Drill String Rod Spigot Sleeve Diameter Ratios
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Solution Overview
Problem
Conventional drill string rods are inadequate for handling larger drill bits due to material failures such as cracking in the sleeve or spigot portions, and simply increasing thickness can lead to weakened structures or reduced flushing capabilities.
Innovation Solution
The drill string rod design involves specific diameter ratios for the spigot and sleeve portions, calculated to relate their maximum bending stresses to that of the central rod portion, ensuring robustness and longevity while maintaining efficient flushing, with Csleeve > 2.31 and Cspigot > 0.68, and suitable for drill bits with diameters over 130 mm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the outer diameter of the drill string rod is increased to handle larger drill bits, then the strength and robustness are improved, but the risk of cracking in the sleeve or spigot portions increases
Solution Approach 1:
The patent applies parameter changes by establishing specific diameter ratios between the sleeve portion, spigot, and central rod portion. The sleeve outer diameter to rod outer diameter ratio is set to 1.05-1.20, and the spigot outer diameter to rod outer diameter ratio is set to 0.60-0.80. These parameter relationships ensure that the sleeve and spigot have adequate thickness relative to the overall rod size, preventing cracking while maintaining the ability to handle larger drill bits.
2Reliability
If the thickness of the sleeve and spigot portions is increased to prevent cracking, then the reliability is improved, but the flushing capability is reduced
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the inner diameters of the sleeve and spigot portions. The sleeve inner diameter is set to maintain a ratio of 0.85-0.95 relative to the sleeve outer diameter, and the spigot inner diameter is set to maintain a ratio of 0.70-0.85 relative to the spigot outer diameter. This ensures adequate wall thickness for crack prevention while preserving sufficient internal cross-sectional area for effective flushing fluid flow.
3Device complexity
If conventional drill string rods are used with larger drill bits, then the device complexity is reduced, but the strength is insufficient leading to material failures
Solution Approach 1:
The patent applies parameter changes to enhance the strength of conventional drill string rod structures. By establishing specific diameter ratios (sleeve outer/rod outer: 1.05-1.20, spigot outer/rod outer: 0.60-0.80), the design strengthens the critical sleeve and spigot portions without fundamentally changing the overall structural configuration, allowing conventional rod designs to handle larger drill bits effectively.
Data Source
AI summary
A drill string rod includes an elongate central rod portion. The central rod portion has a hollow-cylindrical shape with an inner first diameter (drod) and an outer second diameter (Drod). The male end includes a spigot having a base projecting axially from a shoulder that axially separates the spigot and the central rod portion. The female end has a sleeve portion that fits to the spigot. An inner thread of the sleeve portion is attachable to an outer thread of the base of the spigot of a further drill string rod. In a radial plane to the longitudinal axis of the drill string rod, the base of the spigot is defined by an outer third diameter (Dspigot) and an inner fourth diameter (dspigot) and the sleeve portion is defined by an outer fifth diameter (Dsleeve) and an inner sixth diameter (dsleeve), wherein the second diameter (Drod) is >60 mm.