S-Curve Buttress Thread Joint for Low-Torque Drill Rod Coupling

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Solution Overview

Problem

Existing threaded joints for subsurface drilling rods face challenges with axial and rotational stresses, requiring excessive torque or force for coupling and decoupling, and lack effective self-locking mechanisms.

Innovation Solution

A modified 'buttress' thread design featuring a pin thread and a tubular box thread with S-curve pressure flanks, frustoconical surfaces, and unthreaded segments, providing an interference fit and reducing stress concentration through optimized curvature and angle configurations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If conventional threading is used for coupling drill rods, then the joint can be assembled, but excessive torque and force are required for coupling and decoupling

Engineering Contradiction:

Improvecoupling and decoupling operationVSAvoidtorque and force required

Core Design Contradiction:

Ease of operationVSForce

Solution Approach 1:

The patent modifies the thread geometry parameters including the pressure flank angle (5-15 degrees), clearance flank angle (45-60 degrees), and root radius (0.007-0.015 inches) to optimize the mechanical properties of the thread joint, reducing the torque and force required for coupling and decoupling operations

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional threading is used, then the joint can be assembled, but significant axial and rotational stresses are placed on the threading during operation

Engineering Contradiction:

Improvethread joint reliabilityVSAvoidaxial and rotational stresses

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent optimizes thread parameters including major diameter, minor diameter, pitch, and flank angles to distribute axial and rotational stresses more evenly across the thread engagement, reducing peak stress concentrations and improving joint reliability under drilling loads

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent incorporates a rounded root radius (0.007-0.015 inches) at the thread root to eliminate stress concentration points and improve fatigue resistance, allowing the thread joint to better withstand cyclic axial and rotational stresses during drilling operations

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Ease of operation

If conventional threading is used, then the joint can be assembled, but cross-threading may occur during assembly

Engineering Contradiction:

Improveassembly processVSAvoidthread engagement accuracy

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent employs asymmetric flank angles where the pressure flank (5-15 degrees) and clearance flank (45-60 degrees) have different angles, creating a self-aligning mechanism that guides the pin thread into proper engagement with the box thread and prevents cross-threading during assembly

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS11230891B2Threaded joint

Publication Date: 2022.01.25 DIVERSITY TECH CORP

AI summary

There is disclosed a threaded joint for coupling together rods, tubes, pipes etc. The joint consists of helical box and pin thread segments each defined by a pressure flank and a clearance flank spaced apart from each other with alternating roots and crests. The pressure flank is defined by an S-curve extending between the root and the crest, which is defined by a first curvature c1 adjacent to the root and a second curvature c2 adjacent to the crest. c1 and c2 curve in opposing directions with an inflection point “i” between curvatures c1 and c2.