gradual transition from the rod body while the second radius R2 completes the transition to the threaded section diameter, achieving low stress concentrations without excessive axial length consumption.
Solution Approach 2:
The transition section employs different radius curvatures at different locations: the first radius R1 for the initial transition and the second radius R2 for the final transition to the threaded section. This localized variation in curvature quality optimizes stress distribution at each critical point while maintaining sufficient axial space for threading.
3Length of moving object
If multiple threaded couplings are used to extend drill string length, then drilling depth is increased, but the cumulative effect of stress concentrations at each coupling increases the risk of failure
Solution Approach 1:
By implementing the curved transition section with optimized double radius curvature in each coupling, the patent reduces stress concentrations at every joint location. This allows multiple couplings to be used to extend drill string length while each coupling maintains high reliability, preventing the cumulative weakness that would otherwise limit drill string length.
Data Source
AI summary
A drill string including an elongate hollow main length section and a male spigot portion provided at the second end and having an externally threaded section and a non-threaded shank positioned axially intermediate the main length section and the threaded section. The shank includes a transition section positioned adjacent the main length section or a radially projecting shoulder at the second end. The transition section has an outside diameter that increases in a direction from the male spigot portion to the main length section or the shoulder. The cross-sectional shape profile of the outer surface of the transition section in the plane of the longitudinal axis has a segment of an ellipse having semi-major axis (a) and a semi-minor axis (b), wherein the ratio of the semi-major to semi-minor axes (a:b) is within the range 2b<a<8b.