Elevator Receiving Surface with Dual Conicity for Drill Pipe Stress
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Solution Overview
Problem
The traditional 18-degree angle drill pipe-elevator interface induces excessive tangential stresses in larger drill pipes used for CWOR and LS applications, and increasing the interface angle to 45 degrees reduces contact area, leading to excessive bearing stresses and potential fatigue issues.
Innovation Solution
The design features an elevator with a receiving surface comprising two parts: a first frustoconical part with a higher conicity for upward force and a second part with lower conicity to reduce stresses, and a pipe with a corresponding engagement surface, where the second conicity is between 14 and 30 degrees to prevent sticking, optimizing the conicity to around 45 degrees for balanced stress reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the interface angle is increased to 45 degrees to reduce tangential stresses, then the tangential stress component is reduced and balanced with axial stress, but the contact area is reduced resulting in excessive bearing stresses
Solution Approach 1:
The receiving surface is divided into two distinct parts: a first frustoconical part with a steeper angle (30-60 degrees) for reducing tangential stresses, and a second part with a shallower angle (10-30 degrees) for maintaining adequate contact area and distributing bearing stresses. This segmentation allows each part to optimize for its specific function.
Solution Approach 2:
Different regions of the receiving surface are given different geometric properties - the first part has higher conicity to address tangential stress, while the second part has lower conicity to address bearing stress distribution. This local differentiation of properties resolves the contradiction between stress reduction and contact area maintenance.
2Area of stationary object
If the transition radius R is reduced to enlarge contact area, then the contact area between elevator shoulder and bushing is enlarged, but the stress concentration in the transition radius increases adversely affecting fatigue life
Solution Approach 1:
The transition region is given a specific optimized radius that balances two competing requirements: it is large enough to avoid stress concentration and protect fatigue life, yet the overall geometry is designed to maximize contact area through the two-part frustoconical structure. The local quality of the transition radius is differentiated from the overall conicity angles.
3Stress or pressure
If the outside diameter of the tool joint is increased to reduce stresses, then the stress distribution is improved, but most power tongs currently used in the field would not be able to handle such a large tool joint OD
Solution Approach 1:
The stress distribution is improved through the optimized two-part frustoconical geometry and transition radius design rather than by increasing the overall tool joint OD. This allows the pipe to have enhanced stress characteristics while maintaining compatibility with existing power tong equipment through standard outer dimensions.
Data Source
AI summary
A pipe having suspendable from an elevator in a drill tower. The pipe includes an end portion which, in operational use, is suspended from a hole of the elevator, wherein the end portion has a minimum diameter that is greater than a minimum diameter of the hole of the elevator. The end portion of the pipe includes sidewalls shaped with an engagement surface for engagement with correspondingly-shaped sidewalls of the hole. The engagement surface of the pipe includes a first part and a second part neighbouring the first part, the first part defining a frustoconical shape having a non-zero first taper angle, and the second part defining a shape having at least partially a non-zero second taper angle that is less than the first taper angle.