Cambered Downhole Tubular Coupling for Bending Load Distribution

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Solution Overview

Problem

Conical threads used in drill strings for percussion rock drilling are not optimal for distributing bending loads evenly, result in inefficient coupling and uncoupling, and have inadequate wear resistance.

Innovation Solution

Cambered threads with specific design features such as greater camber radii, acute angles, and asymmetric trapezoidal shapes that align better with bending curvature, reducing sliding forces and improving stiffness and wear resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If conical threads are used in drill strings, then coupling and uncoupling can be achieved, but the bending loads are not distributed evenly across the thread length

Engineering Contradiction:

Improvebending load distributionVSAvoidthread geometry uniformity

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The patent applies cambered threads with curved profiles instead of straight conical threads. The camber radius creates a curved thread path that better follows the bending curvature of the drill string, distributing bending loads more evenly across the thread length while maintaining structural integrity

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Ease of operation

If conical threads with small cone angles are used, then thread engagement is achieved, but coupling and uncoupling time is excessive

Engineering Contradiction:

Improvecoupling operationVSAvoidcoupling and uncoupling time

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The patent modifies thread geometry parameters by introducing camber radius and optimizing flank angles. The cambered profile with specific radius values changes the engagement characteristics, allowing faster coupling and uncoupling operations while maintaining adequate thread engagement and load distribution

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conical threads are used, then thread connection is achieved, but wear resistance is insufficient due to sliding forces

Engineering Contradiction:

Improvewear resistanceVSAvoidsliding force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The cambered thread profile with curved geometry changes the direction of contact forces between mating threads. The curvature aligns the contact forces more perpendicular to the thread flanks, reducing the sliding component of the forces and thereby improving wear resistance

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent employs asymmetric thread profiles where the contact flank and non-contact flank have different angles. This asymmetry optimizes the distribution of contact forces, directing more load through the contact flank while minimizing sliding forces that cause wear

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS11598159B2Coupling for connecting downhole tubulars

Publication Date: 2023.03.07 SANDVIK MINING & CONSTR TOOLS AB

AI summary

A coupling for connecting downhole tubulars includes a tubular body, and at least one thread of a male screw thread formed on an outer surface of the body, and a female screw thread formed in an inner surface of the body. The at least one thread has a thread-form including a crest, a root, and a pair of flanks. The crest and the root are each cambered about a respective first and second camber radius. Each camber radius is greater than an outer diameter of the coupling.